My First Tetroons
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| This was my first attempt at making a tetroon. It is much too small to fly
but it allowed me to visualise the construction method and identify some
of the problems that would be encountered in building the full sized balloon. |
This is my second tetroon shown
here being battered somewhat by the wind. This envelope is a little over
1400 ft3 in volume and made from
27 μm HDPE. Seams were heat welded using a
hot knife. This inflation was a great lesson in the need to an adequate
deflation system - it took well over an hour to deflate. |
Construction Sequence
Tetroon construction is quite straight forward as the photo sequence below shows.
| Step 1 |
Step 2 |
Step 3 |
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| Cut out your fabric so that it is 2.3094 times as long as
it is wide |
Join the short sides to make a flattened tube |
Close off the bottom end |
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| Step 4 |
Step 5 |
Step 6 |
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| Now close the remaining open
side at right angles. (Take the centre of the upper and lower layers as the
corners) The paper model shows the idea. |
Scribe an arc from the base point and cut to
give to desired mouth opening. For this model it is just large enough to fit
my inflation (computer) fan. |
Hey Presto! (This model has a
small computer fan taped into the base to keep it inflated) |
History
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.
Links
Some information on other solar balloons, solar flights & tetrahedral shaped
balloons can be found at:
Robert Rochte's Website
Robert has probably done more experimenting with solar balloons, particularly
tetrahedral shaped balloons than anyone in the past 30 years. Some other links
relating to his activities are:
Emmanuel Laurent's Website
A polyethylene natural shape solar balloon.
Ralph Wallio's Website
Ralph obviously has a sense of humour calling his site the
'Middle River Valley Black Hole' -
Where Time, Energy and Money Are Consumed
in a Caldron of Confusion and Chaos
and Only Noise Escape.
This site has more 'science' on high altitude balloons than
anywhere else I have found on the net. He also maintains a list of records of
the various amateur balloon flight groups and an extensive list of links.
Well worth a look!
French Solar
Balloon Group
An english version of some of this groups work.
XAP Project
This is Don Piccard's current project. His plan is the fly into the mesosphere
using a cluster of tetrahedral shape balloons filled with helium. Don has
extensive knowledge of tetrahedral shape balloons.
Julian Nott's Website
Gives limited information on his solar flight.
Keith Sproul's
Hot Air Tetrahedron
Inflation pictures of Keith's terahedron
Tim Cole's Tetrahedron
Some pictures of Tim's Hot Air Tetrahedron at the Snowmass Fiesta
2003
Some Rules of Thumb for Tetroons
- The volume of a regular tetrahedron very closely approximates the volume of a cube
with a side half the length of tetrahedron's side.
eg. If your regular tetrahedron has a side of 6 metres then the volume will be (6/2)^3
= 3^3 = 27m3
- The volume of an inflated tetrahedron is between 26 and 30 %
GREATER than that of a geometric regular tetrahedron of the same side
length.
- The best guess way of determining the volume of an inflated tetrahedron
is to use the formula 0.26*h3
where is the height of the cylinder
used to construct it. (Cylinder circumference ~ 2.31h)
- 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.
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