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Old Oct 14, 2004, 08:06 AM
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Soarbird's Avatar
Johannesburg SA
Joined May 2004
340 Posts
Aerotow tow hook position?

Hi All,

Am in the process of scratch building a Senior Telemaster for two reasons. Firstly because I have always wanted to build and fly one and secondly it will make a great tug for larger gliders, banner towing, etc.

I have made concessions to modern trends and some research and made a few modifications to the original design. The airfoil has been changed to s3021 with flaps to give a wider speed range and the wing constructed in two halves for transporting reasons. Full span spruce box spar used to add a little beef. The lifting tailplane has been changed to a symmetrical section and all control surfaces are now built up instead of solid to save weight. The fus has been lightened and a CF undercarriage is in process of being moulded. The original design weight was 108 oz or 3061 grams and I am shooting for 2500 grams or approx 88 oz AUW. You guessed it, the big change is to go electric.

My existing setup of a Kontronic Fun-400 with 5,2:1 gearbox swinging a 13 x 7 prop will produce approx 90 oz of thrust on 12 cells and give about 5 mins of full throttle flying. This will be fine to learn to fly this model on and perhaps aerotow midrange gliders. I appreciate that the larger gliders will need a bit more grunt from the tug, but that is in the future.

The big question is where, on the top of the fus, to locate the tow mount. Reading through numerous posts both on this site and countless others the closest approximation that I can find is "somewhere between the CG and trailing edge of the wing" Now on the Telemaster this gives a range of almost 230mm or about 9 inches!! Chord is 13,5 inches/343mm. Would it be correct to say that the ideal position would be on the neutral point? Thinking of the forces which would act on the tug from the tow, these will be 3 dimensional and by using the neutral point the effect on the tug would be minimal from these forces? This is from the aerodynamic perspective? On the other hand, if it was located on the CG, any forces should have minimal effect on trim. However, the CG moves relative to the attitude of the plane in all three dimensions.

Guys I would really be grateful for some input and advice on this one. Having had to buy a balsa forest just to build this model, I would like it to be as perfect as it can be.
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Old Oct 14, 2004, 08:37 AM
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Punta Gorda, FL
Joined Apr 2002
4,952 Posts
http://www.scalesoaring.net/tow.html
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