CG ?????

Question

The instructions for my electric sailplane say to balance 68mm from LE. When I check CG using GP CG Machine, the plane shows to be VERY nose heavy even with the battery shoved all the way back to the servos for the tail feathers.

When I look at the figures:

68mm ~ 2.68" ~ 2 11/16 ".

wing chord 7 1/4" tapered LE to 5 7/8" at the end of the aileron.

If I take 25% of root chord, I get 1.81". " " 30% " " " 2.18".

Seems to me that there might be a misprint on the CG. If the figure was 58mm ~ 2.28" ~ 2 1/4", I'd be very close to balancing.

Comments........

David

Frank · Accepted Answer

Is it only the le that is tapered? Is the te tapered at all. If not than itlooks like 2.25 would be 25% of average chord.

SKYLANE42 · Answer

Want a really good online calculator...

David AMA40795 / KC5UH · Answer

The TE is straight.The LE is straight taper as noted.The wing tip is somewhat parabolic from the aileron out to the end.David

David AMA40795 / KC5UH · Answer

Interestingly, your calculator gives me 2.18" at 30% IF I entered the sweep correctly. When I view the page, there is a vertical black strip with a blue grid in it that obscures the right side of the calc box. I cannot see the 'B' or 'S' dimension letters - I assume they are at the wingtip and covered up by the strip.

David

David AMA40795 / KC5UH · Answer

Hmmmmmmmm. After fiddling with the calculator to figure out how to use it, I came up with 2.64" - pretty damn close to 2.68".

Rats, now I have to figure out how to get the battery weight farther back to get balance, since adding lead to balance electrics is a 'last resort' move.

David

David AMA40795 / KC5UH · Answer

Oooooooppppssss. After getting the figure from Jean-Claude's calculator, I went back to Palos RC page and fiddled with it. I had not entered a sweep since the wing is NOT swept, but noticed that the sweep dimension had to be entered to get the tapered LE - DUH.

Anyway, I then got 2.64", just as I did from J-C's calculator.

David

CG ?????

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