Planning & Designing Your Custom Hot Air Balloon
A hot air balloon is an incredibly personal representation of style, personality, image, performance and more. Deciding what your own balloon should become can involve limitless design possibilities - it can be as simple or complex as desired. Not sure where to start? Not surprising! This custom balloon-designing primer will help explain many of the options, choices and design considerations involved in creating an aerial work of art that will fulfill your ultimate vision and provide many years of enjoyment, satisfaction and safe flying.
Build Options - Complete, Kit-Built, or Plans
Apex Balloons can deliver fully-constructed balloons, pre-cut kits which consist of plans and all materials, or construction plans which consist of patterns and detailed instructions for every step of the way. Special shape balloons are also available fully-constructed, as pre-cut kits, or in plan form, though we only recommend the latter options for experienced balloon homebuilders.
We offer the option of sharing the construction labor with helpers at our shop in Elverson, PA (i.e. "balloon camp" style), so we're open to suggestions if that's an approach you'd like to consider. We can also travel to your location to help on-scene if you've got a suitable workspace and the timing is right.
To begin with, what is the preferred envelope style that you might want? A design that is similar in appearance to one of the mainstream manufacturers' models might serve as a reasonable starting point - but feel free to customize to your heart's extent. We can certainly build to match any style of envelope that's out there, but we specialize in new designs of all varieties. You cook it up, and we can probably make it happen - even if it's very unique, a little oddball, or even close to full-blown crazy. Check out the 3-gore design below!
You should consider the number of gores you'd probably like (8, 12, 16, 18 & 24 are common numbers of gores), the shape of the gore (bulbous, semi-smooth, or flat to any degree), and the orientation of the different panels comprising each gore (horizontal, vertical or diagonal). We can quickly draft a 3D rendering of what the balloon will look like based on your design preferences and color/artwork choices.
Envelope Sizing & Intended Use
The most important consideration - apart from what your balloon will look like - is what you plan to do with it. It makes no sense to decide on a 56,000 cubic foot envelope and then later realize you wished you could be able to fly pilot plus two heavy passengers at all times of the year and temperature ranges. In the warmer months, that objective would be difficult to accomplish in a balloon that small without overheating.
You should put thought into at least the following considerations:
Certainly, the larger an envelope is for a given payload, the cooler it will generally fly, the longer the flight duration will be, and the longer the fabric itself will last. It's always better to have a surplus of lift rather than risking overheating the envelope when it gets warm out. An envelope flown at 225°F or less will tend to last longer than one flown constantly close to 250°F. 200-220°F is a good target range to stay within for the best combination of longevity and flight handling characteristics. Fuel economy increases at lower internal temperatures.
Temperature and flight altitude are the two most important factors in determining payload for any given envelope volume. Here is a handy spreadsheet (MS Excel format) that can help you determine rough payload calculations based on ambient temperature, altitude above sea level and internal envelope temperature. In this spreadsheet, you can change envelope volume, ambient temperature, and flight altitude. Important - Press F9 to recalculate the lift figures after making any changes to the variables.
A good exercise to use with the spreadsheet above is to calculate the lift of a given volume based on an altitude of 10,000 feet MSL at different ambient temperatures. This will make an allowance for a 5,000 feet climb above ground level when flying at high elevations such as Albuquerque, New Mexico. For the most part, you will often be flying closer to the ground than this, but it's good to see how a given envelope volume will handle under this extreme set of circumstances.
In general, a good rule of thumb to follow is that 1000 cubic feet of hot air will create 16 pounds of lift. In the real world, this figure will certainly differ due to ambient and envelope internal temperature as well as altitude above sea level, but it's a conservative rule of thumb to estimate the gross lift of any given envelope volume at average internal flying temperatures. This allows for a good margin of free lift available beyond the calculated gross weight, which may be important in situations where the balloon is flying hot, heavily loaded, and in situations where a rapid ascent may be required to clear obstacles.
Most balloon manufacturers calculate the gross weight of their balloon envelopes based on a figure of 16 pounds per 1000 cubic feet, but some have chosen to certificate their balloons at a higher gross weight using a figure of 20 pounds per 1000 cubic feet.
Here is a table of common envelope volumes for a given number of occupants:
If you are unsure of the volume you should be considering for a certain set of variables, contact us for assistance. We'll be glad to help you figure out the right size envelope for your mission.
Artwork & Designs
Any type of artwork or logos can be integrated into the design of your envelope, whether inlaid or overlaid (appliqué). Inlaid cuts of any angle, curvature or complexity can be added to change fabric colors within any panel at any location in the envelope.
Painting directly on the fabric is sometimes useful for smaller accents, and is a technique often used to add detail to special shapes (quite notably, the realistic feathers on the American Bald Eagle were airbrushed on). Silicone coated fabrics are not usually receptive to fabric paints, but the typical 1.9oz. urethane coated nylon is an excellent base fabric.
Types of Fabric
Most standard factory-built balloons are constructed from a coated ripstop nylon fabric that weighs approximately 1.9 ounces per square yard (from here on, referred to simply in "ounces"). 70 denier is the weight of the nylon yarn that this type of fabric is woven from. Urethane or silicone are the two most commonly used coating materials. Silicone-coated fabric tends to last longer than urethane, but is inherently more difficult to work with as it has a much more "slippery" feel.
There are two types of lightweight fabric options available - a coated and uncoated variation of the same base fabric, woven from 30 denier nylon yarn. These lightweight ripstop nylons are spin-offs from the parachute industry and have been well-proven in hot air balloons for nearly 20 years. The lifespan is generally less than that of standard weight (70 denier) balloon fabric, but the savings in weight, easier handling, and extra payload makes up for a slightly shortened lifespan. 300 hours is a reasonable estimate of envelope life using these lightweight fabrics at average flight temperatures.
The uncoated material is a 1.1 ounce, calendared ripstop nylon fabric known in the parachute industry as "Exactachute." It is less than half the weight of typical hot air balloon fabric. "Exactachute" is marketed as a low-porosity fabric with a reading of less than 10CFM (cubic feet per minute) when new. There is no coating, but the fabric is made less porous by the calendaring process. Calendaring involves feeding the woven nylon fabric through high-pressure, high-temperature rollers which flatten the fabric and tighten up the weave. Over time and with handling, the fabric will become more porous than when new, but when used in the bottom portion of a hot air balloon envelope it generally does not affect fuel consumption to a significant degree. Some homebuilders have built entire envelopes from this fabric, but most often it is only used in the lower half of an envelope due to its tendency to become more porous over time.
The coated variation of this lightweight material is referred to in the parachute industry as "Soar-Coat." It is the same 1.1 ounce ripstop nylon base fabric with a silicone coating that brings the finished weight to 1.3 ounces. There is zero porosity throughout the lifetime of this fabric - the fabric strength will typically fall below the required minimums before porosity will ever become an issue. This silicone coated nylon is the most common fabric used in lightweight Experimental balloons, and at one time even Cameron and Aerostar both offered this type of fabric as a weight-saving option on their standard, type-certificated hot air balloons.
A 42,000 cu. ft. envelope constructed entirely of 1.3oz. silicone-coated ripstop nylon will weigh about 70lbs. Add about 8-12lbs. for a full Nomex first panel and scoop (6oz., normal heavy Nomex). One can save more weight by building the bottom 1/3 to 1/2 of uncoated 1.1oz. calendared fabric, which also offers the benefit of making packup much easier and allows the envelope to compress better in the bag for travel. In a 42,000, I'd suggest that one may save up to 8-10lbs. by using uncoated fabric in the bottom.
First vs. Second Quality Fabric
Depending on your budget and desires, you may want to save a little bit of money and use "second quality" fabric, especially if you plan to have a number of different colors in the envelope. One can typically cut the price of fabric in half by using second quality instead of first.
The difference is more fiscal than physical in most cases, as second quality can be just as acceptable and safe for use in Experimental and Ultralight balloons as first quality is. There is often no structural difference, but second quality fabric is characterized by minor flaws in the weaving, dyeing or coating process. These may be in the form of small areas on the fabric where the yarn may have bunched up during weaving, or areas where the coating may not have been spread properly. If a 100-yard roll of fabric has more than a few such minor flaws, it is usually labeled as "seconds." Sometimes the flaws are marked by small stickers or tags for easy spotting, but most often not. In any case, it's easy to see where the fabric imperfections lie by using a fluorescent light to backlight the fabric as it is unrolled for inspection before cutting.
When building balloons constructed of horizontal gore panels, it's easy to cut around the flaws and use only the good fabric on the roll. There's usually a slightly higher percentage of wasted fabric because of this, but it is much less than what would be wasted with a vertically-cut gore design where many yards of fabric might potentially be wasted if there are unwanted flaws in the middle of where a long gore panel would lay.
It is occasionally the case that entire dyelots of fabric (numerous 100-yard rolls) might be dyed improperly for a custom color run and thus become "seconds." This fabric is perfect other than the color being substantially different from what the individual customer ordered. This type of second quality classification is what we always hope for!
With second-quality fabric, color matching between rolls is not necessarily guaranteed. Some designs (i.e. unbroken solid colors) are simply not meant to be sourced from second quality fabric unless it can be absolutely guaranteed that all the rolls of each color came from the same dyelot. If your non-matching colors are separated by at least one panel of a different color, nobody will notice. As an example, the two halves of the nail appendages on "Nailed!" were cut from two rolls of gray 1.3oz. silicone fabric from different dyelots. The casual observer will never notice the slight difference in the shade of gray because of the large separation between the two appendages.
Typical Envelope Pricing
The price for a custom hot air balloon will vary considerably depending on the design of the envelope, the many options involved, and the materials chosen. Because of this, all custom-designed balloons are quoted on a singular basis whether fully-constructed, in kit form, or as a set of easy-to-follow construction plans.
The style of envelope design, number of gores, options such as turning vents, Nomex, skirt/scoop, inlaid or overlaid artwork, etc. factors greatly in the determination of the cost. A more solid price can be zeroed in on with some input as to your envelope style / design preference and desired options. Contact us for a quote.
A rough estimate of a new lightweight 77 envelope constructed of first-quality 1.3oz silicone coated ripstop nylon would be in the ballpark of $9,000 complete. A 90 would be right around $10,000. For a precut "kit" build option for a 77 envelope, the price would be around $6,000, cut out and ready to sew with detailed construction plans included. Custom plan packages are typically priced at $500 regardless of envelope size unless it's necessary to go overboard with unique design considerations.
Options such as Nomex or artwork would be extra and added "at cost" to the rough base prices above. For durability, we recommend a Nomex first panel and scoop, or at least 1.9oz (standard weight) fabric. A direct-pull or 2:1 pulley-assisted parachute vent is standard, but other types of rapid deflation vents can be installed at minimal additional cost.
More to come. Stay tuned!
Please contact us with any requirements or design suggestions you may have.
All content and images ©2000-2012 Jon Radowski unless otherwise noted. All rights reserved.