On Aug 23, 12:00 pm, rektide wrote:
I'm looking at making a powered sailplane with a ducted fan and would
need at minimum 75HP. I'd much prefer something closer to 120HP, but
I dont know what size and weight tradeoffs that would entail.

Ducted fans are usually higher RPM and smaller diameter,
so a direct-drive auto engine might work OK. The Subaru 2.2 litre four-
bangers will deliver around 130 hp at 5600 RPM. Weight of engine + rad
+ coolant is going to be around 300 pounds, something a sailplane
can't afford unless it's a BIG sailplane, and the Vne of sailplanes
also will limit useable HP.
There have been experimenters using ducted fans, only to
switch to conventional props after they found no advantage with the
ducted setup. Be sure to find as much info as possible before
reinventing the wheel and experiencing a lot of disappointment. The
only ducted fans I can think of now are in wind tunnels, on turbofan
engines (necessary for higher cruise speeds than props can deliver),
or on model jets where some attempt at authenticity is expected.

Dan