intro course aerospace wajdi

8/2/2019 Intro Course Aerospace Wajdi

1/47

p. 1Date: 04-02-2009

Introduction course

Aerospace engineering

February 2009


2/47

p. 2Date: 04-02-2009

Program of course

1. Topology of airplanes Top level

Names and location of airplanes parts/structure

Barrels / Typical section names Airbus fuselages

2. Engineering life cycle

DevelopmentDesign and Stress

Certification

Sustaining

3. Failure modes

What is basically our work at GT?: Report smallest Reserve Factor (RF) Applied loadsKnow your structure by knowing your loads

Allowed loads

RF = Allowed load/ Applied load

Types of failure modes with explanations, pictures and references (handbooks, authority requirements,Issy etc.)

4. Detailed description of fuselage engineering process

Skin geometry, loads, relevant failure modes, material, stress state

Frames geometry, loads, relevant failure modes, material, stress state

Stringers geometry, loads, relevant failure modes, material, stress state

NOTE:This is a rough setup

of the course. More chapterswill be added and contentcan be modified!


3/47

p. 3Date: 04-02-2009

Topology of airplanes Top level

Names and location of airplanes parts/structure:There are many aspects of design of aircraft structure. Generally,the main components of an aircraft are :

Fuselage

Empennage

Wings

The next figure shows a detailed structural design of acommercial aircraft.


4/47

p. 4Date: 04-02-2009


Structural Design of commercial aircraft


5/47p. 5Date: 04-02-2009


Typical section name


6/47p. 6Date: 04-02-2009

Movements of an airplane

Yawing: Rotating around itsvertical axis (Z- axis)

Rolling: Rotating around itslongitudinal axis (X-axis)

Pitching: Rotating around itstransverse axis (Y-axis)


7/47p. 7Date: 04-02-2009

Empennage

Structurally, the empennage

consists of the entire tailassembly.

Its main purpose is to givestability to the aircraft.

The fixed parts are the verticaland horizontal stabilizer

The elevator is a movable airfoilthat controls changes in pitch,the up-and-down motion of the

aircraft's nose.

The rudder is a movable airfoilthat is used to turn the aircraft incombination with the ailerons


8/47

p. 8Date: 04-02-2009

Typical arrangement of the transport tail


9/47

p. 9Date: 04-02-2009

Wings


10/47

p. 10Date: 04-02-2009

It conventionally takes form of:

Spars

Ribs

Covering skin

Stringers


11/47

p. 11Date: 04-02-2009

Spars

Webs - resist shear loads and stabilise skin (i.e. increasebuckling resistance).

Flanges - resist compressive loads caused by wing bending.

Stringers

Further increase skin buckling resistance.

Take some of the bending load

Ribs

Maintain aerodynamic shape.

Provide anchorage points for landing gear, weapons, etc.

Skin Resist shear torsion loads ( box shapes of combined skin/web)

React axial bending loads


12/47

p. 12Date: 04-02-2009

Barrels / Typical section names Airbusfuselages

The fuselage is a stiffened shell commonly referred to as semi-

monocoque construction

The different sections of an aircraft fuselage are :

Forward section

Mid section

Aft section

Afterbody

In order to support the skin, its necessary to provide stiffening

members, frames, bulkheads, stringers and longerons .


13/47

p. 13Date: 04-02-2009

Typical section names Airbus fuselages


14/47

p. 14

Date: 09-02-2005

Fuselage structures:shells

Fuselages are too big to be built in one piece. So, instead, they are builtas shells that are later assembled.

C for frame(cadre)

P for stringer


15/47

p. 15Date: 04-02-2009

The fuselage as a beam

contains:

Longitudinal elements :

- Longerons

- Stringers

Transverse elements :

- Frames

- Bulkheads

External skin


16/47

p. 16Date: 04-02-2009

Engineering life cycle

Development-Design

The modern aeronautical engineering of aircraft design has beenan evolutionary process accelerated in recent times from thedemanding requirements for safety and the pressures ofcompetitive economics in structural design.

The primary objective of the structural designer is :

- To achieve the maximum possible safety margin

- To achieve a reasonable lifetime of the aircraft structure


17/47

p. 17Date: 04-02-2009

Development testing of a transport airplane


18/47

p. 18Date: 04-02-2009


Phases of airframe structural design:

Specification of function and design criteria

Determination of basic external applied loads

Calculation of internal element loads

Determination of allowable element strengths and margins ofsafety

Experimental demonstration or substantiation test programs


19/47

p. 19Date: 04-02-2009

Airplane design, development and certification

Design Specification

Design Criteria

Basic Loads

Airplane Design

Certification TestProgram

Approved typeCertificate

LaboratoryDevelopment

Test Data

Flight TestData


20/47

p. 20Date: 04-02-2009


The dotted arrows indicate feed-back where experimental data is

utilized to modify the design as necessary

The laboratory development test is an important feature of anynew vehicle program:

To develop design data on materials and shapes

To substantiate any new theory or structural configuration

The certification test program will demonstrate success withoutdegenerating into more and expensive development work


21/47

p. 21Date: 04-02-2009


Planning and structural weight

A good design is the result of proper planning and scheduling

Every aircraft engineer in a company is concerned about weight.

Finite Element Modeling (FEM)

It is the most versatile tool in structural analysis NASTRAN is one of the earliest FEM programs developed by

NASA in the mid-1960s to handle the analysis of missiles andaircraft structures

NASTRAN is one of the most used program in the aeronautic

field


22/47

p. 22Date: 04-02-2009


Entire airframe finite element model

D il d d i i f f l i i


23/47

p. 23Date: 04-02-2009

Detailed description of fuselage engineeringprocess

Skin geometry, loads, relevant failure modes, material, stress

state:

The largest single item of the fuselage structure is the skin andits stiffeners

It is the most critical structure since it carries all of the primaryloads due to fuselage bending, shear, torsion and cabin pressure

The fuselage skin carries the shear from the applied externaltransverse and torsional forces and cabin pressure

The skin thickness required on a fuselage is thinner than onwing

External pressure loads are much lower on the fuselage than on

the wing


24/47

p. 24Date: 04-02-2009

Skin most important load carrying part of the fuselage.

Carries the cabin pressure load (Dp).

Carried most of the bending loads (e.g. aircraft mass)

Work like membranes (plane stress)

sx

sy

txy


25/47

p. 25Date: 04-02-2009

Frames geometry, loads, relevant failure modes, material,

stress state: It serves to maintain the shape of the fuselage and to reduce the

column length of the stringers to prevent general instability ofthe structure

Frames are generally of light construction

Frame load are generally small and often tend to balance eachother

Fuselage frames are equivalent in function to wing rib

The design of fuselage frames may be influenced by loadsresulting from equipment mounted in the fuselage


26/47

p. 26Date: 04-02-2009

Frames provide stability to the skin in circumferential direction

Work like beams (carry axial, shear, and bending loads)

F

skin alone can not

carry shear load

F

frames have bending stiffness, distribute

the shear load

deformedshape

F F


27/47

p. 27Date: 04-02-2009

Typical frame designs (1)

Normal frame with clip

Clip

Frame outer flange

Stringer

Skin

Frame inner flange

Frame web


28/47

p. 28Date: 04-02-2009


Integral frame (skin connection is integrated in frame profile)

Cleat

Frame outer flange

Stringer

Skin

Frame inner flange

Frame web


29/47

p. 29Date: 04-02-2009


Z-Section can be replaced by C-section profiles

Z-Frame + clip and skin Integral Z-frame and skin

Clip

Frame

Stringer (z-shape)

Continuous under frame

Skin

Inner flange

Stringer (z-shape)

Continuous under frame

Skin

Outer flange

Web


30/47

p. 30Date: 04-02-2009

Stringers geometry, loads, relevant failure modes, material,

stress state:

Further increase skin buckling resistance.

Provide stiffness in axial direction

sy in the skinforces in stringersin axial direction


31/47

p. 31Date: 04-02-2009

F l L


32/47

p. 32Date: 04-02-2009

Fuselage structures : Loads

To understand a structure, you must:

Understand the loads

Make abstraction / find analogies (e.g. fuselage looks like a

beam)

Visualize the deformation:

deformations lead to stresses

stresses lead to reaction forces

reaction forces lead to equilibrium

Important term: Load case.This is applied loads!

The applied loads lead to internalreaction loads, to give equilibrium.


33/47

p. 33Date: 04-02-2009

Mixture of:

Hoop stress

Shear

Longitudinal tension

Typical dominating internal loads in fuselage skin

ShearHoop stress

Longitudinal tension stress

Compression load Compression load

Fuselage weight

Applied fuselagebending moment

Typical dominating load case for a fuselage structure:

symmetric down bending + internal pressure Dp

Wing upload and torsion moment

Horizontal tail plane download

Dp

Applied fuselagecabin pressure

Reactions inthe fuselage

R F t (RF)


34/47

p. 34Date: 04-02-2009

Reserve Factor (RF)

A measure of strength frequently used in Europe is the Reserve

Factor (RF) with the allowed loads and applied loads expressedin the same units .

The Reserve Factor is defined as :

LoadsApplied

LoadsAllowedRF


35/47

p. 35Date: 04-02-2009

The field of aerospace engineering uses generally lower design

factors because the costs associated with structural weight arehigh.

This low design factor is why aerospace parts and materials aresubject to more stringent quality control

The usually applied safety factor is 1.5, but for pressurizedfuselage it is 2.0 and for landing gear structures it is 1.25


36/47

p. 36Date: 04-02-2009

Limit Loads are the maximum loads expected in service

At limit load, the structure may not fail neither have permanentdeformation of the structure.

Before ultimate load, no failure is allowed but permanent

deformation is allowed.

At ultimate load (usually the limit load multiplied with the safetyfactor), the aircraft structure is allowed to fail.

Materials (i e A350)


37/47

p. 37Date: 04-02-2009

Materials (i.e. A350)

Explanation of Failure Mode Types (SAMOD Users


38/47

p. 38Date: 04-02-2009

Explanation of Failure Mode Types(SAMOD User sManual)

B : Failure due to excessive bearing stress

BF : Initial buckling of skin panel at fatigue load cases (FAT..).Activated with SAMOD option sasel Ah: initial buckling of skin atlimit load of flight load cases (Information only).

BL : Lateral Stability (Buckling) of frame

BN : Tension Blunt Notch in GLARE skins

BU : Buckling of structural part, e.g. skin or web CR : Crippling acc. HSB 53211; Check for sufficient support

from a free flange (20%-rule)

Dn : Geometric check for middle flange stiffness accordingDIN4114 for different load types n

FK : Compressive strength analysis acc. to Fokker, see:SAMOD Theoretical Manual


39/47

p. 39Date: 04-02-2009

D1 : Compressive strength analysis of skin acc. to MBB-UT

(Erdmann), see: SAMOD Theoretical Manual D3 : Compressive strength analysis of skin acc. to modified HSB

method (Meier), see: SAMOD Theoretical Manual

DT : Damage tolerance

GB : Global Buckling

FC : Failure due to diagonal folds on the skin panel (forcedcrippling), see: SAMOD Theoretical Manual

FT : Fatigue failure

HS : Allowable stress values acc. to HSB Manual

WM : Allowable compressive forces for web modulations as

described in PROPER Theoretical Manual


40/47

p. 40Date: 04-02-2009

JE : Buckling according to Johnson/Euler, see: SAMOD

Theoretical Manual JM : Web buckling analysis

LS : Lateral Stability analysis of cross-beams

MT : Allowable stress values based on material values

R : Rivet failure

RC : Riveting circumferential (analysis of circumferential joints)

RF : Riveting frame (analysis of frame riveting - clip/shear web)

RL : Riveting longitudinal (analysis of longitudinal joints)

RS : Riveting skin (analysis of skin riveting on the frame)

SH : Shear


41/47

p. 41Date: 04-02-2009

UD : Allowable user-defined stress values Explanation of

Location 1 (LOC1) WI : Windenburg; Geometric check for sufficient support from

free flange

1-8 : Rivet row for reserve factors for riveted joints

Failure due to shear load


42/47

p. 42Date: 04-02-2009

Failure due to shear load

Skin panel failure due to shear :

Failure in the upper critical range differ from those in the lowercritical range

Excessive buckling concentrations occur in panel zones withlarge deformation caused by diagonal tension

This causes a reduction of the skin panel load capacity


43/47

p. 43Date: 04-02-2009

Forced crippling of stringer

Local failure of the compressively loaded stiffener elements (e.g.stringers ) takes places caused by deformation in the diagonaltension field.


44/47

p. 44Date: 04-02-2009

Stringer column buckling failure :

The column buckling is due to compressive stress in thestiffener caused by the effect of diagonal tension in the skin

Crippling of stringer sections


45/47

p. 45Date: 04-02-2009

Crippling of stringer sections

Crippling failure modes :

Compressive strength of stiffened shells


46/47

p. 46Date: 04-02-2009

Compressive strength of stiffened shells

Instability modes :


47/47

p. 47Date: 04-02-2009

intro course aerospace wajdi

Documents