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Takeoff ground run is evaluated using stepwise integration and followed by a circular arc transition and a constant-angle airborne segment to match the 'second segment' climb gradient at the takeoff screen height. If the gradient falls below the minimum requirement (2.4% for twins), flap deflection is reduced as necessary. One-engine-out performance curves are calculated iteratively assuming different failure speeds to determine the 'accelerate-go' and 'accelerate-stop' distances. The critical condition and the corresponding Balanced Field Length (BFL) are found from the intersection of these curves. The TOFL is then the greatest of the BFL and 115% of the all-engines takeoff distance.

The user can control various parameters such as the braking friction coefficient and the takeoff safety speed ratio (V2/Vs, 1.2 by default). It is also possible to adjust the CLmax (max. Lift Coefficient) and Lift/Drag ratio at these low-speed conditions, as these aerodynamic parameters often cannot be known accurately without wind-tunnel or flight tests. Takeoffs can be conducted at ISA (International Standard Atmosphere) or off-ISA conditions and arbitrary field elevations.

Landing Field Length (LFL) is evaluated using similar step-by-step procedures. The airborne phase is typically determined from energy considerations for given final approach and touchdown speed ratios. Reverse thrust may be included optionally.

It is possible to generate plots and tabulations of the takeoff and landing field lengths as functions of range or takeoff weight. WAT curves (weight / altitude / temperature) are used to illustrate performance limits in terms of minimum gradient.

The following is a sample Field Length report:

TAKEOFF PERFORMANCE {37200.kg., altitude 0.feet, ISA+0.deg.C.} ___________________ JAR25 Takeoff Field Length 5638. feet 115% Factored All-Eng.Dist. 5159. feet Balanced Field Length 5638. feet 2nd Segment Climb Gradient 4.02 % Takeoff CLmax 2.31 {trapezoidal ref.area} Takeoff Vstall 117. keas Takeoff Vmc 81. keas Takeoff Vfail 133. keas Takeoff V2 141. keas L/D at 2nd segment 10.43 {incl.windmill & asymm.} Takeoff Wing Loading 108. p.s.f.{trap.W/S} Takeoff Thrust/Weight 0.335 available static LANDING PERFORMANCE {32800.kg., altitude 0.feet, ISA+0.deg.C.} ___________________ JAR25 Landing Field Length 4331. feet Landing Distance (LFL*0.6) 2598. feet Landing Ground Roll 1546. feet Landing CLmax 3.09 {trapezoidal ref.area} Landing Vstall 95. keas Approach Speed 124. keas Approach L/D 5.32 {gear down} |