Lift Flashcards
How is lift created
Two principles:
●Bernoulli
●Newton
What is lift
Gravity acts on all bodies on or near the surface of the earth
●Resultant force on some masses is called weight
In order to rise, an opposite force must be created
●Lift
The physics of lift
Venturi Tube
Static Pressure + Dynamic Pressure = Constant
How air foils create lift
Airfoil speeds up air flowing over it proportional to the amount of area obstructed by the upper and lower portions of the airfoil.
Result – Pressure Differential
Static pressure on airfoils
–More Negative Static Pressure on Top
–Less Negative Static Pressure on Bottom
Newton’s third law
For every reaction there is an equal and opposite reaction
Downwash creates lift also
Lift on cambered airfoils
At 0° AOA will produce some lift
Lift on symmetrical airfoils
At 0° AOA will produce no lift – equal cross section on the top and bottom
Requires greater AOA to get the same amount of lift
Can produce equal amounts of lift in either direction
Center of pressure
Center of pressure does move with changes AOA, but most just talk about the aerodynamic center.
Pressure distribution
●Airfoil Shape
●Angle of Attack
Coefficient of lift
●Non-Dimensional
●Effectiveness of an Airfoil to Produce Lift
●Found Experimentally
Lift equation
Air Density (r)
●Temperature
●Pressure
Velocity (V)
●True Airspeed
●Dynamic Pressure Is Equal to Indicated Airspeed
Coefficient of Lift (CL)
●Angle of Attack
●Airfoil Shape
Factors that determine airfoil lift
●Maximum Camber
●Location of Maximum Camber
●Maximum Thickness
●Location of Maximum Thickness
Flat plate with nose bent down slightly
●Able to achieve a much higher AOA before stalling
●Still only efficient for a small range of AOA
●Led to the modern day airfoil (typical airfoil)
National Advisory Committee for Aeronautics (NACA)
●First was four-digit series
Ex. NACA 2412
●2=maximum camber (percent/hundrenths)
●4=location of maximum camber (in tenths)
●12=maximum thickness in percent of chord
Led to families of airfoils
●Ex NACA 2420 (7% thicker)
Richard Whitcomb, NASA Engineer
●Devised a supercritical airfoil
●Intended to improve drag speeds near Mach 1
●Also applied to General Aviation
GA(W) Airfoils
Wing anatomy
Profile shape
●Need a third dimension
Wingspan
●Length of the wing, or span
Planform
●Shape of wing as viewed from above or below
Wingtip vortex
●Use the basic high to low principle
●At the tip of the wing there is no more wing to block flow, but a pressure differential still exists
Creates Wake Turbulence
Strength is proportional to weight
●More weight requires more lift
●More lift requires a greater pressure differential
The pressure differential is what creates the vortices
Downwash
●Greatest near the wingtips, but is experienced across the entire wing
●Lift is created perpendicular
Air stream tilted downward by downwash, the lift vector is then tilted somewhat aft
Not all lift is acting perpendicular
●Must hold a little more angle of attack
●Induced AOA
Downwash effect
No downwash would result if we had no tip vortices
●Would require a wing of infinite span
Longer span reduces AOA required for a certain amount of lift – wing is more efficient
●Think of a gliders wing
Aspect ratio
Span divided by average chord
So we can deal with wingspan and wing area separately
Typical lift spanwise
Lift spanwise is dependant on two things
●Chord
●Downwash
Shape determines lift = planform determines how lift will be distributed
Stall progression patterns
Of considerable significance
●Desirable vs. Undesirable
Aileron control is usually the issue
Very critical close to the ground
Best for stall pattern – the “Hershey Bar Wing”
