Ioan
The pros here will be able to explain this much better than me but, as I understand it .....
'Jack stall' occurs when the blades overpower the hydraulic servos - the jacks stall - and the controls lock solid.
If you're training in a Robinson that may not mean much because it doesn't have hydraulic controls.
It's most likely to be caused by extreme manoeuvring.
eg In the Gazelle, if you're in a descending right turn and pull really hard, you might experience jackstall.
It's very unlikely to happen in 'normal' flying.
However, if you were flying straight and level at high speed, and suddenly pulled up and to the right (
eg to avoid a bird), it could happen.
Recovery from jackstall:
Release the pressure and the controls will unlock.
If it happened near the ground you'd have a problem because you wouldn't have much time/space to correct it - and possibly exacerbate the problem by instinctively trying to pull away from the ground, instead of releasing the pressure. However, as a PPL, you're unlikely to be doing extreme manoeuvres near the ground.
Is it something that occurs just on the Gazelle?
No.
It can happen in the Squirrel - certainly in the older models. I don't know if the newer models have more powerful servos.
And possibly in some other types.
I associate it with French design helicopters, but that may be wrong.
Military term?
I don't think it is, but the FI who did my Gazelle conversion was a Mil pilot so possibly.
Or something else?
It's called
'servo stall' and
'servo transparency' in America.
I don't know what it's called in France - it’s like those French have a different word for everything.
(
Credit: Steve Martin)
FL