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Sikorsky X2 coaxial heli developments.

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Sikorsky X2 coaxial heli developments.

Old 19th Dec 2009, 04:25
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X2 vs BA609...

While the BA609 might have some autorotation capability under certain AEI conditions, I don't believe it has enough power from one of its PT6's in an OEI condition to maintain a hover. Does anyone know different?

Also, you should take into consideration the fact that most tilt rotor aircraft are capable of increased GTOW's using a STOL technique on a conventional runway.

And finally, I still would be concerned about how well the X2's rigid(?) rotor system will scale up. I don't honestly believe they will ever get a satisfactory solution for an X2 rotor configuration with a 30 or 40 ton payload aircraft like they proposed for JHL. A rigid rotor system at that scale would have horrifying forces and moments to deal with.

Regardless, I think the X2 has a bright future for smaller VTOL applications in the near term. Mostly because it is already flying......

riff raff
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Old 19th Dec 2009, 07:17
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Well, if they can find a way to keep vibration down, then it's all good.

Servo flaps, anyone?
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Old 24th Dec 2009, 14:47
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Helicopter with leading edge servo flaps (Kaman)

Dave,

Check out US 5,409,183; seems to have cover a bit of what you're looking for in connection with Kaman's work in this technology.

This particular patent, issued in 1995, has lapsed for non-payment of maintenance fees. Perhaps they were too far ahead of the art with this particular innovation.

Kaman's patent and patent publications are fairly easy to locate by searching the USPTO's assignment database. Just go to USPTO Assignments on the Web and pop in 'Kaman Aerospace' as the 'assignee;' this will show you what is assigned to Kaman Aerospace - currently some 64 patents and patent application publications.

- Cheers
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Old 24th Dec 2009, 19:49
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Merry Christmas all.

Question: Did the X-2 reach 250 knots yet? I noticed the A400 cleared its envelope in two flight in less than two weeks.

The Sultan
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Old 25th Dec 2009, 00:24
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NonSAC, Thanks.

I'm told that when Kaman did a higher-harmonic control system design that went into the wind tunnel, it had a pushrod as well as a servo flap, but that might have been for other reasons.

John
It looks like NonSAC may have found what you are referring to. The mentioned patent, US 5,409,183, has leading and trailing flaps, non-swashplate hydraulic pushrod control and a higher harmonic control of the leading edge flap.

The patent even mentions electrically energized flap actuators, which are now starting to look promising. A couple of types are piezoelectric actuators and linear electric motors.

Dave
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Old 29th Dec 2009, 07:57
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CEFO

Gee those simple fixed wings do not have any problems which require anything such as wing and tail flutter testing, testing of the radical prop configuration for coupled whirl modes etc...(ever heard of the Electra?)

Is the X-2 delay hardware or software related?

The Sultan
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Old 29th Dec 2009, 19:11
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I have it on good authority, that re-booting of the velocity nowhere curve using the Buckminster fullerene method should enable expansion of the linear trajectory in the New Year.
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Old 2nd Jan 2010, 19:33
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CEFOSKEY

While I certainly know the answer and details to this question, I'm curious as to what you've heard.
We're curious as to what you've heard.



Dave
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Old 7th Jan 2010, 18:27
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Aw, come on guys!

Helicopters are four times more expensive to develope than fixed wings. So this means that either 4 times the number of engineers are involved or it just takes four times as long. Lots of moving parts...

The fact that the unrealised potential of XH-59 has raised its head in this discussion tells me that X2 is now of its time. So what if the machine takes a while longer to do its thing? I can wait.

Nobody ever said that redefining the potential of the helicopter was going to be a walkover. In fact it's a very difficult project, which is why it didn't go forwards in the 70s. The design, development, and flight test teams should be commended for having the gumption to take it on.
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Old 30th Jan 2010, 01:58
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Originally Posted by The Sultan
Is the X-2 delay hardware or software related?
According to this week's Av Week, the X2 TD experienced a transmission failure during a ground test. The aircraft will shortly enter rebuild, with ground testing tentatively resuming in March.

I/C
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Old 1st Feb 2010, 03:40
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Hopefully they keep pushing at it, and sometime within this year they finally hit the 250 knot barrier...
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Old 1st Feb 2010, 18:48
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Originally Posted by Ian Corrigible
According to this week's Av Week, the X2 TD experienced a transmission failure during a ground test. The aircraft will shortly enter rebuild, with ground testing tentatively resuming in March.
Not read the Av Week article, but that's just any new product development i'm afraid...

If the story is true then don't forget this is the first time this gearbox has ever seen this helicopter!


In general, fatigue is a very complex subject indeed! Predicting component failure rates is right at the edge of feasible (eg Brown-Miller). If you are lucky and have data for many many test samples then you can put reasonable statistics into the fatigue code. Even if you have this, it is unlikely to have been tested beyond 10'000'000 cycles. A helicopter will gobble up this number of cycles in less than 700 hours. As a compromise process, the stress engineers will do their utmost by comparing the mean and alternating stress to the material UTS and endurance stress (eg FRF of a Goodman line on a Haigh diagram). But this will only get you so far because many assumptions have to be made about material degradation with time and service. This is even more difficult if the stress cycle is not exactly as the simulations predicted, which is seldom the case.

Basically, it is difficult enough to get it right for the car you drive. In a helicopter this is even more difficult because you are constantly chasing every last kg of mass to shave off. This is why Nick Lappos often explained about loading components as like taking beans from a jar. The engineers do their absolute level best to work out how many beans were there to start with, so you can nibble away at a steady rate. But when the beans run out the jar breaks....


Frankly, if the story is true, then the fact that it was identified and dealt with in a safe manner is testament to the Schweizer/Sikorsky test program put together for X2.

All in all: no big deal. I look forward to March, or later if required.

Last edited by Graviman; 2nd Feb 2010 at 17:32. Reason: This is just background info in case the Av Week article is true.
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Old 20th Feb 2010, 23:38
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Good to see Alastair Campbell has found a new job. The X2TD's problem has gone from being a "transmission failure" to the "detection of a gearbox manufacturing problem" to being "currently out of service for transmission upgrades."

I/C
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Old 21st Feb 2010, 00:58
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Angel

Should have built the ABC in an Intermeshing configuration.
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Here is the transmission proposed by Flettner for his Fl 339; 70 years ago.
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Old 22nd Feb 2010, 17:17
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Dave, no wonder they didn't do it.. I see worm drive in there

Good in differentials, not good for efficiency, and in this case - flight safety. Without torque from the engine, it's a brake.
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Old 22nd Feb 2010, 20:20
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Dave, no wonder they didn't do it.. I see worm drive in there

Good in differentials, not good for efficiency, and in this case - flight safety. Without torque from the engine, it's a brake.
Basically you are correct.

However;
  1. Low-ratio worm drives have a much lower friction than the normally used high-ratio worm drives.
  2. On ratios of 10:1 and below the wheel cannot brake the worm.
  3. The newer 'Double Enveloping Worm Gearing' offers additional advantages.
  4. Ball Worm drives are under development and limited use.

In fact, Sikorsky's earlier S-69 ABC didn't even need a gearbox for the rotors during cruise. Unintentionally, the rotors were driven aerodynamically like a gyrocopter.

I suspect that the X2, even with its modified blade, will experience similar problems.
IMHO, specific improvements such as; reverse velocity utilization, active blade twist, and variable speed rotors and prop need to be done by an Engineering department before the Hyperbole department is unleashed.

_______________

If thread becomes quiet this year, to stop it from being closed perhaps a posting should eventually be placed.

Perhaps the preliminary submission and subsequent rejection of my offer to deliver a paper on 'An Intermeshing ABC Helicopter' to the American Helicopter Society, three years before Sikorsky reopened the ABC with their X2 might be of interest.
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Old 23rd Feb 2010, 01:27
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Building a flying machine, getting to 106 kts, projecting expected performance = Hyperbole.

Building a website, slagging the big helicopter company that is actually trying to do something, and promoting some creative old German designs = ?

I am a simple person. None of this adds up for me.

-- IFMU
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Old 23rd Feb 2010, 13:00
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ABC, X2 Cruise

In fact, Sikorsky's earlier S-69 ABC didn't even need a gearbox for the rotors during cruise. Unintentionally, the rotors were driven aerodynamically like a gyrocopter.

Dave, perhaps I misunderstood, but if the "unintentionally" wasn't there, we could have agreed. The S-61F work led the way on that particular rotor behavior question, along with one or two others, the most attention getting being the tip mach related rotor stability issue.

Thanks,
John Dixson
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Old 23rd Feb 2010, 14:52
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Originally Posted by CEFOSKEY
It would be a shaft brake, but not necessarily a rotor brake, as I am sure there is a sprag-clutch-type device buried somewhere in there.
There could be one, but the worm gear is also what coordinates both rotors there. If at some point they would rotate freely from the worm gear - the helicopter would beat itself to death with it's own rotor blades... the ground tests would be fun to watch

Dave, it's been a while since I was into worm gears, but one allowing the worm gear to be driven by the wheel gear, with the same efficiency as the other way around would be, well... revolutionary. Worm gears are great when the power have to be transfered in one direction, they allow very high ratios with compact and cheap design, but it all comes at a price.

The transmission design like on the Flettner drawing, look unsafe, and probably less efficient than a hydraulic drive would be, and you can do a lot with those... although with the price of efficiency too. I wouldn't be too attached to the design details from the pioneers times... after all , we all know how this one ended:





Ok, back to X2.
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Old 23rd Feb 2010, 20:55
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John;

My web server is currently down. Therefore any linking to it will not bring up the supporting data.

I think that the intended speed for the S-69 ABC was 250 knots. The craft had plenty of power, however the unexpected high profile and negatively-induced drag at the root end of the retreating blades was aerodynamically driving the advancing tips to a speed of nearly Mach 1. To achieve the 250 knots the blades would have entered and exit supersonic flight at a rate equal to the rpm of the rotors.

I believe that gyrocopters operate at a tip speed ratio of around 0.35. It has been said that applying 10 - 15% of the engines power directly (mechanically) to the rotor will increase the forward speed and the efficiency of the gyrocopter.

It can be assumed that X2 airfoil is intended to reduce the high profile and negatively-induced drag at the root end of the retreating blades.


Lt.Fubar;

allowing the worm gear to be driven by the wheel gear, with the same efficiency as the other way around would be, well... revolutionary.
No disagreement. However their is no need to drive from wheel to worm.

An advantage of the worm and wheel is the simplicity of fewer gears and lower weight. A reciprocating engine would direct drive the propeller, and require only 1 worm and 2 wheels to drive the rotors plus assure synchronization.

Probably the most important consideration must be the time that the craft is intended to spend in hover v.s. in cruise. During cruise only a small amount of power need be mechanically directed to the rotors, since the rotors will then be acting like wings.


Dave
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