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Lecture

Principles of Flight. Leading Cadet Training. Drag. Lecture. 3. Drag. DRAG. THRUST. 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.

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Lecture

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  1. Principles of Flight Leading Cadet Training Drag Lecture 3

  2. Drag DRAG THRUST Every part of the aircraft over which air flows produces drag. Thisdragdirectly opposes thrust. The more dragthere is, the more thrustis needed to overcome it. Anyone on a bicycle knows the faster you go, the more air resistance you encounter. The force which hinders your progress is called ‘DRAG’.

  3. Drag What causes Drag ? Drag is formed by the shape of an object. When holding a flat plate in an airflow: Drag will be least whenparallelto the airflow. Drag will be greatestwhen the plate is at 90° The object is to reduce this Form Drag.

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

  5. Drag Other Types of Drag Surface Friction Drag Is caused by the ‘rough’ skin of an object. It is determined by the total surface area, the viscosity of the air, and the thickness of the boundary area. Surface friction drag depends upon the rate of change of velocity through the boundary layer. Which can amount to more than 30% of the total drag under cruise conditions.

  6. Drag Other Types of Drag Interference Drag The drag of one component, can affect the drag of another. When two surfaces meet at a sharp angle, airflow causes drag. This can be minimized by proper fairing and filleting, to induce smooth mixing of air past the affected surfaces.

  7. Drag Streamlined Shape 5lbs drag Smooth - 4lbs drag Zero Lift Drag Form Drag (The Shape) Flat Plate 100lbs drag Surface Friction Drag (Smooth/Rough) Rough - 6lbs drag Interference Drag (Components) 11lbs drag 5lbs drag

  8. Drag Low Pressure Low Pressure Lift Dependent Drag Is the 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 drag. Relatively High Pressure

  9. Drag TIP VORTEX SPILLAGE Wingtip Vortices Are tubes of circulating air left behind a wing as it generates lift. Wingtip vortex trails from the tip of each wing.

  10. Drag Wingtip Vortices The effects of Speed on Wingtip Vortices. LOW SPEED HIGH SPEED LARGE VORTEX SMALL VORTEX

  11. Drag Wingtip Vortices The effects of Aspect Ratio on Wingtip Vortices. HIGH ASPECT LOW ASPECT CHORD CHORD SMALL VORTEX LARGE VORTEX

  12. Drag Drag has several components as this ‘tree’ illustrates : Vortex Drag Surface Friction Drag Form Drag Interference Drag Lift Dependent Drag Zero Lift Drag Total Drag Increments of Zero Lift Drag

  13. Drag How can Drag be minimised ? Bynotbuilding in drag at the design stage. By eliminating as many protruding edges as possible…. By‘streamlining’the design.

  14. Drag How can Drag be minimised ? By designing the shape to have a fineness ratio of between 3:1and4:1 The fineness ratio is the ratio of the length of a body to its maximum width; "short and fat" shapes have low ratios, while "long and skinny" have high ratios.

  15. Drag  AIRSPEED DRAG  Drag and Airspeed The amount of dragvaries with the square of the airspeed - Twicethe airspeed =4 times the drag. 3 times the airspeed = 9 times the drag.

  16. Drag Drag and Thrust In un-accelerated straight and level flight: The aircraft will maintain speed. If thrust is greater than drag the aircraft will speed up. If drag is greater than thrust the aircraft will slow down. Thrust > Drag Thrust = Drag Drag > Thrust  THRUST DRAG 

  17. Summary LIFT THRUST DRAG WEIGHT An Aircraft in Balance In straight and level flight, at constant speed, two pairs of forces act on the aircraft. Thethrustopposes thedragand is equal to it, Theliftequally opposes the weight.

  18. 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

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

  20. Check of Understanding Airflow Which of these objects of equal width, will produce the least drag? A B C D

  21. 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

  22. Check of Understanding What type of drag is formed when two surfaces meet at a sharp angle? Wingtip Vortex Drag Surface Friction Drag Lift Dependant Drag Interference Drag

  23. Check of Understanding When an object passes through the air, what is it accompanied by? Wind Lift Thrust Wake

  24. Check of Understanding What type of drag is dependant upon the rate of change of velocity through the boundary layer? Interference Drag Lift Dependant Drag Surface Friction Drag Wing Vortex Drag

  25. Check of Understanding What is Lift Dependent Drag? Drag caused by the shape of the object Drag caused by the ‘rough’ skin of an object Drag caused by lift associated with the change in the angle of attack Drag caused by the wingtip vortex

  26. Check of Understanding A streamlined shape with an airspeed of 100 kts has a drag of 200 n. If the airspeed is increaded to 300 kts what will the drag be? 400 n 800 n 1800 n 3600 n

  27. Principles of Flight Leading Cadet Training End of Presentation

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