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)

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