Solar Powered airplane

[a[_3_]]

You've all by now seen the news articles. If not, look at

http://nexus404.com/Blog/2010/07/09/solar-impulses-maiden-flight-successful-solar-powered-plane-completes-first-journey-26-hours-after-starting/

Its four engines, each about 10 HP, were spinning pretty big props,
the article says 3.5 meters. First question that comes to mind is, why
not a pusher configuration, that is marginally more efficient. Even
though the wings are thin relative to 3.5 meters, there would be
losses from the air cone impacting the wing, those losses would be
lessened since the inducted air is not as 'directed' and is of a
somewhat lower density.

The article mentioned it took off in the morning, and pretty much
flew circles all day and night. I wondered if there was an intention
to fly so that the solar panels were more nearly orthogonal to the
sun in the morning and evening, you'd gain power at pretty much the
cosine of the angle.

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'd be really interested in someone with an aeronautical engineering
background offering some observations. The proof of performance flight
was successful, so the design as delivered worked, but I'm wondering
what other improvements would be obvious to the skilled observer.

[george]

On Jul 11, 4:47*am, a > wrote:
> You've all by now seen the news articles. *If not, look at
>
> http://nexus404.com/Blog/2010/07/09/solar-impulses-maiden-flight-succ...
>
> Its four engines, each about 10 HP, were spinning pretty big props,
> the article says 3.5 meters. First question that comes to mind is, why
> not a pusher configuration, that is marginally more efficient. Even
> though the wings are thin relative to 3.5 meters, there would be
> losses from the air cone impacting the wing, those losses would be
> lessened since the inducted air is not as 'directed' and is of a
> somewhat lower density.
>
> The article mentioned it took off in the *morning, and pretty much
> flew circles all day and night. I wondered if there was an intention
> to fly so that the solar panels were more nearly orthogonal *to the
> sun in the morning and evening, you'd gain power at pretty much the
> cosine of the angle.
>
> 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'd be really interested in someone with an aeronautical engineering
> background offering some observations. The proof of performance flight
> was successful, so the design as delivered worked, but I'm wondering
> what other improvements would be obvious to the skilled observer.

Should be a pretty cheap hourly hire rate :-)

[vaughn[_3_]]

"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

[a[_3_]]

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.

[george]

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

[a[_3_]]

On Jul 10, 11:51*pm, george > wrote:
> 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

I wonder if they did that -- maybe if the props fully feathered.

[ABLE1]

> > ...
>
> > > > 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

> I wonder if they did that -- maybe if the props fully feathered.


Just a couple of points of interest.

1) The picture appears to be an artist concept drawing and there are
six(6) pods but only two(2) with props.
2) Using electricity for energy the term would be "motors" not "engines".

Have a nice day.

[betwys1]

On 7/10/2010 8:57 PM, vaughn wrote:
> > 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
>
>
Turning that earlier estimate on its head: if it can take off and climb
at 300 fpm, then it would need about 10 HP for level flight.

Brian W

[a[_3_]]

On Jul 11, 11:13*am, betwys1 > wrote:
> On 7/10/2010 8:57 PM, vaughn wrote:> > *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
>
> Turning that earlier estimate on its head: if it can take off and climb
> at 300 fpm, then it would need about 10 HP for level flight.
>
> Brian W

Nice point.

It would be interesting to take an hour or two and do a broad brush
design study wouldn't it? If the 'payload' is 225 pounds of pilot and
life support, and you know how many watt seconds per pound the high
tech batteries are good for, and pounds per horsepower of the motors,
efficiency of the solar cells and some related items, and a guess at
the weight per square foot of wing you can pretty well estimate how
big a shadow the airplane must cast to power itself to altitude and
charge the batteries for overnight operation.

Some people have all the fun!