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#11
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Initial acceleration is certainly much slower with autotow (whether
pulley or direct) than with winching. At both North Weald and Aston Down there was more than one runway, so most launches were broadly into-wind. Such cross wind as there was could be handled. The initial ground run was a phase of flight in its own right - the pilot had to learn to balance on the wheel and taxi straight until flying speed was achieved. Wingdrop was not normally a problem, but training people to taxi was a feature. The same considerations apply when landing, in any case, so they got two lots of taxi training in one flight. On tarmac or concrete the F250 trucks had adequate power and grip. F100' s were not bad, but we didn't have such heavy gliders in those days. Aston Down tried a variety of tow vehicles over the years, including some home-built diesel dragsters, but I believe they ended up with factory-built trucks, as we did, and as Lasham (using straight autotow at one time) also did. I worked for Ford then, and helped to get some advantageous prices for imported US-built vehicles for two if not all three clubs IIRC - Ford used gliders at North Weald as background for some advertisements, and did us a favour in return. My club used LPG rather than petrol/gasoline, which made it a comparable fuel cost to diesel winching, per launch/cable-retrieve. Total depreciation/financing cost was probably about comparable, but needed less cash flow up front. Trucks were cheaper capital cost than new winches, though not as durable - ours lasted for about 50,000 launches each and were not fully worn out - we recycled one old powertrain into a winch when we had to adopt that method for our Ridgewell site. The key features for us at North Weald were that on hard runways we had to use piano wire (single strand steel cable), not stranded, to avoid too much wear and cable cost, and pulley/autotow lends itself to that better, with pulley giving also the benefit of fast launch rate when well organised. We did about 9,000 launches a year, and added considerably to our cash flow, when we had optimised the system. Chris N. |
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