# Landing Field Length (Bizjet)

The landing weight of a Bizjet is 15,800 lb (wing-loading = 48.92 lb/ft2) and with full flap extended, it is CLmax = 2.2. Therefore:

The average velocity from a 50-ft height to touchdown = 168 ft/s. The distance cov­ered before brake application after 6 s (may differ) from a 50-ft height:

Sgtd = 6 x 168 = 1,008 ft

An aircraft in full braking with pB = 0.4, all engines shut down, and the aver­age CL = 0.5, CD/CL = 0.1. Equation 13.2 for average acceleration is based on

0. 7Vtd = 110.6 ft/s; then:

q = 0.5 x 0.002378 x 110.62 = 14.54

For deceleration:

a = 32.2 x [(-0.4) – (CLq/48.92)(0.1 – 0.4)]

= 32.2 x [-0.4 + (0.15 x 14.54/48.92)]

= 32.2 x [-0.4 + 0.0445] = -11.45

The distance covered during braking, SG0Land = (158 x 79)/11.45 = 1,090 ft. The landing distance SGLand = 1,008 +1,090 = 2,098 ft.

Table 13.16. Bizjet takeoff field length with 8-degflap setting

 knot ft/s Vstall @20,600 lb 106.4 179.6 V1 decision speed 109 183.8 V2 = 1.2Vstall at 35-ft height* 128.2 216.5 Vlo at 1.12Vsten** 119.17 201.15 VR at 1.1 Vstall** 117 197.6 Vmu at 1.01 Vr (lower than Vlo) 118.2 199.5 Vmc at 0.94 V1 102 172.2 BFL (ft) (TOFL requirement 4,400 ft) 3,800

V1 is too close to Vstall but is acceptable. If required it can be raised by a few knots. * If required, V2 can be higher than 1.2Vstall.

** If required, Vr and Vlo can be at higher speeds.

Table 13.17. First – and second-segment climb performance

 1st Segment Climb 2nd Segment Climb 35- to 400-ft altitude 400- to 1,000-ft altitude Pave = 0.00235 lb/ft3 Pave = 0.00232 lb/ft3 0.5pSW = 0.3795 0.5pSW = 0.3747 Flap (deg) 8 20 8 20 MTOM (kg) 20,680 20,680 20,680 20,680 Vstall (ft/s) (knot) 179.6 (106.4) 168.4 (99.8) 179.6 (106.4) 168.4 (99.8) V2 = (ft/s) (Mach) 216.50 (0.194) 202.08 (0.181) 216.50 (0.194) 202.08 (0.181) qSw 17,788 15,497.4 17,563 15,301.4 Cl 1.16 1.33 1.177 1.35 CDdean (see Figure 9.2) 0.075 0.100 0.076 0.101 ACD „one „eng 0.003 0.003 0.003 0.003 A CDflap 0.013 0.032 0.013 0.032 ACD-u/c 0.022 0.022 – – CDlstseg 0.113 0.157 0.092 0.135 Drag (lb) 2,010 2,433 1,616 2,081 Thrust Available (lb) 2,740 2,750 2,740 2,750 Gradient (%) +ve +ve 5.4 3.24 FAR Meets Meets Meets Meets

Note: Aircraft flap and undercarriage extended, engine at takeoff rating (one engine inoperative). (Use drag polar Figures 9.2 and 9.12 to obtain drag.)

Multiplying by 1.667, the rated LFL = 1.667 x 1,548 = 3,597 ft, within the requirement of 4,400 ft. As expected, this is less than the BFL at an 8-deg flap. This is not always the case because at a 20-deg flap setting, LFL > BFL.