Turbofans with a BPR Around 4 (Smaller Engines; e. g., Bizjets)
Turbofan performance. An enginematching and aircraftsizing 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 fuelflow 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 50,000ft altitude for three Mach numbers. Intermediate values may be linearly interpolated. There is a break in thrust generation at an approximate 6,000 to 10,000ft 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 800ft 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 50,000ft altitude for Mach numbers varying from 0.5 to 0.8, which is sufficient for this class of engineaircraft 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

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 enginematching and aircraftsizing 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 sealevel static data at takeoff standard day Without afterburner With afterburner

SHPsls 
Dry weight lb 

RR250B17 
450 
195 
PT6A 
850 
328 
TPE33112 
1,100 
400 
GECT7 
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 50,000ft 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 50,000ft altitude for Mach numbers varying from 0.5 to 0.8, which is sufficient for this class of engineaircraft 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 turbofanengine 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)
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