MECN4027 – Aircraft Structures II
Issued 26 February 2020
Assignment 2020
The fuselage frame of an internally pressurized blended wing-body aircraft has an
elliptical profile on its outer surface. The profile has a width of 2a, and a height of 2b.
To reduce bending deflections, the cross section is braced with three vertical tie rods.
The height of the frame is measured perpendicular to the outer elliptical surface and is
increased locally at six points to withstand the loads introduced by the ties. The
maximum height of the frame, hmax, is the same at each tie rod attachment point while
same minimum height, hmin, exists midway between the tie rod attachment points. The
height varies sinusoidally with distance along the outer surface of the frame such that
the height follows a half wave between successive tie rod attachment points. The ties
are all positioned through the neutral axis of the frame. The central tie lies on the
vertical axis of symmetry while the remaining two ties are equidistant each side of the
central tie. The position of these ties can be determined by knowing that they lie on a
line normal to the outer elliptical surface, and that this normal cuts the elliptical surface
at ±l each side of the vertical axis of symmetry. The configuration of the frame is
illustrated in the figure below.
The tie rods are attached through the locations marked with the symbol:
The frame is manufactured from aluminium 7075-T6. The frame has a constant
thickness of 10 mm. The frame carries the internal pressure of the fuselage which is
transferred to it by the skin on the outer surface. The frame spacing is 300 mm. Assume
that the interior of the fuselage is pressurized to 0.25 bar. The total height, 2b, of the
fuselage is 5m and the aspect ratio, a/b, of the elliptic shape is 4.5.
i)
Using complementary energy methods, find the internal moment and axial force at the
top of the frame. Determine the variation of the stress on the outer surface of the frame
from the top of the frame to the bottom. Determine the horizontal and vertical
deflections of the neutral axis, relative to the two axes of symmetry, from the top of the
frame to the bottom.
ii)
Use the finite element method to obtain the results of question i) above.
iii)
Compare and contrast the results obtained from questions i) and ii) providing clear
explanations for any differences between the results. Explain any interesting results that
may be present. Be sure to provide comparison plots for the stresses and deflections
obtained from the two different methods. Additional comparisons are encouraged.
For all questions, make sure to use the format demanded in the marking rubric.
This assignment is used for an individual assessment of ECSA Graduate Attribute
(GA) 5. Please read the appendix to the course outline to familiarize yourself with
the assessment criteria for this GA, and the consequences of not achieving the GA.
l/a
Britz
Choma
Donzella
Govender
Hank
Hardwick
Hlongwane
Hulley
Januk
Khumalo
Krige
Kwadi
Leballo
Lekota
Lund
Mayet
Mbengwa
Mohale
Monnanyana
Moodley
Mudimeli
Musoya
Myburgh
Naude
Ndlovu
Ndunge
Papo
Peerimal
Puckree
Rooy
Rosslee
Seedat
Sibanda
Springate
Struwig
Tannous
Tsekouras
Vallabh
Van Der Spuy
Wrathall
0.20
0.21
0.22
0.23
0.24
0.25
0.26
0.27
0.28
0.29
0.30
0.31
0.32
0.33
0.34
0.35
0.36
0.37
0.38
0.39
0.40
0.41
0.42
0.43
0.44
0.45
0.46
0.47
0.48
0.49
0.50
0.51
0.52
0.53
0.54
0.55
0.56
0.57
0.58
0.59
hmax
(mm)
350
325
300
275
250
350
325
300
275
250
350
325
300
275
250
350
325
300
275
250
350
325
300
275
250
350
325
300
275
250
350
325
300
275
250
350
325
300
275
250
hmin
(mm)
250
240
230
220
210
250
240
230
220
210
250
240
230
220
210
250
240
230
220
210
250
240
230
220
210
250
240
230
220
210
250
240
230
220
210
250
240
230
220
210
This assignment counts 40% towards the total mark for this course. The mark
breakdown will be described in an accompanying marking sheet which will be
distributed in due course.
This assignment will be assessed through oral presentation.
1.
A Google questionnaire which will require you to provide specific values of stresses
and deflections must be completed by 08:00 on 1 May 2020. Furthermore an oral/video
presentation and a clearly documented version of the software used to generate your
CEM results must be uploaded onto SAKAI before that time also. The latter will be
used to check that your software can correctly generate results for an unknown problem.
Although the structure of the presentation is the choice of the student, certain tables and
figures MUST be included in the format specified in the marking sheet. Late
submissions will not be accepted.
2.
Details of the oral/video presentation will be communicated in due course, but it at this
stage is expected that students will have 10 minutes for their presentation with an
additional 5 minutes scheduled for questions. Failure to submit a presentation or to be
available for questions means that the student will automatically fail the assignment and
will not meet the ELO requirement.