Read all about how a special shape hot air balloon comes to life in our latest blog written by ex VABC creative director Mark Lockwood, who has designed many classic shapes himself such as Action Man, the Tesco trolley and Cadbury's caramel bunny. It's not as easy as you might think...
When asked if I could write something about how to design a special shape balloon, my first thought was that this would be like asking “How long is a piece of string?” as there is no hard and fast rules, but when I thought about it a little more, I realised there are some basic tenets that need to be followed to create something eye-catching and, most importantly, flyable. Another problem is that there is a danger it can get very technical because the engineering involved covers everything from thermal and fluid dynamics to complex load and stress calculations.
By definition, a special shaped balloon diverges from the standard inverted teardrop in some way or another and falls into the categories of either a standard balloon with add-ons, such as the Son of the Pink Panther, or a free-form like The Cadburys Caramel Bunny and many of the popular product replicas and characters. So what actually goes into the process of designing one? This is going to depend upon whether you are designing it for everyday commercial use or as a once in a while, with lots of willing helpers, private indulgence. Muir Moffat’s Scottish piper is an example as are the amazing collection of shapes commissioned and flown by the late Malcolm Forbes. Due to the cost of construction compared to its standard brethren, the majority over the years have been designed as giant flying advertising billboards and funded from corporate coffers rather than by individuals with very deep pockets. If you want to stand out in a crowd of ordinary balloons at an event or make a super-sized brand statement, then a special shape is just the tool to do the job, but be prepared to work very, very hard!
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Quite often a designer will just take an image of a product or an object and stick a basket underneath it without considering how it would be built or even what it might look like from another angle. Over the years we learned many sometimes expensive lessons when it came to making mistakes and these have led to the process being much more exact and fault free these days. With current CAD techniques, it is possible to calculate the exact panel shapes required to create a three dimensional object, including all the inner support panels and baffles to hold it together and these go directly to a computer controlled cutting table. The giant jigsaw puzzle that emerges still needs to be carefully sewn together by hand using miles of thread and the skilled eyes and hands of a seamstress.
So, let’s start with the standard balloon. Form follows function here because the shape of the balloon envelope is designed to capture the maximum volume of hot air where it is most efficient at creating lift: at the top. This puts the least stress on the fabric and structure and also safely supports the basket, burners, fuel and passengers. That bubble of hot air is fed from the burners, a little like a mini thermal rising from the ground, and heats the air at the top, slowly cooling and then falling back down the inner sides of the balloon to be re- heated and shoot to the top again. This hot air has a slightly higher pressure however is less dense than the air outside the balloon, which is the basic principle of why it rises and how we are able to fly.
 Diagram of dynamic heat distribution - standard balloon |  Cutaway diagram of a simple 'Can' shape balloon |
The individual fabric panels of a balloon are all held together with tough nylon straps (Load Tapes) that run from the top of the envelope to the mouth to create a super strong net to support the basket. If we make a hole in one of the panels, the hot air will escape but not affect the integral ‘skeleton’ of these load tapes. Creating a ‘blister’ where the hole is, the escaping hot air will inflate it and thus we have our add-on shape. If we also extend the distance from the bottom of the balloon envelope, this colder air filled section can also be a part of the structure. This is the way the first special shape, The Robertson’s Golly, was designed.
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Some examples of add-on special shapes; Radio 1 DJ, Mercury and Son of the Pink Panther
Once you step away from the familiar tear-drop shape, things can get a little more complex. The formula is quite simple, the volume inside whatever the shape must be sufficient to provide lift for the weight of all the fabric and the basket and fuel. The simplest solution is therefore to try and incorporate the internal skeletal structure of a standard balloon if possible, even if it is just the load tapes and all the rest of the shape is just made up of fabric panels. Simple shapes like cans, bottles, jars, balls all use this principle as they are what we call ‘axi-symmetrical’ and can be rotated around a central vertical axis. The recent development of Racer balloons, which are more ‘rugby ball’ shaped, gives a little more flexibility for the designer to incorporate that into a shape as well.
 Churchill, built from a round balloon with add-ons |  G-SATL sphere special shape |  Budweiser beer can special shape |
When it goes completely ‘off the park’ is when there is a shape that does not seem to have a natural balloon space to fit inside. Here is where the engineers get involved as it is necessary to calculate the amounts of load created by each part of the balloon on the integrity of the whole structure. If there is too much force or strain in any one direction, this causes a weakness and can cause a catastrophic failure, which is not good. Once again the whole thing comes down to making sure there are smooth lines of load carrying from the top of the balloon to the basket as well as trying to hold the external shape together. By cutting the fabric panels in the right way, like making a sculpture, the shape will support itself but careful consideration has to be given to any un-even stress. As the pressure is from the inside, it’s possible to support the outer fabric layer with baffles and formers but the flow of hot air into any appendages needs careful calculation. Anything below the equator will need to have ways to trap the air inside as it cools.
This then creates another operational issue of how to get the air back out again when the balloon lands. Once on the ground, any wind will cause the envelope to continue dragging until sufficient hot air has been released so the use of ‘one shot’, Velcro sealed rip panels has been developed. Often these are positioned in the hottest, and therefore highest load, areas of the envelope and need to be carefully closed and locked with a breakable cotton thread before flight. When the pilot has committed to a landing, they are armed with a sharp tug on a rope and then pulled open to allow as much air out as possible in the shortest time.
Smaller non structural Velcro sealed openings are then included in the various appendages to aid the deflation once the balloon has finally come to rest and then comes the long and hard work of returning the balloon envelope into its bag. Because of the size and the additional amounts of material used, special shapes tend to be much heavier than their standard counterparts. A standard 90,000 cubic foot envelope weighs around 70 kilos, a simple shape of the same volume can weigh up to 250kgs.
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As a designer, the process starts with looking at the product or shape to be promoted and then trying to work out if a balloon structure can be fitted inside it. If that is possible then we can move on to looking at the various angles the final design will be seen from and where the main branding will need to be placed. From a commercial perspective it is also essential at this point to look at the operational efficiency of the shape. How will it react in the wind when tethered? How easy will it be to fly and, most particularly, land? How many crew will be needed bearing in mind how heavy it may be and what vehicle and trailer will it fit into?
If there is no obvious shape solution, the next stage is to try and find a way to integrate the product into a viable option. An example here is the Bic Chick. The product itself, the Soft Feel pen, was not a viable shape on its own as it would be too thin to provide enough volume for lift. By using the chick character from the TV advertising that was running at the time as the main part of the balloon and building in the pen, it solved both the operational problem and maximised the branding options for the client. The wireframe designs show how the various parts of the structure fit together as well as much of the inner baffles required to keep the lower part pressurised.
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The Bic chick special shape and wireframe design images
Once you have your special shape, do you need any special qualifications to fly it? Once in the air they fly in exactly the same way as a standard balloon but with little individual idiosyncrasies. There is a tendency to rotate on climb and descent, which can mean having to move around the basket a lot to make sure you can see where you are going and some have bits hanging down below the burner so you need to keep an eye on these. Being heavier than normal balloons, they can cool and descend much faster and some have the unnerving habit of reacting very slowly on cooling at first and then suddenly dropping out of the sky! The biggest thing you need is experience. As the majority are advertising a product, a commercial balloon pilots license is needed with lots of flying hours and even more tethering as they spend more time static displaying than free flying.
This experience counts when it comes to making the decision to fly based on the weather conditions as the inflation, launch and landing are those needing ‘positive decision making’. The reward is often the reaction of a crowd or an individual landowner when a giant character or product appears in their field.
Next time you see one of these giant flying sculptures, think of the skills of the people needed to make it possible from the designers concept through to the engineers, the seamstresses, the artists adding the painted details and finally the pilots and incredibly hard working crews who make it all possible.
Read more about special shape balloons
You can discover lots more about the world of special shape hot air balloons on MJ Ballooning by visiting our Bristol special shapes page, blogs and watching our videos on YouTube.
Thanks to Ballooning Pictures UK for providing some of the older photos - G-BUNI, G-SEGA & G-BVWI, G-OIFM, G-PINX, G-BYEI.