8.3 theory of flight Flashcards
the four fundamental fources that govern how an aircraft flies are
lift
weight
thrust
drag
the total weight of the aircraft is represented where
the centre of gravity
it is common to lump the total lift produced by the wing to a single point known as
the centre of pressure
common engine locations include
in front of the nose, under the wings, internal to the fuselage and on the rear fuselage.
the forward motion of an aircraft is largely determined by
thrust and drag
glide ratio =
ratio of the distance forward to the distance downward
if two aircraft have same lift to drag ratio but weigh differently and start gliding from same altitude what happens.
heavier aircraft glides at higher airspeed and arrives at the same touch down point quicker than the lighter aircraft.
optimum AOA is typically
4 degrees
high performance glider will have an LD max of
between 25 and 60
an aircrafts LD max is
12-20
in steady flight the sum of the opposing forces is what
always zero
the primary factors most affected by perfromance are
rate of climb
ceiling
payload
range
speed
stability
fuel economy
TO and landing distance
manoevrability
induced drag is high or low at low speeds
high and decreases as the speed increases
parasite drag does what as speed increases
increases
thrust is measured in ..
pounds (lb) or newtons (N)
when regarding fuel performance what are two important factors
to extract max flying distance from a given fuel load
to fly a specified distance with a minumum expenditure of fuel
the values of specific range vs speed are affected by 3 principal variables
aircraft gross weight
altitude
the external aerodynamic config of the aircraft
the force of lift during a bank is divided into vertical and horizontal components which are at a right angle to eachother. what are they called
vertical = vertical component of lift
horizontal = centripetal force or horizontal component of lift
if aircraft is to maintain altitude during a turn what must happen
thr lift must be equal to resultant of centrifugal force and weight
to compensate for added lift during a turn, which would result if the airspeed were increased what must happen
the AOA must be decreased or bank angle increased.
to remain a constant rate of turn as airspeed is increased what must happen
AOA must remain constant and bank angle increased
slipping turn =
centrifugal force is less than horizontal lift
skidding turn =
centrifugal force is greater than horizontal lift
limit load factor is
highest load factors that can be expected in normal operation
the load factor is
resultant force of lift in a turn divided by the weight aka G-load
load factor increases at terrific rate after bank has reached what angle
45 or 50 degrees
load factor for any aircraft in a coordinated level turn at a 60 degree bank is how many g
2g
load factor in a 80 degree turn is how many g
5.76 g
an aircrafts stalling speed increases in proportion to the square root of what
the load factor
the steeper the bank angle, the greater the centrifugal force but does the load factor increase or decrease
increases
stall characteristics include
distinctive loss of lift
sudden nose pitch down
warnings such as buffeting before stall occurs
stalls commonly occur at what airspeeds
slow
V-n diagrams shows what
is another way of showing limits of aircraft performance. It shows how much load factor can be safely achieved at different airspeeds
V-n diagram is dependant on factor such as
the aircrafts gross weight
the config of aircraft flaps, landing gear position etc.
the applicable altitude
structural limits. under any loading even 1g what will happen
the aircraft structutre will flex
structural limits can also be referred to as
acceleration limits or limit load factors
aeroelastic limits studies what
interactions between the inertial, elastic and aerodynamic forces that occur when elastic body is exposed to fluid flow
Aeroelastic limit is frequently referred to as the
redline airspeed
ultimate structural limits will result in structural failure of some components and are outside normal operating envelope of the aircraft.
usual design rule is for ultimate structural limit to be 150% of the structural limit.
lift augmentation systems are devices installed on the wing and do what
increase lift at given speed .
useful at low speeds as they reduce the stall speed of the aircraft.
the principal lift augmentation devices are
flaps - trailing edge and leading edge
slats and slots - either auto or controllable by pilot
boundary layer control - used to re-enegrise the boundary layer
plain flap is a basic hinged design to trailing edge.
-allows pilots to fly at steeper angle on approach without increasing airspeed.
-plain flap provides nose down pitching.
-50-55% increase in max lift at 12% AOA
split flap consists of two sections. fixed upper part is extension on top of trailing edge, while lower is moveable and pivots to generate drag.
split flap provides a nose down ptich with a 60-65% increase of max lift at 14 degree AOA
slotted flap is most common on small and large commercial aircraft. gap between wing and flap
a single slotted flap provides 65-70% increase in lift at 16 degree AOA.
Multi slotted flaps give 70% increase in lift at 18 degree AOA
fowler flap one of the most common in modern aircraft because they provide significant lift with minimal drag.
on set of rails or tracks.
provides nose down pitch with 95% increase in max lift at 15 degree AOA
krueger flaps are fitted where
bottom of the leading edge and deploy down and forwards, increasing wings camber to generate more lift .
leading edge flaps are always used in conjunction with
trailing edge flaps and are controlled directly from the flight deck or linked.
cuffs are fixed aerodynamic devices that
are secured to the leading edge, extend leading edge down and forward. they increase camber and CL max and lower ac stall speed
slats do what
prevent flow separation by re-enegising the boundary layer.
a leading edge slot is what
similar to a slat but is a fixed aerodynamic feature of the wing. reduces stall speed and promotes good low - speed handling qualities
a leading edge slot can increase max lift coefficient of an aerofoil section by how much
40%
what are vortex generators and what do they do
metal projections on the upper surface of the wing. VG’s improve performance and controllability of the aircraft, particularly at low speeds. in the climb and at high AOA.
-they also help prevent flow separation by creating mini vortices
what are winglets and what do they do
small upturned structures on the end of the wing. winglet solves problem of wingtip vortex
it is torn apart and distributed vertically.
benefits of winglets are
reduced fuel consumption
increased range
improved performance
lower emissions
