Transcript Aerodynamic Principles I - University of Notre Dame

Aerodynamics
Getting to the Point
Orville Wright
Wilbur Wright
Written for the Notre Dame Pilot Initiative
By the Pilots of the University of Notre Dame
“Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”
Four Forces of Flight
 Lift opposes Weight
 Thrust opposes Drag
 In straight, unaccelerated
flight, L = W & T = D
 Lift created by pressure
differential around wing. High
pressure on lower surface
and low pressure on the
upper surface – low pressure
caused by increased airflow
velocity over top of airfoil.
 Weight – downward force of
gravity
 Drag – rearward retarding force
 Thrust – forward force
propelling airplane through air
Airfoils
What is NACA?
 National Advisory
Committee for
Aeronautics
 Chartered in
1915, operational
from 1917-1958
 The National
Aeronautics and
Space Act of 1958
created NASA
from NACA
Aerodynamic Surfaces
Aerodynamic Surfaces
Prop
Jet
B727 Spoilers
Airfoils - Nomenclature
Low p
High p
 Chord line - straight line connecting the leading and trailing edges of an
airfoil
 Camber line – locus of all points equidistant from top and bottom of airfoil
 Camber – distance between chord line and camber line
 Thickness – maximum distance between top and bottom surfaces of wing
 Leading Edge
 Trailing Edge
 Wingspan (b)
 Aspect Ratio (AR = b2/S)
Frost
If wing is below
dewpoint which is
below freezing, frost
will form
Sublimation of air to
solid ice crystals
Disrupts smooth
airflow over the wing
Why is this bad?
 Decreases lift
 Increases drag
Frost removed
before take-off
Rime Ice
Clear Ice
Angle of Attack
Angle between wing chord line and relative
wind
The angle of attack at which airplane stalls
does not change
Published NACA Data – NACA 2415
Airfoils - Nomenclature
Flaps
Plain Flap
 Flaps increase lift and decrease stall speed
 Flaps allow steep rate of descent for approaches
without increasing airspeed
Split Flap
Fowler Flap
-Fowler Flap effectively increases
the wing area by rolling backwards
on a roller system.
Slotted Flap
-Slotted Flap allows high pressure
air underneath wing to join airflow
above wing. This effectively
increases velocity of top airflow
and thus increases lift.
Laminar v. Turbulent
Laminar flow about a sphere
Laminar v. Turbulent
Turbulent flow about a sphere
Bernoulli’s Principle - Lift
Low Pressure
High Pressure
A1V1=A2V2
 “As the velocity of a fluid
increases, its internal pressure
decreases.”
 From Newton’s 2nd (F=ma)
 Shown by Venturi tube
Bernoulli’s Principle Again
Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B
Bernoulli’s Principle Again
Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B
Bernoulli’s Principle Again
Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B
Lift Vector
Courtesy of FAA: Pilot’s Handbook of Aeronautical Knowledge, AC 61-23B
Drag Types
Induced drag is the unavoidable by-product of lift
and increases as the angle of attack increases
Parasite drag is caused by any aircraft surface
that deflects or interferes with smooth airflow
around airplane
Skin-friction drag - between the outer surfaces
of the aircraft and the air through which it
moves. Reduced by using glossy, flat finishes on
surfaces
Form drag - resistance of air to the shape of the
aircraft. Form drag can be reduced by
streamlining the aircraft shape.
Drag – Body Comparison
sphere
cylinder
airfoil
Wingtip Vortices – “Twin Tornadoes”
A few words on wingtip vortices:
‘High pressure on the lower surface creates a natural
airflow that makes its way to the wingtip and curls upward
around it to the area of low pressure. When flow around
the wingtips streams out behind the airplane, a vortex is
formed. These twisters represent an energy loss and are
strong enough to flip airplanes that blunder into them.’
Wingtip Vortices
Why Winglets?
Equivalent to span extension w/o increased wingspan
Reduces wingtip vortices
Reduces drag
NASA B-727 Wingtip Vortex Test Flight
Learn more about winglets:
http://www.airspacemag.com/ASM/Mag/Index/2001/AS/htww.html
Drag – Ground Effect
TIP:
On a soft-field
runway, you can
takeoff at a lower
speed and then
accelerate while in
“Ground Effect.”
Drag vs Angle of Attack
Relationship between drag and angle of attack
Torque / P-factor (Left-Turning Tendencies)
 Newton’s 3rd law: “For
every action there is an
equal and opposite
reaction.”
 Propeller rotates CW
when viewed from pilot’s
seat.
 Torque reaction rotates
the airplane CCW about
longitudinal axis
 P-factor (asymmetrical
thrust) caused by
descending blade
taking a greater “bite” of
air than ascending
blade at high angle of
attack
Stability & Control
 Inherently stable airplane
returns to its original condition
after being disturbed. Requires
less effort to control
 Center of Gravity concerns:
 Unable to compensate with
elevator in pitch axis
 Weight and Balance becomes
critical – taught in a coming
lecture
Stability & Control
pitch
 The 3 axes of motion:
roll, pitch, yaw
roll
yaw
Tail Placements
Looks like the A-10
Also called “H-Tail”
Canards
Stabilizer located in
front of the main wings
Used on the Wright
Flyer
More aerodynamically
efficient than an
elevator b/c canards
provide positive lift
Accident Report – Loss of Elevator
AIRCRAFT FINAL REPORT
THE AIRCRAFT HAD JUST BEEN REPAIRED AFTER RECEIVING TORNADO
DAMAGE. THIS REPAIR INCLUDED REMOVAL AND REPLACEMENT OF THE
ELEVATOR CONTROL TUBE. THE PILOT TAXIED TO THE RUNWAY FOR THE
PURPOSE OF A TEST FLIGHT. ALL FLIGHT CONTROL CHECKS APPEARED
NORMAL. AFTER LIFT-OFF, THE PILOT INTENDED TO LEVEL OFF AT 5 TO 10
FEET, THEN TOUCH DOWN AGAIN. HOWEVER, AFTER THE AIRPLANE
BECAME AIRBORNE, HE LOST ELEVATOR CONTROL, AND THE AIRCRAFT
CLIMBED STEEPLY TO 50 TO 75 FEET. THE PILOT THEN REDUCED POWER,
THE AIRCRAFT'S NOSE DROPPED, AND THE AIRCRAFT DESCENDED. WITH
NO ELEVATOR CONTROL, THE PILOT WAS UNABLE TO ARREST THE
DESCENT, AND THE AIRCRAFT IMPACTED THE GROUND. A POST-CRASH
EXAMINATION REVEALED THAT A BOLT AND NUT WERE MISSING FROM THE
ELEVATOR CONTROL LINKAGE, WHICH ALLOWED THE LINKAGE TO BECOME
DISCONNECTED.
AIRCRAFT 1 CAUSE REPORT
FAILURE OF MAINTENANCE PERSONNEL TO PROPERLY REINSTALL A BOLT
AND NUT IN THE ELEVATOR CONTROL LINKAGE, WHICH RESULTED IN A
DISCONNECT OF THE LINKAGE AND LOSS OF ELEVATOR CONTROL.