Bax
Posts: 12677
Joined: 4/26/2002
From: Champaign,
IL, USA
Status: offline
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You may be trying to "oversolve" your difficulty. The way it's usually done is you mark where you want the model to balance and then just start adding weight at the farthest point forward or aft where you can attach it. Sometimes a small paper cup is used to hold steel or lead shot. That will get you a very accurate result. Trying to calculate where you put a particular weight, or how much weight at a particular location seems a bit much, unless you just like to do the exercise.
Unless you know the exact moments of all the various components of your model, it will be very difficult to calculate how much weight where you'll have to add/remove to move the balance point.
Full-size aircraft use calculations all the time, but they're trying to get an empty weight and balance so that the balance point is in a particular location. The aircraft is weighed at all three wheels when it's in a particular position, usually dead level fore-and-aft and side-to-side, in reference to the manufacturer's datum line. There is a particular point on the airframe or forward of the airframe for all measurements. By knowing how much each wheel weighs when the aircraft is in its leveled condition, the exact location of the balance point can be determined. You can also then use the formulas to determine what it will take to move the balance point to the desired location.
While this is for full-size aircraft, it may help you determine the solution the way you seem to want:
http://www.zenithair.com/kit-data/ht-90-6.html
_____________________________
Bill Baxter, Manager Hobby Services/Futaba Service/North America
3002 N. Apollo Dr. Ste. 1 Champaign, IL 61822 USA
Service Phone: 217 398-0007
Email: hobbyservices@hobbico.com
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All Forums >> RC Airplanes >> Aerodynamics >> Moving the CG aft 
Moving the CG aft - 
and to the rear at the rudder hinge line (31 3/4" 
