# Turbofans with a BPR Around 4 (Smaller Engines; e. g., Bizjets)

Turbofan performance. An engine-matching and aircraft-sizing exercise that gives the TSLS is conducted in Chapter 11. Chapters 11 and 13 work out the installed thrust and fuel flow for the matched engines of the sized aircraft under study.

Takeoff Rating. Figure 10.45 shows the takeoff thrust in nondimensional form for the standard day for turbofans with a BPR of 4 or less. The fuel-flow rate remains nearly invariant for the envelope shown in the graph. Therefore, the sfc at the take­off rating is the value at the TSLS of 0.498 lb/lb/hr per engine.

Maximum Climb Rating. Figure 10.46 gives 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. There is a break in thrust generation at an approximate 6,000- to 10,000-ft altitude, depending on the Mach number, due to fuel control to keep the EGT low.

Equation 11.14 (see Chapter 11) requires a factor k2 to be applied to the TSLS to obtain the initial climb thrust. In the example, the initial climb starts at an 800-ft altitude at 250 VEAS (Mach 0.38), which gives T/ TSLS = 0.67 – that is, the factor k2 = TSLS/ T = 1.5. At a constant EAS, the Mach number increases with altitude; in

Figure 10.45. Uninstalled takeoff per­formance (^<BPR4)

Altitude (feet)

(a) Nondimensional Thrust

Figure 10.46. Uninstalled maximum climb rating (^<BPR 4)

the example, when it reaches 0.7 (depending on the aircraft type), the Mach number is held constant. Fuel flow at the initial climb is obtained from Figure 10.46b.

With varying values of altitude, climb calculations are performed in small incre­ments of altitude within which the variation is taken as the mean and is kept constant for the increment.

Maximum Cruise Rating. Figure 10.47 shows the maximum cruise thrust and fuel flow in nondimensional form for the standard day from a 5,000- to 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.

The coursework example of the design initial maximum cruise speed is Mach 0.7 at 41,000 ft. From the graph, that point is T/ Tsls = 0.222, which has Tsls/ T =

4.5 (i. e., k2 in Chapter 11). Chapter 11 verifies whether the thrust is adequate for attaining the maximum cruise speed. Fuel flow per engine can be computed from Figure 10.47b.

Figure 10.48. Uninstalled takeoff perfor­mance (^>BPR 5)

(a) Nondimensional Thrust (b) Specific Fuel Consumption

Figure 10.50. Uninstalled maximum cruise rating (^>BPR 5)

Takeoff Cruise

 Model Thrust lb Fan dia (inches) BPR OPR Airflow lb/s Altitude 1,000 ft Mach Thrust lb TSFC lb/lb/hr CF6-50-C2 52,500 134.1 4.31 30.4 1,476 35 0.80 11,555 0.630 CF6-80-C2 52,500 86.4 4.31 27.4 1,450 35 0.80 12,000 0.576 GE90-B4 87,400 134 8.40 39.3 3,037 35 0.80 17,500 – JT8D-15A 15,500 49.2 1.04 16.6 327 30 0.80 4,920 0.779 JT9D-59A 53,000 97 4.90 24.5 1,639 35 0.85 11,950 0.666 PW2040 41,700 84.8 6.00 27.6 1,210 35 0.85 6,500 0.582 PW4052 52,000 97 5.00 27.5 1,700 – – – – PW4084 87,500 118.5 6.41 34.4 2,550 35 0.83 – – CFM56-3 23,500 60 5.00 22.6 655 35 0.85 4,890 0.667 CFM56-5C 31,200 72.3 6.60 31.5 1,027 35 0.80 6,600 0.545 RB211-524B 50,000 85.8 4.50 28.4 1,513 35 0.85 11,000 0.643 RB211-535E 40,100 73.9 4.30 25.8 1,151 35 0.80 8,495 0.607 RB211-882 84,700 – 6.01 39.0 2,640 35 0.83 16,200 0.557 V2528-D5 28,000 63.3 4.70 30.5 825 35 0.80 5,773 0.574 ALF502R 6,970 41.7 5.70 12.2 – 35 0.70 2,250 0.720 TFE731-20 3,500 28.2 3.34 14.4 140 40 0.80 986 0.771 PW300 4,750 38.2 4.50 23.0 180 40 0.80 1,113 0.675 FJ44 1,900 20.9 3.24 12.8 63.3 30 0.70 600 0.750 Olympus593 38,000 – – 11.30 410 53 2.00 10,030 1.150

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

Without afterburner With afterburner

 Model BPR Weight lb OPR Airflow lb/s Thrust-lb TSFC lb/lb/hr Thrust-lb TSFC lb/lb/hr P&WF119 0.45 3,526 35.0 – 23,600 – 35,400 – P&W F100 0.36 3,740 32.0 254.5 17,800 0.74 29,090 1.94 GE F110 0.77 3,950 30.7 270.0 17,020 – 29,000 – GE F404 0.27 2,320 26.0 146.0 12,000 0.84 17,760 1.74 GE F414 0.40 2,645 30.0 170.0 12,600 – 22,000 – Snecma-M88 0.30 1,980 24.0 143.0 11,240 0.78 16,900 1.8

 SHPsls Dry weight lb RR-250-B17 450 195 PT6-A 850 328 TPE-331-12 1,100 400 GE-CT7 1,940 805 AE2100D 4,590 1,548

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 5,000- to 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.

10.11.2 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)