Graphical Method for Predicting Aircraft Component Weight: Civil Aircraft

The graphical method is based on regression analyses of an existing design. To put all the variables affecting weight in graphical form is difficult and may prove imprac­tical because there will be separate trends based on choice of material, maneuver loads, fuselage layout (e. g., single or double aisle; single or double deck), type of engine integrated, wing shape, control architecture (e. g., FBW is lighter), and so forth. In principle, a graphical representation of these parameters can be accom­plished at the expense of simplicity, thereby defeating the initial purpose. The sim­plest form, as presented in this section, obtains a preliminary estimate of component and aircraft weight. At the conceptual design stage – when only the technology level to be adopted and the three-view drawing are available to predict weights – the

Table 8.1. Smaller aircraft mass fraction (fewer than or 19 passengers -2 abreast seating)

Rapid mass estimation method: Summary of mass fraction of MTOM for smaller aircraft. A range of applicability is shown; add another ± 10% for extreme designs.

Group

Small-piston

aircraft

Agriculture

aircraft

Small aircraft 2-engine (Bizjet, utility)

1-Engine

2-Engine

(1-Piston)

(Turboprop)

(Turbofan)

Fuselage

Ffu = Mfu/MTOM

12 to 15

6 to 10

6 to 8

10 to 11

9 to 11

Wing

Fw = MW/MTOM

10 to 14

9 to 11

14 to 16

10 to 12

9 to 12

H-tail

Fht = MHT/MTOM

1.5 to 2.5

1.8 to 2.2

1.5 to 2

1.5 to 2

1.4 to 1.8

V-tail

Fvt = Mvt/MTOM

1 to 1.5

1.4 to 1.6

1 to 1.4

1 to 1.5

0.8 to 1

Nacelle

Fn = MN/MTOM

1 to 1.5

1.5 to 2

1.2 to 1.5

1.5 to 1.8

1.4 to 1.8

Pylon

Fpy = MPY/MTOM

0

0

0

0.4 to 0.5

0.5 to 0.8

Undercarriage

Fuc = Me/MTOM

4 to 6

4 to 6

4 to 5

4 to 6

3 to 5

Engine

Fuc = Muc/MTOM

11 to 16

18 to 20

12 to 15

7 to 10

7 to 9

Thrust rev.

Ftr = Mtr/MTOM

0

0

0

0

0

Engine control

Fec = Mec/MTOM

1.5 to 2.5

2 to 3

1 to 2

1.5 to 2

1.7 to 2

Fuel system

Ffs = Mfs/MTOM

0.7 to 1.2

1.4 to 1.8

1 to 1.4

1 to 1.2

1.2 to 1.5

Oil system

Fos = Mos/MTOM

0.1 to 0.3

0.25 to 0.4

0.1 to 0.3

0.3 to 0.5

0.3 to 0.5

APU

0

0

0

0

0

Flight con. sys.

Ffc = Mfc/MTOM

1.5 to 2

1.4 to 1.6

1 to 1.5

1.5 to 2

1.5 to 2

Hydr./pneu. sys.

Fhp = MHP/MTOM

0 to 0.3

0.3 to 0.6

0 to 0.3

0.5 to 1.5

0.7 to 1

Electrical

Felc = Melec/MTOM

1.5 to 2.5

2 to 3

1.5 to 2

2 to 4

2 to 4

Instrument

Fins = Mins/MTOM

0.5 to 1

0.5 to 1

0.5 to 1

0.5 to 1

0.8 to 1.5

Avionics

Fav = Mav/MTOM

0.2 to 0.5

0.4 to 0.6

0.2 to 0.4

0.3 to 0.5

0.4 to 0.6

ECS

Fecs = Mecs/MTOM

0 to 0.3

0.4 to 0.8

0 to 0.2

2 to 3

2 to 3

Oxygen

Fox = MOx/MTOM

0 to 0.2

0 to 0.4

0

0.3 to 0.5

0.3 to 0.5

Furnishing

Ffur = Mfur/MTOM

2 to 6

4 to 6

1 to 2

6 to 8

5 to 8

Miscellaneous

Fmsc = Mmsc/MTOM

0 to 0.5

0 to 0.5

0 to 0.5

0 to 0.5

0 to 0.5

Paint

Fpn = Mpn/MTOM

0.01

0.01

0 to 0.01

0.01

0.01

Contingency

Fcon = McOn/MTOM

1 to 2

1 to 2

0 to 1

1 to 2

1 to 2

MEW (%)

57 to 67

60 to 65

58 to 62

58 to 63

55 to 60

Crew

6 to 12

6 to 8

4 to 6

1 to 3

1 to 3

Consumable

0 to 1

0 to 1

0

1 to 2

1 to 2

OEM (%)

65 to 75

65 to 70

62 to 66

60 to 66

58 to 64

Payload and fuel are traded

Payload

12 to 25

12 to 20

20 to 30

15 to 25

15 to 20

Fuel

8 to 14

10 to 15

8 to 10

10 to 20

18 to 28

MTOM (%)

100

100

100

100

100

Notes: Lighter/smaller aircraft would show a higher mass fraction.

A fuselage-mounted undercarriage is shorter and lighter for the same MTOM.

Turbofan aircraft with a higher speed would have a longer range as compared to turboprop aircraft and, there­fore, would have a higher fuel fraction (typically, 2,000-nm range will have around 0.26).

prediction is approximate. However, with rigorous analyses using semi-empirical prediction, better accuracy can be achieved that captures the influence of various parameters, as listed previously.

Not much literature in the public domain entails graphical representation. An earlier work (1942; in FPS units) in [3] presents analytical and semi-empirical treat­ment that culminates in a graphical representation. It was published in the United States before the gas-turbine age, when high-speed aircraft were nonexistent; those graphs served the purpose at the time but are now no longer current. Given herein

Table 8.2. Larger aircraft mass fraction (more than 19 passengers – abreast and above seating). Rapid Mass Estimation Method: Summary of mass fraction of MTOM for larger aircraft. A range of applicability is shown; add another ± 10% for extreme designs.

RJ/Midsized aircraft 2 engines

Large aircraft turbofan

Group

Turboprop

Turbofan

2-engine

4-engine

Fuselage

Ffu = Mfu/MTOM

9 to 11

10 to 12

10 to 12

9 to 11

Wing

Fw = MW/MTOM

7 to 9

9 to 11

12 to 14

11 to 12

H-tail

Fht = MHT/MTOM

1.2 to 1.5

1.8 to 2.2

1 to 1.2

1 to 1.2

V-tail

Fvt = Mvt/MTOM

0.6 to 0.8

0.8 to 1.2

0.6 to 0.8

0.7 to 0.9

Nacelle

Fn = Mn/MTOM

2.5 to 3.5

1.5 to 2

0.7 to 0.9

0.8 to 0.9

Pylon

Fpy = MPY/MTOM

0 to 0.5

0.5 to 0.7

0.3 to 0.4

0.4 to 0.5

Undercarriage

Fuc = MUC/MTOM

4 to 5

3.4 to 4.5

4 to 6

4 to 5

Engine

Feng = M ENG/MTOM

8 to 10

6 to 8

5.5 to 6

5.6 to 6

Thrust rev.

Ftr = MTR/MTOM

0

0.4 to 0.6

0.7 to 0.9

0.8 to 1

Engine con.

Fec = M EC/MTOM

1.5 to 2

0.8 to 1

0.2 to 0.3

0.2 to 0.3

Fuel system

Ffs = Mfs/MTOM

0.8 to 1

0.7 to 0.9

0.5 to 0.8

0.6 to 0.8

Oil system

Fos = MOS/MTOM

0.2 to 0.3

0.2 to 0.3

0.3 to 0.4

0.3 to 0.4

APU

0 to 0.1

0 to 0.1

0.1

0.1

Flight con. sys.

Ffc = MFC/MTOM

1 to 1.2

1.4 to 2

1 to 2

1 to 2

Hydr./pneu. sys.

Fhp = MHP/MTOM

0.4 to 0.6

0.6 to 0.8

0.6 to 1

0.5 to 1

Electrical

Felc = Melec/MTOM

2 to 4

2 to 3

0.8 to 1.2

0.7 to 1

Instrument

Fins = MINS/MTOM

1.5 to 2

1.4 to 1.8

0.3 to 0.4

0.3 to 0.4

Avionics

Fav = MAV/MTOM

0.8 to 1

0.9 to 1.1

0.2 to 0.3

0.2 to 0.3

ECS

Fecs = M ECS/MTOM

1.2 to 2.4

1 to 2

0.6 to 0.8

0.5 to 0.8

Oxygen

Fox = MOX/MTOM

0.3 to 0.5

0.3 to 0.5

0.2 to 0.3

0.2 to 0.3

Furnishing

Ffur = MFUR/MTOM

4 to 6

6 to 8

4.5 to 5.5

4.5 to 5.5

Miscellaneous

Fmsc = MMSC/MTOM

0 to 0.1

0 to 0.1

0 to 0.5

0 to 0.5

Paint

Fpn = MPN/MTOM

0.01

0.01

0.01

0.01

Contingency

Fcon = MCON/MTOM

0.5 to 1

0.5 to 1

0.5 to 1

0.5 to 1

MEW (%)

53 to 55

52 to 55

50 to 54

48 to 50

Crew

0.3 to 0.5

0.3 to 0.5

0.4 to 0.6

0.4 to 0.6

Consumable

1.5 to 2

1.5 to 2

1 to 1.5

1 to 1.5

OEW (%)

Payload and fuel are traded

54 to 56

53 to 56

52 to 55

50 to 52

Payload

15 to 18

12 to 20

18 to 22

18 to 20

Fuel

20 to 28

22 to 30

20 to 25

25 to 32

MTOM (%)

100

100

100

100

Notes: Lighter aircraft would show higher mass fraction.

A fuselage-mounted undercarriage is shorter and lighter for the same MTOM.

Turbofan aircraft with a higher speed would have a longer range as compared to turboprop aircraft and, therefore, would have a higher fuel fraction.

Large turbofan aircraft have wing-mounted engines: 4-engine configurations are bigger.

are updated graphs based on the data in Table 8.3; they are surprisingly represen­tative with values that are sufficient to start the sizing analysis in Chapter 11. Most of the weight data in the table are from Roskam [4] with additions by the author notated with an asterisk (these data are not from the manufacturers). The best data is obtained directly from manufacturers.

In all of the graphs, the MTOW is the independent variable. Aircraft – component weight depends on the MTOW; the heavier the MTOW, the heavier

Table 8.3. Aircraft component weights data

Aircraft

MTOW

Weight (lb) Fuse Wing

Emp

Nacelle

Eng

U/C

n

Piston-engined aircraft

1. Cessna182

2,650

400

238

62

34

417

132

5.70

2. Cessna310A

4,830

319

453

118

129

852

263

5.70

3. Beech65

7,368

601

570

153

285

1,008

444

6.60

4. Cessna404

8,400

610

860

181

284

1,000

316

3.75

5. Herald

37,500

2,986

4,365

987

830

1,625

3.75

6. Convair240

43,500

4,227

3,943

922

1,213

1,530

3.75

Gas-turbine-powered aircraft

7. Lear25

15,000

1,575

1,467

361

241

792

584

3.75

8. Lear45 class

20,000

2,300

2,056

385

459

1,672

779

3.75

9. Jet Star

30,680

3,491

2,827

879

792

1,750

1,061

3.75

10. Fokker27-100

37,500

4,122

4,408

977

628

2,427

1,840

3.75

11. CRJ200 class

51,000

6,844

5,369

1,001

1,794

5.75

12. F28-1000

65,000

7,043

7,330

1,632

834

4,495

2,759

3.75

13. Gulf GII (J)

64,800

5,944

6,372

1,965

1,239

6,570

2,011

3.75

14. MD-9-30

108,000

16,150

11,400

2,780

1,430

6,410

4,170

3.75

15. B737-200

115,500

12,108

10,613

2,718

1,392

6,217

4,354

3.75

16. A320 class

162,000

17,584

17,368

2,855

2,580

12,300

6,421

3.75

17. B747-100

710,000

71,850

86,402

11,850

10,031

34,120

31,427

3.75

18. A380 class

1,190,497

115,205

170,135

24,104

55,200

52,593

3.75

are the component weights (see Chapter 4). Strictly speaking, wing weight could have been presented as a function of the wing reference area, which in turn depends on the sized wing-loading (i. e., the MTOW) (see Chapter 11).

To use the graph, the MTOW must first be guesstimated from statistics (see Chapters 4 and 6). After the MTOW is worked out in this chapter, iterations are necessary to revise the estimation.

Figure 8.3 illustrates civil aircraft component weights in FPS units. The first pro­vides the fuselage, undercarriage, and nacelle weights. Piston-engine-powered air­craft are low-speed aircraft and the fuselage group weight shows their lightness. There are no large piston-engine aircraft in comparison to the gas-turbine type.

Figure 8.3 Aircraft component weights in pounds

The lower end of the graph represents piston engines; piston-engine nacelles can be slightly lighter in weight.

The second graph in Figure 8.3 shows the wing and empennage group weights. The piston – and gas-turbine engine lines are not clearly separated. FBW-driven con­figurations have a smaller wing and empennage (see Chapter 13), as shown in sep­arate lines with lighter weight (i. e., A320 and A380 class). The newer designs have composite structures that contribute to the light weight.

Figure 8.3 shows consistent trends but does not guarantee accuracy equal to semi-empirical relations, which are discussed in the next section.

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