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Dethermaliser fuse
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Jetex Dethermaliser Fuse served two purposes. Not only was it a conventional fuse with a “CONTROLLED BURNING RATE”, but it was also “THE IDEAL FUSE for lighting Jetex motor wicks in windy weather". (Whether it was wise to be flying Jetex models in windy weather was another question.)
With Jetex contest models achieving longer and longer flights, there was indeed a call for an effective means of bringing them back to earth prematurely, in order to ensure the motor was not lost along with the model. Since the Jetex engine was generally the most valuable part of the model, the dethermaliser purpose of the fuse was well conceived.
It appears that the burning rate was recalculated after the card was printed. The original ¾" has been emended by hand to 1", while the accompanying leaflet explains that “the burning rate is 1 in. per minute in still air when laid horizontally and 1 in. in 45 seconds when burning vertically or fitted in an exposed position on a flying model”.
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