Consider a glider trimmed to fly at some given angle-of-attack, gliding in smooth air (no thermal convection, ridge lift, wave lift, etc.). If air density is somehow kept exactly constant in all cases, and the glider is launched from the same initial altitude relative to the ground in all cases, would the flight duration be the same in all three cases? (A yes/no question.)
Extra weight has been added to the glider, exactly at the CG, doubling the glider's weight.
We've increased the value of the gravitational constant from 9.8 m/s/s to a higher value (twice as high).
We've caused the earth (and atmosphere) to steadily accelerate straight “up”, at 9.8 m/s/s, thus creating an apparent increase in the gravitational constant (to an apparent value double the actual value). (Acceleration starts well before the glider is launched, not mid-flight. Glider is also accelerating along with everything else at instant of launch, i.e. the atmosphere isn't rushing up past the glider at the instant of launch. For example the glider could launch by rolling off a ramp mounted on a high tower connected to the ground.)
(Edit: to make this more clear, imagine that a giant rocket engine attached to the other side of the earth is causing this acceleration. The earth itself is the only thing that is being directly acted on by the accelerating force; the atmosphere and glider each experience the results of this acceleration in a less direct manner.)
Also, if “yes”, then a second question — launched in equilibrium (exactly at its steady-state trim speed for the existing conditions) from a given height, would the glider stay up for a longer duration or a shorter duration after we've made one of these changes?
The intent of the question is to compare the steady-state in-flight dynamics, not some difference relating to some possible slight variation in the initial kinetic energy imparted at the instant of launch, etc. In each case, the glider is understood to be launched at its steady-state trim speed in relation to the existing conditions.