PRINCIPLES OF FLIGHT

PRINCIPLES OF FLIGHT Click on ‘Slide Show’ then ‘View Show’ to start.

PRINCIPLES OF FLIGHT Chapter 1 Lift and Weight Contents List. Chapter 2 Thrust and Drag Chapter 3 Stability and Control Chapter 4 Stalling Chapter 5 Gliding Chapter 6 Helicopters exit

Contents List. Click on a chapter. PRINCIPLES OF FLIGHT Chapter 1 Lift and Weight Chapter 2 Thrust and Drag Chapter 3 Stability and Control Chapter 4 Stalling Chapter 5 Gliding Chapter 6 Helicopters exit

PRINCIPLES OF FLIGHT Chapter 1 Lift and Weight Return to contents list exit

Lift and Weight How can an aircraft, which is so much heavier than air, be supported by that air? Sir Isaac Newton’s third law states: “To every action, there is an equal and opposite reaction.” A vehicle weighing 1 tonne is supported by the road pressing up with a force of 1 tonne. A boat weighing 10 tonnes is supported by a 10 tonne upward force from the water, otherwise it would sink.

Lift and Weight How can an aircraft, which is so much heavier than air, be supported by that air? Sir Isaac Newton’s third law states: “To every action, there is an equal and opposite reaction.” Aircraft can only remain airborne while they are actually moving – if they stop moving they cease flying. The upward force to support the aircraft is only there when the aircraft is moving forwards through the air.

Lift and Weight How can an aircraft, which is so much heavier than air, be supported by that air? Sir Isaac Newton’s third law states: “To every action, there is an equal and opposite reaction.” This upward force is generated by the aircraft’s wings as they pass through the air. We must understand how wings moving through the air create that upward force, known as ‘lift’.

Lift and Weight In this wind tunnel experiment the air is passing from ‘A’ to ‘C’ through a constriction at ‘B’. As the amount of air leaving at ‘C’ is the same as the amount entering at ‘A’, the air must speed up as it passes the narrowest point ‘B’.

Lift and Weight Another scientist, Bernoulli, discovered that in areas where airspeed increases, the air pressure decreases. In the wind tunnel experiment above, the air pressure measured at ‘B’ will be less than at ‘A’ and ‘C’.

Lift and Weight A simple experiment you can do to demonstrate this principle is illustrated in this picture. Blowing along the top of this sheet of paper causes it to lift into line with the airflow. By blowing and speeding up the air over the top, you have reduced the pressure above the paper, so the normal air pressure below the paper pushes it up.

Lift and Weight The top surface of a wing is shaped so that the air which flows between it and the undisturbed air a little way above the wing is effectively flowing through a constriction. undisturbed air The air flows over the wing at increased speed and therefore at reduced pressure.

Lift and Weight All parts of a wing generate lift, some parts more than others. lift forces oncoming air

Lift and Weight The top surface normally generates more lift than the bottom surface. lift forces oncoming air

Lift and Weight The top surface may generate up to 80% of the total lift. lift forces oncoming air

Lift and Weight The greatest amount of lift on the top surface occurs where the surface is curved the most. lift forces oncoming air

Lift and Weight All of the lift forces act at 90 degrees to the oncoming airflow. lift forces oncoming air

Lift and Weight Instead of looking at the thousands of lift forces generated by a wing, we add them together and represent them with a single line. lift forces oncoming air

Lift and Weight Instead of looking at the thousands of lift forces generated by a wing, we add them together and represent them with a single line. oncoming air

Lift and Weight The point at which all the lift can be said to act is the ‘centre of pressure’. oncoming air

Lift and Weight The point at which all the lift can be said to act is the ‘centre of pressure’. The idea is similar to finding the centre of gravity of a ruler by balancing it on your finger. All the small forces of gravity acting on the ruler balance about the centre of gravity.

Lift and Weight Several factors affect the amount of lift produced by a wing. Airspeed Unsurprisingly, increasing the airspeed increases the amount of lift produced by a wing. What might surprise you is that doubling the airspeed gives four times the lift. Trebling the airspeed gives nine times the lift!

Lift and Weight Several factors affect the amount of lift produced by a wing. Airspeed Angle of attack oncoming air The angle of attack is the angle between the chord line of the wing and the oncoming air (or path of the aircraft).

Lift and Weight Several factors affect the amount of lift produced by a wing. Airspeed Angle of attack oncoming air The chord line of a wing is a straight line joining the leading edge to the trailing edge.

Lift and Weight Several factors affect the amount of lift produced by a wing. Airspeed Angle of attack oncoming air If the angle of attack is increased the amount of lift is also increased - until the angle reaches about 15 degrees when the wing stalls.

Lift and Weight Several factors affect the amount of lift produced by a wing. Airspeed Angle of attack Air density If the air becomes thinner, or less dense (due to increases in altitude, temperature or humidity) the amount of lift is reduced.

Lift and Weight Several factors affect the amount of lift produced by a wing. Airspeed Angle of attack Air density Wing shape and area Designers choose a wing shape and area to suit the role of the aircraft.

Lift and Weight Several factors affect the amount of lift produced by a wing. Airspeed Angle of attack Air density Wing shape and area Wing ‘X’ is a general purpose wing section.

Lift and Weight Several factors affect the amount of lift produced by a wing. Airspeed Angle of attack Air density Wing shape and area Wing ‘Y’ is a high lift wing section.

Lift and Weight Several factors affect the amount of lift produced by a wing. Airspeed Angle of attack Air density Wing shape and area Sections ‘Z’ and ‘W’ are for high speed.

Lift and Weight If the lift force is greater than the aircraft’s weight, the aircraft will climb.

Lift and Weight If an aircraft suffers a sudden reduction in weight by jettisoning fuel or dropping cargo, it will climb (unless the pilot responds).

Lift and Weight If the lift force is less than the aircraft’s weight, the aircraft will descend.

Lift and Weight In steady straight and level flight the lift force exactly equals the force of gravity acting on the aircraft (its weight).

PRINCIPLES OF FLIGHT Chapter 2 Thrust and Drag Return to contents list exit

Thrust and Drag An aircraft is propelled forwards by its engine or engines. This force is called thrust.

Thrust and Drag An aircraft flying through the air encounters resistance from the air itself. This force is called drag.

Thrust and Drag Every part of the aircraft over which the air flows produces drag which resists forward motion.

Thrust and Drag If thrust exceeds drag the aircraft will accelerate.

Thrust and Drag If thrust exceeds drag the aircraft will accelerate. If drag exceeds thrust the aircraft will decelerate.

Thrust and Drag If thrust exceeds drag the aircraft will accelerate. If drag exceeds thrust the aircraft will decelerate. An aircraft in steady straight and level flight will have thrust exactly equal to the drag.

Thrust and Drag As an aircraft’s airspeed increases, then so does the drag. In the previous chapter we saw lift increase four times for double the airspeed and increase nine times for treble the airspeed. Doubling an aircraft’s airspeed will quadruple the drag. Trebling an aircraft’s airspeed will increase drag by a factor of nine.

PRINCIPLES OF FLIGHT Chapter 3 Stability and Control Return to contents list exit

Stability and Control centre of gravity There are three axes about which an aircraft rotates. All three go through the centre of gravity.

Stability and Control The lateral axis generally runs from wingtip to wingtip. Remember: L A T – Links Aerofoil Tips.

Stability and Control The lateral axis generally runs from wingtip to wingtip. The aircraft moves in the pitching plane about this axis.

Stability and Control The longitudinal axis runs from nose to tail. Remember: aLONG the length of the aircraft.

Stability and Control The longitudinal axis runs from nose to tail. The aircraft moves in the rolling plane about this axis.

PRINCIPLES OF FLIGHT