Blackbird's thrust question
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Good video.
What I'm looking for is a better understanding of how it all worked, from a pedants viewpoint of course.
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".
What I'm looking for is a better understanding of how it all worked, from a pedants viewpoint of course.
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".
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One stumbling block was why would it be referred to as a partial ramjet?
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.
Last edited by Brian Abraham; 29th Jan 2013 at 02:13.
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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....
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....
Last edited by Lyman; 29th Jan 2013 at 03:21.
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Was the J58 cycle at all like the Olympus 500 while in cruise?
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Kelly Johnson can call the J58 anything he liked, seems to me. But the classic definition is what it is....
It is well understood in engineering. The following diagram comes from a NASA paper.
A NASA paper on turbo ramjets. Access forbidden!
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!
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 confi guration by itself is not capable of orbital insertion because at some altitude the ramjet mode will lack the inlet mass fl ow 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 effi cient 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 fl ight 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 fl ight regime (with known cruise conditions of approximately Mach 3.2 at an altitude of 70,000 ft).
Can the historic confi guration 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 fi rst stages of compression are present before the mass fl ow 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 classi fied as a TBCC.
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 confi guration by itself is not capable of orbital insertion because at some altitude the ramjet mode will lack the inlet mass fl ow 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 effi cient 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 fl ight 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 fl ight regime (with known cruise conditions of approximately Mach 3.2 at an altitude of 70,000 ft).
Can the historic confi guration 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 fi rst stages of compression are present before the mass fl ow 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 classi fied as a TBCC.
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.
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You seem to be having difficulty in understanding the turbo ramjet Lyman.
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.
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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?
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?
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aterpster,
If you go to this site, there are tables that may answer you question.
Aerospaceweb.org | Ask Us - Mach vs. Altitude Tables
TD
If you go to this site, there are tables that may answer you question.
Aerospaceweb.org | Ask Us - Mach vs. Altitude Tables
TD
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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 term "partial ramjet" has been used so often in this discussion that I thought you may have grasped the concept. 
the engine is never completely in a pure ramjet mode due to the fact that the fi rst stages of compression are present before the mass fl ow is bypassed to the afterburner
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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.
Where do you get the 40% figure Brian?
3. What's the explanation for Col Graham's
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?
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 consumed
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.
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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.
Not true, P&W solved that problem.
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.
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.
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.
Yes...
It is a dill pickle 
TD
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.
I do not deny the J58 satisfies the description of TurboRamjet. That makes it a hybrid, not a Ramjet.
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+.
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"?
If Einstein called a five a four, is he wrong?
If I put a cucumber in brine and vinegar for 48 hours, is it a cucumber or a pickle?
TD
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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......
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......
Last edited by Lyman; 30th Jan 2013 at 01:22.
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,
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,
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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
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 1-56347-035-7
The 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.[
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.[
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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.....
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.....
Last edited by Lyman; 30th Jan 2013 at 10:59. Reason: Spelling mistake
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Lyman,
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/Nev...0of%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,
Also,
And,
TD
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 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.
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/Nev...0of%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.
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.
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.
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.
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.
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.
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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.
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.
Last edited by Lyman; 30th Jan 2013 at 15:34.