(Dan Thomas) wrote:

The engine mount on most light aircraft is designed to withstand 9
G's minimum. And as I said earlier, the 3.8 figure is based on gross
weight. Reducing gross would allow them to take a higher G figure but
the same net force.
Cessna also states in the 172 POH that it's designed to 150% of
the G figures given, or 5.7 G's. I think the 3.8 figure would be the
yield point, where things begin to bend, and the 150% figure would
break them entirely. Or something like that.

One of the earlier posts assumed for the purposes of calculation that
the wings break when exceeding 3.8g at gross weight. I was merely
continuing that assumption. All I was trying to illustrate was that
there are some parts of the airframe where the loads are not
aerodynamic and where the loads do not reduce with reduced aircraft
weight - which is why Va reduces with reduced weight.