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Old 12-20-2007, 11:56 AM
  #5  
Lost
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Joined APC: Dec 2007
Posts: 27
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Those numbers really do not mean too much without a foundation of where exactly they came from.
There are many factors, i.e., is this in level unaccelerated flight? CG location (I would hazard a guess that it is outside the limits aft)? Who came up with the formula? I only see output there? Wind tunnel results?

All I really know is that there would be negative dynamic stability if the CG is between the wing and the elevator. The wing produces a forward pitching moment, and with the the CG in front of the lift, the stab produces the restoring torque (read: down force) to counter act it. If you were to pitch the aircraft over and increase airspeed, the stab generates more down force and restores things back to where they were, after a few oscillations. That is dynamic stability. Works the other way also. Slow down, and some of that restoring torque attenuates, the nose drops, and goes back to "trim" speed. Nothing new here. All tried and true.
Now, go and re-arrange things and make the stab carry some of the lift function, and dynamic stability goes away. That is why we would have a wild (fatal) ride if we load much past the rear CG limit. Increase airspeed, and you get even more lift in the tail, and the nose pushes even further towards the houses.
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