Last updated 1/28/2015
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| Website | Author | Description |
| http://www.skychariot.com/schedule.html | Skychariot Home / Keith's Balloons | |
| http://www.skychariot.com/Homebuilt.html | Keith Sproul | How to make a Hot Air Balloon |
| http://www.skychariot.com/tetconst.html | Keith Sproul | How to make a Tetrahedron Hot Air Balloon |
| http://www.skychariot.com/vent.html | Keith Sproul | How to make Turning Vents |
| http://www.xlta.org/plans/index.html | Dan Nachbar & Paul Stumpf | XLTA Open Plans |
| http://www.apexballoons.com/balloons/ | Jon Radowski | Discussion on Balloon Design |
| http://www.apexballoons.com/tips/ | Jon Radowski | Tips 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
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| 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. |
| Type | Picture | Comments | People that have used this method |
|---|---|---|---|
| Cylinder (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 Panels |  | Vertical 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 Gores |  | Vertical & 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:
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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
| Cut | Finished | ||
|---|---|---|---|
| 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) | Number 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 www.westmarkcorp.com |
| 500+ | Yards | Load Tape | 1 inch Mill Spec IV | www.ballyribbon.com www.pamnarrowfabrics.com kwwebbing.com tnwebbing.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 | ea | Carabineers | Depends on basket type | www.stumpfballoons.com |
| 1 | set | Basket Cables | Steel or Kevlar | Local balloon repair station or make them yourself (For Steel cables use Nicopress fittings) |
| 1 | set | Parachute Shroud Lines |
Steps to make a Vertical Gore Tetrahedron Hot Air Balloon
- Make the design, colors, etc
Do not get too complex (At least not on your first one)
- Buy Materials
- Apply for N-Number
http://aircraft.faa.gov/e.gov/NN/resreqform.asp
- Send in Registration Application and Amateur Built Affidavit
Yes, do this early.
- Cut Panels
Advisable to cut all panels before starting to sew.
- 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.
- Sew Vertical Gores into Sides
Make 3 separate, identical sides, each panel will be shaped like a diamond or kite (see drawings below)
- Install Parachute Centering Line tie-off points
Same on all three sides
- 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
- Cut sides to make 60 degree bottoms and 30 degree tops
Take your time, be careful.
- Sew the three sides together
This is the hard part, take your time and be careful
- Sew load tape around parachute opening
- 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.
- 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.
- 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
- Install Velcro Parachute Holding tabs in balloon
Can't be done until parachute is finished to make sure they are in correct location
- Install Parachute, Centering lines and Red Line
This may take a lot of adjusting
- Test Inflation
Take it slow. Check everything, especially parachute centering lines.
Take lots of pictures!
- 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.
- FAA Paperwork
Fun! 8130-6, 8130-12
- FAA Inspection
DAR (Designated Airworthiness Representative) of FAA direct.
- Test Flights
FAA requires 10 hours of testing in a 25 mi radius of a given airport
Take lots of pictures!!
Sproul Construction Times
| Picture | Registration | Year Made | Gores | Time | Comments |
|---|---|---|---|---|---|
 | N-48KX | 2003 | 16 | 7 Weeks 175 hours | First Balloon Turning Vents |
 | N-73KX | 2004 | 24 | 5 months 250 hours | Pattern took more time Turning Vents |
 | N-72KX | 2004 | 3 sides 48 panels | 5 Months 150 hours | Tetrahedron |
| N-9713T | 2006 | 3 sides 42 panels | 4 months 130 hours | Tetrahedron |
 | N-72KX | 2010 (rebuild) | 3 sides 48 panels | 15 Months 200 hours | Tetrahedron |
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
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List of University Balloons
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