Turbofans with a BPR around 5 or 7 (Larger Engines; e.g., RJs and Larger)

Turbofan performance. Larger engines have a higher BPR. The currently operational larger turbofans are at a 5 to 7 BPR, which has nondimensional engine performance characteristics slightly different than smaller engines, as shown by comparing Figures 10.48 through 10.50.

The engine-matching and aircraft-sizing exercise in Chapter 11 gives the TSLS. Estimation of fuel flow is shown in the graph. Coursework follows the same routine as given herein.

Takeoff Rating. Figure 10.48 shows the takeoff thrust in nondimensional form for the standard day. The fuel flow rate remains nearly invariant for the envelope shown in the graph.

Table 10.9. Military aircraft engine sea-level static data at takeoff – standard day

Maximum Climb Rating. Figure 10.49 shows the maximum climb thrust and fuel flow in nondimensional form for the standard day up to a 50,000-ft altitude for three Mach numbers. Intermediate values may be linearly interpolated.

Maximum Cruise Rating. Figure 10.50 shows the maximum cruise thrust and fuel flow in nondimensional form for the standard day from a 5,000to 50,000-ft altitude for Mach numbers varying from 0.5 to 0.8, which is sufficient for this class of engine–aircraft combinations. Intermediate values may be linearly interpolated.

10.11.4 Turbofan Engine – Military Aircraft

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

.org/Kundu and presents a typical military turbofan-engine performance in nondimensional form (with and without reheat) at maximum rating suited to the classroom example of an AJT and a derivative in a CAS role. Figure 10.51 gives the thrust ratios from sea level to 36,000 ft altitude in an ISA day. Sfc is worked out.

Figure 10.51. Military turbofan engine with and without reheat (BPR = 0.75)