Takeoff Rating (Bizjet): Standard Day
Depending on how the ECS is managed, installation loss typically varies from 6 to 8% of the uninstalled, sea-level static thrust. If required, the air-conditioning can be turned off for a brief period until the undercarriage is retracted. Using a 7% installation loss at takeoff, Section 11.6 works out the matched installed TSLSjNSTALLED = 0.93 x 3,560 = 3,315 lbs per engine for the sized Bizjet. Figure 13.1 shows the installed engine thrust at the takeoff rating.
The fuel-flow rate is computed from the sfc of 0.498 lb/hr/lb at the sea-level, static condition (see Section 10.11.3). Using the uninstalled TsLs = 3,560 lbs per engine, the fuel-flow rate is 3,560 x 0.498 = 1,772 lbs per hour per engine. Fuel flow is kept nearly constant at takeoff up to the enroute climb segment, when the engine is throttled down to the maximum climb rating (computed in the following section).
Figure 13.1. Installed takeoff performance per engine (^BPR 3 to 4)
Maximum Climb Rating (Bizjet): Standard Day
Figure 10.46 shows the uninstalled maximum climb thrust in nondimensional form in terms of TSlS and fuel consumption (sfc) up to a 50,000-ft altitude for three Mach numbers. The installation loss during a climb is 6% of the uninstalled thrust. Using these graphs, the installed thrust and fuel-flow rates are plotted in Figure 13.2. This turbofan has a break in the fuel flow at a 5,000- to 10,000-ft altitude, depending on the flight Mach number, to keep the EGT within the limits, which results in a corresponding break in thrust generation (see Figure 13.2).
Equation 11.15 in Chapter 11 requires a factor k2 to be applied to the TSlS to obain the initial climb thrust. In the example, k2 is 1.5. Continuing with the coursework exercise, the uninstalled, initial climb thrust is 3,560/1.5 = 2,373 lbs per engine and the installed thrust becomes TSlS1nSTalled = 0.94 x 2,373 = 2,231 lbs per engine. Fuel flow at the initial climb is obtained from the sfc graph in Figure 10.46b. For the initial climb, the sfc is 0.7 pound per hour per pound, which results in a fuel flow of 0.7 x 2,373 = 1,661 lbs/hr per engine. Equations for the climb performance are derived in Section 13.4.3 and the coursework example is verified in Section 13.5.2. Estimation of the payload range requires the full aircraft climb performance up to the cruise altitude.
= 600 –
C 400 =
Figure 13.3. Installed maximum cruise performance per engine (^<BPR 4)
Maximum Cruise Rating (Bizjet): Standard Day
Figure 10.47 shows the uninstalled maximum cruise thrust in nondimensional form and fuel consumption (sfc) from a 5,000- to 50,000-ft altitude for Mach numbers varying from 0.5 to 0.8. Figure 13.3 shows the installed-engine thrust at the maximum cruise rating for the sized Bizjet.
The coursework example specified an initial maximum cruise speed (i. e., HSC) of Mach 0.74 at 41,000 ft. From Figure 10.47, that point gives the uninstalled ratio T/TSLS = 0.222 (TSLS/T = 4.5). This is the k in Section 11.3.3 that results in an uninstalled thrust of 3,560 x 0.222 = 790 lbs per engine. Considering a 4% installation loss at cruise, the installed thrust of T = 0.96 x 790 = 758 lbs per engine. Section 13.5.3 verifies whether the thrust is adequate for an aircraft to reach the maximum cruise speed. The fuel in Figure 13.4 (see Web at www. cambridge. org/Kundu) is 0.73 x 790 = 577 lb/hr per engine.