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Aviation Glide Ratio Index Calculator

This calculator requires the use of Javascript enabled and capable browsers. This calculator has many limitations and makes many assumptions. It is designed as a teaching tool for student pilots ONLY; do NOT rely on the generated results under real life conditions, as they are, at best, approximate! The first assumption is that there is NO wind. (Obviously, gliding into a headwind will reduce the estimated distance of travel; and gliding with a tailwind will increase the distance.) A second is that the point on the ground (the ground level altitude), ABOVE which a glide begins, and the targeted landing area are the same altitude. Another is that there are no obstructions in the glide path that would actually hinder the glide. The actual glide condition begins at an altitude ABOVE ground level. Critical assumptions are that the glide ratio is maintained at a constant rate, there are no thermals or down drafts and that all factors remain constant (along with many others...). In real life, you will NOT have those conditions as true but in this learning process, those assumptions point out the logic of the math process.

Determine the best glide speed of the aircraft you fly, for the appropriate weight and atmospheric conditions. That is usually found in the aircraft manual. Also determine the glide ratio from the same information. Enter the speed, either in knots per hour (nautical) or (statute) miles per hour (the other will be calculated), in the indicated airspeed field. Our default vales are for 1 nautical mile per hour (NMPH) and for the equivalent, 1.15077945, in statute miles per hour (SMPH). Some aircraft have both on the airspeed indicator and some only have one or the other. Enter the glide ratio values in the horizontal and vertical fields. The ratio is listed as H:V, for example 8:1. The horizontal distance for the glide is 8 times that of vertical descent. In other words, the aircraft will glide horizontally 8 units for every 1 unit of descent. Our default is 10:1; most aircraft fall between 6:1 and 14:1. (A glide ratio of 20:1 might be appropriate for an Eagle riding the wind while a 1:14 ratio is similar to the glide capability of a brick.) Enter the altitude AGL that the glide condition begins. Our default is 5280 feet, 1 mile, above ground level. (We should all be that lucky if we lose an engine...) Click on Calculate. The information returned is the converted values of the indicated airspeed in various forms. Also, the approximate calculated time from the start of the glide descent until touchdown, based on the assumptions. The time is shown as fractional (decimal or digital) hours, fractional minutes or fractional seconds. It is not cumulative among the fields. For example, if the hours field shows 1, the minutes field will show 60 and the seconds field will indicate 3600. Each is true and each is independent of both others. The are NOT additive. There is an accumulative field that DOES give hours, minutes and seconds.

Glide Ratio Index
Unit
Number
Required Data Entry
Horizontal Distance Ratio Factor Feet
Vertical Descent Height Ratio Factor Feet
Initial Altitude AGL Feet
Indicated Airspeed NMPH
SMPH
   
Calculated Results
Indicated Airspeed Feet/Sec
Indicated Airspeed Feet/Min
Indicated Airspeed Yards/Min
Probable Glide Distance SMiles
Probable Glide Distance NMiles
Probable Glide Distance Feet
Approximate Glide Time Hours
Approximate Glide Time Minutes
Approximate Glide Time Seconds
Appx. Accumulative Glide Time Hr Min Sec
Updated 8.15.11


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