Principles of Flight Leading Cadet Training Thrust and

Principles of Flight Leading Cadet Training Thrust and Drag Lecture 2

Thrust To produce lift a wing needs airflow over the top. This airflow is increased by “pushing” the air back and “thrusting” the aircraft forwards The engine pushes air backwards by either: A propeller - which ‘screws’ the air backwards … or A jet engine – expelling air backwards In both cases throwing the air backwards, thrusts the aircraft forward.

Drag Anyone on a bicycle knows the faster you go, the more air resistance you encounter. The force which hinders your progress is called ‘DRAG’.

Drag Every part of the aircraft over which air flows produces drag. This drag directly opposes thrust. The more drag there is, the more thrust is needed to overcome it. THRUST DRAG

Thrust and Drag An Aircraft in Balance In straight and level flight, at constant speed, two pairs of forces act on the aircraft. The thrust opposes the drag and is equal to it, and the lift equally opposes the weight. LIFT THRUST DRAG WEIGHT

Thrust and Drag If, in un-accelerated straight and level flight; Thrust = Drag the aircraft will maintain speed. If thrust is greater than drag; Thrust > Drag the aircraft will speed up. If drag is greater than thrust; Drag > Thrust the aircraft will slow down. THRUST DRAG

What Causes Drag is formed by the shape of an object. When holding a flat plate in an airflow: Drag will be greatest when the plate is at 90° Drag will be least when parallel to the airflow.

What Causes Drag is formed by the shape of an object. When an object passes through the air it is accompanied by a wake. Wake is the turbulent airflow immediately behind the aircraft. Wake produces drag – the bigger the wake, the bigger the drag.

Types of Drag Surface Friction Drag Is caused by the ‘rough’ skin of an object. Interference Drag Two surfaces meeting at an angle, causes airflow drag. This is minimized by fairing and filleting to induce smooth mixing of air past the affected surfaces.

Types of Drag Lift Dependent Drag Is drag caused by the lift associated with the change in the angle of attack. Most of the drag caused at take-off is lift-dependent. Low Pressure Relatively High Pressure Wingtip Vortices Are tubes of circulating air behind a wing as it generates lift. VORTEX A wingtip vortex trails from the tip of each wing.

Drag and Airspeed Drag can be minimised by not building in drag at the design stage. By eliminating as many protruding edges as possible, and…. and by ‘streamlining’ the design.

Drag and Airspeed The amount of drag varies with the square of the airspeed Twice the airspeed = 4 times the drag. 3 times the airspeed = 9 times the drag. AIRSPEED DRAG

Check of Understanding Which part(s) of an aircraft produce drag? Only those parts producing lift The fuselage but not the wings Every part that air flows over Only those parts producing thrust

Check of Understanding Drag directly opposes what? Pressure Weight Lift Thrust

Check of Understanding To slow an aircraft from straight and level flight. . . Drag must be half thrust Thrust must exceed drag Drag must exceed thrust Thrust must equal drag

Check of Understanding What is one way of increasing lift? Reduce Speed Reduce Weight Increase Drag Increase Weight

Check of Understanding Which of these statements, about an aircraft in steady straight and level flight, is true? Thrust is equal to four times the drag Thrust is equal to twice the drag Thrust is equal to half the drag Thrust is equal to the drag

Check of Understanding To fly, an aircraft must generate lift to oppose its? Inertia Weight Thrust Drag

Check of Understanding The reaction to the rearward movement of air produced by the propeller or jet is called? Thrust Wake Drag Friction

Check of Understanding How can drag best be minimised? By increasing the airspeed By streamlining the design By reducing the weight By decreasing the airspeed

Check of Understanding What is the force called that drives an aircraft forwards? Drag Weight Thrust Lift

Check of Understanding In steady straight and level flight at constant height and speed, the amount of lift produced by the aircraft must be: Equal to the aircraft's weight Greater than the aircraft's drag Equal to the aircraft's thrust Greater than the aircraft's weight

Principles of Flight Leading Cadet Training End of Presentation