It's that whole difference between perpetuating a glide in a super slick plane and trying to take off short field. Unlike cars or bikes, the engine's power gives you your climb ratio - and it's just drag reduction to make you faster.
So while you can "fly" a glider, maybe even take off with a lil tiny motor like these - you'd need three football fields or so to do it - and it better be a cold, calm day lol
Not being able to climb is the most dangerous aspect of a plane's characteristics, as the planet is really the only thing that can hurt you - you do need to avoid it as much as possible
You could always get a hang glider, strap one of these lil puppies as a pusher motor (shaft is pointed wrong but w/e) and jump off a cliff... It would
help your distance... maybe... I dunno though, what with the added weight of motor, fuel, prop, etc.
You'd prolly end up with the same performance as you had w/o the engine, cept now its noisy heh