Project description, TMMI37, spring 2014
2014-04-30
Project description, TMMI37, vt2 2014
The aim of this project, which constitutes a mandatory examination task
in the course TMMI37 (spring 2014), is that you will have the
opportunity to apply the knowledge and skills gained in the course on
concrete engineering problems; this year set up in collaboration with
SAAB, Linköping, which is a world leading producer of products,
services and solutions ranging from military defence to civil security.
In detail you are to
 Part I) Design the nose wheel fork
(for the SAAB Gripen/Griffin fighter aircraft)
 Part II) Evaluate and redesign the flame arrestor bracket
(for the SAAB 2000 AEW aircraft)
The project contains a mandatory part of the course (Part I), the
approval of which is needed for passing the course with grade 3/C,
and an optional part (Part II), which is needed for the higher grades
(4/B or 5/A, resp.)
The project, described on the following pages, is to be reported
according to the course information (see also additional remarks
below).
The oral presentation is to be done in the following way:
Firstly, the mandatory project task is to be discussed in groups of
approx. 8 people, which are to come up with specific questions/issues
of major importance/interest. Secondly, these questions are to be
discussed collectively. The discussions are to be led by moderators.
Looking forward to meet you and to take part of your results and ideas!
Per-Olof Marklund (SAAB) and Kjell Simonsson (LiU)
Project description, TMMI37, spring 2014
Part I
Design of the nose wheel fork for the
SAAB Gripen/Griffin fighter aircraft
2014-04-30
Project description, TMMI37, spring 2014
2014-04-30
Background
Above, the principal design of the nose wheel attachment on the SAAB
Gripen/Griffin aircraft can be found, with the arrow indicating the direction of
flight.
The external forces acting on the design are illustrated below.
where
 D=Drag, attaining a large positive value (spin-up) at the moment of
ground contact (when the landing device is in its fully un-compressed
position), and some hundreds of a second later attaining an approximately
equally large negative value (spring-back).
 B=Brake
 V=Vertical
 S=Side, which attains a large value under turning operations or when
different brake forces are applied on the two main wheels
After landing the spring and damper have been compressed, and the fork is in a
horizontal position, see below. The loading is at that time
Load case 1: V=60kN, S=B=D=0
On the other hand, when the aircraft is subjected to unsymmetric forces from the
brakes, there also exists a side force S. The loading is for this case given by
Load case 2: V=25kN, S=10 kN, B=D=0
The three shafts supporting the fork can be treated as completely rigid, and the
associated bearings can be treated as frictionless. The dimensions that are found
from general requirements and demands on the design is also shown below,
where the radius of the tire is r=200 mm.
Project description, TMMI37, spring 2014
2014-04-30
Project description, TMMI37, spring 2014
2014-04-30
Material data
The fork is to be made of aluminum 7075-t73, with the following data
yield stress Rp0.2=395 MPa
failure stress Rm=475 MPa
density ρ=2.7 kg/dm3.
Task
The task is to find an as light nose wheel fork design as possible under the given
design constraints (see below).
If all other mandatory parts of the course have been passed successfully, the
approval of Part I of the project will give the grade 3/C on the course.
Loading and design constraints
With respect to the maximum stressing of the material, the equivalent stress
according to von Mises is not to exceed the yield stress (no safety factor needs
to be considered in this task).
The shafts and the bearings do not need to be modeled, and the loading and
constraints can be applied directly on lines or surfaces of the fork.
Concerning the load definition, the side force is to be applied on only one of the
fork legs (is chosen such that the worst load case is found). However, it is
important to note that it also has a moment contribution that is taken up by both
fork legs.
Project description, TMMI37, spring 2014
2014-04-30
Part II
Evaluation and redesign of the flame arrestor bracket
for the SAAB 2000 AEW aircraft
Project description, TMMI37, spring 2014
2014-04-30
Background
The flame arrestor under study, is part of the ventilation system for the
fuel tanks in the pressurized zone of the SAAB 2000 AEW (Airborne
Early Warning) aircraft (see Figure 1 below).
Figure 1: Saab 2000 AEW Aircraft
Extra fuel tanks
Figure 2: Internal layout of the aircraft
The purpose of the flame arrestor is to prevent accidents due to ignition
of the fuel. A flame arrestor functions by forcing a flame front through
channels too narrow to permit the continuance of a flame. In this project
the focus will be placed on its attachment to the fuselage, i.e. on the
bracket connecting it to one of the fuselage frames, see the picture on the
front page of this description. More specifically the stress state in the
current design and the possibility for redesign (see below) is to be
investigated.
Project description, TMMI37, spring 2014
2014-04-30
Flame arrestor
9309781-006
9309781-010
7528120-014
Hydraflow
couplings
Fwd Tank
9309781-010
Fixed to
structure
Aft Tank
7528120-521
9309781-006
Hydraflow
couplings
Project description, TMMI37, spring 2014
2014-04-30
Tasks
The specific tasks of the project are to
1.
evaluate the stress state at the bend of the bracket, and to
investigate, based on given material properties, design criteria
(plastic yielding) and safety factors, the possibility of a
redesign towards a lighter part. Here the basic design idea is
to be left unchanged, i.e. only dimensions are to be changed.
If all other mandatory parts of the course have been
passed successfully, the approval of Task 1 of Part II will
give the grade 4/B on the course.
2.
set up a three-bolt redesign, where also the issue of an
increased bolt loading will have to be addressed (at least
qualitatively). Here the basic design is to be modified if
possible, e.g. parts of the bracket which are not needed can be
“cut away”.
If all mandatory parts of the course have been passed
successfully as well as Task 1 of Part II, the approval of
Task 2 of Part II will give the grade 5/A on the course.
Even though the CAD-geometry is available for the bracket, you are to create it
by yourselves, based on specifications/drawings provided by SAAB (see below),
since this will facilitate the redesign work.
Specifications and drawings
Specifications and drawings regarding geometry, material data and safety
factors can be found below
Project description, TMMI37, spring 2014
2014-04-30
Project description, TMMI37, spring 2014
2014-04-30
Project description, TMMI37, spring 2014
2014-04-30
Loading and design constraints
The basic load case to consider is the one steaming from the inner
pressure of the pipe connecting the flame arrestor to the fuel tank. Since
the pressure strives to straighten the bent pipe, it will cause a loading on
the flame arrestor, which in turn will be taken up by the bracket. When
considering the load transfer, it will for the current project be assumed
sufficient to just model the bracket, and to apply the loading to the near
regions of the bolt holes in a way consistent with the actual loading
situation. The loading will be provided by specifications/drawings from
SAAB. The size and direction of the load, as well as the application point
is shown in Figure 3.
9309781-006
FR1
R1
FP1
FP1
R1
FR1
7528120-521
83mm
y
x
z
F=520N (Ultimate load)
(x,y,z) = (0,0,0)
(x,y,z)=(-232, 891, 436)
(x,y,z) = (0,0,0)
Figure 3:Load application
Project description, TMMI37, spring 2014
2014-04-30
General comments
(for both Part I and Part II)
The work you have done is to be orally presented and reported (in written
form) according to the dates and deadlines found in the course
information. In your report you are to present your results, conclusions
and suggestions for future work.
Note specifically that you in your work are to
 Use refined meshes for resolving the stress state in highly stressed
and critical regions. The meshes used are not allowed to include
too distorted elements (important to check this when making mesh
refinements).
 Locally, e.g. at points associated with a loading or a
locking/constraint, very high stresses will arise. However, these
stresses may be forseen/disregarded.
 Do not use boundary conditions that you don’t know exactly how
they work/act (can of course be studied by using the “help”facilities of the program)
Note specifically that you in your report are to
 Specify and discuss all thoughts, ideas, assumptions,
simplifications, approaches, and suggestions for further work. Both
the conceptual work and the detailed FE-analyses shall as far as
possible be motivated and checked by hand calculations (e.g. by
beam theory).
 Specify all applied loads and boundary conditions used (type and
location). Motivate the choice of applied lockings and constraints
if these are not obvious, and discuss how another choice might
have changed the results (this can of course be tested directly in
the program).
 Specify the element type used
 Show used element meshes (the original one as well as all refined
dittos, and from different perspectives if needed)
 From the reports it must be clear how the new designs will look
(all dimensions must be included in one way or another), but no
standardized drawing rules need to be followed. Also state the
weight of your designs.
 Part I and Part II are to be reported separately.
 Please note that your reports will be made available to SAAB.
Project description, TMMI37, spring 2014
2014-04-30
 It is extremely important that your report is well structured with
respect to its content, and that the written language (Swedish or
English) is of a high quality. Detailed instructions of how to write
your report will be made available to you.