Subsonic Wings Pres

8/9/2019 Subsonic Wings Pres

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Subsonic Wingsan introduction

W.H. Mason

Configuration Aerodynamics Class


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VLM Methods – a way to get insight

•

Linear, inviscid aerodynamics – strictly subsonic

• Ignores thickness – bc’s applied on the mean plane

– Finds !Cp, not the upper/lower surface pressures

• Very handy and accurate as seen below

• Really good for understanding interacting surface ideas

Choices: VLMpc, Tornado, AVL


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VLM Models and Tips


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Convergence with number of “panels”

F/A-18

0

2

4

0 40 80 120 160 200 240

Total number of panels

Vortex Lattice Method

(5) (9)

( ) Number of chordwise panels

! Neutralpoint,

percent c


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Panel Models


6/43

F-15 3-Surface VLM Model


7/43

Three-Surface F-15 Longitudinal Derivatives


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Canard Height Effect


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F-15 horizontal tail effectiveness


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F-15 aileron effectiveness


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Warren-12 Test Case

Note: C M about wing apex,

Reference chord is 1.0


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The key:

Define it for

others!

Thereference

trap wing

Source: Stinton, Design of the Airplane

Comment: Reference Area(s)


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Aerodynamics of High Aspect Ratio Wings

• Planforms

• Spanloads

• Pitching moment and pitchup

• Aerodynamic Center

• Isobars/Twist

• Camber

• 2D-3D connection

• Canard and Ground Effects


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Typical Planform Characteristics of

Transport Aircraft


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Clearly the A380 pays a price to satisfy the 80 meter gate box limit

Way offthe trend

line!


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Forward, Unswept and Aft Swept Planforms, AR = 2.8


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Related Spanloads and Section Lift Coefficients

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0.0 0.2 0.4 0.6 0.8 1.0y/(b/2)

Spanload,

Warren 12 planform, sweep changed

aft swept wing

unswept wing

forward swept wing

ccl / c

a

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0.0 0.2 0.4 0.6 0.8 1.0

y/(b/2)

Section CL

Warren 12 planform, sweep changed

aft swept wing

unswept wing

forward swept wing

For an untwistedplanar wing


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Forward, Unswept and Aft Swept Planforms, AR = 8


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Related Spanloads and Section Lift Coefficients

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 0.2 0.4 0.6 0.8 1.0

Spanload,

y/(b/2)

Aspect ratio 8 wings

aft swept wing

unswept wing

forward swept wing

ccl / c

a

0.00

0.50

1.00

1.50

0.0 0.2 0.4 0.6 0.8 1.0

Section CL

Aspect ratio 8 planforms

aft swept wing

unswept wing

forward swept wing

y/(b/2)

For an untwistedplanar wing


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Example: VLM Pitching Moment agrees well

with data until wing pitchup

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

C m

C L

AR = 10, !c/4 = 35°, " = 0.5

data from NACA RM A50K27

Re = 10 million

x ref = c/4

VLMpc calculation


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Aerodynamic Center on Finite Wings

- is it actually at the quarter chord? -

From Shevelle, Fundamentals of Flight , 2

nd

Ed.


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Low Aspect Ratio Wing Neutral Point (ac )For a rectangular wing it moves forward!

From Schlichting and Truckenbrodt,

Aerodynamics of the Airplane

AR

Discovered while making

pre-test estimates

Inboard Wing built/tested at VT

0.25

0.05

1

5 7

3


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Isobars

Note: this is actually a transonic case, M = 0.93, ! = 2°from AFFDL-TR-77-122, February 1978.

These funny NACA report numbers

denote series classified at the time,

“L” stands for Langley, reportsstarting with “A” denote Ames

Without twist and camber: don’t get full effect of sweep


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Typical Twist Distributions

-1.0

0.0

1.0

2.0

3.0

4.0

5.06.0

7.0

0 0.2 0.4 0.6 0.8 1

! ,

deg.

y/(b/2)

-1.0

0.0

1.0

2.0

3.0

4.05.0

6.0

0 0.2 0.4 0.6 0.8 1

! ,

deg.

y/(b/2)

Aft Swept Wing Forward Swept Wing

from LAMDES on the software website

A LAMDES artifact


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Typical Camber Variation

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

-0.2 0 0.2 0.4 0.6 0.8 1 1.2

(z-zle)/c

x/c

! = 0.925

! = 0.475

! = 0.075

Cambers from the LAMDES code on the software website


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Relating 2D and 3D

The airfoil problem is converted to 2D (normal),

solved (designed), and put in the wing 3D


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Canard-Wing Interaction

canard wake extends to indinitywing wake not shown

A A

Canard wakestreams overwing

-2.0-1.5-1.0-0.50.0

0.51.01.5

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

w

Downwash from canard across wingat Section A-A

Upwash outboardof canard tips


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Example for Minimum Induced Drag

Calculations

Sample case in John Lamar’s NASA TN with LAMDES


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Canard Wing Induced Drag

0.0200

0.0250

0.0300

0.0350

0.0400

-0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4

C Di

!x/cForward Aft

Canard lift must benegative to trim

M = 0.3, C L

= 0.5

Canard heightabove wing ,

0.1

0.2

z/b

0.3

Computations from LamDes

Advantage of verticalseparation clearly evident

Static Margin

Stable Unstable

Advantage of relaxedstatic stability evident

Note: The sample case may not be a gooddesign, the canard is too big.


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Typical Required Twist Distribution

-1.0

0.01.0

2.0

3.0

4.0

5.0

6.0

0.0 0.2 0.4 0.6 0.8 1.0

! ,

y/(b/2)

in presenceof canard

without

canard canard tipvortex effect

deg.

-2.0

0.0

2.0

4.0

6.0

8.0

0.0 0.2 0.4 0.6 0.8 1.0

!

y/(b/2)

withoutcanard

in presenceof canard

canard tip

vortex effect

Aft Swept Wing

Forward Swept Wing

Actual twist values are heavily

dependent on the canard load!


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Some Variations: Tip treatment

from Feifel, in NASA SP-405, 1976

A Whitcomb “winglet”

The “Raked Wingtip” used

on the Boeing 767-400

from Kroo, Ann. Rev. of Fluid Mech., 2001

Rounding the intersection

leads to a “blended winglet”

Note “Yehudi”


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Ground Effects from VLM

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

C L!

h/c

AR

4

2

1

Solid lines: computed using JKayVLMDashed lines: from Kalman, Rodden and GiesingSymbols: Experimental data

h

U !

c

c/4

-0.40

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

C M !

h/c

Solid lines: computed using JKayVLMDashed lines: from Kalman, Rodden and Giesing

AR1

2

4


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A completely new category

Slender Wings


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Laser Light Sheet Leading Edge Vortex Flow

Aviation Week & Space Technology, July 29, 1985

Light Sheet is a

great way to see

the LE vortex

Northrop IR & D

example of flow

over a delta wing

configuration.

Exhibited at the

36th Paris airshow.


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Vortex Lift

Drawback?

It’s “draggy” lift


36/43

The Polhamus LE Suction Analogy


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Another View of the Suction Analogy

R.M. Kulfan, Wing Geometry Effects on Leading Edge Vortices, AIAA 79-1872


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Results of the Polhamus Suction Analogy

0.00

0.500

1.00

1.50

2.00

0.0° 10.0° 20.0° 30.0° 40.0°

CL

!

AR = 1.5 ("

= 69.4°)

VortexLift

PotentialLift

Experimental data fromBartlett and Vidal

Prediction from PolhamusLeading Edge Suction Analogy


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Reduce Drag with a Vortex Flap ?

The Concept

The reality?

Flight International, 16 March 1985

This concept was briefly popular,

but it proved too hard to achieve.


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Strakes are also low aspect ratio wings. Because they

don#t stall, even low tail designs can have

a nose-down moment problem

F-16

Forebody

Strakes


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The Concorde Exploited Both Ground Effects

and Vortex Lift to be Even Somewhat Practical

From Poisson-Quinton, Sustained Supersonic Cruise Aircraft Experience

Vortex

Burst


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And VLM works for Hypersonic Class Concepts

Jimmy Pittman and James Dillon, “Vortex Lattice Prediction of Subsonic

Aerodynamics of Hypersonic Vehicle Concepts,” Journal of Aircraft ,

October 1977, pp. 1017-1018.


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To Conclude

This just gives you the very basics

- no end to planform concepts, invent one yourself!

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Subsonic Wings Pres