PPRuNe Forums - Russia accidentally leaks image of high speed rotorcraft

PPRuNe Forums (https://www.pprune.org/)

- Military Aviation (https://www.pprune.org/military-aviation-57/)

- - Russia accidentally leaks image of high speed rotorcraft (https://www.pprune.org/military-aviation/614832-russia-accidentally-leaks-image-high-speed-rotorcraft.html)

chopper2004

27th Oct 2018 22:56

Russia accidentally leaks image of high speed rotorcraft

Accidental revelation 🙏🏽

https://defence-blog.com/news/russia...elicopter.html https://cimg4.ibsrv.net/gimg/pprune....891d3600e.jpeg

Jackonicko

28th Oct 2018 12:24

https://cimg6.ibsrv.net/gimg/pprune....5ac8cf2b64.jpg

https://cimg4.ibsrv.net/gimg/pprune....01d9b7d71a.jpg

Two seat, internal weapons bays, retractable gear, shrouded rotor heads, fairly LO?

57mm	28th Oct 2018 14:12

Why is it that apart from the Kaman Husky, western helos have not adopted the coaxial rotor systems favoured by the Russians?

LowObservable

28th Oct 2018 14:18

G. Andreyvich* OKB at its finest.

* That would be "Gerry Anderson".

dook	28th Oct 2018 15:11

The Germans are doing it.

http://i63.tinypic.com/2ezlh12.jpg

Dan Winterland

28th Oct 2018 15:38

It's not going to be LO with contra rotating rotors.

hoodie

28th Oct 2018 16:19

@57mm, Kaman system isn't coaxial.

https://cimg3.ibsrv.net/gimg/pprune....7c0038e27e.jpg

For US coaxial, see Sikorsky X-2, S-97 Raider and Sikorsky-Boeing SB>1 Defiant.

VinRouge

28th Oct 2018 17:04

Assymetric length blades? Does the coax drive sort out the out of balance forces that would result?

Looks like they have stolen the Americans AIRWOLF programme design...

MPN11

28th Oct 2018 17:19

I always thought that blade tip speed was a limiting factor. Relative to airflow, advancing tip goes supersonic, retreating blade stalls, or simething like that. How does this design overcome that law of aerodynamics to achieve such a speed? Or is it relying on the stubby wing and jet propulsion, with freewheeling rotor blades, in high-speed cruise?

dook	28th Oct 2018 17:24

Blade tip speed is of consequence only in high speed forward flight.

Co-axial systems are not an attempt to overcome that problem. It's a problem with all helicopters.

MPN11

28th Oct 2018 17:27

Quote:

Originally Posted by dook (Post 10294783)

Blade tip speed is of consequence only in high speed.forward flight.

That was my point. Sorry if I expressed unclearly. How fast is this thing supposed to go? Three times as fsst as anyone else ... so HOW?

hoodie

28th Oct 2018 17:33

@VinRouge, the blades are the same length. They look shorter in the side view because there are 3 blades to each head.

dook	28th Oct 2018 17:50

Quote:

How fast is this thing supposed to go

I reckon it has a system to stop the blades and move them to a suitable position.

MPN11

28th Oct 2018 18:57

Quote:

Originally Posted by dook (Post 10294806)

I reckon it has a system to stop the blades and move them to a suitable position.

Transition to the hover should be interesting! ;)

Reduce to c. 150 kts, unwrap rotor blades, apply power, grasp collective, take up wallpaper-hanging in retirement! :)

dook	28th Oct 2018 19:03

Maybe disconnect blades drop collective all the way and then where would the blades rest ?

Any more ideas ?

MPN11

28th Oct 2018 19:08

I am bereft of ideas. I defer to those such as you who have done transitions!! Do you have helipopter time? I was only PPL!

dook	28th Oct 2018 19:35

I have no helicopter time, only fast jet time, but have learnt a bit by doing technical illustrations for a coupe of manuals on the subject, one written and published by a frequent PPRuNe contributor.

Ascend Charlie

29th Oct 2018 05:25

With the coaxial set-up, the retreating blade doesn't have to produce any lift, so it can relax a bit. With a normal helicopter, where the advancing blade can produce 7 x more lift than the retreating side, it has to throw away that extra lift and only develop as much as the poor old retreating blade is struggling to provide.

Coaxially, the advancing blade can produce as much as it wants, and let the retreater have an easier life.

MPN11

29th Oct 2018 10:44

Thanks, A C. That helps me understand much better.

tonytales

29th Oct 2018 19:22

I would also think with the coaxial setup having two sets of blades, you could reduce the diameter thereby reducing the blade tip speed.

KenV	30th Oct 2018 03:49

Quote:

Originally Posted by MPN11 (Post 10294775)

Sikorsky has been working on a coaxial "ABC" (Advancing Blade Concept) for decades. They got it to work, but ran into serious vibration issues. The idea is that only the advancing blades, one on each side of the aircraft produce lift. Thus no need for the retreating blade to produce lift. The rotors essentially feather while retreating. At high speeds the advancing blades significantly unload because they only produce lift, not lift plus thrust because forward thrust is provided by a pusher prop. The cool thing about this is that unlike a conventional helicopter which rotates nose down to accelerate, the ABC rotor system allows the aircraft to accelerates in a flat attitude, much like a fixed wing aircraft. This is especially useful in an armed craft which keeps the weapons pointed ahead all the time, rather than pointed down whenever the aircraft accelerates.

MPN11

30th Oct 2018 08:43

Thanks, Ken V. :ok:

VX275

30th Oct 2018 22:11

Looks like a jet powered Rotodyne without the tip jets to me.

KenV	31st Oct 2018 16:12

Quote:

Originally Posted by VX275 (Post 10297260)

Looks like a jet powered Rotodyne without the tip jets to me.

A rotodyne has a conventional main rotor except they are tip powered and thus there is no counter torque and hence no tail rotor. The rotodyne's rotor disc is also lightly loaded in forward flight because it is producing only lift and not lift plus thrust. So the rotodyne solves two of three problems. However, rotodynes still have the problem of different advancing vs retreating blade lift which fundamentally limits airspeed. The point of the coaxial ABC system is to eliminate that third problem: retreating blade lift. In the ABC system, the retreating blades produce zero lift during high speed forward flight. In addition, because the retreating blades do not need to produce lift, the rotor can be significantly slowed down at speed which reduces the advancing blade tip mach number with huge benefits in drag rise, noise, and blade tip buffet.

JohnDixson

31st Oct 2018 19:01

MPN11, you have a point re the advancing tip mach number, thus the X2 and 97 use a reduced Nr schedule at higher aircraft speeds. I imagine that the rotor speed control schedule is now automated on the 97.

BTW, handling tip speed for compounds involves the same situation, and they will obviously take the same design approach. If you plan on flying year round, implying colder ambient, and do the math for Mach 1* it becomes clear that you have to adjust Nr, not so much for rotor stability questions, although even that can become an issue if there is unacceptably low torsional blade stiffness, but for drag rise and performance impact. Beneficial effect on acoustic signature too, as you’d imagine.
*During the UTTAS development, the Army made a special request to clear the rotor to a free stream mach number of 1.0**, which was done on a cold day flying out of Burlington Vt. The rotor behaved well, and the bonus was that we got some terrific skiing in while the data was being reduced to ensure all was good.
**not an original spec requirement. I do not know if Boeing received the same request. Now that I think about it, that request may have come after the competition was over.

chopper2004

2nd Dec 2018 12:26

https://defence-blog.com/news/tsagi-...elicopter.html

The Central Aerohydrodynamic Institute named after N.E. Zhukovsky (TsAGI) has confirmed the development of a new Russian advanced high-speed helicopter.

https://cimg2.ibsrv.net/gimg/pprune....c7b7893d0.jpeg

unmanned_droid

3rd Dec 2018 10:08

I've done a fair amount of reading around about this, and have decided to adopt a similar approach for an Unmanned Aircraft Design Study.

For a small vehicle, the main emphasis is about what the best compromise is in terms of vertical takeoff and forward flight, whilst accomodating the fact that humans have to interact with it. So the design below is a fixed pitch tandem 'bi-copter' which works in vertical flight and slow forward flight. The transition to forward flight is carried out with fixed 'thrusters' and structure not yet added to the model below. The aim is to offload the rotors as fast as possible to increase overall vehicle efficiency.https://cimg8.ibsrv.net/gimg/pprune....65823a08d8.png

All times are GMT. The time now is 02:46.