Electric Duct Fan (EDF) Self-Launch Glider?

On Jan 17, 3:08*pm, T8 wrote:
On Jan 17, 4:12*pm, bildan wrote:

*People talk about 8 - 10 Lbs
*of thrust per HP at 60 knots.

Well, y'know what they say about "talk".

Ole father physics says you get 5.43 lbf of thrust per hp (550 ft-lbf/
sec) at 60 knots if you can achieve perfect efficiency.

Reality will be substantially less than that.

-Evan Ludeman / T8

This may be another thread, but I like the idea of a microjet with an
electric main gear for takeoff assist. The electric main gear helps
accelerate the glider quickly and efficiently until the wheel leaves
the ground, say 40 knots. This means a jet glider needs less runway.
Also a jet is most inefficient at slower airspeeds. Of course you
could recover a little of the energy with regenerative braking during
the landing, but most likely you would just need to recharge the wheel
battery from the mains.

Anyone have the knowledge needed to size this battery and motor? Lets
say for two take-offs (one for a landout), 850 lb glider, good tire
traction up to 40 knots. Also, what kind of acceleration would be
reasonable to assume? The thrust of the jet would be added to the
wheel thrust, of course.

Dont forget the speed controller for this thing would be a monster
with all the timing issues to go with it just like the RC model kind.
And one of the issues with EDF is the friggen heat from these
brushless motors spinning at such high rpms.
To save the bearings you have to design in some sort of liquid cooling
or heat sink. Then there is the inlet design.
...meaning development of the EDF for this may not be that easy.

On Jan 17, 11:53*am, 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 don't think a ducted fan is the way to go, but I could get excited
about an electric sustainer in the nose if available for say10K with
folding prop, controller and battery. Nose weight of the motor is
counter balanced with battery in aft fuselage, but they wont 25K for
the one installed on a LAK-17.
JJ

On 1/20/2011 6:41 AM, JJ Sinclair wrote:


I don't think a ducted fan is the way to go, but I could get excited
about an electric sustainer in the nose if available for say10K with
folding prop, controller and battery. Nose weight of the motor is
counter balanced with battery in aft fuselage, but they wont 25K for
the one installed on a LAK-17.

Possibly, a folding propeller design like the Carat uses would make
installation a lot easier. The battery, controller, motor, and propeller
might be available for $10K total, but you need a battery/motor guy to
complement your composite construction skills. Any Genesis owners like that?

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)