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#1
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Solar Powered airplane
You've all by now seen the news articles. If not, look at
http://nexus404.com/Blog/2010/07/09/...fter-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. |
#2
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Solar Powered airplane
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/...en-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 :-) |
#3
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Solar Powered airplane
"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 |
#4
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Solar Powered airplane
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. |
#5
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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 |
#6
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Solar Powered airplane
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. |
#7
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Solar Powered airplane
...
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. |
#8
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Solar Powered airplane
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 |
#9
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Solar Powered airplane
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! |
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