tutorial three principles of flight this
flight training tutorial will discuss
key principles of aerodynamics of flight
in order for a pilot to safely execute
maneuvers in flight it is important to
understand the aerodynamic forces acting
on an aircraft in flight although there
are various kinds of pressure
pilots are mainly concerned with
atmospheric pressure it is one of the
basic factors in weather changes helps
to lift an aircraft and actuate some of
the important flight instruments these
instruments are the altimeter airspeed
indicator vertical speed indicator and
manifold pressure gage air is very light
but is still affected by gravity and
acts like a fluid by exerting force in
all directions called pressure
at sea-level the average pressure
exerted by the weight of the air is
fourteen point seven pounds per square
inch and is measured as 29.92 inches of
mercury or one zero one 3.2 millibars
this is the standard pressure if the
pressure is anything different than
standard pressure it is called
non-standard pressure the standard
atmosphere at sea level is a surface
temperature of 59 degrees Fahrenheit or
15 degrees Celsius and a surface
pressure of 29.92 inches of mercury or
1:01 3.2 millibars
a standard temperature lapse rate is one
in which the temperature decreases at
the rate of approximately 3.5 degrees
Fahrenheit or 2 degrees Celsius per
thousand feet up to 36,000 feet standard
pressure lapse rate is one in which
pressure decreases at the rate of
approximately one inch of mercury per
1000 feet of altitude gain to 10,000
feet standard atmosphere is used to
calibrate aircraft instruments therefore
when the pressure changes to a
non-standard pressure the aircraft's
instruments must also be recalibrated
within the aircraft by setting the
outside pressure value or by correcting
until the altimeter reads the airport's
elevation
to read pressure altitude set the
altimeter to 29 92 and what is read is
the pressure altitude density altitude
is simply pressure altitude corrected
for non-standard temperature the
aircraft's performance is affected by
the density of the air so this value
lets pilots take steps to account for
the difference in engine and aircraft
performance the air density can be
affected by pressure temperature and
humidity the higher the pressure the
more dense the air is the lower the
pressure the less dense the area's high
temperatures cause air to be less dense
and cold air is more dense and high
humidity causes less dense air than low
humidity
there are three basic theories that
allow us to explain how airplanes fly
the first being Newton's laws of motion
Sir Isaac Newton developed three basic
laws of motion that describe how objects
interact with each other the first law
states that objects at rest tend to stay
at rest until acted on by another object
so an airplane sitting on the ground
needs some force propeller jet engine
etc to get it moving the second law
states that force equals mass times
acceleration this allows us to see how
much airplanes accelerate from the force
of an engine or how fast they can stop
and the last law of motion states that
for every action there is an equal and
opposite reaction on an airplane if the
propeller is pushing air back the air is
acting opposite and pushing the plane
forward also the wing pushes air down
which causes the air to push the wing up
the second theory that helps explain
lift is the Magnus effect this theory
was created by Heinrich Gustav Magnus
and helps show how the wing functions
when a cylinder rotates in a fluid it
creates a movement of the fluid because
air molecules actually adhere stick or
cling to the surface when the cylinder
is rotating through a moving liquid part
of the liquid is moving fast over the
top and on the bottom the liquid is
slowed down because of friction with the
cylinder surface as shown above at Point
a a stagnation point exists where the
airstream impacts on the front of the
airfoil surface and splits some air goes
over and some under another stagnation
point exists at B where the two air
streams rejoin and resume at identical
velocities when viewed from the side and
up wash is created ahead of the airfoil
and down wash at the rear Magnus's
research shows the basic principle that
a wing causes air to move faster over
the top and slower over the bottom of
the wing causing a higher pressure at
the bottom of the wing and lower
pressure on the top of the wing this
low-pressure area produces an upward
force known as the Magnus effect
the last theory of lift is Bernoulli's
principle Daniel Bernoulli explained
that the faster of fluid moves the less
pressure the fluid has as with the
Magnus effect faster moving air flowing
over the top of the wing causes a
low-pressure area causing lift
an airfoil is a structure designed to
obtain reaction upon its surface from
the air through which it moves by
looking at a typical airfoil profile
such as the cross-section of a wing one
can see several obvious characteristics
of design the end which faces forward in
flight is called the leading edge and is
rounded the other end the trailing edge
is quite narrow and tapered the cord
line is a line drawn from the very front
of the leading edge to the trailing edge
of the wing the cord line cuts the wing
in two parts an upper and lower half of
the wing each half of the wing has what
is called a camber this is the general
curve shape of the wing the greater the
camber the more curved the wing is in
the diagram it is clear that the camber
of the upper surface is quite more
pronounced than the camber of the lower
surface which is almost flat different
air foils have different flight
characteristics for example the scooped
out bottom of the early airfoil gives
lots of lift but is not streamlined and
is not stable at high speeds the laminar
flow airfoil is an almost symmetrical
airfoil that is more streamlined but
does not produce as much lift the middle
designs give some combination of a
scooped out bottom and symmetrical
designs airfoil designs that are
perfectly symmetrical like the circular
arc and the double wedge airfoil are
used on many high-speed planes and
solely rely on their angle of attack to
produce lift these air foils provide
very little aerodynamic resistance and
are stable at high speeds to review
angle of attack is the position of the
wings cord line relative to the wind
that is hitting it for a wing in a
normal angle of attack the wing splits
the air so some flows over and some air
flows under the wing the air flowing
over is pushed faster and when looking
back at the theories of lift
we know the lower pressure created
causes lift also the air that flow
under the wing hits the bottom of the
wing causing the wing to be pushed
upward if the wing is subjected to a
different angle of attack the airflow
over the wing is changed causing the
forces to act in different places and
the difference is in the center of
pressure or the area in which
aerodynamic forces act through some
parts of the wing experience low
pressure and some parts experience high
pressure the center of pressure is the
average of these pressure differences
and affects the aircraft's aerodynamic
balance and controllability the diagram
shows how the center of pressure moves
on the wing for different angles of
attack when we talked about lift we were
talking about the lift caused by air
flowing over the center part of the wing
if we look at the tip of the wing there
is a phenomena that occurs known as tip
vortices when reaching the edge of the
wing there is still a low-pressure zone
above the surface of the wing and a high
pressure below these pressure zones
naturally want to even out so the
high-pressure air tends to flow towards
the low-pressure air the high pressure
area on the bottom of an airfoil pushes
around the tip to the low pressure area
on the top this action creates a
rotating flow called a tip vortex the
vortex flows behind the airfoil creating
a downwash that extends back to the
trailing edge of the airfoil this
downwash results in an overall reduction
in lift for the affected portion of the
airfoil manufacturers have developed
different methods to counteract this
action winglets can be added to the tip
of an airfoil to reduce this flow the
winglets act as a dam preventing the
vortex from forming winglets can be on
the top or bottom of the airfoil
another method of countering the flow is
to taper the airfoil tip reducing the
pressure differential and smoothing the
airflow around the tip we hope you
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