Basics of Flight

Brainstorming and Barnstorming:
Basics of Flight
Flight History
“ First
flight: The Wright Flyer 1903
“ Break Speed of Sound: Bell X-1A 1947
“ Land on Moon: Apollo 11 1969
“ Circumnavigate Earth on one tank of
gas: Global Flyer 2005
“ We’ve come a long way
Major Topics
“Terminology
and Theory
“Forces of Flight
“Aircraft Design
Basic Aircraft Terminology
“ Airfoil:
Cross sectional shape of a wing
“ Leading Edge: Front edge of wing
“ Trailing Edge: Back edge of wing
“ Chord Line: Line connecting LE to TE
“ Camber: Center line between top and
bottom of wing
“ High
camber found on slow flying high lift
aircraft
Wing Layout
“ Planform:
Vertical projection of wing
area
“ Elliptical:
good for high speed
“ Straight: root stalls, but cheap to make
“ Tapered: good stall characteristics
“ Delta: used for supersonic flight
Wing Layout
“ Sweep:
Angle between the lateral axis
and the wing (high speed aircraft)
“ Taper: Chord decreases as you move to
the wing tip
“ Incidence: Angle between the
longitudinal axis and the wing chord
“ Angle of Attack: Angle between the
wing and the relative wind
Wing Layout
“
“
“
Twist: Bending of wing
about lateral axis (helps
prevent tip stall by
changing angle of
attack)
Anhedral: Downward
bend in wing (helps with
stability)
Dihedral: Upward bend
in wing
Corsair: WWII Fighter
Wing Layout
Aspect ratio
“ (AR)= Span^2/Wing
Area
“ More efficient for
slow aircraft
“ Typical Values
“
“
“
“
U2 spy plane: High AR
Glider: 20-30
Trainer: 7-9
Loadstar: 18.5
SR-71: Low AR
6 degrees of freedom
“ Three
axes of an aircraft
“ Longitudinal:
Parallel to the fuselage
“ Lateral: Parallel to the wing
“ Normal: Perpendicular to the ground
Control Surfaces: Change Wing
by altering the Angle of Attack
“ Ailerons:
horizontal surfaces located on
wing tips
“ Roll:
rotation about the longitudinal axis
“ Elevator:
horizontal surface located on
the tail
“ Pitch:
rotation about the lateral axis
“ Rudder:
vertical surface located on the
tail
“ Yaw:
rotation about the normal axis
Stabilizing Surfaces:
Balancing Moments
“ Vertical
Stabilizer: The vertical part of
the tail which prevents unwanted yaw
“ Horizontal Stabilizer: Horizontal portion
of the tail (or the Canard) that prevents
unwanted pitch
Flaps
Change the shape
of wing
“ Increase Lift and
Drag
“ Used on takeoff and
landing
“
“ Neutral
Point: Location of resultant lift
force
“ CG: Center of gravity
“ High Wing: Wing on top (very stable)
“ Mid Wing: Wing in middle (acrobatic)
“ Low Wing: Wing on bottom ( less drag)
Reynolds Number
“
Reynolds Number (Re): ratio of inertial
forces to viscous forces
“
“
“
“
“
Re = (D*V*p)/mu
D=characteristic length
V=velocity
p=density
Mu= dynamic (absolute) viscosity
A non-dimensionalized number that can be
used to relate models to actual aircraft
“ Determines whether a flow is laminar or
turbulent in the Boundary Layer (laminar is
good)
“ Very useful for aircraft design
“
Reynolds Number
S1223 at various Reynolds numbers
2.4
Re=61000
2
Re=101600
Re=122600
1.6
Re=147400
Re=171400
0.8
Re=198100
Cl
1.2
Re=251900
0.4
Re=302200
Re=149500
0
Re=198900
-0.4
-10
-5
0
5
10
15
20
25
Angle of Attack (degrees)
Note the difference in stall characteristics for different Re
Boundary Layer
No slip condition at
surface (V=0)
“ Effectively alters the
shape of the airfoil
“ Separation of the
B.L. results in a stall
“ Lead to major
advances in aircraft
design
“
Boundary Layer
Forces of Flight
Lift
“ Drag
“ Thrust
“ Weight
“
For steady, level flight these four
forces and the moments they generate
must be in equilibrium. An airplane is a
force and moment balancing machine.
Lift
“ Controlled
by
“ Airspeed,
angle of attack, altering airfoil,
and altering the planform area
“ Lift
= ½ * p * V^2 * A *Cl
“ P=density,
V=velocity, A = wing area
Cl=coefficient of lift
“ How
is lift actually generated???
Lift: Equal Transit Time (Wrong)
Air splitting at LE must meet at TE
“ Air on top has a longer path; must travel
faster
“ Example: Boeing 747
“
“
“
“
“
“
Weight: 775,000 lbs
Airspeed: 550 mph or 810 ft/sec
Distance across top: 1.059*bottom
Density: 1/39 lb/ft^3
Wing Area: 5,500 ft^2
Boeing 747 Example
“
Pressure difference:
“
“
Punder-Pover=1/2*p*(Vbottom^2-Vtop^2)
Punder-Pover=18.75 lbs/ft^2
Lift=P*A=(18.75 lbs/ft^2) * (5500 ft^2)
“ Lift=103,000 lbs
“ Weight=775,000 lbs…………Ooops!!!
“ This theory says that air accelerates thereby
causing a pressure gradient.
“ This is completely wrong. A pressure gradient
will cause a fluid to accelerates.
“
Einstein and Lift
“ Einstein
hired by the German Air Force
“ He designed a wing based on the
previously described theory
“ It failed miserably
“ He was still relatively successful
Lift is complicated!!!!!!!!
Newton Vs Bernoulli
“ Newton: deflection of air
Bernoulli: Pressure
gradient
“ Coanda effect
“ Circulation
“ 3-D fluid flow is hard
Pressure Gradient
Newton and Bernoulli
A wing forces air down
“ Thus air forces a wing
up
“ A change in the
momentum of the fluid
results in a force
“ Air in motion creates a
pressure difference
around the wing
“
Air being forced down
Coanda Effect
Tendency of a fluid
in motion to stick to
an object
“ Due to skin friction
between fluid and
surface
“ The top of the wing
also directs air down
“ Experiment with a
rolled up paper.
“
3-D effects of lift
“ Spanwise
flow
“ High pressure on
bottom
“ Low pressure on
top
“ Air from bottom
tries to move to
top
Wing Tip Vortex
Return to the lift equation
“ Lift
= ½ * p * V^2 * A * Cl
“ Lift can be explained by the pressure
gradient as indicated by the equation
“ The gradient cannot solely be explained
by air moving faster over the top of the
wing
“ What about this Cl factor????
Coefficient of Lift
“
“
“
“
“
“
Magic number of lift;
determined
experimentally
Constant for any size
wing with same airfoil
Accounts for unknowns
Varies with angle of
attack
There is an angle where
the wing produces zero
lift
Explains how a wing
can fly upside down
Loss of Lift: Stall
“ Every
wing has a stall angle
“ Stall angle is the angle of attack at
which the wing loses lift
“ Stall angle range from 12-20 degrees
“ What actually causes a stall???
Stall at high AoA
Boundary layer
separates from the
surface (inertial vs
viscous effects)
“ Effectively changes
wing shape
“ Turbulence results
that causes more
drag and less lift
“
Drag:
“ Form
Drag: shape of object
“ Skin Friction Drag: surface of object
“ Induced Drag: component of lift
“ Parasitic Drag = Form Drag + Skin Drag
“ Total Drag = Induced Drag + Parasitic Drag
“ Total
“ Cd
Drag = ½ * p * V^2 * A * Cd
is the key and is determined
experimentally just like Cl.
Form and Skin Friction Drag
Form Drag
“ Greatly affects slow flying planes
“ Depends upon the frontal area
“ Depends upon how streamlined
“ What does it mean to be streamlined??
“ Examples
of things that are streamlined
Skin Friction
“ Depends upon the surface roughness
Form Drag
“ How
do we know if an object is
streamlined?
“ Nature,
wind tunnel testing, conformal
mapping
If these shapes are so
aerodynamic, why aren’t race
cars shaped this way????
Induced Drag
“
Equal to horizontal
component of lift
“
Therefore increases with AoA
Actually caused by the wing
tip vortex discussed earlier
“ Reduced with use of a high
AR wing
“ Can be reduced with the
use winglets
“
Tradeoff: Skin Friction vs Form
“ Turbulators:
prevent the B.L. from
separating
“ Increases skin friction
“ Decreases form drag
“ For slow aircraft; tradeoff is beneficial
“ Found on sea animals, new swim suits,
and golf balls
Turbulator Examples
Aircraft Stability
“ Static
Stability: When disturbed, the
aircraft returns to original flight path
“ Longitudinal,
“ Dynamic
Lateral, Roll
Stability: Returns to original
flight path without excessive oscillation
Longitudinal Stability
“ Longitudinal
Stability: Locate the
Neutral Point behind CG
“ Creates a correcting moment
“ To move the Neutral Point backwards,
increase the horizontal tail area
Lateral Stability
“ Largely
depends upon tail size
“ CLA: Center of lateral area
“ Size tail to locate the CLA 25-28% of tail
length behind the CG
“ Prevents Spiral Instability
“ Side
gust rotates plane
“ One wing speeds up
“ Creates more lift
Directional Stability
“ Also
depends upon tail size and CLA
“ A high wing adds stability
“ The
plain acts like a pendulum
“ Naturally returns to stable position
Aircraft Control
“ Longitudinal,
Lateral, and Directional
“ Control surfaces generate forces
“ These forces create moments that
rotate the plane
“ Proper location and sizing results in
excellent control
“ Stall must always be considered
“ Ailerons
are located at the wing tips
KSU Aero Design Team 2005
Ft. Worth, Texas
3rd Place