Which speed should we look for recommended brake cooling in case of rejected takeoff? (Airspeed or groundspeed)
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$\begingroup$ If the wheels are rolling on the ground, why would airspeed matter? $\endgroup$– FrogJul 4, 2022 at 6:58
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$\begingroup$ This is likely to be type dependent. Consult the manufacturer's documentation. $\endgroup$– CatchAsCatchCanJul 4, 2022 at 8:21
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$\begingroup$ @Frog Because the brake pads are not ground-cooled. $\endgroup$– SneftelJul 4, 2022 at 8:48
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$\begingroup$ @Sneftel I hear you but E=1/2mv^2 relative to groundspeed. Air cooling may be just as effective with airspeed perpendicular to direction of travel. Reductio ad absurdum is that if you choose to take off with a strong tailwind, are you to expect near-zero brake heating? $\endgroup$– FrogJul 4, 2022 at 9:38
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$\begingroup$ @Frog yep, fair point. $\endgroup$– SneftelJul 4, 2022 at 10:50
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Which speed should we look for recommended brake cooling in case of rejected takeoff? (Airspeed or groundspeed)
Generally brake cooling charts/schedules for air carrier type aircraft (e.g. B737, B767, etc.) use the observed knots indicated airspeed (KIAS), at the point of the Rejected Takeoff (RTO), as the reference point for the calculation of brake cooling times.
However, the charts require adjustments in the calculation for a headwind or tailwind, and altiude/temperature, because the brake energy used to stop is dependent upon the actual ground speed when the RTO is initiated and not the indicated airspeed.
If the ground speed is observable and noted at the point of the RTO (instead of the KIAS), which is probably much less likely, the brake cooling chart (for the aircraft noted above) provides for the use of ground speed instead of KIAS in the calculation.