Test Flight Update

December 16, 1996

The following is Virgin's written account of the follow-up analysis of the November 9th test flight:



The follow up analyses to the November 9th test flight shows that the preliminary speculations of fabric leakage of helium or a misfitted rip panel were not correct. The integrity of the balloon and its fabric were further proven to be flight-line ready during a subsequent flight. The following week, the same balloon, with no modifications, was inflated and attached to a gondola designed for a high altitude test. It not only completed the test but broke all previous world records for altitude in this type of balloon. (See Newsflash: Lindstrand Breaks Altitude Record)

The original low altitude test flight, using a very large and heavily weighted basket, was conducted to test various components that will be used on the Global Challenger flight. Included was the data collection system which proved to be extremely accurate and revealed the reasons for the shortened flight time. Other items included the gas valve that will be used for the global flight and an instrument that measures reflected versus absorbed sunlight. The flight was specifically designed to test the balloon's performance and fuel consumption under the least desirable weight conditions.

A De Rozier balloon combines gas balloon and hot air balloon methods, allowing the flight crew to keep the temperature of the helium constant during day and nighttime temperatures. The goal is to prevent the helium from contracting as it cools which in essence produces a smaller balloon. Naturally, a balloon that becomes effectively smaller while carrying the same weight, will begin to sink. Therefore, the test balloon, with a heavier basket and three people on board, required a great deal of fuel to keep it aloft. (A more detailed explanation of the workings of a De Rozier balloon system can be found elsewhere on this web site.)

The flight was shortened for two reasons. First, that the effectiveness of the Lindstrand heating system surpassed the flight crew's expectations. The helium expanded to such an extent that it repeatedly vented though the overfill appendix tube. The tube is designed to relieve internal pressure in the balloon as the helium expands by allowing the helium to escape. For the global flight, this venting will be minimal because it will be limited to that which occurs naturally as the balloon reaches its ceiling altitude and not through the over use of the heaters. However, in the case of the November 9 test flight, the loss of helium meant loss of flight time.

The second reason for the abbreviated flight was that the wind was taking the balloon into territory where a quick retrieval would be unlikely and potential damage to the craft would preclude the more important high altitude flight. To that end, just before dark and before they reached the next mountain range, the crew elected to land while over a valley with dirt roads.

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