Debunking Glider Spoiler Turns Causing Spin Thinking

On Wednesday, June 17, 2015 at 6:14:09 AM UTC-7, wrote:
"Now if you suppose that it's the lift part which is opposed to the weight, then L/D would influence g-load. But this is just not how physics works on this planet.*"

A key point is that g-load is really just an expression of force. That's all it is. It is the vector sum of all the real forces acting on the aircraft, except gravity. Then we divide by weight to get a dimensionless expression.

When we talk about g-load, we really aren't saying anything that we couldn't express just as well by talking about the actual aerodynamic and thrust forces generated by the aircraft.

In a glider, where there is no engine, the g-load is the vector sum of all the aerodynamic forces generated by the glider. In coordinated flight, this would simply be the vector sum of lift and drag.

When we say that g-load affects stall speed, we really should say that the lift-wise component of the g-load vector affects stall speed. Not the total g-loading vector. But all we're really saying is that the magnitude of the lift vector affects stall speed. No extra information or content is added by bringing the concept of "g-loading" into the discussion.

The L/D ratio affects the magnitude of the lift vector, and also affects stall speed. In a powered climb, the T/W ratio affects the magnitude of the lift vector, and also affects stall speed. As per the tables I posted on June 4, and yesterday.

S

You discuss the "lift G-load" as if it was a thing in itself. It is not, it is a mathematical construct of several derived values. When the load on the wing changes many other things change - and perhaps the lift also increases. Let us suppose you are in an unaccelerated glide and a magic wand causes the glider's weight to double. After some time and control input, you return to an unaccelerated glide at the same speed. You will discover that the angle of attack has doubled, the induced drag has quadrupled, the angle of the resultant forces on the wing spar has changed, as has the bending moment. And the L/D is reduced.

As a second thought experiment, I fly my glider at 40 knots, it gets an L/D about 40. I then increase the speed to 80 knots, and still get an L/D of 40. But: the angle of attack is reduced by 75%, the induced drag on the wing reduced even more, the parasitic drag of the fuselage increased by 4x, the angle of the resultant forces on the wing spar changed again. My L/D and "lift G-load" are identical, but nothing else on the glider is. At 40 knots I am very close to stall, at 80 no where near it.

As a third thought experiment, I will take the resultant aerodynamic force on my wing, and split into two vectors: one at 30 degrees above the angle of attack which I will call Lift, one at 120 degrees above the angle of attack which I will call Drag. This is every bit as natural and valid as your Lift and Drag, which are similarly arbitrarily defined. When I am in a high drag configuration and my glide ratio is 2:1, I discover that Lift has disappeared completely. My Lift G-load is 0. Yet I am still in steady state flight, and there is still 1G bending load on the spar.

You cannot take an arbitrary mathematical construct, deal with it in isolation, and draw any momentous (or perhaps even any valid) conclusions.