Sikorsky X2 coaxial heli developments.

[Phoinix]

F-35B, fan is only the fwd lifting system, a turboan engine on the aft... so it's not "solely rotor".

[bat1]

Here is another video from Sikorsky's website about the furture Raider project

http://www.sikorsky.com/StaticFiles/...010_lowres.wmv

[IFMU]

Interesting article and pic of the sail fairing:

facts-figures-and-sail-fairings.html

-- IFMU

[gdbaldw]

Lift-to-Drag effective

Are there any authoritative reports of L/De? I calculate L/De = 5.4 from the data at post #787 and the statement at 17:12 minutes into the video of post #768. Wonder if anyone else has these numbers, and expectations of the sail fairing benefit.

Data used in calculation:

Rolls Royce T800 max continuous power = 1231 HP

Post #787:
GW = 6500lbs
At 250kts (422fps) power is (max continuous - 300 HP) = 931 HP

Post #768:
At 200kts (338fps) power is 60% of max continuous = 739 HP

Assumes SAC is using sealevel Max Continuous Power as reference, and that these reported power levels are both at 6500 lbs GW.

[Rb98]

When is anyone going to start shedding light on the fact that Sikorsky didn't really break any record? If you want absolute with a plane jane fling wing, the Lynx got it... Absolute with any assistance, the 533. Otherwise I am going to start setting records for absolute groundspeed with a tailwind, fastest speed over a 20cm course, hell the world record speed with autopilot on... and feel legit because the claim the X2 is now the fastest thing with a rotor system has not been called out. Nothing against the program; Sikorsky is very smart perusing the whole ABC/Aux Propulsion thing as it is one of the futures of rotorcraft and it is very admirable that they are doing it all on their own initiative (and dime)... but the fanfare is going a bit too far and they are greedily overshadowing a lot of the other notable advancements in helicopter history for the sake of publicity.

Mike

Didn't the record setting G-Lynx get a significant (~10%) amount of forward propulsive force from the engine thrust? I've heard this several times but can't find a difinitive source.

[dangermouse]

sort of...

I went to the RAeS lecture at Yeovil on the record flight, where this was explained. The clever thing that was done was to tune the exhaust pipes to achieve minimum drag and also produce some forward thrust when operating at very high powers as a byproduct of the necessity to get rid of the exhaust gasses . It wasnt compounding as no additional power source was used, just some lateral thinking, I guess it could be applied to any helicopter if necessary, I am sure there must have been some downsides as well...

DM

[Ian Corrigible]

Rb98,

In an earlier post, heli1 quotes "Putting the Record Straight: World Helicopter Speed Record" by David Gibbings as giving the figure as 600 lb. Nick also mentioned previously that "the exhaust was tuned to be sure there was just enough thrust to do this without making the aircraft a compound helicopter."

I/C

[dangermouse]

to quote Mandy Rice Davis

'well he would have said that wouldn't he?'

Surely getting rid of exhaust from the normal driving engines cannot be construed as compounding.

DM

[Hilife]

Unless of course in one’s attempt to set a world speed record, the exhaust is tweaked to provide a not insignificant level of extra thrust to that provided by the main rotor.

[dangermouse]

clever use of gas...

agreed

compounding involves use of another powerplant to provide additional propulsion, using existing powerplants and no new moving parts isn't.


DM

[Ian Corrigible]

DM,

The more common description of a compound is the use of an auxiliary propulsion system, not necessarily an additional powerplant - the X2, X-49A and X3 all use the same powerplants to drive both the main rotor(s) and the aux propulsor(s).

I/C

[heli1]

Doesn't propulsion include propellors then ?

[dangermouse]

Fair point

but to my eyes a necessary exhaust pipe isn't a seperate propulsion system (if it had afterburning etc it would be classed as a new propulsar though)

and the FAI agreed

DM

[Dave_Jackson]

Exhaust Thrust

[Graviman]

Interesting that nobody so far has commented about the benefit of not having a tail rotor on X2.

[heli1]

The benefit....let's see.Would that be not getting your hands cut off when you walk into the tail rotor as opposed to being shredded by the airscrew?

[Ian Corrigible]

That rear mounted prop didn't work out too well for the big German guy in Raiders.

'Course, in the alternate ending it didn't work out too well for Indy, either...





I/C

[Dave_Jackson]

Optimally, the propeller should not be turning when the craft is on the ground or hovering.

The propeller's speed should be inversely linked to the speed of the rotors. and these speeds will be related to the forward velocity of the craft. Variable Speed Rotors and Prop


This was one of the technical subjects that used to be discussed on PPRuNe. Subsequent to this discussion, Sikorsky, in Nick's name, applied for a patent. On October 14, 2008 Sikorsky received US Patent 7,434,764 ~ Variable speed gearbox with an independently variable speed tail rotor system for a rotary wing aircraft.


Dave

[Ian Corrigible]

Dave,

The S-97's prop will indeed be declutchable.

I/C

[Dave_Jackson]

Thanks I/C

The clutch and the variable pitch propeller are steps toward the optimum.

Dave