There is no simple answer to your question. There are many, many electric planes that (with the correct battery pack) can get 15 - 20 minutes of powered flight (not gliding).

One of the guys at our field converted a .25 size Sig plane to electric and gets about the same performance as a .40 size trainer.

If you are interested in electrics try this site, it is much more electric oriented.

http://www.rcgroups.com/forums/forum...?s=&forumid=11

I fly both gas and electric, and its amazing how DISsimilar the two are in terms of common equipment and stuff.

GB