Glide Ratio

on . Posted in Dimensionless Numbers

Glide ratio, abbreviated as E, a dimensionless number, is a measure of how efficiently an aircraft or object can descend or "glide" through the air without propulsion.  It is the horizontal distance an aircraft can travel forward compared to the vertical distance it descends during a glide. 

A high glide ratio indicates that the object can cover a significant horizontal distance for a relatively small loss in altitude, which is desirable for gliders, sailplanes, and other unpowered aircraft.  These aircraft are designed to maximize their glide ratios to stay aloft for extended periods without using an engine.  On the other hand, a low glide ratio means that an object descends rapidly relative to the horizontal distance it can cover.  This is the case for many powered aircraft, as they are designed to have a powered ascent rather than relying on gliding for extended travel.

For example, a glider might have a glide ratio of 40:1, which means it can travel 40 units of horizontal distance for every 1 unit of vertical distance it descends.  In aviation, understanding the glide ratio is essential for pilots to plan their descents, reach a desired landing point, or make emergency landings in the absence of engine power.  Different aircraft have different glide ratios, and these ratios can vary based on factors such as the aircraft's design, weight, and current conditions like airspeed and wind.


Glide Ratio Formula

\( \epsilon \;=\; d \;/\; A   \)     (Glide Ratio)

\( d \;=\; \epsilon \; A \)

\( A \;=\; d \;/\; \epsilon   \)

Symbol English Metric
\( \epsilon \) (Greek symbol epsilon) = glide ratio  \(dimensionless\)
\( d \) = horizontal distance of forward travel  \(ft\) \(m\)
\( A \) = altitude lost in the distance \(ft\) \(m\)


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Tags: Efficiency Aerodynamics