i have a cox ultimate biplane with a 52 saito 4s. manufacture says cg to lower wing. i dont seem to get it balance. move battery and added lead still nogo. seems to balance on upper wing right on. any ideas. are biplanes balanced on upper or lower wing

I've balnced every one I've owned on the top wing....but then, the plans and/or instructions specified the CG on the top wing. If yours specify the CG on the bottom wing, I'd rather strongly suggest you follow that suggestions. Bipes...especially aerobatic ones...do NOT like flying tail heavy. At all.

Measure at 1/3 the mean aerodynamic chord; take a point on the centerline even with the upper wing L.E. and a point on the centerline at the lower wing T.E., find 1/3 of the distance from the front mark to the rear mark and transpose it to the underside of the top wing, and balance it there. That should get you in range, you can start from there. Works on every bipe I've ever flown. I think that Cox misprinted something; I agree with gboulton, I've never seen the c/g measured on the bottom wing of a bipe.

Try the point that cox recommends, and hold the plane upside down when you balance it, see if that works. If it does, try my method and see how close the two marks are. Move the c/g forward for more stability, aft for more agility (within a range of about 1/2 inch or so)

Build yourself a Vanessa CG machine and you won't have the problems. Plans are available here on RCU or The House of Balsa Dust.

You would balance on the bottom of the top wing. Usually the balance point is directly above the leading edge of the lower wing. YMMV.

Daren

Since my earlier post, I've discovered the wonder, joy, and elegance that IS the [link=http://home.mindspring.com/~the-plumber/Vanessa%20CG%20Machine.htm]Vanessa CG Machine[/link]. Works for ANYTHING you are to name...low wing, high wing, bipes. Little planes or big ones (I balanced my 33% Pitts S2S Bulldog on one). Won't cost ya more than $20 to make, and that's if you have NONE of the material laying around.

You can even balance an airplane laterally with the Vanesa. Great machine.