Flex take-off question
Joined: Sep 2002
Posts: 2,188
Likes: 6
From: La Belle Province
It depends on the particulars of your aircraft and the degree to which you are trying to optimise the performance from the specific runway.
Suppose, for example, your aircraft is constrained by V2min rather than any Vr-based considerations. You leave V2 set at V2min. But now the a/c is slower to accelerate (lower thrust). So a higher Vr may be required to ensure that the minimum V2 is achieved at the right height. This in turn may permit a higher V1 to be selected, if it was constrained by V1.
Joined: Jun 2010
Posts: 304
Likes: 0
From: Brisbane, Australia
In an extension to that question....errr...you remember, the original question!
Whether you use maximum power, Derate 1 or Derate 2, for your next takeoff, there is a stabilizer trim setting for each specific t/o power setting.
But you will find that there is no stabilizer setting specific to a Assumed Temp (Flex) power takeoff, that's because the assumed temp power takeoff is not a limiting setting, and the thrust levers can 'legally' be advanced any time during the ground run of the airplane, with the 'normal' stab setting already set, that's no problem!
But, with a combination of not advancing more than the original setting, a normal takeoff, and the fact that the stab trim setting takes into account the 'pitch up' moment created by the applicable power set, in this case it will be a lower power setting (assumed temp), so an amount of out-of-trim (nose down) will be noticeable when rotating at Vr.
Ever noticed that!
Whether you use maximum power, Derate 1 or Derate 2, for your next takeoff, there is a stabilizer trim setting for each specific t/o power setting.
But you will find that there is no stabilizer setting specific to a Assumed Temp (Flex) power takeoff, that's because the assumed temp power takeoff is not a limiting setting, and the thrust levers can 'legally' be advanced any time during the ground run of the airplane, with the 'normal' stab setting already set, that's no problem!
But, with a combination of not advancing more than the original setting, a normal takeoff, and the fact that the stab trim setting takes into account the 'pitch up' moment created by the applicable power set, in this case it will be a lower power setting (assumed temp), so an amount of out-of-trim (nose down) will be noticeable when rotating at Vr.
Ever noticed that!
Joined: Feb 1998
Aviation Qualifications: ATPL
Posts: 1,595
Likes: 0
From: Formerly of Nam
SPC - just look at flex take-offs as a way of protecting the
engines if the next guy happens to lose one, and the only
thing separating him from a violent death is that one and
only remaining engine being operable and not clapped out.
engines if the next guy happens to lose one, and the only
thing separating him from a violent death is that one and
only remaining engine being operable and not clapped out.
