Design of Aircraft Structures Lecture Notes
Engineering over the airplane's life - answer-i. Initial Phases
(approximately 5 years): This stage includes initial creation, design,
tooling, manufacturing, test, and certification.
ii. Production and support (approximately 20 years): this covers
production and program support.
iii. In-service support (approximately 30 years): this includes
modifications, upgrades, modernization, service improvements,
aging fleet issues, and repairs.
iv. The entire process is driven by marketing, customer needs and
requirements, customer orders and customization, and is influenced
by technical requirements, regulations, technology, and lessons
learned.
v. Major derivatives repeat the entire process
Design engineering as an iterative process - answer-Design
engineering is defined as a multi-phased iterative process for
turning ideas into products. The key sequential phases are:
1. Analyze requirements
2. Determine feasibility
3. Develop concepts
4. Prepare preliminary design
5. Prepare detailed design
6. Verify design
7. Support production
8. provide customer support
9. Support product disposal
, Design of Aircraft Structures Lecture Notes
Q&A
Profile of a good design engineer - answer-A successful design
engineer must possess a blend of technical, creative, and
interpersonal skills.
Key characteristics include:
i. possessing a creative and innovative aptitude
ii. being a motivated coordinator and communicator.
iii. having strong visualization skills
iv. possessing a sound basic knowledge of physical and mechanical
characteristics of materials
v. having good appreciation of fabrication and manufacturing
methods
vi. being highly disciplined with an ability to compromise between
technical requirements, cost, and schedule
vii. being end-product/hardware oriented
Additionally, the role of an analyst is to verify the integrity of the
design
Structural components and construction: - answer-Spar: a principal
spanwise beam in the wing, stabilizer, rudder, or elevator structure;
usually a primary load-carrying member
Rib: a fore and aft member of an airfoil structure used to give the
airfoil section its form and transmit load from the skin to the spars
Stringer: longitudinal members in the fuselage or spanwise
members in the wing that transmit skin laods into the body frames
or wing rivs
Frame: a circumferential structural member in the body that
supports the stringers and skin
, Design of Aircraft Structures Lecture Notes
Q&A
Bulkhead: a heavy structural member in the fuselage used to
contain pressures or fluids or to disperse concentrated loads,
Monocoque: a single-shell construction where the skin carries all
shear and bending stresses
Semi-Monocoque: construction where shear and bending loads in
the skin are transmitted to stringers and frames
Web: a thin-guage plate or sheet that provides great shear strength
for its weight.
Material Forms and Manufacturing process - answer-Aircraft
components are fabricated using processes that fall broadly into
two categories: wrought and cast products
Cast vs. Wrought - answer-Wrought products start as castings and
are then plastically deformed at elevated termperatures to achieve
a fully recrystallized structure. This deformation provides superior
properties in the direction of metal flow. Wrought products
generally exhibit higher properties than cast products
Cast products are produced by pouring or injecting molten metal
into molds. Casting provides a means of creating intricate shapes
that are not practical via other methods.
A major limitation of castings is that the FAR 25 requires the use of
a casting factor, which results in a weight increase compared to an
identical wrought products.
Sheets and Plates - answer-Produces by rolling preheated cast
ingots. Properties are more isotropic (uniform in all directions) than
, Design of Aircraft Structures Lecture Notes
Q&A
extrusions. Aluminum sheet can be purchased clad for maximum
corrosion protection. Plate is preferred for "hog outs" (machined
parts)
Limitations:
Machines parts (from 2xxx and 7xxx plate in peak aged condition)
are susceptible to stress corrosion cracking and exfoliation
corrosion
Extrusion - answer-Metal is pushed through a die. Provides a net-
shape part with excellent longitudinal properties. Allows for
consolidation of parts and a low buy-to-fly ratio
Limitations:
results in a high degree of directionality parallel to the extruding
direction, leading to lower elongation and ductility in the transverse
direction.
Forging - answer-Metal is plastically deformed by impact or
compression. Produces a fully wrought structure with the highest
possible properties. Shape can be tailored to acommodate special
loading conditions by orienting the grain flow.
Limitations:
Load times for ordering are long. Requires additional setup time
compared to hogouts.
Engineering over the airplane's life - answer-i. Initial Phases
(approximately 5 years): This stage includes initial creation, design,
tooling, manufacturing, test, and certification.
ii. Production and support (approximately 20 years): this covers
production and program support.
iii. In-service support (approximately 30 years): this includes
modifications, upgrades, modernization, service improvements,
aging fleet issues, and repairs.
iv. The entire process is driven by marketing, customer needs and
requirements, customer orders and customization, and is influenced
by technical requirements, regulations, technology, and lessons
learned.
v. Major derivatives repeat the entire process
Design engineering as an iterative process - answer-Design
engineering is defined as a multi-phased iterative process for
turning ideas into products. The key sequential phases are:
1. Analyze requirements
2. Determine feasibility
3. Develop concepts
4. Prepare preliminary design
5. Prepare detailed design
6. Verify design
7. Support production
8. provide customer support
9. Support product disposal
, Design of Aircraft Structures Lecture Notes
Q&A
Profile of a good design engineer - answer-A successful design
engineer must possess a blend of technical, creative, and
interpersonal skills.
Key characteristics include:
i. possessing a creative and innovative aptitude
ii. being a motivated coordinator and communicator.
iii. having strong visualization skills
iv. possessing a sound basic knowledge of physical and mechanical
characteristics of materials
v. having good appreciation of fabrication and manufacturing
methods
vi. being highly disciplined with an ability to compromise between
technical requirements, cost, and schedule
vii. being end-product/hardware oriented
Additionally, the role of an analyst is to verify the integrity of the
design
Structural components and construction: - answer-Spar: a principal
spanwise beam in the wing, stabilizer, rudder, or elevator structure;
usually a primary load-carrying member
Rib: a fore and aft member of an airfoil structure used to give the
airfoil section its form and transmit load from the skin to the spars
Stringer: longitudinal members in the fuselage or spanwise
members in the wing that transmit skin laods into the body frames
or wing rivs
Frame: a circumferential structural member in the body that
supports the stringers and skin
, Design of Aircraft Structures Lecture Notes
Q&A
Bulkhead: a heavy structural member in the fuselage used to
contain pressures or fluids or to disperse concentrated loads,
Monocoque: a single-shell construction where the skin carries all
shear and bending stresses
Semi-Monocoque: construction where shear and bending loads in
the skin are transmitted to stringers and frames
Web: a thin-guage plate or sheet that provides great shear strength
for its weight.
Material Forms and Manufacturing process - answer-Aircraft
components are fabricated using processes that fall broadly into
two categories: wrought and cast products
Cast vs. Wrought - answer-Wrought products start as castings and
are then plastically deformed at elevated termperatures to achieve
a fully recrystallized structure. This deformation provides superior
properties in the direction of metal flow. Wrought products
generally exhibit higher properties than cast products
Cast products are produced by pouring or injecting molten metal
into molds. Casting provides a means of creating intricate shapes
that are not practical via other methods.
A major limitation of castings is that the FAR 25 requires the use of
a casting factor, which results in a weight increase compared to an
identical wrought products.
Sheets and Plates - answer-Produces by rolling preheated cast
ingots. Properties are more isotropic (uniform in all directions) than
, Design of Aircraft Structures Lecture Notes
Q&A
extrusions. Aluminum sheet can be purchased clad for maximum
corrosion protection. Plate is preferred for "hog outs" (machined
parts)
Limitations:
Machines parts (from 2xxx and 7xxx plate in peak aged condition)
are susceptible to stress corrosion cracking and exfoliation
corrosion
Extrusion - answer-Metal is pushed through a die. Provides a net-
shape part with excellent longitudinal properties. Allows for
consolidation of parts and a low buy-to-fly ratio
Limitations:
results in a high degree of directionality parallel to the extruding
direction, leading to lower elongation and ductility in the transverse
direction.
Forging - answer-Metal is plastically deformed by impact or
compression. Produces a fully wrought structure with the highest
possible properties. Shape can be tailored to acommodate special
loading conditions by orienting the grain flow.
Limitations:
Load times for ordering are long. Requires additional setup time
compared to hogouts.
