Uncontrolled copy not subject to amendment Principles of Flight
Principles of Flight Learning Outcome 1: Know the principles of lift, weight, thrust and drag and how a balance of forces affects an aeroplane in flight Part 2
Principles of Flight Revision
Questions Newton s 3 rd Law States: a. Every object has weight. b. Weight equals lift during flight. c. Every action has an equal and opposite reaction. d. Every force causes an object to move.
Questions In which direction does LIFT operate relative to airflow? a. Parallel to it. b. Perpendicular (at 90 o ) to it. c. Straight up. d. Straight down.
Questions What has happened to the air pressure at point B? A B C a. It is greater than at point A. b. It is greater than at point C. c. It is the same as point C. d. It is lower than at point A.
Drag and Thrust Objectives: 1. Explain Drag and Thrust. 2. Describe the effect that Streamlining has on Drag. 3. State the effect that Airspeed has on Drag. 4. Describe the relationship between Drag and Thrust when an aircraft is: a. At Constant Speed. b. Accelerating. c. Decelerating.
Drag and Thrust Lift Drag Thrust Weight
Thrust How do we produce Thrust? Propellers Jet Engines
Thrust Remember Newton s 3 rd Law? The engine achieves this by pushing the air backwards from either through a propeller or from the rear of a jet engine. The amount of Thrust depends on engine size, etc.
Drag What is Drag? Remember riding a bicycle into a wind or riding faster? PHEW!!
Variation of Drag with Airspeed The amount of Drag varies with the square of the Airspeed. So, Double the Airspeed, then Drag is Four times as much! Triple the Airspeed, then Drag is Nine times as much! Drag Airspeed
Drag Drag is the force which hinders your progress. The faster you go the more drag you feel. We need Thrust to overcome the Drag. Consider: Airflow Maximum Drag. 20 people needed on the team.
Drag What happens we pull a ball of the same diameter as the plate? Airflow Drag is reduced by 50%. Now only 10 people needed on the team.
Drag What happens we streamline a shape of the same diameter? Airflow Drag is reduced to 5%. Only 1 person needed on the team.
Form Drag VERY TURBULENT WAKE REDUCTION IN FORM DRAG 50% 85% 90-95%
Drag This type of drag is Form Drag, ie the shape of the object. So do we need: This Shape? OR? This Shape? Reducing Drag, reduces the amount of Thrust required!
Examples of Streamlining
Surface Friction Drag Boundary layer Total surface area Viscosity of the air Thickness of the boundary layer Surface friction drag is reduced by smooth surfaces
Interference Drag Reduced by adding fairings
JSF
Zero Lift Drag 1. Form Drag (The Shape) Streamlined Shape 5lbs drag Flat Plate 100lbs drag 2. Surface Friction Drag (Smooth/Rough) Smooth - 4lbs drag 3. Interference Drag Rough - 6lbs drag 11lbs drag 5lbs drag
Lift Dependent Drag Low Pressure Low Pressure Relatively High Pressure
Formation of Wingtip Vortices TIP VORTEX SPILLAGE
Effect of Speed on Wing Tip Vortex LOW SPEED HIGH SPEED LARGE VORTEX SMALL VORTEX
Effect of Aspect Ratio on Wing Tip Vortex HIGH ASPECT RATIO CHORD LOW ASPECT RATIO CHORD SMALL VORTEX LARGE VORTEX
Vortex Drag
Drag Drag has several components as the following Tree will illustrate: Surface Friction Drag Form Drag Interference Drag Vortex Drag Zero Lift Drag Total Drag Lift Dependent Drag Increments of Zero Lift Drag
Drag Drag can be represented by the following graph: DRAG TOTAL DRAG ZERO LIFT DRAG LIFT DEPENDENT DRAG IAS V IMD
Thrust and Drag in Straight & Level Flight Aircraft Accelerating: What is the difference between Thrust and Drag? Thrust is Greater than Drag
Thrust and Drag in Straight & Level Flight Aircraft Decelerating: What is the difference between Thrust and Drag? Drag is Greater than Thrust
Thrust and Drag in Straight & Level Flight Aircraft Constant Speed: What is the difference between Thrust and Drag? Thrust = Drag
Straight & Level Flight For Straight & Level Flight at Constant Speed ALL Forces are in Balance Lift Drag Thrust Weight
ANY QUESTIONS?
Drag and Thrust Objectives: 1. Explain Drag and Thrust. 2. Describe the effect that Streamlining has on Drag. 3. State the effect that Airspeed has on Drag. 4. Describe the relationship between Drag and Thrust when an aircraft is: a. At Constant Speed. b. Accelerating. c. Decelerating.
Questions What is the force called that drives an aircraft forwards? Lift Weight Drag Thrust
Questions What is the force called that resists the forward motion of an aircraft? Lift Weight Drag Thrust
Questions If you speed is doubled, by how much would the Drag be increased? x2 x4 x6 x8
Questions If Thrust = Drag and Lift = Weight then the aircraft is: Climbing Flying Straight & Level and Accelerating Flying Straight & Level and Decelerating Flying Straight & Level at Constant Speed