Originally Posted by satinet
sounds like a pretty floaty model.
Hard to say isn't it. try and bit and see how you go. A few ounces won't drastically effect the sink rate.
If the ballast is centered on the CG, there should be no need to change the elevator trim. Under those conditions, the plane will glide along essentially the same glide path independent of the weight of the plane. Increased ballast will result in increased speed down that glide slope. The L/D (lift/drag) will remain nearly the same.
Under the conditions described above, the speed of the plane will be proportional to the square root of the weight. Doubling the weight of a plane will increase the speed by 41% (sqrt(2)=1.414...). Adding 6 oz. of ballast to a 60-oz. plane will increase the speed by 5% (sqrt(1.1)=1.05...). Increased speed means both a higher horizontal speed and a higher vertical speed (rate of descent). If thermals are strong, the increased rate of descent isn't a problem. The increased horizontal speed means that it easier to find new thermals and also easier to come upwind to land.
Increased weight also means the plane will be tossed around less by wind gusts.