On Jan 17, 12:53*pm, CLewis95 wrote:
Electric Duct Fan (EDF) Self-Launch Glider?

I have pondered this for some time now. *Electric Duct Fan (EDF)
propulsion systems have been making strides in the RC model jet world
and are challenging the use of mini turbine jet engines (now used on a
number of full scale SL sailplanes) *Battery technology regarding
power density and safety continues to improve at a rapid pace. (auto
engineer recently stated that within 5 years batteries will approach
the power density of gasoline ... hard to believe but ?? ) *EDF
systems do not have the tremendously high exhaust temperature (~700°C)
and decibel level issues. (Though not as loud, the EDF systems sound
very similar)

Assuming:
- L/D 40:1 850 pound Sailplane (in my case Genesis 2)
- Cluster of (3) currently available EDF Units producing combined ~60
pounds STATIC THRUST (AFTER taking into account loss of efficiency do
to close clustering of intake ducts)
- Battery capacity for ~10 minutes full power .. no reserve
- 2,500ft Paved Runway .. No Tailwind
- Sailplane pre-positioned on runway (not taxied to runway)
- Goal altitude of ~1,500ft AGL

As a "sustainer" I am fairly confident this would yield some
success .. if only buying you ~10 miles *What I would like to hear
from the hobby-physicists out there are comments on these questions:

1 - How detrimental is the loss of efficiency/performance when
clustering duct fan intakes in very close proximity?
2 - With sailplane starting from rest, how long would it take to
accelerate to flying speed? i.e. Would I need 3 miles of paved runway?
and/or .. Would the batteries be dead before the glider left the
ground?

I certainly am not proposing a "replacement" for jet turbines .. only
curious if the above scenario is at all feasible.

Thanks for comments!

Curt Lewis - 95
Genesis 2
Loves Park, IL USA

I think a large one meter EDF would make sense for a tow plane.
Ducted fans "sweet spot" is right in the towing speed range - that's
why they're popular with the new blimps. People talk about 8 - 10 Lbs
of thrust per HP at 60 knots. If so, that would allow a 60 - 80 HP
EDF tug provide the same tow performance as a 235 Pawnee.

As I understand DF's, the bigger they are the more efficient they
are. Retracting a big DF into a SL glider would be a problem but
maybe if the duct were short, it could be rotated 90 degrees before
swinging down into the fuselage.

Why would this be better than the Antares large prop? Speed might be
an answer. The DF's cruise speed is likely to be higher than a large
slow turning prop. Speed would be useful to get to a lift area some
distance from the takeoff point.