8.3- Theory of Flight Flashcards
How does an aircraft overcome the effects of gravity?
Producing a lifting force greater than or equal to its weight.
What are the four fundamental forces?
Lift
Drag
Weight
Thrust
Why is force a vector quantity?
Because it has magnitude and direction.
What is the weight of the aircraft?
The weight of the aircraft is the gravitational pull of the earth acting on the aircraft’s mass.
What is the centre of mass?
Location at which the aircraft would remain balanced if suspended from that point.
What is lift?
A force vector which acts perpendicular to the direction of flight.
How is drag overcome?
Thrust force of the engines.
What is the total aircraft drag proportional too?
Square of the aircrafts flying velocity
What is the glide ratio?
The ratio of distance forward to the distance down.
What effect does weight have on the glide ratio?
It only effects the time the aircraft will glide for.
If two aircraft have the same Lift-to-Drag ratio but weigh differently, and begin a glide from the same altitude, the heavier aircraft gliding at a higher airspeed arrives where?
The same touch down point but sooner.
What is used to calculate the best glide ratio?
The lift to drag ratio and polar diagrams.
What is the optimum angle of attack?
4 degrees
What dictates the lift drag ratio for an aircraft?
Its role
What is the lift drag ratio of a glider?
Between 25 and 60
What is a larger aircrafts lift drag ratio?
12-20
What is a small piston aircrafts lift drag ratio?
10-15
In steady flight what is the sum of all the forces?
0
Where in the aircraft does lift and drag act?
Centre of pressure.
Where does the thrust act on an aircraft?
Parallel to the aircrafts longitudinal axis.
What is the moment value equal too?
Force x moment arm
What is the moment arm?
Shortest distance between the point of rotation and the line of action of the force.
What causes the centre of pressure on the wing to move?
When the angle of attack is altered.
How can the pitching moment be measured?
Experimentally by direct measurement on a balance or by pressure plotting.
What is the aerodynamic centre?
The centre of pressure and gravity where coefficient of lift is highest… often 25% of the chord from leading edge.
What is key about the aerodynamic centre?
It is a fixed point.
What are some of the factors effecting performance?
Take off and landing distance
Rate of climb
Ceiling
Payload
Range
Speed
Manoeuvrability
Stability
Fuel economy
What causes parasite drag to increase?
Speed
Why is total drag high at low speed?
High induced drag
What is the difference between power and thrust?
Thrust is a force or pressure exerted on an object.
Which part of flying is the aircraft potential energy?
Aircraft position
What happens to power with an increase of altitude?
It decreases.
What is specific range?
The NM of flying distance vs the amount of fuel consumed.
What three factors effect specific range vs speed?
Aircraft weight
Altitude
Aerodynamic config
What is banking?
Makes the aircraft turn caused by the ailerons.
What is the force that pulls the aircraft from a straight flight path to make a turn.
Horizontal component of lift (centripetal).
What is the equal and opposite reaction of the horizontal component of lift?
Centrifugal.
What would happen if the angle of bank were held constant and the angle of attack decreased?
The rate of turn would decrease.
How is equilibrium between the horizontal lift component and centrifugal force re-established?
By either decreasing the bank, increasing the rate of turn or a combination of the two.
What does a skidding turn result in?
Excess centrifugal force pulling the aircraft to the outside of the turn.
What happens in a slipping turn?
The aircraft is not turning at the required rate, its banked too much meaning the horizontal lift component is greater than the centrifugal force.
At 400mph what angle must an aircraft be banked at to turn 3 degrees per second?
44 degrees
At bank angle of 44 degrees what percentage of the lift of the aircraft compromises the vertical component of lift?
79%
What is the load factor?
The ratio of lift to it weight.
What unit is given too load factor?
g
What does load factor 3 mean?
Total load felt on the aircraft is 3 times its weight.
What is a limit load factor?
The force that an aircraft structure must be able to withstand for safety reasons.
How is load factor worked out?
Lift divided by weight
At zero degrees of bank angle what is the load factor?
1
At 45 degrees of bank what is the load factor?
1.41
At 60 degrees of bank what is the load factor?
2
At 70 degrees of bank what is the load factor?
3
At 75 degrees of bank what is the load factor?
4
A study of the effect that load factor has on aircraft revealed what?
That an aircrafts stall speed increases in proportion to the square root of the load factor.
What is a V-n diagram?
Plots load factor against Equivalent airspeed (EAS)
What are some of the adverse effects of an aircraft flying above its limit range?
Destructive flutter, aileron reversal and wing divergence.
What does a lower amount of g loading lead too?
Metal fatigue.
What is an aeroelastic limit?
Defines the max operating speeds in both knots, airspeed and indicated mach number.
What is aeroelasticity?
The interaction between the inertial, elastic and aerodynamic forces that occur when a body is exposed to fluid flow.
What is redline airspeed?
Aeroelastic limit.
What is the ultimate structural limit compared to the structural limit?
150%
What are lift augmentation systems?
Devices installed on wings to produce lift.
What are the principle lift augmentation devices?
Flaps
Slats and slots
Boundary layer control
What is a plain flap?
Hinged flap, providing 50-55% increase in the maximum lift.
What is a split flap?
Upper and lower section of trailing edge, lower is the flap, provides 60-65% increase.
What is a slotted flap?
Similar to a plain flap, but with a gap to reduce flow separation. Single slotted provides 65-70% whereas multi slotted provides 70%.
What is a fowler flap?
Used on modern aircraft. Provides 95% at 15 degrees.
What is the issue with leading edge devices?
They cause a increase in the stalling angle.
What is a krueger flap?
Deploy down and forwards, found on swept wing airliners.
What is LE cuff?
They are fixed aerodynamic cuffs.
What are slats?
Small auxiliary aerofoil that can be extended forward.
How do slats prevent flow separation?
They supply more energy to the boundary layer.
How is the boundary layer re-energised by slats?
The added camber increases the air velocity over the upper surface and this is assisted by the flow from lower to upper through the slot.
What is a slot?
Similar to a slat but fixed.
How much does a slot increase the max lift coefficient?
40%
What are vortex generators used for?
Help control the boundary layer by adding kinetic energy from the high energy free stream air into the lower energy boundary layer.
What is adverse pressure gradient?
The pressure decreases before and up to the centre of lift the after it increases again.
What is a winglet?
Small upturned structure at the end of the wings.
How do winglets prevent loss of lift due to vortex’ at the tip of the wing?
The vortex of induced drag is torn apart and distributed vertically.
What do winglets do due to the relative wind?
Bend towards the fuselage.
What are the benefits of winglets?
Reduced fuel consumption
Increased range
Improved performance
Lower emmisions
