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• Takeoff & Landing Field Lengths

The Takeoff Field Length (TOFL) and Landing Field Length (LFL) are calculated from first principles, based on FAR-25 definitions and using the appropriate aerodynamics and engine characteristics.

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}

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