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Old 15th September 2009 | 17:27
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12Watt Tim
 
Joined: Dec 2008
Posts: 130
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From: From Despair To Nowhere
At anything less than 1.41Vs you would have stalled before hitting a load factor of 2.

The lift at a given angle of attack is proportional to the square of the speed. Stall occurs at stall AoA. At Vs and 1g the AoA is stalling AoA, and lift = weight.

So if you are flying at 1.41 Vs then at the stalling AoA your lift = weight * 1.41^2 so lift = 2* weight at the stall so you can just maintain aerodynamic flight at 2g.

However if you are flying at 1.3 * Vs then the lift at stalling AoA is only 1.3^2 * weight. 1.3^2 is 1.69, so as the aircraft pulls through 1.69g it stalls, and never exceeds that load factor.

Have you ever seen the limitations in the AFM that above a certain speed you must not use full deflection of the controls? The reason is that above that speed it is possible to exceed the g limitations. The speed is actually your stall speed at the limiting load factor for the aircraft (typically 3.8, 4.4 or 6g for light aircraft depending on category). Below that speed it is not aerodynamically possible to over-stress the aircraft*, as you will stall first. Note that speed, Va or manoeuvre speed, actually reduces with reduced all-up-weight (i.e. if light you have to be more careful) as you will not stall until a lower speed at a given load factor, including the maximum certified load factor or g limit.

* Not quite true. Most will overstress earlier if there is significant aileron input, but high g while actually rolling is rarely encountered unless attempting aerobatics.
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