ORIGINAL: seanreit
Harley, I have never quite understood this method of CG checking wherein "fly inverted" if no down is required you are properly CG'd. I have always worked it as a percentage of MAC. Fine tuned based on landing speed.
Can you point me in the direction of a good explanation of the inverted flight method, how and why it works? Or someone with some expertise in this area explain?
Thanks,
Sean
Dunno about a high-falutin’ explanation ;-) but the overly simplistic version that works for me is:
If your CG is slightly off, then the aircraft at neutral elevator / stab will naturally shove its nose up or down a little as the incorrect CG induces a pitch moment. To compensate we sometimes tend to use elevator trim to keep the nose up on a nose heavy aircraft, or down on a tail-heavy aircaft. However, if you are carrying up elevator to maintain level flight with the nose heavy aircraft, then when you fly inverted you will have the nose-heavy tendency of the aircaft AND the up (now = down) elevator BOTH trying to shove the nose towards the ground.
By doing the inverted check, you are basically just finding out whether you have any elevator trim compensating for a CG-induced pitch condition, because while it cancels the CG-induced pitch when rightside up, it adds to the pitch when inverted.
Like I said – that’s just my “flying for dummies” intrerpretation ; aerodynamic experts feel free to shoot this down and edcuate us.
Gordon