Electric Duct Fan (EDF) Self-Launch Glider?

On Jan 18, 11:20*am, CLewis95 wrote:
This EDF approach may never compete commercially or performance wise
with Jet Turbine or current conventional gas or electric prop
systems ... I'm just curious if adapting small EDF's could achieve the
very limited goals in my proposed scenario.

- 60lbs Thrust
- 10 minute duration (no reserve)
- Climb from 1,000' MSL to 1,500' AGL
- Using Paved Runway
- No taxi .. prepositioned on runway
- No tailwind component

While certainly not a feasible commercial solution .. it would be a
really neat experiment

It seems to me to be far too little thrust to be useful, except as a
sustainer.

Back in 2000 I ran some calculations for various thrust levels for
glider takeoff using engines of a type where the thrust doesn't vary
with speed (i.e. rockets and, to a large extent, jets):

http://groups.google.com/group/rec.a...484c08689379af

At the time I was not aware of any jet or rocket-power gliders, but
there are now quite a number. I concluded that anything from 100 kg to
250 kg (220 - 550 lbf) of thrust looked very usable.

I see the "BonusJet" in fact has 240 lbf of thrust on a two seat
glider.

Bob Carlton has 225 lbf on his Super Salto. His earlier Silent had
twin 45 lbf engines for 90 lbf total. It obviously worked, but the
videos I've seen make the takeoff look pretty anaemic. I can only
imagine what it would be like with only 60 lbf!

I think these machines verify that my calculations in 2000 were in the
ballpark.

My constant thrust calculations are not as relevant to a prop or
ducted fan where the static thrust is quite a bit higher than the
thrust at 50 or 60 knots, and they're really starting to drop off
after 100 knots.

One conclusion that will still be relevant is that you use less total
energy for the launch if you have a reasonable level of thrust. WIth
low thrust you spend so much more time dragging the aircraft through
the air that you use a lot more energy in total -- my figures showed
17% more fuel needed with 50 kgf (110 lbf) of thrust compared to 100
kgf (220 lbf). WIth only 60 lbf available it would be a lot higher
again, because you'd be using a substantial proportion of the
available thrust just to fly straight and level. 120 lbf for 5
minutes or 180 lbf for 3m20 would be much more useful than 60 lbf for
10 minutes.