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Old 16th Aug 2007, 09:18
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FlightDetent

Only half a speed-brake
 
Join Date: Apr 2003
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The TAS difference margin is yours to keep.

Using this TAS calculator with 1013 hPa 20°C and 130 IAS, TAS comes at 134 kt.
For assumed OAT of 65°, TAS is 144 and FOVE calculates all performance based on G/S 144 (assuming 0 wind).

However, at 20° OAT you will achieve IAS 130 ten knots earlier during takeoff roll than calculated (runway length margin).

For a V1 cut, you also have the energy margin. Performance calculation covers 1/2*60000kg*72mps*72mps = 155,5 MJ to be stopped (TAS 144 kt = 72 mps), but your V1 of 130 kt in fact (OAT 20) represents only 134 kt TAS hence the energy to lose is only 134,7 MJ. That is only 86 per cent of what had been accounted for.

FD.
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