james,

The weight range you mentioned is a little broad, and in my opinion the encompasses 2 classes of engine. If you can keep the weight under 15-lbs I would go with either a Brison 2.4 or the ZDZ-40 (both 40cc engines) as mentioned earlier. If you end up over 15-lbs go a little larger and get a 50cc engine (Brison 3.2, ZDZ 50NG, DA-50R, BME 50, FPE 3.2, Taurus 52 and others). At 16-lbs and with a 50cc engine you will realize a ton of power. Keep in mind a 40cc engine will easily turn a 20" prop, while the 50cc engines swing 22" props. So, check your ground clearance! Anyway, good luck!