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Old 23rd Jun 2002, 04:17
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mutt
 
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1515Blue

If we were only looking at the ability of get off the runway the higher thrust rating would give the greater takeoff weight on a fixed runway length.

But we also have to look at aircraft controllability in the form of VMCG, if the higher rating requires a VMCG of say 135 kts, the aircraft weight must be reduced to a point where the aircraft can accelerate to that speed and abort. The actual takeoff weight must be the lower of these two weights.

If we then use a lower thrust, say 10%, the initial takeoff weight would be lower, but in this case we only have to achieve a VMCG of say 129 kts, so this weight may be higher than the VMCG limiting weight for 135 kts.

So the final result if that for a lower thrust rating you get a higher takeoff weight! This obviously depends on the runway length and surface condition.

Make sense?

Mutt
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