Airfoil selection
• Aerodynamic characteristics (Kmax , CLmax , stall characteristics) • Structural reasons;
1 Airfoil geometry
Airfoil geometry
Camber line
Leading Chord Maximum edge thickness
Trailing edge Maximum Maximum camber thickness position Maximum camber position
2 Angle of attack definition
AoA V∞
Stall
AoA=0° Separation point
AoA=10°
AoA=15°
AoA=20°
3 Airfoil aerodynamic characteristics
Lift coefficient (Cz or C L) Drag coefficient (Cx or C D ) C LMAX Stall
dC /d α ≡≡≡ a α l 0
α KR
Airfoil aerodynamic characteristics
Design Cz
4 Airfoil aerodynamic characteristics
Gliding ratio (C / C ) Power factor z x 3 2 1,5 (C z / C x lub C z /Cx)
Airfoil aerodynamic characteristics
Pitching moment coefficient C m
Derivative dCm/dCz is an indicator of stability.
It is negative for stable aeroplanes and positive for unstable aeroplanes.
5 Maximum thickness – t/c
Maximum thickness - t
Chord - c
Effect of airfoil thickness on lift coefficient
6% 8%
10%
12%
14%
16%
18%
20%
6 Effect of airfoil thickness on lift coefficient
Effect of airfoil thickness on drag coefficient
6% 8%
10%
12%
14%
16%
18%
20%
7 Effect of airfoil thickness on gliding ratio
6% 8%
10%
12%
14%
16%
18%
20%
Effect of airfoil thickness on power factor
6% 8%
10%
12%
14%
16%
18%
20%
8 Camber
Camber line
Maximum camber
Effect of airfoil camber on lift coefficient
0%
0,5%
1%
1,5%
2%
2,5%
3%
3,5%
9 Effect of airfoil camber on drag coefficient
0%
0,5%
1%
1,5%
2%
2,5%
3%
3,5%
Effect of airfoil camber on gliding ratio
0%
0,5%
1%
1,5%
2%
2,5%
3%
3,5%
10 Effect of airfoil camber on power factor
0%
0,5%
1%
1,5%
2%
2,5%
3%
3,5%
Effect of airfoil camber on moment coefficient
0%
0,5%
1%
1,5%
2%
2,5%
3%
3,5%
11 Position of maximum thickness
Maximum thickness
Position of maximum thickness
Boundary layer development
laminar turbulent
separated
transition
separation
12 Effect of airfoil „laminarity” on drag coefficient
15%
20%
25%
30%
35%
40%
45%
50%
Effect of airfoil „laminarity” on lift coefficient
15%
20%
25%
30%
35%
40%
45%
50%
13 Effect of camber line shape on moment coefficient
0° 35%
2°
4°
6°
28%
22%
15%
Effect of camber line shape on gliding ratio
35% 0%
2%
4%
6%
28%
22%
15%
14 Reynolds number effect on aerodynamic coefficients
Effect of Mach number on lift coefficient
15 Effect of Mach number on drag coefficient
Effect of Mach number on moment coefficient
16 Critical Mach number
Historical values of an aeroplane airfoil thickness as a function of Mach number
17 Critical Mach number
Critical Mach number
18 Calculate Reynolds number for design airspeed Airfoil selection
Re>3 000 000 3 000 000>Re>500 000 500 000>Re
Calculate Mach number Wortmann catalogue Selig catalogue for maximum airspeed „Stuttgarter „Summary of low speed Profilkatalog” Vol.1 i 2 airfoil data” Vol.1-3 „Airfoils at low speeds”
Mmax >0,75
Supercritical airfoil eg. NASA SC(2) 714 NASA TM X-1109 M <0,75 max NASA TM X-2977 NASA TP 2969
Abbot catalogue „Theory of the wing section”, raport NACA 824, NASA TN D-7428
Calculate Reynolds number for design Airfoil airspeed selection
Find characteristics for Re des i Mdes
Calculate C L for design airspeed
Compare C D for CLdes of available airfoils and select few best airfoils
Compare CLmax of selected airfoils
Compare stall character of selected airfoils
Compare C M of selected airfoils
Select an airfoil with a combination of above features best suiting to the aeroplane mission
19 Remaining wing features
• Wing incidence; • Mean aerodynamic chord mac, c • Wing area (reference area) S; • Wing span b; • Wing aspect ratio A; • Wing dihedral; Λ • Wing sweep angle (leading edge LE , Λ quarter chord c/4 ); • Taper ratio λ; • Geometrical and aerodynamic twist; • Winglets • Leading edges extensions;
Wing incidence angle
An angle between root chord and fuselage longitudinal axis
20 Taper ratio
b/2
cT c λλλ === R S c T cR
W S === W / S Straight wings: === ⋅⋅⋅ b A S λ=0.4÷0.5 2⋅⋅⋅S c === Swept wings: R [[[][b ⋅⋅⋅ ((()(1+++ λλλ)))]]] λ=0.2÷0.3 === λλλ ⋅⋅⋅λ ⋅ cT cR
Mean aerodynamic chord mac, c
2 (((1+++ λλλ +++ λλλ2 ))) c === ⋅⋅⋅ c ⋅⋅⋅ ; 3 ROOT ((()(1+++ λλλ )))
cR 0,25mac cR b Y = ⋅[](1+ 2⋅λ )(1+ λ ) ; c 6
cT cT
Y
21 Vortices generated by a wing
Vortices generated by a wing and effect of aspect ratio on drag coefficient
b2 C2 A === C === C +++ L S D D0 πππ ⋅⋅⋅π ⋅ A ⋅⋅⋅e
22 Effect of aspect ratio (A, AR) on lift coefficient
=== ⋅⋅⋅ A CLααα Clααα C C 2 lααα lααα 2 +++ +++ A πππ πππ
Helmbolt equation
b2 A === S
Wing dihedral
ϕϕϕ
b 1 b2
b3
b3
b4
Wing position Wing dihedral angle low mid high φ – an angle between Unswept 5 ÷ 7 2 ÷ 4 0 ÷ 2 chords’ plane and Subsonic swept 3 ÷ 7 -2 ÷ 2 -5÷-2 horizontal plane Supersonic swept 0 ÷ 5 -5 ÷ 0 -5 ÷ 0
23 ΛΛΛ ΛΛΛ ΛΛΛ Wing sweep LE , 4/c , c/t
ΛΛΛ === ΛΛΛ +++ [[[((( −−− λλλ))) ⋅⋅⋅ ((( +++ λλλ)))]]] tan LE tan 4/c 1 / A 1
ΛΛΛ ΛΛΛ c/4 LE
Line connecting quarter chords along the wing span
Wing sweep
ΛΛΛ Meff =M ∞cos( LE )
m ΛΛΛ Mkryt ~1/cos ( LE )
Wing sweep reduces effective Mach number. M
ΛΛΛ Mcos ΛΛΛ LE LE
ΛΛΛ t/c 2 ΛΛΛ qeff =q ∞cos ( LE )
2 ΛΛΛ W~tan ( LE )
24 α Wing sweep effect on dC L/d
dC 2⋅⋅⋅ πππ⋅ ⋅⋅⋅π ⋅ A L === α 2 dαα tan ((()(ΛΛΛ ))) +++ +++ ((()( ⋅⋅⋅βββ⋅β)))2 ⋅⋅⋅ +++ c/t 2 4 A 1 2 βββ
βββ === −−− 2 1 Meff
=== ΛΛΛ Meff M∞∞∞ cos LE
Wing sweep effect on separation
25 Wing sweep at supersonic speeds
Winglets
26 Wing twist
Aerodynamic twist Geometric twist
Wing twist
Aerodynamic twist
Geometric twist
27 Delta wings
AoA
V
Leading Edge eXtensions
28 LEX effect on lift coefficient
Vortex generators RAF Museum Hendon
29 30