Hope you folks don't mind a non-FI sticking his oar in, but an instructor friend suggested I might have something to add.
When not doing things with aeroplanes (an odd concept to most people who know me I'll admit), I practice a fairly obscure martial art called "Ryukyu Kempo". The basis of this is a reasonably deep knowledge of the human body and how to use it to make (somebody else's!) body behave in a desired manner.
I can think of a couple of techniques which will do no permanent harm to your student, but should have a rapid effect of making them let go of the controls.
First point is voice projection - shouting or screaming an instruction at somebody can work, but on it's own often won't, what it will do is emphasise a course of action that you are encouraging by a more physical means.
For general release, there are two obvious points on the face. The first is just between the upper lip and bottom of the nose. If you were to reach over and stick the edge of your hand there, wriggle it back and forth a bit (fairly forcefully) whilst shouting "let go", I'd put good money on their complying. A second which requires a little more finesse is to stick a knuckle just under the cheekbone and upwards and wiggle it a bit, whilst doing the same. These are deeply uncomfortable, but won't injure anybody.
If you need to release a specific limb, there are two easy ways to release a hand that is firmly gripping something. The first (which requires a little physical strength on your part) is to grab the back of the student's hand, squeezing across the back of the palm between just behind the little finger and the inside of the thumb - try this on yourself and you'll see why it then becomes easy to pull the hand away.
If you don't have all that much strength, using two of your fingers (or more likely a finger and thumb) create a fulcrum over the back of one of your student's base-finger knuckles, and lever the finger tip up with the other. Bend the finger back forcefully and guide it away from the control. This is known in the trade as a "finger lock", it's very painful but very effective and again does no permanent damage (unless you are really brutal, which is probably impossible in a cockpit anyhow). An important point here, the technique relies upon two points of contact - fulcrum and lever - if you try and grip the finger firmly, it won't work.
Feet are harder, but the best best would be to use your thumb and forefinger to squeeze hard across the top of the leg just above the knee - then move your thumb/fingertips around a bit to vary the pressure - do this quite quickly. That should both get their attention and release the feet.
If all this doesn't work, and your life is in danger, I'd advocate knocking them out; this does not need to be as brutal as it sounds. Feel the front of your throat then keep prodding round to the side, as you do it becomes soft, then hard again at roughly the 11 or 1 O'clock position - this shouldn't be covered by a headset. In chinese medicine this point is called "Stomach 9" and is the confluence of half a dozen assorted arteries and nerve junctions. If you jab your fingers hard and fast into there it will knock somebody out (what actually happens is that it sends a pulse of high blood pressure into the brain, which overreacts, radically drops the bloody pressure in the brain, and causes them effectively to faint). A few points on this:-
- Whilst it's not permanently damaging, unless there's a good reason DON'T, repeated use can be damaging since it can start to slowly damage artery walls.
- They'll come round in a few minutes, but their co-ordination and judgment will be dodgy for a couple of hours (and they may feel like an awful hangover in the morning). Treat accordingly!
- It is possible to bring somebody back to full awareness very quickly from this, but I'd not recommend trying in a cockpit (it requires access to pressure points on their back for a start), also the recovery takes a fair bit of training and defies simple description.
I don't know if that was any help, but for what it's worth I agree totally with homeguard. In self defence / martial arts we teach that avoidance is everything and physical techniques are there as an absolute last resort, and I think that equally true in your profession.
G
N.B. Another point where flying and Martial Arts have something in common is that you never get a technique right first time and skills degrade without practice. If you are, say a small lady instructor worried about being killed by a large dumb male student, I'd strongly recommend sitting in a stationary, non-running, aircraft and practicing these techniques with a friend until they become instinctive. As I said before, apart from the jab to ST9, they'll all hurt but do no damage.
N.B.B. Thinking about Whirly's collective problem, if you have something hard to hand - say a nightflying torch, roll it hard over the back of their knuckles - they'll let go!