Tail Rotor Power Consumption
 

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?

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.

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.

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

Fenestrons need the most power. Up to 25%.

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

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.

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

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

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.

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.

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

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.

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 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

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!

Nick,
Now you've gone and done it.


Nick, you said;Damn rights they would. However I said;
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 Obviously your 70 or 90 mph sideward flight in the Comanche was not a "most".
____________

Then you have the audacity to say;:E 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

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

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.” He could have been talking about tail rotors.

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?

Piasecki Directional Control Power
 

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

X-49 "Speedhawk"
 

http://blog.flightstory.net/126/siko...light-in-june/
http://en.wikipedia.org/wiki/Piasecki_X-49
http://blog.flightstory.net/wp-conte...peedhawk-1.jpg
http://blog.flightstory.net/wp-conte...peedhawk-2.jpg
Video here:
http://uk.youtube.com/watch?v=Yu2CwHwxJYA