Mass balance vs Moment of Inertia - Neverending battle.

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The radian glider took a real beating at the last crash. Although it had a 'soft' landing eventually, going through the trees was not pleasant the foamy airframe. since it wasn't covered, indentations can be seen all over the aircraft.



I made a big mistake. Once I had put the autopilot inside the canopy bay. I thought I was clever that by restoring the center of gravity line through using 2x7g lead weights at the tail of the weight. The reasoning was to minimise the amount of extra ballast by increasing the moment by the c.g. (crazy right!). But unfortunately, I didn't think of considering the inertia effect it will have on the make-up of the airframe.


For you newbies, this is what wikipedia says about inertia: Inertia is the resistance of any physical object to any change in its state of motion, including changes to its speed and direction. In other words, it is the tendency of objects to keep moving in a straight line at constant linear velocity. 

In other words, Inertia favourite cliche line could be: "the more things want to change, the more they should stay the same".

So with every elevator/rudder deflection, a control moment will be produced but now a resisting inertial moment (albeit transitional) will oppose such moment causing the airplane to become less responsive to control inputs. So any effort to avoid a crash, for example, by applying sudden control surface deflection (be it rudder or elevator) will be resisted by this lump of mass at the same point at which you're trying to create the restoring moment. And the rest is history.

It is at this point that when you wish you could say: "Ignorance is bliss".