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timz
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How To Get Helicopter Fuel To Rotortips?

Sun Nov 13, 2011 1:37 am

Dunno how many helicopters propelled their main rotors by jets at the tips of the rotor blades-- but take the Fairey Rotodyne: what sort of connection could get fuel into the blades of a rotating rotor? How did its tip jets work? Were all such helicopters much noisier than a conventional helicopter?
 
tdscanuck
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RE: How To Get Helicopter Fuel To Rotortips?

Sun Nov 13, 2011 4:38 am

Quoting timz (Thread starter):
what sort of connection could get fuel into the blades of a rotating rotor?

I can't speak for any particular design, but the usual way to get fluid into a shaft is to have a hollow shaft with a series of radial holes, then wrap a stationary collar over the section with holes and put seals where the shaft goes through the collar. Then you pump fluid into the collar...it can't get out past the shaft because of the seals so it goes in through the radial holes and flows down the hollow shaft to wherever you need it to go.

There's a whole family of small jet engines (I think they originated with Finmeccanica) that use this method for fuel injection to the combustor.

Tom.
 
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Starlionblue
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RE: How To Get Helicopter Fuel To Rotortips?

Sun Nov 13, 2011 8:29 am

Technically the Fairey Rotodyne was not a helicopter. It was a compound gyroplane (AKA rotodyne AKA heliplane). This was because the rotor did not propel the aircraft forward during cruise. Forward propulsion was achieved by the engines on the wings. Apart from take-off and landing, the rotor was unpowered.

Quoting timz (Thread starter):
Were all such helicopters much noisier than a conventional helicopter?

Yes. The jets at the tips were very noisy and this was one of the reasons for cancellation.
 
BMI727
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RE: How To Get Helicopter Fuel To Rotortips?

Sun Nov 13, 2011 9:09 am

Quoting Starlionblue (Reply 2):
Technically the Fairey Rotodyne was not a helicopter.

McDonnell's Little Henry, however, was a helicopter. But it suffered from the same problems of noise and fuel consumption so the idea was abandoned.

The attraction of having the rotor driven at the tips is that it would not impart a torque on the helicopter itself, eliminating the need for a tail rotor, but proved impractical. McDonnell Douglas did eventually manage to eliminate the tail rotor decades later with the NOTAR system though.
 
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Starlionblue
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RE: How To Get Helicopter Fuel To Rotortips?

Sun Nov 13, 2011 9:43 am

Quoting BMI727 (Reply 3):
McDonnell's Little Henry, however, was a helicopter. But it suffered from the same problems of noise and fuel consumption so the idea was abandoned.

So tip jets are not limited to rotodynes. Interesting.

Quoting BMI727 (Reply 3):
The attraction of having the rotor driven at the tips is that it would not impart a torque on the helicopter itself, eliminating the need for a tail rotor, but proved impractical. McDonnell Douglas did eventually manage to eliminate the tail rotor decades later with the NOTAR system though.

Quite. Then again Kamov has achieved the same effect with counter-rotating rotors.
 
HaveBlue
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RE: How To Get Helicopter Fuel To Rotortips?

Sun Nov 13, 2011 6:24 pm

Quoting Starlionblue (Reply 4):
Quite. Then again Kamov has achieved the same effect with counter-rotating rotors.

And perhaps more successfully Boeing has with its tandem helicopters.. the CH-46 Sea Knight and CH-47 Chinook. Less successfully was the Kaman HH-43 Husky and modern K-Max with side by side rotors, intermeshing and contra rotating.
 
MoltenRock
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RE: How To Get Helicopter Fuel To Rotortips?

Sun Nov 13, 2011 7:52 pm

I had no idea what this thread until I found this:

http://en.wikipedia.org/wiki/Tipjets

For all the others similarly confused. I learned a lot following various links on the Wiki page.
 
SlamClick
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RE: How To Get Helicopter Fuel To Rotortips?

Mon Nov 14, 2011 12:33 am

I remember an old experimental helicopter powered by ramjets on the rotor tips. It used a small electric pump to lift fuel up to a slinger-ring just below the rotor head. This ring spun with the main rotor. Ports on the outside of the slinger ring led to fuel lines inside the blades leading out to the fuel nozzles in the ramjets. It also had a belt arrangement allowing ground crew to spin the main rotor up to some starting speed because the ramjets needed forward speed to work and the fuel system needed centrifugal force to feed.

I was told by the older heads that a trickle at the ring became something like 2000 PSI at the fuel nozzle. Further, all the fuel it could lift off the ground was only good for about twenty minutes flight.

Oh, and it had a single-bladed, counterweighted tail rotor.
 
MD11Engineer
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RE: How To Get Helicopter Fuel To Rotortips?

Mon Nov 14, 2011 8:06 pm

Quoting HaveBlue (Reply 5):
Less successfully was the Kaman HH-43 Husky and modern K-Max with side by side rotors, intermeshing and contra rotating.

Which was an invention by the German engineer Flettner (who built similar helicopters in small numbers just before and during WW2, and later emigrated to the US to become Karman´s chief designer).

Jan

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