ORIGINAL: AERORICH73
Ok Chuck: Not having the calculator program available, I found that Squardron 495 had published their way of finding the CG location.
I am not sure just how large this model is, or its weight, but will give you what I learned from 495. Finished repair, and rebuilding a damaged trainer, I hung the model in a large doorway from the engine cs, vertical stab/ top rudder hinge, and leveled it along the longitudenal axis. Hung a plumb bob from the same hanger above the model, and lowered it until it reached the fuse. Where it pointed
was the CG location. This location proved out correctly as the model was very well balanced during its flying life before my bad landing.
Just finished a 1994 Royal Aire 40T ARF purchased use, and never flown. The instruction manual gave a 4 inch dimension from the leading wing edge for the CG location which mathematically came out at over 38% of MAC. The above method corrected the location to 28% MAC. The plane flys well at this CG location.
Cheers!!!
Rich
Rich, I may be completely misunderstanding your post, my apologies if the is the case, but it sounds like you are ignoring the recommended CG and assuming that the actual CG is correct because the plumb bob points at it? You say that your trainer was meant to balance at 38% but you flew it at 28% because that's where it ended up or did you adjust things to achieve 28%? I'm sure that it flies fine at 28 but it sounds like the manufacturer is suggesting that it will fly better at 38
The method you describe will definitely find where the balance point actually is, but it doesn't tell you anything about where it should be. The idea is that you add ballast (or preferably move heavy things like the battery) to shift the balance point to the recommended position.
Now if you have good reason to think that the manufacturers position is incorrect well no problem balance your model where you see fit.
Most well designed models will balance well enough as built, assuming you don't change things like using a heavier or lighter engine, using a covering that is significantly heavier or lighter than the original etc. but some models will need to have the balance point adjusted to achieve the designers recommendation or indeed to match the pilots requirements.
Please disregard if I have misunderstood your post.
Dave H
Aero rich emailed me to clarify his post, and I have indeed somewhat misunderstood what he was saying.