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Old May 01, 2014, 01:42 PM
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18W Solar Hyper Blimp

First time poster in this subforum, but I wanted to show off a hyper blimp a few friends and I made for a solar competition. We designed and built it using a lot of information we found on this forum and the Yahoo RC Airship Regatta group. The point of the competition was to fly 100 yards solely off of solar power. Charging batteries was allowed, but heavily penalized. This was our entry that we constructed for about $120.

The vehicle had about a 350 liter envelope, 18W worth of solar cells, two 6W DC motors spinning 7x3.5 inch propellers, and two 50 farad capacitors to smooth out the power supply. Overall it flew great, but major improvements in solar cell placement, and motor selection could be made. But not bad for first time blimp builders! We definitely could not have done it without all the information in this forum!

Edit: Youtube video was taken down due to "Hyperblimp" being a trademarked name. I'll post the new video when it is up.
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Old May 03, 2014, 08:10 PM
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You did pretty good on cost. The guy who originally coined the term "hyper blimp" and came up with the long aspect ratio also built a solar powered one several years back. I seem to recall he spent considerably more money on the solar cells. His blimp had a transparent envelope and he used a long flexible type solar cell strip that ran end to end across the entire envelope. The wind took it away from him one day and he never got it back, which must have been pretty rough considering the cost.
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Old May 04, 2014, 12:41 PM
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You are absolutely correct and that is where we got the idea. I believe he used "Heptax" (?), which I believe is a food grade heat sealed plastic. The cells in bulk run just over a dollar per watt, so it was fairly affordable; however these were single crystalline glass cells. Which are very very easy to fracture. The main advantage is they have twice the power density at nearly an tenth the cost compared to the flexible cells. (1.8W for solid, 0.72W for flexible)
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Old May 05, 2014, 08:59 AM
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Yes, heptax is what he used. I actually have a roll of it somewhere myself I bought back when he was reselling it online. Toray Plastics has something called LumLife which is a metalized film with better gas retention than traditional metalized nylon film used in toy balloons. I've been trying to get my hands on some but even getting a sample from them has been unsuccessful. Minimum order is 1000 lbs and it runs $4 a pound, so it is financially prohibitive for the hobbyist. I think it would be a superior material for building RC blimps though, since it has both very light weight and really good gas retention. The foil balloons you see in stores now are probably all using it. I thought about investing $4K in a roll and then reselling it to the hobby blimp community in order to recover some of the cost, but there does not appear to be enough people building RC blimps to make this a viable plan. You can tell by how little activity there is on this forum that it just isn't a popular hobby. Of course part of the reason could be that there is no easy way to get the proper films for building RC blimps!

Seems like the glass solar cells would be a lot heavier than the flexible type. I didn't realize there was such a big power output difference between the two. i guess glass must let more light through than whatever they are using as the protective layer on the flexible ones. Using them as the control surface is clever though. You could add another set at the front for more power, then it would counter balance the weight of the tail and you'd be free to put your motors wherever you wanted.
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Old May 05, 2014, 02:02 PM
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Finding the film is no easy task. It took myself easily a week to educate myself, and then locate the correct materials. The film from balloonkits weighs about 32 g/m^2, which adds up pretty quick.

The glass cells we used were about 7 grams in mass (1.8W) while the flexible cells we had on hand were 7.2 grams (0.72W) and slightly larger in area. So the power vs mass provided is significant.

I wish we could have added more cells to the blimp. If we nosed down too much, the cells would be out of the sun, resulting in no power and lose of altitude. So it was a fine balance between flying up and straight. Fortunately the blimp was negatively buoyant.
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Old May 05, 2014, 02:52 PM
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Originally Posted by pyronaught View Post
Seems like the glass solar cells would be a lot heavier than the flexible type. I didn't realize there was such a big power output difference between the two. i guess glass must let more light through than whatever they are using as the protective layer on the flexible ones.
We hear about breakthroughs in solar cells every day, but unfortunately, it's a lot like Lipo battery breakthroughs. Commercial high end solar cell efficiency is still basic about 30%. And that's not for solar cells the average person can buy. That's for special made cells for things like satellites where the cost for weight is no object.

The rest of us are stuck with solar cells closer to 7% efficiency. The only thing that changes is how expensive they are to purchase. So you can by more of those 7% cells for less money these days. Fine if you're going to screw a bunch of them on to your house, but not much of an improvement if you intend to use them in a flying aircraft. The consumer ready higher efficiency solar cells still tend to be old school solid silicon wafers.

I wish there were more readily available envelope materials...
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Old May 15, 2014, 07:48 PM
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I wish there were more readily available envelope materials...
If I ever get this saucer project off the ground on a commercial level I would be able to resell Lum Life film by the yard as an off-shoot, which is otherwise unobtainable unless someone wants to invest $4K in a minimum quantity order. You can only heat seal it on one side and since it only comes in silver it is not as ideal for printing graphics on, but as far as light weight and gas permeability goes I think it is the best thing out there. They claim four times longer gas retention compared to the traditional aluminized nylon that BalloonKits.com sells.
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