Originally Posted by
DrIsotope
The OP has never made any sort of indication that this is about a recumbent, just that he's going to do 50mph on flat ground. Even if it does turn out to be something not diamond-framed, we're looking at a sustained effort of ~120rpm @ 1,300-1,400W. Unless it's fully faired, in which case who cares. Fully faired can go really fast without a pie-plate in the front.
The world record for fully-faired upright on level ground with no outside assist is 51.28 mph on a Moulton AM 7. That record is about 33 years old. Jim Glover did that with a full cowl and 82x10 gearing.
Godspeed OP!