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Thread: Wet V1
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Old 22nd Jun 2007, 01:24
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BelArgUSA
 
Join Date: Jun 2005
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Braking performance old A/C (V1)

Hola CC -
xxx
I would not say that old turbojet planes had better or worse ability to stop, to compare with modern aircraft types...
xxx
Well to the contrary, if you consider the 727 as an example. that aircraft has outstanding braking performance, so much that V1 is equal to VR... we never considered a V1 reduction for a wet factor to reduce V1, actual V1 being way beyond rotation speed. And the 727 goes back to 1964... The original 727 had nose wheel brakes, later found unnecessary, and were deactivated as redundant, and to save on maintenance...
xxx
I am not knowledgeable about modern airplanes, as the 747s I fly presently were manufactured in the early 1980s, also with outstanding V1 aborted T/O performance, but certainly not as outstanding as the 727 is... In the 747-200 I fly currently, we reduce V1 in ANY case, runway dry OR wet, when the actual runway available, and its stopway if present, exceeds the runway limit weight in actual condition. That reduction is at times some 20 knots, but not less than VmcG. obviously.
xxx
Also to mention that 747 are permitted to operate with 1 or 2 sets of brakes deactivated (with a slight weight reduction) - and as usual, recall the factor of reverse thrust of at least a pair of engines (not accounted for in the FAR 25 performance certification) is still a bonus. I would say that the 747 has outstanding aborted takeoff braking performance.
xxx
Was not the case of some other types I flew. The worst were probably the DC8-50/61/71 series as far as brakes, yet the DC8-62/63/73 had much better brakes, much to be compared to the 707-300... On landing with a typical DC8-61, it was company policy not to touch brakes until the speed had decayed to 80 KIAS or less, and the reversers were worthless...
xxx
Knock on wood, I never had a catastrophic abort at speeds near V1, and I do takeoff where actual V1 out of the performance tables that must be in the last 3,000 feet of the runway. I would never attempt to abort at that point.
xxx
The concept of a reduced V1 (well in excess of 10 KIAS) was researched by TWA with their 707 fleet, and adopted, by many airlines, and was procedure for dry or wet runways, based on actual conditions.
xxx
All this is academic... only experience, surprisingly, tells a pilot where to take his hands off the thrust levers, and say to himself "it is a GO, no matter what happens".
xxx

Happy contrails -
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