Most low cost radio control toys are 27Mhz or 40Mhz. I tested one that is 27Mhz using Tx antenna length of just 4inches and receiver antenna length of 8inches; the toy car worked for over 40feet.
And they have a loading coil before the antenna. Giving an electrical length of well over 4 inches. A straight wire for an antenna will need to be the lengths given above.

I will suggest you pick up a book about antennas and wave propagation. Then start on a project like this.

Here is a good place to start
http://www.arrl.org/