Bell Helicopter Hybrid Tandem Rotor - The DEW Line

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http://www.flightglobal.com/blogs/the-dewline/2009/05/bell-helicopter-reveals-hybrid.html

Bell Helicopter reveals "Hybrid Tandem Rotor" to replace AH-64 and UH-60

The mysterious sign in Bell Helicopter's exhibit space today at the Army Aviation Associaton of America's (Quad-A) convention simply reads: "It's not a tiltrotor ... what is it?"

http://www.youtube.com/watch?v=ll_bIhnV2Es&feature=player_embedded

It is Bell's candidate for replacing both the AH-64 and UH-60 with an all-new configuration called the Hybrid Tandem Rotor, Robert Kenney, Bell's executive VP for government programs, told me in an interview a few minutes after I filmed this clip.

The HTR "splits the difference between a helicopter and a tiltrotor," said Kenney.

While the BellBoeing V-22 can tilt its tandem rotor 95 degrees, the HTR's wing tilts by 25 degrees and gains 5 degrees more by adjusting the cyclic controls.

That means the HTR could achieve a forward speed of 225kts, Kenney said. A V-22 cruises at more than 300kts, while the fastest helicopters are limited to about 170kts.

If this particular configuration has ever been attempted before, Bell's engineers are not aware of it.

"When I first saw it I tried to figure out why it was a bad idea," said Kenney. "And I peppered the poor designers with questions and they answered them all. And then my question was 'why hasn't anyone tried this before?' Now that you see it it's kind of a no-brainer."

But don't expect to see a prototype flying any time soon. Kenney said Bell has no plans to launch a prototype demonstrator. The HTR will remain a design concept only unless the US Army launches a competition to replace the AH-64 and UH-60, he said.

That notional program, known as the Joint Multi-Role (JMR) requirement, exists, but has so far not been funded to enter a long-term development phase. According to Kenney, the army is more likely to continue improving its existing aircraft fleets, rather than develop an all-new aircraft.

By exhibiting the HTR at the Quad-A convention, Bell simply hopes the concept sparks the army's interest.

"This is kind of it's coming out party," said Kenney, "so we'll see what the interest levels are."

That's a very interesting approach but I wonder about the cost/benefit ratio. Cruise/max speeds of the UH-60 Blackhawk are about 150/159 knots vs. 241/305 for the V-22 Osprey. If the HTR max speed is 225, then I'd guess cruise would be 180-200 knots, which doesn't seem to justify the expense and complication.

If the tiltrot0r is a concept midway between the airplane and the helicopter, and the HTR is somewhere between a tiltrotor and a helicopter, I've often wondered about the pros and cons of something between an airplane and a tiltrotor: a partial tiltrotor or tiltwing to achieve super-STOL but not VTOL performance.

I have a couple of Richard Pawling pics of the MAI Sokol - Soviet VTOL concept from 1936 on my desktop at home. This picture from his site www.rp-one.net fascinates me



Partially tilting engine nacelles or the whole wing combined with generous slotted flaps, and perhaps roll spoilers to supplement the ailerons, ought to provide near-VTOL, super-STOL performance without the complicated control issues of full VTOL conversion and horizontal-vertical conversions. 45 degrees could be enough tilt to make it work and perhaps less with a high wing and smaller, and perhaps more, props.

Such an aircraft, matching or exceeding the speeds of the V-22 but sacrificing the ability to hover and requiring, say, a 100 meter clearing to operate, might be a lot more cost effective and leave enough money left over to buy more helicopters to do the job of...wait for it...helicopters.

I can think of plenty of tilt-rotor, tilt-wing and flap-channeled slipstream designs that aimed for VTOL operation, but does anyone know of any such designs that deliberately sacrificed true VTOL operation and settled for much simpler super-STOL performance?

Cheers,

Matthew

Interesting, could be mechanically simpler and cheaper? ;D Yeah right

Mole,

I suspect that Bell is fishing. Trying to find out what their government customer is thinking. Thus the point "no hardware unless there is a government program". Tilting the wing slightly is a lot less complex than a full tilt rotor conversion and probably a lot lighter too, although I am on thin ice with that particular thought. IF it is just a sideways tandem, with canted transmissions, then the dynamics ought to be no more complex than a CH-47. From the picture it looks like it might be even simpler because the rotors do not intermesh so there is not any synchronization problem. A BIG jump is that it might be even less complex than the Sikorsky X-2.

But since the government customer is starting to think that they may need faster rotorcraft because of the large areas they have to deal with (point made last week I think by an Army general saying Afghanistan is as big as Texas or something like that), and considerations like MEDEVAC golden hour, troops in contact wanting guns in less than 30 minutes, etc., I'm thinking that everyone is looking to push past the 200 knot barrier. Then there is the USMC who after the H-1 is likely not looking for aircraft much slower (if at all) than the V-22.

Mole said:

I can think of plenty of tilt-rotor, tilt-wing and flap-channeled slipstream designs that aimed for VTOL operation, but does anyone know of any such designs that deliberately sacrificed true VTOL operation and settled for much simpler super-STOL performance?

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One example is the Canadair CL-246 tilt wing transport concept which sprang from the CL-62/-73/-74/-84 series of designs. American Airlines didn't need full VTOL so Canadair just limited the degree of wing tilt.

yasotay said:

Tilting the wing slightly is a lot less complex than a full tilt rotor conversion and probably a lot lighter too, although I am on thin ice with that particular thought.

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I would say your thought ice is solid. A few aircraft have had variable incidence wings (slight tilting) the F8U Crusader being the most well known (plus the Martin XB-51 and a few designs). The level of complexity seems to be a significant factor below that of the tilt wings. Though neither the FBU or XB-51 had engines mounted on their wings. But the less movement of the wing means the less movement for normally fixed features; things like fuel lines and controls. When the variable angle is say under 15-30 degrees that is a lot easier to accomplish than 90 degrees.

Is this a sign that Bell is throwing in the towel on future applications of the Tiltrotor?

A more extreme example of the concept is the Vought XC-142, although the Bell concept is far more conservative with its limited range for wing incidence.

How would you yaw the aircraft while hovering? Puffer jets?

Other than that, it looks like a pretty solid concept.

Bell like all the others does not believe that the Army is willing to invest in high technology for rotorcraft... look at the lack luster last thirty years of rotorcraft S&T. So they are trying to find what the Army is willing to invest in. This design gets at some of the areas that the Army concedes it has gaps without a major tech investment.

CFE said:

How would you yaw the aircraft while hovering? Puffer jets?

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Probably yaws in the same way the CH-47 Chinook does, differential control of the two rotors.

I wonder if the concept could be applied to a single rotor, basically a compound helicopter with a tilting wing/transmission?

Would a larger version of this concept be consider for the JHL program?

It probably does not meet JHL speed requirements.

POSTER: Bell's new Hybrid Tandem Rotor
Source:Flight Global Blogs - The Dew line

I sense a bit of Sikorsky X-2 envy. :

-----JT-----

I sense intense pain. Right about here:

sferrin said:

I sense intense pain. Right about here:

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I know you're joking, sferrin, but is there some reason this design would be more or less vulnerable than any other rotorcraft?

Mole said:

sferrin said:

I sense intense pain. Right about here:

Click to expand...

I know you're joking, sferrin, but is there some reason this design would be more or less vulnerable than any other rotorcraft?

Click to expand...

I was referring to pain of design not so much vulnerability.

sferrin said:

I sense intense pain. Right about here:

Click to expand...

Autch, aiii, Arrrggggg screams the gearbox in that engine box
and Wat about one engine goes out ?
has this Tandem Rotor fail save system like in V-22 ?
if yes then MORE pain for gearbox

My mistake. For some reason I was thinking they wanted to tilt the rotors relative to the nacelles. If they are fixed then it shouldn't be too bad.

From the picture it looks like the nacelle/engine/transmission are all fixed, so there should be less of an engineering problems than a tilt rotor. I think they are fixed and the wing does all the moving to tilt the rotors fore and aft. I can't imagine there not being some sort of cross shafting to keep engine out from becoming catastrophic from a aircraft control perspective. Really should't be any more difficult a dynamic layout than a Chinook.

A bit off topic perhaps, but studying all these various configurations for high speed rotorcraft (HTR, tilt rotor, X2, etc), I can't but help wonder if it's a bit of overkill, particularly with attack variations. I can see the need to hover for CSAR, air assault, spec ops, and perhaps reconnaissance. But is hover and shoot the best tactic for attack?

Since the vast majority of these aircraft are based at airbases, would it not be more simple, effective, and cheaper to build a CTOL aircraft for escort and attack? It would have higher speed, higher altitude, and likely more payload. A modern Shturmovik or A-10 derivative?

An interesting point. Also by the time you buy and field them there may be no reason to have a manned attack platform.

Still for the Army, reliance on airports is not a popular idea as they are very easy targets. Also one of the benefits of VTOL is that you can put a rearm and refuel position well forward at forward operating bases, so if the attack aircraft has to rearm or refuel it does not have to go all the way back to the airfield to do so.

Is this concept still live?