John,

Skymaster recommends that you use a 17-28lb thrust turbine for the flap and aileron version for F-15. We also recommend a 12 to 28lb. the elevon version. The 14 lb. thrust can fly the elevon version of F-15 However, the performance will not be as high and we definitely don’t recommend such a small size engine on a grass runway. People may question if it is possible to fly such a big plane with just a 12lb. engine. In fact, if you check the Skymaster website, you can see that we’ve tested a plane with a WRAM 54 (12 lbs.). This shows that it is possible

We recommend a 14-35lb. thrust for the F-18C or E. However, a 14lb. engine is only recommended in the elevon version, no rudders and keep very light (this version is special order only, not legal for AMA in the U.S.). For the regular flap and aileron version, as other people recommend, 28 lbs. or higher is recommended. We don’t believe a 14 lb. engine can fly the standard F-18 though. I hope this answers your question.

The new batch of F-15B, F-18C and F-18E are near completed production. They are lighter and stronger! We will receive these new planes very soon.