Uncontrolled copy not subject to amendment 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 Thrust Weight Lift Drag

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? Drag is reduced to 5%. Only 1 “person” needed on “the team”. Airflow

REDUCTION IN FORM DRAG 50% % 85% Form Drag VERY TURBULENT WAKE

Drag This type of drag is “Form Drag”, ie the shape of the object. So do we need: OR? Reducing Drag, reduces the amount of Thrust required! This Shape?

Examples of Streamlining

Total surface area Viscosity of the air Thickness of the boundary layer Surface Friction Drag Surface friction drag is reduced by smooth surfaces Boundary layer

Reduced by adding fairings Interference Drag

JSF

Streamlined Shape 5lbs drag 1. Form Drag (The Shape) Flat Plate 100lbs drag Smooth - 4lbs drag 2. Surface Friction Drag (Smooth/Rough) Rough - 6lbs drag 3. Interference Drag 5lbs drag 11lbs drag Zero Lift Drag

Relatively High Pressure Low Pressure Lift Dependent Drag

Formation of Wingtip Vortices TIP VORTEX SPILLAGE

Effect of Speed on Wing Tip Vortex LOW SPEED LARGE VORTEX HIGH SPEED SMALL VORTEX

Effect of Aspect Ratio on Wing Tip Vortex LARGE VORTEX LOW ASPECT RATIO CHORD HIGH ASPECT RATIO SMALL VORTEX CHORD

Vortex Drag

Drag Drag has several components as the following “Tree” will illustrate: Surface Friction Drag Interference Drag Form Drag Vortex Drag Zero Lift Drag Lift Dependent Drag Total Drag Increments of Zero Lift Drag

Drag Drag can be represented by the following graph: V IMD TOTAL DRAG ZERO LIFT DRAG LIFT DEPENDENT DRAG DRAG IAS

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 Thrust Weight Lift Drag

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