How does a decrease in gross weight affect the best glide airspeed?

A decrease in gross weight leads to a lower best glide airspeed due to the relationship between weight, lift, and drag. When the weight of the aircraft is reduced, there is less lift required to maintain level flight. Consequently, the airspeed at which the aircraft can achieve the optimum lift-to-drag ratio—allowing it to glide the furthest—also decreases.

Best glide speed is determined by the point at which the aircraft's drag is minimized relative to its weight. With a lighter aircraft, the lift can be generated at a slower airspeed, which allows the aircraft to achieve better performance in terms of distance traveled during a glide. Additionally, the rate of descent typically decreases as the weight drops, allowing for a longer and more controlled glide, since the airplane can maintain a more efficient glide path at the lower airspeed.

Other possible answers suggest that best glide speed either increases or remains unchanged, which does not align with the basic principles of aerodynamics concerning weight and drag. The effect on glide performance is directly related to how weight influences the balance of aerodynamic forces acting on the aircraft.