Tetrahedron Hot Air Balloon Construction

Last updated 1/28/2015

How to build:
A Tetrahedron shaped Hot Air Balloon

© 2006-2013 Keith Sproul

Website Author Description
http://www.skychariot.com/schedule.html Skychariot Home / Keith's Balloons
http://www.skychariot.com/Homebuilt.htmlKeith SproulHow to make a Hot Air Balloon
http://www.skychariot.com/tetconst.htmlKeith SproulHow to make a Tetrahedron Hot Air Balloon
http://www.skychariot.com/vent.htmlKeith SproulHow to make Turning Vents
http://www.xlta.org/plans/index.htmlDan Nachbar & Paul Stumpf XLTA Open Plans
http://www.apexballoons.com/balloons/Jon RadowskiDiscussion on Balloon Design
http://www.apexballoons.com/tips/Jon RadowskiTips on making a balloon

!!!! DISCLAIMER !!!!

Materials and ideas listed here are in part unproven and may be hazardous to use in the construction and operation of experimental hot air balloons. Building and flying experimental aircraft involves significant risk and may lead to serious injury or death. Always obtain professional advice when building or flying human-carrying aircraft!

Copyright Notice

© Keith Sproul This balloon design, this web page, and this documentation are copyright © 2006 - 2012 by Keith Sproul. The design maybe freely used by anyone wanting to make home-made, experimental hot air balloons. If you make a balloon using this or a similar design, please let me know so I can put pictures on my Tetrahedron website http://www.skychariot.com/tetrahedron/
If you have suggestions for improvements to the design, and/or the documentation, please send them to me: ksproul@skychariot.com

Project Description

This site is aimed at people who have already made hot air balloons and are interested in making Tetrahedron shaped hot air balloons. If you have questions, or suggestions on things that should be added, PLEASE let me know. This is a work in progress.

A Tetrahedron is the simplest three-dimensional object there is. It has 4 points, that is it. There are three completely different ways to make a Tetrahedron Hot Air Balloon. I am sure there are even more, but this documentation will discuss these three methods.

TypePictureCommentsPeople that have used this method
(also called SPIRAL)
All Load Tapes are very hard, if present at all
Parachute and Mouth are difficult
Cutting is very easy
Tracy Barnes
Bert Padelt
Greg Winker
Horizontal PanelsVertical Load Tapes are easier
Horizontal Load Tapes are very easy
Parachute and Mouth are easy
Cutting is easy
Steve Hunter N-2536K
Barbi Hann N-72KB
Vertical GoresVertical & Horizontal Load Tapes are very easy
Parachute and Mouth are easy
Cutting is very easy
Triangle shaped parachute is very easy
Keith Sproul N-72KX
Keith Sproul N-9713T
Andy Richardson
Keith Sproul N-9713T

To make any hot air balloon is a large project. However, it isn't as huge as you might think. Depending on complexity, size, and design, a hot air balloon may take from 100 to 500 hours.
Making a Tetrahedron hot air balloon is somewhat simpler than making a normal round balloon. If you use the CYLINDER method, it can even be easier, however this method has other draw backs and I recommend against this method.

Before starting to make a tetrahedron hot air balloon, (or any hot air balloon, for that matter), you need to decide on several things:
  1. What are you going to use the balloon for?
  2. How many people do you want to be able to carry?
  3. Size of balloon? which depends on the answers to 1 and 2
  4. What type of basket do you plan to use?
  5. Kind of fabric
  6. Width of fabric
  7. Color, Design, Artwork, etc
If using the VERTICAL GORE METHOD (my favorite), there is a very efficient way to make the panels. By making the height of each panel based on the width of fabric, you can reduce the amount of effort, especially when it comes to cutting panels. The angle in a tetrahedron is 60 degrees. If you make the panel height to width ratio such that you would end up with a 60 degree triangle, you can make your job much much easier.

With this method, all you need is 200 to 400 panels, all the exact same size. This makes cutting easy (although somewhat boring after awhile).
NOTE: This calculation has to be done on the FINISHED size, then add the seam allowances.

60 Degree Panel Sizes

Width Height Width Height
48.0 81.50 45.75 79.25
60.0 102.25 57.75 100.0
64.0 109.20 61.75 106.95
65.0 110.80 62.75 108.5

Number of Panels

60" fabric 65" fabric
Vertical Gores
(per side)
of Panels
Width (ft)Volume
(cu ft) *
Width (ft)Volume
(cu ft) *
12 180 57.8 22,700 62.8 29,100
14 240 67.4 36,000 73.2 46,200
16 306 77.0 53,800 83.7 69,000
18 378 86.6 76,600 94.1 98,200

* NOTE: These are flat-sided volumes. Actual volume is higher

Materials Needed

Qty Units Description Comment Sources
500-1000 Yards Rip stop Nylon Urethane or Silicone www.noahlamport.com
500+ Yards Load Tape 1 inch Mill Spec IV www.ballyribbon.com
20-30 Yards Nomex 6-7 oz nomex Difco Performance Products, Canada
1 ea Crown Ring From a Dead Balloon
12 ea V-Rings or V-Quick Links
1 ea Red-Line Any good polyester red rope (non stretchy)or From a Dead Balloon
1 or 2 ea Pulley for Red Line From a Dead Balloon
4 eaCarabineersDepends on basket typewww.stumpfballoons.com
1 set Basket Cables Steel or Kevlar Local balloon repair station or make them yourself
(For Steel cables use Nicopress fittings)
1 setParachute Shroud Lines

Steps to make a Vertical Gore Tetrahedron Hot Air Balloon

  1. Make the design, colors, etc
    Do not get too complex (At least not on your first one)
  2. Buy Materials
  3. Apply for N-Number
  4. Send in Registration Application and Amateur Built Affidavit
    Yes, do this early.
  5. Cut Panels
    Advisable to cut all panels before starting to sew.
  6. Sew Panels into Vertical Gores
    Easy sewing, LOTS of five foot long seams
    The top panels are sewn onto the side panels as one continuous vertical piece.
  7. Sew Vertical Gores into Sides
    Make 3 separate, identical sides, each panel will be shaped like a diamond or kite (see drawings below)
  8. Install Parachute Centering Line tie-off points
    Same on all three sides
  9. Install Red-Line guide tie-off points on bottom side panel
    Install 2 on load tapes about half way up side.
    Install V-bridle and pulley later
  10. Cut sides to make 60 degree bottoms and 30 degree tops
    Take your time, be careful.
  11. Sew the three sides together
    This is the hard part, take your time and be careful
  12. Sew load tape around parachute opening

  13. Attach load tape to crown ring
    Use basic geometry to determine the lengths of the load tapes. Overlap the load tape by 24". Sew at least 4 passes over the load tape.
  14. Sew Mouth Girdle
    Lots of small things to do here. Attach the V-Rings. Put a second layer of load tape up 24" inside and outside of the envelope.
  15. Make Parachute
    This needs to be done after the top is sewn so the dimensions are correct
    Make it at least 24" larger on each side
  16. Install Velcro Parachute Holding tabs in balloon
    Can't be done until parachute is finished to make sure they are in correct location
  17. Install Parachute, Centering lines and Red Line
    This may take a lot of adjusting
  18. Test Inflation
    Take it slow. Check everything, especially parachute centering lines.
    Take lots of pictures!
  19. Write Manual
    FAA requires a flight manual. Look at other balloon manuals. Keep it simple. Don't put in any undo restrictions. Make your options flexible. Remember, If it is in the manual, it is probably okay.
  20. FAA Paperwork
    Fun! 8130-6, 8130-12
  21. FAA Inspection
    DAR (Designated Airworthiness Representative) of FAA direct.
  22. Test Flights
    FAA requires 10 hours of testing in a 25 mi radius of a given airport
    Take lots of pictures!!

Sproul Construction Times

PictureRegistrationYear Made GoresTimeComments
N-48KX2003167 Weeks
175 hours
First Balloon
Turning Vents
N-73KX2004245 months
250 hours
Pattern took more time
Turning Vents
N-72KX20043 sides
48 panels
5 Months
150 hours
N-9713T20063 sides
42 panels
4 months
130 hours
N-72KX2010 (rebuild)3 sides
48 panels
15 Months
200 hours

Vertical Gore Load Tape Placement

Load Tapes, Side View

Load Tapes, Top View

Load Tapes, Combined View

3 Diamond Shaped Pannels

Make THREE panels like what is shown in gray
Then sew the 3 panels together

FAQ about Tetrahedron Balloons

Questions Answers
You have a triangle shaped parachute. How does this compare? The triangle shaped parachute is a LOT easier to make, looks neat, and behaves no different than normal parachutes.
Your parachute top seems fairly small. Do you find it adequate for normal operations?The parachute in Wings of Wind, (Yellow Tetrahedron) is too small. The parachute in the blue/white Tetrahedron is bigger, the balloon was a lot smaller, so it ended up being almost too big, I am going back to a smaller parachute, but not as small as the first one. The parachute in the red/white/blue tetrahedron seams about right
How many centering lines are there?12, There are three on each side (on the load tapes) and one on each point (Also on a a load tape)
What is your opinion of the 1.3oz silicone fabric? I LOVE IT. I would highly recommend it. However, I also put Nomex on the bottom row (bottom 5 feet)
How are the climbing and descending characteristics of the envelope?

I have found that it spins on rapid rise and descent. Other than that, it is just fine. I have had it up to 600 fpm up and 600+ fpm down. Never any problem. I don't think I would want to go above 1000 fpm down. With the flat top, it is hard to go much faster up anyway.

Any issues on hot inflation?I highly recommend having a rope on the top corner and having someone 'PULL' you up. If you don't do this, any breeze will catch the corner and twist you QUICKLY. This person works in conjunction with your crown-line person. They play a gentle game of tug-of-war. The windier it is, the harder this top-line person has to work. They also have to pay attention to try to keep the point directly into the wind.
Do you have any issues with carrying passengers in this design?None what so ever.
You have made 3 tetrahedrons. Are you going to make any more?Yes, absolutely
What about glowing or tethering?Each corner has a loop to attach a rope. I leave a rope on the top corner for hot inflation (see question above).
If I am going to glow or tether, I fasten ropes onto the other two corners so that I can have people on all three corners hold me down during the glow.
NOTE: These ropes should be light weight ropes. They will pull the corner down a little. Heavy ropes will pull the corners down a lot.

"For once you have tasted flight you will walk the earth with your eyes turned skywards,
for there you have been and there you will long to return."

- Leonardo da Vinci

"Life is not measured by the number of breaths we take, but by the number of moments that take our breath away."
- Anonymous

Keith Sproul's Festival History

Pandy Hot Air Balloon
Tetrahedron Hot Air Balloon
Birthday Cake Hot Air Balloon
Pig Headed Hot Air Balloon
Fred B Rabbit Hot Air Balloon

Meteor Crater Flight
Letchworth State Park, NY Gorge Flights
Shooting the Delaware Water Gap PA/NJ
Palo Duro Canyon State Park, Amarillo, TX Balloon Flight
Red Rock Balloon Festival, Gallup, NM
2007 Switzerland Balloon Festival
Dawn Patrol Flights

Chariot Balloons
Balloon Flights in 3D
Balloon Parachute Artwork
Balloon Pictures from the Bottom
Red, White & Blue Balloons
Arrow Design Balloons
Aerostar Aurora Balloons
Parachute Drop Pictures
List of University Balloons


Charles Tyrwhitt Coupon

Created 1/27/2006
Modified 1/28/2015
Copyright Keith Sproul
EMail ksproul@skychariot.com