Glide Ratio Explained: Best Glide and Engine-Out Range
Learn what glide ratio means, how to fly best glide speed, and how to estimate engine-out reach so you can pick a landing spot with confidence.
What the ratio really tells you
Glide ratio is the clean geometric relationship between how far you travel forward and how far you descend, with no engine adding energy. A 10:1 ratio means every foot of height buys ten feet of forward travel, which is why it is often quoted as lift over drag at the best glide condition. Because it is a pure ratio, it holds at any altitude, so the same 10:1 gives you 50,000 feet of reach from 5000 feet or 20,000 feet from 2000 feet. Understanding that scaling is the fastest way to build an instinct for how far a stricken aircraft can actually go.
Flying the best glide speed
The published best glide ratio only appears when you hold the matching best glide airspeed, a single indicated speed listed in the flight manual. Fly faster and drag rises steeply, cutting your range; fly slower and induced drag climbs while you sink faster toward a stall. Weight matters too, because a lighter aircraft reaches its best glide at a slightly lower speed, though the ratio itself changes very little. In practice, pitching for the book speed and trimming to hold it is the highest value action in an engine-out situation.
Turning altitude into a landing plan
Once you know your still-air reach, the next job is to spend it wisely. Draw a mental circle of reachable ground, then shrink it for the wind, for the altitude you will burn setting up an approach, and for any turn back toward a field. A common mistake is planning to just reach a runway with zero margin; energy vanishes fast in a bank, and a headwind on final can erase the last mile. Aim to arrive over your chosen spot with height to spare so you can maneuver rather than stretch a glide.
Measuring your own aircraft in practice
You do not have to trust the manual blindly. On a calm day at a safe altitude you can note a starting height, establish best glide, and record how much altitude you lose over a measured ground distance, then divide distance by altitude lost to get the ratio. That is exactly the derivation this calculator performs when you leave the ratio blank and fill in the distance and altitude fields. Repeating the test into and downwind and averaging removes most of the wind bias, giving you a realistic number for your specific airframe and loading.