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Article "Bulle d'orage"

Press article from X-Passion n°12 year 1994-1995

A stratospheric hot air balloon inflated with thunder

Stay aloft at an altitude of 10 000 m without engine, flame, helium, or hydrogen. This is an utopian idea! but nevertheless our new hot air balloon is able of such performances. It is filled with humid hot air and reproduce the thermodynamics conditions that make the cumulonimbus clouds stays aloft and doesn't fall on our head.

A balloon inflated with humid and hot air

The principle

A physic professor whom I was explaining the project asked to me : "hot I understand, but why humid ?". This is because we hope to pickup the water vaporization latent heat. More precisely wile climbing (our balloon is filled with hot air and tend to rise by it self), the mixture within it ill expand; so it will cool down and the water contained in vapor form will condense. So there will be a thermal output that will slow down the cooling of the air within the balloon.
In this way, for an ascent of 1000 m, the (adiabatic) expansion will cool a standard hot air balloon by about 10°C, wile our balloon only loose 2 to 4°C, depending on the quantity of water contained at the beginning . so there is indeed a cooling of the balloon but the atmosphere cool down by 6,5°C meanwhile.
Conclusion : if our balloon is hotter than the atmosphere it will rise and the differential of temperature will keep increasing as long as the atmosphere get cooler with altitude which is true up to the troposphere altitude (12000 m) . It will easily reach this altitude and doing this not using complexes technologies: "Bulle d'Orage" is very easy to build.

The envelope

A flight permitted us to verify our expectations; the temperature into the balloon varies between 0 and 40°C. Our hot air balloon is open at the bottom so it doesn't experience over pressure: we can use a very thin and light plastic (8 µm). The absence of strong constraint also permit to use a common adhesive tape similar to the one used for cardboard parcel to assemble the parts of the balloon. Our envelope weight only 10g per square meter in stead of 50 to 100g for the gas balloon or the fabric made hot air balloon. As an example, a balloon 10m diameter only weight 2 kg and one 17m weight 14 kg The photos show how light they are. We are using a black plastic supplied by "Bolloré Technologie", in order to also pickup the sun energy.
Our envelope doesn't withstand situations of extreme temperature, but it is never in such situation : our inflator produce water saturated air at 40°C compared to more than 120°C for the standard hot air balloon.

The inflator

It is made up of industrials burners on which we spray the water, they are provided by the company "Société Saulnier-Duval". They must be quite powerful. If we want to inflate our balloon in less than 10 minutes (mean time in which there is a reasonable chance to avoid a wind gust), we will need to vaporize the corresponding water quantity in the same time. And it is about 30 kg of water for a balloon 10 m diameter filled up with water saturated air at 40°C, 200 kg water for a balloon 17 m diameter in the same condition of temperature and hygrometry ; that's about 100 kW for the first balloon 1 MW for the second one, this is one standard appliance propane tank in 10 minutes.

A very low cost of building

Summing up here the needed stuff for the flight of "Bulle d'Orage" : a very low cost plastic film (same trash bag), adhesive tape similar to the one used for cardboard parcel, propane tank and metal tubes to build the reusable inflator that will stay on ground. We stay a way under the cost of a conventional hot air balloon.

The performances

The flight levels reached are impressive ! further more considering the ease of building. We have flown during May 1993 and obtained good result.

40 kg at 12 000 m under a cell 10 m diameter

With the help of "CNES ballons stratosphériques", we have sent a probe. Hanging from a 10 m balloon , a probe weighing 40 kg, composed of pressure and temperature transducer, a radar transponder (mandatory for the safety of air navigation) and a g.p.s. (GPS-ARGOS), This probe have gone up to an altitude of 12000 m.
The flight lasted 3 hours, and the vertical speed reached 2 m/s. The temperature of the balloon at takeoff was 28°C, for an outside temperature of 14°C. the balloon reached it's apogee at 12000 m where the outside air temperature was -50°C, for 0°C within it.
Encouraged by those performances, we have decided to build a much bigger balloon where the effects of the condensation are more obvious

Soon : 100 kg at 20 000 m

The picture here is a 17m balloon inflated with cold air. As soon as the needed inflator will be built, we think flying to an altitude of 20000 m with a load of 100 kg. With the help of the CNES and radio ham, we hope to pickup enough data to try a human flight (well need to be very careful, and build a very light pressurized sphere).

An altitude world record with hot air balloon

"Bulle d'Orage" is a hot air balloon, but the way it does heat the air is different; it is probable make a new altitude world record.

Bulle d'Orage : a cheap lifter (to 25000 m)

More seriously, it is a cheap way to lift loads to the upper atmosphere.

A new vehicle for stratospheric experiences

With the same performances, but at a much lower cost (thinner envelope assembling easier), "Bulle d'Orage" could carry the same experiments (Infra-Rouge Telescope, ozone measure aerosols measure) as the stratospheric hydrogen or helium balloon. It could also be used as a temporary cheap telecom relay (TV transmission for example).

A stratospheric solar glider

Even more fun, why not carry a glider and drop it at 20000 mit could fly more than 400 km (I am talking here of hobby model made of balsa). It could use an electric engine wit solar cells for example. It could be 12m wing span and 4 kg, with solar cell . It would fly at 30 000m , at a speed of 100m/s, and it could stay aloft 1 or more days.

A "first step toward orbit" ?

An other advantage of "Bulle d'Orage" is that it can be very big (100m diameter) There is no major technologic constraint : no need to find huge amount of helium or hydrogen; The envelope which bear very few stress is build able, while no material could resist to the pressure of a closed envelope. We ca consider to lift several ten metric tons for a very reduced cost, to altitudes where only rocket can goes. For example we could hope to get rid of the first stage of the Ariane rocket that weigh 350 tons of 400, and which is only used to reach the high atmosphere.
"Bulle d'Orage" is only a prototype. Before beginning industrial applications, we are seeking records and demonstrate the reliability of our new vehicle. There are many projects. We are seeking help either technical or financial, there are a lot of interest from media (several minutes on TV on prime time and scientific press articles)

Laurent PAPIERNIK (X92) Jean-Paul DOMEN 1994-1995

 

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