Wouldn't have thought so. Paint or seals arn't affected on your car. And you can try it on any old perspex before using it in anger.
If you are going down that route why don't you buy a B&Q garden pump sprayer. Then get a bottle of windscreen wash and mix it with warm/hot water then spray it using the pump sprayer.
And if that works out expensive a bottle of meths would do the trick as well. Woudn't use a salt solution though due to corrosion.
Just watch out you don't de-grease important bits.
It would be alot better than fannying around with a spay can.
As for flying schools, its a legal thing because we are on Public C of A and have paying punters on board. Although I am sure some out of the way schools will do it.
MJ