The Chengdu Jian-20Kris Douglas, Sam Kantor, Michael Palles and Grant Parrish

Image: defensetec.org

Configuration and Geometry

• Geometry estimated using

3-view drawing and graphics

application

• Relatively long, high-volume

fuselage compared to existing

5th generation fighters

J-20 AIRFRAME GEOMETRY

Length

(ft)

Height

(ft)

Span

(ft)

Swet

(ft2)

Vfuse

(ft3)

70.5 14.4 42.6 3025.7 2377.3

Configuration and Geometry

Non-Wing-Mounted

Control Surface

Area

(ft2)

Average

Chord (ft)

Length

(ft)

Dihedral

(°)

Centroid Location

Relative to Nose (ft)

x y z

Canard 48.0 6.6 7.3 10.7 25.2 8.3 1.8

Tail 53.5 6.6 8.2 59.8 60.2 4.1 3.9

Aft Ventral Fin 16.7 4.9 3.4 -60.3 59.6 7.1 -2.2

Wing-Mounted

Control Surface

Area

(ft2)% Cave % b/2

Centroid Location

Relative to Nose (ft)

x y z

Aileron 20.8 13.0 38.7 55.7 17.2 0.1

Trailing Edge Flap 30.8 23.2 32.0 56.1 10.3 0.6

Leading Edge Slat 17.9 9.7 44.6 44.0 14.8 0.3

J-20 PLANFORM GEOMETRY

Swing

(ft2)

b

(ft)

Sref

(ft2)AR

Cr

(ft)

Ct

(ft)

Cave

(ft)λ

ΛLE

(°)

ΛTE

(°)

Γ

(°)

493.2 42.6 829.9 2.19 34.0 4.9 19.5 0.15 49.9 -8.4 -3.9

Weight EstimationAircraft

ComponentMultiplier and Reference

Reference

Value

Weights

(lb)

CG Location Aft of

Nose Apex (ft)

Main Wing 9.0×Wing Area (ft2) 493.2 4438.8 48.8

Horizontal Tail 4.0×Horizontal Tail Area (ft2) 125.3 501.2 40.0

Vertical Tails 5.3×Vertical Tail Area (ft2) 73.0 386.9 60.7

Fuselage 4.8×Fuselage Wetted Area (ft2) 1566.7 7520.3 33.0

Landing Gear 0.033× GTOW Guess (lb) 75000 2475.0 37.9

Installed Engine 1.3×Engine Weight (lb) 5000 6500.0 53.2

"All-Else Empty" 0.17×GTOW Guess (lb) 75000 12750.0 33.0

Empty Weight (lb) 34572.2 Wing Loading (lb/ft2) 90.5

Fuel and Payload (lb) 40427.8 Thrust-to-Weight 0.507

CG Location (%MAC) 20Thrust-to-Weight

(Afterburners)0.853

CG Estimate based on Gear

Placement (%MAC)18.6

Gear Placement Guidelines

• Tipback angle between

12 and 15 degrees

• Overturn angle

between 54 and 63

degrees

• Results in CG location

of approximately

18.6% MAC

Stability Characteristics

• Varied Number of Panels– Chordwise

– Spanwise

• Multiple Runs Varying– Mach Number

– Angle of Attack

– Sideslip Angle

– CG Location

• Produced – Stability Derivatives

– Lift Induced Drag

– Trim Drag

• Wing Airfoil: NACA 64206

• Tail Airfoils: 7% Thick Biconvex

AVL 3.27 Model (960 Panels)

Convergence History

300 400 500 600 700 800 900 10003.5

4

4.5

5

5.5

Number of Panels

Neutr

al P

oin

t Location in %

MA

C

Neutral Point Location vs. Number of Panels and Mach Number

0.0

0.1

0.2

0.3

0.4

0.5

0.6

300 400 500 600 700 800 900 10002.85

2.9

2.95

3

3.05

3.1

3.15

3.2

Number of Panels

CLalfa

CL Alpha vs. Number of Panels and Mach Number

300 400 500 600 700 800 900 10000.41

0.415

0.42

0.425

0.43

0.435

0.44

0.445

0.45

Number of Panels

Cm

alfa

Cm Alpha vs. Number of Panels and Mach Number

0.0

0.1

0.2

0.3

0.4

0.5

0.6

200 400 600 800 10000.078

0.079

0.08

0.081

0.082

0.083

0.084

Number of Panels

Cnbeta

Cn beta vs. Number of Panels and Mach Number

Mach

Mach

Stability Derivatives

Mach

Mach

Mach

Mach

Drag Estimation: Viscous Drag

• Viscous Drag calculated using friction2k6 code on course website, at

Mach 0.1 to 2.9 and altitudes of 15, 25, and 35 kft

• Combined skin friction and form drag coefficient did not vary with

altitude (identical to four decimal places)

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.0 0.5 1.0 1.5 2.0 2.5 3.0

Dra

g C

oe

ffic

ien

t, C

D

Mach Number, M∞

Chengdu J-20 Viscous Drag (35 kft)

CDF+CDForm

CDF

CDForm

Drag Estimation: Lift-Induced Drag

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.00 0.03 0.06 0.09 0.12 0.15 0.18

Lift

Co

eff

icie

nt,

CL

Drag Coefficient, CD

Chengdu J-20 Subsonic Drag Polar

• Calculated using AVL and FRICTION.exe

− FRICTION.exe for profile drag

− AVL for induced drag

• Trim drag included

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

-30 -10 10 30 50

CL

Canard Deflection (DEG)

Canard Schedule

Drag Estimation: Trim Drag

• Balanced 14% unstable

• Minimum trim drag

near 30% unstable

• Suggests other factors

drive static margin

• Varies little with Mach

number

-40 -35 -30 -25 -20 -15 -10 -5 0 5 105

6

7

8

9

10

11

12x 10

-3

Static Margin (%)

Induced D

rag C

oeff

icie

nt

(CD

i)

Center of Gravity Effect on Trim Drag

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Drag Estimation: Wave Drag

• Wave drag estimated using AWAVE and awaveFileMake.m

updated to include arbitrary fuselage shapes

• Little variation with angle-of-attack for small α

0.00

0.01

0.02

0.03

0.04

0.05

0.06

1.0 1.5 2.0 2.5

Wa

ve

Dra

g C

oe

ffic

ien

t, C

Dw

Mach Number, M∞

Chengdu J-20 Wave Drag Coefficient

Drag Estimation: Wave Drag

0

10

20

30

40

50

60

70

80

1.0 1.5 2.0 2.5

Wa

ve

Dra

g,

Dw

(klb

)

Mach Number, M∞

Chengdu J-20 Wave Drag

ISA 35,000 ft

ISA 25,000 ft

ISA 15,000 ft

• Volumetric wave drag represents a high percentage of

the available thrust at high Mach

Drag Estimation: Total Drag

0

10

20

30

40

50

60

0.0 0.5 1.0 1.5 2.0 2.5

Tota

l D

rag

, D

(k

lb)

Mach Number, M∞

Chengdu J-20 Total Drag Buildup (35 kft)

• Note the jump in drag at the sonic speed due to onset of wave drag

• Maximum Mach clearly impacted by engine performance

Performance: Maximum Speed

• M = 2.13 (shock forms on nose cone)

• M = 2.81 (shock forms on probe)

• Enough thrust to achieve M ≈ 2.5

M = 2.25 M = 1.6+ M = 2.1-2.5

F-22 F-35 J-20

Performance: Range

• Max range calculated using Breguet Range equation and

weight fractions

• V/C assumed constant at each speed for these calculations

Performance:

Takeoff Distance & Climb Rate

• Ground roll required: 1398ft (black)

• Distance to achieve MIL 50’ clearance requirement: 144ft (red)

• Total take-off distance: 1542ft

• Climb angle for best rate of climb: 19.2°

Conclusions

• Configuration characteristics

– large internal volume (i.e. munitions capacity)

– long range

– supercruise capability

• Optimized for use as a long-range interceptor

and air-to-surface attack platform

• Actual performance dependent upon engine

development

References• Lake, J. “Out in the Open, Chengdu’s Jian-20.” Air International. February 2011.

• Bharat Rakshak: Consortium of Indian Defence Websites. March 9, 2011.

http://forums.bharat-rakshak.com/viewtopic.php?f=3&t=3827&start=3800

• Raymer, D. P. (2006). Aircraft Design: A Conceptual Approach. Reston, Virginia: American

Institute of Aeronautics and Astronautics, Inc.

• Mason, W.H. “AOE 4124: Configuration Aerodynamics.” Department of Aerospace and

Ocean Engineering at Virginia Tech. March 20, 2011.

http://www.dept.aoe.vt.edu/~mason/Mason_f/ConfigAero.html

• “Chengdu J-20: Stealthy Multi-Role Fighter.” MilitaryToday.com. March 1, 2011.

http://www.military-today.com/aircraft/j20.htm

• Sweetman, B. “J-20 – Denial Is Not an Option.” Aviation Week. March 12, 2011.

http://www.aviationweek.com/aw/blogs/defense

Questions?

http://www.freerepublic.com/focus/f-news/2655343/posts