Originally Posted by Tinstaafl
The 'g' limit is another way of specifying a limiting acceleration. Accelerating the airframe applies loads to it. One 'g' is an acceleration of 9.8 m/s/s. If the limit is 3 'g the the aircraft mustn't exceed 3 x 9.8 m/s^2.
At a given weight & speed elevators can apply a certain maximum force to pitch the a/c. This, in turn, causes an increased AoA leading to increased L (ie a force) and a resulting acceleration to the airframe. If speed is increased then the sequence will result in an increased acceleration ie a greater load. If speed is reduced then the sequence leads to a lower load. Starting at low speed - ie below Va -the wing will reach its critical AoA before the limiting acceleration is reached. As speed increases then the airframe experiences more & more load prior to the wing stalling. Increase speed enough & the airframe eventually reaches its limiting load just as the wing stalls. Any faster & the limit will be exceeded prior to the wing stalling.
Since this is all about accelerations & the forces that cause the acceleration then mass also is a factor. A given force will cause a greater acceleration the lower the mass. The L force goes up by 'X', accelerating the mass of the whole aircraft. The lighter the aircraft then the more it will be accelerated for the same increase in L. Max Va is at max weight because the heavier aircraft can't be accelerated as much by the increased Lift as when it is lighter.
Not sure I follow this. Surely the stress on the aircraft is to do with the total force it encounters. By Newton's second law F = Ma and therefore it follows that for a given F if M drops then a can go up. It is not the acceleration that defines the total force - it is the prduct of mass and acceleration. Putting it another way if the max 'g' force allowed on the aircraft is 3.8g then the most upward force will be required at the wings at max weight. At this point the total force will be 3.8 times the force on the aircraft due to gravity. If the plane then becomes lighter if you want to exert the same force you can actually pull more than the 3.8g so the wings should be capable of this at lighter weights. However, as Rivet Gun pointed out there are parts of the aircraft (such an egine mounts) that always support a fixed load and these could be overstressed. So as I see it the reason to slow down a lighter plane in the presence of turbulence is for this reason - to avoid pulling more than the rated 'g's on these parts - not the wings.
I did find this useful document on the web -
http://www.flightlab.net/pdf/8_Maneuvering.pdf. Page 8.3 section 5 pretty much confirms that (unless anyone else has another theory in which case please post!).