Tracy Barnes made the first pure solar balloon flight on the 1st May 1973. His balloon ' Barnes Solar Firefly Tetrahedron' built from a spiral tube of fabric formed into a tetrahedron shape. There were apparently a number of flights made in this balloon but the details are scant.
Dominic Michaelis is recorded as having owned the first pure solar balloon in Europe. This balloon was flown by Julian Nott across the English Channel.
Records compiled for the FAI show that on 6th February 1978 Frederick Eshoo also made a solar flight.
Some information on other solar balloons, solar flights & tetrahedral shaped balloons can be found at:
Robert has probably done more experimenting with solar balloons, particularly tetrahedral shaped balloons than anyone in the past 30 years.
French Solar Balloon Group
Julian Nott's Website
Keith Sproul's Hot Air Tetrahedron
Some Rules of Thumb for Tetroons
The volume of a tetrahedron very closely approximates the volume of a cube with a side half the length of tetrahedron's side.
eg. If your tetrahedron has a side of 6 metres then the volume will be (6/2)^3 = 3^3 = 27m3
The surface area of a tetroon equals 2 times the length of the side squared.
eg. Side = 6 metres Area = 2 * (6^2 ) = 72 m2.
The weight of your tetroon can be approximated by multiplying the surface area of the tetroon by the weight per square metre of the film / fabric and adding the weight of your rigging. HDPE and Mylar both weigh about 1 gm/m2 for every µm of thickness
eg. Our tetroon with a surface area 72 m2 is made from 12 µm HDPE.
Its weight will be approximately 72 * 12 = 864 gm.
You can approximate the total lift of a solar balloon to about 60 gm/m3 at sea level and 12.6 gm/m3 at 15,000m. These figures are based on your balloon operating in International Standard Atmospheric (ISA) conditions and achieving 15oC of superheat. (the air in your balloon is 15oC warmer than the surrounding air).
eg. Our 27m3 balloon should generate about:
27 * 60 = 2295gm = 1.620kg @ sea level
27 * 32 = 864gm @ approx 7,500 m. ( lift = balloon weight = operating ceiling)
27 * 12.6 = 340.2 gm @ 15,000m. ( It won't get to here)
To work out the available lift you can you this standard atmosphere calculator
Of course these figures will vary significantly based on the amount of superheat that your balloon develops.