90 mm Mig - 15 build - RC Groups
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Oct 18, 2017, 08:15 AM
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Larry Dudeck's Avatar
Very nice work. What airfoil? Looks like a Clark Y.
Oct 18, 2017, 05:48 PM
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Scarey's Avatar
I choose the airfoil from a Thingyverse (3D print file website) search for airfoils. The airfoil was scaled to the size I wanted. It turned out to be a bit thicker
then I imagined. From a search, it seems to be a Clark - Y (low speed ULM ?) airfoil. I am not sure what type of flight characteristics It produces.
I am concerned about CG location with this type of airfoil. Calculated CG was around 9.5 in. from LE which seems a bit further back then I imagined.
Oct 19, 2017, 03:46 AM
jofro
Looks similar size to my "Top Gun" foamy I did lot of mods and fly on 12S, rather heavy at 5 kilos for my 90mm set up.
I remember the Instr. manual totally miss printed the CofG so it took me a while to work it out based of few larger turbine powered ones my friends fly.
After check when measured my fuse from the nose to the exhaust outlet (not the tail) it is 128cm (52.5") and my CofG is 23.5cm (9.5") from the LE. To my memory the chinese miscalculated it by some 4 inches which would make it so nose heavy that I doubt it would ever lift off! What AUW you expect and power unit fitting in it?
Oct 19, 2017, 09:24 AM
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Scarey's Avatar
I will re-measure again once again, First flight CG will be at 8.5 in otherwise, 90mm Midi fan for 10-11 S Lipo 3000 - 4000 Watts. AUW without motor and batts around 4 - 5 Lbs (2-2.5 Kg) . Other then my wing that foamy looks similar.
Oct 27, 2017, 07:54 PM
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Scarey's Avatar
Old canopy might work? Time for power system and balance with batts.
Nov 04, 2017, 01:59 AM
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Scarey's Avatar
Almost done. AUW with out Batts was 6.5 Lbs (3.2 Kg).
Nov 04, 2017, 08:10 AM
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Larry Dudeck's Avatar
I have used two different methods of determining the balance point, neither of which are air foil dependent. All of my scratch builds used the Clark Y and all flew just fine on the calculated value with 10 percent static margin.
I have scratch built an 48" ws F86 and calculated the balance point to be about 2" ahead of the TE when measured at the wing root. I did not believe that to be correct so I built a 1/4 scale (12" ws) "chuck " glider to check the balance point. Turned out the calculated value was just fine.
Where are you making your measurement? At the MAC or root?
Nov 05, 2017, 03:01 PM
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Scarey's Avatar
This is what was calculated.
Nov 05, 2017, 06:11 PM
Registered User
Nice job, Scarey!

Substituting balsa for stringers & such is a good idea. Saw a club member fly his all printed Spitifire, which broke up due to very brittle printed parts.

Phil


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