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Aviation History
1970
1970 - 1570.PDF
240 FLIGHT Inte HOT-AIR BALLOON in the Air liSititlllllftl becoming lost, but 1 avoided this by staying close to Tim Godfrey, a member of the London Balloon Club, who was to pilot Golden Eagle on this trip. Watching a balloon drift gently over the countryside one might imagine that this was one of the least active sports possible. This is not at all true as far as the preparations for flight are concerned. Ordinary, simple ambient-type air has to be introduced into the canopy before any heating can be done. In still air this is achieved by opening and closing the neck as if shaking a sheet. Ripples then flow up the body as it starts to breathe. This is the time to light the burner, which hangs from the base of the balloon on 12 steel wires. It feeds from propane cylinders in the basket (four is a typical load although we carried only three) each of which holds 351b of liquid at a pressure of up to 1001b/sq in, depending on ambient air temperature. The fuel is vaporised in coils surrounding the burner jet. The whole unit is quite a piece of precision engineering formed of welded-up stainless steel tubing and costing about £120. Protective clothing is something normally associated with technical complexity and it seemed incongruous to see the crash-helmeted pilot pull out a box of matches to start things going. But a helmet is a necessary piece of equipment with the hefty burner installation just above head level. Once the pilot burner was alight, Tim Godfrey tested the main jet which is controlled by a small lever. I wasn't really ready for the 6ft of flame which shot out at about 14ft/sec like the tongue of some demon chameleon. Exceeding the output of most industrial heaters, the burner produces around five million Btu/hr with a burning temperature probably near the 1,900°C maximum for propane. This ensures almost total combustion which, in turn, prevents build-up of an explosive mixture inside the balloon. Tim Godfrey crouched behind the burner, half in the basket which lay over on its side. He aimed the jet at the mouth of Golden Eagle which Don Cameron and I held open, feeling like Lilliputian, dentists. When the hole was big enough he fired the burner in short bursts and gradually the great whale like canopy began to heave and expand as it gulped in huge breaths of air. With only three crew, we were rather short- handed since normally someone would have held down the crown of the balloon until the canopy had filled quite sub stantially. We lacked this team member which resulted in Golden Eagle making its own decision on when to rise. It soon did this, floating gracefully upwards, an awe-inspiring brightly coloured genie, towering above the house and up to the height of the trees. All this caused a problem, for the canopy was still filling and after each burst of the burner it sucked in more air, the pressure difference closing up its mouth. Don Cameron and 1 heaved away at opposite wires above the burner to try to force the gap open but this also pulled the balloon down, plus the burner, plus Tim Godfrey, who sank ever lower into the now upright basket until only a white helmet and two gloved hands tussling with the fearsome flame-thrower could be seen. At this point we conceded to Tim's urgent request to release our grip on the rigging lines and' to allow the canopy to ascend to the full extent of the wires. We then repeated the performance until eventually the big. colourful bubble had filled. The next stage was to heat the air enough to make the balloon ascend, a process which involved the same short burner bursts alternated with a basket-rocking procedure by the crew as if to release suction but in fact to see how near to flight the craft was becoming. The safe operating temperature for the canopy material is 110°C. Thermometers are carried by some balloonists but the long wire necessary lies in wait for the toes of wayward boots in the fraught period during inflation and Don Cameron has abandoned the idea. On a hot day, the trapped air must clearly be made hotter than in cooler weather to maintain the difference in pressure required for an ascent. So on hot days load has to be limited and the permissible figure is worked out from a weight versus ambient temperature grid drawn for each craft. A way of overcoming this weight restriction is to use material—already available—which will withstand higher temperatures, but this costs three times as much as proofed nylon and its heat loss is greater.
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