FLYING • People dreamed of be able to fly like the birds from the beginning of time. • Some people did more than just dream. They spent years and years of research, experiments, trial and error, learning all about flight. • At last, in 1903, the Wright Brothers made the first powered, controlled, aeroplane flight. • By 1910 ‘Bristol’ aeroplanes the first were being built at Filton. • Today millions of people have had the chance to fly thanks to those early experiments.
FORCES One of the things that had to be understood before humans had a chance to fly were the four forces of flight. These are: • LIFT – the upward force that comes from air moving over and under the aeroplane’s wings. • WEIGHT – the downward force that comes from gravity. • THRUST – the forward force that comes from the aeroplane’s engine or propeller. • DRAG – the backward force that comes from the resistance caused by the air moving against the aeroplane.
LIFT UP THRUST FORWARD DRAG BACK DOWNWARD WEIGHT BRISTOL FREIGHTER 1950s
CLIMBING Thrust has to be greater than drag if an aeroplane is to climb steadily. BRISTOL BOMBAY 1936
DIVING In a steady dive the weight of the aircraft is partly pulling it forwards. If the dive is steep enough the aircraft will speed up even if the engine is switched off and thrust is zero (like freewheeling downhill on your bike). BLACKBURN SKUA WITH ‘BRISTOL’ ENGINES, 1936
WINGS GIVE LIFT When an aeroplane is flying, air is passing over and under its wings. The air pushed over the top of the wing is moving faster than the air below so is spread out more thinly. This creates lower air pressure above the wing than below. The curve of the wing increases the speed at which the air flows. The difference in air pressure above and below the wing keeps the aeroplane in the air until the pilot wants to land.
Sucked upwards from above o Pushed upwards from below AIRBUS A350 2000s
SOME AEROPLANES GET THRUST FROM A PROPELLER The propeller is usually turned by a piston engine. The power comes from four separate actions taking place one after the other inside each engine cylinder. SUCK – the piston is pulled down, and air and fuel is sucked in through the inlet valve at the top of the cylinder. SQUEEZE – the inlet valve closes, the piston is pushed up and the air inside the cylinder is squeezed (the technical word for this is ‘compressed’). BANG – the fuel is set alight with a spark. This causes an explosion inside the cylinder (this is called ‘combustion’). The piston is pushed down strongly. This provides the power to turn a crankshaft. The crankshaft then turns the aeroplane’s propeller. BLOW – the exhaust valve opens at the top of the cylinder and hot gas from the explosion is pushed out. The exhaust valve closes, the piston is pushed up and the sequence begins again.
PISTON SEQUENCE SUCK SQUEEZE BANG BLOW
This is a famous ‘Bristol’ piston engine built by the Bristol Aeroplane Company. It has nine cylinders. ‘BRISTOL’ JUPITER 1920s
PROPELLERS All piston engines need propellers to generate thrust. The BANG of the engine turns the propeller which then pulls or pushes the aeroplane through the air.
SOME AEROPLANES GET THRUST FROM A JET Like the piston engine, the jet engine SUCKS, SQUEEZES, BANGS and BLOWS. The difference is that these actions are taking place CONTINUOUSLY in different parts of the engine. If the engine can continuously produce energy it can be more powerful and efficient. SUCK – air is sucked into the engine by the rotating blades at the front of the engine. SQUEEZE – the air is driven through the engine by the compressor blades which squeeze the air into a tighter and tighter space. BANG – fuel is sprayed into the compressed air so it bursts into flames. BLOW – the hot gases of the flames produce energy to turn the turbine blades. The turbine produces the power to drive the compressor. The gases blow out the back of the engine, thrusting the aeroplane forward.
SUCK SQUEEZE BANG BLOW A JET ENGINE
The Olympus used in Concorde was a type of engine known as a TURBOJET. In a turbojet, the thrust only comes from the jet of hot gases blown out the exhaust. CONCORDE’S OLYMPUS ENGINE, 1970s
This cutaway picture is of the RB.211. The engine is assembled at Rolls-Royce in Derby but some of the parts needed for it are made at Rolls-Royce at Filton. This is a type of engine known as a TURBOFAN. In a turbofan, the thrust comes from the jet of hot gas blown out the exhaust and also from the cold air that the huge fan at the front pushes around the sides of the core engine. An extra turbine is needed to drive the fan. All modern airliners are powered by turbofans which can be quieter and cheaper to run than turbojets. TURBOFAN, 1980s
CONTROLS Imagine three lines running through the aeroplane. Another word for line is axis. The LONGITUDINAL axis runs from the nose to the tail. The VERTICAL axis runs from top to bottom. The LATERAL axis runs from one side to the other. The lines cross at the aeroplane’s centre of gravity. When the aeroplane is flying forward, it can rotate around the centre of gravity on each axis. On most aeroplanes, the pilot can control the movement using three moveable flaps: the AILERONS, the RUDDER and the ELEVATORS. When these move, they change the flow of the air around the aeroplane. By changing the flow of air, the direction in which the aeroplane flies is also changed. Controlled movement is SAFE, STABLE and PREDICTABLE. That’s just what you want, when you are flying an aeroplane!
LATERAL LONGITUDINAL VERTICAL ‘BRISTOL’ BLENHEIM 1940s
AILERON BRISTOL M1D MONOPLANE 1920s
RUDDER BRISTOL BABE 1919
ELEVATOR BRISTOL BULLDOG 1920s