bildan wrote:
On Feb 5, 9:20 pm, Brian Whatcott wrote:
bildan wrote:

....

I've looked at the ducted fan issue and it looks like they can be
optimized to produce 8 -10 Lbs of thrust per HP in the 80 knot speed
range. The only airplane I know of that would benefit from that is a
glider tug.
9 lb of thrust at 60 kt takes 1.6 HP
Perhaps you had 30 kts in mind for 9 lb thrust per HP at 80% efficiency?

Brian W

Yeah, that sounds about right. I was looking at the acceleration of a
glider being towed.

A glider tug is one of the few airplanes where the 0 - 60 acceleration
time matters since you have to get the glider up to an airspeed where
the ailerons are effective enough to balance on a single wheel. 30
knots is in the middle of that range.

A glider tug looks like a nearly perfect application for a ducted fan.

You set off that hunger for the likes of the Fournier RF4 which could
travel a hundred miles over water on a certified (modified) VW without
going into Auto-rough, after a take off using that one retractable
mainwheel and wing outriggers.
Memorable moments when an approach controller once queried the type
(RF-4) as a military jet :-)

Brian W