Blackbird's thrust question

[peter kent]

Please can someone give some ideas?
The following extract comes from "F-12 series aircraft propulsion system performance and development" by D. Campbell

BTW Was unable to include Table 1 but it just shows usual falling contribution from the engine mounts with speed.

"In order to understand the importance of each of
the three propulsion system components, it is interesting
to note the proportion of the thrust which is supplied by
each component while operating in maximum afterburner.
Table 1 indicates how the actual thrust forces are distributed
while the engine is inducing flow and heating it
up with maximum afterburner. If the AB is reduced to
minimum AB, the engine would actually be dragging on
the engine mounts at high Mach numbers. Further reduction
of engine thrust below military power will result in no
propulsive thrust on the aircraft."


Q referring specifically to 'is inducing flow and heating it up with maximum afterburner'

I take this to refer to the induced secondary flow which flows over the red-hot afterburner casing and the intimation that this is significant in producing thrust. However due to the high air flow rate (1/3 intake entry flow) and it being a poor design of heat exchanger would the heat transfer really be significant (ie per lb/sec)?
Do I have the wrong end of the stick?
Thank you.

[Jhieminga]

I may be off here, but here's my two cents:
Thrust of a jet engine is caused by a whole lot of mass x acceleration which produces a force. So the goal is to accelerate the air. In supersonic applications the problem is that in order to keep the jet engine going, you first need to slow the air down to below M=0.7 (or thereabouts) in the inlet to avoid surges, stalls etc. The engine can then add energy and a bit of mass (think fuel) to this airflow but if we are talking about high Mach numbers then the resulting exit speed may actually be slower than the aircraft's current speed, and this causes the 'engine to drag on its mounts' as mentioned in your book.

Afterburning can help in this respect as it adds mass, but more importantly heats it up considerably. This causes the air to expand rapidly but as it is moving through a confined tube, the end result is rapid acceleration of this mass of air, and that is what we were after all along. After all it is the increase in speed between entry and exit which causes thrust. The 'inducing flow' then refers to the main engine delivering an airflow to the afterburning section, which is its main task at this point.

There are some side effects which I've overlooked here, such as the pressure rise in the inlet caused by the slowing down of the air mass which also produces thrust, but that's not what your question was about I think.

Hope this helps, or have I just added another wrong end to the stick...

[Machaca]

Airflow of J58 as fitted to YF-12A, A-12 and SR-71:

http://i337.photobucket.com/albums/n385/motidog/SR71_J58_Airflow1.jpg

[peter kent]

Thank you for your replies.
I think I have a good grasp of where all the air goes and what it does having read the patent for both the famous but poorly understood engine bleed bypass and the patent which explains all those arrows on the 5 diagrams and Peter Law's presentations in AEHS website.
Since the author of the extract knew all this stuff as well (he wrote the intake patent) and knew the lingo, when he says induced flow I'm pretty certain he was referring to the secondary flow which bypassed the engine and was induced at the ejector nozzle by the afterburner flow from the primary nozzle (and of course helped by the pressure in the intake).
Hence my question on that particular air which flowed around the engine.

I believe he is saying something beyond all the usual explanations. OTOH I may just be reading too much into one word. Any ideas?

[Lyman]

If true, that the engine's mounts 'float' at some stage....

First, the idea w/AB is not to pinch the nozzle, to accelerate flow, but to enlarge it, to maximize the AB flow on the cross section of the nozzle outlet: expansion, not restriction, is the goal.

At the point where the mounts float, the gaspath is effectively and functionally part of the airframe.

No distinction need be made to define the gaspath as thrust, or drag, it is neutral.

The AB reacts against the mass of the gaspath, several tons of it. In such a powerfully dynamic status, it becomes easier to get how the intake provides such a large component of Thrust, and the AB drag

It was always easier for me to understand thrust as exquisitely tied to its opposite, and compression also to extremely low pressure.

Don't mind me, I don't make any representation about this other than I think it has merit, maybe.

Lyman :ok:

[gums]

Salute!

Go to this site and read and learn:

SR-71 Online - The Blackbird Archive (http://www.sr-71.org/blackbird/)

Was privileged to know and fly with a few of the Blackbird pilots, and that sucker was amazing for its time.

The J-58 was a key aspect of the design, although with less-powerful motors the thing still ran well.

Unlike today's "monitoring function" for the crew, the Blackbird required actual piloting skills and decisions and such. My friends that flew the U-2 have similar war stories.

[peter kent]

If the AB is reduced to
minimum AB, the engine would actually be dragging on
the engine mounts at high Mach numbers

Isn't this case just the plane slowing down so the dragging on the mounts is just an unbalanced phase until new equilibrium?

Further reduction
of engine thrust below military power will result in no
propulsive thrust on the aircraft
Isn't this even more slowing down to an even lower speed?

[Brian Abraham]

During high-speed flight in the Blackbird, compression of air in the inlets generated most of the vehicle’s thrust. At Mach 2.2 the inlet produced 13 percent of the overall thrust with the engine and exhaust ejector accounting for 73 and 14 percent, respectively. At Mach 3 cruising speeds the inlet provided 54 percent of the thrust and the exhaust ejector 29 percent. At this point the turbojet continued to operate but provided only 17 percent of the total motive force. The inlet had a compression ratio of 40:1 at cruise conditions where each inlet swallowed approximately 100,000 cubic feet of air per second.

Source: Urie, David, “Case Studies in Engineering: The SR-71 Blackbird,” Course Ae107, Presented at the Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena, Calif., April-May 1990.

A significant percentage of air entering the inlet bypassed the engine through ducts and traveled directly to the afterburner. At cruise Mach conditions, fuel burned more advantageously in the afterburner than in the main burner section. Hence, engineers described the powerplant as a turbo-ramjet.

Source: Matranga, Gene, and William J. Fox, “YF-12A Development and Operational Experience,” unpublished paper presented at the Supercruiser Conference, Wright-Patterson AFB, Ohio, February 17-20, 1976, p. 3. NASA Dryden Historical Reference Collection.

[nitpicker330]

Download and read:-

Flying the SR-71 Blackbird

In the cockpit on a secret operational mission

By Col Richard H Graham USAF ( ret )

A good read that has a lot of tables and graphs for thrust settings Perf etc. including checklists and flight plans.

[peter kent]

I've found it's worth treating some Blackbird writings with scepticism even when from seemingly authoritative sources.
A significant percentage of air entering the inlet bypassed the engine through ducts and traveled directly to the afterburner
No air bypassed the engine and went straight to the ab. Most of the ab air,80%, went through the whole engine. A small amount, 20% which was required to make the compressor function properly at high inlet temps, was bled from the 4th compressor stage and then to the ab.
Sources: US Patent 3,344,606 which is the bleed air patent, F-12 Flight manual Fig 1-1G for example. Also the popular colored airflow diagrams in a previous post which don't show any engine bypass air going to the ab.
engineers described the powerplant as a turbo-ramjet
The engineers who designed and built the engine(P&W), those who designed and built the installation (Lockheed) and those that serviced and maintained it called it a bleed bypass turbojet with afterburner, eg see Flight manual. This knowledge alone sets the alarm bells off when you see the word ramjet. It was, after all, a turbojet with a bit more compressor bleed than usual.
One of many good sources: 'F-12 series aircraft propulsion system performance and development' by D. Campbell, the Lockheed engineer who also took out US Patent 3,477,455 for the inlet. Incidentally one of the drawings in the patent is the basis for the popular colored airflow diagrams which, in fact, are taken from the flight manual.

[Brian Abraham]

Most of the ab air,80%, went through the whole engine. A small amount, 20% which was required to make the compressor function properly at high inlet temps, was bled from the 4th compressor stage and then to the ab.I'd be interested where you get those figures from peter. Also the popular colored airflow diagrams in a previous post which don't show any engine bypass air going to the abThe bleed bypass can be identified on the engine by six very large pipes running from the forth stage to the afterburner.

The bleed air from the forth stage was scheduled by the main fuel control as a function of compressor inlet temperature and engine speed. The transition normally occurred in a compressor inlet temperature range of 85° to 115° C, corresponding to a Mach range of 1.8 to 2.0.

If the AB is reduced to minimum AB, the engine would actually be dragging on the engine mounts at high Mach numbers. Further reduction of engine thrust below military power will result in no propulsive thrust on the aircraft.
At sea level static conditions military thrust constitutes 70% of maximum thrust, whereas at high altitude it is approx 28% of the maximum available.

The engine will always be producing thrust irrespective of throttle position - assuming it hasn't been shut down that is.engineers described the powerplant as a turbo-ramjeWhile I don't have any evidence that Kelly Johnson or Ben Rich ever referred to the engine as a "turbo ramjet", the term was used by Lockheed and NASA people, the principle behind the term, and what it meant, being well understood.

[peter kent]

Hi Brian, 20% appears in the internal P&W memo written by Bob Abernethy when he had solved the challenge of converting the j58 from a Mach 2 engine into Mach3.
http://www.bobabernethy.com/pdfs/Never%20Told%20Tales%20of%20P&W3.pdf
It also appears in his patent
Patent US3344606 - RECOVER BLEED AIR TURBOJET - Google Patents (http://www.google.com/patents/US3344606)
The whole story is in the patent. Basically the problem revolved around getting the compressor to behave at M3 cruise, ie 100% mechanical N1 and M3 CIT. This condition for the compressor is similar to starting the engine to idle on the ground, ie same low corrected N1. Just as this engine, like others, needed a start bleed to get to idle so it needed a similar bleed at cruise (because it was the same regime on the compressor map), which turned out to be 20%. The bleed was then available to put into the ab to give additional benefits.

The patent is arguably the best primer I have ever come across anywhere for explaining how jet engine compressors suffer from CIT at high supersonic speeds and what to do about it.

six very large pipes They may look big for 20% but would have been overlarge to reduce flow losses. The 20% would have been controlled at the compressor case to prevent excess bleed if a pipe cracked.

"turbo ramjet", the term was used by Lockheed and NASA people, the principle behind the term, and what it meant, being well understood
This is a hard nut to crack but only because it is steeped in folklore. With all what was once secret info now available on the web we now know exactly what the engine was and can even deduce it for ourselves by reading the patent for example or the Flight Manual. We no longer have to rely on descriptions from years ago.
Again as spelled out in the patent, a turbo ramjet was one possible solution to get to M3. It was not adopted. The engineer given the task of 'fixing' the engine says in his patent why not. Another would have been variable stators. That's how the XB-70 engines got there.
Few people at Lockheed, NASA or P&W would have been privy to what were secrets back in those days. The facts are all laid bare for us today and we are better informed. They were wrong as stated in the patent. The bleed bypass was a much more cost effective solution due to its simplicity.
BTW Ben Rich called it a bleed bypass turbojet in "F-12 Series Aircraft Aerodynamic and Thermodynamic Design in Retrospect".
With all the fine details available to everyone we basically have to forget all the descriptions from years ago and start again with the facts.
Interesting stuff. Cheers.

[Lyman]

Ram means 'to compress'. For "Ram" to apply to the J58, the engine would have to be able to shut down its compressors, and rely on inlet air only to propagate its motive power.

I am guessing that could not be the case with this engine. 'Ram Effect'? All turbine engines experience ram "Effect".

That is the 'semantic' description of "Ramjet". The term 'Ram' and 'jet' are not synonymous. One implies a confined and controlled gaspath (jet), the other, a 'passive' (Ram) supply of airmass whose characteristic energy is created by the velocity of the inlet through the air....

impo....

[Brian Abraham]

G'day peter,

You were quite right re the 20%. Found it in some saved files (I'm a real fan of the aircraft).

With respect to the "turbo ramjet", it was interesting to see in your Bob Abernethy link where he says,Bypass the bleed air around the compressor at high Mach number into the afterburner and it would solve the surge problem, provide cool air to afterburner and increase the mass flow and thrust significantly. Actually it converted the engine into a partial ramjet with capability above Mach 3.As to who may have been first to use the term "turbo ramjet" is moot I feel, as that is was what it was, as Bob alludes to.

[Lyman]

If increasing mass flow and thrust is the purpose, doesn't water injection do the same? Technically, since bleed air is already mechanically compressed and not "inlet" air, it is not "Ram Air"....

Inlet air that bypasses the mechanicals into the nozzle for combustion, is Ram Air.

1. Inlet air that has migrated through the spike is not ram air, it is "managed"
(slowed).

2. To qualify as a true hybrid, not a 'partial', the J58 needs to derive its power from "unmanaged" air, non 'mechanical' derivation.

3. Question. Can a Ramjet develop thrust (drag "plus") without itself burning fuel?

[peter kent]

Being of a left brain I shy away from wooley classifications because they need explanations to go along with them.

I'm guessing that the partial ramjet idea is because at a flight speed typical of some ramjets some proportion of 'engine-compressed' air goes straight to the ab.

This classification for the J58 (if I've got it right) now includes all Mach2+ afterburning bypass engines when they are going at full speed. The F100/TF-30 etc have become partial ramjets?

The turbo ramjet classification is not open to interpretation though as illustrated by Bob himself. In his patent he says re his 3rd possible solution for M3 flight "Such an engine configuration would be called a turbo-ramjet..etc..both large and heavy..etc...combustion efficiency low rel to turbojet" "My solution to the problem is the recover bleed air turbojet (not the turbo-ramjet)".

He's got a lot to answer for. He's making us think for ourselves.

[Brian Abraham]

Colonel Richard Graham spent seven years as a pilot, and later, instructor on the aircraft, 1st Strategic Recon Squadron Commander, Director of Program Integration at the Pentagon, and finally, 9th Strategic Recon Wing Commander at Beale.

His words from "SR-71 Revealed", page 50. The J-58 was the first dual cycle engine put into service. At subsonic and transonic speeds it was a standard , single spool turbojet engine, and it essentially transitioned to a ramjet engine around Mach 2.One would hope the gentleman knew what he was talking about. :E

Ben Rich himself opined that the engine was an ancillary (my interpretation) in the production of thrust in the cruise, when he famously commented on the compressors as "pumps to keep the inlets alive".

Interestingly, in the cruise if the engine is deriched its contribution to thrust drops to 10% approx of the total, vice the normal 17%.

The F100/TF-30 etc have become partial ramjetsNot at all, they are engines designed and optimised for a completely different mission (fighter), and used in aircraft which are not designed for the sustained Mach 2+ flight necessary.

[peter kent]

Just bought my own copy of Col Graham's"Flying the SR-71 Blackbird" only a week ago and have just borrowed from library Paul Crickmore's "Lockheed Blackbird".:ok:

3. Question. Can a Ramjet develop thrust (drag "plus") without itself burning fuel?
"Meredith effect"?

How about SR71 nacelle secondary flow just because it picks up a little bit of heat from the red hot ab duct.

[Brian Abraham]

Here is Kelly Johnson himself uttering that dreaded word - ramjet. :)

Discovery Channel - SR-71 Blackbird -Part 1- - YouTube

[Lyman]

Henceforth, the J58 shall be known as "RAMJET"........

No squawks here :ok:

[peter kent]

Good video.
What I'm looking for is a better understanding of how it all worked, from a pedants viewpoint of course.:8
Not sure if I'm allowed to make any more comments or ask any questions but I'll risk it.
One stumbling block was why would it be referred to as a partial ramjet?
I've just skimmed through my new book.
Fortunately (for me) the author says "the faster you flew the more fuel efficient it became....at Mach 3.0 it used 38,000 lb/hr. Accelerate to Mach 3.15 fuel flow drops to 36,000 lb/hr. The faster you flew the more it became a ramjet utilizing the high Mach air to augment the thrust of the engines."

Brian, maybe this explanation was also in the same authors "SR-71 revealed".

[Brian Abraham]

One stumbling block was why would it be referred to as a partial ramjet?You have to think of the entire installation as an integrated whole - inlet, engine, afterburner, nozzle. No single item would work without the other.

Take the afterburner for example. When the engine was deriched its thrust output was reduced, but without affecting the thrust produced by the inlet or afterburner.

With the engine deriched, although it is producing less thrust, the rotor RPM remains unchanged, so it's still pumping the same amount of air to the afterburner via the bypass from the 4th stage compressor.

The downside was that the exhaust from the engine was now reduced to a temperature where a blowout of the afterburner was possible.

The partial ramjet feature is the bypass air from the 4th stage to the afterburner. The bleed valve on the bypass doesn't open until the compressor inlet temperature is in the range 85° to 115° C, which corresponds to Mach 1.8 to 2.0. Up until that temperature range is reached the engine is operating as a normal axial flow turbojet with an afterburner. Once reached, the 4th stage bypass opens, and you have your partial ramjet. Highly compressed air being fed directly to the afterburner, up to 40% of the air consumed.
Not sure if I'm allowed to make any more comments or ask any questions but I'll risk it.The more the merrier peter. We all learn something in the interaction. eg I found Kelly did mention ramjet. :8

[galaxy flyer]

Any Concorde experts, please chime in....

Was the J58 cycle at all like the Olympus 500 while in cruise?

GF

[Lyman]

peter

One picture I have of the mechanism. The engine without afterburner peaks at some mach value, say 1.7. After that, the a/c cannot accelerate any further, the drag prevents it. The afterburner lights, and acceleration resumes, but the afterburner is reacting against the gas path, not the engine. The engine mounts are pinned back at the point where the turbosystem peaks, and remain so beyond that velocity. The Afterburner makes its thrust pushing on the gas flow at the start of the AB cabinet cross section.

A friend flew the F4 and recounted his experience at M2. It had to be done in a dive. He tells of pulling the engines out of AB, and it felt like he had hit a brick wall. Until he decelerated to some lesser Mach, the extreme deceleration was unnerving, indicating the drag had been there all along. He explained it in a way similar to that above, that the engine mounts were driven back into the frames, not pulling forward on them. Even in full burner at 2+.

Sounds counterintuitive.

Kelly Johnson can call the J58 anything he liked, seems to me. But the classic definition is what it is....

[Brian Abraham]

Was the J58 cycle at all like the Olympus 500 while in cruise?No GF, she operated on dry thrust in the cruise, though like the 71, the inlet provided a great deal of the motive force. The Concorde thread spells out a great deal of info.

[Brian Abraham]

Kelly Johnson can call the J58 anything he liked, seems to me. But the classic definition is what it is.... You seem to be having difficulty in understanding the turbo ramjet Lyman.

It is well understood in engineering. The following diagram comes from a NASA paper.

http://upload.wikimedia.org/wikipedia/commons/thumb/2/25/NASA-Turboramjet.jpg/800px-NASA-Turboramjet.jpg

A NASA paper on turbo ramjets. Access forbidden! (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19970001125_1996093653.pdf)

It opens by saying "Advanced airbreathing propulsion systems used in Mach 4-6 mission scenarios, usually involve turbo-ramjet configurations. As the engines transition from turbojet to ramjet, there is an operational envelope where both engines operate simultaneously." In the case of the J-58 both are operating simultaneously when above Mach 1.8 - 2.0, below that figure it's just a turbo jet with afterburner as previously mentioned.

It is what is alternatively called a dual cycle engine. Straight turbo jet to start with, becoming part turbo jet and part ramjet once up to the necessary speed for the ramjet function to begin operation.

A further NASA paper Access forbidden! (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110013567_2011014030.pdf)

A few extracts The engines considered are based on or extrapolated from known performance parameters of rocket-based combined cycle (RBCC) (the Marquardt Corporation ejector ramjet) and turbine-based combined cycle (TBCC) (the Pratt & Whitney J-58 engine used in the Lockheed SR-71 Blackbird).

B. Turbine-Based Combined Cycle Engines: Background
Turbine-based combined cycle engines operate by using a gas turbine propulsion cycle which transitions to a ramjet cycle; they bypass the turbomachinery at high Mach numbers, where pressures, temperatures, and flow velocities make such machinery impractical or redundant or both. Such a configuration by itself is not capable of orbital insertion because at some altitude the ramjet mode will lack the inlet mass flow to sustain thrust; however, TBCC engines hold strong promise for use with carrier vehicles or atmospheric ascent stages. Turbojet propulsion systems are generally limited to Mach 3 due to the rise in inlet temperature present at the compressor face; turbine engines are also in general more limited in altitude with respect to their ramjet counterparts as well. They provide more efficient operation, however, at lower altitudes and Mach numbers relative to ramjet-based engines.14 The limitation to lower Mach numbers and altitudes is not universal, especially if the ramjet mode is effective enough to compensate for the additional weight of the turbomachinery.

Turbine-based combined-cycle engines have seen actual flight time, a qualification which is not shared by RBCC engines. For example, the SR-71 J-58 engine is a turbine-based engine that operates in multiple cycles depending on the flight regime (with known cruise conditions of approximately Mach 3.2 at an altitude of 70,000 ft).

Can the historic configuration of the Pratt & Whitney J-58 with the Lockheed variable-geometry inlet be considered a true TBCC? From an aerospace purist view, the engine is never completely in a pure ramjet mode due to the fact that the first stages of compression are present before the mass flow is bypassed to the afterburner. In the viewpoint of the aerothermodynamist, however, the engine transitions through at least two modes or cycles and, thus, coupled with the turbine, can be classified as a TBCC.

From Colonel Grahams book "this bypass (air to the afterburner) led to the description of the J-58 as being a turbo-ramjet engine." As the Colonel acknowledges "Mr. A. J. "Arnie" Gunderson of Pratt and Whitney, better known as "Mr. J-58" among the crews was instrumental in helping me with specifics of the engine."

I'm somewhat loss Lyman why you can't accept the description provided by the designer, the crews who flew it, the people who instructed on it, and the P & W technical rep.

[John Farley]

You seem to be having difficulty in understanding the turbo ramjet Lyman.

So true Brian.

To be honest Lyman writes at great length about so many topics without seeming to understand them that I am starting to wonder whether he is one of those funny 'things' that crop up on PPRuNe from time to time.

Hey ho.

[Lyman]

I think communication is the problem, not specifics, or even theory.

If I put a cucumber in brine and vinegar for 48 hours, is it a cucumber or a pickle?

I do not deny the J58 satisfies the description of TurboRamjet. That makes it a hybrid, not a Ramjet.

A Ramjet engine derives compression and ignition from capturing passive airflow, not in compressing it mechanically.

Is that incorrect?

If a GE 90 captured some airflow aft of the fan and directed it back into the engine ( it does), is it a partial "Ramjet"?

If Einstein called a five a four, is he wrong?

[aterpster]

Doesn't Mach 1 remain a constant TAS above the tropopause? If so, what would be the TAS in knots for this bird doing Mach 3.2 at, say, 65,000?

[Turbine D]

aterpster,

If you go to this site, there are tables that may answer you question.

Aerospaceweb.org | Ask Us - Mach vs. Altitude Tables (http://www.aerospaceweb.org/question/atmosphere/q0112.shtml)

TD

[Brian Abraham]

Lyman, I give up. It's obvious from your last post that you have no understanding of first principles. Should you reread my last you will see where it says,the engine is never completely in a pure ramjet mode due to the fact that the first stages of compression are present before the mass flow is bypassed to the afterburnerThe term "partial ramjet" has been used so often in this discussion that I thought you may have grasped the concept. :ugh:

[peter kent]

a couple of questions:

1. At fixed max afterburner throttle angle, for example, when derich is selected what keeps engine speed constant? What happens to nozzle area?
2. Highly compressed air being fed directly to the afterburner, up to 40% of the air consumedWhere do you get the 40% figure Brian?

3. What's the explanation for Col Graham's
"the faster you flew the more fuel efficient it became....at Mach 3.0 it used 38,000 lb/hr. Accelerate to Mach 3.15 fuel flow drops to 36,000 lb/hr.
ie. out of all the various efficiencies that define the overall eff of the complete aircraft/propulsion system which one (or more) go up (or down) to give the net improvement as reflected in reduced FF?

[Turbine D]

Peter, Brian, Machaca & Gums,

Thanks for the discussions and information on the J58 engine, it has all been enlightening to an old jet engine guy. There have been some posts that have been both confusing and humorous which I intend to address here. There have been four types of jet engines in this discussion:

1. A turbo-ramjet engine, better known as a P&W J58 engine (main topic)
2. A turbojet engine, better know as a GE J79 engine
3. A turbofan engine, better known as a P&W F100 or GE F129
4. A high by-pass turbofan engine, better known as a GE90
All are different and one should not be confused with another. So bear with me here.

A turbo-ramjet engine is exactly that, a turbojet working together with a ramjet to power an aircraft to Mach 3+ that could not be achieved independently of one another. To simplify this, A ramjet generates no static thrust and needs a booster to achieve a forward velocity high enough for efficient operation of the intake system. The turbojet is the booster. Ramjets generally give little or no thrust below about half the speed of sound, and they are highly inefficient until the airspeed exceeds 1000 km/h (600 mph) due to low compression ratios. The turbojet is very efficient in this regime. Ramjets work by ingesting relatively low speed air and expelling the air at a higher speed. The difference in speed results in a forward thrust. The burning fuel creates higher pressures inside the engine, causing higher exhaust speeds. But the thrust of the engine depends entirely upon how much air flows through it. No matter how hot the burning air-fuel mixture is, and how high the pressure, if not much air flows into the front of the engine not much thrust is produced. So the trick to improving ramjet efficiency is to increase airflow through the engine. This is accomplished by the spike or obstruction called an innerbody. It is pointed on both ends and thick in the middle and fits inside the intake tube. Air passing into the tube must flow around the innerbody, and the area around it is less than the area of the intake opening. Consequently the air is compressed as it flows around and reaches a maximum pressure in the narrow throat between the innerbody and the intake tube. The same amount of air flows into the engine, but it is raised to a higher pressure. This increases the pressure that the burning gasses must push against, causing the overall pressure inside the tube to increase. Higher internal pressures mean greater amounts of air in the engine, so more fuel can be burned. The result is still higher pressures, increased exhaust gas speed, and greater thrust. But there is a problem that must be dealt with in the turbojet compressor area. When the pressure becomes too high in compressor, the blades tend to flutter, may break, the compressor can stall and the high temperatures can result in mechanical failures. So the P&W designers cleverly bled off air from the compressor to lower the pressure and temperature and fed it back to the burner in the afterburner section, it worked well.
Ram means 'to compress'. For "Ram" to apply to the J58, the engine would have to be able to shut down its compressors, and rely on inlet air only to propagate its motive power.
Not true, P&W solved that problem.
I do not deny the J58 satisfies the description of TurboRamjet. That makes it a hybrid, not a Ramjet.
Not true. You are thinking of an automotive description of some modern cars and SUV, a turbo-ramjet work together as a team, both at the same time once the speed becomes great enough.

In a turbojet engine such as the J79, all the air ingested passes through the core of the engine and upon exit may, be mixed with fuel and relighted to obtain additional thrust for acceleration needs in AB mode. In particular, the two engine F-4 phantom jet had the capability to achieve Mach 2.3 at 40,000 feet in level flight, Mach 2.5 minus external stores and fuel tank. It was designed to accelerate rapidly during climb to 40,000 feet and dash even more rapidly to a target. But it did have limitations.
A friend flew the F4 and recounted his experience at M2. It had to be done in a dive. He tells of pulling the engines out of AB, and it felt like he had hit a brick wall. Until he decelerated to some lesser Mach, the extreme deceleration was unnerving, indicating the drag had been there all along. He explained it in a way similar to that above, that the engine mounts were driven back into the frames, not pulling forward on them. Even in full burner at 2+.
Although this description is somewhat sketchy, the aircraft, being of aluminum exterior was painted with heat resistant paint good to 400℉. The friction caused by the Mach 2 speed in a dive from 40,000 feet or less if continued long enough would be disastrous and the abrupt slowdown was in effect lifesaving for the pilot, the wings and the engines. The panels on either side of the fuselage just forward of the engine intakes were not for decorative purposes. This plane was simply overpowered for its construction.

The F100 and F110 engines, being turbofan engines take most of the air through the core but the excess from the fan is funneled around the core engine exterior and dumped back into the afterburner where it is mixed with the core exhaust or where fuel is added and ignited in the AB mode. This is much more efficient than a normal turbojet AB engine system.

The GE90 high by-pass turbofan engine develops 60% of its cruise thrust from the fan by-pass. The air is ducted by the nacelle around the engine core and dumped into the air but does not mix with the core exhaust air.
If a GE 90 captured some airflow aft of the fan and directed it back into the engine ( it does), is it a partial "Ramjet"?
No, because a ramjet doesn't produce hardly any thrust at all at 0.83 Mach and the air passing through the fan is only lightly compressed.
If Einstein called a five a four, is he wrong?
Yes...
If I put a cucumber in brine and vinegar for 48 hours, is it a cucumber or a pickle?
It is a dill pickle :p

TD

[Lyman]

Frankly, the six bleed ducts are superchargers, the pressure is created mechanically, something a ramjet does NOT do. Any additive pressure to the gas path that is created mechanically is not RAM. By definiton.

PW did not "solve" anything by routing bleed to the ejector, neither do they create a ramjet.

"Hybrid" predates automotive usage by fifty years....

Turbo Ramjet is fine, not difficult at all.

Nomenclature is not a problem, but know this, the standard definition of a Ramjet engine is one that does not rely on mechanical compression of air. The air routes into a combustion chamber directly, fuel is added and ignited, and the exhaust creates thrust.

You do a great disservice to Pratt, Whitney (and the ampersand) by denigrating the J58 with terms that imply it is a ramjet. it simply is not.

The Ramjet is the simplest concept in aviation, one of. The J58 is a masterpiece of ingenuity and engineering. I used to pass one in the hall on my way to work (it was on a stand), and got to speak to pilots of the Blackbird....

Your usage of all the terms is just fine, to each his own.

" In a ramjet, the high pressure is produced by "ramming" external air into the combustor using the forward speed of the vehicle. The external air that is brought into the propulsion system becomes the working fluid, much like a turbojet engine. In a turbojet engine, the high pressure in the combustor is generated by a piece of machinery called a compressor. But there are no compressors in a ramjet. Therefore, ramjets are lighter and simpler than a turbojet. Ramjets produce thrust only when the vehicle is already moving; ramjets cannot produce thrust when the engine is stationary or static. Since a ramjet cannot produce static thrust, some other propulsion system must be used to accelerate the vehicle to a speed where the ramjet begins to produce thrust. The higher the speed of the vehicle, the better a ramjet works until aerodynamic losses become a dominant factor". .....NASA Glenn Research Center

bog simple....

great respect......

[gums]

Salute!

I'll stick with the SR-71 manual and other sources that the J-58 never quite got into a "ram jet" mode at all. It simply bypassed air from one of the compressor stages when the "core" engine couldn't use all of it efficiently, but the burner could. Let's face it, the core couldn't handle all the air and then we had temp problems down stream.

So the extra air from those bypass ducts in the J-58 allowed the burner to work really well. Lottsa air and somethat cooler that that going straight thru the core. We saw this in the F100 motor from Pratt in the Eagle and Viper. The difference in burner thrust was a much higher percentage than with the older motors that simply added JP-4 to the air that had not burned completely going thru the core and the turbines.

The problem with our fan motors was instability in the bypass duct, which was not like those tubes in the J-58. So think another ten years of design and knowledge gained from the J-58. We never had the classic compressor stall effects - loud and physical bangs or chugs. We would have an unpooling motor and "torching" out the burner nozzles, and associated loss of thrust - called it "stall stagnation". Pratt worked on this a lot, and I think the solution was in the nozzle control. BTW, our initial Viper squadron tech rep from P&W had been involved in the J-58 design and testing.

The only Blackbird pilot I have discussed this with said they "inlet unstarts", and whoa! Lottsa loss of thrust from one side and it required some good ruddeer and other "pilot things".

One of the more intriguing designs would have had the spikes at the inlet and the geometry of the engine close down the core airflow even more than the J-58. An annular bypass and not a half-dozen tubes as the J-58 had. In other words, an F100 type motor with a fancy inlet spike as the SR-71 had.

We got by just fine, thank you. That fan really helped with range, and I had flown the SLUF with the TF-41 for a thousand hours and it worked the same.

Great discussion here,

[Brian Abraham]

I'll stick with the SR-71 manual and other sources that the J-58 never quite got into a "ram jet" mode at allThe flight manual in fact makes absolutely no mention of the word "ramjet". Nor does it tell us whether the engine operates on an Ericsson cycle, Joule cycle, Otto cycle, or Brayton cycle.

Not all detail makes it into a flight manual, and that's why you have tech reps who understand what is/isn't going on, as the case may be.

A pilot does not need to know the nuts and bolts, or principles behind the engineering. What he needs to know is how to operate the machinery, and sort the problems as they arise. You will find the flight manual goes into immense detail on the operation, both normal and emergency, of the spike, front bleed, rear bleed, nozzle, afterburner, derich, EGT trim, shifting of the IGV, and compressor inlet temperature and pressure. An organ player doesn't have it so tough. What he is doing is managing the operation of the ramjet function and keeping it on song.

From,

Kerrebrock, Jack L. (1992). Aircraft Engines and Gas Turbines (2nd ed.). Cambridge, MA: The MIT Press. ISBN 978-0-262-11162-1

Heiser, William H.; Pratt, David T. (1994). Hypersonic Airbreathing Propulsion. AIAA Education Series. Washington D.C.: American Institute of Aeronautics and Astronautics. ISBN 1-56347-035-7The air turboramjet engine is a combined cycle engine that merges aspects of turbojet and ramjet engines. Air passes through an inlet and is then compressed by an axial compressor. That compressor is driven by a turbine, which is powered by hot, high pressure gas from a combustion chamber.

The air compressed by the compressor bypasses the combustor and turbine section of the engine, where it is mixed with the turbine exhaust. The turbine exhaust can be designed to be fuel-rich (i.e., the combustor does not burn all the fuel) which, when mixed with the compressed air, creates a hot fuel-air mixture which is ready to burn again. More fuel is injected into this air where it is again combusted. The exhaust is ejected through a propelling nozzle, generating thrust.[Perhaps Lyman can expound on why compressor inlet pressure is of importance.

[Lyman]

Perhaps Lyman can expound on why compressor inlet pressure is of importance.

Hello Brian

Our disagreement seems to revolve around the definition of "compression".

Bleed air originates in a mechanical (axial) cabinet, ramjet inlet air originates from the mere capture of air in an intake. There is no mechanical enhancement of pressure; the high velocity of the inlet relative to the airstream provides compression sufficient to ennable combustion, after addition of fuel.

So it is simply the lack of mechanical enhancement that creates the criterion for the definition.

So to me, any "aspect" of ram "effect" would by definition need to have its source of compression separate from the mechanical core of the engine.

It seems a workable distinction to me.

I can't imagine why it is so difficult. In creating criteria, the format can include or exclude certain aspects that allow for more restrictive or more general conclusions.

The easiest thing to do is to agree to disagree. We have different criteria for the discussion, which allows for both of us to be correct.

If enough people, especially wise people, use terminology that they agree on, the purpose of understanding is done. You and I use a slighly different set of criteria.

It seems important to you that I disagree with your definition. We have no fundamental disagreement, only a slightly different opinion on the background of the mechanical aspect of the origination of the air supplied to the combustor.

Consider me wrong, and let's move on?

With great respect.....

[Turbine D]

Lyman,
PW did not "solve" anything by routing bleed to the ejector, neither do they create a ramjet.
You do a great disservice to Pratt, Whitney (and the ampersand) by denigrating the J58 with terms that imply it is a ramjet. it simply is not.
Frankly, the six bleed ducts are superchargers, the pressure is created mechanically, something a ramjet does NOT do. Any additive pressure to the gas path that is created mechanically is not RAM. By definiton.
You just don't get it yet, do you?

There is much information on the internet about this subject, if you would only search and find it.

Start by reading this beginning on Pg.2 and continuing to Pg.4:
http://www.bobabernethy.com/pdfs/Never%20Told%20Tales%20of%20P&W3.pdf

So if you want to take issue with the P&W guy who recognized the problem, developed the solution idea (Bleed Tubes), and patented it, be my guest. I am sure you will, holding true to form.

If you are still having trouble understanding,
Then,
From the USAF, Hill Air Force Base:
The variable-geometry inlets for the engines were quite complex and intricate. The most prominent feature was a hydraulically-actuated conical spike which was automatically moved forward or aft by the Air Inlet Computer as required to keep the supersonic shockwave properly positioned in relation to the inlet throat. Working in conjunction with a series of bypass ducts and doors, the spike prevented supersonic air from entering the inlet and maintained a steady flow of subsonic air for the engine. At Mach 3.2 cruise the inlet system itself actually provided 80 percent of the thrust and the engine only 20 percent, making the J58 in reality a turbo-ramjet engine.
Also,
From Aircraft Engine Design:
Turbojet/Ramjet Combined Cycle Engine
The J58 operates as an afterburning turbojet engine until it reaches high Mach when the six large tubes (Fig. 13a) bypass flow to the afterburner. When these tubes are in use, the compressor, burner, and turbine of the turbojet are essentially bypassed and the engine operates as a ramjet with the afterburner acting as the ramjet's burner.
And,
From Aerostories
Mach numbers the new engine would be unable to cope with the volume of air coming through the air-intakes. This would result in compressor stalling with accompanying loss of efficiency and thrust at high speeds. Pratt & Whitney therefore modified their JT-11 by installing a series of fixed flow-vanes downstream of the 4th compressor stage, which directed the surplus airflow along six longitudinal jet pipes running along the engine casing. The surplus was then carried straight to the afterburner chamber serving to cool the burners, whilst enriching the mixture; so enabling higher combustion temperatures or increased thrust.

TD

[flyboyike]

I like this thread. Such deep knowledge displayed here, it's starting to make my teeth hurt.

[Lyman]

I cannot isolate any further the kernel of my position.

If the airflow feeding what you term the Ramjet "section" of the J58 is isolated from the internal machinery of the turbojet in toto, there would (technically) be a Ramjet "component" to the engine's power. If the source of this air is the compressor section, you are completely, and patently, wrong. I do not care who endorses the definition, Ramjets operate from passive air, not mechanically enhanced air.

There is bypass air that is directed into the ejector, from forward of the internal part of the Turbojet. It, however, passes through the spike, and also (technically) fails the uninterrupted nature of what has been (classically) the definition of a Ramjet engine.

The important part (to me) of this discussion is how you won't address my very basic point, "enhanced airflow disqualifies the definition".

My worry is not to be accused of being stupid, but that I seem to have failed completely in receiving even an acknowledgement of this most basic definiton.

w/o extraneous data, would you simply say if you understand my position?

You do not need to affirm/deny it.

[Turbine D]

Lyman,
I cannot isolate any further the kernel of my position.
That is because your position is weak.

w/o extraneous data, would you simply say if you understand my position?
No, I do not understand your position.

The "extraneous data" are facts that you, for whatever reason, choose to ignore in attempt to reenforce your position.

I know this is a waste of time but, I will give it one more try. Simplistically, for the SR-71 mission, the engines required a level of thrust capable of flying at 80,000 feet and Mach 3.3. To achieve this, an engine had to be designed to provide enough initial thrust to propel the aircraft to a high Mach (~2.2) when a ramjet function could take over to accelerate and maintain a speed of Mach 3.3. To achieve this goal, the turbojet (generator for the ramjet) had to function as well as the ramjet, itself. However, there was a problem at high Mach with the turbojet compressor. The air in the compressor could stagnate causing compressor blade flutter or even compressor stall where the turbojet engine would cease to function at all. So the solution was to take excess air somewhere from the turbojet engine and duct it back to the AB (ramjet burner). This could be accomplished a couple of ways, pull air out as it entered the engine or pull air out at a convenient location in the turbojet compressor. So as to make the engines fit into the hole in the designed nacelles and not make them bigger in diameter adding weight to the aircraft, the latter solution was chosen. In doing so, it does not modify the basic definition of a ramjet or the ramjet function, in fact it enhanced it by providing more air for combustion when mixed with fuel. It is still a ramjet working with a turbojet or a turbo-ramjet engine. All the by-pass tubes do are to ensure the turbojet still works at Mach 3.3.

TD

[Lyman]

You confuse nomenclature with theory...

I call my Tabby "Butterscotch".

Does that make her a dessert topping?

[peter kent]

Some very embarrassing statements from somebody here.

There is much information on the internet about this subject, if you would only search and find it.
First, best not to believe what you read on the internet.
All I can do is hopefully lead you to water.
Bob Abernethy's Untold tales is very good. It is too short unfortunately to explain much but we are in luck because we have the essential complement to his 'tales' in the form of the 'bible' he wrote on how he fixed the J58 to work at Mach 3.2. It is called US Patent 3,344,606.

From Aerostories
Mach numbers the new engine would be unable to cope with the volume of air coming through the air-intakes
Read the patent and then tell us what you have learned.
installing a series of fixed flow-vanes downstream
Read the patent and then tell us what you have learned.

From Aircraft Engine Design:
Turbojet/Ramjet Combined Cycle Engine.When these tubes are in use, the compressor, burner, and turbine of the turbojet are essentially bypassed Bear in mind 'Bob' designed and built real engines that made money. He didn't write textbooks.Read the patent and then tell us what you have learned.

If you are still having trouble understanding, Embarrassing statement
The air in the compressor could stagnate causing compressor blade flutter or even compressor stall where the turbojet engine would cease to function at all Embarrassing statement. Read the patent. Tell us what you have learned.

[Lyman]

peter....

In the description portion of the patent, the author describes "Increasing Ram air temperature" as the drawback to high speed turbojet operation, then further, that the purpose of the bleed air is to cool the compressor then reinject the bleed into the ejector to be "reheated"...

My sense thus far is that rather than ennabling a Ram function, his purpose is to defeat it.....

The document resists copying, so I guess I could say:

Read the patent......

Continuing, the inventor actually suggests possible options to the turbojet problem. His "Option 3" he actually labels the "Turbo-Ramjet", which he rejects as too heavy. This option involves bypassing completely the Turbo machinery.

:ok:

[peter kent]

If the airflow feeding what you term the Ramjet "section" of the J58 is isolated from the internal machinery of the turbojet in toto, there would (technically) be a Ramjet "component" to the engine's power. If the source of this air is the compressor section, you are completely, and patently, wrong. I do not care who endorses the definition, Ramjets operate from passive air, not mechanically enhanced air.
I think this makes sense.
Too many classifications add no value . They require explanations. Just say what it is.
Engine A is a dual cycle. What does that mean? Well, above a certain speed it bleeds off some air.
Engine B is a dual cycle. Oh you mean... No! It's got variable stators...
Engine C is like a ramjet at high speeds. Right, that's because.... No It's got a spike like ramjet intakes. Oh, thanks.
J58? Just tell it like it is.

However there is an audience that wants classifications and intuitive 'understanding'.
KJ knew this (Discovery video for public consumption). Why didn't he call it a flow inducer on the program? Wrong audience. He saved that for "Our good friends at Pratt and Whitney do not like us to say that at high speeds their engine is only a flow inducer and that, after all, it is the nacelle pushing the airplane".

Continuing, the inventor actually suggests possible options to the turbojet problem. His "Option 3" he actually labels the "Turbo-Ramjet", which he rejects as too heavy. This option involves bypassing completely the Turbo machinery.
Exactly. He defines what a turboramjet is. He worked in the aero engine industry. He created a world beating engine. He didn't write textbooks or work at a think tank coming up with schemes and definitions that would never see the light of day. Some textbooks had the same definition BTW, eg Hesse and Mumford "jet propulsion for aerospace applications"' written by LTV engineers.

the purpose of the bleed air is to cool the compressor then reinject the bleed into the ejector to be "reheated"...
Don't understand, I'll read again.

[peter kent]

Lyman, I can't find itpurpose of the bleed air is to cool the compressor then reinject the bleed into the ejector to be "reheated"

What line?

[gums]

Salute!

This is getting ridiculous about "names".

I have to agree with those here that do not think/believe the J-58 was in any way a "ram jet" once above 2.x M.

The clever engineers at Pratt figured out how to use all the air being crammed into the motor to use it in the burner. At the same time, they reduced some temperature and other bad things on the "core" engine. They also realized that you couldn't get a lotta thrust with a pure turbojet at the speeds they were trying to reach.

Had the J-58 been a combined cycle turbo-ramjet, it would have resembled the F100 that Pratt developed for the Eagle and Viper. An annular bypass, but a mechanism to close off most, if not all, air entering the core. The hot, compressed air from the intake would go directly to the "burner" section and act just as a traditional ram jet.

The J-58 did some of this, but the air being bypassed was nowhere near enough or hot enough to provide what is needed for a ram jet.

It should be noted that many of the early ( 1950 - 196x) turbojets had burners that could still add fuel to the unburned air that came thru the core. So the Pratt folks developed a way to bypass a lotta useless air and feed it directly to the burner and gain a lotta efficiency and thrust - up to a point.

A complete changover to a ram jet above 2.x M would have allowed the Blackbird a much higher speed/altitude, but the materials for the structure could not handle the heat. And the Blackbird did not have "thrusters" to control pitch, yaw and roll once really high - it was all aero forces on the control surfaces, shock waves and all.

The J-58 was a super motor, and it served us well for many years. But it was not a "turbo-ramjet".

That's my story, and I am stickin' to it.

[Turbine D]

Peter,

I assume the embarrassing statement from somebody here, you point out, are contributed to me, so I will respond accordingly. First about Dr. Bob Abernethy:

From his web site, Bob Abernethy.com:
Dr. Robert B. Abernethy is known worldwide for his expertise in jet engine performance, measurement uncertainty analysis and Weibull analysis. He joined Pratt & Whitney Aircraft in 1955. He retired from Pratt & Whitney Aircraft in 1987 after 32 years as Manager of Reliability, Safety, Maintainability, and Statistical analysis to teach Weibull analysis. He holds the patent on a feature of the J58 Pratt & Whitney engine that powers the world’s fastest aircraft. His invention converts the afterburning turbojet into a partial ram jet at high Mach number.
Dr. Abernethy did indeed write a number of books and publications which are listed on his web site.
Bear in mind 'Bob' designed and built real engines that made money. He didn't write textbooks.Read the patent and then tell us what you have learned.
Bob didn't design and build real engines, he happened to come up with a solution to a problem that a real engine was having and it fixed that problem, making it a money maker instead of a money loser. Actually teams of people design jet engines, not one individual.
First, best not to believe what you read on the internet.
It is where I got the Abernethy/P&W patent some time ago but thought it might be too technical for some to fully understand. Also, Abernerthy's web site would be a source of information I would believe.
Read the patent and then tell us what you have learned.
I've read the patent. You do know that patents are written to generally disclose the invention, but, not to give too much information away. A couple of things I will point out to you:
From the patent:
A second solution to the flow blockage problem has been suggested in the form of mechanical rotation of the stator vanes in the front and rear compressor stages to improve the air angles. This proposed solution has several severe disadvantages in that the stator control must be precise and the angular rotation would have to be different for each compressor stage. Consequently, an intricate control mechanism would be required and malfunction of the control would be disastrous. In view of the complexity of the control mechanism, leakage through the actuating mechanism would be almost impossible to eliminate. Further, engine weight would be substantially increased thereby and it would be almost impossible to rotate the stator vanes to an angle which would be optimum for both stator vane angle and its associated blade air angle, whereas, my recover bleed air engine rematches both vanes and blades.
Actually, this would have solved the problem in the compressor which had two different problems, Stall and Choked, however, it happened there was patent for this feature: Us Patent 2,931,168 titled Variable Stator Engine Control System, Application Date - 5/24/1955, Patented 4/5/1960, Assigned to General Electric Company. You can easily hold the actuator arm in one hand and the piston controlling the arm in the other, not that heavy, and leakage is not a problem, Would have required modifications to the compressor casing and vanes, plus some time, but the patent was a problem.
Pratt & Whitney therefore modified their JT-11 by installing a series of fixed flow-vanes downstream of the 4th compressor stage
From the patent claims:
A plurality of guide or turning vanes are positioned within fish-tail inlet to smoothly guide the bleed air into ducts which are of substantially circular cross section.

I could go on, but I think you can see the information I provided is not embarrassing even if you may think so. I think Gums is right, forget the names, the engine worked and Dr. Abernethy had a great idea....

TD

[Lyman]

Hi gums...

you say...."The clever engineers at Pratt figured out how to use all the air being crammed into the motor to use it in the burner. At the same time, they reduced some temperature and other bad things on the "core" engine. They also realized that you couldn't get a lotta thrust with a pure turbojet at the speeds they were trying to reach."

I was about to sit down and take four paragraphs to say just that. Clear, concise, in english.... :ok:

In the patent, a guy lays out the problem, offers options, and proposes a solution, making claims, and offers drawings and supporting material. I have been through it, and have a patent pending for a novel helicopter controls system.

For the record, the words "Partial Ramjet" are oxymoronic. A Ramjet is not a ramjet until a very specific point is reached, at which it becomes an engine, full on, no partial about it. It is either running, or it is not. It does not fill the role of "conttributory", as if it was some form of "Turbocharger".

Believe it or not, the Patent Office does not require a working prototype, or that the solution even work....

The inventor in question, here, Abernethy, calls his invention a bleed air recapture system.

He proposes the problem that all turbojets have, loss of power, efficiency, and off the chart temps, as it approaches very high Mach.

He says there are two causes, excess Temperature, and excess airflow, which "chokes" the compressor.

Both of these problems are....ready? Created by RAM AIR. So the problem is Ram AIR, too hot, too thick, and what do we do? Here he proposes to drain some bleed air from the fourth stage of the Compressor, which instantly unblocks the compressor (choke) and moves aft through the six ducts, to enter the Ejector, for added mass, and expansion.

This process also cools the compressor and Turbine, and the Ejector LINER, the case.


I am going back in to find the text where he identifies cooling function, and reheat.

back in a bit.......

from the PATENT (claims)...

"...my new engine provides cool bleed air to the afterburner for cooling purposes."

That does not sound like he is "turning the afterburner into a "partial RamJet".
As the "website" purportedly claims.

He specifically eliminates the nomenclature "RAMJET" as one of his"proposed" and ELIMINATED options. Number (3). "TURBO RAMJET", the name itself, is rejected by this man as descriptive of "his engine"...in hisown words (through his patent attorney).

But do read the patent, it is informative, seems to have cleared up some murk, and is pretty typical of Patent text in general.

cheers, Lyman

[peter kent]

Turbine D,
I apologise for any misunderstandings. I felt that explanations like "the engine would be unable to cope with the volume of air" and "the air in the compressor could stagnate.." would not help people trying to grasp what was happening, whilst the patent explains the whole high inlet temp/low corrected speed problem correctly in a nutshell.
As you were suggesting these sources of information I got the wrong end of the stick.
Although you say the patent should not give much away, it seems an amazing first primer in compressor operation in general terms and more specifically at high inlet temps. Just seemed too good to not be made more visible.

I'm fully aware of Bob Abernethy's role as the 'father' of the M3 J58 ref my copy of Jack Connors book.and unfortunaley, again, was not on your wavelength. I have

Thank you for the variable stator story.
:\

[Brian Abraham]

But it was not a "turbo-ramjet"Of course you are entitled to an opinion, but that doesn't make you correct.

In the adoption of the position that the engine featured no "ramjet" function, you need to explain,

Why Kelly Johnson, the aircrafts designer, refers to "ramjet"

Why the aircrafts pilots refer to "ramjet"

Why the aircrafts instructors refer to "ramjet"

Why the P & W engineer assigned to oversee the in service use of the engine refers to "ramjet"

Why the people assigned to command the operation of the aircraft refer to "ramjet"

Were all these people so stupid that they didn't know what they were talking about?

[Lyman]

Abernethy is very specific about "Turbo-Ramjet". He introduces it as a potential approach to solve the problem of high inlet temperature and blocking, (choking) of the compressor. He describes it as heavy, utilizing 100 percent air flow from around, (bypassing) the core and unworkable.

As to "Partial Ramjet" I write above re: Abernethy utilizing the bleeds to "cool" the afterburner. By cool, he means a titch shy of melting. That does not describe a ramjet, and as I wrote above, a RamJet is an all or nothing concept, there is no "kind of" pregnant.

As to why the term "ramjet" became au courant in the fraternity, I can only guess. In the fifties and sixties, a Ramjet was a concept that was tantalizing, though the idea had been around since the early nineteen hundreds.

Abernethy does refer to "Ram Air" in passing, and defines it as the source of the problem for high speed supersonic turbojet propulsion... He describes it as too hot, and too dense, to manage through the compressor inlet,, it choked the compressor section, (not a stall, essentially the opposite), and prevented the turbojet from getting into seriously high speed regimes.

His resolution of the obstacles caused by 'Ram Air', got the attention of everyone, and though misunderstood, came into the jargon as "Ramjet", when in fact Abernethy specifically denied the concept in his patent....

So the J58 is not a Ramjet, not a Turbo Ramjet, and not a Partial Ramjet...

It is a "Recovered bleed air system"....

I think the misunderstanding perpetuated throughout the community as 'jargon' since it really wasn't utterly wrong, and had a cachet that fit the times, it leant myth and mastery to the fraternity, a fraternity that was in serious competition with Mercury, and Canaveral, for big dough, and bragging rights....

I don't particularly enjoy the pedantic role, but I love a spirited discussion....

:ok: great respect, Brian Abraham...

[Brian Abraham]

Well, we have a real problem on our hands, seems Bob Abernethy doesn't know what he's talking about.
Actually it converted the engine into a partial ramjet with capability above Mach 3! I called it the Recover Bleed Air engine on my patent. Here you see my drawing of the duct in my patent disclosure

[Lyman]

I went out on a limb as to "partial ramjet", if that is accurate there is a "partial problem".

First, he did nullify the 58 as a Turbo Ramjet. That much is in the patent, unless he said something to contradict, elsewhere. It most certainly is not a pure Ramjet, that is obvious....as to "partial", I may be the only one, but I stand by my statement, there is no such thing.

If this "partial Ramjet" is working, from whence comes the Ram? If you answer "Bleed" then you put yourself in a corner, by definition, linguistically if not technically also.

The origin of inlet Air for a Ramjet is from the airstream. If it is mechanically enhanced, it does not meet the standard definition and is not a ramjet, partial or otherwise.

Abernethy describes this engine's inlet (J58) as being frustrated by "Ram Air".

The Ram creates high temps, and blocks the Compressor section.

So Abernethy reduces the temperature and block by decreasing the pressure at the compressor initial stage. At this point, having decreased the Ram, the bleed travels back to the combustor. The bleed has lower pressure and cooler temperature than the core gaspath and enters the afterburner, and becomes by definition only a Ram Jet? By decreasing pressure and cooling? That is the opposite of the standard mechanism for a Ramjet. Reducing pressure and temperature in the chamber describes ramjet?

Arse About....

[Brian Abraham]

I hate repeating myself. Bob Abernethy himself wrote.
Actually it converted the engine into a partial ramjet with capability above Mach 3! I called it the Recover Bleed Air engine on my patent. Here you see my drawing of the duct in my patent disclosure You saying he doesn't understand what it was he patented? I'll repeat his partial quote in big letters

it converted the engine into a partial ramjet

[Lyman]

I got it the first time. Put that aside and explain why my opinion is wrong....

His description is extensive in the patent, he adds mass to the ab and it is combusted, increasing thrust. The term partial ramjet does not appear...

How is that different from a standard turbojet. Can you explain?

And no, I am not saying he does not understand, only that I do not....

Abernethy's design introduces compressed air into a combustion chamber.

"A Ramjet has no mechanical compressor..." NASA Glenn Research Center

[Brian Abraham]

Lyman, I don't know why you continue to be so obtuse, and fail to understand what Bob Abernethy is saying. I'll spell it out for one very, very last time.

Bob Abernethy said it's a partial ramjet, but I called it a Recover Bleed Air engine on my patent

Confine yourself to that one statement. What part of it do you not understand?

[Lyman]

Hi Brian

The disconnect is most clear. I have a point of view. The reality as I see it is the function, not the name.

The title does not matter to me so much as it matters to you.

To be Precise. The owner of the patent knows his work. He has assigned two titles to it. One title is informal, the other official.

I will continue to refer to it by its officially recognized title. I am less insistent in its title than in its function, which you seem to be disconnected from, as you refuse to discuss the machine on its merits.

I am not being unreasonable. I wish to discuss the function, the purpose, and the theory. The name has caused some interest in the discussion. At every turn, you jump in, get excited, and focus on the progenitor of the interest, instead of recognizing the worth of the give and take.

If I have been guilty of that, I apologize. I acknowledge the statement you make.

A Ramjet system has no mechanical compressor. A true statement. The argument should be about why Abernethy calls his invention a partial ramjet.

The tension should be between the official rule for Ramjets and the inventors apparent dismissal of it.

There be the treasure...

Be well...:ok:

[Dick Whittingham]

Lyman,

To be precise, Abernethy did not "assign two titles" to his engine. He assigned a title to his patent, but said the engine was "actually", that is, in reality, a partial ramjet. I'll go along with that

Dick

[Lyman]

Excellent point.....

[peter kent]

Dick,
Brian helped us out earlier saying the J58 behaved like a partial ramjet at about M2 and above due to the 20% of its inlet flow having 4 stages of work and then bypassed straight to the afterburner.
From a pedants POV, can we consider a TF30, for example, at M2 with 50%? of its inlet flow having 3 stages of work and then bypassed straight to the afterburner also behaving like a partial ramjet? If not, why not?
Thanks
PK

[Jhieminga]

When this thread started I was hoping for an interesting discussion about supersonic propulsion. Instead three pages are devoted to a heated discussion about who called what and why, debates about names when (it seems) the principles are not really understood.

Moving on...

[Lyman]

Hi peter

Abernethy claims a twenty percent plus increase in thrust from the bleeds scheme. This augmentation is not only purposeful, but the system, by his desription, allows the engine to travel at 3M when it was essentially paying out at 1.7. So the engine, functionally, has two separate modes.

His lead in to the description of the challenge claims the problem was ram air, causing high temperatures and choking (blocking) of the inlet area. Now ram air is without doubt a precursor to a Ram System of propulsion, and the problems he describes present a possibility of utilizing this "problem" to accomplish ignition and sustenance for a true RamJet.

He also describes a Turbo Ramjet solution to the problem. For this, he proposes a true bypass around the core, not just bleeds, but dismisses the possibility as heavy and not workable.

I wonder if he was dismissive too early?

Are you aware of any work done to pursue this?

Your post above is compelling. When is a cucumber a pickle? At what point does Abernethy's "PARTIAL RAMJET" become a true RJ engine?

:ok:

[Dick Whittingham]

Peter,

I shouldn't have done that. I had hoped to give Lyman pause to check his mass of verbiage for errors, contradictions, non sequiturs, pointless metaphors, et al. Instead I have unlocked another floodgate. I'm off.

Dick

[Loose rivets]

Just happened to have put this in JB


http://www.pprune.org/jet-blast/506704-difference-between-space-shuttle-airliner-exhausts.html#post7666481

[Lyman]

Leaving, instead of replying to peter? Too much pique, methinks, here....

[Machaca]

I had hoped to give Lyman pause to check his mass of verbiage for errors, contradictions, non sequiturs, pointless metaphors, et al.


Don't succumb to our resident concern troll.

Simply add them to your ignore list!

Through your User Control Panel: User CP (http://www.pprune.org/usercp.php), Settings & Options, Edit Ignore List (http://www.pprune.org/profile.php?do=ignorelist). Then, type their name into the empty text box and click 'Okay'.

[john_tullamarine]

Folks, we appear to be getting off track just a little here. Please do keep in mind that the aim is to play the ball, not the player.

If one or more of our number adopt (a) hardline position(s) in respect of any particular point that should be noted .. and then we should move on.

Little in the way of useful outcome is achieved by belabouring such points.

[Brian Abraham]

I beg the indulgence of the forum if I took umbrage at Lymans continued insistence that post #52 the J58 is not a Ramjet, not a Turbo Ramjet, and not a Partial Ramjet...I felt that once we could get Lyman to stop banging on with a fallacious argument the discussion could return to matters of fact, and teasing out why things might be as they are. I have a question of my own to follow.

peter kent provided the proof at post #12 that it is a "partial ramjet", and I pointed out that fact in my post #14. That particular posters are unable to accept iron clad proof I can only say they need to check their level of comprehension.

peter, re the 20 to 40% bleed figure. I came across the figure in a number of places, in particular one by Colonel Graham, so I give it some credence. Seems logical if you think about it, 20% when the bleed first opens at about Mach 2, increasing to 40% in the cruise as the increasing needs of the "ramjet" are met. I'll need to go back over the thread to tease out your other question/s that remain to be answered.

peter, edited to add re reduction in fuel flow with increasing speed.

Specific impulse is a way to describe the efficiency of rocket and jet engine. It represents the force with respect to the amount of propellant used per unit time. The higher the specific impulse the greater the efficiency. From the following ramjet formula you can see that the specific impulse (Isp) is directly proportional to Mach (Mo).

http://web.mit.edu/16.unified/www/SPRING/propulsion/notes/img1319.png

[Shaka Zulu]

Lyman please check your "facts" before posting. Both here and the post you made in the general section as to why the 787 needs batteries are factually wrong.
You clearly are no specialist in aviation related matters which in itself is fine but accept the fact that others know more than you instead of arguing the toss

[peter kent]

Hi Lyman,
At what point does Abernethy's "PARTIAL RAMJET" become a true RJ engine?

I have to quantify partial ramjet in some more concrete terms just for myself first.
I would choose to focus on the rapidly diminishing but still remaining residual contribution of the compressor to the overall installation Pressure ratio.
For the SR-71 at cruise, Intake PR 38.8, engine PR 2.9, overall PR 112. Numbers from Peter Law's presentations on AEHS website.
The engine contribution still remaining is only 2.6% of the overall. It's almost a ramjet, unless the ramjet had not yet been invented in which case it's a turbojet at very high Mach number.
This definition also applies to the XB-70, for example. It must also be a partial ramjet.
This definition is, I think, intimated by Col Graham "the faster you flew, the more it became a ramjet, utilising the high mach air to augment the thrust of the engines."

However, since the generally accepted term, partial ramjet, applies only to the SR71 I have to, for my own piece of mind, try and understand the definition given by Bob Abernethy. I think it basically revolves around the same criterion, ie diminishing involvement of the compressor. But, instead of a gradual diminution from the compressor with rising flight speed, as in the above definition, we have a sudden diminution when the bleed is opened, but not because the pressure ratio contribution has suddenly dropped. Instead the flow has suddenly increased (see the patent maps) from bypassing some of the compressor. This map shows no significant change in PR and if it was significant to the story I'm sure it would have been highlighted as have all the other effects.

Using the term partial ramjet does not necessarily add value to the picture. After all, if the ramjet had not yet been invented we would say "it is an afterburning turbojet with bypass bleed" and it, by definition, behaves like one.

Since the ramjet has been invented and due to it's perceived extreme simplicity, it can be an aid to understanding and, I believe, that's why the term is so widely used. It's taken me a long time to come to this conclusion but at last have piece of mind. I am no longer irritated with the term.

Brian
re the 20 to 40% bleed figure
20% is the right number because Bob Abernethy was quoting all his stuff at the design point. In the definitive memo, which really deserves framing on the wall (well mine anyway), he says "...at both Mach3 and Mach3.5 with 20% bleed." Not wishing to dismiss the 40% I would be interested in more details.
The Flight Manual information,I believe, shows just a 2 position Bleed, closed or open. Thus when open it was a fixed orifice and as such controls to pretty much a fixed percentage irregardless of the actual mass flows.

[Lyman]

Hi peter...

Thanks for your response. I too had the wish to understand the inventor's explanation. The part on which I fixed was in his 'descriptions' and 'claims'. My takeaway was his solution to the problem as he stated it: 1) ram air caused excessive temps, and choked the compressor, functionally limiting its performance to mach 2 (or so). 2) bleeds that removed flow from the core reduced these unwanted temps, and in unblocking the compressor, ennabled the engine to increase its potential (his claim was twenty per cent, as you state)

I am unnable to copy the patent here, so please check my perceptions of the document?

You have read his claim that the bleed, escaping the rest of the core, (and combustion) was "cool, and utilized to cool the afterburner, and liner"?

My expertise is not technical; I have never tried to portray my skills as anything they are not. So I am remaindered in logic, reading, and a license to fly, which is in itself a license to learn.....

In his description of the invention, do you not see where a person might conclude that the inventor who has identified 'Ram' Air as a distinct 'problem' to solve would not likely then claim that he had invented a way to turn a Turbojet into an RJ? I did, so especially when he claimed cooling instead of heating, and flow, rather than compression, it seemed that a conclusion of "Ram Jet" was not in order.

I am in your debt, for your patience, and intellect shown in your response....

:ok:

and your restraint, in limiting your post to single color, and consistent font....

[CliveL]

Peter,

I wasn't going to say anything whilst that stupid semantics argument was raging, but responding to Brian's plea to get back to teasing out a factual explanation of what might be going on and also returning to your original question that related, IIRC, to the effect of afterburner on the secondary induced flow I can offer a explanation based on the Concorde flow set up which, when you look at it closely, is virtually identical to the J58 set up i.e. the intake throat (trap ) bleed flow is passed over the engine as cooling air and then exhausted as an annulus around the primary convergent jet.

I'm no expert on the J58, but I cannot see any reason why the two flows should differ substantially.

http://i1080.photobucket.com/albums/j326/clivel1/Nozzleflowexplanation_zps4a66f211.jpg


For efficiency the secondary flow must be accelerated to supersonic conditions by the time it gets to the final nozzle exit. To my eyes the diagram of the J58 looks to be simplistic in this area because on Concorde at least there wasn't any appreciable mixing of the two flows.

Because it has to be accelerated to supersonic velocity the secondary air must pass through its own aerodynamic 'throat' formed by the expanded primary jet and the solid nozzle surface. The local Mach number at this point will of course be 1.0 and the secondary mass flow will be controlled by the available area at this point. This area will depend on how fast the primary jet expands and this is turn will depend on the pressure ratio between primary and secondary flows at the primary nozzle exit.

The net result (at least for us) was that there was a definite relationship between the corrected secondary mass flow (Ws.sqrt Ts) and the primary jet equivalent Wj.sqrt Tj. as shown on the diagram.

If I have it right, when you light up the afterburner keeping the primary jet exit area the same, the primary jet pressure doesn't change, the mass flow is increased slightly (5% ish?) by the addition of fuel, and the temperature rises substantially. On the cooling side the pressure doesn't change and the temperature will rise a bit because of the hotter jet pipe.

Taken together this means that the corrected mass flow ratio doesn't change much if at all, but because of the increased Tj the secondary mass flow will be increased. I think this is what you were getting at?

OK, if you want to be pedantic the secondary pressure at the nozzle will drop a bit because the starting pressure (intake bleed pressure)and temperature are unchanged but there will be a greater pressure drop through the engine bay as a result of the increased velocity.

If you want to be even more pedantic, when you get to Mach 3 with the spike shock on the lip the total intake capture will be frozen, so any increase in induced cooling flow will be accompanied by a reduction in flow through the engine, so Wj will drop and therefore Ws must drop etc. etc.

[Lyman]

Hello Sir.

Can it be inferred that each discrete flow can be associated with ram effect, and turbo effect? Hopefully not a dumb question.

Thank you

[CliveL]

Can it be inferred that each discrete flow can be associated with ram effect, and turbo effect? Hopefully not a dumb question.

The secondary flow doesn't get anywhere near the turbomachinery and any 'ram' effect is limited to whatever you get from decelerating the freestream flow down to Mach 1.0 and thence the static pressure at the intake throat bleed.

As to the primary flow I'm not going down that road again :bored:

So I think the answer to your question is "No"

[Lyman]

I apologize, and thanks for the reply. I wish I hadn't been such a stubborn fool, I am starting to get what the inventor had in mind, and it intrigues me.

Thank you sir,

One last question CliveL?

I promise to stay away from primary flow. My picture is of two discrete zones, bound by streamline, in the nozzle? One, the primary, a circular section, bounded by a ring of secondary flow adjacent the Nozzle liner?

If they are discrete, and do not mix, can we call the secondary flow Ram Effect?

Also, since there is no fuel added to the Ram effect, and therefore no Ignition, can we actually call it a RamJet, partial or otherwise? If CliveL is busy, peter kent, can you help?

[peter kent]

Lyman, my only J58 understanding comes from what I read. I can only learn from what other people offer in terms of explanations as well as questions.

bleeds that removed flow from the core reduced these unwanted temps I believe, although I can't find it, that it would say something more like "..reduced the effects of these unwanted temperatures" ie the compressor inlet temp was still the same.

You have read his claim that the bleed, escaping the rest of the core, (and combustion) was "cool, and utilized to cool the afterburner, and liner"?
This is only half the story. There are 2 distinct aspects to the bleed. It was required to sort out the debilitating way a compressor responds to high inlet temperatures ( the XB70 compressor used variable stators to do the same thing, I believe). Once taken it could not be allowed to go to waste so it was put back upstream of the afterburner. "without the afterburner the bleed air could not be heated to the energy level of the airflow and most of the increase in thrust would have been lost".

when he claimed cooling instead of heating I couldn't find this.:confused:

[CliveL]

If they are discrete, and do not mix, can we call the secondary flow Ram Effect?

Also, since there is no fuel added to the Ram effect, and therefore no Ignition, can we actually call it a RamJet, partial or otherwise? If CliveL is busy, peter kent, can you help?

Only by a gross distortion of the usual understanding of those terms. The secondary flow start life with some pressure above atmospheric by virtue of the intake shock system, but it only gets some fraction of the STATIC pressure at the intake throat and nothing whatsoever from the subsonic diffuser part of the intake. As I understand the term a ramjet cashes the temperature rise accompanying flow compression to give a sufficiently high temperature to provoke combustion of the fuel. The bleed flow gets nowhere near this condition.

No way the bleed flow can be regarded as any form of ramjet.

[Lyman]

peter thanks for your time...

this: "Quote: when he claimed cooling instead of heating"


is an interpretation of his text where he claims the bleed air, being cooler, serves to cool the nozzle liner, and the afterburner section.

So I will go in to the patent, and locate by page and paragraph this part of the text.

I am using a google page of the original, it is an archaic font and jumps around when I sweep my screen.

My understanding of the device is that it is at least twofold, serving to "unchoke" the compressor, by relieving the compressor of the "block" and reduced compressor created temps. That is as far as I have gotten.

So you know, it is from that "understanding" that I derive an opinion, so both may easily be incorrect.

I'll be back, thanks for your help.

Also, having written patent language, for myself, (with my Attorneys) I am thankful for TurbineD's caution that Patent domain is tricky, one must explain enough to differentiate one's work from other similar work (known as prior art),
to prove "novelty", yet refrain from divulging data that makes one's proposal too "complete". Mystery is important. That is why Abernethy chose his title carefully.

Had he chosen "Ramjet Engine", he is open to rejection since it is not actually a Ramjet engne, and "Partial Ramjet" may not satisfy "novelty".

Also, as explained to me by my Attorney, a patent does NOT have to function to qualify for protection....or be in any way useful.

[Lyman]

Hello CliveL

thank you for the response. I was hesitant to discuss Primary Flow. Since you brought it up, I can ask a question back?

you say..."No way the bleed flow can be regarded as any form of ramjet."

I do not expect to be excused, I behaved badly relative to nomenclature.

However, that is the point I was trying desperately to make. The bleed scheme is not Ramjet, nor does it create one, even partially.

I do not want to be a pest, so for now, I'll pause.

thank you again :ok:

[peter kent]

Clive,
What am I missing please?
On the nozzle efficiency chart:
If pj goes up, say, ps/pj goes down. Also if pj goes up the primary jet will expand some more and the 2ndary annulus area would decrease.
But 2ndary annulus area decreasing arrow is pointing up. I'd have expected down.
I'm thinking of what's happening at a particular nozzle plane. Perhaps the "2ndary annulus area decreasing" arrow means in the direction of flow?

[flyboyike]

Clive,
What am I missing please?
On the nozzle efficiency chart:
If pj goes up, say, ps/pj goes down. Also if pj goes up the primary jet will expand some more and the 2ndary annulus area would decrease.
But 2ndary annulus area decreasing arrow is pointing up. I'd have expected down.
I'm thinking of what's happening at a particular nozzle plane. Perhaps the "2ndary annulus area decreasing" arrow means in the direction of flow?


Some day I'll be smart enough to just barely understand that question, let alone the answer thereto.

[peter kent]

flyboyike, I didn't understand the question either after I'd written it. BTW I can barely control my car never mind a plane.

[peter kent]

Lyman,

"Quote: when he claimed cooling instead of heating"

I misunderstood. Don't waste time following up.

[Lyman]

peter

US PATENT NO. 3344606, Robert Abernethy

PAGE FIVE, PARAGRAPH THREE, SENTENCE TWO.

"Additional Benefits...."

"....cool air is provided to the afterburner....for cooling purposes..."
( via bleed ducts)

Thanks for your time

:ok:

[Turbine D]

Peter,

Check your PMs

TD

[Brian Abraham]

stupid semantics argument was raging
Clive, for my part I felt unless Lyman could accept that all those associated with the program, including Bob Abernathy, called it a partial ramjet, we would be unable to move forward. How is one able to discuss something if you refuse to acknowledge its existence? Lyman was quite adamant that there is no such thing as a turbo ramjet or partial ramjet.
and your restraint, in limiting your post to single color, and consistent font
Just trying to get your attention Lyman
The Flight Manual information,I believe, shows just a 2 position Bleed, closed or open. Thus when open it was a fixed orifice and as such controls to pretty much a fixed percentage irregardless of the actual mass flows.
You are correct that the bleed is an either open/closed system. It operates as a function of engine speed (rotor RPM) and CIT (Compressor Inlet Temperature), which has a maximum allowable limit of 427°C. As to a fixed percentage, I’m not so sure. Some detail.

The engine rotor RPM schedule (see attached graph) shows a continual decrease in RPM, starting at a CIT of about 110°C.

At high Mach number and constant inlet conditions, engine speed is essentially constant for all throttle positions down to and including IDLE.
At a fixed throttle position, engine speed will vary when CIT (Mach) changes.

The position of the nozzle is controlled by engine rotor RPM. Throttle movement in the afterburner range will also change nozzle position. At high altitude and maximum afterburner the nozzle will be 80-100% open normally.

As speed (Mach) increases the engine is provided less and less of the overall thrust. It seems intuitive to me that as the inlet, combined with the afterburner, is producing a continually increasing percentage of the thrust, then more and more bleed air, as a percentage, must be being bled off the 4th stage. Hope I make sense.

http://i101.photobucket.com/albums/m56/babraham227/z138_zps33e60098.jpg
http://i101.photobucket.com/albums/m56/babraham227/z137_zpse285722b.jpg
http://i101.photobucket.com/albums/m56/babraham227/z140_zpsc67143d1.jpg

MAXIMUM ALTITUDE CRUISE PROFILE
The maximum altitude cruise profile is 1,000 feet below the maximum afterburner ceiling. Continuous use of maximum afterburner should not be required.

Effect of Mach Decrease
The Mach must not decrease appreciably below the desired cruise Mach. A small decrease in Mach at constant altitude will cause the aircraft to intercept the maximum afterburner ceiling for that speed and become thrust limited. A descent of several thousand feet may he required to re-establish the desired Mach.

Turn Restrictions
NOTE
Turns must be anticipated when flying near maximum altitudes. A descent of approximately 2,000 feet should he completed prior to turn entry.
Use of the maximum altitude cruise and maximum afterburning ceiling profiles is restricted to non turnlng flight. If 35° bank turns are attempted at these altitude schedules, the angle of attack will exceed 8 . Inlet angle of attack biasing will cause compressor inlet pressure to decrease as much as 2 to 3 psi.

Due allowances must be made for the expected altitude loss if maximum power will not be sufficient to maintain level flight.

Effects of Changing Air Temperature
Because of the high true airspeed at cruise, ambient air temperature may change abruptly as different air masses are encountered. Initially, if a constant altitude is maintained, flight into a warmer air mass will cause a decrease in Mach and KEAS, and the true airspeed (TAS) and compressor inlet temperature (CIT] will remain constant. A higher TAS and CIT will result as the desired Mach is reestablished. The opposite would occur as a result of flying into a colder air mass. New cruise altitudes or speeds may be required to compensate for effects of variations in ambient air temperature.

Effect Of Mach Number
For any given gross weight and ambient temperature, the altitudes for maximum range and maximum altitude cruise profiles increase with Mach. This increase is aprox 1,000 feet per .05 Mach. A related characteristic is that if Mach increases slightly above that desired and the throttles are not retarded, excess thrust increases. It is easy to exceed target Mach inadvertently. (peter, this I think is the kernel to your reducing fuel flow question.)

Mach, KEAS, Altitude Relationship
The selection of values for any two of the Mach, KEAS, or altitude variables automatically defines the value of the third, regardless of ambient temperature. For instance, if cruise is scheduled for Mach 3.0 and the desired initial cruise altitude is 72,000 feet, the KEAS must be 396 knots.

[CliveL]

Peter,
If pj goes up, say, ps/pj goes down. Also if pj goes up the primary jet will expand some more and the 2ndary annulus area would decrease.
But 2ndary annulus area decreasing arrow is pointing up. I'd have expected down.
I'm thinking of what's happening at a particular nozzle plane. Perhaps the "2ndary annulus area decreasing" arrow means in the direction of flow?

Ah! I see your problem. My fault - when I edited the original for general consumption I removed some of the labeling. The three lines actually represent three different nozzle designs with varying physical annulus area for a constant primary jet area. The top line has a minimum secondary area 1.66Aj, the middle line 1.83Aj and the lowest line 2.0Aj. The 'aerodynamic' annulus area will of course depend on this and the jet expansion
So when the arrow shows a lower annulus area (pointing up) that is more restrictive of the secondary flow and is consistent with your point - if the secondary flow is squeezed it will require a bigger Ps/Pj to pass a given secondary flow. So when, for a given nozzle geometry, Pj changes the flow characteristic moves along whichever of those three lines is relevant to that nozzle, not across them.
Sorry about that, hope it is clear now

Clive

[CliveL]

Lyman,

The bleed scheme is not Ramjet, nor does it create one, even partially.
I definitely do not want to get involved in all that again !

I will just say that nobody has ever claimed that the cooling bleed flow was some sort of ramjet - it cannot be so, if only because there is no burner anywhere in the stream. What others have said is that the designer of that bit of the engine regarded the compressor bleed being fed back into the jetpipe downstream of the turbine and then exposed to afterburning as having some of the features of a ramjet, and he chose to describe the engine as a turbo-ramjet or partial ramjet.

That's fine by me - it was his engine, and as Juliet said "A rose by any other name would smell as sweet"

Brian

I recognised your position - the semantics came from the other side :ok:

[CliveL]

Brian
You are correct that the bleed is an either open/closed system. It operates as a function of engine speed (rotor RPM) and CIT (Compressor Inlet Temperature), which has a maximum allowable limit of 427°C. As to a fixed percentage, I’m not so sure.

I don't think it can be a fixed percentage. Bleed open/closed is the equivalent of Concorde's secondary air doors (between intake and engine bay) being either open or shut. Once open the bleed flow would be controlled by the flows in the nozzle as explained in my other posts. It would vary with primary jet nozzle area for example, with bigger bleed flows possible at reduced Aj

[Lyman]

CliveL

I failed to make it sufficiently clear. I was not in denial about who said "Partial Ramjet" or other language.

I was surprised to see Brian quote the inventor "I called it a Partial Ramjet"...Since I had previously stated "There is no such thing...."

I do not seek to perpetuate unpleasantness, and in my stubborn way, by defending the lack of a connection of "Partial Ramjet" to the actual mechanics of such, I put many people off. I note this, and am regretful.

Thank you for all your help.....

Brian, for the record, I did not claim that a "Turbo Ramjet" does not exist, only that the inventor specifically took the time in his patent to say that his device is NOT a "Turbo Ramjet".

So, I am left wondering WHY the good doctor claimed "partial Ramjet". There is no passive compression, there is no fuel introduced, and there is no "auto-ignition". I'll keep looking.

:ok:

[Turbine D]

Lyman,
So, I am left wondering WHY the good doctor claimed "partial Ramjet". There is no passive compression, there is no fuel introduced, and there is no "auto-ignition". I'll keep looking.
Lyman, why don't you stop this expedition you have been on, no need to continue to keep looking. Dr Bob Abernethy is still alive.

Dr. Bob welcomes questions by email at [email protected].

E-mail him and ask your questions...

TD

[Brian Abraham]

There is no passive compressionI'm not sure what you mean by the term. The inlet increases pressure from an ambient of .4 PSI at 80,000, feet to 18 PSI.

I think there may be a little disconnect in thought as to what constitutes a ramjet.

Taking the engine in isolation does not a partial ramjet make. Asking if a TF30 is a ramjet, the answer is no, though could be if the correct inlet was attached, all other things being considered equal (engine metallurgy etc).

For a ramjet to begin operation, the vehicle has to be accelerated to a speed where the inlet will "start". On the SR-71 the inlet will "start" between 1.6 and 1.8 Mach usually. This is when the normal shock moves from the front of the inlet to a position near the shock trap bleed in the throat.

When above Mach 1.6 the spike will retract approx 1-5/8 inches per 0.1 Mach number. Total motion is approx 26 inches. This increases the captured stream tube area 112%, from 8.7 square feet to 18.5 square feet. The throat closes down to 4.16 square feet, 54% of the area t Mach 1.6.

Have read, starting at page 21 of http://ftp.rta.nato.int/public//PubFullText/RTO/EN/RTO-EN-AVT-185///EN-AVT-185-05.pdf

[peter kent]

Brian,
Thanks for all the charts. All a bit mystifying.

more and more bleed air, as a percentage, must be being bled off the 4th stage. Hope I make sense.
That's good , thanks. The only value I have ever seen quoted for the cruise condition is 20% . In the patent, in 'Untold tales' and in Peter Law's presentations in AEHS website for example. Never seen a higher value to go with all the other oft-quoted thrust, etc benefits at M3.

What I have just found is the min value when the bleed is opened at M2.
In 'More never told Tales' ... "My solution was to open the valves at a lower Mach number, around 2.0 where there would be no bleed flow and no hiccup." I guess the turbine exit pressure wasn't much lower than the 4th stage exit at that flight speed.

I have more Qs coming.

[peter kent]

Brian,
A related characteristic is that if Mach increases slightly above that desired and the throttles are not retarded, excess thrust increases. It is easy to exceed target Mach inadvertently. (peter, this I think is the kernel to your reducing fuel flow question.)

That's good. Thanks.

Also can we see it in terms of reaching its design point ?
ref Col Graham:
"The faster it flew the more efficient it became. For example the range charts show.."

If we plot FF v Mn from the range charts we get a steady increase in FF peaking at M3.0 then a dip to M3.15 and increasing again at M3.2 (for all but one condition).
Isn't this FF trough an indication that the whole aircraft has finally reached its design point. ie it's more efficient at M3.15 than at M3.0 or M3.2?

eg the spike shock doesn't meet the cowl lip until the design speed, the terminal shock is now correctly positioned with minimum intensity, etc.

eg the nacelle drag is a minimum. ref Col graham "Any time the SR-71 was at of above M3.05 the aft bypass was always placed in the CLOSE position."

eg the engine/afterburner/exhaust expansion are all where they should be.

[Brian Abraham]

peter, I'll post fuel flow figures for a few different Mach points so you can see the differences. Unfortunately I have a trip on and won't be able to do it until Wednesday at the earliest.

[peter kent]

Hi Lyman,
I have woken up in the middle of the night and cannot sleep, which is OK because I'm retired.:ok:

Whether we accept or not that there may exist a particular arrangement of machine called a turboramjet perhaps we can invent a definition for ourselves.

A ramjet consists of a static compressor followed by a combustor followed by a static expander.

There can also be a machine consisting of a static compressor followed by a rotary compressor, or supercharger, coaxial with a gas producer consisting of a rotary compressor, combustor and rotary expander with waste heat recovery. This combination of supercharged air and waste heat recovery is fed, for enhanced combustion efficiency, to a main combustor, also called an afterburner. This is followed by a static expander.

We now have a supercharged ramjet, or, in the rotary compressor/expander vernacular of turbomachinery, a turbocharged ramjet or turboramjet.

Depending on the operating conditions and degree of supercharge, if the static compressor contribution be low and the supercharge be zero, we can call the machine an afterburning turbojet.

May be all rubbish but I did do it in all seriousness because I have a:8 brane.

[Brian Abraham]

Peter, no such things as compressors or superchargers, they are called pumps. :E

If you like to send me your home email I'll copy the range charts for you and you can play around deducing what information you wish. 29 charts in all.

Edited to add a few data points.

I've assumed a gross weight of 115,000 pounds and an ISA isothermal atmosphere of -56.5°C. These are for best range.

MachxNautical Miles/1,000 FuelxAltitudexKTAS
x2.4xxxxxxxxxx34xxxxxxxxxxxxxxx63,400
x2.8xxxxxxxxxx37xxxxxxxxxxxxxxx67,000xx1606
x3.0xxxxxxxxxx40xxxxxxxxxxxxxxx70,000xx1721
x3.1xxxxxxxxxx42xxxxxxxxxxxxxxx71,400xx1777
x3.15xxxxxxxxx43.5xxxxxxxxxxxxx72,600xx1806
x3.2xxxxxxxxxx42.5xxxxxxxxxxxxx73,800xx1835

[peter kent]

Turbine D, I'm not sure how PMs work so I'm figuring it out and will reply. I thought it meant previous messages but have made one step forward from there so far.
PK

[Lyman]

Peter

Hi... I need to repeat. I have not claimed "TurboRamjet" is not real. As you know, Dr. Abernethy describes one in his patent number 3344606 "Recover bleed air system..."

He goes to pains to claim his RBAS, is NOT Turbo Ramjet. i am forwarding a patent that describes a STATIONARY RAMJET, used in power generation.

You might be interested in its function. And its inventor.

Thanks BRIAN, your data is most welcome, I learn alot....

[flyboyike]

You guys are still going at it? Admirable.

[keith williams]

Shhhhhhhhh They're sleeping. Do not disturb!

[Lyman]

TurbineD

I received the following via email from Dr. Bob Abernethy this morning....


Bill,

At cruise conditions, Mach 3.2, about 80% of the air goes through the engine and 20% bypasses from the fourth stage into the afterburner thru 6 big pipes around the engine. The bypass air is in effect a partial ram jet and produces thrust. However at this condition the inlet produces most of the thrust and this inlet thrust is significantly increased by the bypass air. If all the air bypassed the engine it would be a pure ramjet.

My patent is dated October 1958 so I am amazed that the A12 Blackbird still holds all the speed and altitude records.

[Turbine D]

Lyman,

Thank you for the information you received from Dr. Abernethy.

[gums]

Very good technical thread despite the ad hominid attacks and such, unless they are directed to this old fighter pilot, heh heh. And I think we all learned a lot.

No doubt that the J-58 work helped in the design and performance of the F100 that powered my beloved Viper ten years later. So TNX to Dr Abernathy.

I wonder if we should call that sucker ( the F100) a "turbo-ramjet", as it bypassed a gob of air from the third comperssor stage via an annular duct back to the exhaust/burner ( versus 4th stage in the J-58). Certainly helped the overall thrust when in mil or burner power. Also allowed us a higher Mach than you would expect from a fixed inlet.

One pearl of wisdom from Dr Abernathy's article ( http://www.bobabernethy.com/pdfs/Never%20Told%20Tales%20of%20P&W3.pdf) has to do with the compressor blade flutter and deformation. So I lost a friend who liked to "run it out" after completing a test hop. Sure enough, one day he got a bit fast (I figure 800 knots indicated or so) and one of the compressor disks went boom and he didn't survive the ejection. Think it was the 4th stage one, not one of the fan ones up front.

All in all, one of the best technical threads I have seen.

[Lyman]

hi gums....

I have seen a working sectioned F-100 turning (under electric power) on a stand. It is a marvel.

Abernethy references an annular duct option for the J58, but concludes the cross section allows too much loss of pressure prior to entry into the AB. So he chose the "six big pipes".

I still regret taking such an energetic position v/v "Partial Ramjet"....

[Brian Abraham]

about 80% of the air goes through the engine and 20% bypasses from the fourth stage into the afterburnerA Pratt & Whitney advertisement at Pratt & Whitney, Aviation Pioneers of Groom Lake - Area 51, Nevada (http://www.roadrunnersinternationale.com/pratt_whitney.html) quotes bleed bypass ratio as 20 to 40% (above Mach 2 only). The >Mach 2 is understood, as that's when the bleed is scheduled to open.

[Lyman]

Brian

If 80% goes through the engine (core), and the rest, 20% the bleeds, what is the percentage of air that bypasses the engine internals by transiting the area between the engine and case (nacelle)? Prior to the Engine intake?

[CliveL]

Lyman,

Be careful with the basis of your percentages! 80% of the ENGINE flow goes through the core and 20% of the ENGINE flow through the bleed that feed back to the afterburner. The other bits (shock trap bleed, porous spike bleed etc) should/must be related to INTAKE flow

[Lyman]

Hi CliveL. Yes, i thought of that. Here is my problem. The Engine is a "recovery" bleed powerplant. That means that a portion of Engine intake is only temporarily removed, and later re-introduced. So far so good.

How is an accounting of the gaspath accomplished after the reintroduction? The gaspath is still entirely within the confines of the engine Core.

I think Brian has touched on it, but I am interested in the complete inventory of the power profile, by reference to Thrust, not mass. This is the fundamental area I have been trying (badly) to address, and the distillation of what two eminent people claim relative to this complex and amazing engine....

You claim that if related to Bleed recovery, there can be no claim of RamJet.

The inventor claims the opposite, that his Recovery Bleed system is a "Partial Ramjet".

On a technical forum, I woud expect explicit agreement. "Because I say so", has never been a satisfactory reply. I also do not understand the passion relative to this very very minor point.

Thanks for your reply, I remain a BIG FAN.......

[CliveL]

Bill

You claim that if related to Bleed recovery, there can be no claim of RamJet.

The inventor claims the opposite, that his Recovery Bleed system is a "Partial Ramjet".You are mixing things up again! My earlier remarks were specifically directed at the flow that starts at the shock trap bleed and passes over the outside of the engine as cooling air. This is not in any way a ramjet.

The inventor's remarks relate to the internal bleed off the compressor returned to the engine aft of the turbine. Whether or not this can be regarded as a partial ramjet has been thrashed to death already in this thread.

[Lyman]

CliveL, noted, and again, thank you for a personal response.

:ok:

[peter kent]

Clive,
I've gone through your flow explanation and appreciate it.
I'd like to add, ref
If I have it right, when you light up the afterburner keeping the primary jet exit area the same...
From, for example, "Fast Jets - the history of reheat development at Derby" by Cyril Elliott "... in order to keep the mass flow constant, the area of the nozzle must increase with the sqrt of the jet temperature." (Since gas specific volume has increased significantly).

This book incidentally probably holds the world record for foldout size, 66" for the Adour reheat fuel system schematic.

[peter kent]

Hello Lyman,
Don't know if I can help but for an attempt can you be a bit more explicit?
How is an accounting of the gaspath accomplished after the reintroduction?
Do you mean, for example, why/how do we get an increase in thrust as a result of the bleed flow becoming available at the afterburner?
Or maybe something else?

[peter kent]

Clive,
I've just noticed a Pj/Ps of 0.29 for the SR-71 at M3.2 (Peter Law's presentations on AEHS website). Can that tell us anything by itself on how the SR71 installation compared to Concorde?

[CliveL]

Peter
I've just noticed a Pj/Ps [Ps/Pj?] of 0.29 for the SR-71 at M3.2 (Peter Law's presentations on AEHS website). Can that tell us anything by itself on how the SR71 installation compared to Concorde? Not by itself Peter, because as you point out the primary jet pipe area will be increased when you light up the afterburner and that will 'squeeze' the secondary flow. Concorde of course operated 'dry' in cruise. That same website (I think) gives the cooling air temperature at the nozzle and the primary jet nozzle pressure and temperature, so if one knew the fully open jet pipe area (can anyone help?) it should be possible to make some sort of comparison.

As it stands Ps/Pj is higher than a typical Concorde value (0.25) so there should be more cooling airflow, but this will be offset by that squeezing effect.

PS I left out the effect of increased Aj in my earlier explanation as I thought it would complicate things :ouch: - that's was why I was careful to specify primary jet area unchanged. I'm guessing that if Abernethy says cooling flow was increased when one lit afterburner than the temperature effect would outweigh the area change ....

[peter kent]

The increased airflow really helped Kelly’s inlet performance.

Where would the intake contribution to the +47% come from? ie not the fundamentals of where intake thrust comes from, but specifically what would have caused the change.

eg would it have been from upsizing the intake to handle the +22% engine flow and hence a greater area of rear-facing surfaces?



Recover Bleed Air Benefits Bleeds Open to Bleeds Closed
• Airflow Increase +22%
• Net Thrust Increase +19%
• Installed Thrust Increase +47%

[CliveL]

Where would the intake contribution to the +47% come from? ie not the fundamentals of where intake thrust comes from, but specifically what would have caused the change.

eg would it have been from upsizing the intake to handle the +22% engine flow and hence a greater area of rear-facing surfaces?Difficult to say for sure without knowing more of the intake characteristics [I'm looking for something that might explain it ]

AS A GUESS, from the fact that it was an installed thrust improvement, it could have been that at Mach 3.0 the intake was actually too big for the engine without bleeds, so that they may have been spilling air through the forward bypass doors (to maintain the normal shock in its correct location). This air was spilled out sideways so no thrust recovery - just momentum drag. This could have been the case if they originally sized the intake assuming the engine would swallow more than it actually would without those bleeds or because the intake was actually sized by some other design case and they had to compromise a little bit. With the increased engine mass flow possible with the returned bleed open, they could keep the forward bypass doors closed.

One more question to add to the list .....

[peter kent]

Clive/ Brian,
This is probably too-simplistic a viewpoint to have any merit for such a complex subject, but have to ask.

A lot of interest is always shown in the thrust contribution from the intake at high speeds. For a given installation it goes up with speed, eg for the SR-71 at M2 13%, at M3 54%.

If we now look at Concorde at M2 it's even higher at 63% than the SR-71 at M3.

Both installations were state-of-the-art for their respective design points.

Whilst I understand the actual numbers defining all the flows/thrusts, etc were very different I'm clinging to the idea that a comparison of different installations is perhaps valid using these percentages as they are ratios (non-dimensional).

Question. Is there some fundamental (simple?) reason why Concorde's intake thrust contribution is somewhat higher at a significantly lower speed?

Thanks.

[Machaca]

Is there some fundamental (simple?) reason why Concorde's intake thrust contribution is somewhat higher at a significantly lower speed?


Because it was optimized for M2, and Blackbird for M3.

[CliveL]

Is there some fundamental (simple?) reason why Concorde's intake thrust contribution is somewhat higher at a significantly lower speed?

It may sound trite, but as I see it the reason why percentage intake (and nozzle) contributions to installed thrust increase with increasing Mach number is just because the engine contribution to the total gets smaller!

For any given technology level there will be a finite limit to the top temperature in the cycle - usually set by turbine entry conditions. OTOH, the temperature of the air delivered to the combustion chambers will increase with increasing Mach number (and design pressure ratio of course). The amount of energy you can supply to the cycle, and therefore the thrust the engine can develop, is set by the gap between these two temperatures. As you increase Mach number this gap narrows, so diminishing the thrust potential.

At some point the engine becomes that apocryphal pump that keeps the intake going and supplies the nozzle.

You can bridge the gap to some extent by using afterburner, but sooner or later the temperature problem will kick in.

I think this fits with the engine share of installed thrust:

Concorde, M 2.0 dry - 8%
SR71, M 2.2 afterburner - 73%
SR71, M 3.0 afterburner - 17%

So I would say that the reason why Concorde's intake contribution to the thrust at M 2.0 was as high as 63% was because the engine contribution was only 8%.

It would be easy, I suspect (for someone who understood the thermodynamics better than I), to concoct a more complicated explanation, but this one satisfies me at least.

[Lyman]

Hello. CliveL. From Dr. Abernethy, he describes the Bleed system's purpose as twofold. First, reduce the temp in the forward compressor section, and second, unblock the "choke" in the aft part of the Compressor.

Since the last little bit of velocity occurs with a reduction in fuel burn, is it possible that reducing the "choke" opens up the core/gaspath, reducing drag?

Also, doesn't this reduction in drag unleash some more power from the Bypass?

I am not fearful of appearing stupid, but this is what I glean from the patent language.

How wrong am I?

[CliveL]

How wrong am I? For once Bill only a little bit :D

Removing the choke and increasing the engine mass flow could have reduced intake spillage drag as you suggest - see my post #118

But I don't understand what you mean when you talk about 'bleed drag' What bleed? What sort of drag? How do you think reducing 'drag' (an external force) could 'unleash power from the Bypass' (whatever that might mean)

And of course that has nothing at all to be doing with Peter Kent's question

[peter kent]

Bulls-eye, Clive.
Thanks

[gums]

This is prolly the best technical thread I have seen here, with the current 787 battery discussion coming in very close.

Would be nice to have Doc Abernathy involved so we could ask questions that he would be most qualified to answer, ya think?

One thing lingers in my rapidly-decreasing mental ability ( had to be all those gees I pulled that moved cells down south in my body, but I digress....)

Our TF30/TF41 and F100 motors had the fan bleed at the 3rd stage/disk. The TF30 and Allison TF41 had very high bypass ratios, but the F100 was down to about 36%.

So I would question the Doc about not going with a design like the F100 - an annular bypass for the air to both help cooling, help the process back in the 'burner section, etc. and account for the inlet flow phenomena. Apparently, he discarded that design due to weight or something.

All I know from actually flying those motors was the burner in that F100 was a lot more efficient than the J57's I flew in the late 60's. Actual increase in thrust had slightly better ratio, but the early non-fan motors used a lot more JP4 to get there.

Maybe we can the good Doc to come online here for us to share all the war stories and technical stuff, huh?

[Brian Abraham]

And of course that has nothing at all to be doing with Peter Kent's questionI'll have a go Clive
'is inducing flow and heating it up with maximum afterburner'From the brief quote peter I don't understand as to whether David is talking about cruise or low speed. The only "induced" flow by my understanding would be that provided at low speed by the tertiary doors and the suck in doors.

The tertiary doors are located immediately in front of the nozzle, hinged at their leading edge, and actuated by varying internal nozzle pressure (a function of Mach and engine thrust). At subsonic speeds when open, ambient air is entrained (induced) in the exhaust gas flow.

The second induced flow is that provided by the suck in doors, located on the nacelle in the region of the compressor section, during ground operations. Once again this flow is a result of venturi effect of the exhaust gas flow. The purpose is to provide cooling air to the space between engine and nacelle, before becoming entrained in the exhaust gas flow. In flight, the inlet shock trap bleed and the aft bypass doors (when open) provide the engine/nacelle space cooling air. A third source of cooling air to the engine/nacelle area is the external bleed (a bleed on the six bypass pipes) which are scheduled as a function of rotor RPM and Mach.

peter, you may be interested in David Campbells inlet patent

Patent US3477455 - SUPERSONIC INLET FOR JET ENGINES - Google Patents (http://www.google.com/patents/US3477455?dq=3477455)

[DozyWannabe]

Would be nice to have Doc Abernathy involved so we could ask questions that he would be most qualified to answer, ya think?

At the risk of sounding "gushy", I'd say that in terms of understanding the engineering principles involved, having Clive on hand is as near as damn-it.

For a thorough, fascinating and entertaining discussion of how Concorde's engine inlets worked (providing background knowledge, as well as a reminder of the time when Bill went by the "bearfoil" moniker), look no further than here:

http://www.pprune.org/tech-log/426900-concorde-engine-intake-thrust.html

And from that same thread, a demonstration of how one of Clive's slide rule-toting colleagues wowed the USAF brass and Rockwell's B1 engineers:

If I may, I would now like to mention the 'some oil lamps and diesel oil' story. This is a true story told to me by Dr Ted Talbot, the father of the Concorde Intake, brilliant aerodynamicist and all round amazing gentleman. Ted had been invited in 1975 to speak to the US test pilots at Edwards Air Force Base in California, and after he landed he was invited to take a tour through one of the top secret hangars there, and in this hangar were a few glistening Mach 2.5 design B1A development aircraft. Now Ted had heard that Rockwell were having major difficulties with the engine intakes, and obviously had more than a passing interest in such things, and was allowed to take a close look. Just above and slightly forward of each intake he observed several beautiful made precision total pressure probes mounted under the wings, and although he had a good idea what they were for, said nothing at the time.
That evening, Ted gives his presentation speech to the assembled Test pilots, explaining in fair detail how the Concorde engine intake operated, and that the fact that unlike most other supersonic designs, the engine power was more or less freely variable at Mach 2 and above, even to the extent that if necessary the throttle could be closed all the way to the idle stop. There allegedly many gasps of amazement and disbelief in the room at this, and one B1A pilot was heard to ask his boss 'why the hell can't WE do that John'?. (It should be borne in mind here that the 'traditional' way of slowing down Mach 2+ aircraft is not to touch the throttles initially, and just cut the afterburners. If you don't do it this way many designs will drive into unstart and even flame-out).
After the audience had asked Ted several questions about Concorde, Ted was then invited to ask the assembled USAF and Grumman personnel about the B1A programme, which would be honestly answered within the confines of security considerations. Ted said that he only had one real point to raise; 'I see that you are having major difficulties with wing boundary level interference at the engine inlets'. There was now a gasp of horror from various members of the USAF entourage, 'That's top secret, how the hell do you know that?'. Ted chortled 'it's easy, I saw that you have a multitude of precision pressure sensors under the wing forward of the intakes, that I assume are to measure the wing boundary flows'. Ted then unhelpfully comes up with 'Oh, and you've got the design completely wrong, your intakes are mounted sideways, and that allows the intake shocks to rip into the wing boundary layer, which will completely screw up your inlets at high supersonic speeds. That in my opinion is where most of your problems lie, with wing boundary level interference, but I think that your probes for measuring boundary layer are beautiful, we never had such things'. According to Ted there was not so much uproar at the meeting as much as horror and amazement that this (even then) quite senior in years British aerodynamicist had in a few seconds observed the fundamental design flaw in an otherwise superb but top secret aircraft, and could even see what they were trying to do about it. Ted was asked, 'so you had no boundary layer issues with Concorde then?' Oh we had a few, mainly with the diverter section mounted above the intake' replies Ted, 'but we sorted out the problems relatively easily. 'You said that you did not use precision pressure probes under the wing to measure boundary layer flow fields, so what DID you use then?', asks a Rockwell designer. 'Some oil lamps and diesel oil' replies Ted. The room is now filled with laughter from all those assembled, but Ted shouts 'I am serious, it's an old wind tunnel trick. You mix up diesel oil with lamp black, which you then paint over the wing surface forward of the intakes, where it forms a really thick 'goo', which sticks like glue to the wing'. The pilots in particular seem quite fascinated now, and Ted goes on; 'You fly in as cold air that you can find (we flew out of Tangiers and Casablanca) and flew as fast as you could. As the skin temperature increases with Mach number, the diesel and lamp black 'paint goo' becomes quite fluid, and start to follow the boundary layer flow field. You then decelerated as rapidly as possible, and the flow field 'picture; is frozen into the now again solid 'goo'. After we landed we just took lots of pictures, repeated the process for several flights until we know everything that we needed to know about our difficulties. After doing some redesign work we then repeated the exercise again several times, eventually proving that we'd got things right'. The audience asked Ted if this technique might help them with the B1A, but he replied that although it might help them with accurately illustrating the problem, in his opinion it was irelevant, 'because the intakes are the wrong way round'.
The B1A intake problems were never resolved, and in 1977 the project was cancelled, due to performance and cost issues. However the project was reborn as the B1B, not entering service until 1986. Although an amazing aircraft, with astonishing low altitude performance and capability, it is a fixed intake design, limited to Mach 1.6 at altitude. Ted was right it seems.

:)

EDIT : An additional hair-raiser, the tale of a test pilot who ejected from an SR-71 at almost full chat - and lived to tell the tale!:

SR-71 In-Flight Breakup (http://www.barthworks.com/aviation/sr71breakup.htm)

[CliveL]

Brian,

And of course that has nothing at all to be doing with Peter Kent's question

That was really aimed at my response to Bill Lyman's questions not the original question.

I assumed he (Peter) was talking about Mach 3 conditions, but the subsonic conditions are of course as you describe them.

Since posting that contribution on ejector nozzles I have found another useful source which gives a good explanation of how they work:

NASA TM X- 67976
FACTORS WHICH INFLUENCE THE ANALYSIS AND DESIGN OF EJECTOR NOZZLES
by Bernhard H. Anderson, Aerospace Engineer
Lewis Research Center

Dozy

I have to disappoint your expectations I'm afraid - I will own up to sort of understanding intakes and a working knowledge of nozzles, but what goes on in the guts of the engine is a mystery to me - a bit like the dark arts of the rugby front rows :ouch: For that sort of discussion you need real experts and I would, like gums, dearly like to have Dr Abernethy in on it!

I can confirm M2dudes story of Ted's US visit however - I got it from the horse's mouth. A bit off thread perhaps, but I thought folks might like to see the evidence ....

http://i1080.photobucket.com/albums/j326/clivel1/scan0031-1_zps192ffd15.jpg

[peter kent]

Hi gums,
Apparently, he discarded that design due to weight or something

My understanding comes from reading the patent and other first-hand writings by Dr A.
Having calculated what was required to do the job, ie to sort out the compressor and then use the air to advantage in the a/b, his genius lay in how to do it with minimum carve-up to the existing a/b J58 and with minimum impact fitting it into the nacelle.
The six tubes did just that, requiring the minimum mods to as few existing engine components as possible. This equated to a very cost effective solution and very reliable I believe especially when you look at things like the expansion bellows on the tubes.

Glad you rate the thread.:ok:

[DozyWannabe]

Because [Concorde] was optimized for M2, and Blackbird for M3.

Indeed - though the difference in design brief is considerably greater once you get into specifics.

Concorde was designed to "supercruise" at M2 (i.e. without reheat/afterburner) because it was a hundred-seater airliner intended to provide supersonic service on the transatlantic and (initially) some of the old "Empire" routes. It had to use regular Jet A-1 (or equivalent) and the presence of passengers and luggage meant there was limited fuel capacity. Because of all these factors using reheat to sustain M2 was out of the question. The genius in Concorde's design was not so much in the speeds achieved as it was the way in which such speeds could be achieved and maintained over a long distance - with relatively remarkable fuel economy.

The SR-71's design brief was relatively straightforward - make it as fast as possible so that SA missiles of the type that downed Gary Powers' U-2 could not be a threat. Its payload was a pilot and high-tech imaging apparatus, meaning that it could also carry a boatload of fuel. Being the height of the Cold War, no expense was spared - even a type-specific fuel (JP-7) was developed for the project. As far as the propulsion was concerned, only a ramjet design was capable of sustaining M3, hence having the burners lit was a cornerstone of the brief from the beginning. The genius in this design was all about the speed, however special mention should be made of how pre-existing technology was leveraged and modified in a very economical way.

Apologies for the newbie talk on a thread that clearly has gone into the "expert" realm!

[Turbine D]

Hi Gums,

Here is a cut-away of the TF30 turbojet afterburning engine.
http://i1166.photobucket.com/albums/q609/DaveK72/TF30_zps9350d62b.gif
Airflow leaving the fan is split into two flow streams, that which bypasses the core and is ducted (annular duct) to the afterburner, thought of to be a low flow bypass, and the flow stream entering the core of the engine.

The compressor section consists of a 9 stage low-pressure compressor, including the core portion of the three stage fan and a seven stage high-pressure compressor. Interestingly, there are 3 bleed points:
1. A 7th stage bleed which opens in flight at Mach numbers above 1.75
2. A 12th stage bleed which automatically opens to discharge air to the bypass duct when a surge condition is sensed
3. A 16th stage bleed to cool the high-pressure and low-pressure turbine blades.

The differences you experienced between the J57 engine and the F100 engine as to fuel burn and power can really be contributed to technology that came along over time. The J57s had cannular combustors, whereas the F100s had annular combustors which gave the burner folks much more design latitude and creativity to develop high combustor efficiencies. Also, the afterburner technology advanced in design, material capabilities and improved flow patterns resulting in enhanced fuel burn characteristics.

The A-7 aircraft used a non-afterburner TF30 engine in which the bleed systems were probably simplified verses the afterburning engine.

I think the problem with the J58 being modified to an annular bypass system would have been not only added weight, but all the external plumbing changes that would have been required, adding to the overall diameter of the engine.

[peter kent]

Brian,

From the brief quote peter I don't understand as to whether David is talking about cruise or low speed

He's referring to M2.2 and M3+ from his Table 1 of 'Propulsive thrust distribution'.

It's on page 672 of the paper.

Thanks for the intake patent.

[gums]

I flew the Allison TF-41 in the SLUF, not the TF30 of the early variants, and I understand that the Brits added a "re-heat" to the sucker ( Spey) for their F-4 model. Only thing that sticks with me was how efficient that motor was.

The A-7D and A-7E used the licensed Spey - the TF-41.

I am wondering about the comment that the J-58 was already a prototype that needed to have the bypass ducts for the Blackbirds. I realize that by the time the Blackbird was in the design stage that somebody somewhere was already working on a high thrust motor. I also realize that development of a totally new motor would have been a bitch to test and employ.

Hats off to the Concorde folks that had a "super cruise" jet as early as they did. That thing not only looked good but flew good, maybe great.

[peter kent]

Clive,

Q referring specifically to 'is inducing flow and heating it up with maximum afterburner'

I take this to refer to the induced secondary flow which flows over the red-hot afterburner casing and the intimation that this is significant in producing thrust. However due to the high air flow rate (1/3 intake entry flow) and it being a poor design of heat exchanger would the heat transfer really be significant (ie per lb/sec)?

My original question basically revolved around the above interpretation of mine, ie the heating up of the induced flow took place before it got to the ejector,ie heating it up with max a/b meant? through heat transfer from the red-hot outside of the a/b duct....... or was the author referring to something else?

I see in NASA TM X- 67976
FACTORS WHICH INFLUENCE THE ANALYSIS AND DESIGN OF EJECTOR NOZZLES
page 3 'However, it is evident that heating the secondary
inlet flow would result in a decrease in nozzle
efficiency.'

I don't know if I have taken it out of context but understand it to say that any heat transfer into the nacelle secondary flow upstream of the ejector would not be good? theoretically at any rate, but perhaps not significant in practice.

Don't know if you can make any sense of this rambling.

[DozyWannabe]

Hats off to the Concorde folks that had a "super cruise" jet as early as they did. That thing not only looked good but flew good, maybe great.

The proposed "B" model (which sadly never left the drawing board) actually dispensed with reheat/AB entirely!

[peter kent]

Hi gums,

I flew the Allison TF-41 in the SLUF, not the TF30 of the early variants, and I understand that the Brits added a "re-heat" to the sucker ( Spey) for their F-4 model. Only thing that sticks with me was how efficient that motor was.

Your comments prompted me to look up a couple of things.

"During (TF-41) development testing with M61 gun and missile firing the only sign of engine malfunction was a slight pop surge when missiles were fired simultaneously. Since the engine recovered immediately with no pilot action, the test was deemed to be satisfactory.

The ultimate handling demonstration consisted of gross weight launches with fully degraded catapult. The engine was surge free with maximum steam ingestion, in contrast to violent surges and flame-out on the TF-30."

Have you always had carefree throttle-handling on all your planes or were there restrictions in the old days?

[gums]

This is getting off topic, but since you asked....

The Pratts seemed more sensitive to rapid throttle movements until they implemented the super duper electronic fuel control systems. The GE motors were lots less sensitive, and you could slam the throttle to max or idle with no problems.

The TF-41, aka Spey, was great about rapid throttle movement, but it took awhile to respond. So in formation you pushed up/pulled back and then resumed the original throttle setting once you saw movement. The F100 in the Viper was much quicker on the response.

One characteristic about the Pratts was they did not like going to burner under a gee load. Saw it with the J57 and then the F100 years later.

But back to the main topic, huh?

I still wonder about an annular duct as we had on the fans I flew. Maybe some intake or bleed doors, but use all that fresh air back in the burner.

[Brian Abraham]

peter, I think perhaps the "induced flow by the engine" may be a reflection of the Ben Rich statement "the engine compressor is just a pump to keep the inlet alive". If you think of it in those terms the engine is indeed "inducing flow", and of course that air is being heated by the afterburner.

One part of the paper I'm having trouble getting my head around is the statementIf the AB is reduced to minimum AB, the engine would actually be dragging on the engine mounts at high Mach numbers.Why? Most of the range charts include the figures for a minimum afterburner setting. The base engine is operating at military power whenever a afterburner setting is selected. Selecting some range figures, min A/B, Mach 3.2 cruise, -66.8°C OAT, 105,000 pounds AUW, 72,600 feet, specific range 47.5 nautical miles/1,000 lbs fuel. The flight manual notes under descent procedures that at military power, Mach 3.2, 350KEAS, the angle of descent is approx 1°. Confused is an understatement. Perhaps JF with his expertise may jump in.

[Lyman]

Hello CliveL

But I don't understand what you mean when you talk about 'bleed drag' What bleed? What sort of drag? How do you think reducing 'drag' (an external force) could 'unleash power from the Bypass' (whatever that might mean)

I did not mention "bleed drag". My comment was based on Dr. Bob's PATENT, in which he fully describes the purpose of his bleed pipes, and his offer of a TurboRamjet solution: which he discards, as "too heavy".

Part of his claims, specifically, was to offer his bleed system as having a twofold cooling effect. First, reducing Temperature at the vicinity of bleed "entry", and secondly, upon re-introduction to the ejector, cooling the AB "LINER".

I DID infer that relative to his claim of partial RAMJET gains, he was linking this increase of thrust to a prior DECREASE in choke pressure.

What I think is a logical inference from that is that he is relocating what can be thought of as RAM EFFECT, (choke), from the compressor to the EJECTOR, via this bleed scheme.

That is all.

:ok:

[CliveL]

Lyman

Part of his claims, specifically, was to offer his bleed system as having a twofold cooling effect. First, reducing Temperature at the vicinity of bleed "entry",

Where in the patent does he claim this please - I cannot find such a claim. The nearest I see is p5 (27~30) but that is not at all the same thing. He is talking there of the fact that the bleed air is lower temperature than the burner and that helps reduce weight of the bleed tubes.

[Lyman]

Thanks Clive, looking....

From PATENT 3344606

PAGE ONE. Paragraph 2

"...performance deteriorates primarily because of ram air temperature rise...at high supersonic speeds..."

PAGE ONE Paragraph 1

"...air is bled from an intermediate compressor stage...to be reheated in afterburner....."

[CliveL]

Peter

Q referring specifically to 'is inducing flow and heating it up with maximum afterburner'

I take this to refer to the induced secondary flow which flows over the red-hot afterburner casing and the intimation that this is significant in producing thrust. However due to the high air flow rate (1/3 intake entry flow) and it being a poor design of heat exchanger would the heat transfer really be significant (ie per lb/sec)? My original question basically revolved around the above interpretation of mine, ie the heating up of the induced flow took place before it got to the ejector,ie heating it up with max a/b meant? through heat transfer from the red-hot outside of the a/b duct....... or was the author referring to something else?That's the way I interpreted it also, and why I initially suggested that lighting up the burner would induce more secondary flow because of the primary jet temperature increase. Now I'm not so sure :ugh:

Using Peter Law's data and the SR 71 FM I get
Compressor inlet temp 427C (700K) this is also the cooling air entry temp.
Turbine exit temp 795C (1068K) this would be Tj with no afterburner
Tj Primary nozzle temp with A/B 1760C (2033K)
Secondary temp at nozzle A/B on 649C (922K)
Ps/Pj 0.29

I am 'guesstimating' the secondary temp at the nozzle to be around 550C (823K) when the afterburner is switched off.

The nozzle efficiency seems to peak at around a corrected secondary flow ratio of 0.08. Keeping that for the moment those temperatures give secondary (cooling)/primary mass flow ratios of 0.09 without A/B and 0.12 with A/B, which is consistent with my original explanation even though a lot lower than the 1/3 intake flow you mentioned originally. BUT, the primary nozzle area would increase when A/B comes on, which would reduce the secondary flow ratio from 0.08 to I don't know what (yet!). If the original quote is correct then this effect would be lower than the heating effect.

I see in
Quote:
NASA TM X- 67976
FACTORS WHICH INFLUENCE THE ANALYSIS AND DESIGN OF EJECTOR NOZZLES
page 3 'However, it is evident that heating the secondary
inlet flow would result in a decrease in nozzle
efficiency.'

I don't know if I have taken it out of context but understand it to say that any heat transfer into the nacelle secondary flow upstream of the ejector would not be good? theoretically at any rate, but perhaps not significant in practice.It might be evident to the author, but it sure ain't to me :hmm:
Part of the problem is that there are so many variables and he doesn't say what he is keeping constant with that remark. It certainly reads as if heating the secondary would be bad news, but everything else being unchanged that would increase the secondary flow ratio so the result would depend on which side of the optimum (mu = 0.08) you started.

Brian

Just a suggestion - when one reduces A/B flow on the SR71 the rpm and engine mass flow stay unchanged, as does the intake entry flow. Following up my argument in an earlier posting that would imply that although the actual engine contribution to thrust was dropping (from 13% towards zero) the intake, and to a lesser extent the nozzle, thrusts would be little changed. Could it be that at minimum afterburner the engine is, in fact, behaving like that apocryphal pump which connects the two?

[CliveL]

Lyman,

Sorry, but if that editing was intended as your response I have to say that it does not in any way address my question!
Still waiting ....

[Lyman]

Let me do it this way. From a reading of the first two paragraphs of the PATENT application I infer that The Applicant proposes to reduce temperature and Pressure in the compressor, caused by Ram Air effect at high supersonic speeds, by creating a bleeds scheme that redirects some of the gaspath to the Ejector.

That is my conclusion. I am happy with it.

[CliveL]

Well if that is what you infer and you are happy with it let's draw a line and be done with it :ok:

[Brian Abraham]

As I intimated in my post #138, I was, and remain so, confused by a couple of sentences in the "F-12 Series Aircraft Propulsion System Performance and Development" by David H. Campbell, so sent an email to Doctor Abernethy for enlightenment.

1. If the AB is reduced to minimum AB, the engine would actually be dragging on the engine mounts at high Mach numbers.

2. Further reduction of engine thrust below military power will result in no propulsive thrust on the aircraft.

The good Doctors answer1. This is a transient condition and is very complex. Most of the thrust at high Mach comes from the inlet, not the engine. Many years ago I took a course for a year on supersonic inlets and it was very difficult. Same answer for 2.

Sorry ....not much help.....Reading David Campbells paper one would assume it to be a steady state condition he is referring to, rather than transient.

Well, I guess we'll just continue to argue the toss. ;)

[peter kent]

Clive,
the 1/3 intake flow you mentioned originally I'll find where I got that. I'm sure there is a lot of other stuff that goes with it that may help.

Here it is, Fig 12 at M2.8

Access forbidden! (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770011073_1977011073.pdf)

What now?

[peter kent]

gums,
Thanks for your reply.:ok:

[CliveL]

Peter
I'm sure there is a lot of other stuff that goes with it that may help.

Here it is, Fig 12 at M2.8

There is indeed a lot of stuff in the link you posted which will be a lot of help.

Many thanks

[Lyman]

Hi peter

Thanks for the reply. I think it is possible to see it both ways. From the language in the patent document, we see the bleed enters the AB to cool the liner, but that is only one of the benefits claimed. Cooling the liner from the inside does not relate to heating the secondary flow outside and around it. Those are separate issues, imo. "Cooling" is counterintuitive, when thrust is increased, right?

The benefit to Thrust lies in the added mass, not its increase/decrease in temperature. ANY increase in mass in the ejector wil increase thrust, right?

The inventor references "full throttle", so "added fuel" is off the table. My reference to increase in SFC has to do with this added mass. Is it because in this added mass is added Oxygen? Better (more complete) combustion? One would think so.

Added mass, also yes?

As to the early reference to ram air effect? The inventor's juxtaposition of this drawback with the reference to "bleed system" is self explanatory, especially when considered in light of his later reference to his "solution"?

thanks again...

edit... At some point, it would be interesting to extrapolate this platform's potential to became an actual RamJet. I have drawings.....

[peter kent]

Hi gums,
I still wonder about an annular duct

TurbineD said it all with, for example
all the external plumbing changes that would have been required

I have found 2 photographs which illustrate the plumbing nightmare and how tight it was to get 2 of the tubes out of the compressor case. For some reason I am not allowed to add attachments to my posts.
You can see them if you google J58 images though.

[Lyman]

gums....

The first reference to annular ducting is in Abernethy's patent, by reference, "it would be too heavy"

:ok:

[Turbine D]

Hi Peter,

The best photo I think you saw, illustrating the plumbing problem, is from AirpowerWorld:

http://i1166.photobucket.com/albums/q609/DaveK72/pratt-whitney-j-58_zps70c3a908.jpg

It is the plumbing under the engine that if an annular bypass were to have been used, would have no place to go but outward, increasing the OD of the engine.

[Lyman]

Hello TD..

It is the plumbing under the engine that if an annular bypass were to have been used, would have no place to go but outward, increasing the OD of the engine.

I think if that were the case, the annulus could have been severed, into two separate axial ducts, allowing for the retention of the plumbing.

A better solution would have been to reroute the plumbing into the wing, around the annular duct. The annulus would not have to be much thicker in profile than the "pipes" themselves, the bleed accounted for 20 percent flow. Keeping the same depth as the pipes, an annular duct could have surrounded the case, and been ten times the cross section of the fitted bleeds.

The inventor rejected the ducting as "too heavy". In the patent......

[peter kent]

Clive,

Extra background, the F-12 with chines at M3 had L/D about 6.6 as you figured for the SR-71.
See Fig 6 "F-12 Series Aircraft Aerodynamic and Thermodynamic Design in Retrospect" Ben Rich.

The following is a previous post of mine. Is there any merit in my "schoolboy" plot and conclusions? I know it's just observed FF and not sfc, etc but was I just lucky or have I misinterpreted things? The range charts I got from his book.

Thanks.

ref Col Graham:
"The faster it flew the more efficient it became. For example the range charts show.."

If we plot FF v Mn from the range charts we get a steady increase in FF peaking at M3.0 then a dip to M3.15 and increasing again at M3.2 (for all but one condition).
Isn't this FF trough an indication that the whole aircraft has finally reached its design point. ie it's more efficient at M3.15 than at M3.0 or M3.2?

eg the spike shock doesn't meet the cowl lip until the design speed, the terminal shock is now correctly positioned with minimum intensity, etc.

eg the nacelle drag is a minimum. ref Col graham "Any time the SR-71 was at of above M3.05 the aft bypass was always placed in the CLOSE position."

eg the engine/afterburner/exhaust expansion are all where they should be.

[Turbine D]

Lyman,

This is how it is done:
http://i1166.photobucket.com/albums/q609/DaveK72/4f48a182-3ed4-48a6-9e3b-b380e83f51b0_zps1ad5ce61.jpg
The OD of the annular bypass duct is the golden colored section. Note the plumbing is on the outside of the duct. This happens to be an image of a F110-129, the F100-PW-229 engine is the same.

The idea is to permit the engine to be slid into the hole and have predetermined connection points for fuel, electrical and other connections made through access panels in the nacelle, the less number of panels, the better. Your solution would be an absolute nightmare from both an install/uninstall basis for any engine, be it nacelle or fuselage contained. As I previously said, patents do not tell all that might be known, only the minimum necessary for the invention. The next engine out of the chute at P&W was the TF30 that used the annular approach for the F-111.

I think this thread is really about the technical understanding of the aero, thermo and complexity of the inlet system enabling the engine to achieve the power needed to propel the aircraft to Mach 3 or more and not so much about the technology of the engine itself.

[Lyman]

Dr. Abernethy did not have the luxury of the "white sheet". Who could keep up with Kelly Johnson? (the airframer).....

From my understanding, the geometry was done, the engine built. Dr. Abernethy's invention was an elegant solution to a "how do we do this"?

Thanks for your cool photos!

The F-111 was (initially) intended for carrier ops, as I recall. One of the first test pilots: "There isn't enough thrust in the free world to get this turkey off a carrier deck...."

[CliveL]

Peter,

Here it is, Fig 12 at M2.8That figure does indeed show the TOTAL bleed to be around 1/3 intake capture, but the bit we are interested in is the shock trap bleed which becomes the cooling air and the eventual secondary nozzle air. That bleed is 5% of the intake capture, but since at that point the engine flow is only 75% of the intake capture the secondary airflow would have been 6.7% engine flow. Less than my estimate for M 3.0 from Peter Law's data but reasonably close all things considered.

The following is a previous post of mine. Is there any merit in my "schoolboy" plot and conclusions? I know it's just observed FF and not sfc, etc but was I just lucky or have I misinterpreted things? The range charts I got from his book.There is something like that going on, although one needs to be careful what data one plots. At constant altitude and weight for example the fuel flow increases steadily with increasing Mach No up to Mach 3 then rises much less up to M 3.15 then resumes its inexorable increase. But the specific range is better at M 3.15 than at either M 3.0 or M 3.2.

It certainly looks as if the powerplant gets close to its maximum efficiency around Mach 3.1~3.15 probably, as you say, because it gets to maximum capture (shock on lip) conditions and the engine can swallow enough air to eliminate the need for any forward bypass bleed. Maybe some of the other references you have posted will show up why.....

[Brian Abraham]

Re max/cruise Mach. The flight manual quotesMach 3.2 is the design Mach number. Mach 3.17 is the maximum scheduled cruise speed recommended for normal operations However, when authorised by the Commander, speeds up to Mach 3.3 may be flown if the limit CIT of 427°C is not exceeded.

Perhaps you can draw some conclusions Clive from the following numbers (from the flight manual).

Minimum afterburner thrust at sea level is approx 85% of maximum afterburner thrust and approx 55% at high altitude.

Military thrust at sea level is approx 70% of maximum thrust. At high altitude military thrust is approx 28% of the maximum available.

Some temperature and pressure ratio (compared to ambient) engine numbers.

Compressor face ccccccc427/38.8
Compressor discharge 1ic704/
4th stage bypass tubes i566/
Combustor cccccccccci1093/112
Turbine ccccccccccccic788/35.5
Afterburner ccccccccc1760/
Ejector secondary ccccccc/9.1 (flow accelerated from Mach .4 to 3.0)
Exhaust cccccccccccci649/31.2

Following is a plot of thrust (and drag of the spike) provided by the various engine components at various speeds with max A/B.

http://i101.photobucket.com/albums/m56/babraham227/z184_zpsed5e397c.jpg

It would be interesting to get hold of Brown, William H. “J58/SR-71 Propulsion Integration,” Studies in Intelligence 26:2 (Summer 1982), 15-23. Probably be able to shed some light.

[CliveL]

Brian

Perhaps you can draw some conclusions Clive from the following numbers (from the flight manual).There is a lot of data there Brian, it will take a while to work through it!

Some interesting Concorde M 2.0 numbers for comparison with that chart:

Zone 1~2 12% drag
Zone 2~3 75% thrust
Zone 3~4 8% thrust (dry)
Zone 4~5 29% thrust

Very similar aren't they!

[Turbine D]

Hi Brian,
It would be interesting to get hold of Brown, William H. “J58/SR-71 Propulsion Integration,” Studies in Intelligence 26:2 (Summer 1982), 15-23. Probably be able to shed some light.
The only way I see to get a copy of this is through the CIA. It is declassified and is listed as an article on their web site. If you are interested, I could go through the process to attempt to get a copy and see what it says.

[peter kent]

Hello Lyman,
I agree with your reasoning.

The increase in engine thrust at the afterburner nozzle (gross) is, I believe although not quoted, of the same order as the airflow increase. I guess the a/b temperature did not change significantly, otherwise the jet velocity contribution to the engine thrust would have had a more noticeable effect on the engine thrust.

Thanks for the stimulation.

[flyboyike]

Can't you old-timers just talk about golf and Ensure?

[DozyWannabe]

Disregard previous post (tongue-in-cheek or not) - this stuff's fascinating!

Ike - if you haven't worked it out yet, the so-called "old-timers" always have the best stories.

[flyboyike]

They certainly think so.

[DozyWannabe]

Actually, most of the contributors to this thread tend to be the most self-effacing on PPRuNe. And in this case, they really do have the best stories.

I :mad: you not - if you ignore this thread, you're missing out.

[roulishollandais]

Ike - if you haven't worked it out yet, the so-called "old-timers" always have the best stories
@Dozy
You seemed to be estonished when I wrote some months ago that the first AF447 threads were the best : Old-timers were the first who were able to analyse the few informations we had before the black boxes were found.
I am glad to read your last post

[gums]

TNX, Rouli, we dinosaurs needed that!

I joined the old farts after the AF447 accident because I have always been interested in an accident involving a FBW aircraft. Being in the "charter members" of the first operational aircraft with full FBW, I felt I could both learn and contribute. I have my engineer diploma and then a lot of hours in real planes, and remember there's no such thing as a "dumb fighter pilot".

We may have to search the archives, but I suggested early on once the wreckage pattern was shown that it seemed the thing hit in a classic "deep stall". Turned out it wasn't quite that simple, but humans and not the aero characteristics of the jet caused the crash.

I continue to value the contributions and experience of the old farts when they post on these forums.

[gums]

While we were examining Dr. Abernathy's neat way to keep the motor going above 3.0 M, GE was testing their new motor that implements some of the same concepts and reflects my view of the annular bypass.

"Superjet" variable cycle jet engine could power future fighter aircraft (http://www.gizmag.com/ge-aviation-develop-advent-variable-cycle-jet-engine/25556/)

Worth a look to see motor concepts of the next century compared with what the good Doctor did 50 years ago!

My own view is not to have an extra "fan" disk but use the outside duct as a true "ram jet" and same sorta inlet configuration the Blackbird had. CAUTION!! Don't get all excited, Lyman.

[DozyWannabe]

roulishollandais

I'd say about half the input turned out to be right in the early threads. The discussion started to go somewhere after the recovery of the flight recorders. I don't think the age of the contributors was as big a deal as it is in this thread though... :)

[Chris Scott]

Yes Doze, it's a sobering thought that the most rookie pilot or engineer ever involved in supersonic civil transport must be at least in his/her fifties. And roughly the same applies to Mach 3+ in the military?

[DozyWannabe]

I hope he won't mind me saying this, but given that Clive - no rookie at the time - comes across as eternally engaged and excited by the subject (not to mention sprightly in general) and is clearly keeping abreast of things, it would appear that working on projects of that ilk can confer a certain extended "youthful" outlook. Long may it continue! :)

The M3+ military projects were effectively rendered obsolete much faster by the advent of the space programme. I'm sure that the engineers to come that are worth their salt will be smart enough to engage with their predecessors and their work. I barely understood half of the stuff in this thread and I'm still hooked!

[gums]

Last SR-71 pilot I had dinner with was my age at the time - 40 years old when he lost an engine and landed at my base.. A student of mine 5 years younger flew the beast over Libya in 1986 ( El Dorado Canyon, I believe - Brian Shul), so would have been in late 30's.

Only the shuttle guys were lots older than the early days of NASA. My roomie flew first hop back in '87 or '88, and would have been in his late forties, but had been selected about 8 years earlier. He then flew on the MIR about 8 years after that, so figure it out.

Make no mistake, experience counts. However, that experience must involve a few instances of abnormal systems or situations. Our profession exposed us to many while we were very young, and they turned the keys over to us when we were 22 or 23 years old. Think about a troop in his late 20's flying a Raptor or Lightning that costs about as much as many airliners.

[DozyWannabe]

Only the shuttle guys were lots older than the early days of NASA.

Wasn't that because they erred heavily on the side of caution regarding the effects of zero-G on health and fitness? I'm assuming that because Skylab gave them hard data to work with it became less of an issue by the time of STS-1.

[gums]

Actually, Doze, the problem had to do with the snail's pace of the shuttle program and not physical condition.

Cooper in Mercury was 36 and White was 35 in the Gemini spacewalk. I knew White, as his brother was a classmate in my squad at USAFA and was the one that convinced me I could make it if I tried.

The Mercury, Gemini and Apollo guys moved ahead very quickly. From selection to first flight was three or four years at most. Shuttle was 7, 8 9 years.

My roomie was selected at age 40 and flew 9 years later! Of course, he had to stand down for two years due to the Challenger disaster.

but I digress......

[CliveL]

gums
Worth a look to see motor concepts of the next century compared with what the good Doctor did 50 years ago!

Fascinating stuff, but when one reads the article it becomes clear that the engine is for military use. Cutting down the airflow to increase thrust at take-off is the last thing you want to do if your problem is airfield noise!

Dozy

Knock it off Joe, it is becoming embarrassing - besides, the spirit is willing but the flesh is weak :ouch:

[robdean]

Well here's the Hollywood pitch:

PpruNe pensioners crowd-source a replica SR-71 from souvenir paper-weight components, a junk airframe and lashings of old-timer Skunk Works / Concorde physics. Having learned that a craven State Department is delaying vital surveillance of a rogue state nuclear programme, Gums battles his demons to eventually dust off his G-Suit for One Last Mission, sanctioned only by PPruNe, and to finally fly this historic marvel. Suspense builds, because the audience know that PpruNe thread-lurkers from Iran have just completed a YF-12 based on the same data.

Gums gets the crucial recon. pictures but, unarmed of course, finds the YF-12 on his tail. Just when all seems lost he gambles on the expertise of his PpruNe pals, and pulls a manoeuvre just beyond the stated structural limits of the airframe. The YF-12 has to pull the same manoeuvre to achieve missile-lock, and comes apart. Credits roll over a PpruNe guard of honour at the culmination of Gum's Presidential ticker tape parade.

In flashback, the young CliveL will be played by Simon Pegg, based on his performance as Scotty in the Star Trek reboot...

[gums]

Good grief, Robs!

@ Clive: Yeah, and the ADVENT uses the extra air for a higher bypass ratio and not to help the burner. Seems to make it more like the TF-41, which gave the Sluf super range/loiter time compared to the Double Ugly, Thud, Hun, et al.

[DozyWannabe]

it is becoming embarrassing - besides, the spirit is willing but the flesh is weak :ouch:

OK, no more after that, I promise (as agreed). But, just this once and with all due respect - take the bleedin' compliment!

gums

One thing I do know is that during the Apollo era, the late, great Alan Shepard was at the top extreme of what NASA would allow when he commanded Apollo 14 at 47 years of age. Because the surviving Mercury 7 tended to retire during the Apollo era in their early 40s I'd wager that he was actually probably over what they originally intended, but Deke Slayton didn't have the heart to deny him after fighting his way back to flight status following experimental surgery for Ménière's disease - which had until then left him grounded.

[Turbine D]

Hi gums,

Thanks for the ADVENT video, it is indeed rather interesting. IMO, It is the wave of the future for military combat aircraft engines.

GE Aviation completed testing its engine core for the ADaptive Versatile ENgine Technology (ADVENT) program with the U.S. Air Force Research Laboratory on Feb. 6, achieving the highest combination of compressor and turbine temperatures ever recorded in aviation history.

The accomplishment is a result of GE's most advanced core propulsion technologies including lightweight, heat-resistant ceramic matrix composite (CMC) materials. These core technologies, along with an adaptive low pressure spool, result in a 25 percent improvement in fuel efficiency, a 30 percent increase in operating range and a five-to-10 percent improvement in thrust compared to today's fixed-cycle engines.

I do want to point out this technology is not new and has been in the works for a long time. Following initial studies by Gerhard Neumann in the 1960s, GE's YJ101 was the first full engine to demonstrate variable cycle capabilities in 1976 (see report below). The YJ101 was the forerunner of the F404 engine for the Navy's F-18 fighter.

Access forbidden! (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19810009323_1981009323.pdf)

The next engine to use the variable technology was the GE YF120 engine under a demonstration contract for the Advanced Tactical Fighter (ATF). An engine is on display at the USAF Museum and was one of two YF120 engines installed on the YF-23, Northrop-McDonnell Douglas' entry to what is the F-22 Raptor fighter. The contest was lost to Lockheed YF-22 and P&W's F119 engine.

The technology then carried over to the Joint Strike Fighter (JSF)(F-35) program where a collaboration between GE Aircraft Engines, Allison Advanced Development Company, and Rolls-Royce. Allison provided components and some technology for the engine core and low pressure turbine; Rolls-Royce designed and manufactured the fan module, but the overall design was based on the variable cycle YF-120 engine. Again though, P&W was awarded the engine contract using the F119 engine.

[749CONNIE]

I've been lurking on this forum for awhile and found it an interesting pastime. As I came across this discussion on the SR's thrust, I figured I'd add my 2 cents. I flew the Blackbird from '86 to the close of the program in '90. The thrust generated to attain Mach 3+ came from the combination of inlet, turbine, and AB/nozzle section. Rich Graham's 3rd book ( 4th available in May) is your best source on specifics from a pilots point of view. As an example, when things started to go wrong thrust wise, the first item checked was the inlet (spike, forward doors, aft bypass), then the AB/nozzle, then the turbine. More than 50% of thrust was produced by the inlet, +/-30% by the AB nozzle, the rest via the J-58. Our last SR lost (21 Apr '89) was via a turbine blade failure with the loss of #2 and B hydro and the slow loss of #1 and A hydro due to blades cutting those lines. The initial indication was only a fluxing yaw moment at level off at speed and altitude. There were 65 bold face procedures for this aircraft. I now have 3 on the 757/767. How times have changed.

[Brian Abraham]

At last, someone who knows what he's talking about. Welcome 749, I'm guessing you're now taking on the task of answering a deluge of questions. No question from your tag as to where your heart lies. Looking forward to whatever contribution you deign to make. Magical aircraft.

[John Farley]

I second all of Brian's remarks.

[Brian Abraham]

I wish to say thank you to Lyman for forcing me to contemplate where I stood in this discussion, and erred I might add. Off line discussion with other contributors are also to be thanked – they know who they are.

How I view it at the moment.

Briefly, the engine, taken in isolation as per Abernethys Patent, is a pure turbojet with afterburner. Just about every axial turbine requires compressor bleed to control stall or surge, and are normally closed when at operating RPM. The J-58 requires compressor bleed to unchoke the compressor when operating above 1.8 to 2.0 Mach. Up to that point it’s your regular pure turbojet with afterburner. It is not a bypass engine in the general understanding of the term.

Even though Abernethy himself says, “Bypass the bleed air around the compressor at high Mach number into the afterburner and it would solve the surge problem, provide cool air to afterburner and increase the mass flow and thrust significantly. Actually it converted the engine into a partial ramjet with capability above Mach 3”, the J-58 taken in isolation, as on the test bed, does not have a ramjet mode, partial or otherwise. Abernethys use of the “ramjet” word I take as being recognition of the type of inlet that would be necessary to make his Patent a viable high supersonic powerplant. When combined with that inlet it does give the J-58 a “partial ramjet” feature.

A ramjet requires the inlet to “start” in order to become operational. The SR-71 inlet “starts” between 1.6 and 1.8 Mach, so once the bleed opens at 1.8 to 2.0 Mach, the J-58 can be said quite correctly to have a “partial ramjet” feature.

Sorry Lyman that we were at cross purposes re the patent. I was viewing the installation in its entirety (inlet, J-58, afterburner, nozzle) rather than the J-58 as a stand alone item. The J-58 was after all, purpose designed for one particular aircraft. If that can be taken as an excuse. :)

[749CONNIE]

This may or may not help the discussion. Speaking from the operators point of view. In an earlier posted graph you will note a line depicting the supersonic shock wave from the tip of the spike meeting the lip of the intake as speed increases and the spike retracts. Looking three dimensionally, it is a conical shockwave forcing all the air molecules into the inlet. We are flying in around 4 mm of mercury. 70% of this supersonic air is routed around the J-58 via 6 ducts, compressed and dumped into the AB section where fuel is added then ignited. This produces 54% of the thrust. The remaining 30% of this supersonic air passes through a, internal to the inlet, shock wave and comes out subsonic. Here's where the pilots work load really starts. We refer to the bypasses as the "forward doors" and the "aft bypass". The forward doors allow air to exit external to the engine nacelle. The aft bypass take excess air off the turbine face and routes it around the J-58, internal to the nacelle, and dump it in to the AB section. The objective is to feed the J-58 14 psi of air pressure while at speed and altitude. The J-58 thinks it is at sea level on a hot day. 427*c CIT max limit. Interestingly, the J-58 is rated at max rpm - continuos, max AB - continuos. If one over pressures the turbine, you get an "unstart" of that inlet. That is to say the spike is automatically/manually driven full forward, you lose 54% of your thrust on that side and the "fun" begins as she, SR-71, hits you up the side of the head. Followed quickly by a slap to the other side of your head as the opposite side sympathetically follows suit. The worst "unstarts" are at max Q of 2.6 mach in the climb while accelerating. Obviously, bleeding air external to the nacelle creates drag and depending on OAT you want them closed. The aft bypass allows a manual selection of varying amounts of air bypassed to close the forward doors. With extremely cold temps we may,believe it or not, actually want to bleed air externally to keep the mach within desired flight planed speeds. Just to make it more interesting, the left/right inlets have no common settings. At speed this 1950s technology produced 500,000 lbs of thrust.

[jtsjc1]

Thank you 749Connie! Absolutely fascinating. I've read Col. Graham's books and they're excellent.

[peter kent]

A couple of dimensions to add to the data bank, Clive/ Brian.

I was at Duxford a while ago and there are 2 J-58s under the Blackbird.
Someone thoughtfully displayed them with one nozzle fully closed and the other fully open.
Closed dia 33", open 45".
Who knows what they really are with the cooling layer. Maybe an inch less.
Or how they grow when hot.

Do let me know if you find the numbers useful at all. I suspect not as effective nozzle areas have to be calculated from other stuff.

[CliveL]

Thanks Peter. I'll plug it into the sums and see what difference it makes.

[peter kent]

Since raising this question (ie what did David Campbell mean...) over a year ago (post #1) I can now tie up my loose ends. I have concluded his statements are most insightful. I hope I've interpreted them correctly.

It revolves around an afterburning turbojet reaching the flight speed at which the engine becomes a "drag item" (compressor still at 100% mechanical RPM but fuel flow now limited by "new-high" (J58 1300 F) comp delivery temperature and existing "redline" turbine entry temp (J58 2000 F). The afterburner is still getting 100% flow together with its temperature rise of about 1700 degF (P.Law's presentation Fig. 9).

So, ref D. Campbell "engine is inducing flow and heating it up with maximum afterburner".
He was not referring to the secondary flow as I originally thought but the main engine flow.
Engine is pumping (but not much else, in terms of thrust production that is, except the very necessary cooling flow for the afterburner, at 1050 F instead of at EGT 1450) at 100% speed, ie flow part of thrust. Afterburner is enabling airframe secondary nozzle to provide the velocity part.

ref D. Campbell "If the AB is reduced to minimum AB, the engine would actually be dragging on the engine mounts at high Mach numbers."
The engine is already a "drag item" at this speed because even with min AB the force on the mounts (ie complete engine incl AB) is still a drag.
Perhaps the engine "drag" is intimated by the engine pressure ratio being less than one? (see P.Law's Fig. 17 epr 0.9 at cruise). High Mach number still obtainable since thrust still from 100% flow and airframe secondary nozzle still has high pressure ratio.

ref D. Campbell "Further reduction of engine thrust below military power will result on no propulsive thrust on the aircraft".
The engine has been throttled back so reduced flow means high intake losses from off design, amongst many other things. No net thrust.

Comments welcome. Always trying to learn.

[tdracer]

Peter

We studied the SR-71 installation back in my college days (~40 years ago). As noted, most of the 'thrust' comes from the inlet and exhaust, not the engine itself (at least at cruise Mach).

On the SR-71, the engine is there mainly to initiate the airflow through the ducts and to get the airplane up to speed. At ~Mach 3, ram jets are quite efficient, the problem being getting the aircraft going ~ Mach 2 so that the ram jet will actually work.

At cruise Mach numbers, the engine itself is of minimal benefit, except to provide hydraulics and electrical power. If not for the need for electrical and hydraulic power, and the weight of the associated hardware, it would probably be better for net thrust fuel efficiency to simply close off the inlet to the J58, let all the airflow go around, and make it a pure ramjet.
Of course, there would also be the concern of getting at least one of the jet engines running again at the end cruise (not trivial, after a prolonged high altitude cold soak :uhoh:) for landing....:sad:

[Brian Abraham]

not trivial, after a prolonged high altitude cold soakNo cold soaking in the cruise on this baby, quite the reverse.

[peter kent]

tdracer

Thank you for your comments.

would probably be better for net thrust fuel efficiency to simply close off the inlet to the J58, let all the airflow go around, and make it a pure ramjet

Russian turboramjet experiments of the same era using a MIG-21 engine kept the engine windmilling after transition to a ramjet. They identified the bearing temperatures as being the main problem (needing oil cooling above M3.2 even though there was no friction heat from high RPM and axial loads).
Didn't see the sfc trade offs though.
https://www.cso.nato.int/Pubs/rdp.asp?RDP=AGARD-LS-194

[peter kent]

Hello Brian,

I have gone through old posts to see what I missed.......

Actually it converted the engine into a partial ramjet with capability above Mach 3”, the J-58 taken in isolation, as on the test bed, does not have a ramjet mode, partial or otherwise

The engine didn't need any ram to run in its cruise operating mode, just the right inlet temperature and pressure. It did it on the ground. Nobody would have signed it off as flightworthy if it hadn't.

Whatever the operating mode of the engine as part of the complete propulsion system at cruise it would also have had to have been run in the same modes in isolation on the ground to qualify it for flight since it was the primary thrust producer for the aircraft (not test engine on an FTB).

Since it ran at cruise design-point inlet conditions on the ground it would have operated in the same modes as in flight. See use of J57/J79 exhaust, etc to condition inlet air SR-71 J-58 Powerplant (http://www.wvi.com/~sr71webmaster/j-58~1.htm)

I presume it would have had to run a 50 hour endurance test (called a PFRT) to qualify it for flight throughout the envelope including some hours of continuous running at the cruise design point plus some margins.
The engine would have been stripped and inspected before every detail in that particular design build got the OK to fly.

The value of the cruise part of the PFRT is that the engine is running in cruise mode (and will show up problems) but it happens to be on the ground with no ram from a Mach 3 intake.

[Brian Abraham]

Fully agree Peter. :ok:

[peter kent]

Since starting this topic, which generated a lot of discussion on the relevance of ramjet terms in describing the engine, I've done a lot of digging so why keep it to myself when a few of you showed interest in applying various partial/turbo/ramjet appellations. The question I set myself was "Is there anything unique about the J58 installation which warrants any ramjet term?"

Brian in an early post identified the Lockheed-originated "It's a ramjet" from KJ. KJ didn't give an explanation though. I now know that he wasn't interested in the workings of the engine, not surprising with the weight he carried on his shoulders. I have just bought his book "Kelly, More Than My Share of It All". Quote "..bypassing the high compressor..and flying as a ramjet....with no machinery obstructing the flow...". I think it's worth pointing out this red herring because it could well be the mother that spawned the most common 'understanding' out there.
(P&W documentation tells us 80% of what went into the afterburner was turbine exhaust. About 13% was cooling air from the compressor and 7% was compressor air for burning)

As a baseline for judging uniqueness I used the only other flight-tested afterburning turbojet installation we know about which was designed for Mach 3, the J93 in the Valkerie.
What happened to the air going through the intakes and ejector nozzles was much the same. In both compressors the air hit all the blades at the right angles, despite running at design 100% mechanical RPM and very high inlet temperature. The afterburners were a bit different though as the J58 was the forerunner of high boosts seen in future fan engines, with cooling air cooler than EGT and reduced EGT at entry.

Is this significant? Well we know the machinery was a drag item at cruise, ref D.Campbell's "F-12 Series Aircraft Propulsion System Performance and Development". And just noticed another reference to this in "SR-71 Revealed" quote "at cruise the rotor of the engine actually had a small negative thrust load on the engine" (I wont quote the sentence before that :E). So it seems that the J58 had just gone over the edge of conventional operation with the afterburner now assuming a greater relative importance than ever before, even making up for a thrust shortfall from the machinery. This could well be what makes it unique. The Valkerie wasn't there yet with its still-positive epr (stick my neck out with fig3 pumping characteristics Emission Measurements of a J93 Turbojet Engine (http://www.dtic.mil/docs/citations/AD0766648) )

[TrumanHW]

So, is the COMBINED thrust upon exceeding mach 2-x ... 400,000 - 500,000 ...?
Per 749CONNIE remark (unchallenged) above..? It'd seem more plausible

...(based on all the "common sense" I LACK regarding the behavior of 150,000 pound vehicles going fast enough to have 45,000 lbs of friction (in the mach 2.6+ range) making the inertial frame of reference about 195,000 pounds ... which needs to still accelerate another 250mph to reach mach 3.0 (cruising speed) as they accelerated to mach 3.2 (quite easily apparently) as the default reaction to missile launch-alerts .... WITHOUT any other changes to their trajectory).

This couldn't POSSIBLY have been done on less thrust than an F-22s max ... and weighing 2.5x as much, CAN IT!?

[TrumanHW]

Literally TRANSCRIPTS of an SR-71 Pilot from the video
Blackbird: The Fastest Spy Plane (Extended Cut) - SR-71@ 12:53. www youtube com /watch?v=mHjhgeyhuKk(Replace spaces with . between www + com)

TO READ ONLY TRANSCRIPTS, ARE ALL INDENTED, BELOW

Video TRANSCRIPT & EXACT TIMES of statements (FORMER SR-71 PILOT) written VERBATIM, below:
To include a phrase analogous to "J58s PULLED him through the air more than the turbines pushed!".
Did he just know how to fly it and not understand the engine's physics for thrust..?
The video / talk is good irrespective this one snippet. Skeptical of my claim? exact times & verbatic text below.


All from:
Blackbird: The Fastest Spy Plane (Extended Cut) - SR-711. @ 12:53: And then it reenters the engine there in the afterburner section where it gets reburnt and that equates for the ramjet cycle which means that at Mach 3 and above, 80% of my power was basically a ramjet, which meant that that engine and the inlet system associated with it was actually pulling us through the air as opposed to the engine pushing us through the air. So you save a lot of fuel by doing that.

2. @ 42:48 Also, look at the precision of it's astro-inertial nav: traveling at 36-miles a minute! They could GUARANTEE staying within a ± 100 yard track..!?

3. Blackbird: The Fastest Spy Plane (Extended Cut) - SR-71@ 29:04 We had an astro-inertial navigation system onboard. It tracked three stars. Not unlike Star Trek, we had a stardate. We put a stardate in the airplane and the airplane system would know what stars to track and once it saw the sky, it would lock on to three stars. (Per 42:48 ...going 36 miles a minute) We promised the president, because of the sensitivity to our missions, that we would never be more than 300 feet now, 300 feet off the centerline of the mission track we were supposed to fly, and that astro-inertial tracker would keep us there. ...The reason we did that is like our flights along the Soviet and Chinese border. Back in those days, I don't know what they do now but in those days, the Soviets declared supremacy out to 15 miles that they owned out there. We said we gave them out the three miles, international law. So our missions were at the three-mile point along the borders.

[Goldenrivett]

Video TRANSCRIPT & EXACT TIMES of statements (FORMER SR-71 PILOT) ....... "J58s PULLED him through the air more than the turbines pushed!".
Did he just know how to fly it and not understand the engine's physics for thrust..?

Hi TrumanHW,

I should think all Blackbird pilots were exceptionally well qualified and understood the engine's physics better than yourself.

If you read all the previous posts including Post #8 (https://www.pprune.org/7654654-post8.html), Brian Abraham explains that "During high-speed flight in the Blackbird, compression of air in the inlets generated most of the vehicle’s thrust. At Mach 2.2 the inlet produced 13 percent of the overall thrust with the engine and exhaust ejector accounting for 73 and 14 percent, respectively. At Mach 3 cruising speeds the inlet provided 54 percent of the thrust and the exhaust ejector 29 percent. At this point the turbojet continued to operate but provided only 17 percent of the total motive force."

Later he explains that this was only possible because the J58 "vacuum cleaned" the high pressure from the back of the inlet. The "thrust" they refer to is that which is transferred into the airframe by various parts of the inlet, engine and exhaust ejector.

See also M2Dude's explanation (https://www.pprune.org/5924479-post5.html) of Concorde's power plant.
"The engine itself now only generates 8% of the total thrust, a mere shadow of its subsonic glory. The now divergent secondary nozzle produces a sizeable 29%, this being produced in a similar way to how the intake subsonic diffuser produces its thrust. (The main difference in the case of the secondary nozzle is that instead of a subsonic decelerating flow, we now have a supersonic accelerating flow). A huge 75% OF THE TOTAL THRUST is produced by the intake subsonic diffuser section, this being due to the huge rise in static pressure that is occurring in this section. The 'negative thrust' from the forward ramp section this time is 12%, produced by the supersonic compression forces acting on the divergent section of the intake, resulting in an intake thrust component of 63%. So it can be seen that the vast majority of the Mach 2 thrust forces are transmitted to the airframe not via the engine mountings, but via the mountings of the intake, and to a lesser extent the TRA nozzle. It might seem that the two cases, and in particular the latter one, are very demeaning to the role of the engine, but nothing could be further from the truth. By the laws of conservation of energy, thrust (or any other force for that matter) cannot be created out of thin air, the whole process is about maximising the powerplant thrust that is potentially 'on tap'. (O.K. I know, this entire subject is about providing thrust from thin air!!). Without the engine, the entire process of course falls apart and all components of the powerplant produce exactly the same amount of thrust - ZERO! It is also doubtful if any engine currently in existence could do the supersonic job anywhere near as effectively as the OLYMPUS 593. (Not bad for a design that can be traced back over fifty-four years!). The 593 produces the necessary gas flows to produce these stated levels of thrust, and in the final analysis all powerplant thrust of course is really generated by the engine, what we have been looking at how this thrust is transmitted to the airframe."

[megan]

So, is the COMBINED thrust upon exceeding mach 2-x ... 400,000 - 500,000 ...?To put the record straight Connie should have said "horsepower" rather than "thrust". The oft quoted comparison is in cruise each J-58 engines was producing more horse power than the RMS Queen Mary (160,000 SHP).