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Old July 11th 10, 04:51 AM posted to rec.aviation.piloting
george
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Default Solar Powered airplane

On Jul 11, 2:45*pm, a wrote:
On Jul 10, 9:57*pm, "vaughn" wrote:

"george" wrote in message


....


They did not tell us what the minimal sink rate of this beast was, but
it had to be pretty low. If it's as much as 300 feet a minute (I think
the weight was 3,500 pounds) that means one would need to deliver
about 30 horsepower to the air). That is not going to happen with only
40 shaft horsepower available.


I don't know where you came up with 30 horsepower for level flight, but if it
has reasonable takeoff performance on 40 horsepower, it can probably sustain
level flight with considerably less.


Vaughn


The assumptions I wrote included a weight of 3500 pounds and a sink
rate of 300 feet per minute. That is an energy loss of about 100, 000
foot pounds a minute, or about 30 hp. I am pretty sure I saw the
weight as 3500 pounds, and admit guessing at the best endurance rate
of descent. If it's only a hundred feet a minute down 10 delivered
horsepower would be enough for level flight and the balance could be
used to hoist it to altitude.

The sink rate was an admitted guess, but am pretty sure of the energy
balance requirements I mentioned about -- *pretty sure does not mean
peer review certain! I'm hoping someone skilled in Aeronautical
Engineering will offer some insights.

The fun mind experiment is to try to figure out a reasonable flight
profile when the sun is say 45 degrees from overhead. Are the flight
inefficiencies of trying to present the cells normal to the sun rays
made up by the roughly 40% more power available that at 45 degrees?

And I am sure thought went into using 4 engines as opposed to 2 or 6.
I don't know how engine weight varies with horsepower, maybe 10 HP is
the limit for convective cooling.

The technology of the design is simply fun to think about, the only
really obvious feature is very long very slender wings. Even then,
there's a trade off in spar weight and length

All in all, it's a neat proof of concept airplane.


After launch you could shut several engines down