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Old 08-11-2009 | 05:35 AM
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From: FrederickMD
Default RE: weight VS stability


ORIGINAL: Korps

I have found that a CG which is aft - tends to make the plane floaty and it just wants to fly on a landing.

A plane which is more nose heavy will tend, apart from making it land faster, but will make it easier to get the plane down won't it?
Sorry, but this is probably the worst description and reflects a misunderstanding of the relationship between CG and the handling characteristics.

A plane that is truly neutrally balanced (not a CG that is aft) will not normally drop the nose when it stalls. Depending on the lateral balance, the similarity of the wings on both sides, and the torque from the motor, when the wing stalls, the plane will tend to drop a wing and enter a spin. This is the "floaty" behavior described above. The stall is quick to occur, and why many people have difficulty learning to land an aerobatic plane.

A nose heavy plane WILL drop the nose. This behavior requires using the elevator to compensate. As the plane slows down, the elevator becomes less effective, requiring more up elevator to keep the plane level. It is possible that the plane will not have enough airspeed to keep the nose level, which causes the nose to drop, and then air speed increases until the plane reaches an equilibrium, or hits the ground. This is why nose heavy planes must land faster. It is not easier to get them on the ground.

If any plane won't descend with the engine at idle, wings level and nose level, then the idle speed is way too high. This can be addressed by lowing the engine idle, or trying a lower pitched prop. To land the plane, the lift produced by the wings must be less than the weight of the plane. Once the engine idle is low enough, its simply a matter of using the elevator to reduce the airspeed (up elevator will slow the plane down) and allow the plane to sink onto the runway. Some people do this just before touchdown (the flair) and others set the plane in that attitude during the approach. Personnally, I think the flare is more difficult. I teach my students the mantra "Wings level, Nose Up" on approach.

Brad