My Mt M ( ) /2 6 - UFL MAE · See Table 1.3 From C.T Sun, Mechanics of Aircraft Structures. Role of...
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Transcript of My Mt M ( ) /2 6 - UFL MAE · See Table 1.3 From C.T Sun, Mechanics of Aircraft Structures. Role of...
Aerospace Structures
Lecture notes 8/23/17 Lecture 2
Comparing structural efficiency of different materials.
See posted Section 11.3 from Peery’s Aircraft Structures, 1950!
Tension: / A / Wrequired allowable required requiredP A P Aσ σ ρ= = ∝ . For two materials
1 21
2 2 1
required allowable
required allowable
WW
σρρ σ
= See Peery Eq. 11.4
For bending of rectangular cross section with thickness t
( )
3 2
/ 2 6 W= t/12
M tMy MI t t
σ ρ= = =
So 1 21
2 2 1
required allowable
required allowable
WW
σρρ σ
=
For buckling 2
2
EIPL
π= get 1 1 2
2 2 1
required
required
W EW E
ρρ
=
Implications for wing constructions: Complicated structural stiffening to recover the loss of efficiency compared to wood.
Tidbits: Ford now has an aluminum F-150. 16-story wood high-rise building is being completed, because wood is more carbon-efficient.
Quasi isotropic laminates (black aluminum) has about half the stiffness, and are comparable to aluminum at about 60% of the weight. See Table 1.3 From C.T Sun, Mechanics of Aircraft Structures.
Role of structural elements: Skin provides most of the bending rigidity and bending stress. Spars are needed to provide enough torsional stiffness. Ribs and spars keep skins apart. Stringers protect skin from buckling.
