I have the pumped version of the O.S. .91 FS in my UCD3D. I have been extremely pleased with the performance. It is easy to set up, reliable, and hovers great. It does not rocket out of hover, but it does pull out of a hover. Engine has never missed a beat. I love doing low and slow fly bys and pull into a "wall" then 1/4 turn into a hover about 25' off the ground. I am buy no means an expert 3D flier. The UCD3D has really helped me to learn some basic 3D stuff though. If ya got it...bolt it on!