LY744 From Canada, joined Feb 2001, 5536 posts, RR: 9 Posted (5 years 11 months 3 weeks 6 days 18 hours ago) and read 4324 times:
How come V1 speeds are depicted in speedbooks as a function of TOW only, shouldn't the length of the actual runway used play a part in figuring out the appropriate V1? Do the tables just assume accelerate-stop distance = take-off distance at that particular weight?
Goldenshield From United States of America, joined Jan 2001, 6123 posts, RR: 14
Reply 1, posted (5 years 11 months 3 weeks 6 days 17 hours ago) and read 4294 times:
The actual runway length IS is used to determine V1. However, it is only a baseline V1. Other factors, such as runway slope, wind, etc., will influence V1.
Of course, for the purpose of this topic, the number in the flip books are all based on weights, as the maximum weights for the flight (which includes maximum takeoff weight for a given runway, 2nd segment climb, enroute driftdown, and maximum landing weight) are figured out during the pre-flight planning stage. And to answer your second question, ASDA is NOT used for takeoff distance, but rather the takeoff distance required is 115% that of the takeoff runway distance available where the plane must reach a minimum of 35 feet above the runway plane.
That's with U.S. regs. Other counties may vary.
[Edited 2009-02-08 14:46:12]
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Tdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 2, posted (5 years 11 months 3 weeks 6 days 12 hours ago) and read 4227 times:
Quoting LY744 (Thread starter): How come V1 speeds are depicted in speedbooks as a function of TOW only, shouldn't the length of the actual runway used play a part in figuring out the appropriate V1?
If you have more runway than you need for a balanced-field takeoff, you can take it into account. Then it's an improved climb takeoff. That's usually done via computer, not by books.
Quoting LY744 (Thread starter): Do the tables just assume accelerate-stop distance = take-off distance at that particular weight?
The normal approach is accelrate+RTO distance = accelerate+single-engine takeoff distance. That's the normal definition of a balanced field takoff...this is why airplanes almost never use the whole takeoff-distance-required length (the accelerate+two-engine takoff is shorter than either of the balanced field lengths).
When you throw all the other regulations in there, you may be limited by something other than the balanced field length (e.g. V1 can't be higher than VR, you may have an engine-out climb gradient limit, an obstacle limit, V1 can't be lower than Vmcg, etc.).