Modern Trends in Airframe Structural Design

EWADE 2007 Komarov V.A.

Modern Trends in Airframe Structural Design Professor Komarov V.A. Director of Institute AVIKON Of Samara State Aerospace University

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Plan of the presentation 1. General view on the modern structural design problems. 2. New ideas for improving design process. 3. The example of using a new ideas for research aerodynamic and weight efficiency of morphing wing.

2


Airframe design process

3


Time and resource expediture

The main reason of greater charges of time and resources in sequential design paradigme is use very simple, (insufficiently exact) mathematical models on early stage of design. For reduction of designing time it is suitable use of highly accuracy mathematical models on early stage design. 4


New paradigm for Airframe Structure Design

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The problem of weight estimation in structural design 1. 2. 3. 4.

Choice of structure topology (skeleton design). Estimation of structural mass fraction. Weight estimation of the wing, fuselage, etc. Weight check.

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Choice of structure topology

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Estimation of structural mass fraction Definition of flight vehicles takeoff gross weight via “equation of existence”

mo =

m pl 1 − mst − msys − m f − m pp

where

mst mst = mo 8


Example of calculation a wing mass fraction via “weight equation” Typical weight equation (Eger) m st =

7 k1n pϕλ m0

η + 4  µ − 1  4,5k 2 k3  + ∗ 1 − + 0,015 0, 75 4 1, 5 + + p η η 1 3   10 p0 c 0 cos χ 0

( )

∗

m0,4 st

m o = 270 000 kg m o = 685 000 kg

0,35 0,3 0,25 0,2 0,15 0,1 0,05

Average

Shejnin

Torenbeek

Pattersson

Eger

Raymer

Badyagin

Driggs

Kozlovsky

Dent

Taye

Farren

Liptrote

Melvill

0

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Weight Check 1. Definition of the weight limits for different part of structure before design. 2. Analyses of weight penalty after design (if necessary). Looking for decrease of structural mass.

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Unconventional flight vehicles Morphing Wing from TUDelft

(http://www.lr.tudelft.nl/live/pagina.jsp?id=fd5540a7-0cfe-44e5-b1bc-c806fa0410b8&lang=en )

mst = ?

mst = ?? 11


New ideas for improving design process 1st idea. Load-carrying factor n

Frame

G = ∑ N i ⋅ li i =1

n

Thin-wall structure

G = ∑ Ri ⋅ S i i =1

3D-structure

G = ∫σ V

eqv

dV 12


Definition of structural mass via “load-carrying factor” Theoretical structural material volume n n Ni VT = ∑ ⋅ li = ∑ Fi ⋅ li i =1 [σ ] i =1 Real mass of structure

G or mst = ϕ σ G – take into account topology, geometry and external loads G mst = ϕ ⋅ ρ ⋅ VT = ϕ ⋅ ρ ⋅ [σ ]

σ – specific durability of material coefficient of full-mass structure, (it depends on design and ϕ –technology perfect) G-criteria allows to calculate absolutely mass of unconventional structure with high accuracy 13


2nd idea. Size less criteria of load carrying perfection of structure Load-carrying factor is proportional to the linear sizes (coordinates of nodals) of structure and value of nodal forces (at retaining of the law of distribution of external loading) – dimensional quantity

Sizeless criteria– coefficient of load carrying factor where P- specific load G CK = L- specific size P⋅L whence G = C K PL

(aerodynamic analogy :

Y = C y qS

)

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Example of simple structures CK = 1,00 a) a

b

Pa

c)

d

CK = 3,41

Pa a

b

l

d

CK = 2,00

c

l

b) Pa b

a

α

CK = 10,00 Pa d)

a

b

h

l c

l

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New weight equation for definition of full wing mass and wing mass fraction Specific size – square of wing in degree ½ Specific load – lift Y = n ⋅ m0 ⋅ g

S

G = C K ⋅ n ⋅ mo ⋅ g ⋅ S whence

CK =

G* n* ⋅ mo* ⋅ g ⋅ S *

Weight equation :

mwing

ϕ = CK ⋅ n ⋅ g ⋅ S σ

m wing

ϕ = C K ⋅ n ⋅ mo ⋅ g ⋅ S σ 16


Example of structural topology choice

Panel structures Wing

Membrane structures

Strategy I

Strategy II

δ = 0,6

δ = 0,5

δ = 0,4

δ = 0,6

δ = 0,5

δ = 0,4

1

1,62

1,68

1,70

1,71

1,84

1,94

2,07

2

1,68

1,76

1,78

1,81

1,83

1,89

1,98

3

2,55

2,69

2,75

2,83

2,68

3,03

3,56

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Example of morphing wing aerodynamic and weight efficiency research 2

6

12

ctip = 3

croot = 4

Wing 1a

Grant CRDF: REO-1386

2.387

4.774

Wing 1b

2

4

Wing 2a

2.1935

4.387

Wing 2b

1

4

Wing 3a

2

4

Wing 3b

b/2 = 20 Axis of symmetry

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Scheme of wing parts joints 1

Fuselage joints

Inner wing Beam

Outer wing

Rolls 2

3

Rigid connection

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3rd idea. Using 3D-model with variable density Model

Traditional material

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Hypothetic material with variable density [σ ] = ρ ⋅ [σ ]

.

E = ρ ⋅E

Algorithm of density distribution optimization 1. ρ0i = const 2. σ i eqv σ 0 3. ρ1i = i

[σ ]

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Test

3D-model of the wing structure p

8-layers of 3D-solid finite elements Boundary conditions of console

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Comparison of load-carrying factor coefficient calculations for thin-wall structure and 3D-solid model with variable density CK

As pec t ratio b /c = 8

30

28.10

28

25.05

26 24 22

s olid (8 layers ) 23.81 23.14

22.75

22.50

22.34

22.23

22.16

22.11

w ing box

20

19.58

18 1

2

3

4

5

6

7

8

9

10

11

Iteration n

CK

As pe c t ratio b /c = 12

52 50 48 46 44 42 40 38 36 34

51.74 46.11 43.73 42.41

s olid (8 la ye rs ) 41.63

41.15

40.83

40.61

40.45

40.35

w ing box

1

2

3

35.56

4

5

6

7

8

9

10

11

Iteration n

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Wind tunnel model 1

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Wind tunnel model 2 with pressure of orifices

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Spanwise load distributions

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3D-model with variable density of material

Y X Z

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External loads

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dimens ionles s eqvivalent of wing weigh

Comparison of weight perfection C35,000 K

30,000 25,000 20,000 15,000

Morph

10,000

Tra p

5,000

Morph for uniform load dis tribution

0,000 0

0,25

0,5

0,75

c1t

ge om e trica l pa ra m e te r of te le s cope wing

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Comparison maximum aerodynamic efficiency maximum aerodynamic efficiency

40.000 L/D max Morph

35.000

Trap

30.000 25.000 20.000 15.000 10.000 5.000 0.000 0

0.25

0.5 0.75 geometrical parameter of teles cope wing

ct1

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Pressurized cabin, pressure vessel Specific volume – volume - V Specific load– pressure – P G CK = P ⋅V

Some results for reservoirs: Spherical –

CK = 3

Cylindrical –

CK = 3

Spherical from CM –

2

CK = 3

Cylindrical from CM – C = 3 K

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Conclusion Load-carrying factor C K allows: 1.

To put in according to load-carrying scheme (topology of structure) the certain dimensionless value which defines weight perfection of a design. 2. To build "weight" formulas for any designs. 3. To accumulate the knowledge in convenient form (dimensionless!) for analysis of existing and perspective designs. There are 3 new ideas in the lecture, which can be useful to increase efficiency of early stage design. 32