Some numbers on an electric turbo:
For a 500Kg glider with 50:1 glide you need 3 KW to keep it in level
flight at 30m/s(about 60 knots). Prop efficiency is about
50%(miserable). So a 6KW continuous motor. I've seen a 7KW model
arcraft electric motor that delivers 7KW for up to 30 seconds so
you'd want a bigger one than that for continuous operation but it
should only weigh about 3KG.
Allow for 30 minutes of operation and even on NiMh batteries about
40Kg of batteries. Of course this is level flight only and you want
some climb ability so the motor might have to deliver up to about
20KW for short bursts of up to a couple of minutes. Better batteries
would deliver some of this. Safe lithium like from A123 systems is
about 20-25% better than NiMH which might be good enough with 40 Kg
of batteries. Or maybe you can have up to 50Kg batteries for an
installed mass of around 60KG. 30 minutes level flight is of course
fairly marginal. Better lithium batteries have safety issues so far
which mean that by the time you take the safety measures they aren't
much better than the A123 cells for energy density.
In any case a turbo is one of the most useless things on this Earth.
Take a look at the extreme measures with the Antares. The battery
cells are individually monitored and heated. You plug it in back at
the hangar and it can report back to mother on the net on the state
of the batteries.
I'll get excited about electric gliders when the energy density of
batteries increases by a factor of about 3. There is a scheme for a
rechargeable aluminium air battery that looks promising but it is a
long way from prime time.
Mike
At 09:55 AM 2/04/2009, you wrote:
If Dg put their battery pack in the motor compartment, per the latest
newsletter, or anywhere in the fuselage as they reckon is safer (I can see
their point but would call it bunk, If I had a heavy landing I would want
that battery mass to be within the cart-wheeling wing some 50 metres in
front of me, not crushing my spine into the instrument panel)- perhaps they
could put it on a sliding beam?
Just a few hundred millimeters would allow the mass to move the overall CG
for improvements to run/climb attitude, surely?
Or is that a false theory?
Input please!-enlighten me (hey there is a pun)
Wayne
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