Originally Posted by
abufletcher
I've used the Vanessa rig method on three models, but I guess I still don't entirely understand it or trust it. It's almost seems like using a divining rod!
The thing I guess I can't get my mind around is that the model itself is never "free balancing." You adjust the angle at which the fuselage hangs by turning the rod, and this affects where the plum bob points to. But, now, through the haze of time, I can't understand how this would indicate were on the wing the model is balancing.
And then there's the question of how to "level" the fuselage. Don't get me started on all the different ways that different modelers interpret the term "balanced." "Oh, yeah, I always balance my models with the nose down." That's like a scientist saying he always "balances" his chemicals with one pan a bit heavier than the other. Level has to be defined relative to the incidences and thrust angles.
Anyway, remind me again about how to use the Vanessa rig.
The plumb bob always points directly at the CG! It doesn't matter if the plane is hanging level, nose up, or nose down...the bob always is pointing directly at the CG. The CG of a plane is located in 3 dimensions, not just fore and aft. It is located somewhere within the volume of the plane. The reason that you level the plane is to determine where the CG falls in relation to the wing chord. Actually, leveling the fuselage is just an approximation...what you really want is the wing to be at the same angle it will be when the plane is flying straight and level...usually several degrees positive angle of attack. When the wing is at this orientation in the V rig the plumb bob points to a location on the wing that is directly above or below the actual CG (depending on if its a high wing or low, or both). The idea is to adjust the weight of the plane so that this point is in the proper location (approx 25-30% of the chord line).