The wheels have grooves to take the tyres. You either need to remove the tyres, clean the tyres and wheels then replace them OR, remove the tyres and replace with new tyres OR, replace the wheels with wheels without tyres.
That's right Eric. The things they tried are amazing. Guess it kept them busy. I met somebody who escaped from Colditz. He escaped inside a matress and then planned to run to Switzerland dressed as a member of the Hitler Youth. I was in his house and he had a picture of the castle. I said that looks familiar where is it and he then told me his tale.
Caiptean there are quite a few full sized powered gliders about. Gliders have to get airborne one way or the other. Some are towed by another acft, some are launched using a giant bungee and others with a winch. The engine is another option.