AIRCRAFT SYSTEMS Flashcards
5 LOADS APPLIED TO AIRCRAFT
Tension
Compression
Shear
Bending
Torsion
Tends to “stretch” structural members.
Components used to resist this load are known as “ties”.
TENSILE LOAD
Tends to “shorten” structural members.
Components used to resist this load are known as “struts”.
One example of strut is “oleo-pneumatic strut” which resist compressive load on aircraft landing gear.
COMPRESSION LOAD
Tends to “slide” one face of the material over an adjacent face.
Riveted joints are designed to resist these forces.
SHEAR LOAD
Combination of tension, compression, and shear.
Tension on the outer side, compression on the inner side, and shear across the structure.
BENDING
Twisting force.
Combination of tension, compression, and shear.
Tension on the outer edge, compression on the center, and shear across the structure.
TORSION
Occurs to thin sheet materials when they are subjected to end loads and to ties if they are subjected to compressive forces.
BUCKLING
Stress is the internal force inside a structural member which resists an externally applied force and, therefore, a tensile load or force will set up a tensile stress, compression loads, compressive stresses etc.
STRESS
When an external force of sufficient magnitude acts on a structure, the structural dimensions change. This change is known as strain.
Expressed as ratio of change of length to original length.
STRAIN
Stresses will tend to elongate, compress, bend, shear, and twist components.
ELASTIC LIMIT
Maximum load that the designer would expect an airframe or component to experience in service.
Defined as a load factor (ratio of lift to weight of aircraft)
DESIGN LIMIT LOAD
DLL for public transport aircraft is ____, for Utility is _______, and for Acrobatic is ______.
2.5G FOR PUBLIC TRANSPORT
3.4-3.8G FOR UTILITY
6G FOR ACROBATIC
Is the Design Limit Load multiplied by the safety factor (1.5 minimum).
DESIGN ULTIMATE LOAD
The aircraft manufacturer will intend to design an aircraft to take into account all the loads it may experience in flight.
An airframe is designed with good fail-safe and damage tolerant structures.
DESIGN PHILOSOPHIES
Is defined as the minimum number of flying hours, landings, pressurization cycles, etc. which should elapse before a major structural failure occurs.
SAFE LIFE
After the permitted safe life count has been reached, the relevant item is ___________.
replaced or overhauled
To minimize the effects of metal fatigue, aircraft designers apply this principle.
This is based on the principle of component redundancy.
_____ structures have multiple load paths. The loads are then shared by adjacent members.
FAIL-SAFE
In fail safe, if one path fails, the load it carried will now be carried by the ___________ for a limited period, until the next periodic inspection.
adjacent member
What is the disadvantage of a fail-safe?
It is very expensive in terms of weight as each of the members must be strong enough to do the work for both.
Stressed skin style of construction where each piece of the airframe including stressed skin plays its part in spreading loads throughout the entire airframe and is tolerant to a certain amount of damage.
These structures eliminate the extra structural members needed in a fail-safe design by spreading the loading of a particular structure over a larger area.
Damage Tolerant Structure
A structure subjected to continual reversals of loading, such as the landing gear or the fuselage of a pressurized aircraft, will fail at a load less than that of a steadily applied load. This is known as fatigue.
FATIGUE
_________ will depend on the number of reversals experienced.
FAILURE LOAD LEVEL
This is a graph of the magnitude of a cyclical stress against a logarithmic scale of cycles to failure.
In high cycle fatigue situations, material performance can be graphically characterized by this.
SN CURVE OR WOHLER CURVE
A main aircraft structure. It carries the aircraft payload, whether passengers or freight, as well as the flight crew and cabin staff.
This also houses the flight deck or cockpit for operating the aircraft and space for controls, accessories, and other equipment.
Transfers loads to and from the wings, empennage, landing gear, and possibly the engines.
FUSELAGE
Pressurized fuselages must also be able to withstand stresses (________) imposed by pressurization forces.
AXIAL AND HOOP STRESSES
Axial or longitudinal stress tends to _______ the aircraft.
elongate
___________ tends to expand the fuselage’s cross-sectional area.
HOOP OR RADIAL STRESS
3 main types of fuselage construction
Truss or framework type
Monocoque
Semi-Monocoque
It is generally used for light, non-pressurized aircraft
Consists of light gauge steel tubes welded together to form a frame of triangular shape to give the most rigid of geometric forms with each tube carrying a specific load of magnitude.
It is covered by a lightweight aluminum alloy or fabric skin.
Truss or framework type fuselage
In French word meaning “single shell”.
In this structure, all loads are taken by the stressed skin with light internal frames or “formers” to give the required shape.
The skin may be made of a sandwich type construction, a honeycomb core with a skin of composite material or aluminum alloy, to provide rigidity and strength.
Monocoque
Semi-Monocoque structure was found to be not strong enough. Additional structural members such as stringers (stiffeners) and longerons are added to run lengthwise along the fuselage joining the frames together.
Semi-Monocoque
Monocoque and semi-monocoque are generally referred to as ________.
STRESSED SKIN
What is the disadvantage of a monocoque?
A slight damage to the skin can seriously weaken the structure
Skin is attached to the frames and stingers by __________
riveting or adhesive bonding
When cut-outs are made such as for access panels, passenger windows, etc., reinforcement in the form of _________ is required around the cut-out.
doublers (backing plates)
Must withstand both pressurization loads and bird strike impacts.
Constructed from toughened glass panels attached to each side of a vinyl interlayer, surrounded with a rubber seal, and attached to the frame by bolts passing through the extended edge of vinyl interlayer.
FLIGHT DECK WINDOWS
The shock loading of a bird strike impact is absorbed by the ability of the ____________ to stretch and deform should the impact be great enough to shatter the outer glass.
vinyl interlayer
On some aircraft, an opening window to the side of the windscreen, known as a __________ window is provided to enable the pilot sufficient visibility to land the aircraft safely should the windscreen become obscured.
direct vision or dv
Designed based on fail-safe principle, and normally have two panes of acrylic plastic mounted on an airtight rubber seal fitted to a metal window frame.
Inner and outer panes are each individually capable of taking the full cabin pressurization load.
PASSENGER CABIN WINDOWS
One function is to support the weight of the aircraft in the air; thus, it must have sufficient strength and stiffness.
Strength and stiffness can be determined by thickness of the _____, with the thickness and type of the construction used being dependent on the speed requirements of the aircraft.
WING (MAINPLANE)
3 types of wing type constructions
Bi-plane
Braced Monoplane
Cantilever Monoplane
Very few _____ fly at more than 200 knots in level flight and so the air loads are low. This means that the truss type design covered in fabric is satisfactory.
The wing spars, interplane struts, and bracing wires form a lattice girder of great rigidity which is highly resistant to bending and twisting.
BI-PLANE
what is the disadvantage of a bi-plane?
this construction has a large amount of drag which contributes to the fact that bi-planes fly relatively slowly.
Wing is connected by a brace to a fuselage or a landing gear.
In flight, _____ is subject to tensile loads and acts as a tie. On the ground, it is under compression and acts as a strut.
BRACED MONOPLANE
Wings in this configuration have to absorb the stresses due to the lift and drag in flight and their own weight on the ground.
Absorbing the stresses is achieved by building the wing around one or more main load bearing members known as “spars”. Wing spars pass from wing tip to wing tip, either as single structure or as connected sections.
CANTILEVER MONOPLANE
4 WING CONSTRUCTION
Spar
Skin
Stringers
Ribs
______ would normally be an I-beam either manufactured as a single part or made up of two or more parts to give it fail-safe characteristics.
These are constructed so they can absorb the downward bending stresses when on the ground and the upwards, rearwards, and twisting stresses when in flight.
SPAR
Takes the load due to the differences in air pressure and the mass and inertia of the fuel (if any) in the wing tanks.
Generates direct stresses in a spanwise direction as response to bending moments and it also reacts against twisting forces (torsion).
SKIN
Spanwise members which give the wing rigidity by stiffening the skin in compression.
STRINGERS
Maintain the shape (airfoil) of the wing.
Support the spars, stingers, and skin against buckling.
Pass concentrated loads from the engines, landing gear, and control surfaces into the skin and spars.
RIBS
Skin attached to spars, stringers, and ribs form a ________.
Torsion box
Major structural components of the wing are generally manufactured from __________.
aluminum alloys
Composite materials, such as Glass Reinforced Plastic (GRP) and Carbon Reinforced Plastic (CRP), and honeycomb structures are used for __________.
more lightly loaded structures
4 types of tail unit or empennage type construction
Conventional
T-tail
H-tail
V-tail
Provides, in most cases, the longitudinal and the directional stability and control.
TAIL UNIT OR EMPENNAGE
Provides longitudinal stability, by generating upward or downward forces as required.
Longitudinal control (pitch) is provided by either elevators.
HORIZONTAL STABILIZER (TAILPLANE)
Provides stability about the normal axis.
Directional control (yaw) is provided by the rudder.
VERTICAL STABILIZER (FIN)
_______ is the rapid and uncontrolled oscillation of a flight control (or the surface to which it is attached) which occurs as a result of an unbalanced surface.
_______ is caused by the interaction of aerodynamic forces, inertial forces, and the elastic properties of the surface or structure. Poorly maintained aircraft also contributes for _______ to occur. This can lead to the catastrophic failure of the structure.
______ must not occur within the normal flight operating envelope or below the limit airspeed of the aircraft.
Flutter
_________ is an aluminum and copper-based alloy which has poor corrosion resistance except when clad with pure aluminum. It also has good fatigue resistance and good thermal and electrical conductivity but is difficult to weld.
Duralumin
the most popular material in used for commercial aircraft skins.
aluminum clad duralumin
_______ and its alloys are relatively heavy but are very strong. Therefore, they are only used where strength is vital and weight penalties can be ignored.
Steels
Is much lighter than steel, but just as strong and can be used where fire protection is required.
They have good strength; it retains this strength and corrosion resistance up to temperatures of 400 degrees Celsius but is expensive to produce.
TITANIUM
They are often used in the construction of gearboxes.
This gives an excellent strength to weight ratio
MAGNESIUM ALLOYS
this is used where structural strength is required. This can be produced with the same strength as an aluminum alloy but with the weight saving of about 20%.
Carbon Fiber Reinforced Plastic
It is often used for fairings and non-load bearing panels because of its light weight.
Glass Fiber Reinforced Plastic
It has very low electrical conductivity and high fire resistance. Aircraft cabin doors, overhead bins, and bulkheads may be built with honeycomb cores made up of this.
Kevlar
Have good resistance to corrosion and can be easily formed to complex shapes, but their fatigue behavior is different of that conventional metal alloys.
Interest for ________ for structural use is due to their high specific strength, high specific stiffness, and their ability to retain these properties even at high temperatures.
Composite materials
Formula for Specific Strength
Ultimate Tensile Strength / Density
Formula for Specific Stiffness
Young’s Modulus (E) (Stress/Strain) / Density
What is the maximum descent velocity for an aircraft?
10ft/s or 3.15m/s
On some aircraft, it is specified that if no damage is found in the primary areas, then the secondary areas need not be __________
inspected
what are the maximum structural masses?
Maximum Zero Fuel Mass (MZFM)
Maximum Structural Takeoff Mass (MSTOM)
Maximum Structural Taxi Mass
Maximum Structural Landing Mass
Is the maximum permissible mass of an aircraft with no usable fuel.
Represents the total weight of the aircraft, including its structure, payload (passengers and cargo, instruments, but excluding the weight of the fuel.
Maximum Zero Fuel Mass
Is the maximum permissible total aircraft mass at the start of the takeoff run.
Represents the allowable weight at which an aircraft is certified for takeoff, including the aircraft’s structure, fuel, payload (passengers and cargo), and any other items on board.
Maximum Structural Takeoff Mass
Maximum Structural Takeoff Mass is also know as what?
Maximum Takeoff Weight (MTOW)
Is the maximum permissible mass of an aircraft at the commencement of taxi.
May also be referred to as maximum ramp mass.
Maximum Structural Taxi Mass
Is the maximum permissible total aircraft mass on landing in normal circumstances.
Maximum Structural Landing Mass
The _________ refers to the numbering system and referencing standards for commercial aircraft documentation.
ATA 100 Chapters
Method of locating components in the aircraft must be established in order that maintenance and repairs can be carried out easier. This is achieved by identifying reference lines fore and aft, left and right, and from bottom to top.
Station Numbers
________ are determined by reference to a zero-datum line (fuselage station 0.00), at or near the nose as defined by the manufacturer. They are identified in inches or millimeters forward or aft of the datum.
Fuselage Station Numbers
Wing station numbers are measured in inches, left or right from the center line of the aircraft.
Wing Station Numbers
_______ is identified from the horizontal datum. These vertical positions are also called as water line or buttock line.
They are measured in inches from the datum.
Vertical Position
Zoning of large aircraft is specified by the _________ in the ATA-100 Specification.
Air Transport Association of America
A zone is identified by one of three indicators, depending upon whether it is a _________
major zone, sub-zone, or simply just a zone
The major zones are divided into major sub-zones, which are shown by the ______ digit of the major zone number.
Second
The major sub-zones are further divided into zones using the ______ digit of the major zone number.
third
