On 12/01/2016 22:16, Andy Blackburn wrote:

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.

If I were investing in a sustainer, my preference would also be for a
pylon mounted electric unit. Pylon retraction should be as reliable as
u/c retraction and time to extend/retract would not equate to
significant hight loss. Once the prop is in the breeze an electric drive
is equally reliable on a pylon as it is on a FES.

Pylon installation in existing fuselage designs should be easier than
FES and there would be fewer complications with cooling and instruments.
When a pylon motor is stowed, there is less drag than there is with a
folding prop and unlike FES there is very little chance of accidental
damage.

I am not sure what the drag/efficiency is of a FES verses a pylon +
large prop once they are both running. Maybe FES has an advantage,
giving it longer range?

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.

I think the biggest requirement for a sustainer is reliable starting,
with minimum pilot work load and minimum hight loss. Electric has got to
win every time.

Now if FES technology and experience was to put into a pylon mounted
electric sustainer which could be retrofitted it into any 15m or 18m
fuselage originally designed to accommodate a sustainer, I might be
tempted to pawn my pension....

The tricky part is that the batteries may have to go into the wings.

Ian