On Thursday, January 7, 2016 at 10:40:33 PM UTC-8, Surge wrote:

How about FES in an EDF (electric ducted fan) configuration instead of pylon mounted FES? The EDF could be mounted in the fuselage with doors than open and close for the inlet and exhaust.
Would this make any sense or be simpler than a pylon mounted system?
Would a smaller prop size make it less efficient and impractical?
The one advantage would be the removal of most of the pitching issue associated with pylon mounted systems.


FES is by definition the front mounted ('F') variety not pylon mounted - just to nit-pick.

As to EDF, you might be able to get one big enough to climb a glider, but the efficiencies would, I suspect, be poor and electric sustainers already face a weight/range tradeoff that is marginal for many pilots. I expect the pylon-mounted sustainers with a larger prop would be the best compromise (reliable and fast deployment, minimal drag, acceptable range, low enough weight for an 18m glider to not face too much of a weight penalty. Whether it is appreciably more efficient than an FES prop would be interesting to know - my guess is they'd be a bit more efficient. FES wins for pure simplicity..

I'd rather carry batteries around than gasoline any day. Internal combustion engines (and turbines) are a recipe for lots of mechanical fiddling and maintenance in my experience.

9B