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-   -   Sikorsky SB-1 flies for first time (https://www.pprune.org/rotorheads/619699-sikorsky-sb-1-flies-first-time.html)

noneofyourbusiness 22nd Jul 2021 23:41


Originally Posted by IFMU (Post 11083396)
Totally wrong. The coax limitation for yaw is in autorotation. They leave room for differential collective on top of collective.

"Leaving room" doesn't leave much margin when operating in the mountains of Afghanistan. The question isn't can it yaw at all, but how fast can the helicopter yaw at its limits? Fast yaw has not been demonstrated to date.

IFMU 23rd Jul 2021 09:25


Originally Posted by noneofyourbusiness (Post 11083423)
There is a major difference between a prop and a tail rotor. Answer how the side force is counter-acted when both rotors are tilted in the same direction. Don't just give an arm wave. The reaction torque from a pusher prop is a pure torque. The torque from a tail rotor provides side thrust and moments (above the cg). Conventional helicopters have a much smaller roll torque from the engines. Did you ever take a physics class?

When you get an answer from your bosses at Sikorsky, I am willing to learn and be educated.

I've got no Sikorsky bosses anymore. I moved to another UTC division when they closed Schweizer. I was the responsible engineer for the X2 flight controls though. And yes I've studied physics. Still use it at my space job. You?

You had mentioned the UH60 high tail rotor before. The torque would be the thrust from the tail rotor times the lever arm. Really no torque from the engines as you say. The torque from the X2 propeller would be the power it absorbs times 5252 divided by RPM. I'll leave it to the student to do the math.

noneofyourbusiness 23rd Jul 2021 17:29

The S300 - now spun off as a separate business?. I am retired from my day job, mechanical engineer, same industry as you, passing my time working on an invention.

Clearly the Raider rolled side to side pretty quickly when it crashed, with the rotors not parallel. You say the design is intended to keep the rotors parallel, I believe you.

I wasn't comparing a tail rotor torque to the pusher prop torque. Clearly most engine power goes through the prop at high speeds, unlike the tail rotor. I was just trying to point out, the tail rotor is a flight control device, but the pusher prop isn't. There is high speed flight, and there is low speed flight with the pusher disengaged. For high speed flight, what keeps the x2 type design going straight forward, if the main rotors are canted to offset prop reaction torque? Are the vertical stabilizers enough? Secondly at hover, is the only difference between a sideways movement and a roll, the degree of tilt of the rotors?

I never worked flight controls, so I may miss the obvious. I appreciate your input.

IFMU 24th Jul 2021 02:42


For high speed flight, what keeps the x2 type design going straight forward, if the main rotors are canted to offset prop reaction torque?
Think in terms of a fixed wing Cessna with two wing fuel tanks. One full, and one empty. You have to put in enough aileron to react the unbalanced fuel load, but the airplane still goes straight. Same as a helicopter using cyclic to balance other forces and moments. They can be prop torque, tail rotor twisting moment, unbalanced fuel/crew loading, or whatever.

Sikorsky pretty much destroyed Schweizer. Somebody bought the 269/300 type certificate and I think they are building them again. Probably with chinese parts but I don't know.

henra 29th Jul 2021 14:41


Originally Posted by noneofyourbusiness (Post 11083878)
For high speed flight, what keeps the x2 type design going straight forward, if the main rotors are canted to offset prop reaction torque?

The cant itself will be largely irrelevant for straight flight because it is only relative to the fuselage. The only small effect would probably result from slightly increased drag of the rotors on the side where the rotors need to produce a bit more lift to counter the torque. On the other hand you will have a drag force on the opposite side resulting from the fuselage being displaced to the opposite side by the torque and the resulting cant.
But realistically this will be negligeable and be easily countered with a tiny bit of crab.

The Sultan 11th Sep 2021 15:42

SB-1 FLRAA Proposal Submitted
 
It has been rather boring in the waning days of summer (coming not too soon) until this gem dropped on Verticalmag:

https://verticalmag.com/news/sikorsk...x-to-u-s-army/

This has a number of things to comment on:


“Today, Team DEFIANT completed and submitted the proposal for the U.S. Army’s FLRAA competition
Amazing that for the first time in the FLRAA program Sikorsky-Boeing actually met a schedule. Proves they are better at writing fiction than they are at program management and cutting metal (actually molding composites).


“We’re very excited to be at this point. It’s been a long journey in a very short period of time.”
It has been EIGHT years since the FLRAA concept demonstrators were selected. Five years is a normal development cycle so where did the "very short time" come from?


Army’s need for an advanced rotorcraft capable of at least 230 knots and preferably capable of cruising 280 knots, much faster than traditional rotorcraft.

Data gathered in the ensuing flight test campaign, including level flight at 230 knots, was incorporated into the team’s FLRAA proposal.

Defiant X delivers speed where it matters
This ignores the original goal of the FLRAA requirements to have a 250 kt minimum cruise speed. The final requirements were changed once the shortfalls of the SB concept were known. What does "speed where it matters" even mean? For a long range assault aircraft (the LRAA in FLRAA) where high speed matters is in the cruise segment of a mission getting to the objective. This shaves hours off a mission. Where does SB think speed matters more?


while operating in the same footprint as the BLACK HAWK,
Was that a requirement in the final RFP? If it was? Why? Who cares?


Defiant X also has a tricycle-style landing gear with one wheel under the cockpit and two wheels aft whereas the operational prototype Defiant sported two front wheels and a tail wheel that protruded down from its tail boom.
What!!! The original concept made sense as it at least tried to keep the pusher prop out of the dirt. Going to a nose gear can only be a last resort to move the cg forward to reduce rotor loads at the sacrifice of operability. You strike the pusher on the ground flaring into a hot LZ, you are there for the duration.

Relative to the images released is it just me or does the gap between the rotors been significantly increase?





CTR 11th Sep 2021 16:51

Amazing
 
“Amazing that for the first time in the FLRAA program Sikorsky-Boeing actually met a schedule.”

Sikorsky and Boeing saved a lot of RFP response time by not having to compile and analyze hundreds of hours of flight testing like Bell had to. Smart move by the Defiant program not to waste time and money in unnecessary flight testing to prove concept viability.

SplineDrive 11th Sep 2021 20:49


Originally Posted by CTR (Post 11109743)
“Amazing that for the first time in the FLRAA program Sikorsky-Boeing actually met a schedule.”

Sikorsky and Boeing saved a lot of RFP response time by not having to compile and analyze hundreds of hours of flight testing like Bell had to. Smart move by the Defiant program not to waste time and money in unnecessary flight testing to prove concept viability.

If there is any sanity in this world, this RFP submission is the beginning of the end of the ABC concept.

The Sultan 15th Sep 2021 03:25


Sikorsky and Boeing saved a lot of RFP response time by not having to compile and analyze hundreds of hours of flight testing
Didn't SB get millions $ more than Bell to fund this phase? Don't they have to account for this money? Time to check SB leaders 1offshore accounts.


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