Table 11.1. Bizjet takeoff sizing

Computing and listing in tabular form:

circuit. Pilots prefer to approach as slow as possible for ease of handling at landing. For this class of aircraft, the approach velocity, Vapp (FAR requirement at 1.3 Vstall) is less than 125 kts to ensure that it is not constrained by the minimum control speed, Vc. Wing CLstall is at the landing flap and slat setting.

For sizing purposes, an engine is set to the idle rating to produce zero thrust. At approach:

11.4 Coursework Exercises: Civil Aircraft Design (Bizjet)

Both the FPS and the SI units are worked out in the examples. Sizing calculations require the generic engine data in order to obtain the factors used (see Section 10.11.3). The Bizjet drag polar is provided in Figure 9.2.

11.4.1 Takeoff

Requirements: TOFL 4,400 ft (1,341 m) to clear a 35-ft height at ISA + sea level. The maximum lift coefficient at takeoff (i.e., flaps down, to 20 deg, and no slat) is CLstall(TO) = 1.9 (obtained from testing and CFD analysis). The result is computed in Table 11.1. Using Equation 11.7a, the expression reduces to:

W/S = 4,400 × 1.9 × (T/ W)/37.5 = 222.9 × (T/ W)

Using Equation 11.7b, it becomes:

W/S = 4.173 × 1,341 × 1.9 × (T/ W) = 10,633.55 × (T/ W)

The industry must also examine other takeoff requirements (e.g., an unprepared runway) and hot and high ambient conditions.

Table 11.2. Bizjet climb sizing

Computing and listing in tabular form (use Figure 9.1 for the drag polar):

11.4.2 Initial Climb

From the market requirements, an initial climb starts at an 800-ft altitude at a speed VEAS = 250 knots (Mach 0.38) = 250 × 1.68781 = 422 ft/s (128.6 m/s) and the required rate of climb, RC = 2,600 ft/min (792.5 m/min) = 43.33 ft/s (13.2 m/s). From the TFE731 class engine data, TSLS/T ratio = 1.5 (factor k2 from Section 10.11.3, Figure 10.46). The undercarriage and high-lift devices are in a retracted position. Lift coefficient:

CLclimb = W/(0.5 × 0.002378 × 4222 SW) = 0.004723 × W/SW

Using Equation 11.14:

[TSLS/ W]/1.5 = 43.33/422 + (CD × 0.5 × 0.00232 × 4222 SW)/ W)

TSLS/ W = 0.154 + 310 × CD × (SW/ W)

11.4.3 Cruise

Requirements: Initial cruise speed must meet the high-speed cruise (HSC) at Mach 0.74 and at 41,000 ft (flying higher than bigger jets in less congested traffic corridors) using k = 0.972 in Equation 11.14.

In FPS at 41,000 ft:

ρ = 0.00056 slug/ft2 and V2 = (0.74 × 968.076)2 = 716.382 = 513,195 ft2/s2

In SI at 12,192 m:

ρ = 0.289 kg/m3 and V2 = (0.74 × 295.07)2 = 218.352 × 47,677.5 m2/s2

Equation 11.18 gives the initial cruise:

CL = 0.972 MTOW/(0.5 × 0.289 × 47,677.5 × SW)

= 0.0001414(W/SW)

where W/SW is in N/m2. Equation 11.19 gives:

TSLS/ W = k1 × 0.5ρ V2 × CD/(W/SW)

(Use factor k1 = TSLS/ Ta = 4.5 from Figure 10.47.) In FPS:

TSLS/ W = 4.5 × 0.5 × 0.00056 × 459,208.2 × CD/(W/SW) = 565.73 × CD/(W/SW)