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 5,000to 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 k1 in Section 11.3.3 that results in an uninstalled thrust of 3,560 × 0.222 = 790 lbs per engine. Considering a 4% installa- tion loss at cruise, the installed thrust of T = 0.96 × 790 = 758 lbs per engine. Section 13.5.3 verifies whether the thrust is adequate for an aircraft to reach the maxi- mum cruise speed. The fuel in Figure 13.4 (see Web at www.cambridge.org/Kundu) is 0.73 × 790 = 577 lb/hr per engine.

13.3.2 Turbofan Engine (BPR > 4)

Larger engines have a higher BPR. Current large operational turbofans have a BPR around 5 or 6 (new-generation turbofans have achieved a BPR > 8). These engines have performance characteristics slightly different than smaller engines – specifically, the maximum climb rating has no break in thrust with altitude gain. Using Figures 10.48 through 10.50, the installed thrust and fuel-flow rates can be worked out as in previous sections.

13.3.3 Military Turbofan (Advanced Jet Trainer/CAS Role – Very Low BPR) – STD Day

This extended section of the book can be found on the Web at www.cambridge

.org/Kundu and presents a typical military turbofan-engine installed performance (with and without reheat) at maximum rating suited to the classroom example of an AJT and a derivative in a CAS role. The installed performance is computed from the graph given in Subsection 10.11.4.