Chapter 1 - Airframe Structure Flashcards
What factors are considered in the design of an aircraft?
Stress Strain Stiffness or rigidity Design Limit Load (DLL) Temperature Corrosion Natural/Environmental Hazards - Lightning, bird strikes, hail, saline environments, erosive atmospheres (e.g. sand), pollutants, etc
What is stress?
Load per unit area of cross-section
What is strain?
Deformation caused by stress
What is stiffness (or rigidity)?
Ratio of stress over strain
What is the Design Load Limit (DLL)?
Maximum load the designer would expect and airframe to experience in service
What two sources of heating need to be considered when taking temperature in account during aircraft design?
Local heating - Structures near engines, heat exchangers, hot gas ducts, etc
Kinetic heating - High ambient temp, surface of airframe at high speeds due to friction
What are the two key types of corrosion that must be considered during aircraft design?
Chemical corrosion
Stress corrosion
What are the ideal properties of materials used in aircraft construction?
High strength and stiffness
Lightness
Low cost
Ease of construction and production
Name some materials commonly used in aircraft construction?
Aluminium alloys
Titanium alloys (fire resistant + light and strong)
Magnesium alloys (light but rare due to flammability)
Steel
Carbon Fibre Composites (CFCs)
Glass Reinforced Plastic (GRP) - Radomes
Wood
What is the primary consideration when designing a fuselage?
The load it has to carry, this governs its shape.
Aerodynamic features are secondary to the necessity to accommodate payload.
What are the 3 common types of fuselage structure?
Truss
Monocoque
Semi-monocoque
What does a truss structure consist of?
Longerons
Vertical Web Members
Diagonal Web Members
Stringers
Bulkheads
What does a monocoque structure consist of?
Bulkhead
Stressed skin to support load
Frames
What does a semi-monocoque structure consist of?
Bulkhead
Stressed skin attached to sub structures
Frames
Stringers
Note - Can have longerons running the length of it as well, see diagrams in section 5-1-2 of manual and memorise
Note - See manual for the roles of the different parts making up the fuselage.
Is this information required for the exam?
What makes up a typical wing structure?
Front Spar
Rear Spar
Ribs
Stringers
Skin
Note - Memorise diagram in section 5-1-3 of the course manual
What parts of the wing structure carry wing loading forces?
Spars, stringers, ribs and skin (all)
What are the 3 typical wing configurations used in aircraft design?
High wing
Mid wing
Low wing
Why might a high wing be used?
Enables ease of loading for cargo aircraft + gets the wing spar out of the way for greater internal stowage
Why might a mid wing be used?
Presents a smaller radar signature, used on “stealth” aircraft
Why might a low wing be used?
Shorter undercarriage, crash protection
What design features can be used to make an aircraft efficient in both subsonic and supersonic flight?
Variable sweep wings
Moderate sweep - Thin wings with high light devices (flaps and slats)
Anhedral wing - Unstable
Dihedral wing - Stable
What does the empennage consist of?
Fixed surfaces - Fin and Tailplane
Moveable surfaces - Elevator, Rudder and Trim Tabs
Ground Adjustable surfaces - Fixed Tab
What is the primary purpose of the empennage?
Provides stability and control for the aircraft about the normal and lateral axis.
What is the role of the tailplane?
Provided longitudinal stability about the lateral axis.
Name four common tailplane configurations.
All flying tailplane
Taileron
Tailless
V Tail
Explain what an all flying taiplane is/why it is used?
An all flying tailplane means the entire tailplane’s AoA can be adjusted by trim actuators to compensate for the increased nose down trim forced at higher speeds and any changes in the CoG due to payload and fuel distribution, with MINIMAL increase in trim drag.
I.e. great control over wide trimming range for cargo/fuel distribution and is far more fuel efficient than greatly trimming the control surface itself (less drag).
How does a taileron work/what advantage does it offer?
Each side can be actuated separately to the other or together, provides the ability to act as either an aileron or an elevator, providing control in both pitch and roll.
How does control work in a tailless aircraft?
Control power is provided by trailing edge elevators or elevons.
Wing trailing edge flaps cannot be used.
Consequences are the ineffectiveness of trailing edge controls at high supersonic speeds.
How does a V tail work?
Two fins, each performing the functions of both a rudder and elevator.
What is the purpose of a canard?
A canard reduces trim drag at high speeds.
Up-load will be required on the canard for trim.
What are the main features influencing the fuselage design for a combat aircraft?
Powerplant installation
Fuel and undercarriage stowage and weapon carriage
Low frontal area with a smooth build-up of cross-section area over the forebody, canopy and wings, followed by a gradual decrease over the afterbod
Stealth technology (both radar and IR)
What are the main features influencing the fuselage design for a transport aircraft?
Cabin length
Cabin width (i.e. usable floor area)
Freight volume
Passenger and freight distribution to maintain the correct CG
What are the primary flying controls?
Rudder
Elevators
Ailerons
What are the secondary flying controls?
Spoilers
Flaps
Slats
Describe wing loading?
Forces arising on the wing due to the aircraft’s manoeuvre and the payload.
