Fuel Cells?

" wrote in message
:

snip


The Antares has a windmilling sinkrate of 1.25 m/s, with the prop running
freely. So if you start braking the prop it'll be much more.





Are you sure of this? My understanding is that a stationary prop has
less drag than a freely turning one (counterintuitively!). Therefore,
one would then surmise that the drag would decrease as you slow the prop
down by loading it with charging.



Larry "01"

-- zero one - USA

ORT wrote:
Marc Ramsey wrote:
Of course, one will probably be able to get between two and three Apis
Es for the price of one Antares, and the Apis is able to recharge it's
batteries in flight 8^)

Have you got any performance data on that particular feature?
I'd like to see
- the sink rate you have when on windmilling (charging)
- the charge current produced at that point
- how long does it take to actually get some useful energy back into the
batteries? (like, how long for another 500m climb later on?)

Even if such numbers were known, the production version of the Apis E
will no doubt have different performance than the existing prototype.

Without these data it's hard to say if it's really practical or not. Mind
you, propellers are bad as windmills, the efficiency will be rather low. I
wonder if anyone would actually use this feature at all if they have to fly
around at 2-3 m/s sink rate for hours instead of just soaring.

It's a trade-off, like anything else in the sport. If they do it right,
they will allow the pilot to determine the charge rate. That way you
could either cruise at a low charge rate, or tank up at high rate near
the top of a 10 knot thermal. It could actually add to the fun if one
had to figure out how best to manage the available battery capacity for
a given day.

The Antares has a windmilling sinkrate of 1.25 m/s, with the prop running
freely. So if you start braking the prop it'll be much more. The charging
feature was dropped just because it seemed rather pointless, even though
the hardware itself is quite capable of doing it.

The Antares is a wonderful piece of technology, but it has a fatal flaw
from my perspective. The price is so high that buying one is beyond my
means, even with two other partners (which is the most I would have in a
single seat glider). If I hit the lottery, there is still a point at
which one has to decide that one is just investing too much in a toy.
The Antares is well past that point for me.

Whether the Apis E ends up being practical, or not, in the near term an
affordable electric motorglider is going to require some major
compromises. Since batteries are currently a significant part of the
cost and weight of the glider, one can obviously get a lighter, smaller,
cheaper glider by simply carrying fewer of them. But, you end up at a
point where you have enough capacity to self-launch or retrieve, but not
both. So, yes, if it meant I could actually afford an electric
motorglider, I'd be happy to trade-off an hour or so of "pointless"
recharging time, for the option of a 1500m get-home climb later.

Marc

Marc Ramsey wrote:

Even if such numbers were known, the production version of the Apis E
will no doubt have different performance than the existing prototype.

Allright, no real numbers yet.

cheers,
Ola

ORT wrote:
Marc Ramsey wrote:

Even if such numbers were known, the production version of the Apis E
will no doubt have different performance than the existing prototype.

Allright, no real numbers yet.

Do you have a point, or do you just enjoy typing?

Here's the website for the Alisport Silent 2 Electric.
They are reporting a climb of 6500', or cruise of
around 60 miles per charge.

http://www.alisport.com/eu/eng/silent2_b.htm



At 22:00 03 April 2006, Marc Ramsey wrote:
ORT wrote:
Marc Ramsey wrote:

Even if such numbers were known, the production version
of the Apis E
will no doubt have different performance than the
existing prototype.

Allright, no real numbers yet.

Do you have a point, or do you just enjoy typing?