Tail Rotor Power Consumption

[Dave_Jackson]

I was just reading an article on Piasecki SpeedHawk, which is a modified YSH-60F with Vectored Thrust Ducted Propeller. It mentions that they "were required to trade a 500-hp tail rotor for" the new thruster.

Wikipidia says that the Powerplant is two General Electric T700-GE-401C turboshaft engine at 1,620 hp for a total of 3,240 hp, continuous.

Is it correct to assume that the tail rotor on a standard YSH-60F can draw up to (500 /3,200) * 100 = 15.5% of the engines' power?

[Igor13]

The 500hp tail rotor trade off could be a bit of marketing hype, but the general rule of thumb for a conventional helicopters tail rotor is to draw 10 - 15% of total output. This isn't far from the mark although I believe the H60 tail rotor would be on the more efficient side of the 10-15% envelope.

I don't have any reference manuals with me at the moment but when I get back to work I can look into the average power of the tail rotor. You have aroused my curiosity.

Do those funky wings cancel out the effects of compressibilty or RBS, that spinning thing on top will still limit the VNE if I am thinking correctly. What are they really hoping for with this monster.

[Tailspin Tommy]

For fear of being thrashed by the aeronautical engineer-types of this forum, I've always heard that depending on the type of aircraft, up to 20% of the engine performance is directed to the tailrotor. I had an opportunity in 92 to fly the Kamov 32 in the mountain south of Kraznodar. The instructor pilot mentioned that with counter-rotating rotor systems that the aircraft gained almost 25% more performance over an anti-torque tailrotor system.

I will pass this on for a more articulated and accurate response from Mr. Lappos.

[maxtork]

I wouldn't know for sure either but I can guess that that number may be reasonable as far as the amount of HP comsumed but for a different reason. Remember the Blackhawk has the TR canted so as to produce lift as well in some cases so it may cost a bit more power but it should convert some to lift as well as just anti torque. The speedhawk may be able to do the same if it is vectored downward too I suppose but then it would be subject to the same requirement of total thrust. I'm sure Nick wil be along soon to set us straight.

Max

[tecpilot]

Fenestrons need the most power. Up to 25%.

10-15% for a conventional "open" tail rotor is usual.

that the aircraft gained almost 25% more performance over an anti-torque tailrotor system.


It´s on the first view correct to assume that without a tailrotor like the coaxials the ship will have a big power push. But in reality not so much as you think. At first is the lift production on the coaxial not the same like a single disc. (means factor 2 with the half diameter of the coaxial). Only round about 1,6 is to reach mainly due to aerodynamic losses and influences between the both rotor discs.
And at second is the weight of a technical coaxial construction much higher than of a single rotor with tail rotor. Thats why also a KA-32 needs really big engines. Coaxial is interesting, but it´s not a perfect solution.

[John Hill]

Hmmmm, if as I understand the tail rotor is to counteract torque surely it would consume less power if the tail boom was longer?

[skadi]

Hmmmm, if as I understand the tail rotor is to counteract torque surely it would consume less power if the tail boom was longer?


Yes, but more weight and greater longitudinal dimensions.
Same reason, MD made the tailboomextension for their 900/902s.

skadi

[Graviman]

Dave, that 500SHP is there to give Black Hawk a good sidewards flight capability. I'll bet it only uses a hundred for hover.

[jessie13]

But the faster a helicopter flys, the less power a tail rotor requires. The Black Hawks design includes provision for this by automatically reducing pitch through the yaw trim system by sensing collective position and airspeed, and rely on the forward speed to maintain some directional control. I think the Black Hawk produces about 400 lbs of lift from the tail rotor.

[NickLappos]

The thrust/power relationship for the tail rotor is like any medium loaded disk. I am intimately familiar with the S76:

At a zero knot hover, it uses about 35 to 50 HP in a steady hover (51 HP at 11700 lbs comes to mind.)

At 50 knots sideward flight to the right, it uses about 400 HP.

The typical power consumption for a tail rotor is between 3 and 6% of the main rotor in a steady hover, and the peak TR power depends on the max sideward speed. At 17 knots, it is typically about 3 times the steady hover (making it 10 to 15%). But at those speeds, the MR consumes about 25% less power, so the net hover capability of the machine is somewhat better at 17 knots than it is at zero, even with the wind from the worst quadrant.

[Dave_Jackson]

As mentioned on this thread, the 15.5% (500 hp) is probably the maximum that could ever be expected at the tail-rotor. However, I did some calculations based on this and the data on Wikipedia.

Eliminating the tail-rotor appears to show a substantial increase in the payload carrying ability.

During this maximum yaw the Maximum Power going to the main rotor is 3,240 - 500 = 2,740 hp.
The Maximum Takeoff Weight is 21,884 lb.
Therefore, the lift capability is 21,884 / 2740 = 8 lb/hp.

This implies that if the 500 hp going to the tail-rotor were sent to a second main-rotor, which was aerodynamically remote from the first main-rotor, the craft would be able to increase its payload by up to a theoretical 500 hp * 8.0 lb/hp = 4,000 lbs.

The Empty Weight is 13,648 lb., which gives a Maximum Payload is 8,236 lbs.

The additional 4,000 lbs of payload represents a hypothetical maximum increase in the carrying capacity of this helicopter of 50%, during maximum yaw or sideward flight.

Dave

[NickLappos]

Dave, as usual, your analysis is sandbagged in favor of your pet configuration, because you are adding apples and oranges. Nice, but poor engineering.

For an 11,000 lb class helo, the 500 HP is not the tail rotor penalty when you determine performance. At a steady hover, the penalty is 50 horsepower. The greater HP is not a tax on the engines, since they need to produce the extra only when there is 50 knots of wind through the rotor, so that the main rotor power is perhaps 600 horse power less, thus the sideward performance is perhaps 100 horsepower less than a steady hover.

Also, your 8 lb/HP is a very low disk loading (large rotor) and you have not accounted for the weight of the new rotor nor its shafting/gearboxes. Of course, by eliminating the TR you have saved that system's weight, so there is a budget to spend toward the new main rotor. For the S76, the TR and gearboxes/shafting probably weighs about 250 lbs)

Kamov wrote some papers on this to show the coax's advantages, but the extra drag of the higher head made the fuel burn far greater, so at any decent range, his coax carried less payload.

[Dave_Jackson]

Nick,

You drive a good argument. :D

The Piasecki SpeedHawk was brought up because it is the first time I have seen 'hard' information relating to the power consumed by a tail rotor. This hard information being the statement "a 500-hp tail rotor".

There is much 'soft' information available;

Western aerodynamic texts have mathematically shown that the tail rotor wastes 8 - 10% of the power.
Kamov has stated in an article entitled Aerodynamic Features of Coaxial Configuration Helicopter that (http://www.kamov.ru/market/news/petr11.htm) the tail rotor wastes 10-12% of total power.
Stepniewski in 'A comparative study of Soviet vs. Western Helicopters' says that the tail rotor consumes approximately 11% of the power, during hover.
Prouty in 'Military Helicopter Design Technology' says, "... tail rotor absorbing 10 to 20 percent of the engine power".I'll buy into your statements; up to the point where you start to implying that a single main-rotor + torque arrester can match the efficency of twin main-rotors.

Dave

[NickLappos]

Dave,
Two of those sources drink the same KoolAid that you do, and none of them is specific enough to design a blender with, let alone an aircraft.

I recall the 50 HP number for the S76B precisely, since we designed the Fantail and its ducting to match the conventional TR power at half the disk diameter. I wrote a paper for the AHS forum in 1992(?) that published the HP vs thrust for the TR and Fantail, it is surely available in your tech library. If I felt like busting open the boxes in my garage, I'd post a copy! BTW, the S76B eats about 1060 HP in a hover, 50 TR HP is therefore about 4.9%. That is slightly hig because the 76 TR is designed for 50 knots side flight, thus it swings way too much paddle for low thrust efficiency. Most TR's are designed for 17 knots of max sideward speed, thus thrusts 1/2 of that the 76 can produce.

Even with the Koolaid cocktail, Makhayev gives his coaxial 10% more drag in cruise, with the concurrent reduction in range. If your 60 second analysis held water, designers would kill for the numbers you think you'd get. Nobody is running for the patent office, Dave!

[Dave_Jackson]

Nick,
Now you've gone and done it.
http://www.unicopter.com/Argue.gif
It's tasers at 200 meters.


Nick, you said;
"If your 60 second analysis held water, designers would kill for the numbers you think you'd get."


Damn rights they would. However I said;

"...the craft would be able to increase its payload by up to a theoretical 500 hp * 8.0 lb/hp = 4,000 lbs" ~ and ~ "...a hypothetical maximum increase in the carrying capacity of this helicopter of 50%, during maximum yaw or sideward flight."
Your example used the optimal lateral flight speed for minimum main rotor power. You know that at maximum speeds and/or yaw rates the horsepower demands will be higher.

You said "Most TR's are designed for 17 knots of max sideward speed," Obviously your 70 or 90 mph sideward flight in the Comanche was not a "most".
____________

Then you have the audacity to say;:E Nobody is running for the patent office Says who? Your Sikorsky has eleven new (and frivolous) patents related to the upcoming X2 coaxial.
____________

Obviously, I cannot debate your S76 figures. I must therefore assume that you would not bull**** the public.

However, you might wish to read chapter 14 entitled 'All Torqued Off' in Leishmans latest book. One of his concluding remarks is "it [the tail rotor] is not the the optimum design solution by any means. It has simply become a technological survivor of sorts."


Now for that KoolAid. http://www.unicopter.com/DrinkingSmile.gif

Dave

[Graviman]

Dave, reading your post #11 then the tandem is the best design for power consumption. If you have to design in an extra g/box and d/shaft it makes sense to put that that "aerodynamically remote" rotor somewhere sensible. If you put the rotors beside each other, then for sidwards flight the trailing rotor will suffer increased pitch to cope with the increased inflow caused by the leading rotor.

Unless you have extendible main shafts to find clean air? :E

[NickLappos]

Dave,
You've gone thick again. Time to cool down!

You said something that shows where you've gone so wrong, "Your example used the optimal lateral flight speed for minimum main rotor power. You know that at maximum speeds and/or yaw rates the horsepower demands will be higher."

Dave, the power that the TR equipped aircraft needs is highest in a steady hover. As the aircraft accelerates sideward, and the TR begins to need more power, the MR needs far less. The result is that you "new" discovery that a TR can consume 500 HP is both true, and irrelevant to your search for greater efficiency through symmetry in all things.

Gordon Leishman is very good, and he is also right. His statement is not a condemnation of the TR, it simply admits that, in the world of hard reality, where only internet posters get to live their dreams, all others must build stuff that works.

As Churchill explained, “It has been said that democracy is the worst form of government except all the others that have been tried. (http://en.thinkexist.com/quotation/it_has_been_said_that_democracy_is_the_worst_form/15815.html)” He could have been talking about tail rotors.

[Graviman]

For american rotation i would expect tail rotor in right sidewards flight to be more efficient than in hover. This increases the mass flow rate through the rotor, so rotor requires less change of momentum for the same thrust. Power goes up from increased airflow mass, and increased thrust required to overcome drag, but actual efficiency is also going up. Besides that extra thrust means Ct/Sigma is getting nearer the magic 0.15 mark as blade AOA approaches max Cl/Cd before stall.

Left sidewards flight has to get through VRS where tail rotor efficiency will be least. Then windmill brake state provides power back into drivetrain to main rotor. Here though the vertical stabiliser drag will actually help you.

In addition there is the transverse flow inproving main rotor efficiency, as Nick comments. This will also benefit tail rotor in forward flight. Non of this includes tail rotor direction making use of main rotor downwash for free thrust.

Dave, you should concentrate on tail rotor power when outflow is equal to left sideward flight velocity. Even so, i'm betting that your "wasted" power in this worse case is still less than 10%.

Besides, apart from for videos showing the impressive sidewards flight capability of a low observable attack helicopters, how often do you cruise sideways?

[JohnDixson]

The initial note that started this thread brought up what I thought was an interesting question, that being: what was the design point for the directional control capability for this YSH-60B?

My thought was that putting a thruster on the Seahawk is an interesting engineering exercise, but that machine operates in an environment where the pilot needs a lot of directional thrust capability. The straight ahead, one "G " maximum performance take-off case does not by itself at all define the directional thrust requirements.

So, does anyone know what this thruster is designed to do?

John Dixson

[Graviman]

The helicopter is the subject of a US$26.1 million U.S. Navy-sponsored project that consists of a Sikorsky YSH-60F helicopter modified by Piasecki as a testbed to test the "Vectored Thrust Ducted Propeller" (VTDP) system. One YSH-60F will be converted to test the feasibility of VTDP under an advanced technology demonstration program.

The X-49A flight demonstrator is being developed with funding from the US Army's Aviation Applied Technology Division to demonstrate the ability to increase the speed of existing helicopters to 200 kt (360 km/h) or more. The flight demonstrator has been updated with a lifting wing taken from an Aerostar FJ-100 business jet. A ring tail has been added and the helicopter drive train modified to accommodate VTDP. Piasecki conducted integrated tests of the modified drive train at the Navy's helicopter transmission test facility.

http://blog.flightstory.net/126/sikorsky-piasecki-x-49-speedhawk-first-flight-in-june/
http://en.wikipedia.org/wiki/Piasecki_X-49
http://blog.flightstory.net/wp-content/uploads/speedhawk-1.jpg
http://blog.flightstory.net/wp-content/uploads/speedhawk-2.jpg
Video here:
http://uk.youtube.com/watch?v=Yu2CwHwxJYA

[JohnDixson]

Sorry, should have been specific:

What I meant was to ask if anyone knew what the design requirements for the thruster were in terms of directional control power, directional manuever capability or standard, and the like.

Thanks,
John Dixson

[Dave_Jackson]

Gravimanthe tandem is the best design for power consumptionhttp://www.unicopter.com/1507.jpg
Consider the downwash on this as compared to the downwash from the retreating blades on an ABC Intermeshing or Interleaving.

If you have to design in an extra g/box and d/shaft Who has to design an extra g/box and d/shaft? (http://www.pprune.org/forums/showthread.php?p=3848506#post3848506)
________________

Nick,Time to cool down!Are you suggesting more KoolAid?
Perhaps the 'Jim Jones' brand. ;)

To get simple about the 1st post;
If Sikorsky (your company) did provide "a 500-hp tail rotor" (safety, durability and strength factors on top of this), one must assume that they felt that the tail rotor could, or would, be operating at near to this 500-hp, on occasion. At these times will not the tail-rotor be drawing 15.5% of the maximum total power?

[NickLappos]

Dave asked, " To get simple about the 1st post;
If Sikorsky (your company) did provide "a 500-hp tail rotor" (safety, durability and strength factors on top of this), one must assume that they felt that the tail rotor could, or would, be operating at near to this 500-hp, on occasion. At these times will not the tail-rotor be drawing 15.5% of the maximum total power?"

The simple answer is, Yes, as I have repeatedly said, the TR can consume 500HP on occasion, but that the aircraft sees no loss in performance when the TR consumes that power, since the total aircraft (that is the big greasy thing ahead of the tail rotor, Dave) uses LESS TOTAL POWER when the TR is consuming 550 HP, since the main rotor is consuming far less than the increase in the tail power. Therefore, the aircraft carries the SAME PAYLOAD as it does otherwise. Therefore, your belief that there is a 500HP "tail rotor penalty" is bogus.

No wonder nothing you have ever designed has flown! Are you always this thick, or is it something you practice just to get me going?

[Dave_Jackson]

TR can consume 500HP on occasion, but that the aircraft sees no loss in performance when the TR consumes that power, since the total aircraft (that is the big greasy thing ahead of the tail rotor, Dave) uses LESS TOTAL POWER when the TR is consuming 550 HP, since the main rotor is consuming far less than the increase in the tail power. On these occasions the twin main-rotors also use LESS TOTAL POWER, without having to power a tail-rotor.

No wonder nothing you have ever designed has flown! Are you always this thick, or is it something you practice just to get me going?
Aw Nick that's not fair. When one starts attacking the individual it is usually a sign that they are no long able to attack the topic.


There are many technical reasons why the single rotor should never have become the predominant configuration. However, for a non-technical perspective, here are a couple of selections from the book by William Hunt, Igor's designer and project leader for the XR-4 and XR-5.

"By the mid 1930's Europe was more advanced in helicopter development than the USA. However, the European models that enjoyed initial success were all multi-rotor types: ....... Not one successful single-main-rotor helicopter existed anywhere. It was just the type of challenge that Igor Sikorsky needed to reactivate his thoughts regarding aircraft that did not need running takeoffs and landings."
"Another of Igor's talents was his ability to 'sell' his ideas to others." Apostrophes by William Hunt.http://www.unicopter.com/confused.gif http://www.unicopter.com/confused.gif Is William Hunt saying 'The single rotor became predominant because it was a challenge to do something different, then sell like hell'?

"1938:-- [Young] Impressed by Igor Sikorsky's film, he concentrates on main rotor/antitorque tail rotor configurations."Quite naturally, you have a strong bias toward Sikorsky. I would prefer to trust the 'neutral' rotorcraft aerodynamicists. IMHO, Igor took rotorcraft down the wrong road 60 years ago.


Dave

[soupisgoodfood]

On these occasions the twin main-rotors also use LESS TOTAL POWER, without having to power a tail-rotor.

Except that in a Chinook, if you fly side on, you will have to increase power to fly at the same speed because of the huge drag. I'm also guessing even your sleek designs will suffer a bit in this way.

[NickLappos]

soupisgoodfood,

Theperformance is measured where it is worst, and that establishes the WAT (weight, altitude, temperature) curve in the flight manual. For virtually all designs, that is a still air hover. Once the weight to hover in still air is published on the chart, that becomes what you can legally (and practically) carry.
Were there to be a helo that lost performance in some other mode (imagine one where a moderate hover turn, or cyclic acceleration cost 200 pounds of performance) then that other maneuver state would become the basis of the wat curve. A few Bell helicopters are limited by tail rotor authority and not main rotor hover performance, and for these, the wat curve is "penalized" a few hundred pounds.
For the case where a Chinook (or an S76) has high fuselage drag at 50 knots sideward flight (which is identical to a steady hover in a 50 knot crosswind) if that were a "typical" mission maneuver, the FAA might check that no big performance loss was occurring, and if so, it would have the charts marked accordingly so the pilot would not get in trouble. That is why wat curves have adjustments for doors open, anti-ice on, or other performance changes.

[Graviman]

Dave, every helicopter manufacturer in Europe now uses the single main rotor and single tail rotor configuration. If there was a performance disadvantage over symetrical layouts, other than retreating blade at speed, it would have been abandoned by now.

In the real world: how much power is lost in the Kmax from blade vortex interaction through lower blade tip? It must be pretty noisy.

[Dave_Jackson]

Trivia:

Someone once mentioned that to minimize vibration the Chinooks flew sideways when aircraft were taking off and landing on aircraft carriers. The combined speed of the carrier and the head wind would probably be around 50 kts.


Graviman,

A response to your first paragraph:

Can you please show me any research work that has been done on the pros & cons of symmetrical configurations over the past 60 years?

If not, could this be the reason? Bilateral Symmetry (http://www.unicopter.com/Lateral_Symmetry.html)

A response to your second paragraph:

Why will the "lower blade tip" on the Kmax rotor configuration experience more blade vortex interaction than that of any other 2-blade rotor?


Dave

[NickLappos]

to Grav's point, over 95% of the helos ever built have a single main rotor and a tail rotor.

That means either that the single MR with TR is the reasonably best configuration, or 95% of all helo designers know less than Dave. I wonder which is right.....

[JohnDixson]

Hi Nick . Guess no one has any info re the Piasecki Seahawk's directional controllability spec, maybe because there is none to be had?

Just for fun ( well not quite "just" ), here is a tandem rotor anecdote with a strong subliminal message:

Just out of flight school in 1963, I was able to convince a pilot at the Test Board down at Ft Rucker to check me out in our one and only CH-21C. he had just returned from a tour in the Mekong Delta flying H-21's with the 121st Trans. Co. I think it was.

Anyway he showed me a technique to get that machine to climb when the trees were getting bigger in your windscreen and there wasn't any additional power to be had. On takeoff, he had me accelerate to 60 kts or so at about 40-50 ft altitude, stabilize there, then advising to lock the collective in position. There was a tree line at the edge of this stage field and as we were getting ready to make a hole in it, he told me to ease in some left pedal, thus getting the rear rotor out from under the downwash of the forward rotor. Magic; we climbed over the tree line with ease.

[NickLappos]

Here, John, look at time :47 to :59 and note that there is FULL rudder deflection in a gentle hover turn, as well as a normal landing. I think the yaw control is near nil.
Note later in the flick that the nose is going over fairly rapidly - not enough stabilizer.

I don't know what they were shooting for in yaw control, but I can see what they ended up with!

http://www.youtube.com/watch?v=Q5ihDwz5l7s

Regarding the tandem's power losses that you can cure with a 90 sideslip, Mark Vineberg of the Mil Bureau always told me the "Vantikeryl" (sp??) was the best configuration - a side by side tandem. He said the rotor interference was non-existent. Kamove built one once:
http://avia.russian.ee/vertigo/ka-22-r.html (http://rds.yahoo.com/_ylt=A9gnMilcLZRHBmQBv0ijzbkF/SIG=11virkfra/EXP=1200979676/**http%3A//avia.russian.ee/vertigo/ka-22-r.html)



http://www.aviation.ru/Ka/Ka-22.jpg

[Dave_Jackson]

Nick says;to Grav's point, over 95% of the helos ever built have a single main rotor and a tail rotor.

That means either that the single MR with TR is the reasonably best configuration, or 95% of all helo designers know less than Dave. And, you know for a fact that these are the only two options?


I previously asked the reasonable question;Can you please show me any research work that has been done on the pros & cons of symmetrical configurations over the past 60 years? This question is still awaiting an answer.


The only two evaluations of the intermeshing helicopter that I know of, are;

The Prewitt Aircraft Company;

In 1948, the Prewitt Aircraft Company, a U.S. company with no reason for bias, evaluated and conducted twenty hours of flight-testing on one of the two remaining Nazi Flettner-282s. "The performance of the helicopter was found to be very high, ...".
In addition, Prewitt recommended "That all eligible and interested helicopter organizations be permitted to have their pilots fly this helicopter." Prewitt's grandson mentioned that he did not know of any US helicopter company that took up this offer to fly the craft.
This is additional information from my copy of Prewitts 146 page report (http://synchrolite.com/0474.html#Evaluation).The Rotorcraft Aerodynamicist W.Z. Stepniewski has done comparative analysis of the;

The Single rotor, Winged helicopter and Tandem evaluations, which are in his published book.
The Cold-jet-driven, Single rotor and Synchropter w/ ABC comparisons, which are hand-typed with additional hand-written information, probably in preparation for publication. Stepniewski's conclusion was that the Synchropter-ABC was best.
This is the public information about this (previously?) unpublished material. (http://www.unicopter.com/1093.html)Nick, come to think about it, you may be correct. I possibly do know more about bilateral configured rotorcraft than 95% of the helo designers.

Thank you for the recognition. http://www.unicopter.com/RollLaugh_2.gif

Dave

[maxtork]

Ya know I wonder how it would compare if one were to use Sikorsky's old idea of the swiveling tail rotor like on the H3 prototype, on the Blackhawk. You could have all your tail rotor control bennefits and turn that 500HP tail rotor into a pusher prop! Of course to get the best of it you would still have to have the stub wings which is a downer in the hover but obviously that doesn't seem to be slowing anyone down from spending money on the speedhawk program.

Max

[Heli-phile]

Tailrotors only draw power when they are being utilised.
Ie highest demand would be high power setting, High temp/alt, zero speed, opposing a crosswind.

Lowest demand would be high forward speed, tail rotor is just along for the ride and you could quite happily do without the thing completely (until you want to slow down or hover!!

[JohnDixson]

"Wow", was my reaction to the video and the thruster exhaust vane angle for a very gentle turn indeed!

Can't you see that machine trying to fly tethered hover performance data? Hope the test pilot is good at maintaining situational awareness while performing a tethered corkscrew manuever.

[HELOFAN]

Would there be a compressability issue with a full deflection at a slower IAS vs inducted air?

Thinking...wondering...
Just considering if there would be more response at a lesser rudder angle when the forward induced air speed is less?

Is there lift lost due to the loss of the tilted anti torque rotor?

HF

[Graviman]

Helofan, it is just difficult to get the air to change direction 90 degrees in the Speed Hawk. The thruster vane is a compromise which ideally does nothing in forward flight, but magically revectors the air at slow airspeed. More parts/mass might help, but then so would a tail rotor.

They might consider cyclic control of the tail fan, as well as collective thust. This would improve the situation, but would still suffer in hover due to low mass flow of air.



Why will the "lower blade tip" on the Kmax rotor configuration experience more blade vortex interaction than that of any other 2-blade rotor?


Because at 90' and 270' azimuth the vortex shed form the "upper" blade will impact the "lower" blade away from the tip. This means the tip design must be a compromise to avoid excessive drag from vortex messing up the local flow. There will also be audible blade slap.

No one in Europe has done any recent research on lateral symmetry, AFAIK. If you are only considering a cruise of say 165kts then the expense of extra drivetrain/structure mass/cost would put most engineers off. I just don't think the performance benefits are high enough to tempt any one. The increase in popularity of fenestron designs demonstrates this point.

The fact that Stepniewski is discussing ABC means he is considering high speed. That is a different ball game, and the standard has to be against X2.

[IFMU]

"Wow", was my reaction to the video and the thruster exhaust vane angle for a very gentle turn indeed!
John,

When I saw the video and looked at it, I wonder if the thruster vane angle is connected to the pedals, or scheduled with airspeed. One means of control would be to have the vanes hard over, and the half-cover thing on the duct, and vary thrust of the propeller in proportion with pedal position. I would still come to the conclusion that yaw power is weak. You can't beat a good tail rotor for yaw control.

-- IFMU

[HELOFAN]

Instead of a mechanical drive on a "standard" tail rotor g/box, why not have a variable output pump servo controlled or PLC to a hydraulic motor?

There might be more power consumption?

Is it more or less reliable/costly even if it was a component c/o based on hours?

Always wondered.

Hmm can it be poissible to have a hydraulic system be in back up of a mechanical drive?

HF.... back to the bar?

[NickLappos]

helofan,

Typical hydraulic drives are not very power efficient, they waste about 10% of the power that they transmit, but they are great at putting precise amounts of power on demand in odd places, such as servos and landing gear.

The shaft systems employed for tail rotors are very efficient, usually consuming perhaps 1.5% of the power they transmit (mostly in the gear boxes.)

The rudder in the fan wash of the X-49 does show how marginal the control is, I noted that the rudder slews almost full angle as the aircraft gently accelerates to a side speed of perhaps 10 to 15 knots, in a gentle yaw turn that is perhaps 1/4 the rate needed for operational use, and also when the aircraft settles into a gentle hover from an approach. Since the baseline Hawk family can easily go 40 to 50 knots sideward, this represents a stunning loss of yaw control margin for the Pathfinder.

I also note the extra inertia in the tail upsets the control harmony, note the overcontrolling in pitch in hover liftoff and also during the entry to the "high-is" speed runs. Shows that the pitch sas is wallowing, probably because the pitch axis sas gains are too low for the extra pitch inertia. Also says hat removal of the stabilator and replacement with the ring is not entirely satisfactory. My guess is a full mil qual of the pitch axis HQ would leave something to be desired.

Also, the "177 knots in a slight dive" shows what had been guessed, the drag and weight of the fan assembly probably cost most of whatever advantage the propulsor gives as extra speed. A normal Hawk at 19000 pounds has a max level speed with full engine power of about 156 knots, a slight dive easily gives 170. Ripping the aircraft apart for 7 knots isn't a game-changer.

So far, I would rate the X-49 as a valiant attempt, but little proven. Yaw control = D, pitch control = C, Speed = C-

That being said, hats off to the Piasecki group for doing something, at a time when most R+D is done with Power Point and laser pointers.

[HELOFAN]

Thanks Nick for taking the time.


Were the blades on tail thrust device for the X-49 variable pitch?
Maybe at a higher the pitch needs to be less/more to allow a better induced flow & reduce drag?

At lower speed the pitch is more/less to give greater control where drag is not an issue, possibly give stability as well
Or maybe that might make the fan very inefficient and pointless.

Ok so the X-49 didn't really gain that much due to drag due to mass, a less than desirable yaw control & a marginal gain in airspeed.

A mechanical drive so far gives us the X-49 or a tail rotor type helo.

Why not a gas thrust vectored system?

The thrust comes from the power plant turbine engine that is also coupled to the gearbox that provides drive to the main rotor.

Or could even be a separate engine

Also...
Gas is ducted down the shorter tail and nozzle vectored to provide anti torque thrust.
Using a similar type nozzles like the Harrier.

The NOTAR uses a fan driven from the engine to provied a cold gas thrust for the tail vectoring nozzle.

Why not a hot gas?

Also the engine(s) that is providing the thrust could also be thrust vectored to give stability and might help should there be a tail thrust vectoring control failure?

And lets use the thrust vectored nozzle for assisting high load take offs would be an alternative and an efficient way of managing gases at low airspeed.
Again if it can get a stuck wing off the ground straight up.....

Now I am not thinking it will fly at speeds that jets do but it may just be a little faster than what we are doing now as I am not talking engines for thrust the size of a large fighter jet, but perhaps something the like on a personal jet.

Now, if we can de-couple the gearbox in flight and use the some gas from the engine to be diverted to the rotor system for tip thrust jet drive.......

Damn, my napkin is all soggy and the picture is all blurry... ooh a peanut.
:E

[Graviman]

Helofan, you have some interesting ideas but they would all suffer from poor efficiency. This translates as increased fuel burn and reduced payload/range.

The key to good propulsor efficiency is to have it handle a high mass flow rate of air. At high speeds you get a high mass flow rate, so can get away with a small diameter fan. At lower speeds to get the same mass flow rate you need a proportionately larger area. This is where any fan designed for a large speed range will suffer, being too heavy for high speed and too inefficient for low speed.

When X2 flies, likely sometime next year, it will outperform the X-49. It has a pusher prop which, by the constraint of physics, must be a compromise. My guess is that the test pilot will use the main rotor to accelerate up to 100 Ktas, then gradually feed in more propellor pitch to get to 250Ktas. It's interesting to note that some of the larger development variants have 2 pusher props, widely seperated. This will address the need for positive yaw control, which would otherwise be provided by a tail rotor.

John, are you penciled in as one of the X2 TPs when the machine is ready?

[Dave_Jackson]

Graviman,


:confused: In your first paragraph, are you moving the vortex, or moving the goal posts?

___________________

the expensive of extra drivetrain/structure mass/cost would put most engineers off. http://www.unicopter.com/FlettnerPrincipalAssy.gif

:confused: Where are the 'extras' in this COMPLETE drivetrain?
This drivetrain also INCLUDES the rotorhubs and flight-controls, plus there is no need to include any "extra drivetrain/structure mass/cost" for a tail-rotor.

Are you saying that Germans are poor engineers?
_____________________

the standard has to be against X2 :confused: What 'standard' has the X2 set?
The 'standard' was set 30 years ago by the Sikorsky ~ S-69 (XH-59) ABC (http://www.unicopter.com/0891.html). The upcoming X2 will be compared against the S-69.

[Dave_Jackson]

http://www.unicopter.com/Propulsion_Efficiency.jpg
From Ga6riel on Rotary Wing Forum

The graph was probably intended for fixed-wing aircraft. However, it raises an interesting thought.

On the fixed-wing craft, the propulsor is responsible for overcoming; the parasitic drag of the fuselage, plus the induced and profile drag of the wings.

On the helicopter, the propulsor is only responsible for overcoming the parasitic drag of the fuselage. This is because the induced and profile drag of the rotor(s) will be overcome by the mechanical power going directly to the main-rotor(s). One caveat will be that the advancing blades have a higher velocity than that of the fuselage and this higher profile drag must be countered by the propulsor. Of course, with slower rotor rpm the profile drag to be counter by the propulsor will be reduced.

Perhaps this might imply that a given propulsor will propel a very clean helicopter at a faster speed than it would propel a comparable fixed-wing craft.

[Graviman]

Dave, blade vortex interaction is a fact of life. At the very least it means that the tip cannot be profiled to use as high a Cl/Cd as in a free stream. Even X2 designers have recognised this by using that neat tip profile (the tip vortex is thus a larger diam, so reducing its rotational velocity). An intermesher in hover puts the BVI further away from the tip, so would need to limit lift produced at this radius (ie max lift radius would move inboard).

My original question remains: how much power is lost in the Kmax from blade vortex interaction through lower blade tip? There must be some estimates somewhere?

Regarding powertrain: i have always agreed that the FL-282 has a very well thought out gearbox. I sent you some photos from Coventry air museum at one point. But you seem to be championing the interleaver over the intermesher, which from your layouts will need a more complicated drivetrain - perhaps it is you that is changing the goalposts.

But the general point remains. The conventional has very well understood dynamics up to 165Ktas. Since each new project is a risk you will have some convincing to do that the intermesher should be the config and not conventional.

For example R22 handles well enough, once you learn the quirks (mostly a cyclic response lag). If you don't wish the pilot to learn the quirks then SCAS is the way to go. If you don't like the sometimes messy development of hydraulics then electric actuators are becoming more powerful each year. This makes it hard to justify moving away from the positive yaw response provided by a tail rotor for some purist aerodynamic handling advantage.

Above 200Ktas it is a different story. The benefit of lateral symmetry (at least projected to plan view) is that the retreating side no longer needs to balance the advancing. Agreed S-69 has set the standard for X2 to beat.

Regarding your last post: it is unlikely that rotor aerodynamics will ever be as efficient as a wing, because as rotor technology moves on so does fixed wing technology...

[Dave_Jackson]

Graviman;

My original question remains: So does mine. Are you talking about the vortex generated by the lower blade tip (which happens to be outboard of the other rotor) or are you talking about the lower blade tip cutting through a previously generated vortex.

A partial answer to your question is; the Kmax rotor has a low tip speed and a relatively low disk loading.


But you seem to be championing the interleaver over the intermesher, which from your layouts will need a more complicated drivetrain - perhaps it is you that is changing the goalposts.
I'll research and champion anything that offers the possibility of an improvement over the existing.

Perhaps your perspective is from applied engineering, as opposed to design engineering.


Dave

[IFMU]

John, are you penciled in as one of the X2 TPs when the machine is ready?
On his public profile it says he is retired.

-- IFMU

[HELOFAN]

It may be costly and inefficient but it could work, lets let the gen II folk figure out how to make it efficiant, lets just make it work.

I am a multi gazillionaire, I dont care that I cant go as far or carry as much, I just want a different ride to the rest. ;)

Its kinda like owning a V8 when a 2 liter will do the same thing with 2/3 less fuel. It might be over kill, but heck it sure is fun to drive.
( the only thing that should come in 2 liters is milk and orange juice )

:}


You are right this thread has taken a different fork again.

Sorry all.

Back to the theories of tail rotor ( anti torque ) alternatives etc...

HF

[Graviman]

Helofan, the point is that the conventional cannot be faulted for technical reasons. It is flawed, and a small percentage of power is lost driving the tail rotor. But any of the proposed alternatives have flaws too, either through lack of yaw authority or weight. The job of an engineer is to figure out which flaws the customer will accept.

I have no doubt Dave would gladly spend some of your gazillions for you:
http://uk.youtube.com/watch?v=CkDKb65daaA
http://uk.youtube.com/watch?v=6xeLhPBI2QU&feature=related

[NickLappos]

Grav,

Fear not, Dave's theories are sullied by neither experience nor practicality. It is always amusing to me that he assumes those rotorcraft experts who built 20,000 helicopters (which is 20,000 more than he) are all wrong. With some internet search and a grainy photo of a 1941 rotorhead, he can demolish any argument!

The pursuit of symmetry that is his mantra seems to be sparked by some internal asymmetry, frankly! Even Charlie Kaman, the inventor, dumped the syncropter configuration that Dave is wedded to, Dave has never tried to find out why.

[Shawn Coyle]

As you said, Nick - at least Piasecki is doing something. We've got a terrible record for R&D in the helicopter world compared to the fixed wing world.
Personally, I'd like to see more done with electric ducted fans on the side of the fuselage - some very high efficiencies have been developed with these devices. Also probably easier to schedule power with electrics...

[Graviman]

Shawn, I think part of this is that it costs 4 times the amount to develop a helicopter as a fixed wing, for a given payload mass. So i would expect helicopter design to be 4 times as conservative, or for there to be 1/4 of the R&D.

Electric drive definately offers many new possibilities.

[slowrotor]

Shawn said: "Personally, I'd like to see more done with electric ducted fans on the side of the fuselage - some very high efficiencies have been developed with these devices. Also probably easier to schedule power with electrics..."

Good idea. If these side thrusters could be rotated 90 degrees for vertical lift for takeoff the craft might lift an additional 30%. Could be attached to an existing helo. I have been considering this idea for some time.

slowrotor

[Dave_Jackson]

Nick;

The subject of this thread was 'Tail Rotor Power Consumption'; until; in Post #12 you said "Dave, as usual, your analysis is sandbagged in favor of your pet configuration" and then followed it up in Post #14 with "Two of those sources drink the same KoolAid that you do".

Your technical responses are underwhelming. :=


Then in Post #51 you go on to say "Even Charlie Kaman, the inventor, dumped the syncropter configuration that Dave is wedded to, Dave has never tried to find out why."

Perhaps it is you who should try to find out why.
Every concern that I have been able to discover about the intermeshing configuration, plus potential solutions. (http://www.unicopter.com/B280.html)


To hell with me, let Charles Kaman, a former employee of United Technologies, talk to you in his own words. ~ from his book 'KAMAN: Our Early Years'.

"A tail rotor, used to counter the torque of the main rotor, used precious power without providing lift. But proposing an alternative to the tail rotor would have been premature--and out of the question for United Aircraft--as Sikorsky was completely committed to the tail rotor configuration."

"I remember once during the war encountering Reggie Brie, the British chief pilot, after a flight in one of the Sikorsky R-4 trail blazers. His arm was in muscular spasm from his effort to overcome these control forces."

Nick, a couple of questions.
~ Did, or did not, Sikorsky take a slow-motion film of Igor movements while piloting an early craft?
~ Is this relevant? "[Arthur Young (Bell)] Impressed by Igor Sikorsky's film, he concentrates on main rotor/antitorque tail rotor configurations." - from Charles Lumsden.


At a meeting with Erle Martin, Charles Kaman said " Erle, I'd like to develop this system [Synchropter] for United Aircraft. I'll continue to function with my own basic job, and I'll do this work on over-time or extra time, or however. All I ask is that you pick up the costs and provide me with the place and technician to do the basic spade work."

'His answer was swift, decisive and clear. "Charlie, we have our inventor at United Aircraft. His name is Igor Sikorsky. We don't need another one."'

________________________

Nick;

If you believe so strongly in the main&tail rotor configuration, you may wish to tell Boeing that they have be building helicopters wrong for the past 50 years.

Knowing where you're coming from, I love your arguments ~ flawed as they are. http://www.unicopter.com/KissingFaces.gif


Dave

[Jim Dean]

A slightly different tack. A little while ago I was told that the fenestron design was not only using the effect of the fan as anti-torque but the load was shared with the force created by the curved surface around the ducting (courtesy of Mr Bernoulli). Obviously this is only in the hover and at low speeds as the aerofoil of the fin is helping in forward flight. Any comments?

[NickLappos]

Jim,
Your assertion is quite correct - the issue is a hover power one, and the fenestron would be a loser because of its high disk loading, which consumes more power than a large open tail rotor. But the designers cleverly made the housing shape to expel the plume of air efficiently, like a rocket nozzle, so that the air "sees" an equivalently larger disk. This controlled efficient expansion of the air from the fenestron almost halves the power consumption, and makes the fenestron a real player as far as power consumed.

The design cost is still an issue, the wider ducting weighs more and has quite high drag. On the S76 fantail, the ducting added about 2 square feet to the total drag of the aircraft over a tail rotor. That is about 12 to 15% drag increase, a real design issue.

When the Boeing-Sikorsky team built the Fantail demonstrator, I joked that since the ducting was worth half the thrust of the device, why not just build two ducts and leave the fan off. I got some pretty silly stares from the engineers on that one! It took 600 hours of wind tunnel work to shape the duct properly to reduce the fan's power usage.



Dave, It is a shame, but you are starting to sound a bit manic, frankly.

[HELOFAN]

So electric motors either driving a fan or a fixed pitch ( or even variable would be nice ) power generated by the aircraft is out of the question?

If its safety thats an issue in this sort of device, it could be backed up by an emergency ducting system coming off the engine gases?

Should I stick to Leggo blocks and my little miniature Air Hog helicopter?
:}

I'm a good driver!
:8

HF

[Graviman]

Helofan,

Some of the new generation high rpm pancake motors offer very good power to weight. There is also the possibility of designing in redundacy into the motor, which if brushless DC (IGBTs in place of commutator) will already be very reliable. This redundancy cannot be designed into a single tail rotor driveshaft, which is probably the conventional Cat A weakest link. I think e-drive fenestrons is a very real possibility in the near future.

[HELOFAN]

Thanks Graviman.

HF

[Dave_Jackson]

Nick said;
Dave, It is a shame, but you are starting to sound a bit manic, frankly. You are correct, if you are implying a 'preoccupation' or 'compulsion', when it involves staying close to the topic of a technical thread.

However, when you provocatively and repetitively personalize your attack in a defamatory manner, I will respond.

Dave

[IFMU]

The pursuit of symmetry that is his mantra seems to be sparked by some internal asymmetry, frankly! Even Charlie Kaman, the inventor, dumped the syncropter configuration that Dave is wedded to, Dave has never tried to find out why.

So why did he dump the syncropter? It appears they put the Seasprite up in front, at least in terms of the picture coverage. It also seems they build blackhawk cabins:
http://www.kamanaero.com/images/PDFs/01-23-08%20Aerostructures%20MOA%20w%20Sikorsky.pdf

The K-max is still there, looks like it can lift a decent amount but you could just about catch it with a S300CBi.

-- IFMU

[Dave_Jackson]

IFMU,

About a year ago Kaman mentioned that they would not be producing any more K_MAX's and that they were trying to sell the two that they were leasing out; as I recall.

They plan to stay strongly in the helicopter industry, but as a component manufacturer and not as a complete helicopter manufacturer.

Charles Kaman's failing health may have something to do with this.

Dave

[Cyclic Hotline]

The end of the K-Max has been driven by the horrifying accident rate.

http://www.markusherzig.com/kmax/

I'll let you interpret the data yourself! :eek:

[HELOFAN]

Though most of the Kmax isues look to be pilot error, hitting trees, shutting off fuel accidently etc.

The splines houseing issues are a concern.

So it seems if that the drive from the engine is lost Rotor RPM decays very quickly or would that be from the material breaking up and causing drag?

Most likely the latter I imagine though reading the reports the RRPM drops quickly doesnt it.

Are they stopping producing the Kmax then?

I dont really see why, I dont think that is it a design issue though they dont have that many aircraft produced and have quite a few destroyed.

Interesting sites.

HF

[NickLappos]

I doubt that the configuration has anything at all to do with the accident rate, but the mission (long hours hovering OGE close to obstructions) is certainly a difficult one.

I don't know why the synchropter config was not used for the later Kaman airfraft designs, which were naval shipboard aircraft ostensibly well suited to the syncropter design. If we are saying that Charlie Kaman dropped the syncropter from his bag of tricks, does that mean Dave must add him to Dave's private list of "Designers who don't know what a GOOD helicopter looks like"?

[Dave_Jackson]

Nick;

Perhaps the teetering rotor is slowly being replaced by rotors with greater control authority. Thereby relegating this simpler and lower cost rotor to the recreationalists, in a manner similar to that of the gyrocopter.

Kellett (http://www.unicopter.com/0896.html) wanted to produced a rigid 3-blade intermeshing helicopter many decades ago.

Dave

[Cyclic Hotline]

Though most of the Kmax isues look to be pilot error, hitting trees, shutting off fuel accidently etc.

The splines houseing issues are a concern.

So it seems if that the drive from the engine is lost Rotor RPM decays very quickly or would that be from the material breaking up and causing drag?

Most likely the latter I imagine though reading the reports the RRPM drops quickly doesnt it.

Are they stopping producing the Kmax then?

I dont really see why, I dont think that is it a design issue though they dont have that many aircraft produced and have quite a few destroyed.

Interesting sites.

HF


They stopped production of the K-Max some time ago. The future of the aircraft will be dictated by the limited parts inventory at hand. Other issues included high acquisition costs, single engine operation in the operating environment they specialize in (dependent entirely on your point of view), and the extremely high insurance costs driven by a helicopter with a 42% loss rate - something that is incomparable in the helicopter business, or maybe even the entire aviation business.

The K-Max is not a bad machine, in fact it is very good at what it does. It is phenomenally slow however. There is also a very limited market for helicopters that only perform external load operations, as the Skycrane also found out when compared to a Chinook (oops, another dual rotor reference).

The facts above provide a pretty fair explanation as to why the K-Max has a limited future at this time, not to say it won't get ressurected in the future, perhaps by someone other tham Kaman even!

[old rotorman]

X49-A update.
This program still being funded. The aircraft has accumulated about 70hrs and is now undergoing an annual inspection. Testing will strart up again next month.

[AdamFrisch]

What would you say, in percentage, was the power the tail rotor steals from the main unit when used to full right pedal?

[deeper]

Seventy eleven percent at least from the main unit and eleventy nine percent from each and every one of the other secondary units and none,nil,nada from all third and fourth units exept on odd days. On these days it is best to stay in bed with your wifes sister and not fly.:}:rolleyes:

[WhirlyBob]

What would you say, in percentage, was the power the tail rotor steals from the main unit when used to full right pedal?

I'll make a leap of faith and take it that you really mean "when the tail rotor is producing maximum thrust to counteract main rotor torque" since the answer would otherwise depend on whether you're talking about a Eurocopter, which spins the main rotor in a direction that God never intended, or say, a Bell or Sikorsky that turn the main rotor in the proper manner. :}
But with that nit picked, I offer this quote: "Tail rotors typically consume up to 5-10% of the total power" ... click here for source document (http://terpconnect.umd.edu/~leishman/Aero/merits.html)

This is from a helicopter aerodynamics course taught by Prof. J. Gordon Leishman at the University of Maryland.
The complete document is an interesting although fairly brief discussion of "conventional", tandem, and co-axial rotor configurations. :ok:

[topendtorque]

On these days it is best to stay in bed with your wifes sister and not fly.http://static.pprune.org/images/smilies/badteeth.gif:rolleyes:


Which goes to debunk the old adage that Helicopters are inherently dangerous, it's really the pilots.

[Dave_Jackson]

Leishman's recent papers are devoted to the coaxial configurations.

A quick overview of Tail Rotor Power Consumption (http://www.unicopter.com/B329.html#Tail_Rotor)