ANNEX
B8ACCELERATING CLIMB AND FLAP RETRACTION
This usually follows the initial climb. As for all flight segments, the start-point altitude h1, true airspeed VT1, and thrust (Fn/δ)1 are those from the end of the preceding segment. The end-point calibrated airspeed VC2 and the average climb rate ROC are user inputs (bank angle ε is a function of speed and radius of turn). As they are interdependent, the end altitude h2, end true airspeed VT2, end thrust (Fn/δ)2 and segment track length Δs have to be calculated by iteration; the end altitude h2 is guessed initially and then recalculated repeatedly using equations B-16 and B-17 until the difference between successive estimates is less than a specified tolerance, e.g. one foot. A practical initial estimate is h2 = h1 + 250 feet.
The segment track length (horizontal distance covered) is estimated as:
(B-17) |
where
- 0,95
is a factor to account for effect of 8 kt headwind when climbing at 160 kt
- k
is a constant to convert knots to ft/sec = 1,688 ft/s per kt
- VT2
- = true airspeed at segment end, kt:
where σ2 = air density ratio at end altitude h2
- αmax
= maximum acceleration in level flight (ft/s2)
=
- G
= climb gradient
where ROC = climb rate, ft/min
Using this estimate of Δs, the end altitude h2′ is then re-estimated using:
h2′ = h1 + s · G/0,95 | (B-18) |
Note:
If during the iteration process (amax – G·g) < 0,02 g, the acceleration may be too small to achieve the desired VC2 in a reasonable distance. In this case, the climb gradient can be limited to G = amax/g – 0,02, in effect reducing the desired climb rate in order to maintain acceptable acceleration. If G < 0,01 it should be concluded there is not enough thrust to achieve the acceleration and climb rate specified; the calculation should be terminated and the procedure steps revised42.
The acceleration segment length is corrected for headwind w by using:
(B-19) |
Accelerating segment with cutback
Thrust cutback is inserted into an acceleration segments in the same way as for a constant speed segment; by turning its first part into a transition segment. The cutback thrust level is calculated as for the constant-speed cutback thrust procedure, using equation B-1 only. Note it is not generally possible to accelerate and climb whilst maintaining the minimum engine-out thrust setting. The thrust transition is assigned a 1 000 ft (305 m) ground distance, and the corrected net thrust per engine at the end of 1 000 ft is set equal to the cutback value. The speed at the end of the segment is determined by iteration for a segment length of 1 000 ft. (If the original horizontal distance is less than 2 000 ft, one half of the segment is used for thrust change.) The final thrust on the second sub-segment is also set equal to the cutback thrust. Thus, the second sub-segment is flown at constant thrust.