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Author Topic: Building a 55' motor glider without a plan  (Read 174 times)
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Kurt
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« on: February 16, 2017, 12:50:42 PM »

Dears,
it all started out with an old glow O.S. .10 FP lying around and a sketch in 1:10 scale drawn in the sixties for a FF motor glider called "Barra". So I called the new project "Barra 2". How would I build a model without a plan? I started to cut out a ply tray for the essentials: motor, tank (Sullivan 2 oz), battery 4x1200 mAh NiMH and two 9g servos. These components were placed strategically an the tray and made the necessary cut-outs for the motor, tank and a hole for routing the servo cables upward. Done this I cut from a 5mm Balsa sheet two side pieces (all measures taken from the 1:10 sketch) and glued the tray to one side piece. Then I drew up the left fuselage side and glued all the sticks together, fixing the sticks to the side piece. You can see all that on the fotos.
Well, next time more.
Greetings,
Kurt
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Kurt
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« Reply #1 on: February 16, 2017, 03:16:36 PM »

Second part: what is the advantage, building a model without a detailed plan? During the building progress you have complete freedom to modify details according to your experience, a plan forces you to follow the ideias of others.
O.K. lets continue the building: when I cut out the hole for the tank I built a little box below it with a double purpose: first, that the tank would not fall through and the second to keep any fuel out of the fuselage, tanks may leak. As you will see on later pictures, the tank has a very easily acessible lid, so that you can clean it once in a while and see its level when fueling.
Te left part of the stick fuselage was built upon the right half for exactness of the dimensions and after having fixed the left front part glued on it and the joined the two fuselage halfs, see pictures (I dont know why all my pictures appear 90 degrees turned?) Then I soldered the front legs and fixed them flush with wheels attached to the fuselage.
Greetings,
Kurt
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OZPAF
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« Reply #2 on: February 16, 2017, 04:48:46 PM »

It's progressing well Kurt. Good luck with it.

john
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Kurt
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« Reply #3 on: February 16, 2017, 04:53:58 PM »

Third part: some design data
-main wing 1400 x 200 mm (aprox 55" x 7.9"), streching rario 1:7, air foil Gö (MVA) 301, area 27,5 dm²
-stabilizer 400 x 150 mm (aprox 15.7 x 6") ratio 1:2,7, air foil Clark Y, area 5,7 dm² (20%, which is a bit small, normally values from 25 t0 30%, I shall report flight results)
-distance main wing - stabilizer 500 mm = 2,5 times main wing chord
-EWD 2,5°
CG theoretical 167 mm, the measured is much more forward, flight results will show the final one.
dihedral value 5%
Value are very conservative for high stability
Greetings
Kurt
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OZPAF
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« Reply #4 on: February 19, 2017, 03:59:27 AM »

A 20% tail should be fine Kurt as you I imagine you won't nbe using free Flight endurance aft CG positions.

John
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