Glide Ratio & Glide Distance
How far a glide reaches from a height at the glide ratio (or sink rate and speed), with head- or tailwind, its time, and the height needed to reach a point.
The glide distance in still air and over the ground with the wind, the glide ratio and angle, the time in the glide, and for a point at a given distance the height needed with your margin and whether it is reachable.
Example: A 9:1 glide at 65 kt from 5,000 ft into a 10 kt headwind: 7.4 nm in still air, 6.3 nm over the ground in 6.8 minutes; a field 5 nm away needs 3,990 ft, 4,790 with 20 % — reachable.
Height times ratio,
scaled by the wind.
What a glide ratio is and how it comes from sink rate, how the wind scales the distance, how the height-needed figure is built, and what the handbook glide assumes.
Ratio and sink
Glide ratio is distance forward per unit of height lost at the best-glide speed, the same number as lift over drag. From a sink rate and an airspeed it is speed ÷ sink in the same units: 70 kt is 7,087 ft/min forward, so at 800 ft/min down the ratio is 8.9:1. Distance in still air is simply height × ratio.
Wind
The glide angle through the air does not change with wind, but the distance over the ground does, in the ratio of ground speed to airspeed: a 10 kt headwind at 65 kt takes 15 % off, a tailwind adds. That is why the best-glide airspeed is needed as soon as a wind is entered, and why a strong headwind can make a field ahead unreachable that a downwind one would not be.
Height needed
Reversed, the height to reach a point at a distance is distance ÷ (ratio × ground-speed factor); the margin you add covers the turn towards the field, a windmilling propeller and the pattern. The page says whether the height you have clears that figure.
What the number does not settle
Handbook glide figures are for a clean aircraft at best-glide speed in smooth air; every turn, every knot away from best glide and any flap costs height. A planning aid, not a substitute for the pilot’s operating handbook, the aircraft’s limitations or the rules that apply to the flight. Inputs stay in your browser; the same anonymous usage counts as the rest of the site apply.