<p> Principles of Airframes Revision Sheet</p><p>Design</p><p>A tie is a member which is subject purely to Tension (Pulling) </p><p>A beam is a member which carries Loads at an Angle </p><p>To get the best possible performance an aircraft must be designed to have the minimum possible drag </p><p>Aircraft engines placed as close as possible to the aircraft's centreline to help prevent yaw when an engine fails </p><p>Aircraft with diagonal ties between the wing and the fuselage are called Braced Monoplanes </p><p>The four main components of an airframe are the wings, fuselage, tail and the undercarriage </p><p>The main structural link between an aircraft's wings and tail unit is the fuselage </p><p>A structure which is strong enough to take the loads applied it both in compression and tension, despite being supported at one end only is called a Cantilever structure </p><p>When designing an aircraft an increase in weight in one area which leads to other areas being strengthened, and therefore made more heavy, is called the Weight spiral effect </p><p>To get the best possible performance an aircraft must be designed to have the minimum possible drag </p><p>If only one piston engine/propeller combination or turbo prop engine is fitted to an aircraft it will normally be fitted In the nose </p><p>Materials</p><p>Steel is an alloy of iron and is very heavy </p><p>One main advantage of composite materials when used in airframe construction is they have a very high SWR and low weight </p><p>At a precise temperature two pieces of titanium pressed together will fuse and become a single piece. This process is called diffusion bonding </p><p>Titanium is relatively expensive </p><p>Fibres of materials such as glass, carbon or kevlar inside a thermosetting resin such as epoxy are known as Composites </p><p>A material's tendency to break under a high number of relative stresses, such as take-offs and landings, is called Fatigue </p><p>1 Pure aluminium is often plated onto its alloys to form a protective layer because aluminium Is very resistant to corrosion </p><p>Fibre-glass is the best material for a radome </p><p>If a metal chosen for airframe construction has the same properties throughout it is said to be homogeneous </p><p>The most widely-used group of airframe construction materials is Aluminium and magnesium alloys </p><p>Magnesium alloys are rarely used in carrier-based aircraft construction as they are prone to attack by sea-waters</p><p>Manufacturing Technology</p><p>The three main classes of forging are Squeezed, Upset and Drawn out </p><p>The skin, stringers and spar flanges of stressed wing skins are machined from a single piece of alloy called a Billet </p><p>Bending and Turning are techniques used in the manufacture of aircraft structures</p><p>Fuselage</p><p>Stringers are metal strips which run the length of the fuselage joining the frames</p><p>The ideal shape of a window in an aircraft fuselage is elliptical </p><p>In a transport aircraft the approximate altitude at which the fuselage is pressurised is 2400m (8000ft)</p><p>Fatigue meters are fitted to most RAF aircraft to record g loadings </p><p>Wings and Tailplane</p><p>If we take the weight of an aircraft and divide it by the wing area, the result is known as its Wing Loading </p><p>The aspect ratio of a wing is the Span (squared) divided by area </p><p>Aircraft with diagonal ties between the wing and the fuselage are called Braced Monoplanes </p><p>Aircraft wing ribs often have large lightening holes in them which can allow fuel to flow along the wing </p><p>To avoid boiling at high altitude fuel in aircraft tanks is pressurised</p><p>Wing skin construction normally used for aircraft of medium-to-high speed is stressed skin </p><p>The main purpose of an aircraft's wings is to generate lift</p><p>Yaw is controlled by the Rudder which is hinged to the fin spar</p><p>2 Pitch is controlled by the elevators or foreplanes </p><p>A multi-spar wing layout is particularly useful in constructing wings for high speed aircraft</p><p>The aircraft's fixed vertical fin is contained in the tail unit</p><p>The ailerons are hinged to the wing rear spar </p><p>At speeds near to the speed of sound the pressure waves generated in front of an aircraft is known as a Shock wave </p><p>De-icing of leading edges, tailplanes and engine intakes is often performed by using Compressor bleed air </p><p>A large rudder will counter the yaw which results from engine failure on a large four-engined aircraft</p><p>The tail unit houses the control surfaces which provide stability and control in pitch and yaw: </p><p>Foreplanes, or canards, are almost always all-flying as the entire surface moves to provide control movements </p><p>The above type of construction is STRESSED SKIN </p><p>If the wing of a high-speed aircraft deflects too much, damage and loss of control can be caused by an aerodynamic phenomenon known as Flutter </p><p>Hydraulics and Pneumatics</p><p>Pneumatic systems use high-pressure air</p><p>In order to reduce the risk of fire from hydraulic fluids they are usually Inhibited</p><p>Pressure Gauges and Valves are components of a Pneumatic System</p><p>An OLEO PNEUMATIC undercarriage system compresses air or nitrogen gas </p><p>A major disadvantage of pneumatic systems over hydraulic systems is that air is Compressible </p><p>Pumps and Actuators are components of a Hydraulic System</p><p>Hydraulic Actuators are used in an airframe for Deploy high lift devices , Lowering and retracting the undercarriage and Moving the flight control surfaces </p><p>Radial and Axial are two types of Piston Pump</p><p>3 Gear/Vane and Piston are two main types of power pump used within a Hydraulic System</p><p>Pressure Gauges and Valves, Selector Valves and Actuators, Storage Cylinder and Air Lines are all components of a Pneumatic System</p><p>Flaps, Primary Flight Controls and the Braking System are powered by or use a hydraulic system</p><p>Hydraulic fluid is a fire risk because it is a type of oil </p><p>Hydraulic System are advantageous because they can develop unlimited force or torque, are smooth and responsive to operator inputs and are easy to maintain </p><p>A Hydraulic System achieves a 'Multiplication of Forces' by using cylinders of different sizes </p><p>Blaise Pascal developed the principles of hydraulics</p><p>Pumps and Actuators are components of a Hydraulic System</p><p>Undercarriage</p><p>The aircraft's main wheels are often stowed in the wings during flight </p><p>An undercarriage should be as light as possible because it is dead weight when airborne </p><p>The nose-wheel steering is part of an undercarriage system which is normally disconnected before towing</p><p>The undercarriage sequencer valve extends and retracts the undercarriage </p><p>The undercarriage serves two main purposes, one is to absorb landing shocks, the other is to support the aircraft on the ground </p><p>If an aircraft's main wheels are too far back behind the centre of gravity high loads will be taken on the nose wheel during landings </p><p>Nose-wheel or tricycle undercarriages have two main disadvantages, they are stronger and therefore heavier than tail-wheels and damage is greater if a nose-wheel collapses </p><p>When brakes overheat they tend to fade</p><p>The pilot can use differential braking to steer the aircraft</p><p>A ground lock ensures that an undercarriage cannot be retracted accidentally on the ground </p><p>The two main types of aircraft brakes are Drum and Disc </p><p>Nose-wheel or tricycle undercarriages have two main disadvantages, they are stronger and therefore heavier than tail-wheels and the C of G is forward of the main wheels </p><p>General</p><p>4 Routine flying for long periods on one heading can be easily performed by a mechanical or electronic system called the autopilot </p><p>An autopilot performs two fundamental operations. It detects when an aircraft has strayed from the required flight path and calculates and performs correction control movements</p><p>W is a biplane</p><p>The above instrument is a Vertical Speed Indicator (VSI)</p><p>The above instrument is a Horizontal Situation Indicator (HSI)</p><p>5</p>