Chinooks, further upgrade for forward flight in gyroplane mode
 

I am not an engineer but may I discuss a question.

It is possible to configure the engines of Chinooks to provide forward thrust for forward flight, such that the rotors can be unloaded and even fly as gyroplane in forward flight.

Even if you may need to upsize the engine, would this be a easier (cheaper, safe in terms of less technological risks) way of getting more speed, rather than to having to put additional pusher propellers like in the case of X2?

Thank you.

Helicopter engines are designed to extract the maximum energy from the fuel burnt and send it to the gearboxes, with little left over at the tailpipe, maybe 50lb thrust.

Turbojet engines take as little as possible from the fuel burnt to leave it with more energy blasting out the back, i.e. thrust. Completely different designs.

And for a Chook to turn into a gyrocopter, the blades have to go from sucking air in at the top and pushing it down to generate lift and thrust (and being tilted forward), to then go to being tilted back and having air come in from underneath, and extract energy from it to stay up (autorotation mode). Again, a big jump to make.

With pusher props from another engine, and with stubby wings to provide lift, the rotors can be unloaded (not turned into gyrocopters), which just means it can fly with less collective lever, using less fuel.

The Boeing 347 was a lift compounded version of the Chinook to unload the rotor system. It was abandoned after flight tests as not providing a big enough advantage to warrant the development costs as the US Army at the time was perfectly happy with what they had. Nowadays, with advances in digital engine and rotor control, and more advanced modelling of aerodynamics, it would likely be a smoother and easier process. However, there would still need to be a requirement to do so - and a "clean sheet" design may well be more efficient.....

There's still the issue of retreating blade stall which limits Vne, so what would be the point?

If there is a wing providing lift, then the retreating blade doesn't have to work so hard, and the stall will occur at a higher speed.

And Vne is less dependent on RBS than other factors.

The "compound helicopter" operates on the principle that in the cruise the wing generates the lift to carry the weight while the rotor is run at zero (collective) pitch and is just used for pitch/roll control (cyclic). At zero pitch there is no retreating-blade stall. But this is only true for a proper compound helicopter where there is both a fixed wing AND a separate means of forward propulsion.

PDR

Being an old, stubborn-ass, died in the wool, West Texas boy who cut his teeth on the stuff coming out of Ft. Worth (Hurst) way back in the day..., I'd be doing myself a huge injustice if I didn't mention the Bell 533. Late 1950's through late 1960's technology.

(...being that I still don't have my secret clearance to post pictures, y'all just gonna have to "cut and paste")

https://i.pinimg.com/originals/43/70...0c1ef4a096.jpg

4.bp.********.com/-2vTNUzqr48c/T1nwZdarL0I/AAAAAAABVWY/gtTTxozj7H8/s1600/Bell533-bia2.jpg

http://www.aviastar.org/foto/bell_533.jpg

http://image.slidesharecdn.com/12112...?cb=1426424062

...Which was the driver behind the Unload Lift Offset Rotor (ULOR) concept.

https://i.imgur.com/8Te7K57.jpg

I/C

Oh, that is sooooo ugly. Did it ever get beyond a concept? Those engines look like they were borrowed from a Hercules.

Well the examples I would have chosen would have been the Lockheed experimental XH-51A:

http://www.aviastar.org/foto/lok_compaud_2.jpg

And the AH-56 Cheyenne attack helicopter developed as a result:

https://upload.wikimedia.org/wikiped...6_Cheyenne.jpg

The AH-56 Cheyenne programme developed and matured most of the features seen on subsequent attack helis - integrated nav/attack, helmet-slaved gunsighting etc.

PDR

I suspect if/when the all electric tail rotor becomes a reality then it would be quite a simple task to make it pivot around from providing anti-torque at low speed to providing forward propulsion at high speed.

Thanks everyone for all the comments and input.

Regarding this above concept ("to make it pivot around from providing anti-torque at low speed to providing forward propulsion at high speed"), I have also been thinking about similar concept.

But, there will still be the problem of RBS, unless there is a set of fixed wing, right?

Charlie,

I don't believe so. The last time I saw ULOR referenced was at the AUSA annual convention in October 2011, 3½ years after the concept first appeared at AHS Forum 64 (and 4 years after the idea was patented).

One development that does appear to be proceeding is installation of the CH-53K's 7,500 shp GE T408 engine on the CH-47F, in place of the current 4,867 shp T55-L-714A. The T408 - whose heritage includes the T407 prop unsuccessfully offered for the C-130J in the early 1990s - will nearly quadruple the Chinook's installed power from the 1,940 shp YT55-L-5 installed in the original YHC-1B.

I/C

You mean rather like this?

[QUOTE
Regarding this above concept ("to make it pivot around from providing anti-torque at low speed to providing forward propulsion at high speed"), I have also been thinking about similar concept.
[/QUOTE]


I think you'll find someone already had that idea in the 1930's, its called the Gyrodyne.