One thing I've found that seems to work with them--if you get them early on in their training--is to have them guess the HP of the engine. They'll usually guess somewhere is the 300-600 horsepower range and, when I tell them it's a mere 180 (or less, depending on the plane), it gets them to rethink their assumptions. When I'm lucky, they'll then become interested in how a plane works instead of imagining it as some sort of souped-up car... Then I pawn them off on the poor maintenance guys for a few hours