V2 Speed - Definition?
Joined: Aug 2003
Posts: 882
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From: Skagness on the beach
(d) VMU is the calibrated airspeed at
and above which the airplane can safely
lift off the ground, and con- tinue
the takeoff. VMU speeds must be selected
by the applicant throughout the
range of thrust-to-weight ratios to be
certificated. These speeds may be established
from free air data if these
data are verified by ground takeoff
tests.
and above which the airplane can safely
lift off the ground, and con- tinue
the takeoff. VMU speeds must be selected
by the applicant throughout the
range of thrust-to-weight ratios to be
certificated. These speeds may be established
from free air data if these
data are verified by ground takeoff
tests.
Fleet Manager
Joined: Apr 2001
Aviation Qualifications: ATPL
Posts: 7,448
Likes: 310
From: various places .....
phnuff,
"Screen Height" is the prescribed certification height above the runway at which runway aspects of the takeoff (ie distances) are deemed to be completed. Sometimes used in respect of landing in a similar way - the height at which the landing distance measurement commences.
Originally 50 ft was chosen for both - reputedly a figure plucked out of the air by the early antecedents of the FAA. Supposedly this was based on some then recent military trials of an early biplane which had been demonstrated in/out of a particular parade ground which happened to be surrounded by trees of height approximating 50 ft. .. and why not ? .. as good a place to start the regulatory ball rolling as any.
Can't recall just when the 35 ft came into vogue for takeoff without digging into the dusty drawers but probably it was when the performance PAMC which predated CAR 4b surfaced. The extra distance associated with the more complex takeoff analyses was a bit too penalising were 50 ft to be retained. Those of us who have little hair, and/or significant grey portions of whatever hair we may have left will recall that the performance PAMC came in during the early days of the F27 and similar aircraft. The document marked a change from "simple" takeoff analyses to the more complex protocols we follow today which are based on a more rational and sound approach to risk management. I know I have a copy of that document somewhere in the archives ... somewhere.
Subsequently, wet runway screen heights nominally half the normal screen (rounded to 15 ft) came into the equation and the whole exercise continues to become more complicated but, at the same time, far more sensible.
"Screen Height" is the prescribed certification height above the runway at which runway aspects of the takeoff (ie distances) are deemed to be completed. Sometimes used in respect of landing in a similar way - the height at which the landing distance measurement commences.
Originally 50 ft was chosen for both - reputedly a figure plucked out of the air by the early antecedents of the FAA. Supposedly this was based on some then recent military trials of an early biplane which had been demonstrated in/out of a particular parade ground which happened to be surrounded by trees of height approximating 50 ft. .. and why not ? .. as good a place to start the regulatory ball rolling as any.
Can't recall just when the 35 ft came into vogue for takeoff without digging into the dusty drawers but probably it was when the performance PAMC which predated CAR 4b surfaced. The extra distance associated with the more complex takeoff analyses was a bit too penalising were 50 ft to be retained. Those of us who have little hair, and/or significant grey portions of whatever hair we may have left will recall that the performance PAMC came in during the early days of the F27 and similar aircraft. The document marked a change from "simple" takeoff analyses to the more complex protocols we follow today which are based on a more rational and sound approach to risk management. I know I have a copy of that document somewhere in the archives ... somewhere.
Subsequently, wet runway screen heights nominally half the normal screen (rounded to 15 ft) came into the equation and the whole exercise continues to become more complicated but, at the same time, far more sensible.
