Some old hobby before AWES, looking like an earlier form of yoyo. Please can you guess how it works?
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I have thought for so long on how to make a solar balloon work! I’ve given up and decided hydrogen is the best solution now. That looks so much fun!
Thermals?..
It is not so difficult: using black HDPE film. Here I added a transparent envelope, putting the aerostatic lift from about 80 grams per cubic meters (only one black envelope like this)
to about 120 grams per cubic meters adding a transparent envelope.
It is a black envelope hot-air balloon as the greenhouse effect is used.
But the question is how do I get up, how do I get down?
I wanted to make something that could stay airborne indefinitely. So I thought mostly on how to make a light envelope that would have excellent insulation against convection losses.
You seem to be using a bungee cord? The balloon doesn’t have enough buoyancy to lift you, but you overcome that by using the elasticity of the bungee?
Right, about 1/4 or 1/3 (about 15 to 25 daN), not more (more than 1/2 on the single black envelope video, the jumps being 10 meters high) as it can be dangerous in case of thermal. It is dangerous in all ways.
No, the helical shape of the rope is only to avoid catching the rope during lift.
The two videos show the principle.
The solar balloons are subject to huge convections losses due to the relative wind, for example if they are used as tethered balloons. I experimented it as I walked with the wind (the wind speed being low) avoiding both loss of heat due to the wind and the wind force.
The second transparent envelope partially helps to avoid some convection losses.
There is also a permanent use of a solar balloon adding other features on https://cnes.fr/fr/web/CNES-fr/9276-mir-principes-du-vehicule.php (in French language), English translation summarized on http://ballonsolaire.pagesperso-orange.fr/en-historique3.htm.
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I was aware of some of the projects, including yours and the one you linked. I decided to move away from solar balloons, as you wouldn’t be able to both insulate them well enough and have them collect solar energy. Toward the end I decided a useful product might be a tethered electrically heated advertising platform. But how useful is that really? And a hydrogen balloon would work better for that anyway.
This convinced me to stop, for now. All that energy input for so little performance:
http://aeroix.de/fileadmin/user_upload/aeroix/redakteure/Dokumente_HeiDAS/2007AIAAHeiDASUH.pdf
I conceived and used the solar balloon jumping as a (dangerous) game, not for any other use.
The balloon accelerates while it gets up during the 10 m rope. The obtained kinetic energy is: 1/2 V² x m where V is the balloon vertical speed in m/s (here 3 m/s), m is its mass (envelope = 10 kg + air = about 450 kg for a 400 m3 balloon = 460 kg).
1/2 x 9 x 460 = 2017 J.
The buyoancy is 200 N. So the weight is 800 N - 200 N = 600 N.
The jump height is 2017/600 = 3.45 m.
A 400 m3 double envelope balloon is shown on the first video. A 800 m3 single black envelope is shown on the second video.
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That’s a very nice game. I’d be trying to jump higher and higher with a longer elastic tether.
Dont get too close to the hill in the background or you might se some brutal thermals…
I inadvertently experimented it, when an upslope wind makes me to go up the hill near my house, being dragged by the balloon that worked like a parachute.
I do like the idea. Design it like a gas balloon, add a tether to the ground, and you might have an attraction for the beach or a fair. Worry about the regulations later. I don’t like the idea of using HDPE foil for the outer envelope though, no strength and it degrades too quickly in the sun.
It would be too heavy for a solar balloon, and also very expensive. HDPE is about only 20 to 30 grams/m², and when it is degraded by the sun (after 200 or 300 hrs of use) the user is tired far before.
The xf-film (cross layers film) https://www.arktarps.com.au/product/lightweight-tarp/ used for tarps is very strong and have a high lifetime (I tested it outdoor for more than two years), but it weight (70 grams/m²) would be possible if the balloon is large enough.
Beside it I wonder if this xf-film could be used for low technology AWES thanks to its high lifetime compared to some months for fabric kites, that in spite of its low dimensional qualities.
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Thanks for the link.
If you make it sealed, you can do something like: have an inner balloon at something like 75 degrees centigrade and 70 degrees relative humidity, to get the density of the air to below 0.9 kg/m^3. Then add as many balloons around that as necessary to reduce the temperature gradient between layers so much that convection is greatly reduced. A 5 meter radius sphere would give you 157 kilogram buoyancy, your envelope can then weigh 0.5 kg/m^2 to reach neutral buoyancy.
I’m now learning math and physics to perhaps later be able to do simulations on things like this.
The convection is a big problem when there is relative wind. The more there are envelopes, the more there is weight.
I obtained about 0.16 kg/m² with a triple enveloppe (one black envelope inside + a transparent envelope + another transparent envelope), about 0.12 kg/m3 with a double envelope, and 0.09 kg/m3 with a single black envelope. 0.5 kg/m3 looks to be an unrealistic value for a solar balloon.
Also as the lift is low as the balloon is large, its air mass involving in more kinetic energy.
And also there is loss of solar radiation due to the reverberation from transparent envelopes before it reaches the black envelope inside.
I wonder if that wasn’t also because as the wind hits the balloon, hot air is expelled out of the balloon.
You can mitigate convection maybe by inflating the balloon a bit harder so it doesn’t deform so much when the wind hits it. Blowing it up harder would also independently improve its performance in higher wind conditions, and when it is rising rapidly.
To me that almost looks like a single-use plastic. I’m not so interested in making a product that generates so much waste. That’s another reason why I gave up on it.
Yeah… I would also put the black envelope on the outside to mitigate UV damage, making that issue worse.
When the wind hits the balloon, the balloon is cooling (less if the black envelope is inside), goes down due also to the wind force. In all ways one cannot hold the balloon with wind. And the opening allows rapid deflation by turning.
200 hrs leads to numerous times, but with repairs with adhesive tape. I think the xf-film I mentioned could be a possible solution if building it as 50 grams/m² or less is possible.
In all ways the balloon will be out of use before UV damage. It was an experience, but is not suitable for any market.
Deformation and convection are two different things.
The balloon deforms as it rises, and inflates by the opening as it goes down. The opening is required for numerous reasons; to inflate it by shaking it with arms, deflating by turning it…