ppl_05_e2
.pdf
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 11: STABILITY QUESTIONS
7.Longitudinal stability is provided by:
a.the fn
b.the wing dihedral
c.the tailplane
d.the ailerons
8.An aircraft wing is constructed with dihedral in order to give:
a.lateral stability about the longitudinal axis
b.longitudinal stability about the lateral axis
c.lateral stability about the normal axis
d.directional stability about the normal axis
9.If the wing Centre of Pressure is forward of the C of G:
a.changes in lift produce a wing pitching moment which acts to reduce the change of lift
b.changes in lift produce a wing pitching moment which acts to increase the change of lift
c.changes in lift give no change in wing pitching moment
d.when the aircraft sideslips, the C of G causes the nose to turn into the sideslip thus applying a restoring moment
10.When the C of G is close to the forward limit:
a.small movements are required on the control column to manoeuvre the aircraft in pitch
b.longitudinal stability is reduced
c.larger control movements are required to manoeuvre the aircraft in pitch because the aircraft is very stable
d.control movements are the same as required for an aft C of G
11.If a disturbing force causes an aircraft to roll and slip towards its lower wing:
a.wing dihedral will cause a rolling moment which tends to correct the sideslip
b.the fn will cause a yawing moment which reduces the sideslip
c.wing dihedral will cause a yawing moment which tends to correct the sideslip
d.wing dihedral will cause a nose up pitching moment
12.Wing dihedral produces a stabilising rolling moment by causing an increase in lift:
a.on the up-going wing when the aircraft rolls
b.on the up-going wing when the aircraft is sideslipping
c.on the lower wing when the aircraft is sideslipping
d.on the lower wing whenever the aircraft is in a banked attitude
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Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 11: STABILITY QUESTIONS
13.A high wing confguration with no dihedral, compared to a low wing confguration with no dihedral, will have:
a.greater longitudinal stability
b.the same degree of longitudinal stability as any other confguration because dihedral gives longitudinal stability
c.less lateral stability
d.greater lateral stability
14.If an aircraft with strong lateral stability and weak directional stability suffers
alateral disturbance and enters a sideslip, the aircraft will:
a.go into a spiral dive
b.develop simultaneous oscillations in roll and yaw, known as Dutch Roll
c.develop oscillations in pitch
d.develop an unchecked roll
15.A wing whose angle of incidence decreases from root to tip is said to have:
a.washout
b.taper
c.sweep
d.anhedral
16.The lateral axis of an aircraft is a line which:
a.passes through the wing tips
b.passes through the Centre of Pressure, at right angles to the direction of the airfow
c.passes through the quarter-chord point of the wing root, at right angles to the longitudinal axis
d.passes through the Centre of Gravity, parallel to a line through the wing tips
17.Loading an aircraft so that the C of G exceeds the aft limits could result in:
a.loss of longitudinal stability
b.excessive upward force on the tail, and the nose pitching down
c.excessive load factor in turns
d.high stick forces
18.Stability about the normal axis:
a.is increased if the keel surface behind the C of G is increased
b.is given by the lateral dihedral
c.depends on the longitudinal dihedral
d.is greater if the wing has no sweepback
248
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 11: STABILITY QUESTIONS
19.If the Centre of Gravity (C of G) of an aircraft is found to be within limits for take off:
a.the C of G will always be within limits for landing
b.the C of G limits for landing must be checked, allowing for planned fuel consumption
c.the C of G will not change during the fight
d.the fight crew will always be certain of being able to adjust the C of G during fight in order to keep it within acceptable limits for landing
20.An aeroplane is in straight and level fight and a gust causes one wing to drop.
If the aeroplane tends to return towards wings level without any intervention from the pilot:
a.the aircraft has neutral stability
b.the aircraft is stable
c.the aircraft is unstable
d.the aircraft cannot return to wings level unless the pilot intervenes
21.The surface that gives an aircraft directional stability is:
a.the rudder
b.tailplane
c.the rudder trim tab
d.the fn
22.Movement of the aircraft about its normal (vertical) axis is known as:
a.yawing
b.rolling
c.pitching
d.side slipping
23.When an aircraft is disturbed from its established fight path by, for example, turbulence, it is said to have positive stability if it subsequently tends to:
a.remain on the new fight path
b.re-establish its original attitude without any input from the pilot
c.become further displaced from its original attitude
d.continue to pitch in the disturbed direction until the displacement is resisted by opposing control forces
24.When an aircraft is disturbed from its trimmed attitude by, for example, turbulence, it is said to have neutral stability if it subsequently:
a.oscillates about its original attitude before settling back to that original attitude
b.immediately re-establishes its original attitude
c.remains in the new attitude
d.continues to move in the disturbed direction until the displacement is resisted by opposing control forces
249
Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 11: STABILITY QUESTIONS
25.By design, the Centre of Pressure on a particular aircraft remains behind the aircraft’s C of G. If the aircraft is longitudinally stable and is displaced in pitch, nose down, by turbulence:
a.the tailplane will generate an increased upward force
b.neither an upward nor a downward force will be generated by the tailplane, as the aircraft will already be in equilibrium
c.the aircraft will maintain its nose-down attitude
d.the tailplane will generate an increased downward force
26.The tendency of an aircraft to develop forces which restore it to its original fight situation, when disturbed from a condition of steady fight, is known as:
a.manoeuvrability
b.controllability
c.stability
d.instability
27.An aircraft has directional static stability. If it sideslips to the right:
a.the aircraft will initially tend to roll to the left
b.the aircraft will initially tend to yaw to the left
c.the aircraft will initially tend to yaw to the right
d.the nose will remain pointing forward
28.Which of the following components provides longitudinal stability?
a.Engines
b.Wing
c.Fuselage
d.Horizontal stabiliser (tailplane)
29.To improve lateral stability certain features may be built into an aircraft. Which of the following lists of features would best contribute to an aircraft’s overall lateral stability?
a.High wing, dihedral, high keel surface, sweep back
b.Dihedral, high keel surface, Frise ailerons
c.Wash-out, dihedral, Frise ailerons
d.Slats, dihedral, Fowler faps
250
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 11: STABILITY QUESTIONS
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The answers to these questions can be found at the end of this book.
251
Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
252
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12
FLIGHT CONTROLS
AND TRIMMING
253
Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING
Figure 12.1 The flying control surfaces allow the pilot to manoeuvre the aircraft about its three axes.
254
ID: 3658
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING
FLIGHT CONTROLS AND TRIMMING.
INTRODUCTION.
Whatever the degree of stability that an aircraft possesses about its longitudinal, lateral and normal axes, the pilot needs to control the aircraft about those axes in order that he may manoeuvre and steer the aircraft as he requires. Then, having selected the aircraft’s attitude, a pilot must be able to trim the aircraft so that the attitude can be held without his having to apply a constant pressure on the control column or control wheel and rudder pedals.
In this chapter, then, you will learn about how an aircraft is controlled and trimmed.
We will begin by looking at control.
THE FLYING CONTROL SURFACES.
The aerodynamic forces required to manoeuvre an aircraft about its three axes are generated through moveable fap-type control surfaces ftted to the main aerofoil sections at the extremities of the wings and fuselage. Sometimes, however, especially in the case of control in the pitching plane, the complete aerofoil section will be able to move under the pilot’s direction. Because an aircraft rotates about its Centre of Gravity (C of G), in all three planes, the control surfaces are positioned at the aircraft’s extremities so that the aerodynamic forces they create have as long a moment arm as possible.
The Flying Control Surfaces and their Primary Effects.
An aircraft, generally possess three sets of fying control surfaces, each of which has an important primary effect on the movement of the aircraft about the respective axis.
•A rudder which controls the aircraft in yaw, about the normal axis. This type of control is called directional control.
•An elevator which controls the aircraft in pitch, about the lateral axis. This type of control is called longitudinal control.
•Ailerons which control the aircraft in roll, about the longitudinal axis. This type of control is called lateral control.
Make sure that you learn well the above defnitions of the primary effects of the fying control surfaces. These defnitions are popular with examiners. Take special care over the words longitudinal and lateral, and do not confuse the plane of control with the axis about which control is achieved. For instance, the elevator gives longitudinal control about the lateral axis, and the ailerons give lateral control about the longitudinal axis.
The most common location and arrangement of the fying control surfaces on a light aircraft are illustrated in Figure 12.1.
Movement in yaw, pitch and roll is generated by the defection of the respective control surface: rudder, elevator or ailerons. The defection of the control surfaces changes three characteristics of the aerofoil section: its effective camber, the orientation of its mean chord line and, thus its angle of attack with respect to the relative airfow.
Yaw is rotation
about the aircraft’s
normal axis
and is controlled by the rudder.
Pitch is
rotation about the aircraft’s
lateral axis
and is controlled by the elevator or stabilator.
Roll is rotation
about the aircraft’s
longitudinal
axis and is controlled by the ailerons.
255
Order: 6026
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
Customer: Oleg Ostapenko E-mail: ostapenko2002@yahoo.com
CHAPTER 12: FLIGHT CONTROLS AND TRIMMING
The change in the aerofoil’s angle of attack also modifes the lift force produced by that aerofoil, by varying the value of CL, which, in turn, creates an out of balance turning moment about the aircraft’s C of G which initiates a movement about the corresponding axis. Figure 12.2 illustrates the principle of how the mean chord line, angle of attack, and lift force of a wing are modifed through displacement of the aileron.
Control about any axis is
always relative to the aircraft,
NOT to the natural horizon.
Figure 12.2 Displacement of a control surface modifies the aerodynamic force generated by the aerofoil. Here, aileron displacement is shown changing the lift force produced by a wing.
As we have mentioned, on some aircraft the complete aerofoil section can be displaced by the pilot to modify angle of attack. Figure 12.3 illustrates this type of horizontal control surface in the tail assembly, on a PA28 Warrior. This type of control surface is called a stabilator, or, in older parlance, an allfying tailplane.
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Figure 12.3 A stabilator or all-moving (flying) |
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controls alone, by the pilot, does not manoeuvre the aircraft with reference to the natural horizon or any other line or point on the Earth’s surface. Movement of the fying control surfaces always has the same primary effect on the aircraft, no matter what attitude the aircraft has in relation to the surface of the Earth; (except when the aircraft is at the point of stall); in other words, response to control movement is relative to the pilot, and the amount of response relative to the amount of control defection. Also, the aircraft will continue to react until the controls are returned to their neutral position. It is only after the pilot has mastered the effects of controls that he can go on to use them to change the attitude of the aircraft relative to the Earth’s surface.
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