Lift

Question 1

How is lift created

Answer 1

Two principles:
●Bernoulli
●Newton

Question 2

What is lift

Answer 2

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

Question 3

The physics of lift

Answer 3

Venturi Tube
Static Pressure + Dynamic Pressure = Constant

Question 4

How air foils create lift

Answer 4

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

Question 5

Static pressure on airfoils

Answer 5

–More Negative Static Pressure on Top
–Less Negative Static Pressure on Bottom

Question 6

Newton’s third law

Answer 6

For every reaction there is an equal and opposite reaction
Downwash creates lift also

Question 7

Lift on cambered airfoils

Answer 7

At 0° AOA will produce some lift

Question 8

Lift on symmetrical airfoils

Answer 8

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

Question 9

Center of pressure

Answer 9

Center of pressure does move with changes AOA, but most just talk about the aerodynamic center.

Question 10

Pressure distribution

Answer 10

●Airfoil Shape
●Angle of Attack

Question 11

Coefficient of lift

Answer 11

●Non-Dimensional
●Effectiveness of an Airfoil to Produce Lift
●Found Experimentally

Question 12

Lift equation

Answer 12

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

Question 13

Factors that determine airfoil lift

Answer 13

●Maximum Camber
●Location of Maximum Camber
●Maximum Thickness
●Location of Maximum Thickness

Question 14

Flat plate with nose bent down slightly

Answer 14

●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)

Question 15

National Advisory Committee for Aeronautics (NACA)

Answer 15

●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)

Question 16

Richard Whitcomb, NASA Engineer

Answer 16

●Devised a supercritical airfoil
●Intended to improve drag speeds near Mach 1
●Also applied to General Aviation
GA(W) Airfoils

Question 17

Wing anatomy

Answer 17

Profile shape
●Need a third dimension
Wingspan
●Length of the wing, or span
Planform
●Shape of wing as viewed from above or below

Question 18

Wingtip vortex

Answer 18

●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

Question 19

Downwash effect

Answer 19

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

Question 20

Aspect ratio

Answer 20

Span divided by average chord
So we can deal with wingspan and wing area separately

Question 21

Typical lift spanwise

Answer 21

Lift spanwise is dependant on two things
●Chord
●Downwash
Shape determines lift = planform determines how lift will be distributed

Question 22

Stall progression patterns

Answer 22

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”