Respectfully, these are all pretty good answers.

However, doubling back the receiver antenna is not as bad as indicated as long as it doesnt cross back and forth over itself. I know because I (we) do it all the time.

On our foamies, we make a flat spool and carefully roll the antenna up around the spool so that the wire never overlaps itself but continually wraps from the front of the spool to the back. Then we leave a tail off the end of the spool that is just enough antenna to extend to the back of the airplane. It works perfectly over and over again. And I can range check and fly a foamy almost out of sight this way, just as far as with a fully extended antenna. This is not opinion,,, its fact. My little spool is a flat piece of depron about 2" long. Again, this is a very careful and definite wrap. You do not overlap the wire, you just wrap it around the spool carefully without an overlap in the wire. If you overlap the wire you are headed for a crashWe also double the antenna back on a heli. There is usually a plastic tube that is about 12" long that mounts through a couple of premade holes in the landing gear on 1 side of the heli. You simply run the antenna through the tube from back to front and then run it back along the outside of the tube from front to back and then secure it with a piece of shrink wrap tubing or a little o ring. Again, this is a tried and proven technique. Given the choice I would always run my antenna full length, but Im stating experience based fact when I tell you that the antenna can be not only doubled back, it can be wrapped around and around.