G2 down in Switzerland - 15 June 2022
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.
Join Date: Jan 2010
Location: South of France
Age: 67
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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°.
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.
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.
We also don't know what he did with the throttle or collective that might have affected the rate of spin.
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.
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?
Yes the TR gains from ETL just like the MR does.
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?
I would like to see that - personally I think you may be deluded slightly.
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.
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.
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).
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).
Completely feasible in a left stuck pedal, or operator error.
That is a strong cell around the drivers.
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.
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.
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.
