18 Control Flashcards
What are the basic requirements for flight control systems?
- Force: must not be too heavy or too light
- Feel: must vary proportionally to the aerodynamic forces
- Responsiveness: Minimise delay between between input and action
- Movement: Proportional movement in controls to action
- Harmony: Proportional movement in control to pitch and roll
Hinge moment (Feel) is given by
Hinge moment (Feel) = d x F
d = distance the force acting is from the hinge F = force produced by the control surface
What are aerodynamic balances?
Devices used to modify the forces felt by the control stick
Name the 7 types of aerodynamic balances
- Inset hinge: reduce distance between force and hinge to reduce hinge moment
- Internal balance: small internal gap with a flexible seal, uneven static pressure assists moving the control surface.
- Balance hinge: moving main control surface moves a tab on the trail edge in the opposite direction causing a force in the same direction as control surface movement
- Anti-Balance hinge: tab move in the same direction as control surface. Makes controls heavier.
- Servo hinge: a servo moves a tab at the end of the control surface in the opposite direction desired for the control surface. This creates a force in the desired direction of movement which moves the control surface.
- Spring hinge: as with servo hing but at low speeds the aerodynamic forces don’t over come the springs and so the servo moves the control surface directly.
What is Mass Balancing?
- Control surfaces can twist if CG of surface is aft of hinge
- This can cause ‘flutter’
- Weight or a Horned hinge is added to move CG on or forward of hinge
What is Q-Feel?
An artificial ‘feel’ added to AC with fully powered controls
What is Aerodynamic dampening?
During a roll, as the wing moves down through the air it has the effect of angling the EAF to increase effective AOA. Therefore an increase in Lift.
Forward on the controls has what effect on the tail plane?
Forward on controls -> either, Elevator moves down (increased camber) or all moving tail plain moves down (increased AOA) -> increases lift from the tail plane -> Tail moves up -> nose pitches down
The camber of a tail plane can be:
Either symmetrical or negatively cambered
Where is the CP in relation to the CG?
The CP is kept aft of the CG to promote a nose down pitch
Rudder Travel limiter
Limits the amount a rudder can move based on the speed of the AC.
If the rudder is used with a high AOA at high speeds this can lead to it breaking off.
Describe Adverse Aileron Yaw
As the the AC rolls, the downward wing reduces in lift. This reduces the induced drag on that wing. At the same time the up ward wing increases lift which increases induced drag.
The combination of these produces a Yaw in the direction of the upward wing.
Describe Frise Aileron
These are used to counter adverse aileron yaw.
A section of the aileron sticks out behind which increases parasite drag of the downward wing to counter the increased induced drag on the upward wing.
Describe the methods to control roll on large AC.
- Inboard and outboard ailerons: outboard are locked at fast speeds to avoid wing twisting and aileron reversal
- Spoilers: reduce lift on a wing to assist roll
- Control coupling: auto-pilot automatically applies rudder to counter adverse aileron yaw
- Differential roll: an aileron on one side will move more than the other to counter adverse aileron yaw
- Frise ailerons
Control surfaces, primary and secondary effects
- Ailerons (Rate controls): Primary: Roll, Secondary: Side slip then Yaw
- Rudder (Displacement control): Primary: Yaw, Secondary: Roll (outboard wing moves faster, more lift)
- Elevator (Displacement control): Primary: Pitch
