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Aerospace Solar Impulse

  1. Mar 21, 2009 #1
    I am doing a Mini-Project on the solar impulse aircraft.


    You may or may not have heard about if before, but guess you would have.

    --- Aim of the project is to suggest ways to improve the project under several catagories

    - Propulation
    - Design/Aerodynamics
    - Solar cells / Battery / Power
    - Materials
    - Cost

    I am more mechanical, thus when it comes to things like solar cells, i am a little lost on whats the latest and greatest.

    The main aim of the project (3000 words) is come up with improvements, and base it from a cost point of view.


    I was looking at the design, and it would seem it has a fairly large cockpit, was thinking maybe this can be made smaller.

    I was also looking at a similar project where the engine was deployed for power, and then stowed. Would stowing the engine decrease drag in the glide?

    I am sure despite a huge team there must be improvements that can be made, but not much is sticking out to me at the moment.

    So any help/hints and the likes are very welcome.

    I was also thinking, even though the question has not been asked, could pilot technique play a critical role, as its just a glider, so finding thermals would give you height gain with no power required. Does any one know what height thermals become not existant at? I have seen some amazing height records by gliders, but how much more is possible?

    Thanks again =)
  2. jcsd
  3. Mar 22, 2009 #2
    Very cool! Thanks for the link. I have no doubts in my mind they will succeed. The NASA/AEROEnviornment Helios is a solar powered airplane that can stay up for months at very high altitudes. So, provided they have the right tail winds, its entirely possible. Built light enough, the aircraft can have some pretty low power requirements in order to get away with being solar. A helicopter, on the other hand, wouldn't work. They eat up power for breakfast. As an example, a mid sized airplane would require on the order of 2-300HP. A similar sized helicopter might be up near 800+ SHP.

    My estimate is that they are going to be under about 100HP, maybe even under 60HP. (Im basing this off of a piper cub)
    Last edited: Mar 23, 2009
  4. Mar 23, 2009 #3
    Thanks for that.

    Any ideas on how one could improve this design, if not improve then ways to reduce costs as the costs i am guessing for this project will be on a large budget and large scale.

    Is it possible that the cockpit could be made more streamline, or is there a reason its designed as its is?

    Was looking at some of the Rutan designs, would using two wings provide any more advantage other than increasing surface area for solar cells?

    This is been built for endurance and not speed, so what techniques could one implement to get max endurance?

    Is it possible to thermal by day and sole charge the batt's from solar, then gain as much altitude as possible and glide down to x height by neight then use batt power to maintain altitude till the morning when you can one again use thermals to gain height and start over?

    Solar cells are very heavy, so not sure on what glide charictoristics the glider may have.

    If you look at:



    http://www.solar-flight.com/sunseeker/index.html [Broken]

    This is a motor glider with solar cells.

    I am also lead to think that the origional solar impulse design was similar to the solair one, but cant find anything concrete.
    Last edited by a moderator: May 4, 2017
  5. Mar 23, 2009 #4


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    Pretty nifty! It should be mentioned that Helios only flies for months at a time over the Arctic or Antarctic, where there is sunlght 24/7. As the website states, the real challenge will bwe getting through the night.

    I'm guessing that they plan to climb to the highest altitude they can during daylight hours, then descend as slowly as possible (like a glider) through the night. I didn't see anything in their website pertaining to the kind of speeds they anticipate. If we knew what their cruise speed was, we could determine if there would be any advantage in turning east just before sunset and flying eastward through the night to get to sunrise just a little bit earlier.
  6. Mar 23, 2009 #5
    Well it doesnt say the plan, but i would climb as high as possible, and decent via night till i got to around 8k ft and then use the batt power to maintain altitude till daylight.

    Its possible to glide to 60k ft, as done by Mr Fossett some years back.

    I am sure i have read that cruise is a slow 40 Kmh.

    I am surprised more people dont know about this, i have followed if for some time now (years), i think its a feat of engineering in its self.

    Getting a UAV to fly 36hours is one thing, a piloted aircraft is another in my opinion.

    However, at that speed, it will take 6 weeks or so to fly around the world, so maybe i have my fact about speed wrong.

    To take the record it would have to be a non-stop flight right? it can land, take off, land, etc, or can it.
  7. Mar 23, 2009 #6
    Why do you think you're going to come up with solutions to improve their design without doing any analysis or study? Upon viewing their website, most of them are aerospace engineers with 10+ years experience. It's rather arrogant to simply say "I am sure despite a huge team there must be improvements that can be made, but not much is sticking out to me at the moment."

    If you want to evalute their design, then you have to run some numbers and do some calculations. Otherwise, this is just speculation.
    Last edited by a moderator: May 4, 2017
  8. Mar 24, 2009 #7


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    My sarcasrtic side's BS meter is pretty pegged right now. While I can very much appreciate their efforts, I get the feeling that there is nothing there of substance other than a slick web site and some CG graphics. When I see nothing but statements like "it is all about optimising the different links in the propulsion chain and integrating an environment blah blah blah..." I think of Office Space.

    "Multiple forms of energy have to be managed and their conversion phenomena understood and optimized" Gee. Do ya think?

    Good luck to them. I hope they manage to actually make something.
  9. Mar 24, 2009 #8


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    I think Fred's comments address the reason there isn't more popular knowledge about this project. I would guess that most people take a look at it and file it away just one drawer short of a web site with a perpetual motion machine.
  10. Mar 25, 2009 #9
    Well FredGarvin, you have pointed out the fact that the website does seem flash and does seem like all is well and on time. I like the fact you have pointed out one of the many, many lines that state the obvious =)

    I am been lazy, should have at least thought of a few basic concepts myself first.

    I was guessing that they may have missed some "basic" things, or some "simple" things, and some how over complicated the whole design and project, maybe wishful thinging as you point out there are many experienced engineers on this project, but hey, these type of people can tend to over complicate things.

    I think the basics of the project are, and here i am pointing out the obvious

    - A structure that flys efficient, and plenty of surface area
    - Gathers solar energy and stores into battery
    - Uses thermals to gain height and preseve battery
    - Flys by night on battery, guessing at constant level.

    So the challenge really is to have enough battery storage to store power needed at night, and ensure that the solar cells can charge fully the batterys from projected performance of cells.

    Again, a guess, but the weight of the cells wont make it a brilliant glider, thus i guess =) it will need some sort of power by day too.

    Its got a huge wing span, and maybe this is why it flys so slow, combined with the fact its heavy, and needs to use minimal power for propultion.

    Guess i have stated the obvious, and guessed at many wrong things.

    I was looking at one of those other links with the solar glider which has actually flown since the mid 80's, and read some research about a HPA converted to a solar aircraft, that too did fly.

    Seems that a massive different between these that have flow and solar impulse is the weight (stating the obvious again).

    I am working on the Rutan endurance aircraft design as it did fly around the world, and there is plenty of info, inc the weight around. So i was then thinking about optimizing it for weight as many material advances have been made, and then adding electric motors, and then using wing surface area for solar cells and calculating how much power at 100% efficienty i may get from them.

    My guess is, it will never leave the ground, but its theory and can make my assignment about just how hard this challenge is, and factor in the comments that maybe the website contains more marketing goodies than actual facts.

    I am right in thinking that solar impulse has flow only as a similator?
  11. Mar 25, 2009 #10


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    It has a large wingspan because high aspect ratio wings are much more efficient than low ratio wings as well as to gove more surface area for solar cells. Look at the U-2.
  12. Mar 25, 2009 #11
    Again, please stop speculating everything about their design. You've shown no real analysis as to why it 'would never leave the ground'. I strongly disagree with this comment. Back in the late 80's MIT made the dadelus HPA, which flew 74 miles on human power. Built correctly, the power requirements can go wayyyyyyyyy down. This power level is something solar cells could do - and have done. Again see the NASA helios. So your comments that 'it will never get off the ground' is just nieve.

    You really need to do more research and less speculating here.

    Also, this is an engineering trade off. Yes, you want large areas for more solar cells. But you add weight and skin friction which contributes to overall drag. Please put more thought behind your comments.
  13. Mar 25, 2009 #12
    That's funny, because I don't really see any techincal stuff when I visit boeings website, or Pratt, or GE either. I don't see why you would expect them to give away tech. info that is proprietary.
  14. Mar 25, 2009 #13


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    I'm not looking for proprietary or technical comments. What I do notice are BS phrases like optimizing links and integrating environments. There is a difference between stating "hey we can do this" versus "we use complicated phrases to describe what we want to do." It may be subtle, but there is a difference. I've worked with too many start up companys to not see think this way.

    Like I said, I may/hope I am wrong.
  15. Mar 25, 2009 #14
    I agree with Fred. It looks like another flashy presentation with nothing to back it up. There's a lot of very ambitious people out there, but very few that have the knowledge and skills to do anything with their ambition.
  16. Mar 25, 2009 #15


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    In their defense, they do appear to be making some parts (see the blog section). Who knows? Like I said, I wish them luck, but my BS meter is still registering.
  17. Mar 25, 2009 #16
    I honestly don't see why this cant work if the NASA helios already does the exact same thing.
  18. Mar 25, 2009 #17


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    Maybe I'm a bit behind in m yNASA news, but didn't Helios fail?
  19. Mar 25, 2009 #18
  20. Mar 25, 2009 #19

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    Pathfinder is an unmanned vehicle. There is a big, big difference between Pathfinder and Solar Impulse. Solar Impulse has to accommodate the extra weight of a pilot and operates at low altitudes, thus limiting performance.

    My BS meter is similarly off-scale high.

    In their defense, they are Europeans. From my albeit limited experience with European projects, Europeans have taken the silly US concept of vugraph engineering to the nth degree. In the US, a website like that would be a sign of all fluff, no stuff. In Europe, a startup without all that fluff is a sign of a project in trouble.
  21. Mar 25, 2009 #20
    The solar cells on the pathfinder provided roughly 10HP. This is more than enough to power flight of a person. A HPA uses roughly 300watts, and flies at low altitude.


    There's no reason why you cant get off the ground with a person using the power of the Pathfinder.
  22. Mar 26, 2009 #21
    I cant remember the exact power required, but one of the HPA project said how many watts was needed to maintain level flight.

    It was the same as riding a bike on the flat at 20kph, but i cant seem to find the power...

    But like said, its been done on a UAV scale, and its been done using a glider and HPA.

    Getting a solar powered aircraft airborne is not the "big" issue here for me.

    Its how is it going to stay up for around 6 weeks. More to the point, how will it stay airborne for 36 hours taking into account the weight of the batterys.

    I also think its a pretty heavy machine, i read somewhere that the weight is close to 2t.

    I posted the link to the glider, so it can be done as it has been done, and wikipedia also has the HPA that was converted to solar.

    So to me the challenge is "endurance" and thats what i am trying to focus my study on, keeping it in the air for at least 36 hours with some failsafe options, maybe 4 hours extra power.

    I have read some place about a solar para-motor that drags the solar cells behind it, and a blimp covered in solar cells, looks like solar is the future...
  23. Mar 26, 2009 #22
    I don't agree with that statement.
  24. Mar 29, 2009 #23
    Well neither do i when i think about it.

    As my real thoughts are that Hydrogen and Biofuels may power aircraft of the future, even though they are powering aircraft of today in small trials.

    I would like to think that solar has its uses in static based applications, and that hydro and wind power will have its place in static applications too.

    However, in a UAV setting, i think solar can offer some great possibilities for endurance.
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