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Random Hints, Tips, Calculations, References, Myths, Deconstructions, Explanations, Diagrams, and other Fun Stuff relating to the Building and Fixing of Hot Air Balloons and other Thermal Aerostatic Conveyances.

This page contains specific and sometimes very technical information which may prove useful to Hot Air Balloon Designers, Homebuilders, and even Repairfolks. This section will be updated sporadically, yet enthusiastically, when the dispersal of such random enlightenment is deemed worthy.

Last update: 5/28/2020



3D Printed Seam Folder Attachments

It's a fact - good, quality seam folders & attachments for industrial sewing machines are expensive! It's not unheard of to spend $150 to $450+ on a custom-made stainless steel French Fell seam folder from Atlanta Attachment or Tennessee Attachment which screws to the throat plate of your double-needle sewing machine. Sure, you can take your chances with a $10-20 folder on eBay from China, but you're likely to be disappointed, or you might need to modify it to fit your intended use case.

In recent years, I've been experimenting with 3D printing to bring some of my designs into the physical world in a different way than usual. The very first reason why I considered buying a 3D printer was that I might be able to rapid prototype some custom seam folders and sewing attachments of my own design. Would printing my own save me money? Probably not (at least then - now is a different story!). I took the plunge, because aside from seam folders, I certainly had many more reasons to put the printer to good use (and it sure has come in really handy!). I started designing and soon had a few prototypes printed.

First-Generation 3D Printed French Fell Seam Folder
My very first stab at a seam folder. It didn't work exactly to plan, but it was a somewhat serious-looking piece of PLA that could fool someone who didn't know the precise target objective.

My first 3D Printed french fell seam folder was fun to look at, but didn't give me the consistent finished seam that I wanted. Being quite tall on its own accord, and with the exit end of the folder fairly high above the "deck height" of the throat plate, this folder allowed too much fabric into the fold, which then flattened out to make the finished seam a bit wider than the requirement. Back to the drawing board.

On a ballooning adventure in India soon after, I showed a few other pilots some photos of these 3D printed folders. Ben Cleyet-Marrel, French balloon builder and owner of Ballons Chaize, took a keen interest, and we discussed potential improvements. He made a few really smart suggestions that gave me inspiration to continue down a new design path. I started with a clean sheet and the next series of folders were designed to be printed directly on their own integrated throat plates to save the trouble of needing to be screwed on, nor ever having to be adjusted, and especially to keep the height of the output end of the folder to a bare minimum (and avoid the seam width problems of my first design).

Many months and many spools of PLA later, after untold birds' nests of tangled filament and crashed prints, and a number of incremental improvements along the way, I've ended up with some custom seam folders that I'm pretty happy with. Are they perfect? No! Will I stop improving them? Never! Are they ready for prime time? Kind of, yeah!

This design is in fact quite well proven, as these folders have been used to construct an Experimental 90,000 cubic foot envelope and a number of nylon ground tarps already. Some of the earlier-printed, less-optimized folders did break from time to time in the thin-walled area near the exit end, but I beefed up the exterior wall thickness in the important areas to avoid this fate on later designs such as the one that is available here.

First-Generation 3D Printed French Fell Seam Folder

 First-Generation 3D Printed French Fell Seam Folder
9th Generation 3D Printed French Fell Seam Folder (the "09A") as mounted on a Juki LH-1152

This particular 3D Printed French Fell Seam Folder produces a nominal 9/16" - 5/8" wide finished seam (depending on print tolerances, fabric, and sewing techniques) and is suitable for any double-needle industrial sewing machine of 3/8" gauge or narrower. It is designed to optionally enclose a single layer of 1/2" wide, 2500-pound, Kevlar load tape (typical of commercial products such as Herculine or Mule Tape) inside the seam. The fabric encapsulates the Kevlar webbing inside the finished seam to protect it from UV degradation.

As an aside, Cameron Balloons US offers this construction method as an option ("Kevron") on many of their envelopes to save weight and avoid interrupting artwork or other designs with often-contrasting load tapes. I've been using this construction method in my own balloons for a while now and love it. Panel replacements are insanely easy - just take scissors and zip out a panel along the inside stitch line, and sew the new panel onto the outside of the envelope with a double needle stitch and a turned-under hem, right on top of the four original boundary seams. No unstitching of any seams is required, especially not those really tedious vertical load tape seams! The vertical load tape stays inside the original fabric fold for the lifespan of the balloon, never to see the light of day.

  First-Generation 3D Printed French Fell Seam Folder 
Exemplar seam with 1/2" Kevlar Herculine hidden inside the french fell. Finished width is just under 5/8".

A seam without webbing inside offers a finished width slightly closer to the design target of 9/16".

Not all double needle machines have the same throat plate dimensions, so I've made available two variations of this folder to fit the two most common double-needle machine throat plates I've encountered.

First-Generation 3D Printed French Fell Seam Folder
The Juki LH-1152 variant seam folder test-fitted in a Singer 212w140, which has a 6mm longer throat plate.

 First-Generation 3D Printed French Fell Seam Folder
Juki LH-1152 plate at left, Singer 212 plate at right.

The variation above left fits machines like the Juki LH-1152. The variation at right fits Singer 112/212, Juki LH-512/515, and other double-needle machines. The Singer variation has a 6mm longer throat plate. The Singer folder style will NOT fit in a machine with the smaller throat plate dimension, but the smaller plate folder will fit in a Singer 212 or equivalent, using a narrow spacer between the rear of the folder plate and the bobbin cover plates on the machine.

DOWNLOAD Juki LH-1152 Folder STL

Download Juki LH-1152 Folder STL (Reversed fold direction)

DOWNLOAD Singer 212 Folder STL

Download Singer 212 Folder STL (Reversed fold direction)

Any fused filament 3D printer can be used to print one, and no special materials are required - typical PLA does just fine. You will definitely need to tweak your own 3D printer's settings to get your best print quality. 100% infill is recommended. Printing with the folder in a vertical orientation (nose down) is really the only way to do it. I use build supports and a raft. Make the nose of the throat plate have a fairly tight tolerance to the raft, because the smaller the gap, the more the plate will adhere to the raft. This makes for less printing errors in the first few layers of the curved front "nose" of the throat plate that have minimal supports.

First-Generation 3D Printed French Fell Seam Folder 
Print Orientation. A Skirt (light blue) is shown at left encircling the folder & supports, but I highly recommend printing the folder on top of a Raft (minimum 3-5mm radius around the folder, as shown at right) for better adhesion and minimizing print errors in the first few layers of the throat plate "nose."

After printing and removing supports, the side rails of the throat plate where it slides into your machine must be sanded down carefully with a square-faced file to fit your machine. Don't file away too much! You want the plate to have a slightly tight fit so that the rear of the folder doesn't have a chance to move at all left or right (and off-center the seam).

I will make available a few more styles of folders in due time. Next up for this treatment is an Aerostar-style 3/4" folded fell seam with an integrated 1" Tape Feeder on top.

Please send me an email if you make and use one, and feel free to send me any suggestions you may have for future modifications and designs.

Good luck and have fun!



Balloon Builders Journal Archive

For anyone looking to build a hot air balloon, there is an invaluable resource freely available to all. The Balloon Builders Journal was a newsletter edited by Bob LeDoux from 1993 to 1998, which came to be one of the authoritative collections of Experimental balloon-building knowledge, information, tips and methods. Bob has since made the incredible archives available to download for free. It is a must-read resource, and a wonderful starting point for all considering building a hot air balloon.

Click Here to visit the Balloon Builders Journal Compendium

Update: In early 2019, the web host that hosted the Balloon Builders Journal was shut down. Bob has graciously given his blessing for us to continue to make it available here in perpetuity. Original BBJ Website Archive



How To Sew A Hot Air Balloon!
( a.k.a. How To Build A Hot Air Balloon! )

One of the great mysteries in life is how to properly sew a hot air balloon together. OK, maybe it's one of the more esoteric mysteries, but shoddy hot air balloon construction workmanship is an epidemic widespread enough that I've decided it's time to write a tutorial on some of the proper methods and techniques to use in order to get the best results when sewing together a hot air balloon.

In this section, you will learn how to create a perfect French Fell hot air balloon seam, at full speed, with or without a seam folder. If you're building your first hot air balloon, you want to sew it right - Right?  Well, read on and you'll learn how to avoid many of the mistakes I made on my first ever hot air balloon over a decade ago. Important considerations are in spectacular bold type.

This should be one of the more popular and perhaps more confusing sections on this entire website. Skim over it, then read it again in detail, and read it again and again until it makes sense. I don't guarantee I've typed out the instructions with the clearest possible wording, but if you pay close attention and practice along at home, you should get it. When "it" gets there, you'll know, because you will have made that perfect folded fell seam and it no longer seems like work to get repeatable, quality results.


A Short Background on Seams, Stitching and the Mechanics of Such

The double-needle French Fell seam, folded fell seam, felled seam, folded seam, flat fell (a misnomer) - whatever you want to call it, is technically known as Federal Seam Type LSc-2. Each thread stitch goes through four layers of material if the seam is properly folded. This diagram shows each thread stitch passing through only three layers, which is just fine, as long as the fold width doesn't vary wildly or begin to come unfolded. The ultimate goal of a folded fell seam is to attach two pieces of material together while hiding/protecting the raw, cut edges inside the seam.

The standard single- and double-needle lockstitch sewing machines commonly used in sewing hot air balloons create a locking stitch using two threads in each stitch, known as Federal Stitch Type 301. The upper thread is fed to the needle from large spools on the thread stand attached to the sewing machine table. The lower thread comes off of bobbins situated in the throat of the machine, which must be refilled or replaced somewhat regularly, as the bobbin thread capacity is limited by the thread thickness and bobbin size.

Tip: Pre-wound bobbins can typically hold more thread on the same size bobbins because they are wound more tightly under uniform tension. Pre-wound bobbins come at a fairly higher price than the same quantity of thread on a 1-pound spool, but they save so much time and frustration that you'll likely never go back to winding your own once you experience the convenience of pre-wound bobbins.

In a lockstitch sewing machine, the upper thread (A) is passed down through the material by the needle, and a hook on the bobbin case underneath the bed of the machine captures the resulting loop of upper thread that protrudes from the eye of the needle. The upper thread loop takes a ride around the bobbin case, and when it completes the revolution, it is interlocked with the lower thread (B). The needle passes back up through the material being sewn and both threads are pulled tight against the material to complete one stitch. This cycle is repeated 40-60 times per second at full speed on a double-needle sewing machine.

If you've got your needles and hooks in proper timing, your upper and lower thread tensions properly set, and the machine well-lubricated with oil, you can sew as fast as your machine's recommended maximum stitches per minute, all day, every day, and get a perfect stitch every time at full throttle. If your machine is skipping stitches or being temperamental, which forces you to "throttle" the machine (by partially engaging the clutch pedal) to sew slower than it wants to go in order to make it sew right, something is off. Perhaps just a slight turn of a few set screws or another tiny adjustment is necessary to get things working again. Maybe you've got old needles or your thread is threaded wrong. Timing and adjusting an industrial sewing machine is a very involved subject on its own, perhaps for another rainy day here.

In any case, this tutorial intends to prepare you to become more comfortable with sewing at full throttle, all the time, to get the most out of your sewing machine's potential and save many hours of construction. After all, time is the most valuable commodity. Once your machine is running at its peak, it's time to start getting comfortable folding a felled seam, and then get comfortable doing it FAST.


Getting Started

Like riding a bicycle, a French Fell seam is simple to do once you get the proper hang of it. Getting there, however, is very much a mystery to many first-time builders.

If you've never tried sewing a folded fell seam, it might be best to watch the first half of this sewing video, starring yours truly (with a lot more hair than I normally ever have - yeah, that's really me!). Take note of all the different things my hands do. There are a lot of actions going on that are not immediately obvious from the video, which I will explain a little further down.

I am right-handed, but that doesn't really make a difference. Everyone sewing balloons should sew with their right arm through the machine to help push material through and keep excess clutter from creeping underneath the presser foot and needles. I sewed my first balloon with my left arm leading, before I knew any better, since it seemed unnatural to stick my arm through the machine. My first balloon turned out just fine, with very few "sew-unders," but that's par for the course on nearly any balloon construction project. However, I was compelled to change my sewing technique, this time with my right arm leading, when I started working for a balloon manufacturer shortly thereafter. Good thing, otherwise I'd probably still be sewing wrong!

"Sew-unders" are where excess material slides under the presser foot and gets stitched underneath the main pieces being sewn. They are very inconvenient at best, so it's good to avoid them by all means necessary. A "sew-over" is often many times more frustrating. That's where excess material above the pieces being sewn get sucked into the needle/thread area and get sewn into the seam. The presser foot stops quickly, because it has just sewn itself to the fabric and comes to a dead stop. A sew-over is a big pain to remove, and sometimes the only way out of a really bad sew-over is to cut it all out of the foot by brute force. You may even have to put a small patch on the resulting hole(s) if you can't snip the mess of threads without getting the fabric as well. Sewing with your right arm leading will help tremendously in the fight against sew-overs and -unders, since your arm automatically clears extraneous fabric from the throat of the machine as you sew.

If you pay close attention in the video, you'll notice I pull evenly on both the front AND the back ends of the seam, to keep the entire length of the material being sewn under tension. This serves two purposes: It keeps the two pieces of fabric in the French Fell seam from unfolding and falling out of the seam, and it also reduces the amount of pucker introduced by the stitching. Every time something is sewn, it puckers slightly, and as a result shortens the finished dimensions very slightly from the original. When a sewing machine's thread is in proper tension, this puckering is kept to a minimum - however, it's still there. Pulling on both ends of the material being sewn will reduce this puckering to a bare minimum. You'll also notice I'm moving my entire upper body as one unit. I'll get back to this later, but first I shall briefly explain one highly useful benefit of shrinkage.



The more times a piece of material is sewn, the more it shrinks. This is a handy technique that balloon repairmen utilize to make replacement panels fit into the area previously occupied by the original fabric (shrink-sewing). The original fabric has often shrunk over the lifetime of the balloon, so the exposed edges of the new (original size) panels may need to be shrink-sewn to be able to fit evenly into the hole without unsightly folds or puckering. A run of double-needle stitching is first zipped up the edge in order to shrink it before installation in the shorter space left by the old panel. With time and flight-induced heating, the rest of the fabric will assume the same shrunken stature as the edges were installed to fit. Now, back to our regularly scheduled program!


To Use a Seam Folder, or Not To Use?

I sewed my first balloon over a decade ago without one (and it really shows). Somewhere in between beginning that balloon and now, I became skilled enough at hand-folding to where I can fool just about anyone into thinking I used a seam folder. However, it's always easier and usually more consistent to use a well-made seam folder if you've got one. I prefer using one whenever possible. It takes a little getting used to lining up the beginning of the fold, but once you get it down perfect, you never forget. Just like learning to ride a bike or motorcycle, it never leaves you.

Here are two different styles of seam folder attachments. They both accomplish the same exact thing but look a little bit different. The one at left creates a 1/2" wide finished fold, while the one at right makes a 3/4" finished fold.


Lightweight fabric doesn't work in your seam folder? Try Harder!

> I was talking to **** ****** on the balloon makers list, and he said he can't
> even get seam folders to work on that 1.3 oz silicone coated fabric because
> it's too thin.  He also said that's the hardest possible fabric to learn how
> to sew on.  Yikes!  I'm starting to dread how this thing might turn out.

Yes, 1.3 oz. silicone-coated ripstop nylon is tougher to work with overall, but once it's properly in a seam folder (or folded manually) and sewn down, there's very little difference between sewing the lightweight stuff and 1.9oz fabric other than the fact that it's more slippery and half as thin.

I find that it is way easier to get silicone fabric into a folder than it is to get Nomex or even 1.9oz fabric with a faintly tacky urethane coating. The silicone fabric slides easily over the other half of the fabric in the fold and thus can be positioned more easily. HOWEVER, it's definitely more difficult to LOCK it into position once you get it right, because it is so prone to sliding around over itself. Use as many fingers as necessary as well as your forearms to make sure the two pieces don't move out of position before you can trap the fold under the presser foot and lock it with the needles.


OK... Let's Use A Seam Folder!

Seam folder technique (regardless of fabric used) generally consists of the following steps:

1. Insert left (lower) side of fabric into the folder, from the left, so that the far end of the piece is slightly behind (i.e. all the way through) the folder. You might need to wiggle it front to back while pushing from the left until it slips into the fold, but that's not always necessary if you use your right hand in the following manner. Your right pointer and thumb should be used to upturn the fabric in front of the folder (closer to your body) and influence the whole fold to be an even 3/4" wide. By folding the front evenly at the same time as the rear goes through the folder, you can keep the fold pretty perpendicular the whole time.

2. Once you make the foldover an even 3/4" wide along the first 6", keep both hands where they are and slide it into position under the raised presser foot (move your upper body to do that without messing things up). If you don't have a knee (or foot) lifter for the presser foot... Good luck. Drop the presser foot to lock it in place. The best place to position the fabric under the foot is so that the rear edge is just behind the rear of the foot. Use the whole foot to keep it down for now.

3. With the presser foot down, don't let go with your right hand just yet - BEND the folded fabric over and down the table's edge. This "locks" the 3/4" fold width in place at the front end of the piece, and the presser foot locks the fold at the rear end. This keeps the left side from migrating while positioning the right side. Some folks use magnets to lock each side in place, but they would just get in my way. They probably help while learning, though.

4. Now, for the right side. Repeat step 1, except reversed. Use your left pointer and thumb to roll the front fold while you push/slide the fabric into the folder with your right hand.

5. Tricky part: With the presser foot raised, use your left forearm to keep the left side fabric from shifting. You need to slide the right side fabric towards the back so that the left and right edges line up under the foot. When sliding, use your fingers and thumb to push the entire right side back while trying to keep the fold at its optimal 3/4" width the whole time. When the back edges are lined up, you can put the foot down again. Your folds should still be 3/4" wide for the first 6" or so. They don't need to interlock for that 6", but a properly prepared fold should interlock at least for a short bit out the front of the folder.

5A. If the fold is too narrow under the presser foot when you put the foot down, or if it is slightly tapered towards the back, or any other combination of "not quite right", you need to do some repositioning with the foot up. I can't really explain this properly, but each hand needs to control its individual side. Keep gentle pressure inwards to keep the pieces from migrating out of the fold when the foot is up, and reposition as necessary. This is the most critical point in the process where it's easiest to mess up and then have to start over. When everything goes just right up to this point, quite often it's not even necessary to reposition things - just slide the right side back, drop the foot, and continue.

6. [This step is not necessarily required if you have a machine with reverse, or if you don't mind that the first 3/4" of the fold isn't stitched.]
I prefer to follow this step because it allows me to start sewing at the extreme edge of the fabric, rather than starting 3/4" in from the edge and having the very first bit of the fold unsewn. With hands in place on the fabric to keep both sides from migrating, and with the foot raised, I pull the whole fabric setup in one piece towards me to place the rear edge of the fabric closest to the needles. If you have a machine with reverse, you may be able to skip this step by starting out sewing in reverse when that time comes. That will close up this open gap and also lock the stitching at the same time. I've never had a habit of doing this, so I can't really recommend starting in reverse. It probably adds complexity to the process and it certainly removes the use of your right hand for more important things. I'm so used to this step that it's second nature even when I'm using a machine that has reverse.

7. You're almost ready to sew - but first, you must get the run of the fold ready. Position the needles down through the fabric to lock the beginning of the fold so that it's positively secured in place. If the needles aren't into the fabric, it might be pulled out from underneath the presser foot while the run of the fold is being set up. There is some pulling and tension involved, and it's easy to pull the fabric out from underneath the presser foot if the needles aren't down in place.

8. With needles in place, grab the front edge of the left side with your left hand, about 12-18" in front of the needles. For a beginner, shorter spans are easier. I prefer my thumb on top, forefinger on bottom. Do not hold it with a fold yet. Clasp the edge tightly in between your fingers.

8A. With the left side held straight, wrap the right side around the tight left edge and 3/4" wide. Hold the wrapped right side with your right hand, then fold that over to the left side. Grab the completed fold again with your left hand and keep it in place - it will remain there for sewing. When folding (and more importantly, sewing), your other three fingers (middle, ring, pinky) should be used to great effect to pull the fabric on each side of the fold tight so that there is no slack that can cause grief.

9. Your right hand should then be behind the presser foot, gripping all four threads firmly so they don't get sucked back under and tangled in the hook/bobbin. Some machines are notorious for doing that to loose thread ends, so it's a good habit to get used to which only takes a second. It's a good habit to get used to sewing with your right arm through the machine head. You have the benefit of automatically clearing the fabric through the arm as the pile gets higher.

10. With the fold held tight in your left hand and your right hand pulling on the threads, you are finally ready to start sewing! Go for it! Use your forearms and other three fingers on each hand (against each palm) to keep the fabric on both sides of the fold wrinkle-free and tight. Your rear hand and front hand should be pulling equally away from each other so there is constant tension on the fold (often a moderate amount is necessary), but allow the action of the feed dog and stitching to actually advance the fabric. Move your upper body as necessary to allow the fabric to be advanced through the machine, and keep your hands and arms as still as possible. The opposing hand tension does two things - it minimizes the inevitable shrinkage from stitching, and it ensures the fold doesn't come undone. Long runs can be done, but more tension is necessary to maintain a longer fold.


Watch the video and take notes on the sewing technique. Pay special attention to my hand and arm placement, and try to see what I do with my three minor fingers and forearms to keep things taut. I'm holding the closest three inches aside of the fold with each hand, which does (at least) three beneficial things:

A. Helps keep the fold width consistent
B. Avoids pesky sew-unders
C. Helps keep the stitching straight and consistent by constraining my movement strictly front to back. Having both hands involved makes you sew straighter for that reason also - it's harder to stray when you control both ends of a long run, rather than just the near end.


Hand-Folding Your Seams

Folding WITHOUT a seam folder starts off with a different set of instructions, but the latter portion and subsequently sewing it is all one and the same.

Making consistent folds without a folder:

1. Start with the left piece flat on the machine to the left of the presser foot.

2. Place the right piece directly on top of the left piece, but upside down. Offset the top piece 3/4" to the left of the bottom piece's right edge.

3. Place your left pointer finger and thumb even with the edge of the top piece, about 4" apart from each other. Position your fingers close to the beginning of the piece (furthest away from you).

4. Use your right pointer and thumb to fold the bottom piece up and over the edge, while making sure you keep some tension with your left fingers. This ensures the edge stays well-defined and allows the fold to be made around it without influencing its position.

5. After the first fold is made, position your right pointer and thumb just inside your left fingers to now hold the newly-created fold's edge in the same manner as Step 3. Your middle finger will probably get involved.

6. With tension held by your right two fingers, use your left pointer and thumb to fold the top piece up and over the taut edge in the same fashion. Use your left fingers to hold everything in place, and your right hand can come out. Flatten the fold. You should have a perfectly-formed 3/4" wide fold for the first 4-6". If not, practice more.

7. Once the fold is made, grab the end of the fold with one hand, and grab the front end of the proper fold with your other. Reposition the assembly under the presser foot and enter into the folding and sewing instructions above (Step 7). I find that things migrate minimally if I grab each end of the fold with my hands, but keep the fabric flat against the throat of the machine as much as possible. Lifting it off the throat when moving it sometimes causes unnecessary migration, which should be avoided entirely. It should wind up under the presser foot exactly the way it was folded - perfectly. If not, something happened - start over!


Clutch Problems?

> I think my Juki has a problem with the clutch, as there is no way to start
> off sewing slowly with it.  It just goes from zero to full blast no matter
> how slowly I push down the pedal.  Guess I'll have to take it into a repair
> shop and see what they can do.

Industrial sewing machines' clutch motors are designed for on-off operation. When you get used to sewing fast, you will rarely sew at less than full speed. Check out that video for how it's done. However, if you ever need to sew slowly, i.e. for detail work, or at the very beginning of starting out a seam, you can slip the clutch carefully by pushing down very gently at the point of contact, which allows the clutch to barely touch the motor plate. Sometime's it's a fine art. Motorcycle riders call this "feathering" the clutch.

Another technique is to tap the foot pedal quickly but lightly to engage and disengage the clutch in order to sew slower than the motor is spinning.

Recently (it's 2013 now as of this edit), servo motors have become more widespread in industrial sewing use. Those folks who have trouble learning to sew with a fast clutch motor will certainly have better results using a servo motor. The maximum motor speed can be easily and instantly set by an adjustable hand knob, and the foot pedal will also throttle the motor from zero to the set motor speed, smoothly and proportionally, depending on how far the foot pedal is depressed during operation. Servo motors are a great option to be able to switch speeds instantly. One can go from wide-open-throttle, straight-line-full-speed-ahead for sewing gores together, to very slow speeds for detail sewing of accessories and other small items - all at the twist of a knob. My next machine will have a servo motor.

Some even newer sewing machines are direct drive, where the motor is an integral part of the machine head. Some advantages to a direct drive machine include integrated needle positioning, zero friction losses due to belt slippage (no rubber belts are used), and more direct torque to punch through extra heavy layers of material. Needle positioning offers the user the option of automatically stopping the needles in either the "up" or "down" position each time the machine comes to a stop. For a person sewing long balloon seams, the needles should be stopped in the "down" position. This alleviates the need for the user to manually spin the hand wheel so that the needles are down in the fabric. Fabric tension should then be applied while the needles are down in the fabric, so the material will not slip under the presser foot. Once the fabric is tensioned properly, the next long stretch of sewing can be accomplished.



Sewing Machine Suggestions

(Expanded excerpts from emails to a first-time builder)

Look on eBay, Craigslist, or any "for sale" avenues for a used Singer 212w140 or equivalent. These were built in the 1950's and 60's, but are more modern and less finicky than their 112w140 predecessors (WWII vintage) which a lot of repair stations and homebuilders still use. They are still great machines, but the 212 is superior. I consider it the Cadillac of domestic industrial sewing machines. If you wait around long enough, you can find a good one for under $300-500 with a table. I have four Singer 212's in various needle gauges, as well as a few double-needle Juki's. Parts are widely available for the 212 and should continue to be for a long time. Many other brands of sewing machines use parts that are interchangeable with the 212.

Singer 212w140
Business end of a 3/8" gauge Singer 212w140

If you only plan to procure a single sewing machine, you would do well to stick with 3/8" needle gauge, as that's the most common needle gauge most balloon manufacturers use. Your machine might come in handy to fix a standard type certificated balloon someday. If you find a machine on eBay or Craigslist which is a bargain, but has the wrong gauge, get it anyway, because the parts to convert between gauges only cost about $50-60. Don't be afraid to buy a 1/4" gauge machine and then convert it to 3/8". If you know what you're doing, the conversion can be done in less than 2 hours, but if not, it's best to let an experienced mechanic handle it.

A double-needle machine can be quickly converted to single-needle use by removing a bobbin and a needle on one side. This takes about 30 seconds. Therefore, there's no need to have a separate single-needle machine, unless you plan to do SERIOUSLY heavy sewing. In that case, I'd recommend a single-needle walking foot machine such as a Singer 111, Singer 211 or equivalent.

The Juki LH-512 and LH-515 (515 is the same as a 512, but with reverse) are also very solid double-needle lockstitch machines. If you ever see one of these come up for under $300-500 in good working condition, with or without a table (i.e. head only), GRAB it - that's a great price for an awesome machine. A table with 110-volt motor can be bought new for under $200. Juki 512's and 515's (and many other machines) sit on top of an oil pan/reservoir, so be sure that's included if you're buying the machine head only. A Juki is a top tier machine, and you shouldn't have any big problems with it as long as all the replaceable parts still have reasonable wear/lifespan left on them and everything's in good timing. If the 212w140 is a Cadillac, the Juki is an Acura... Made of cast iron.

Juki LH-515
Juki LH-515 with reverse lever

An industrial sewing machine head will last practically forever unless you drop it off a loading dock or it rusts and seizes irreparably. If any of the replaceable things ever break (not often!), most parts will be relatively easy to swap in to get it back up and running perfectly. The hooks and tension assemblies are most often necessary to replace, because they wear down over time. The hooks are the pointy bits (around the bobbin case) which catch the top threads when they enter the material, and then loops the top threads around the bobbin to complete the lock stitch. The points of the hooks will wear down over time, which necessitates sharpening (and retiming) them, and eventually hook replacement. But that might only be necessary every several thousand hours of operation time (oh, say maybe every 30-50 balloons or so).

Every machine (even the venerable LH-515) will certainly have its ups and downs at times. When that happens and you feel like leaning it back, unhooking the clutch belt, picking up the machine head out of the table and THROWING ALL 70 POUNDS OF IT out the nearest window, it's always good to just go away for a while and do something else. Punching inanimate objects also helps, at least if said objects are softer than your fist.


Walking Foot Feed

You don't necessarily want a "walking foot" machine for normal balloon fabric seam construction. This is a heavy-duty type of feed mechanism which is only suited for heavy layers of webbing, etc. You want "needle feed," which is what the above-mentioned double-needle machines are. If you plan to do a lot of heavy sewing and/or upholstery, you will certainly find good use for a walking foot machine, but for standard balloon fabric in folded fell seams, it'll mess up your plans. 212w140's are needle feed, so if that's the number, you're generally safe. When you get into 212w141 / G141, etc. the type of machine or feed mechanism may be different, so be aware. I believe the 141 suffix may be walking foot, but don't hold me to that. Always confirm with the seller, and if they're unsure, be careful and ask someone who knows for sure.

There are many double-needle machines suitable for balloon construction, but the preceding suggestions are my personal preferences at the current moment.



Threading A Typical Double-Needle Sewing Machine

Juki LH-515 shown in diagram. Most double-needle machines are similar.

The post on top of the machine head is self-explanatory. There are four holes on it, two in each direction 90° from each other. The left thread typically uses the top two holes, the right thread uses the bottom two. I usually skip out and only use one hole per thread - the hole which most closely allows the thread to pass through with the least resistance (closest to parallel to the thread path). In the photo, this would be the topmost and bottom-most holes. Ignore the other two - just another step that adds more tension BEFORE the tension discs. It's best to add the least amount of uncontrollable tension to the top threads as possible, but you do want to ensure that your thread doesn't decide to go sightseeing after it leaves the spool and before it gets to the machine. If a top thread ends up getting caught or wrapping itself around something, that tends to stop a good seam pretty quickly!

From the top post, each thread runs down (1), up (2), and down (3) again through the 90° bent thread guide bar. Don't wrap the thread around the front of the bar - just down, up, down as if it were a dolphin jumping out of the water. The thread then goes around the posts of the tension discs (4) and then makes a sharp bend around a small guide post (5). After the small guide post, each thread enters its own channel (6) where the take-up spring is located. Just after this, the threads bend around a guide bar (7), around another guide bar (8), then each thread passes through its respective eye located at the end of the take-up arm (9) - (left thread through the upper eye). After that, through a guide loop (10), then through the needle bar (11), then through the needle eyes (12). Many machines have an additional guide loop between (10) and (11).

The proper way to orient and thread the needles is crudely shown at right in the image above. The needles (usually 135x7 or 135x17) will have an indentation on one side and a long, narrow groove running up the opposite side. The long groove should face towards the inside of the needle (this groove is where the thread is pushed into when the needle passes through the material being sewn), and the indentation should face towards the outside. This indentation is where the point of the hook will pass by to pick up the top threads. If the indentation is not in that position, the hook may strike the needle, definitely breaking the thread, and perhaps even shattering the needle. The threads need to go through the needle eyelets from the inside to the outside. The thread passes through the needle exactly perpendicular to the sewing direction (though the quick sketch doesn't show this properly because of perspective).

If you're a perfectionist like me, you'll want to pull the end of the threads through their respective openings in the presser foot before sewing. Grabbing hold of the ends of the spare thread and holding slight tension as you begin a seam ensures the loose threads are kept from being drawn into the stitching. Some machines are a little finicky and demand that slight tension be held on these loose ends, or they get sucked under and tangled in the bobbin case. Not a fun mess to clean up. So, get into the good habit of grabbing your loose threads and pulling at the beginning of each seam and you'll probably never have this problem.

Most balloon construction applications will necessitate the use of spun multifilament bonded polyester thread in either Size 69 or 92.  Size 69 is lighter, 92 is heavier. Most balloon manufacturers use size 69, one I know of uses 92. FireFly uses 46, which is even lighter. The tensile strength of Size 92 thread is 14.5 lbs compared to 69's 10.9 lbs.

Thread comes on one-pound spools. The Juki LH-512 and LH-515 prefer one spool RIGHT TWIST (aka reverse twist) and one LEFT TWIST (the standard variety). The Right Twist is used in the LEFT needle. Singer 212's seem to get along fine with the same thread configuration, though left twist in both needles is what the manual actually specifies.

Needle size: Size 18/110 needles for 69 thread, 20/125 (sometimes known as 20/120) for 92 thread.

Bobbins: If you are only doing small projects, wind your own bobbins. Your machine should have a few spares. If you are building a balloon, airship, or other large project that requires continuous sweatshop-like conditions, you may have the patience to wind your own bobbins, but I certainly don't. I buy prewound bobbins - Size "G". The price was around $40 per box (144 bobbins) last time I ordered. Two boxes will last through the construction of a typical 140-sized envelope. It's considerably more expensive than thread on the spool, but it's well worth the extra for the convenience factor, and the pre-wound bobbins are typically wound tighter than home-spun and thus will sew a little farther.


A Friendly Admonishment Regarding First-Timers' Ill-Founded Fear of More Complex Designs

Let me apologize in advance if this section sounds "angry," because I am!

A lot of first-time balloon builders exhibit a phenomenon which baffles me. I've heard more prospective builders tell me that for their "first balloon," they are going to stick with a "simple color pattern," or perhaps cut the panels the "easy way," rather than pushing their creative forces to the limit and conjuring up a really striking design and refined construction method right off the bat. Why do these folks consciously impose unnecessary, illogical mental limitations on their projects?

I believe there is definitely a fear of the unknown coming into play which tends to stifle the imagination. It leads first-time balloon builders to make technical and aesthetic compromises which deviate from their initial vision, simply in order to guarantee an easy, well-proven construction workflow. What's funny is that there may never be that second balloon, since the first one will prove so enjoyable to fly that the desire to build a successor evaporates! While building balloons certainly can be an addiction (affliction?) which leads many first-timers back to build more balloons, I'm still baffled why someone would consciously limit their creativity, even on their very first balloon, in order to save just a smidgen of labor during construction. It's a labor of love - love the labor!

You're probably going to be flying this balloon for a very long time... Choose your design or color pattern wisely, and make it unique and memorable. Don't be of the nearsighted mindset that a simpler pattern will be that much easier to build than something that involves some extra cuts, some complex curvature, or some added diligence in making sure you don't sew the wrong panels together. Make the construction a masterpiece in all areas. You are challenging yourself to create something altogether new, from scratch - make it amazing.

In the grand scheme of things, the complexity of your chosen color pattern or panel contours and cuts will have fairly little effect on how much actual work is involved in the whole project. Treat the build process as though you'll be stuck with the balloon forever, and plan accordingly to make it the best damned balloon that you can.

Worried about getting lost in a pile of fabric or sewing the wrong things together? Make a map/diagram of the entire balloon, panel by panel, refer to it constantly, label all panels, and always check the pieces before you begin a seam. Don't skimp out on the little construction details (I didn't install the parachute velcro on my first envelope until nearly a season later!), and take the care to sew everything right the first time rather than have to drag it back inside later on when stitching comes undone because it wasn't back-tacked or sewn heavily enough.

For a first time hot air balloon construction project, don't underestimate your skills and expertise going into the build. You may have never built a balloon before, but by the time you get around to finally sewing the first real pieces of it, you will have considerably more skill at sewing than you'd think. Practice a lot on scraps, practice some more, and only when your sewing is consistently good should you begin on the balloon itself.

Your sewing skills will increase exponentially once you start working with the actual fabric your balloon will be built from. For someone who hasn't built a balloon before, I recommend starting off sewing stuff that will not actually be part of the balloon, but will approximate the type of construction that you will be using. For instance, cut a bunch (maybe 10-20) of 60"x6" rectangular strips of lightweight silicone nylon and then sew them into two equally long pieces by connecting all the short sides together first with folded fell seams. Then go back and sew down the middle of the two long pieces and see what it takes to make all the horizontal rows line up properly. If you're up for a challenge, lay down the load tape at the same time as you fold the seam. This is excellent practice that doesn't waste very much fabric. It's good to master this first rather than only improving your skills as you progress on construction of your balloon.



A brief visual explanation of Bulbous / Lobular Gore Envelopes versus their flat panel counterparts:

bulbous gore hot air balloon panel patterns

Here we see a rough representation of the flattened panel patterns of a lofted bulbous gore envelope. Compare the heights of the centers of each panel to the heights of the sides. The side edges of the panels near the equator are shorter in height than those near the crown and mouth. This corresponds to the degree of "corpulence" desired in the gore at that point.


This view shows blue panel outlines of a properly-lofted bulbous gore envelope, overlaid onto flat panels which are the representative geometry of a theoretical flat envelope with the same number of gores and panel heights (the gray panels are trapezoidal). One might try trimming the corners of these panels to approximate a bulbous envelope, but take note that the proper panel dimensions are wider than the flat panels allow one to start with!

If you're planning to build a semi- or fully-bulbous envelope, it is wise to determine the dimensions of the proper lofted patterns before any fabric is cut, rather than after the rough trapezoidal panels are cut.


In this diagram, load tapes are shown as the red curves. The blue curves show the center of the gores. Note that the blue lines are the same length, but the path of the load tape is shortened considerably in the bulbous gore envelope at right. This allows the load to be properly aligned along the load tape.

On the flat-paneled envelope at left, most of the load is transferred directly to the fabric in the lower panels which are directly adjacent to the cable/webbing interface at the mouth. The path of the load is parallel to the blue line in the flat panel envelope, but begins at the corner where the red line intersects the mouth. Two separate concentrations of vertical stress begin at each cable attachment point, often causing long vertical wrinkles to appear in envelopes constructed with this style.


One can lose a lot of volume when trimming the panels of a flat envelope to replicate a bulbous gore envelope. Beware!

Another quite dangerous aesthetic hazard of trimming trapezoidal panels to approximate a bulbous gore is the high likelihood of the gore "peaking" if one trims even slightly less than the ideal curve (this "peaking" is not shown here). Rather than ending up with a perfectly rounded gore as viewed from above, the center of the gore might jut out with a relatively sharp angle at the center. Computer-lofted patterns eliminate this possibility.



Owner-Produced Parts in Certificated Aircraft

For many older "legacy" aircraft (those which are no longer manufactured or supported by an existing manufacturer), replacement parts may be unavailable from any current source. There is a way for owners to have parts constructed for their aircraft by a certificated repair station. This article in Sport Aviation magazine explains it in detail.

Owner-Produced Parts: Click Here For Article (Click the link to Page 100 in table of contents)

Another excellent article in FAAAviationNews July-Aug 2002 issue.


Fabric Usage Estimates:

These figures are the minimum yardage required to construct a flat to semi-bulbous gore natural shape hot air balloon envelope using 60" wide fabric, horizontal panel cuts, assuming minimal cutting wastage. You will certainly want to buy more than these amounts.

15,000 cu. ft. = 220 yards
25,000 cu. ft. = 330 yards
31,000 cu. ft. = 380 yards
35,000 cu. ft. = 410 yards
42,000 cu. ft. = 430 yards

FAI AX-Sizes:

(upper limit of class shown)

Class: Volume (cu. meters) Volume (cu. feet)
AX-1 250 8828
AX-2 400 14125
AX-3 600 21188
AX-4 900 31783
AX-5 1200 42377
AX-6 1600 56503
AX-7 2200 77692
AX-8 3000 105944
AX-9 4000 141259
AX-10 6000 211888
AX-11 9000 317832
AX-12 12000 423776
AX-13 16000 565035
AX-14 22000 776923
AX-15 above 22000 above 776923


Type Certificated
Balloon Manufacturers
Data Reference

Please email with any corrections or updates


  Volume Lift (#)
Little Devil
34,000 610 (?)
Little Devil Stretch
39,000 700
A50S 56,000 1250
(KFC Chicken)
62,000 1250 (?)
A55 77,000 1500
A55S 83,000 1500
A60S 105,000 2000
Air Bus
125,000 2000



  Volume Lift (#) Gores
S-40A 31,000 800 16
S-49A 54,000 1100 16
S-50A 56,000 1400 20
S-51A 62,500 1275 16
S-52A 65,000 1400 16 or 20
S-53A 69,000 1275 16
S-53H 69,000 1275 16
S-55A 77,500 1435 24
S-57A 90,000 1650 24
S-57H 90,000 1650 24
S-57S 90,000 1650 40
S-60A 105,400 1800 24
S-60H 105,400 1800 24
S-60S 105,400 1800 40
S-64A 126,500 2225 24
S-66A 141,000 2500 24
S-71A 175,000 2650 24
S-77A 211,000 3450 28
S-81A 245,000 3800 28
RX-6 56,000 1430 12
RX-7 77,500 1480 12
RX-8 90,000 1650 14
RXS-8 105,400 2000 14
RX-9 126,500 2225 14


Type Certificated Special Shapes
  Volume Lift (#)

Alpo Dog Food Can


Paint Can


Drinks Can

77,500 1400

Drinks Can


Noah's Ark

175,000 (?) 1670

Shopping Bag

110,000 (?) 1700

Magellan T. Bear

127,000 (?) 1900

BrainLAB Brain

(?) 2500

Cologne Bottle

110,000 1550

Energizer Bunny

180,000 2100

Birthday Cake

141,000 2100

Cell Phone

(?) 1500

Eat 'N Park Cookie

110,000 1650

Chili Ristra

145,000 (Cactus)
0,000 (Ristra)


Miss Daisy

200,000 2250

Epcot Center

(?) 2000

Re/Max Soaring Home
Old MacDonald's Barn

136,000 (?) 2000

Popcorn Bag

100,000 (?) 1700

Mr. Peanut

180,000 (?) 1650

Smokey Bear

120,000 1560

Snowman (Mr. Winter)

120,000 1600

Pumpkin (Mr. Autumn)

100,000 (?) 1500

Sunny Boy

141,000 1650
Light Bulb
100,000 (?) 1200
Box Truck

80,000 (?)



  Volume Lift (#) Gores
Sparrow 42,000 700 16
Falcon II 60,000 830 20
Skyhawk 80,000 1200 20
Turbo 8 105,000 1800 24
Magnum IX 140,000 2500 24
Magnum IX-XL 158,500 2500 28


  Volume Lift (#) Gores
A-105 105,000 2100 20
A-120 120,000 2400 20
A-140 140,000 2800 20
A-160 160,000 3200 20
A-180 180,000 3600 20
A-210 210,000 4200 20
A-250 250,000 5000 20
A-275 275,000 5500 20
A-300 300,000 6000 20
A-315 315,000 6300 20
A-400 400,000 8000 20
C-60 60,000 1200 12
C-80 80,000 1600 12
C-100 100,000 2000 16
M-34 34,000 680 16
N-31 31,500 620 24
N-42 42,000 840 24
N-56 56,000 1120 24
N-65 65,000 1300 24
N-70 70,000 1400 24
N-77 77,500 1540 24
N-90 90,000 1800 24
N-90S 90,000 1800 24
N-100 100,000 2000 24
N-105 105,000 2100 24
N-120 120,000 2400 24
N-133 133,000 2660 24
N-145 145,000 2900 24
N-160 160,000 3200 24
N-180 180,000 3600 24
N-210 210,000 4200 24
O-31 31,000 620 12
O-42 42,000 840 12
O-56 56,000 1120 12
O-65 65,000 1300 12
O-70 70,000 1400 12
O-77 77,500 1540 12
O-84 84,000 1680 12
O-90 90,000 1800 12
O-105 105,000 2100 12
O-120 120,000 2400 12
O-140 140,000 2800 12
O-160 160,000 3200 12
V-31 31,000 620 8
V-42 42,000 840 8
V-56 56,000 1120 8
V-65 65,000 1300 8
V-77 77,500 1540 8
V-90 90,000 1800 8
Z-31 31,000 620 24
Z-42 42,000 840 24
Z-60 60,000 1200 24
Z-65 65,000 1300 24
Z-69 69,000 1380 24
Z-70 70,000 1400 24
Z-77 77,500 1540 24
Z-90 90,000 1800 24
Z-105 105,000 2100 24
Z-120 120,000 2400 24
Z-133 133,000 2660 24
Z-140 140,000 2800 24
Z-145 145,000 2900 24
Z-150 150,000 3000 24
Z-160 160,000 3200 24
Z-180 180,000 3600 24
Z-210 210,000 4200 24
Z-225 225,000 4500 24
Z-250 250,000 5000 24
ZL-56 56,000 1120 24
ZL-60 60,000 1200 24
ZL-65 65,000 1300 24
ZL-70 70,000 1400 24
ZL-77 77,000 1540 24
ZL-84 84,000 1680 24


Type Certificated Special Shapes
  Volume Lift (#)

Bacardi Mixers Cup

(100,000 lifting volume)

American (Car) Battery

(81,300 lifting volume)

Budweiser Select 55 Bottle

(105,000 lifting volume)

Burger King Whopper

(59,400 lifting volume)

Kodak Film Canister
Maxwell House Coffee Can

77,500 1540

Ray-O-Vac Battery
Iron City Light Beer Can
Pepsi Supercan

90,000 1800

Champagne Bottle

90,000 1800

Winston Cigarette Pack

(89,000 lifting volume)

Ben & Jerry's Ice Cream

(105,000 lifting volume)

Cuervo Tequila Bottle

(110,000 lifting volume)

Donald Duck

(90,000 lifting volume)

American Bald Eagle

(110,000 lifting volume)

Early Times Bottle

(77,500 lifting volume)

Gas Flame

92,600 1852

Kotenco / Matenco
a.k.a. "Jim & Betty

(90,000 lifting volume)

Jack Daniel's
Lynchburg Lemonade

(90,000 lifting volume)

IWI the Kiwi

(90,000 lifting volume)

Energy One Light Bulb

(100,000 lifting volume)

Mickey Mouse

90,000 1800

Birthday Mickey Mouse

(90,000 lifting volume)

ViewSonic Monitor

(80,000 lifting volume)

AOL Monitor

(105,000 lifting volume)

Mr. Potato Head /
Bud E. Beaver

(95,000 lifting volume)

Polar Bear

(90,000 lifting volume)

Pepe the Penguin

(77,000 lifting volume)

Miss Penny / Lil' Buck

(90,000 lifting volume)

Famous Footwear

(90,000 lifting volume)

Space Shuttle

(90,000 lifting volume)

84 Lumber Golf Ball

90,000 1800

Greenpeace Earth
Angry Bird

101,000 2020

Wells Fargo Stagecoach

(110,000 lifting volume)

Herring Gas Tank
"C3 Gasser"

100,000 2000

Uniroyal Tire

(100,000 lifting volume)


  Volume Lift (#) Gores
5 42,000 870 12
6B 56,000 1050 12
6B-15 56,000 1200 12
6 56,000 (?) 1050 12
7B 65,000 1050 12
7B-15 65,000 1300 12
7 77,000 1660 18
7-15 77,000 1750 18
8B 90,000 1660 18
8B-15 90,000 1900 18
8 105,000 2450 24
8-24 105,000 2020 24
9B-15 120,000 2800 24
9 140,000 3285 36
10 180,000 3600 36
11B 210,000 3600 36
11 240,000 3940 36
12B 280,000 3940 36


Type Certificated Special Shapes
  Volume Lift (#)
Bottle (?) 1660

Little Old Lady/Shoe

127,000 (?) 2000


(?) 2140

Coors Light Can (?)
Yellow Condom (?)

77,000 1150
KFC Bucket
65,000 1150
Box Truck
(77,000 lifting capacity)
C8 105,000 (?) 2000
8B Sphere
Bank of American Fork
Piggy Bank
90,000 1900
8 Cube 105,000 (?) 2000
TV-180 180,000 (?) 2800


30-AL 30,000 cu. ft.
Model T 53,000 cu. ft.
Challenger 75,750 cu. ft.
TC-4 91,000 cu. ft.
TC-4A 91,000 (?)
AX-10 (? - non-TC'd)
Mark V 56,000 cu. ft.



All content and images copyright ©2000- Jon Radowski unless otherwise noted. All rights reserved.