B5TAKEOFF GROUND ROLLU.K.
Take-off thrust accelerates the aeroplane along the runway until lift-off. Calibrated airspeed is then assumed to be constant throughout the initial part of the climbout. Landing gear, if retractable, is assumed to be retracted shortly after lift-off.
For the purpose of this document, the actual takeoff ground-roll is approximated by an equivalent take-off distance (into a default headwind of 8 kt), sTO8 , defined as shown in Figure B-1, as the distance along the runway from brake release to the point where a straight line extension of the initial landing-gear-retracted climb flight path intersects the runway.
On a level runway, the equivalent takeoff ground-roll distance sTO8 in feet is determined from
where
is a coefficient appropriate to a specific aeroplane/flap-deflection combination for the ISA reference conditions, including the 8-knot headwind, ft/lbf
is the aeroplane gross weight at brake release, lbf
is the number of engines supplying thrust.
Note: U.K.
Since equation B-9 accounts for variation of thrust with airspeed and runway elevation, for a given aeroplane the coefficient B8 depends only on flap deflection.
For headwind other than the default 8 kt, the takeoff ground-roll distance is corrected by using:
where
is the ground-roll distance corrected for headwind w, ft
(in this equation) is the calibrated speed at takeoff rotation, kt
is the headwind, kt
The takeoff ground-roll distance is also corrected for runway gradient as follows:
where
is the ground-roll distance (ft) corrected for headwind and runway gradient,
is the runway gradient; positive when taking-off uphill