4m glider
SoarNeck,
Down in Pensacola we towed up a 26lb DG 800 with a Hangar 9 Taylorcraft with a ZDZ 40 gas engine. Granted the tow pilot was Peter Goldsmith of TOC fame.
A gas 40-45cc towplane with 80" wingspan is plenty for a 16-20lb sailplane, just takes longer to get to altitude. More power = faster climb to release.
John