ABSTRACT

The hot-air balloon with its large surface and low operation temperature is a  perfect candidate for solar operation. Simply take a black envelope or -- a bit more sofisticated -- a transparent window plus an absorber sail inside can convert a normal balloon to a flying greenhouse.
But there are some problems to solve: As ballooning and solar radiation are hardly compatible, a solar balloon can be used during times with low solar radiation only. Due to this fact it is quite large and has low internal pressure. To avoid handling problems the design has to be optimized to create a balloon with minimal weight and as high operating temperature as possible.

INTRODUCTION

The solar powered balloon SULLOON will help us to make the dream of flying become true, of real flying without producing noise and emissions. To fullfill this dream we catch some air in a transparent plastic film and let it heat up by the sun, the air will rise up into the sky.taking us with it The idea is simple, the realization is a bit more complicated.

PROTOTYPES

was our first model, built in summer 1983
a huge (2800 m3) cigar-shaped envelope taped together from polyetylene-film. A black absorber sail of the same material was mounted inside. But as we were really new to ballooning we started our experiments in the early afternoon. The result was a pretty effective welding process of transparent and black material. It was completely impossible to get some air into this 'sandwich'. For the next balloon

we used a polyester-polythene sandwich film normaly used for packing sausages. From this transparent foil we welded together a cigar-shaped envelope containing 4100 m3 of air. An absorber sail of black polyester was mounted inside the envelope, the payload is carried by a net similar to one used for a gas-balloon. This balloon was able to lift 250 kg into the sky! The next version was a bit smaller jet big enough to carry 80 kg.

has the shape of a lying lens (2600 m3) and is made of nylon film. With this   model we we were able to make a number of successfull captured take off's,
To make a further step to free flight another prototype has been built. It is an very old Cameron N-77, where we replaced one third of the envelope-fabric by a transparent nylon film. Due to it's age

   is just able to lift the envelope weight under solar power. But it is good for tests. We were able to measure the temperature stratification inside the envelope. With these data we can model the thermal behavior to find a best design.

FREE FLIGHTS

What we have learned so far will help us in the design of our first real free balloon. Some basic details:

- A commonly shaped envelope is containing a transparent window, in the inside black absorber sails convert the radiation to heat The balloon can be rotated to control the solar input.
- Top and back will be metalised to reduce losses
- The envelope could be pressurised be be less sensible to thermals