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G2 down in Switzerland - 15 June 2022

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G2 down in Switzerland - 15 June 2022

Old 29th Jun 2022, 12:39
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AMDEC - I agree with what you say, the ability to cope with at least 17 kts at various test points must be demonstrated.

But what happens in dynamic manoeuvres or when the wind is gusting in excess of 17 kts? That is where a poorly designed TR causes problems..

You said yourself you have little pedal margin when it comes to critical azimuth. Which operator is going to limit themselves to 17 Kts cross or downwind?
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Old 29th Jun 2022, 14:35
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Just out of curiosity, since you guys don't agree that in certain wind angles the tail rotor becomes "less effective" thus requiring more left pedal, do you also disagree when we (FAA land) say that when the tail rotor passes through ETL on takeoff it becomes "more efficient" thus requiring less left pedal?
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Old 29th Jun 2022, 15:06
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As much as I like to discuss this (again), I'd rather like to know, why you can not stop the spinning of a Cabri, if that wasn't a mechanical failure. I don't know, but that looks to me like a design flaw and should not pass a certification.
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Old 29th Jun 2022, 15:14
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Originally Posted by Rotorbee View Post
As much as I like to discuss this (again), I'd rather like to know, why you can not stop the spinning of a Cabri, if that wasn't a mechanical failure. I don't know, but that looks to me like a design flaw and should not pass a certification.
Well, like the "design flaw" of the R22, just slap an SFAR onto it, and go about your day.
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Old 29th Jun 2022, 16:27
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Originally Posted by Rotorbee View Post
As much as I like to discuss this (again), I'd rather like to know, why you can not stop the spinning of a Cabri, if that wasn't a mechanical failure. I don't know, but that looks to me like a design flaw and should not pass a certification.
I fully agree Rotorbee and a tail rotor that would lose effectiveness at any time should neither pass.
The spinning of the Cabri is not stopped either because there is a failure or because the pilot has a much too centered pedal position. Full right pedal makes the quickest stop but is not mandatory. The Gazelle tests have shown that the headwind hover pedal position was sufficient to stop the turn in less than 360°.
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Old 29th Jun 2022, 17:51
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The thing that puzzles me in these videos is the rate of spin. If you have that kind of a problem in a R22 or even a 206, the whole thing is relatively gentle. You have no problem to shove the cyclic forward and point the nose in a direction and fly out of it, even with an general direction of your choice. But in these videos the Cabri just looked out of control. In the one from Switzerland, he even got the spinning stopped and then it started again. That is really odd.
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Old 29th Jun 2022, 18:21
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We don't actually know what the problem in the Swiss one was, might have been stuck pedals or something jamming them.

We also don't know what he did with the throttle or collective that might have affected the rate of spin.
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Old 29th Jun 2022, 18:22
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Originally Posted by Rotorbee View Post
The thing that puzzles me in these videos is the rate of spin. If you have that kind of a problem in a R22 or even a 206, the whole thing is relatively gentle. You have no problem to shove the cyclic forward and point the nose in a direction and fly out of it, even with an general direction of your choice. But in these videos the Cabri just looked out of control. In the one from Switzerland, he even got the spinning stopped and then it started again. That is really odd.
Its also odd that after he's on the ground, he picks it up again for one more spin? Would you do that if it were a mechanical failure?
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Old 29th Jun 2022, 18:26
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Just out of curiosity, since you guys don't agree that in certain wind angles the tail rotor becomes "less effective" thus requiring more left pedal, do you also disagree when we (FAA land) say that when the tail rotor passes through ETL on takeoff it becomes "more efficient" thus requiring less left pedal?
Those certain wind angles don't make the TR less effective but demand more pedal to counter the effects of the wind on the fuselage - ie weathercocking tendency.

Yes the TR gains from ETL just like the MR does.
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Old 29th Jun 2022, 18:46
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Its also odd that after he's on the ground, he picks it up again for one more spin? Would you do that if it were a mechanical failure?
You know, that pilot was purely running on instinct. I don't think there was a lot of thinking going on in these moments of helicopter hell. If he picked it up again, that might have been just a reflex, being so low. I wonder if he remembers everything that happened.
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Old 30th Jun 2022, 01:16
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Originally Posted by Rotorbee View Post
You have no problem to shove the cyclic forward and point the nose in a direction and fly out of it, even with an general direction of your choice.
I would like to see that - personally I think you may be deluded slightly.
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Old 30th Jun 2022, 05:31
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I would like to see that - personally I think you may be deluded slightly.
I bet you would. As I explained way up there, I was in that situation. In my case it was main rotor down wash interaction, I suppose and the tail rotor trust was just diminished, not completely lost. Can't prove it, but it was the logical conclusion at that time. Friend of mine had the same problem under the same circumstances. We both had no pedal travel left to push, but it was slow and by far not as violent than what the Cabri had. After less than 180 degrees of "unintentional yaw" I was out of it. I But since we found out how to prevent it, that will not happen again. You are out of luck. As for the delusional part, when you experience something once, one's brain tend to overload with input and things might get a bit fuzzy in your memory, but if you do things several times and you start to recognise the early signs, the old brain is much better in remembering how an event happens. Still, I can't prove that I don't live in the matrix and all this is just a very strange dream.
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Old 30th Jun 2022, 06:47
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Rotorbee - perhaps things are getting confused here - I think your reference to just push the cyclic forward is about a situation in a hover taxi with some MR/TR vortex interaction giving some undemanded yaw and NOT as a cure to the wildly spinning Cabri - am I right?

We used to demonstrate MR vortex entering the TR on the Wessex, usually at high AUM in a hover taxi with the wind from the 10' o'clock position (anti-clockwise rotor) - it caused vibration and some minor heading variations but nothing more. Changing the speed or the wind angle removed it entirely.
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Old 30th Jun 2022, 07:32
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Crab, you are right. I do not suggest in any way, how to stop the spinning in a Cabri. What I wonder is, why the Cabri starts spinning like crazy that fast and can not get stopped by pedal input or naturally by pointing the nose into the wind. My experience was just to explain, that in other helicopters, it does not happen that fast, if the tailwind and the resulting interaction with the down wash was the cause of the problem. If you are in that situation in a Cabri, I very much doubt that you are even able to react properly, unless you expect it to happen. In the Swiss video the pilot literally dove down and the spinning stopped and started again when he levelled out. That is why I do not exclude a mechanical problem. The whole thing is a complete mystery to me, including how to get out of it.
When I had my little incidents, I did not stay there just to find out, if I could go all the way round. Therefore I can not say, if it would have stopped by itself, once the nose got into the wind. Probably would have. A friend of mine flying a 206 at high altitude, between 10'000 and 12'000 and low airspeed (looking at the Eiger north face) did go around a couple of times and entered autorotation. No biggie since he had a lot of free air below. For that Cabri thing, I don't know how the get out of it and why it is so fast and violent. I would have thought that the tail fin would put up quite a resistance. For me, in my little brain - and I do not suggest that this actually happened - it looked like something reversed the pedals by magic and the fenestron pushed the Cabri around. That is only my imagination because I find the rate of spinning is beyond what physics should allow (just my thought on it, not what I think what could be the cause, because I do not have an idea, so don't fixate on it).
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Old 1st Jul 2022, 10:32
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Originally Posted by Rotorbee View Post
That is only my imagination because I find the rate of spinning is beyond what physics should allow (just my thought on it, not what I think what could be the cause, because I do not have an idea, so don't fixate on it).
The yaw rate in that video is about 160 degrees per second.
Completely feasible in a left stuck pedal, or operator error.
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Old 1st Jul 2022, 12:48
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That is a strong cell around the drivers.

Originally Posted by Rotorbee View Post
But I learned two methods to stop the spinning when I felt it coming. Just wiggle the cyclic for a second and it disappears. The second is a quick down and up movement of the collective. Don't like that one, but it works, too.
Interesting observation on the cyclic wiggle...It is conceivable that the cyclic motion is affecting the local flow in the downwash that affects the tail rotor, as otherwise, the torque demand would rise for steady rotor height. Am curious if there is a known reason why cyclic motion would improve TR effectiveness. It may be that the cyclic gives also a slight overspeed condition through the hysteresis of the governor, which would give increased TR authority.







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Old 2nd Jul 2022, 07:22
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Interesting observation on the cyclic wiggle...It is conceivable that the cyclic motion is affecting the local flow in the downwash that affects the tail rotor, as otherwise, the torque demand would rise for steady rotor height. Am curious if there is a known reason why cyclic motion would improve TR effectiveness. It may be that the cyclic gives also a slight overspeed condition through the hysteresis of the governor, which would give increased TR authority.
I think it was just the change in downwash. With that little wiggle and it disturbs whatever is building up around the tail rotor.
For the overspeed condition, I don't think so. The governor of the R22 wasn't very fast. When you are flying with a steady power setting like in that slow flight, I never felt a lot of movement in the twist grip.
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