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Old Nov 26, 2014, 12:28 PM
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Joined Nov 2014
1 Posts
Solar Plane Motor

Hey Guys,
I'm a senior in college working on designing a solar electric plane for a research project. I know it's been done before, I know it's very hard to make it work, but I think I'm up for the challenge, and worst case I'll fail and still have a blast working on it. That said, my expertise is more in the power system end of things (although even that I'm not the most experienced in), so I'm looking for some advice in terms of choosing planes and motors. I'm probably going to build and test the power system (solar panels, batteries, etc.) first without the plane, then purchase a glider and modify it to carry the power system.
With that in mind, I've done some basic calculations and decided I'll need about a 3m wingspan plane to make it work, and I'm shooting for about 5.5-6.5 pounds total. With that in mind, I've been trying to choose an engine. I visited a local hobby store and they suggested the E-flite 32 or 46 based on the weight. My issue is that I think this draws much more power than my panels will be able to supply; I'm hoping to use something like a 300 W motor. The calculations I've done say that this should be enough to climb slowly if I use a fairly efficient sailplane design, which would be fine for my purposes. I don't need anything like vertical ascent, I'm shooting for just a bit more than level flight. What does it sound like to all of you? Do I need something much more powerful? Any motor recommendations?
Thanks very much for all the help.
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Old Nov 26, 2014, 02:08 PM
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Joined Apr 2012
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Hi, cbrooks8593.

Approximately how many volts and amps will your solar cells provide? We will need those numbers to recommend a motor range. My guess is that your best efficiency will come with a geared setup and I really don't know much about them other than the theory.

For an airframe light enough to fly on low power you will probably have to build from a kit or plans or spend a whole lot of money for a pre built. Something like an Oly II would, I think, be ideal. The OlyII is a bit under 3 meters but it has a smaller, lighter, fuselage than the other versions and excels at low speed. It would be relatively simple to extend the wing a bit and you might even be able to shave some weight off by using lighter spars since you won't need to use a winch or Hi-start to launch. This is where i would begin my search.


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Old Yesterday, 04:19 AM
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Romania, Dolj, Craiova
Joined Sep 2007
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The weight estimation is too much by any standards, even the Bird of Time "turkey" is under 5 pounds.
"it's been done before", but just as a rechargeable patch for the main lipo, not as main propulsion source.
The solar efficiency is still too weak as a permanent power source for a normal plane. We talk about 1W per square dm effective power delivered to lipo charger, the central section of Bird of Time for example can't deliver more than 20W, done that.
A 3m performance glider need at least 35W (3Amps from 3s 11V) to cruise level in calm air, and this means 35 sq dm of flat wing full of cells... is not easy to find so much flat surface on a 50-60 sq dm wing that has curved lines, ailerons, bends, dihedral...

As motor, my take would be one of the modern low kv multirotor motors, about 4-500kv, that can turn a 14-15" prop without gear, and draw 2-3 Amps from 3s, for 500 grams thrust, more than enough to fly level with a 2kg glider.
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Last edited by renatoa; Yesterday at 04:24 AM.
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