Flight Controls

Question 1

FLIGHT CONTROLS

Answer 1

Primary and Secondary Flight Controls

Question 2

Primary Flight Controls

Answer 2

Ailerons, Elevator, and Rudder

Question 3

Secondary Flight Controls

Answer 3

Wing flaps, leading edge devices, spoilers, and trim systems

Question 4

Airfoil Nomenclature

Answer 4

Airfoil
Chord Line
Chord
Mean Camber Line
Maximum Camber
Thickness/Chord Ratio
Leading Edge Radius

Question 5

a shape capable of producing lift with
relatively high efficiency.

Answer 5

Airfoil

Question 6

a straight line joining the centers of
curvature of the leading edge and trailing edges of
an airfoil.

Answer 6

Chord Line

Question 7

the distance between the leading edge and
trailing edge measured along the chord line.

Answer 7

Chord

Question 8

a line joining the leading edge
and trailing edge of an airfoil, equidistant from the
upper and lower surfaces.

Answer 8

Mean Camber Line

Question 9

the maximum distance of the
mean camber line from the chord line. Maximum
camber is expressed as a percentage of chord, with
its location as a percentage in tenths of the chord aft
of the leading edge. When the camber line lies above
the chord line, it is said to have a positive camber.
When the camber line is below the chord line, it is
said to have negative camber. A symmetrical airfoil
has no camber because the chord line and camber
line are co-incidental.

Answer 9

Maximum Camber

Question 10

the maximum thickness
or depth of an airfoil section expressed as a
percentage of chord, with its location as a
percentages of the chord aft of the leading edge. The
thickness and thickness distribution of the airfoil
section have a great influence on its airflow
characteristics.

Answer 10

Thickness/Chord Ratio

Question 11

the radius of curvature of
the leading edge. The size of the leading-edge radius
can significantly affect the initial airflow
characteristics of the airfoil section.

Answer 11

Leading Edge Radius

Question 12

also known as relative wind or
free stream flow.

Answer 12

Relative Airflow

Question 13

Relative airflow has three qualities:

Answer 13

Direction, Condition, Magnitude

Question 14

air parallel to, and in the opposite
direction to the flight path of the aircraft, in fact the
path of the CG; the direction in which the aircraft is
pointing is irrelevant.

Answer 14

Direction

Question 15

air close to, but unaffected by the
presence of the aircraft; its pressure, temperature,
and velocity are not affected by the presence of the
aircraft through it.

Answer 15

Condition

Question 16

the magnitude of the relative airflow is
the true airspeed (TAS).

Answer 16

Magnitude

Question 17

If airflow does not possess all three qualities, it is
referred to as ___________.

Answer 17

effective airflow

Question 18

can also be referred
to as aerodynamic incidence. It is the angle formed
between the chord line and the relative airflow. The
angle between the chord line and the effective
airflow is referred to as the effective angle of attack.

Answer 18

Angle of Attack (α or alpha)

Question 19

the angle between the chord
line and the horizontal datum of the aircraft. (This
angle is fixed for the wing, but may be variable for
the tail plane.)

Answer 19

Angle of Incidence

Question 20

the aerodynamic force which acts 90 degrees
to the relative airflow.

Answer 20

Lift

Question 21

the aerodynamic force which acts parallel to
and in the same direction as the relative airflow (or
opposite to the aircraft flight path).

Answer 21

Drag

Question 22

the resultant of all aerodynamic
forces acting on the airfoil section.

Answer 22

Total Reaction

Question 23

the point on the chord
line, through which lift is considered to act.

Answer 23

Center of Pressure (CP)

Question 24

For steady flight, the aircraft must be in a state of
_________ and the
controls enable this to be achieved for all possible
configurations and center of gravity (CG) positions.

Answer 24

balance (zero moments around the axes)

Question 25

the controls will be required to maneuver the aircraft around its three axes. What are those?

Answer 25

Longitudinal, Lateral, Normal or Vertical Axis

Question 26

The __________ used on tail-less aircraft gives both pitching and rolling.

Answer 26

elevon (elevator and aileron)

Question 27

The __________ gives both pitching and yawing.

Answer 27

ruddervator (V tail)

Question 28

The _______ or a movable tailplane combining the dual function of horizontal stabilizer and elevator in which gives both longitudinal stability and control.

Answer 28

stabilator

Question 29

The moment around an axis is produced by changing the aerodynamic force on the appropriate airfoil (wing, tail or fin) and this may be done by:

Answer 29

Changing the camber of the airfoil Changing the angle of attack (incidence) Decreasing the aerodynamic force by spoiling the airflow

Question 30

The increased lift on the up-going wing gives an increase in the induced drag, whereas the reduced lift on the down going wing gives a decrease in induced drag. The difference in drag on the two wings produces a yawing moment which is opposite to the rolling moment, that is, a roll to the left produces a yawing moment to the right. This is known as _________.

Answer 30

adverse yaw

Question 31

Various methods have been adopted to reduce the adverse yaw, the main ones in use are:

Answer 31

Differential Aileron Frise Ailerons Aileron-rudder coupling

Question 32

The aileron linkage causes the up-going aileron to move through a larger angle than the down-going aileron. This increases the drag on the up aileron, and reduces it on the down aileron, and so reduces the difference in drag between the two wings.

Answer 32

Differential Aileron

Question 33

The _______ has an asymmetric leading edge. The leading edge of the up-going aileron protrudes below the lower surface of the wing, causing high drag. The leading edge of the down-going aileron remains shrouded and causes less drag.

Answer 33

Frise aileron

Question 34

In this system, the aileron and rudder systems are interconnected, so that when the ailerons are deflected the rudder automatically moves to counter the adverse yaw.

Answer 34

Aileron-rudder coupling

Question 35

The ailerons are normally situated at the wing tip, to give the greatest moment for the force produced. However, this also means that they cause the maximum twisting and bending loads on the wing. This can cause a loss of effectiveness or even reversal of the aileron. To reduce these effects, the ailerons can be mounted further inboard. Alternatively, two sets of ailerons may be fitted, one set at the wing tip for use at low speeds when the forces involved are low, and one set inboard for use at high speeds when the forces are greater and could cause greater structural distortion.

Answer 35

Inboard Ailerons

Question 36

The flaps and the ailerons both occupy part of the trailing edge of the wing. For good take-off and landing performance the flaps need to be as large as possible, and for a good rate of roll, the ailerons need to be as large as possible. Another system is to use the trailing edge moveable surfaces to perform the operation of both flaps and ailerons.

Answer 36

Flaperons

Question 37

if the space available is limited, and one solution is to ______ the ailerons symmetrically to augment the flap area. They then move differentially from the _____ position to give lateral control.

Answer 37

droop ; drooped

Question 38

________ may be used to give lateral control, in addition to, or instead of ailerons. The _______ consists of part of the upper surface of the wing which can be raised.

Answer 38

Spoilers

Question 39

Raising the spoiler will disturb the ____ over the wing and reduce the lift. To function as a lateral control, the spoiler is ______ on the wing which is required to move downwards and remains in its retracted position on the other wing.

Answer 39

airflow ; raised

Question 40

Advantages of spoilers compared to the aileron

Answer 40

There is no adverse yaw. Wing twisting is reduced. At transonic speed, its effectiveness is not reduced by shock induced separation. It cannot develop flutter. Spoilers do not occupy the trailing edge

Question 41

The aerodynamic force acting on a control surface through its center of pressure will tend to rotate the control around its hinge, in the direction of the force. The moment will be the force multiplied by the distance from the hinge to the center of pressure. This is called the ___________. The force may be due to the angle of attack of the airfoil or the deflection of the control surface. It is assumed that the total _________ is the sum of the separate effects of angle of attack and control surface deflection.

Answer 41

hinge moment

Question 42

The aerodynamic force on the control at a given deflection will depend on the_____ of the control surface, and the speed squared.

Answer 42

size

Question 43

_________ involves using the aerodynamic forces on the control surface, to reduce the hinge moment

Answer 43

Aerodynamic balance

Question 44

Aerodynamic balance may be done in several ways, those are?

Answer 44

Set back hinge line Horn Balance Internal Balance

Question 45

The moment arm of the control surface force is the distance from the hinge to the center of pressure on the control surface. If the hinge is moved back into the control surface, the arm and the hinge moment will be reduced. Setting the hinge back does not reduce the effectiveness of the control, only the hinge moment of the force is reduced, not the force itself.

Answer 45

Set Back Hinge Line

Question 46

The principle of the _________ is similar to that of the set-back hinge, in that part of the surface is forward of the hinge line, and forces on this part of the surface give hinge moments which are in the opposite direction to the moments on the main part of the surface. The overall moment is therefore reduced, but not the control effectiveness.

Answer 46

horn balance

Question 47

This balance works on the same principle as the set-back hinge, but the balancing chamber area is inside the rear of the main airfoil section. Movement of the control causes pressure changes on the airfoil, and these pressure changes are felt on the balance area.

Answer 47

Internal Balance

Question 48

The balance tab causes a force to act on the control surface trailing edge, which is opposite to the force on the main control surface. The tab is geared to move in the opposite direction to the control surface whenever the control surface is deflected. Unlike the previous types of balance, the balance tab will give some reduction in control effectiveness, as the tab force is opposite to the control force.

Answer 48

Balance Tab

Question 49

The ________ is geared to move in the same direction as the control surface, and so will increase the control effectiveness, but of course will increase the hinge moment and give heavier stick forces.

Answer 49

anti-balance tab or anti-servo tab

Question 50

The purpose of the ________ is to enable the pilot to move the control surface easily. In this system, there is no direct movement of the control surface as a result of moving the cockpit control.

Answer 50

servo tab

Question 51

The_______ is a modification of the balance tab, such that the tab movement is proportional to the applied stick force. Maximum assistance is therefore obtained when the stick forces are greatest. This is achieved by putting a spring in the linkage to the tab. The spring tab is used mainly to reduce control loads at high airspeeds.

Answer 51

spring tab

Question 52

________ is a weight attached to the control surface forward of the hinge. Most control surfaces are __________. The purpose of this is to prevent control surface flutter.

Answer 52

mass balance ; mass balanced

Question 53

______ is an oscillation of the control surface which can occur due to the bending and twisting of the structure under load. If the center of gravity of the control surface is behind the hinge, its inertia causes it to oscillate about its hinge when the structure distorts. In certain circumstances the oscillations can be divergent, and cause failure of the structure.

Answer 53

Flutter

Question 54

The _____________ consist of lift augmentation devices (flaps and slats), lift dumping devices (spoilers except when they are used for roll control), and air brakes and trimming controls. Some or all of these devices may be fitted to a particular aircraft

Answer 54

secondary flight controls

Question 55

The purpose of __________ is to increase the lift generated by the wings at low speed. They are normally only used for takeoff and initial climb out, and approach and landing.

Answer 55

trailing edge flaps

Question 56

These may consist of slats, Krueger flaps, or variable camber flaps or some combination as on the Boeing 747 which uses Krueger flaps for the inboard section and variable camber for the outboard and Boeing 737 which also uses Krueger flaps for the inboard section and slats for the outboard section.

Answer 56

High Lift Devices Leading Edge