The Radio Control Airplanes project provides an opportunity for the students to fly some simple low cost radio control airplanes with supervision.   To do this I use the Air Hogs airplanes.   Air Hogs has a biplane, “jet” and helicopter.   These are low cost ($25 - $30 / each), are fairly durable and have two axis control. My preference is to fly them inside a gymnasium but they can also be flown outside if the wind is calm (i.e. more likely to occur at the beginning or end of the day).
To demonstrate more complex remote control airplanes, I have one of the members of the local Radio Control Model Aircraft Club fly their aircraft to demonstrate the capabilities of more advanced/expensive models.
As part of this, I have purchased a ParkZone Vapor.   The Vapor is a very light weight three channel airplane that, for practical purposes, should be flown indoors.   This airplane does offer an advantage.   It can be flown in areas as small as a classroom and thus opens up many alternatives as to where it can be flown.