Originally Posted by
Mad (Flt) Scientist
Both Part 23 and Part 25 require stall speeds to be for the most adverse (i.e. forward) cg position. I assume that would apply to your data too.
Very roughly, you can turn the cg shift into a tail download and thus into a pseudo-weight effect.
Say the distance from 1/4 chord wing to 1/4 chord tail is 50". Say the cg shift is 5" forward. The increase in nose-down weight moment is 5" * weight. The change in downforce at the tail to balance that is (5" * weight) / 50" i.e. 10% of weight. So if the cg went forward 5", you'd have an increase in tail load equivalent to 10% of a/c weight, so you could say that the stall speed should increase as if the a/c were 10% heavier (i.e. about 5% increase in stall speed). That's pretty crude but should give you a ROM to work with.
Although, for many aeroplanes at forward CG the stall definition shifts from the classic aerodynamic stall to something more pitch authority limited (the "mush"). Once in that region, the stall speed can go up somewhat more significantly, and this can be hard to predict.
The TB20, being of conventional configuration with fully reversible controls, I'd certainly expect to fall into that category.
G