Primary Controls Flashcards
Elevator axis + movement
Lateral Axis
Pitch
Aileron axis and movement
Longitudinal axis
Roll movement
Rudder axis and movement
Yaw around normal axis
Essentials req for flight control systems
Forces need to be balanced
Feel system (airspeed increasing etc)
Response
Movement and harmony with other axis controls
Aerodynamic Balance - Inset Hinge
Reduce the distance of the moment arm
Only a small inset to around 25% otherwise behind CP can cause full selection with smaller inputs
Aerodynamic Balance - Horn Balance
Extends forward of the hinge and causes drag
Usually found on elevators and rudders
Aerodynamic Balance - Internal Balance
Flexible sealed diaphragm using static pressure to provide opposing hinge moment
Aerodynamic Balance - Balance Tab
Small control surface tab on TE that deflects in opposite direction to control surface
Reduces control effectiveness
Aerodynamic Balances - Anti Balance Tab
Tab deflects in same direction as control surface
Opposes the movement of control surface making the controls heavier.
Reduce possibility of over stressing aeroplane + light control feel at low speeds
Aerodynamic Balance - Servo Tab
Pilot moves the control tab which moves the control surface via force generation
Very ineffective at slow speed due to low forces over AC
Aerodynamic Balance - Spring Tab
Better version of servo tab
Prevent operation of servo tab at low speed and control directly.
High speeds spring compresses and pilot moves tab
Why do we need mass balancing
To prevent flutter
How do we avoid flutter
Adding mass ahead of hinge line to move CG forward of hinge line
Stay within flight envelope (reduce speed)
Power assisted controls
Provide additional force to operate control surfaces
Still feedback from controls
Full powered controls
Provide all power to remove control surfaces force
Via hydraulic forces
No direct connection between pilot and control surfaces
No aerodynamic feel don’t require aerodynamic balanced control surfaces
Artificial feel system is…
Controls provide no natural sense of forces acting on plane therefore Q feel system added (generates force in proportions to dynamic pressure)
Aileron controls - Up going wing
Deflected aileron downwards
AOA reduces on up going wing
Aileron - down going wing
Aileron is deflected upwards
AOA increases on down going wing
Ideal tailplane fin
Swept back and low aspect ratio
Larger stalling AOA
Elevator controls pitch down
Elevator deflected down
Tailplane will pitch upwards
Nose pitches down
“Pitch down the elevator must go down”
Elevator control pitch up
Elevator deflected upwards
Downwards reaction on tailplane
Nose pitches up
“Pitch up the elevator must go up”
Stabilator
All moving tailplane no elevator
Angle of attack changes of elevator
Pitch down the stabilator moves up to create total reaction upwards
To move nose down
Pitch up the stabilator moves down to create downward reaction
To move nose up
Comparison between elevator and stabilator
Elevator is a camber changing device where as stabilator is a AOA changing device
Better L/D ration on stabilator
Trimmable horizontal stabiliser
Change angle of incidence via trim
Pitch control still controlled by elevators
CG vs CP
CG is always in front of CP
Forward limit CG and aft limit CG
Downwash on pitch control T-tail vs normal
T-tail planes more effective as clear of undisturbed airflow
Normal tails - change in relative airflow has to cope with turbulent air over TE
Rudder Limiting Devices
Forces generated by tailplane could shear with high aerodynamic loads
Main purpose of mass balancing
To stop control surface oscillating in front of the hinge line
All Moving tailplane (stabilator) pitch up and down
Controls forward to pitch down the stabilator moves upwards
Controls rearward to pitch upwards the stabilator stabilator moves downwards
Displacement controls
Rudder and elevator
Rate controls are
Ailerons
Adverse Aileron Yaw
Increased lift produced on upgoing wing increases induced drag
Reduce lift produced on downgoing wing reduces induced drag
Therefore:
Difference in drag between produces a moment that yaws the ac towards the upgoing wing
Use rudder
Differential Aileron
Up going aileron is deflected more than the downgoing wing to induce higher form drag on the down going wing to counter higher induced drag on the up going wing
Fries Ailerons
Increase drag on the up going aileron to induce form drag when deflected downwards remains inside the wing
Large A/C controls in roll
Outboard ailerons only used in low speed flight - flaps extended for TO/LD
Lift spoilers used on upper surface with ailerons - up going aileron spoiler lifted to increase drag and reduce lift to create differential drag and yaw /roll
Advantages/Disadvantages of spoilers
- Reduce overall lift
+ Do not suffer from flutter
+ No twisting moment on the wing
Flaperons
Combines flaps and aileron in single control surface
+ Improved lateral control
+ Reduced weight
Coupling Unit
Unit that assists pilot with rudder inputs when roll is commanded
Ground Spoilers
Dump lift once on ground
Speed Brakes
Increase amount of drag
+ reduce airspeed rapidly
+ increase angle of descent
+ increase rate of descent
+ control airspeed in descent
Speed Brakes on CL/CD
On polar curve moves down and right
Reduced L/D ratio
CLMAX reduced
Higher parasite drag
Fuselage mounted speed brakes should have no effect on CL
Combined Controls
Flaperons - flaps + ailerons
Elevons - elevator + ailerons
Ruddervator - rudder + elevator
Airbus side stick
No direct connection
Control inputs are request to computer
Executed/modified or ignored
No need for artificial feel system no trim
Risk of loss of situation awareness pilots cannot see each others inputs
Equilibrium is
Forces/Moments equal and opposite (steady flight)
A/C can be in trim or out of trim in equilibrium
Causes of out of trim forces
Change in thrust
Change in speed
Thrust asymmetry
Propeller slipstream effects
Loss of control authority
Pilot runs out of elevator travel - CG is too far forward or aft when flaring on landing
Reduced control in one direction
Countermeasures for a jammed THS
Reduce IAS if less control effectiveness needed
Increase IAS to improve effectiveness of a jammed primary control
Essential requirement for flight controls are
Force
Feel
Response
CG forward + Nose Up trim =
Rotation will be normal using normal rotation technique
Stabiliser is moved down to create downwards force on tailplane
CG Aft + Nose Up Trim
Early nose wheel raising possible tail strikes
CG Foward + Nose down trim
Rotation will require extra stick force
CG Aft + Nose down trim
Rotation will be normal using normal rotation technique
Aerodynamic balancing devices which improve control effectiveness
Horn balance
Anti balance tab
(Upforce together)
Aerodynamic balancing devices which decrease control effectiveness
Balance tab
Servo tab
Spring tab
(Move in opposite direction to control surface)
Aerodynamic balances devices which are neutral to control effectiveness
Inset hinge
Internal balance
Factors that influence stabiliser position on take off
CG position
Take off mass
Flap setting
