Undercarriage And Airframe Flashcards
Explain different types of loading which an airframe must be designed to accept (5)
Landing and takeoff loads
Gust loads - caused by sudden change in velocity of the air
Manoeuvring loads - load factor or g loading
Control surface loads - caused when a control surface deflects and imparts force on the wings
Pressurisation loads - causes the cabin to expand and contract
Explain the effects of the application of a load to an airframe structure (stress and strain)
Any load placed on a structure causes a stress, Stress is measured as a unit of force per unit area. The SI unit is the pascal (Pa)
Strain is the measure of the deformation of the material, The more stress an item is under, the more the strain.
Differentiate between bending, tensile, compression, torsional, and shear loads
Tensile - trying to stretch a structural member of an aircraft
Torsion - the twisting of an object due to torque. Torsion is a concept meaning its been twisted.
Compress - tries to shorten something
Bending - tries to bend a structure, involves torsion and compression forces.
Sheer - stress force produced when one object slides over another.
Briefly describe the various construction styles of a fuselage.
Truss - box girder style, gives strength with struts and braces.
Monocoque - loads absorbed only by the skin, generally rounded shape. Framework if any plays little or no part in absorbing stress forces
Semi-monocoque - blend of the two, consists of bulkheads with attached loungers and skin is attached over the frame and stiffened by stringers. Both the skin and frame absorb any stress
Briefly describe the common types of wing construction.
Bi plane - double set of wings placed above the other.
Braced monoplane - have a strut that supports the wing either above or below it.
Unbraced monoplane - high wing/low wing but no struts.
Describe the construction of the typical semi-monocoque wing
Wing is connected to fuselage at the roots, ribs form the shape of the wing and spar help with the structural support of the wing. Skin is placed over and is connected to stringers for strength.
What are spars, ribs, skin and stringers?
Spars - beams which are the main-load bearing structural member of the wing. Made of aluminium alloy
Ribs - attach to provide the shape of the wing/ cross sectional shape. Made of aluminium alloy
Skin - covered over the wing frame and absorb the majority of the load
Stringers - long thin structure members which run the length of the wing under the skin.
Briefly describe the construction of:
(a) the tailplane;
(b) the vertical fin;
(c) control surfaces.
(A) (B) similar construction of the wings with spars, ribs and skin to absorb some of the load. The main structural member in the fin is called the sternpost.
(C) similar to that of the wing, lighter in construction with one spar near the leading edge and ribs joined by a narrow trailing edge member.
Briefly describe the method of operation of the primary control surfaces found in a light twin aeroplane.
In a light aircraft, the primary controls are generally controlled via cables and push rods, They use deflection of the air to create a force (Newton’s 3rd law)
Balance controls consist of mass balance and aerodynamic balance. Larger systems use hydraulic controls.
Explain the requirements which the undercarriage/landing system must be able to meet (7)
- Support the aircraft on the ground at MAUW
- Absorb loads produced by landing and taxiing across ground undulations
- Withstand side loading due to crosswind take offs and landings
- Minimal drag and friction
- Maximum possible traction for efficient braking
- Retractable – provide against accident retraction on the ground
- Maximum strength for minimal weight
Describe the features of a typical undercarriage construction.
Front wheel with two on the sides near the wing. Gives better visibility, safer and better braking, better crosswind and more stable on takeoff and landing.
Explain the operation of an oleo-pneumatic shock strut
Consists of two tubes that go into each other which are connected by torsion links.
Upper tube is called the cylinder and contains a type of hydraulic oil.
Lower is called plunger tube and mostly contains compressed air but allows oil to enter the top of the tub (when forced upwards) through a flutter valve.
Oil and air are kept seperate by a separator, which is Able to slide up and down inside the plunger tube and prevent the plunger from rotating inside the cylinder.
Describe the pilot checks of oleo-pneumatic undercarriage legs.
For nose oleos, the extension should be about 7cm (length of the shiny part of the leg)
- If oleos are fitted to the main undercarriage, extension will be around 10cm
- If there is any doubt, consult an engineer
- On a pre-flight inspection, check for any leaks, abnormal extension, any cracks, and ensure the wheel is correctly aligned
Describe the construction of aircraft wheel assemblies and tyres.
Wheels - strong enough to withstand the loads of landing and braking.
Sometimes have one or more wheels to ensure that theres a large enough footprint to spread the load and provide sufficient traction for braking.
Tyres - can be of two piece (inner and outer tube) tyres have tendency to creep ‘move’ around the tyre rim so a creep mark is painted to indicate the allowable amount of creep.
Explain the requirements for tyre care and checks.
Excessive braking should be avoided especially at high speed as this can cause wheels to lock up.
Correct inflation of the tyres is important and tyres should be checked for excessive wear seen as bald spots.
Check for cuts and creep.
