load factor is the ratio of the maximum
load and aircraft can sustain to the
gross weight of the aircraft
the load factor is measured in G's which
is the acceleration of gravity if an
aircraft is pulled up from a dive
subjecting the pilot to 3 G's he or she
would be pressed down into the seat with
a force equal to 3 times his or her
weight load factors are important for
two reasons it is possible for a pilot
to impose a dangerous overload on the
aircraft structures and an increased
load factor increases the stalling speed
and makes stalls possible at seemingly
safe flight speeds in a constant
altitude coordinated turn in any
aircraft the load factor is the result
of two forces centrifugal force and
gravity to maintain altitude during a
turn the aircraft must sustain the loads
shown at the chart on the right the
maximum Bank for the average general
aviation aircraft is 60 degrees
when an aircraft experiences a load as
in a turn the speed at which the
aircraft stalls increases this means
that an aircraft with a normal
unaccelerated stalling speed of 50 knots
can be stalled at 100 knots by inducing
a load factor of 4 G's the maximum speed
at which an aircraft may be stalled
safely is now determined for all new
designs this speed is called the design
maneuvering speed or VA a thorough
knowledge of load factors induced by
varying degrees of Bank and the VA aids
in the prevention of two of the most
serious types of accidents stalls from
steep turns or excessively maneuvering
near the ground and structural failures
during acrobatics or other violent
maneuvers resulting from loss of control
relatively high load factors can be
experienced in the following flight
maneuvers turns stalls spins high speed
stalls Shondells which is a maximum
power 180-degree climbing turn lazy
eights which involved tracing the nose
through a figure 8 pattern and rough air
care should be exerted in these
situations by the pilot to ensure that
load limits are never reached
the flight operating strength of an
aircraft is presented on a graph whose
vertical scale is based on load factor
the diagram is called a VG diagram or
velocity versus G loads or load factor
each aircraft has its own VG diagram
which is valid at a certain weight and
altitude for any given load factor a
straight line may be drawn across the
diagram to see at which airspeed certain
operating ranges exist also for certain
air speeds a load factor can be checked
at certain levels negative and positive
for example if you wanted to know how
many g-forces you could exert on the
aircraft at 160 miles per hour indicated
airspeed you would find on the bottom of
the diagram 160 and then draw a line
straight up to see that any load under
negative 2 and any load above 4.2 will
cause structural damage to this aircraft
according to its VG diagram
an airplanes bank angle and speed affect
how quickly and in what distance it can
turn in the above example two planes
enter a canyon
they both Bank the same amount but one
aircraft is traveling twenty knots
faster than the other the result is a
larger turning radius for the faster
aircraft that aircraft will not be able
to make it out of the canyon traveling
at its given speed the way to correct
this would be to either Bank more or to
slow down to shorten the radius of the
turn
weight and balance is very important in
any pre-flight pilots often overlooked
weight and balance calculations which
leads to an unknown center of gravity as
stressed earlier in the lesson a center
of gravity that is positioned in the
wrong place on an aircraft causes
accidents other things to consider are
gross weight even if the center of
gravity of the aircraft has not been
displaced outside the envelope the gross
weight may be too high for the aircraft
overloading the aircraft's structure can
cause serious damage to the aircraft and
even small overloads can build up into
larger damage as shown above a higher
gross weight causes the aircraft to
behave differently and change its flight
characteristics
in subsonic aerodynamics the theory of
lift is based upon the forces generated
on a body and a moving gas air in which
it is immersed at speeds of
approximately 260 knots air can be
considered incompressible in that at a
fixed altitude its density remains
nearly constant while it's pressure
varies even when an aircraft is
traveling slower than the speed of sound
the air over the wing may be traveling
faster than the speed of sound the speed
of sound is labeled as Mach one twice
the speed of sound would be written as
Mach two and half the speed of sound
would be written as Mach point-five the
above pictures show the points where
this happens and also the resulting drag
Mach speed is always given in relation
to the aircraft's actual speed through
the air and not the indicated airspeed
when an aircraft flies at subsonic
speeds the air in front of the wing acts
to warn the air around it that it's
going to be separated when it occurs the
air is able to move out of the way and
easily let the wing pass through
however when speeds increase to speeds
more than the speed of sound
this cushion of air does not warn the
oncoming air quickly enough to get out
of the way having had no advanced
warning of the airplanes approach and in
the next instant the same air particles
are forced to undergo sudden and drastic
changes in temperature pressure density
and velocity the boundary between the
undisturbed air and the region of
compressed air is called a shock or
compression wave the above picture shows
the transition from just before to
during the formation of a compression
wave on a wing
one side effect to high-speed flight is
that the flight controls become harder
to control because of airflow over the
wing causing separation to counteract
this wings are often swept back on
aircraft that make constant transonic
flights this design tricks the wing into
thinking it is flying slower than it is
because the wind is not hitting the
leading edge at 90 degrees
this helps to delay the formation of
shockwaves one problem however with the
swept back design is that the wing tends
to stall at the tip first rather than
the wing root which reduces the ailerons
effectiveness during a stall
the stall situation could be made worse
by a t-tail configuration which affords
little or no pre stall warning in the
form of tail control surface buffett
shown above the t tail being above the
wing wake remains effective even after
the wing has begun to stall allowing the
pilot to n advertently drive the wing
into a deeper stall at a much greater
angle of attack if the horizontal tail
surfaces then become buried in the wings
wake the elevator may lose all
effectiveness making it impossible to
reduce pitch attitude and break the
stall things like stick pushers which
automatically push the nose forward and
a stick shaker which gives the pilots a
warning of the stall both help to reduce
the risk of this situation from ever
developing
on high-speed aircraft flight controls
are divided into primary flight controls
and secondary or auxilary flight
controls the primary flight controls
maneuver the aircraft about the pitch
roll and yaw axes they include the
ailerons elevator and rudder secondary
or auxilary flight controls include tabs
leading-edge flaps trailing edge flaps
spoilers and slats spoilers are used as
speed brakes to slow down high speed
aircraft they can also be used to help
turn the aircraft because the ailerons
are quite small leading-edge slots slats
and flaps are used to improve the
low-speed characteristics during takeoff
climb and landing
these devices can provide on average of
50 knot reduction in the stall speed of
an aircraft the tail uses a stabilizer
as well as an elevator to allow the
elevator to rest in the neutral position
and have full deflection in either
direction even when the aircraft is
trimmed because of the size and high
speeds of jet transport aircraft the
forces required to move the control
surfaces can be beyond the strength of
the pilot consequently the control
surfaces are actuated by hydraulic or
electrical power units
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