How to calculate climb gradient for dep?
A SID leading straight into mountanious terrain, no "at or above" waypoints, but "8% required".
So how do i calculate my gradient? Thx |
Gradient = ROC / GS
Of course you need to use the same units for ROC and GS, so some conversion will have to be done. |
Rule of thumb
As this is a simple relation between gained height over travelled distance you can easily express it in an equation and build your own rule of thumb:
Gradient (%) x 60 (precisely it`ll be 60,75) = Gradient (ft/nm) eg. 8 (%) x 60 (factor) = 480 (ft/nm). Then just look for your avg. GS during climbout (~V2 +-). Each 60kts of GS equals 1Nm/min, hence if you go at 180 you`ll make 3NM/min and therefore require, with the above approximation 3 x 480ft = 1440 ft/min. Since you only approximate the factor, put a little safetymargin on top and end up at 1500ft/min. Cheers BG |
For quick reference there is also a useful table in the Aerad Supplement for this.
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An approximate value for the required feet/minute can be calulated by taking the groundspeed in knots and multiplying it by the required % gradient.
So for example to get a 5% gradient at 100 knots ground speed requires 100 x 5 = 500 feet/minute ROC. This is based on the fact that 1 knot = approximately 100 feet/minute. 1 knot is actually closer to 101.3 feet/per minute so a better approximation in the above example would be 506.5 feet/minute ROC. But 500 feet/minute is reasonable approximation. |
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