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Building Tips and technical articles. => 1/2 A building. => Topic started by: Mark Mc on January 20, 2023, 09:25:01 PM
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I'm making up seven Skyray kits for our club 1/2A day to do a fun competition. I bought the .pdf from Pat King for his Skyray Racer, which he says is the same dimensions as the SIG kit, just made with bass wood. So I'm cutting the kits from balsa. But looking at the .pdf from Pat, the c.g. is at the 10% position. Good for strict upright racing, but too far forward in my opinion for Gentleman's Aerobatics. If I remember correctly, as it's been quite a good while since I've built a SIG kit, the c.g. is not specified on the printwood or in the assembly drawings. I believe SIG figured that if you built it as supplied and put a tanked reed valve engine on it, it should come out about right.
So what does everyone think is a good c.g. for these? I'm figuring 20% to start, but I'm open to suggestions.
Mark
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McMark,
The kit plan shows their recommended CG on the backside, with their pre-flight checklist. With a wing chord of 5" that corresponds to 12-1/2%. The checklist also specifies 30' maximum for the Dacron lines. I have been flying with .008x42' stranded cable.
With two-wheel landing gear on mine, I'm flying it right around 3/4" (15%) with no trim weights added. It is used solely as an ab initio trainer with a huge tip weight so we're ready for the afternoon breezes. No upsidedowning, but it probably would, if asked....
The Divot
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Dave,
Thank you very much! I did not remember ever seeing that. I'll note that and use the 15% as my starting point.
Mark
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Mark,
The 10% is for stability for a racer. For a stunter I start with 20% (twice the distance of the 10%). With a straight leading edge any % is just a multiplier of the 10% distance. At 25% the airplane might not be stable. For trainer stability with minimal stuntability start with 15%.
Pat
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I built two Skyrays for grandkids. I made wider elevator- 1 3/16 inches, belcrank 60 mm spacing and 15 mm shoulder, modified nose to fit the intake of the .049 , two pennies in the “weight box”, no landing gear. The blue Skyray is powered by .049, weight is 6.34 oz dry, 34 ft Dacron lines. C/G is 20% with empty tank. Model flies most of the PA routine. The yellow Skyray is powered with Big Mig .061 Norvel with RC carburetor open full bore. C/G is 10%, weight is 7.44 oz dry. It flies fast, and I will get dizzy. Both models built identical, engines and tanks can be swapped.
Jerry
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A Norvel .061 on 34' lines. Wow!
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A Norvel .061 on 34' lines. Wow!
Originally the yellow Skyray was equipped with.049. But it did not have enough power on that old engine. So for science I tried Norvel .061 . I think it helped to explain the difference about C/G topic.
Jerry