I instructed for three years, including formation and aerobatics and
never had a student sick in the aircraft!
(I did have one or two vomit
after getting off.
)
I used to get a bit ill when I began learning, and so was always sympathetic, and aware of the problem. Every time I took up someone new I gave them a short speech, along the lines of:
"Feeling sick is normal, some do, some don't - it has nothing to do with your ability. I used to feel sick, and the tendency goes away as soon as your body gets used to the new environment. the important thing is that you stop learning as soon as you start to feel ill - the "It's not so much fun anymore" syndrome, and after that we are just wasting your money. Please
tell me as soon as you get that feeling, and we will level the wings and return to base, and stop wasting your cash."
That speech, so they didn't feel embarrassed and "hold on" until it was too late, coupled with a cheery "How do you feel?" after every series of manoeuvres, kept me vomit free for three years.