Do you know what these two aircraft have in common? The one on the left is a typical glider, while the space shuttle on the right also functions as a glider. Most aeroplanes can fly without power for a considerable duration, albeit some perform better than others. This video explores the reasons behind this.

In straight and level flight, there are four forces acting on an aeroplane when the engine is operational. However, when thrust is reduced to zero, the drag force, which opposes forward motion, is no longer counteracted. This rear-facing drag slows the aeroplane unless it descends. During a descent, the aeroplane's flight path points towards the Earth, and the relative airflow opposes this path, allowing the aeroplane to maintain airspeed as a component of the weight force acts in the direction of flight.

For airspeed to remain constant, the forward weight component must be strong enough to counteract drag. In a steady glide descent, lift and drag balance out the weight force. Lift decreases as the opposing weight component diminishes. Increasing drag, such as by extending flaps, steepens the descent angle and shortens the glide range.

The aeroplane must have a greater forward weight component to maintain airspeed, further reducing lift. The shallowest angle of descent and optimal glide range are achieved when drag is minimal for the required lift, indicating a high lift-to-drag ratio.

A typical training aeroplane's lift-to-drag ratio, represented by a curve, is 9 to 1. This means it can glide 9 miles for every 1 mile of altitude lost in still air. The best lift-to-drag ratio occurs at approximately a 4 degree angle of attack.

Comparing a glider with the Space Shuttle, aerodynamically, the glider is more streamlined and has a much longer wingspan. These factors contribute to differences in glide performance, with the Shuttle's low lift-to-drag ratio resulting in a steeper descent and shorter glide range. However, the Shuttle benefits from high altitude.

The angle of attack and airspeed are directly related, with the best lift-to-drag ratio occurring at 4 degrees. Since pilots cannot easily determine their angle of attack, they use airspeed, known as the best glide speed, to achieve the best glide range. Changes in glide speed alter the angle of attack and, consequently, the glide range.