C-130 Hercules

[Mossie]

Groen Brothers Aviation have recentley been contracted by DARPA to produce a 'Heliplane' based on Rotodyne technology.

Looks fantastic, & promises a whole new class of aircraft, but why has it taken so long?!?!?  The Rotodyne was cancelled because of developmental costs & political problems, not because the technology wasn't ready.  I guess that immediately after Rotodynes cancellation the concept was a political hot potatoe (not to mention being patent protected), but since then the helicopter has matured & larger companies have gone down this route, rather than risk a whole new development despite the fact the technology has been proven & the obvious advantages of the concept.  This leaves small companies like GBA (they already make commercial gyroplanes) to pick up where Fairey & Westland left off.


Proposed design for DARPA contract


Other GBA gyrodyne design


GBA Monsoon, a converted C-130 waterbomber gyrodyne

GBA have just completed a major DARPA milestone & should now be able to produce a 'proof of concept' which will hopefully lead to a fully cpable aircraft.  Fingers crossed eh?

Some of GBA's designs like the C-130 conversion would make lovely builds, any takers?

Simon.

[kitnut617]

A Herc type rotodyne would be quite a neat project to do.  I'll have to give it some thought as to what to change, judging by some comments I've read on here and ARC.  Maybe a couple of hi-bypass turbo-fans instead of the props, hmmm!

Or a pair of un-ducted contra-fans    

Robert

[jcf]

A Herc type rotodyne would be quite a neat project to do.  I'll have to give it some thought as to what to change, judging by some comments I've read on here and ARC.  Maybe a couple of hi-bypass turbo-fans instead of the props, hmmm!

Or a pair of un-ducted contra-fans   

Robert

...and clipped wings, say just outboard of engines 1 and 4 with downturned tips if you keep 4 engines and at the engine 1 and 4 locations of you go for the turbo-fans or unducted fans.

Cheers, Jon

[jcf]

Note the high aspect ratio wings, podded fuselage and raised boomed tail features...all of which combine to reduce the structural area under the rotor disc.
DARPA just canceled the Boeing X50A Dragonfly Canard Rotor Wing because of crashes caused by control problems that were produced by the interaction of the tip-driven rotor and the proportionally large fuselage area.

Just looking at the design its obvious that Groen and the Georgia Tech team are trying to avoid the interaction produced control problems and increase the vehicle's VTO and hover ability.

So rather than a C-130 based Gyrodyne, how about using a C-119 for the conversion?

Cheers, Jon  

[kitnut617]

...and clipped wings, say just outboard of engines 1 and 4 with downturned tips if you keep 4 engines and at the engine 1 and 4 locations of you go for the turbo-fans or unducted fans.

Cheers, Jon

We are talking big here aren't we,  but all the same, I was thinking of shortening the wings by the distance between the inner and outer engine, and go with just a pair of engines  B) You wouldn't need all that wing area because you have the rotor, which could be orientated like the Rotodyne where the start of the blade aerofoil are set out quite far from the hub.

When the blades are at 90 degrees to the fuselage, this would be where the blade aerofoil would start.  There's not much you can do with the fuselage as you would need the length, but the round shape of a Herc would surely benifit aerodynamically better than the flat top of the C-119.

I notice that the large Groen design has a rounded top to the fuselage and so did the Rotodyne 'Z'

Robert

[Mossie]

You wouldn't need all that wing area because you have the rotor, which could be orientated like the Rotodyne where the start of the blade aerofoil are set out quite far from the hub.

I think you still need a large wing area Robert.  On a Helicopter, the rotor gives downwards thrust, on a gyroplane, it's upwards.  This why you tend to see a helicopter's nose pitched down in forward flight & a gyrocopters pitched up.  A gyrodyne is designed to give neutral thrust (ie, no lift), so you still need the lift from the wing in forward flight.  I think this is why Westland redesigned the Rotodyne Z to have a 75ft wing & why the GBA designs all have large wing areas.  The larger of their designs above has stubby wings but has a very large tail, presumably to increase lift.

The Wikipedia page on gyrodynes gives a good overview.

I don't mean to p**s on your bonfire mate!  A Herc gyrodyne would look great despite the 'real' world impracticalities!

Simon.

PS I've just bought a couple of Rotodynes form Kingkit.  I still intend doing this Rotodyne Z conversion!

[kitnut617]

Hi Simon,

Don't worry, the bonfire hasn't fizzled yet.  Maybe I just need to adjust what I have thought about.  From all the comments said and looking at all the pictures, the wing would be better if it had a shorter span, but maybe it should have a wider chord too. But in either case, whether it's a gyrodyne or a helicopter, the rotor creates lift ( it's the safety feature in helicopters when the flame fizzles out in the engine and it goes into auto-rotation) when the aircraft is in forward motion.

Edit:  I would say that the larger tail is required to counter the pitch-up attitude when in forward motion.

If Groen was to convert a Herc' I think that the only bit that should be used is the fuselage.  New wings (main and tail) and new engines for sure anyway.  

Another thing I've thought about is one of the problems that hounded the Rotodyne, at least in the end, which is the noise from the rotor tip jets.  With the size of the rotor pylon needed for a project this big, it could quite easily house one or two turbines, and instead of having them set up for forward motion, have them set up to provide compressed bled air to the tip nozzles.  I don't know if this will make it quiter but it wouldn't be as loud as powered jets that's for sure.

Robert

[Mossie]

Your're right Robert, the rotor will provide some lift, (although probably not huge amounts).  Sorry about that!

If I've got it right, the noise of the tip jets wasn't an insurrmountable problem.  Silencers fiited to the jets had considerably reduced the noise & the design team expected to get within the specified limits fairly easily & quiter than contemporary airliners.  The noise problems we're mainly brought up by the loudest detracters of the project.

They still would have been damn noisy though, especially by todays standards when your not expected to hear a jet any further than three foot away.  The approach you've got with the turbines sounds like a good one.

I remember we talked about the 'Z' being fitted with RB.176 boost engines.  I thought it was purely about increasing lift, but maybe they had some role in an attempt to decrease the noise levels too?

Simon.

[kitnut617]

Your're right Robert, the rotor will provide some lift, (although probably not huge amounts).  Sorry about that!

If I've got it right, the noise of the tip jets wasn't an insurrmountable problem.  Silencers fiited to the jets had considerably reduced the noise & the design team expected to get within the specified limits fairly easily & quiter than contemporary airliners.  The noise problems we're mainly brought up by the loudest detracters of the project.

They still would have been damn noisy though, especially by todays standards when your not expected to hear a jet any further than three foot away.  The approach you've got with the turbines sounds like a good one.

I remember we talked about the 'Z' being fitted with RB.176 boost engines.  I thought it was purely about increasing lift, but maybe they had some role in an attempt to decrease the noise levels too?

Simon.

Yes I remember that too only I had forgotton the RB.176 designation.  

If I understood it correctly, (and I can't double check right now as everything I have model related is now in storage)  from what I read these were to provide compressed air to the tip nozzles only.  These engines did not provide any thrust for forward motion.  I think this was the noise solution but until you reminded me of them I had forgotten about it.

Robert

[Mossie]

I found a link a while ago describes the RB.176  as a 'specialised lift engine': RB.176

I found this passage in the article that you passed on to me too:

"It was obvious that the enlarged design would require more power that even that which would be produced by the Rolls-Royce Tyne power plant. It was suggested that power be increased by fitting a Rolls-Royce RB. 176 auxiliary booster engine in the rear of each Tyne nacelle."

Saves you digging out the info mate!  Whether this was for thrust or lift I don't know.

Simon.

[jcf]

I think you still need a large wing area Robert.  On a Helicopter, the rotor gives downwards thrust, on a gyroplane, it's upwards.  This why you tend to see a helicopter's nose pitched down in forward flight & a gyrocopters pitched up.  A gyrodyne is designed to give neutral thrust (ie, no lift), so you still need the lift from the wing in forward flight. 

True when the rotor is in free-wheeling mode but not when it is in powered mode... then it functions in the much the same fashion as a helicopter rotor and that is when the area beneath the rotor disc is critical. The layout shown in the Groen/Georgia Tech artwork for their DARPA proposal actually makes the most sense. The earlier version showed a low-mounted wing, now it is top-mounted and evidently of increased aspect ratio. Check the Link down the page for an earlier concept illustration. The Adams A700 light jet is being used as the basis for the machine.

About noise and rotating blades, its not just the passage through the air that causes the noise there are secondary(tertiary in the case of jet-tip rotors, the jets being the primary source ) soundwaves produced by the accelerated air bouncing off the airframe structure...another issue the Groen/Georgia Tech layout would mitigate.

As to Robert's notion of using compressor section bypass bleed air to power the rotor, referred to as "warm cycle" drive...that is evidently one of the options being researched.

GBA/DARPA project


Just to be clear, I love autogyros and related critters(Brooks's "Cierva Autogyros" is an excellent book and I recommend it wholeheartedly), but bald statements along the lines of "only politics have prevented Gyrodyne development" as made by the head of the current project, to my mind smack of boosterism and gloss over the technical realities. Best of luck to them all, but it aint' the best thing since sliced bread.

Cheers, Jon

[kitnut617]

From what you've just said Jon, that probably explains why on a Mil-24 Hind, the large wings are sloped downwards as they are.  Now what if the wings on our theoretical gyrodyne were sloped down too?  Would this address the problem?

Robert

[Archibald]

In every case, the rotodyne seem much less risky than the tilt-rotor concept...
just a tough : I heard of a (future) four tilt-rotor... the size of a Herc! Are those designs in competion with it?  

[kitnut617]

In every case, the rotodyne seem much less risky than the tilt-rotor concept...
just a tough : I heard of a (future) four tilt-rotor... the size of a Herc! Are those designs in competion with it?

Yes I read about that one too,  it was proposed as a Herc' with two wings with the same engines from the Osprey.  I would say that they are competitors and I would imagine to keep things standard, the tilt wing might have an edge.

Check this out:   http://www.vtol.org/vertiflite/BellTiltrotors.htm

Robert

[jcf]

In every case, the rotodyne seem much less risky than the tilt-rotor concept...
just a tough : I heard of a (future) four tilt-rotor... the size of a Herc! Are those designs in competion with it?

Nope, the Georgia Tech team that Groen was part of didn't make the final cut in the battlefield transport contest.

The four-poster tilt-rotor design is actually a very good concept and far superior to the two-rotor layout of the V-22...the cruciform helicopter layout is not suited to larger craft, while it worked fine on the XV-15 it is the source of some of the V-22's inherent stablility problems. It doesn't scale well vis the Kamov Ka 22.
The four-rotor setup doesn't have those problems.

Cheers, Jon