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How Hot Air Balloons work If you actually need to get somewhere specific a hot air balloon is a fairly impractical mode of transport. You cannnot really steer it with accuracy and it travels with, and as quickly or slowly as the wind blows. However if you simply want to enjoy the experience of flying there is nothing quite like it with no sensation of motion or wind. Most people who have experienced it describe flying in a hot air balloon as one of the most serene, enjoyable activities they have ever taken part in.
Hot air balloons work on a very basic scientific principle: warm air rises in cooler air. Essentially, hot air is lighter than cool air, because it has less mass per unit of volume. A cubic foot of air weighs roughly 28 grams (about an ounce). If you heat that air by 100 degrees F, it weighs about 7 grams less. Therefore, each cubic foot of air contained in a hot air balloon can lift about 7 grams. That's not much, and this is why hot air balloons are so huge - to lift 450 kilograms you need about 65,000 cubic feet of hot air! A detailed load calculation is carried out before each flight, taking into account the variable of the external ambient temperature. Our largest balloon has a volume of 250,000 cubic feet and a lifting capacity of almost 2000 kg or almost 2 tons.
To keep the balloon rising, the air contained within the envelope has to be intermitently reheated. Hot air balloons do this with a burner positioned under the balloon envelope. As the air in the envelope cools the pilot reheats it by firing the burner otherwise the balloon will start to descend at a rate up to approximately 1000 feet per minute after levelling out. This is the basis of lighter than air flight. The internal air temperature at the top, or crown, of the balloon in level flight is approximately 100 -110 degrees centigrade. It is remarkable to contemplate that this temperature - the boiling point of water - is not causing any damage to the ripstop nylon envelope.
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| A hot air balloon has three essential components: the burners which heat the air; the envelope which holds the air; the basket which carries the passengers.
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THE BURNERS
Modern hot air balloon burners heat the air by burning LPG (liquified petrolium gas) generically known as propane or sometimes Calor, the name of the major supplier, which is stored in compressed liquid form in insulated stainless steel cylinders positioned in the balloon basket. The off-take is from the bottom of the cylinder in order that liquid gas, rather than vapour from the top of the cylinder, is drawn off. A small balloon operates with a single burner unit but larger passenger carrying craft may have up to four burners clustered over the centre of the basket. |
|  | Because the LPG is highly compressed in the cylinders it flows quickly through the hoses to the heating coil. The heating coil is simply a length of stainless steel tubing arranged in a coil around the burner. When the pilot fires up the burner the LPG flows out in liquid form and is ignited by a pilot light which is constantly alight during the flight. As the flame burns it heats up the metal in the surrounding tubing which in turn heats the LPG flowing through it. The vapourising process changes the LPG from a liquid to a gas, before it is ignited. This gas makes for a more powerful flame and more efficient fuel consumption.
This increased power and efficiency is at the price of some noise and during most stages of the flight, particularly when operating at low levels where disturbance at ground level could be an issue, 'whisper' burners are used which burn liquid propane direct and can be 'feathered' on and off as opposed to the sudden blast of the main burners. |
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THE ENVELOPE
In modern hot air balloons the envelope is constructed from long ripstop nylon gores, reinforced with sewn-in webbing. It is the webbing and not the nylon which supports the load. The gores, which extend from the base of the envelope to the crown, are made up of a number of smaller panels. Each panel edge is folded back on itself, interleaved with the next folded edge, and then all four thicknesses of fabric are sewn through twice by machine using a lock-stitch. Tailors call this a French felled seam and it's very strong.
Nylon works very well in balloons because it is lightweight, durable and has a high melting temperature. To maximise heat retention the nylon has a polyurethane coating applied and the upper portion of the envelope which is subjected to the maximum temperatures is usually made of a stronger, heavier and more closely woven ripstop with the trade name of Hyperlast. |
| | The lower panels of the envelope around the mouth are made of Nomex, a fire resistant cotton material which is also used for the scoop which helps direct the burner flame. |
| The hot air cannot escape from the mouth at the bottom of the envelope because buoyancy keeps it moving up. If the pilot continually fires the burners the balloon will continue to rise at rates of up to 800 feet per minute. There is an upper altitude limit, however, since eventually the air becomes so thin that the buoyancy force is too weak to lift the balloon. The buoyancy force is equal to the weight of air displaced by the balloon, so a larger balloon envelope will generally have a higher upper altitude limit than a smaller balloon. The current Altitude World Record for a hot air balloon is 68,986 feet!
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| | | Hot air balloons traditionally use a wicker basket constructed around a stainless steel tubular frame for the passenger compartment. Wicker works very well because it is sturdy, flexible and relatively lightweight. It also looks good. The flexibility helps with heavy landings, absorbing some of the energy and usually going back into shape.
Baskets can be open, where passengers, pilot and fuel tanks occupy the same space or partitioned as in the case of larger baskets providing a safer environment for landing and greater comfort during flight. |  |
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FLYING THE BALLOON
Flying a balloon takes skill and practice but the controls are actually very simple.
To make the balloon climb the pilot operates one or more blast valves on the burner unit. The greater the heat input, the quicker the rate of climb. Additionally burners have a whisper valve which allows liquid propane to bypass the heating coils thereby burning liquid propane instead of propane in gas form. Burning liquid propane produces a less efficient, weaker orange flame, but is much quieter than burning gas.
To initiate a descent the pilot can open the re-sealable parachute valve at the top of the envelope for a short period by pulling on a heat resistant Kevlar line which runs from the top of the envelope into the basket. When the pilot pulls the line some hot air escapes from the envelope which decreases the inner air temperature. This causes the balloon to slow its ascent and eventually go into a descent.
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| Essentially, these are the only controls - heat to make the balloon climb and venting to make it descend.
This raises an interesting question: If the pilot can only move the balloon up and down, how does he get from place to place? As it turns out, the balloon can move horizontally by changing vertical position, because wind blows in different directions at different altitudes. To move in a particular direction, the pilot climbs or descends to the appropriate level and uses the wind. Also as wind speed usually increases with height the pilot can to some extent control horizontal speed by changing altitude.
Of course even the most experienced pilot cannot have complete control over the balloon's flight path and you cannot really fly a hot air balloon along an exact course or return to your starting point. It is usually only in the particular Alpine winter valley conditions that the landing can sometimes be at the same point as take off. In flight navigation involves the use of 1:50,000 Ordnance Survey maps of the area and Aeronautical Charts. GPS systems provide an additional and increasingly accurate back up and answer the often raised question of 'how fast are we flying?'
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| For this reason the crew have to remain on the ground, staying in radio contact and having their own adventure, following the balloon by Land Rover with trailer to collect the passengers and equipment on landing. This can test their navigational skills when sight of the balloon is lost because the pilot has dropped down behind a hill or trees. Before entering the landing field permission is obtained from the landowner for the un-announced arrival of the balloon and for entry by the recovery team in accordance with a Code of Practice agreed between the ballooning and farming/land owning communities.
LAUNCHING AND LANDING
A lot of the work in hot air ballooning comes at the beginning and the end of the flight when the balloon is inflated and deflated. This is a time when passengers and spectators can, under instruction, participate in the activities and become part of the whole process.
At the launch site the burner system is first attached to the basket and its correct operation is checked. The basket is then tipped on its side and the balloon envelope attached to the burner frame before pulling the envelope out of its bag and spreading it over the ground. The basket is tied off to the Land Rover to restrain the balloon against gusts during inflation. |
|  | Once the envelope is laid out it is cold inflated using a powerful fan at the base of the envelope. When there is enough air in the balloon the pilot directs the burner flame into the envelope mouth. This heats the air, building pressure until the balloon inflates all the way and stands in the vertical, lightly bouyant. |
| The ground crew hold the basket down whilst the passengers climb on board. Remember that the balloon basket is also attached to the Land Rover until the last minute in order that the balloon will be restrained until it is ready to launch. When everything is ready and all pre-flight checks complete the final heat is applied and the pilot pulls the quick release to allow the balloon to climb gently away.
Amazingly this entire process only takes 15 or 20 minutes! Following the landing the deflation and re-packing of the envelope, takes a little longer.
The balloon landing can occasionally be a little bumpy if the surface breeze has increased but an experienced pilot will use his skills to minimize the impact. It is not unusual, and of no cause for concern, to brush the basket through the tree tops to slow down before the final landing. If the ground crew is already at the landing site they will hold the basket down once it has touched down and reposition it if necessary to make loading onto the trailer easier.
Then the pilot opens the parachute valve and deflation system all the way so the hot air can escape out the top of the balloon. The ground crew pulls on the crown lines attached to the metal ring at the top of the balloon, pulling the envelope down to the ground. The air is then squeezed out of the envelope from the basket end before it is packed away in the bag and loaded onto the trailer.
After all that excitement and hard work a glass of chilled champage, the traditional toast of balloonists, is more than welcome!
If this has sparked your interest to try a balloon flight for real or to treat someone special you can purchase our Gift Vouchers easily and securely online or over the telephone by calling our Sales Office on 015394 47599,.
The traditional Balloonists Prayer may sometimes be recited by pilots at the successful conclusion to a flight. Its origins are unknown but it is suggested that it is a modified version of an ancient mariner's prayer of thanks for a safe voyage.
The winds have welcomed you with softness.
The sun has blessed you with warm hands.
You have flown so high and so well,
that God has joined you in your laughter.
And he has set you gently back again
into the loving arms of Mother Earth.
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