Interesting concept but given such vestigial rudders on the empennage, what form of prop/pitch/throttle control for yaw?

http://www.youtube.com/embed/8ljxyDtCsaM

Rod

I'm sure they are varying the pitch on the propulsive propellers (for want of a better word)

For anti torque, adding power to the main transmission and one of the props takes a bigger "bite" of air. (or the opposite takes a smaller bite).

For yaw control, one takes a bigger bite, the opposite a little less.

All this done by those clever ones & zeros, of course.

I think this thing could do the Osprey's mission at a lot less money.  

That part about filming it running along with that high speed train was one real smooth piece of marketing.

rmw

At hover and low forward speed, differential speed and/or (more likely) differential pitch control of the tractor propellers would be essential for yaw control.  I can't tell which they use.  Either would probably be too sensitive at high forward speed unless the gain is reduced or clipped with increasing forward speed; I have no knowledge of the matter, but it seems possible.

No, on reflection, it seems likely.  Note that the vestigial rudders don't seem to have trim tabs.  Which suggests that perhaps they _are_ trim tabs.  Only one short sequence toward the end of the video shows them deflected a few degrees.  They don't seem to have enough 'authority', if that's the right word, to offset a thrust asymmetry; that might be of concern.

Agree, ones and zeros must be there.

I wonder if they reduce the main rotor rpm at high forward speed, too; I'd guess they'd have to, to keep the advancing tip speeds subsonic.  Or maybe it doesn't really go that fast?






 

Mike Halloran
Pembroke Pines, FL, USA

evelrod,

The yaw control/anti-torque is provided by a combination of rudder and prop pitch, which can vary depending upon forward speed.  During hover, the rudders are obviously not effective, so differential prop pitch would be used.  At higher speeds, using the rudders as much as possible would seem to be more efficient.

There's recently been quite a bit of renewed interest in compound helicopters, like this Eurocopter X3, the Sikorsky X2, Piasecki X-49, or the AVX concept.  There currently is a debate over whether compounds or tiltrotors are the best way forward. It will be interesting to see how it all plays out in the next few years.

Terry

Check out the gyrodyne. That used one forward facing airscrew on a stub wing on one side to provide both rotor torque reaction and forward thrust.

I'd love to see the tradeoff analysis on these designs.

 

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

Thanks for teaching me something today, Greg.
 

Mike Halloran
Pembroke Pines, FL, USA

Greg, didn't the (Fairey) Gyrodyne use reaction jets on the blade tips, thus no torque reaction?

Regarding the main rotor advancing blade going supersonic, I would thing the "wing" would provide enough lift at speed, to allow the pitch of the main rotor blades to be decreased, unloading the main rotor, and pushing the blade stall back somewhat.

Yeah, the wing should help.  Like Greg said, an n-dimensional tradeoff, where n could be large.

Mike Halloran
Pembroke Pines, FL, USA

Thru the Fence,
I think you meant the Fairy Rotodyne.
It was the reaction jets on the rotor tips that killed the project ( It was too noisy.), but the concept was good.
Here is a link to a video of the bird at Farnborough.
B.E.

http://www.youtube.com/watch?v=SJqcVVnk3DM

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

Exactly so.....The tip jets were shut off in cruise flight, making it a sort of super autogyro.

here's another link for those interested.

http://www.aviastar.org/helicopters_eng/fairey_rotodyne.php

IMHO the British aerospace industry missed a bet with this thing.

So what we have here is a repeat of the Gyrodyne using improved engines and controls 63 years later.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

http://en.wikipedia.org/wiki/Fairey_FB-1_Gyrodyne is the one I meant, apparently though gyrodyne can mean something else.

Why were all British helicopters of that era designed to look like cartoon characters?

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies  http://eng-tips.com/market.cfm?

Thanks for that link, Greg, i had my Fairey's confused!

The one I refered to was the later version,the jet gyrodyne, which had two propellors.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

The Cartercopter is another of these aircraft with the rotor for low speeds and the wing for high speeds.  You can see it here:

http://www.cartercopters.com/index.html

The Cartercopter has an autogyro rotor and without the tip jets turned on, the Fairey Rotodyne was the same.  These types do not have torque to overcome as the rotor rotation is independent of the aircraft.  The X3 has a conventional gearbox driven rotor.

You can read what Jay Carter has to say about their rotor performs at higher speeds:

http://www.cartercopters.com/mu-1.html


 

Reading the wiki page on the gyrodyne...I never new about the earlier version which is indeed very similar to the X3.  I made the same mistake others have made in this thread...referring to either the "Jet Gyrodyne" and the Rotodyne that resulted from it.

Well now I can't get it out of my head. What is the disadvantage of the gyrocopter vs a conventional helicopter?

My guess is that control of hover is more difficult, every time you yaw the thing it starts to move forwards or backwards. This could be compensated for by using the cyclic. These days that could be done by a $2 chip (with a million dollar validation program).

 

Cheers

Greg Locock


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A gyrocopter cannot hover. It must be moving forward to drive to overhead rotor, which has no motor. I think there is a light drive shaft on it, just to get it started rotating.  

The term "Gyrocopter" and "Autogyro' were both trade marked terms to describe an unpowered rorary wing aircraft
The Eurocopter, Cartercopter and Rotodyne all have powered rotors which enable true vertical flight.

I found a rather long winded article which covers these aircraft in great detail.
B.E.

http://www.gyropilot.co.uk/downloads/Rotodyne%202%20RTF%20Mod.pdf

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

The Cartercopter is able to perform jump take-offs but the rotor is otherwise unpowered.  This means the air passes up and through the rotor instead of being pushed down as with a conventional helicopter.  The Rotodyne did have tip jets but these were only for take-offs and landings and the rotor otherwise operated in the same manner as the Cartercopter or other Autogyros.  From everything I've seen, the X3 is a bit different in that the rotor is always powered.  

The X3 can hover whereas the Cartercopter or Rotodyne could not.  The Cartercopter can however "Kite" or hold position over the ground with sufficient wind (i.e. windspeed >= minimum airspeed).  Helicopters used for heavy lift in hover usually don't have that far to go or at least don't have to go very fast.  Big exceptions would be SAR rotorcraft or troop transports.

An aircraft of the style of the Cartercopter could have a significant advantage over an aircraft of the style of the X3 for missions where you are looking purely for VTOL with high speed transport.  The Cartercopter conceptually is a simpler and potentially a lower maintenance aircraft as it does not have the main rotor gearbox.

SAITAETGrad.
You said;
"The X3 can hover whereas the Cartercopter or Rotodyne could not."

Wikepedia says:
""The Rotodyne performed to expectations and set a world speed record in the convertiplane category, at 190.9 mph (307.2 km/h) on 5 January 1959, over a 60 mi (100 km) closed circuit.[8] As well as being fast, the craft had a safety feature: it could hover with one engine shut down with its propeller feathered,""

B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor

Yes, that's true.  Thank you for the correction.  But, do you think it would have been used for hover tasks such as firefighting, construction, or logging?  Seems very unlikely due to the large wing and hstab acting against the hover forces, the fuel consumption of the tip jets, etc.

The tip jets were primarily for VTOL.  Otherwise, the aircraft was designed to fly with the rotor in auto-rotation.

True,
The rotodynes original task was short haul, city center to city center passenger service, to avoid going to the airport, or the railway station.
 There were certain factions in Great Britain that did not want to see this happen.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them.  Old professor