Principles of Airframes Revision Sheet

Design

A tie is a member which is subject purely to Tension (Pulling)

A beam is a member which carries Loads at an Angle

To get the best possible performance an aircraft must be designed to have the minimum possible drag

Aircraft engines placed as close as possible to the aircraft's centreline to help prevent yaw when an engine fails

Aircraft with diagonal ties between the wing and the fuselage are called Braced Monoplanes

The four main components of an airframe are the wings, fuselage, tail and the undercarriage

The main structural link between an aircraft's wings and tail unit is the fuselage

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

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

To get the best possible performance an aircraft must be designed to have the minimum possible drag

If only one piston engine/propeller combination or turbo prop engine is fitted to an aircraft it will normally be fitted In the nose

Materials

Steel is an alloy of iron and is very heavy

One main advantage of composite materials when used in airframe construction is they have a very high SWR and low weight

At a precise temperature two pieces of titanium pressed together will fuse and become a single piece. This process is called diffusion bonding

Titanium is relatively expensive

Fibres of materials such as glass, carbon or kevlar inside a thermosetting resin such as epoxy are known as Composites

A material's tendency to break under a high number of relative stresses, such as take-offs and landings, is called Fatigue

1 Pure aluminium is often plated onto its alloys to form a protective layer because aluminium Is very resistant to corrosion

Fibre-glass is the best material for a radome

If a metal chosen for airframe construction has the same properties throughout it is said to be homogeneous

The most widely-used group of airframe construction materials is Aluminium and magnesium alloys

Magnesium alloys are rarely used in carrier-based aircraft construction as they are prone to attack by sea-waters

Manufacturing Technology

The three main classes of forging are Squeezed, Upset and Drawn out

The skin, stringers and spar flanges of stressed wing skins are machined from a single piece of alloy called a Billet

Bending and Turning are techniques used in the manufacture of aircraft structures

Fuselage

Stringers are metal strips which run the length of the fuselage joining the frames

The ideal shape of a window in an aircraft fuselage is elliptical

In a transport aircraft the approximate altitude at which the fuselage is pressurised is 2400m (8000ft)

Fatigue meters are fitted to most RAF aircraft to record g loadings

Wings and Tailplane

If we take the weight of an aircraft and divide it by the wing area, the result is known as its Wing Loading

The aspect ratio of a wing is the Span (squared) divided by area

Aircraft with diagonal ties between the wing and the fuselage are called Braced Monoplanes

Aircraft wing ribs often have large lightening holes in them which can allow fuel to flow along the wing

To avoid boiling at high altitude fuel in aircraft tanks is pressurised

Wing skin construction normally used for aircraft of medium-to-high speed is stressed skin

The main purpose of an aircraft's wings is to generate lift

Yaw is controlled by the Rudder which is hinged to the fin spar

2 Pitch is controlled by the elevators or foreplanes

A multi-spar wing layout is particularly useful in constructing wings for high speed aircraft

The aircraft's fixed vertical fin is contained in the tail unit

The ailerons are hinged to the wing rear spar

At speeds near to the speed of sound the pressure waves generated in front of an aircraft is known as a Shock wave

De-icing of leading edges, tailplanes and engine intakes is often performed by using Compressor bleed air

A large rudder will counter the yaw which results from engine failure on a large four-engined aircraft

The tail unit houses the control surfaces which provide stability and control in pitch and yaw:

Foreplanes, or canards, are almost always all-flying as the entire surface moves to provide control movements

The above type of construction is STRESSED SKIN

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

Hydraulics and Pneumatics

Pneumatic systems use high-pressure air

In order to reduce the risk of fire from hydraulic fluids they are usually Inhibited

Pressure Gauges and Valves are components of a Pneumatic System

An OLEO PNEUMATIC undercarriage system compresses air or nitrogen gas

A major disadvantage of pneumatic systems over hydraulic systems is that air is Compressible

Pumps and Actuators are components of a Hydraulic System

Hydraulic Actuators are used in an airframe for Deploy high lift devices , Lowering and retracting the undercarriage and Moving the flight control surfaces

Radial and Axial are two types of Piston Pump

3 Gear/Vane and Piston are two main types of power pump used within a Hydraulic System

Pressure Gauges and Valves, Selector Valves and Actuators, Storage Cylinder and Air Lines are all components of a Pneumatic System

Flaps, Primary Flight Controls and the Braking System are powered by or use a hydraulic system

Hydraulic fluid is a fire risk because it is a type of oil

Hydraulic System are advantageous because they can develop unlimited force or torque, are smooth and responsive to operator inputs and are easy to maintain

A Hydraulic System achieves a 'Multiplication of Forces' by using cylinders of different sizes

Blaise Pascal developed the principles of hydraulics

Pumps and Actuators are components of a Hydraulic System

Undercarriage

The aircraft's main wheels are often stowed in the wings during flight

An undercarriage should be as light as possible because it is dead weight when airborne

The nose-wheel steering is part of an undercarriage system which is normally disconnected before towing

The undercarriage sequencer valve extends and retracts the undercarriage

The undercarriage serves two main purposes, one is to absorb landing shocks, the other is to support the aircraft on the ground

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

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

When brakes overheat they tend to fade

The pilot can use differential braking to steer the aircraft

A ground lock ensures that an undercarriage cannot be retracted accidentally on the ground

The two main types of aircraft brakes are Drum and Disc

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

General

4 Routine flying for long periods on one heading can be easily performed by a mechanical or electronic system called the autopilot

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

W is a biplane

The above instrument is a Vertical Speed Indicator (VSI)

The above instrument is a Horizontal Situation Indicator (HSI)