The thrust HP Calculator shows that an APC 18x6 will give you 15.4 lbs of static @ 7,000 rpm and will absorb 1.5 hp. This is as close as I could get going on the engine ratings. I think you may not be getting the most out of the engine at 5,200 rpm. The 20x8 is absorbing 1.28 horsepower @ 5,200 rpm. Let us know.

Gis

[quote]Well.... turns out im only putting out about 6 lbs of thrust (fish scale). That explain's the horrible performance on its only flight so far.