Making a Tetrahedron Hot Air Balloon

Keith Sproul

http://www.skychariot.com

http://www.skychariot.com/tetrahedron/

http://www.fredbrabbit.com/

Keith Sproul's Hot Air Balloon Schedule


! 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

© 2006, 2007, 2008 Keith Sproul This balloon design, this web page, and this documentation are copyright © 2006,2007,2008 by Keith Sproul. The design maybe freely used by anyone wanting to make home-made, experimental hot air balloons. 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.

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


WidthHeight Volume Example
(ft) (ft) Flat Sides
(cu ft)		 Estimate
(cu ft)		BalloonBuilder
60 52 25,500
65 56 32,000
70 60 40,400
73 63 45,800 60,000 N-9713TKeith Sproul
75 60 49,700
80 69 60,000
83 72 72,000 90,000 N-72KB Barbi Hanna / Kent Barnes
85 73 75.000 100,000 N-72KXKeith Sproul
90 78 86,000
95 82 101,000 120,000+ Andy Richardson
100 86 118,000
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

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 3/4 inch or 1 inch Mill Spec IV
(1inch recommended)		 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 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

Step Description Comment
0Make the design, colors, etc Do not get too complex (At least not on your first one)
1 Buy Materials  
2 Apply for N-Number http://registry.faa.gov/aircraftinquiry/defimg.asp
It is easier to apply for a special N-number than it is to get one 'assigned'
3 Send in Registration Application and Amateur Built Affidavit Yes, do this early.
4 Cut Panels Advisable to cut all panels before starting to sew
5 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.
6 Sew Vertical Gores into Sides Make 3 separate, identical sides, each panel will be shaped like a diamond or kite (see drawings below)
7 Install Parachute Centering Line tie-off points Same on all three sides
8 Install Red-Line guide tie-off points on one side (Bottom Side) Install 2 on load tapes about half way up side.
Install V-bridle and pulley later
9 Cut sides to make 60 degree bottoms and 30 degree tops Take your time, be careful
10 Install top Parachute Girdle on the three sides If doing a triangle parachute, do it here.
If doing a round parachute, this gets done later
11 Sew sides together This is the hard part, take your time and be careful
12 Sew Mouth Girdle Lots of small things to do here
13 Make Parachute This needs to be done after the top is sewn so the dimensions are correct
14 Install Velcro Parachute Holding tabs in balloon Can't be done until parachute is finished to make sure they are in correct location
15Install Parachute, Centering lines and Red Line This may take a lot of adjusting
16 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.
17 FAA Paperwork Fun! 8130-6, 8130-12
18 FAA Inspection DAR (Designated Airworthiness Representative) of FAA direct.
19 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



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.
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 winder 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 2 tetrahedrons. Are you going to make any more? Yes, absolutely. I have two more already designed that I plan on making
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.

 

AmazingCounters.com
Charles Tyrwhitt Coupon
Created Jan 27, 2006
Modified May 2, 2009
ksproul@skychariot.com