How to calculate climb gradient for dep?

[FCS Explorer]

A SID leading straight into mountanious terrain, no "at or above" waypoints, but "8% required".

So how do i calculate my gradient?

Thx

[FlyingStone]

Gradient = ROC / GS

Of course you need to use the same units for ROC and GS, so some conversion will have to be done.

[bestglide140]

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

[CAT3C AUTOLAND]

For quick reference there is also a useful table in the Aerad Supplement for this.

[keith williams]

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.