ppl_05_e2
.pdf
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING
If, for instance, an aircraft, at cruise speed, requires the pilot to hold the control column slightly to the right in order to maintain wings level, this condition may be corrected by adjusting the fxed trim tab on the aircraft’s starboard (right) aileron. This type of adjustment should be carried out by a qualifed aircraft technician. In this case, the fxed trim tab is bent down slightly, in order to create an aerodynamic force which will defect the starboard aileron upwards slightly so that the aircraft is trimmed for wings-level fight at cruise speed.
It is usual to fnd that ailerons have a fxed trim tab ftted to one aileron only. Adjustment is naturally a case of trial and error and, so, trim corrections will probably require several fights to achieve.
Fixed trim tabs are generally found on low performance aircraft, only. You should note that there can be only one speed, normally the cruise speed, at which the fxed trim tab will hold the aircraft in trim.
The Adjustable Trim Tab.
The greatest changes in stick force with speed tend to occur in pitch. The elevator or stabilator is, therefore, invariably ftted with a trim tab which can be adjusted in fight.
A typical adjustable elevator trim tab is shown in Figure 12.36.
Figure 12.36 An adjustable trim tab fitted to the elevator of a Cessna.
If, for instance, a pilot were to ease back on the control column to raise the nose of the aircraft (See Figure 12.37).and wished to maintain this new attitude, he would have to continue to apply a rearwards force to the control column, unless he re-trims the aircraft.
Figure 12.37 To hold a higher nose attitude, the pilot has to apply a rearwards force to the control column, until he re-trims.
277
Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING
In order to remove the stick force, the pilot must re-trim the aircraft for the higher nose attitude. The trimming system is so designed that the pilot moves the cockpit trim controls in the instinctive sense: rearwards to trim for a ‘stick back’ force, and forwards for a ‘stick forward’ force, regardless of actual attitude. (See Figure 12.38).
Figure 12.38 Two methods of pilot trim control, manual and electric.
In this case, by moving his cockpit trim control rearwards, the pilot causes the adjustable trim tab to move in the opposite direction to the direction of elevator displacement (See Figure 12.39), thus creating a balancing force which holds the elevator in its new position and maintains the new nose-high attitude, without the pilot having to apply any further force to the control column.
The simple trim tab will retain its
fixed position relative to the control surface, whatever the
control surface movement.
Figure 12.39 The balancing aerodynamic force from the trim tab holds the elevator in the new position. The aircraft is now trimmed for the new nose-high attitude.
Once the aircraft has been trimmed for a given fight attitude, the position of the simple trim tab relative to the control surface will remain fxed, whatever the subsequent displacement of the control surface. However, some adjustable trim tabs also serve as balance tabs, in which case the adjustable trim tab will move about the mean trimmed position as the control surface moves.
278
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING
Disadvantages of Trim Tabs.
There are three principal disadvantages to using a tab type control to trim an aircraft. First, there is a slight reduction in control effectiveness due to the tab force being in opposition to the force generated by the main fying control surface. Secondly, the defection of the tab will increase drag. Thirdly, trim tabs can reduce the effective area of the control surface when defected.
The Spring Bias Trimming System.
The spring bias trimming system works on the principle of an adjustable spring force opposing and, thus, decreasing the stick force applied by the pilot. Spring bias trimming has none of the disadvantages associated with the trim tab system.
Figure 12.40 The spring bias system.
The spring bias system differs from the trim tab system in that the trim control system is not linked to the fying control surface but to the associated control linkage. As illustrated in Figure 12.40, in the spring bias system, the trim control applies a force to the control linkage, to remove stick force, or, in this case, rudder pedal force.
The Variable Incidence Tailplane.
A further method of achieving trim in pitch is the variable incidence tailplane. This system, because it adjusts the angle of incidence of the complete tailplane, is very powerful and has the ability to trim for large changes in speed, aircraft confguration and centre of gravity position, while keeping trim drag to a minimum.
Figure 12.41 A variable incidence tailplane.
279
Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING QUESTIONS
Representative PPL - type questions to test your theoretical knowledge of Flight Controls and Trimming.
1.Which of the following provides aerodynamic balance?
a.A weight on an arm which protrudes forward of it
b.An area of control surface forward of its hinge line
c.A fxed trim tab
d.A simple, adjustable trim tab
2.Which fying control surface(s) give(s) control about the aircraft’s normal axis?
a.The rudder
b.The ailerons
c.The elevator
d.The faps
3.A control surface may have a mass balance ftted to it, in order to:
a.help prevent a rapid and uncontrolled oscillation which is called
“futter”
b.keep the control surface level
c.lighten the forces needed to control the surface
d.provide the pilot with “feel”
4.On an aircraft ftted with a stabilator incorporating an anti-balance tab, pulling back on the control column will cause the:
a.stabilator to move up and the tab to move up
b.stabilator to move down and the tab to move down
c.stabilator to move down and the tab to move up
d.stabilator to move up and the tab to move down
5.The respective primary and secondary effects of the rudder control are:
a.yaw and pitch
b.pitch and yaw
c.roll and yaw
d.yaw and roll
6.Fixed trim tabs on ailerons:
a.can be adjusted during fight
b.should never be adjusted
c.can be adjusted on the ground after a test fight to make wings-level fight easier
d.can be adjusted on the ground after a test fight to make turning easier
280
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING QUESTIONS
7.The respective primary and secondary effects of the aileron control are:
a.roll and pitch
b.pitch and yaw
c.roll and yaw
d.yaw and roll
8.On an aircraft with a simple trim tab incorporated into a control surface, when the control surface is moved, the tab remains in the same position relative to the:
a.relative airfow
b.control surface
c.boundary layer airfow
d.aircraft horizontal plane
9.The primary and secondary effects of applying the left rudder alone are:
a.left yaw and left roll
b.left yaw and right roll
c.right yaw and left roll
d.right yaw and right roll
10.Which fying control surface(s) give(s) longitudinal control?
a.The rudder
b.The ailerons
c.The elevator
d.The faps
11.Ailerons give:
a.lateral control about the lateral axis
b.longitudinal control about the lateral axis
c.directional control about the normal axis
d.lateral control about the longitudinal axis
12.Yawing is a rotation about:
a.the normal axis controlled by the rudder
b.the lateral axis controlled by the rudder
c.the longitudinal axis controlled by the ailerons
d.the normal axis controlled by the elevator
281
Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING QUESTIONS
13.If the control column is moved forward and to the left:
a.the left aileron moves up, right aileron moves down, elevator moves up
b.the left aileron moves down, right aileron moves up, elevator moves down
c.the left aileron moves up, right aileron moves down, elevator moves down
d.the left aileron moves down, right aileron moves up, elevator moves up
14.The purpose of differential ailerons is to:
a.increase the yawing moment which opposes a turn
b.reduce the adverse yawing moment when making a turn
c.induce a pitching moment to prevent the nose from dropping in the turn
d.improve the rate of roll
15.When displacing the ailerons from the neutral position:
a.the up-going aileron causes an increase in induced drag
b.induced drag remains the same, the up-going aileron causes a smaller increase in profle drag than the down-going aileron
c.both cause an increase in induced drag
d.the down-going aileron causes an increase in induced drag
16.The purpose of aerodynamic balance on a fying control surface is:
a.to bring the aircraft into balance
b.to prevent futter of the fying control surface
c.to reduce the control load to zero
d.to make it easier for the pilot to move the control surface in fight
17.An aileron could be balanced aerodynamically by:
a.making the up aileron move through a larger angle than the down aileron
b.attaching a weight to the control surface forward of the hinge
c.having the hinge set back behind the leading edge of the aileron
d.having springs in the control circuit to assist movement
18.A control surface may be mass balanced by:
a.ftting a balance tab
b.attaching a weight acting forward of the hinge line
c.ftting an anti-balance tab
d.attaching a weight acting aft of the hinge line
282
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING QUESTIONS
19.If the control column is moved to the right, a balance tab on the left aileron should:
a.move up relative to the aileron
b.move down relative to the aileron
c.not move unless the aileron trim wheel is turned
d.move to the neutral position
20.The purpose of an anti-balance tab is to:
a.trim the aircraft
b.reduce the load required to move the controls at all speeds
c.reduce the load required to move the controls at high speeds only
d.ensure that the pilot’s physical control load increases with increase of control surface defection
21.When the control column is pushed forward, a balance tab on the elevator:
a.will move up relative to the control surface
b.will move down relative to the control surface
c.will only move if the trim wheel is operated
d.moves to the neutral position
22.A fxed trim tab on an aileron should:
a.be adjusted on the ground after a test fight to achieve laterally level fight
b.not be adjusted once it has been set by the manufacturer
c.be adjusted on the ground after a test fight to achieve longitudinally level fight
d.be adjusted from the cockpit to achieve laterally level fight
23.The purpose of a spring-bias trim system is:
a.to maintain a constant tension in the trim tab system
b.to increase the feel in the control system
c.to reduce to zero the effort required by the pilot to counter stick force after making a control movement
d.to compensate for temperature changes in cable tension
24.The purpose of a trim tab is:
a.to assist the pilot in initiating movement of the controls
b.to zero the load on the pilots controls in the fight attitude required
c.to provide feel to the controls at high speed
d.to increase the effectiveness of the controls
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Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING QUESTIONS
25.To trim an aircraft which tends to fy nose heavy with hands off, the top of the elevator trim wheel should be:
a.moved forward to alleviate the back-pressure needed to hold the attitude, and this would cause the elevator trim tab to move down
b.moved backwards to alleviate the back-pressure needed to hold the attitude, and this would cause the elevator trim tab to move down
c.moved backwards to alleviate the back-pressure needed to hold the attitude, and this would cause the elevator trim tab to move up
d.moved backwards to alleviate the back-pressure needed to hold the attitude, and this would cause the elevator trim tab to move up
26.Compared with an aircraft with a central or aft C of G, following re-trimming for straight and level fight, in an aircraft with a C of G near its forward limit, and an elevator ftted with a conventional trim-tab:
a.nose-up pitch authority will be reduced
b.nose-down pitch authority will be reduced
c.longitudinal stability will be reduced
d.tailplane down-load will be reduced
27.An aircraft’s rudder is ftted with a balance tab. Movement of the rudder bar to the right, to yaw the aircraft to the right, will:
a.move the rudder to the left; the balance tab will move to the left
b.move the rudder to the right; the balance tab will move to the right
c.move the rudder to the left; the balance tab will move to the right
d.move the rudder to the right; the balance tab will move to the left.
28.Adverse yaw is partially counteracted by:
a.Fowler faps
b.a fxed aileron trim tab
c.aileron anti-balance tabs
d.differential ailerons
29.‘Differential Ailerons’ are a design feature that helps to counteract:
a.stability about the longitudinal axis
b.adverse yaw
c.positive aircraft stability
d.adverse roll
30.Controls are mass balanced in order to:
a.eliminate control futter
b.aerodynamically assist the pilot in moving the controls
c.provide equal control forces on all three controls
d.return the control surface to neutral when the controls are released
284
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING QUESTIONS
31.Where are mass balance weights located relative to a control surface hinge line?
a.Always on the hinge line, irrespective of the type of aerodynamic balance
b.On the hinge line if the control surface does not have an inset hinge
c.On the hinge line if the control surface has an inset hinge
d.In front of the hinge line
32.Roll is:
a.a result of aileron defection and is motion about the lateral axis
b.rotation about the normal axis
c.a pitching movement about the lateral axis
d.rotation about the longitudinal axis
33.If mass balance is used to eliminate futter, it should be attached to a control surface:
a.on the hinge
b.behind the hinge
c.above the hinge
d.in front of the hinge
34.If the pilot moves the cockpit trim lever or wheel such that the trim tab on the elevator moves up relative to the control surface, how has the aircraft’s trim been altered?
a.It has not been altered
b.More nose up
c.More nose down
d.More nose left
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The answers to these questions can be found at the end of this book.
285
Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
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