Design of the wing box structure for the given wing geometry, weights and load factors. Microsoft Excel was used for all the calculations needed for this design. The complete structure was drafted using Solidworks CAD software.
1. POLITECHNIC UNIVERSITY OF PUERTO RICO
DEPARTMENT OF MECHANICAL ENGINEERING
HATO REY, PUERTO RICO
ME5930: AerospaceStructures
SP-13
Box Structure Design
Final Project
Carlos J. Gutiérrez Román
#54543
Javier A. Colón Toledo #64547
Submitted to:
Dr. Héctor Rodríguez
May 22, 2013
2. Table of Contents
Executive Summary....................................................................................................................................... 2
Introduction .................................................................................................................................................. 3
Assumptions.................................................................................................................................................. 4
Design Approach- Standards and Considerations......................................................................................... 5
Calculations and Results ............................................................................................................................... 6
Final Selection and Recommendations ......................................................................................................... 9
CAD Drawings.............................................................................................................................................. 19
References .................................................................................................................................................. 21
Appendix ..................................................................................................................................................... 22
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3. Executive Summary
Aircraft wing boxes are a very complex structure because they need to withstand not only the
forces of drag and lift but also its own weight and in most cases the weight of the engines and
the trust these produce. All these forces create a lot of stresses on the wing and each
component job is to withstand a corresponding stress. In this project we are designing a wing
box that has to be able to survive a set of specified constraints. We started by using the
Schrenks span wise load approximations to obtain the shear and bending moments that the
forces produce on each section (rib) across the wing. Then we used these stresses to design the
stringers and the skin of our wing box using the theories and procedures learned in class. Our
design consisted of twelve ribs, two spars and eight stringers.We have to repeat this procedure
for each of the sections we divided the wing span. We used the Von misses and maximum
shear stress theories to calculate the margin of safety associated with each component to
evaluate if our design was successful. In order to facilitate the calculations we used Microsoft
Excel to make the calculations and Solidworks to draw the CAD and obtain values for area and
skin lengths. The result is a very simple but effective wing box that fully complains with the
design specifications.
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4. Introduction
When designing an aircraft many factors contribute to the process. Depending on the type of
aircraft,its shape, mission, performance parameters and weight distribution between others all
the structural requirements change dramatically. Most of the loads that will be acting on the
aircraft produce different stresses that act on different structural elements but all need to be
designed simultaneously. While designing the wing structure the factors are simplified and the
design depends on loads affecting only the wing, which cause shear forces and moments. Using
an industry standard factor of safety we analyzed the acting stresses caused by the loads and
from here on we designed the structure to obtain a positive margin of safety. In this paper the
preliminary design for a wing box structure is explained. The students were given a specific
wing shape with its dimension; also known was the weight of the engines that each wing will
carry and the total weight of the aircraft. With this information we designed the complete wing
box structure and completed a full analysis for each stringer and the skin of the wing.
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5. Assumptions
Weight
Nlimit
F.S.
W. Engine
W. Span
Half Span
Cr
Ct
Ơ
7075
Ơ
7178
0
0
145000
2.25
1.5
5400
1344
672
108
48
73000 psi
78000 psi
0
0
According to the FAA (Federal Aviation Administration) FAR (Federal
Aviation Regulations) a factor of safety of 1.5 must be applied to the limit
load which has external loads on the structure considered.
Limit maneuvering load factors.
(a) Except where limited by maximum (static) lift coefficients, the airplane is assumed to be subjected to
symmetrical maneuvers resulting in the limit maneuvering load factors prescribed in this section.
Pitching velocities appropriate to the corresponding pull-up and steady turn maneuvers must be taken
into
account.
(b) The positive limit maneuvering load factor "n" for any speed up to VD may not be less than
Page | 4
6. Design Approach- Standards and Considerations
Airfoil:
NACA0012 – 12.5% from the leading edge and 25% from the trailing edge where eliminated for the wing
box design.
Ribs:
Twelve ribs were used with the following areas:
Rib
Area
12.00
706.57
11.00
927.49
10.00
9.00
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
1148.17 1369.09 1589.78 1810.70 2031.38 2252.30 2472.99 2693.91 2914.59 3135.52 3356.20
Stringers:
Eight 672 inch long stringers with an area that varies with its length as follows:
Section
Area
12.00
12.00
11.00
11.00
10.00
10.00
9.00
9.00
8.00
8.00
7.00
7.00
6.00
6.00
5.00
5.00
4.00
4.00
3.00
3.00
2.00
2.00
Skin and spars:
Skin and rib length are specified according to the rib area. A common thickness of 0.125 inch was used
for the skin and 0.5 inch for the spars.
Cross section example of root rib:
All the components were verified for its corresponding bending moment stress or shear stress according
to the principles learned in class. Maximum Shear Stress and Von Misses Theories were utilized to
calculate the margin of safety.
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1.00
1.00
7. Calculations and Results
Examples of calculations made by hand:
Schrenks Span Wise Load Approximations
Ultimate Vertical Load
Wing span lift factor
Average local lift coefficient
Strip Area
Force Between the Strips
Distance to Forces
Shear
Moment
Page | 6
8. Bending Moment stresses
(Station #1, Stringer #3)
Assumptions
Dist. To Yc
Bending Stress
Shear Flows and shear stress
(Station #1, Surface 3,4)
Page | 7
19. Final Selection and Recommendations
Material for stringers:
Material for skin:
Page | 18
20. All the stringers and skin sections meet the desired requirements and obtain a Margin of safety greater
than 0.
Our design consists of 12 rib sections with 8 stringers running across the wing. To minimize overdesign
we choose a variable area stringer design.All the sections consist of the same layout reduced in size by a
factor given on the following table. All the corresponding dimensions and coordinates for all the 12 ribs,
spars and stringers are also found in the table.
% from 12
0.21
0.28
0.34
0.41
0.47
0.54
0.61
0.67
0.74
0.80
0.87
0.93
1.00
Station
12.00
11.00
10.00
9.00
8.00
7.00
6.00
5.00
4.00
3.00
2.00
1.00
0.00
Length
30.00
39.38
48.75
58.13
67.50
76.88
86.25
95.63
105.00
114.38
123.75
133.13
142.50
Spar 0 Y
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Spar 1 Y
9.99
13.11
16.23
19.36
22.48
25.60
28.72
31.84
34.97
38.09
41.21
44.33
47.45
Spar 2 Y
20.01
26.27
32.52
38.77
45.02
51.28
57.53
63.79
70.04
76.29
82.54
88.80
95.05
Spar 4 Y
30.00
39.38
48.75
58.13
67.50
76.88
86.25
95.63
105.00
114.38
123.75
133.13
142.50
Upper Arc
30.07
39.47
48.86
58.26
67.66
77.05
86.45
95.85
105.25
114.64
124.04
133.44
142.83
Lower Arc
30.07
39.47
48.86
58.26
67.66
77.05
86.45
95.85
105.25
114.64
124.04
133.44
142.83
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