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Published by Exotic Flights Ultra Private Jet Service, 2017-12-08 01:22:17

PilotHandbook

PilotHandbook(FAA) FULL BOOK

Keywords: exoticflights,privatejet,rudygonzalez,exoticblade

120 knots

20 I0 20
I0
20 I0
I0
20

STBY PWR TEST

4,430 feet feet
2,215

5,000 feet

R = V2 R= 1202 = 14,400 = 2,215 feet
11.26 x tangent of the bank angle 30°
11.26 x 0.5773 6.50096

140 knots 20 I0 20
I0
6,028 feet 3,014 feet 20 I0
I0
5,000 feet 20

STBY PWR TEST

R = V2 R= 1402 = 19,600 = 3,014 feet
11.26 x tangent of the bank angle 30°
11.26 x 0.5773 6.50096

Figure 4-54. Two aircraft have flown into a canyon by error. The canyon is 5,000 feet across and has sheer cliffs on both sides. The pilot in
the top image is flying at 120 knots. After realizing the error, the pilot banks hard and uses a 30° bank angle to reverse course. This aircraft
requires about 4,000 feet to turn 180°, and makes it out of the canyon safely. The pilot in the bottom image is flying at 140 knots and also
uses a 30° angle of bank in an attempt to reverse course. The aircraft, although flying just 20 knots faster than the aircraft in the top image,
requires over 6,000 feet to reverse course to safety. Unfortunately, the canyon is only 5,000 feet across and the aircraft will hit the canyon
wall. The point is that airspeed is the most influential factor in determining how much distance is required to turn. Many pilots have made
the error of increasing the steepness of their bank angle when a simple reduction of speed would have been more appropriate.

4-36

to exceed CG limits in these aircraft, pilots should never Effect of Weight on Aircraft Structure
overload an aircraft because overloading causes structural The effect of additional weight on the wing structure of an
damage and failures. Weight and balance computations are aircraft is not readily apparent. Airworthiness requirements
not required, but pilots should calculate weight and remain prescribe that the structure of an aircraft certificated in the
within the manufacturer’s established limit. normal category (in which acrobatics are prohibited) must
be strong enough to withstand a load factor of 3.8 Gs to take
Effect of Weight on Flight Performance care of dynamic loads caused by maneuvering and gusts. This
The takeoff/climb and landing performance of an aircraft are means that the primary structure of the aircraft can withstand
determined on the basis of its maximum allowable takeoff and a load of 3.8 times the approved gross weight of the aircraft
landing weights. A heavier gross weight results in a longer without structural failure occurring. If this is accepted as
takeoff run and shallower climb, and a faster touchdown indicative of the load factors that may be imposed during
speed and longer landing roll. Even a minor overload may operations for which the aircraft is intended, a 100-pound
make it impossible for the aircraft to clear an obstacle that overload imposes a potential structural overload of 380
normally would not be a problem during takeoff under more pounds. The same consideration is even more impressive in
favorable conditions. the case of utility and acrobatic category aircraft, which have
load factor requirements of 4.4 and 6.0, respectively.
The detrimental effects of overloading on performance are not
limited to the immediate hazards involved with takeoffs and Structural failures which result from overloading may
landings. Overloading has an adverse effect on all climb and be dramatic and catastrophic, but more often they affect
cruise performance which leads to overheating during climbs, structural components progressively in a manner that
added wear on engine parts, increased fuel consumption, is difficult to detect and expensive to repair. Habitual
slower cruising speeds, and reduced range. overloading tends to cause cumulative stress and damage
that may not be detected during preflight inspections and
The manufacturers of modern aircraft furnish weight and result in structural failure later during completely normal
balance data with each aircraft produced. Generally, this operations. The additional stress placed on structural parts
information may be found in the FAA-approved AFM/POH by overloading is believed to accelerate the occurrence of
and easy-to-read charts for determining weight and balance metallic fatigue failures.
data are now provided. Increased performance and load-
carrying capability of these aircraft require strict adherence A knowledge of load factors imposed by flight maneuvers
to the operating limitations prescribed by the manufacturer. and gusts emphasizes the consequences of an increase in
Deviations from the recommendations can result in structural the gross weight of an aircraft. The structure of an aircraft
damage or complete failure of the aircraft’s structure. Even about to undergo a load factor of 3 Gs, as in recovery from
if an aircraft is loaded well within the maximum weight a steep dive, must be prepared to withstand an added load
limitations, it is imperative that weight distribution be of 300 pounds for each 100-pound increase in weight. It
within the limits of CG location. The preceding brief study should be noted that this would be imposed by the addition
of aerodynamics and load factors points out the reasons for of about 16 gallons of unneeded fuel in a particular aircraft.
this precaution. The following discussion is background FAA-certificated civil aircraft have been analyzed structurally
information into some of the reasons why weight and balance and tested for flight at the maximum gross weight authorized
conditions are important to the safe flight of an aircraft. and within the speeds posted for the type of flights to be
performed. Flights at weights in excess of this amount are
In some aircraft, it is not possible to fill all seats, baggage quite possible and often are well within the performance
compartments, and fuel tanks, and still remain within capabilities of an aircraft. This fact should not mislead the
approved weight or balance limits. For example, in several pilot, as the pilot may not realize that loads for which the
popular four-place aircraft, the fuel tanks may not be filled to aircraft was not designed are being imposed on all or some
capacity when four occupants and their baggage are carried. part of the structure.
In a certain two-place aircraft, no baggage may be carried
in the compartment aft of the seats when spins are to be In loading an aircraft with either passengers or cargo, the
practiced. It is important for a pilot to be aware of the weight structure must be considered. Seats, baggage compartments,
and balance limitations of the aircraft being flown and the and cabin floors are designed for a certain load or
reasons for these limitations. concentration of load and no more. For example, a light

4-37

plane baggage compartment may be placarded for 20 pounds cruise speed. Theoretically, a neutral load on the tail surfaces
because of the limited strength of its supporting structure in cruising flight would produce the most efficient overall
even though the aircraft may not be overloaded or out of CG performance and fastest cruising speed, but it would also
limits with more weight at that location. result in instability. Modern aircraft are designed to require
a down load on the tail for stability and controllability.
Effect of Weight on Stability and Controllability
Overloading also effects stability. An aircraft that is stable A zero indication on the trim tab control is not necessarily
and controllable when loaded normally may have very the same as “neutral trim” because of the force exerted
different flight characteristics when overloaded. Although by downwash from the wings and the fuselage on the tail
the distribution of weight has the most direct effect on this, surfaces.
an increase in the aircraft’s gross weight may be expected
to have an adverse effect on stability, regardless of location The effects of the distribution of the aircraft’s useful load
of the CG. The stability of many certificated aircraft is have a significant influence on its flight characteristics, even
completely unsatisfactory if the gross weight is exceeded. when the load is within the CG limits and the maximum
permissible gross weight. Important among these effects
Effect of Load Distribution are changes in controllability, stability, and the actual load
The effect of the position of the CG on the load imposed imposed on the wing.
on an aircraft’s wing in flight is significant to climb and
cruising performance. An aircraft with forward loading is Generally, an aircraft becomes less controllable, especially
“heavier” and consequently, slower than the same aircraft at slow flight speeds, as the CG is moved further aft. An
with the CG further aft. aircraft which cleanly recovers from a prolonged spin with
the CG at one position may fail completely to respond to
Figure 4-55 illustrates why this is true. With forward loading, normal recovery attempts when the CG is moved aft by one
“nose-up” trim is required in most aircraft to maintain level or two inches.
cruising flight. Nose-up trim involves setting the tail surfaces
to produce a greater down load on the aft portion of the It is common practice for aircraft designers to establish an aft
fuselage, which adds to the wing loading and the total lift CG limit that is within one inch of the maximum which allows
required from the wing if altitude is to be maintained. This normal recovery from a one-turn spin. When certificating an
requires a higher AOA of the wing, which results in more aircraft in the utility category to permit intentional spins, the
drag and, in turn, produces a higher stalling speed. aft CG limit is usually established at a point several inches
forward of that permissible for certification in the normal
Load imposed by tail category.

Gross weight Another factor affecting controllability, which has become
more important in current designs of large aircraft, is the effect
CG of long moment arms to the positions of heavy equipment
and cargo. The same aircraft may be loaded to maximum
Forward CG Center of lift Stronger gross weight within its CG limits by concentrating fuel,
Down load on tail passengers, and cargo near the design CG, or by dispersing
fuel and cargo loads in wingtip tanks and cargo bins forward
Load imposed by tail and aft of the cabin.

Gross weight

CG Lighter With the same total weight and CG, maneuvering the
Down load on tail aircraft or maintaining level flight in turbulent air requires
AFT CG the application of greater control forces when the load is
dispersed. The longer moment arms to the positions of the
Figure 4-55. Effect of load distribution on balance. heavy fuel and cargo loads must be overcome by the action
of the control surfaces. An aircraft with full outboard wing
With aft loading and “nose-down” trim, the tail surfaces exert tanks or tip tanks tends to be sluggish in roll when control
less down load, relieving the wing of that much wing loading situations are marginal, while one with full nose and aft cargo
and lift required to maintain altitude. The required AOA bins tends to be less responsive to the elevator controls.
of the wing is less, so the drag is less, allowing for a faster

4-38

The rearward CG limit of an aircraft is determined largely • The aircraft cruises faster with an aft CG location
by considerations of stability. The original airworthiness because of reduced drag. The drag is reduced because
requirements for a type certificate specify that an aircraft in a smaller AOA and less downward deflection of the
flight at a certain speed dampens out vertical displacement of stabilizer are required to support the aircraft and
the nose within a certain number of oscillations. An aircraft overcome the nose-down pitching tendency.
loaded too far rearward may not do this. Instead, when the
nose is momentarily pulled up, it may alternately climb and • The aircraft becomes less stable as the CG is moved
dive becoming steeper with each oscillation. This instability rearward. This is because when the CG is moved
is not only uncomfortable to occupants, but it could even rearward it causes an increase in the AOA. Therefore,
become dangerous by making the aircraft unmanageable the wing contribution to the aircraft’s stability is
under certain conditions. now decreased, while the tail contribution is still
stabilizing. When the point is reached that the wing
The recovery from a stall in any aircraft becomes progressively and tail contributions balance, then neutral stability
more difficult as its CG moves aft. This is particularly exists. Any CG movement further aft results in an
important in spin recovery, as there is a point in rearward unstable aircraft.
loading of any aircraft at which a “flat” spin develops. A
flat spin is one in which centrifugal force, acting through a • A forward CG location increases the need for greater
CG located well to the rear, pulls the tail of the aircraft out back elevator pressure. The elevator may no longer
away from the axis of the spin, making it impossible to get be able to oppose any increase in nose-down pitching.
the nose down and recover. Adequate elevator control is needed to control the
aircraft throughout the airspeed range down to the
An aircraft loaded to the rear limit of its permissible CG stall.
range handles differently in turns and stall maneuvers and
has different landing characteristics than when it is loaded A detailed discussion and additional information relating to
near the forward limit. weight and balance can be found in Chapter 9, Weight and
Balance.
The forward CG limit is determined by a number of
considerations. As a safety measure, it is required that the High Speed Flight
trimming device, whether tab or adjustable stabilizer, be
capable of holding the aircraft in a normal glide with the Subsonic Versus Supersonic Flow
power off. A conventional aircraft must be capable of a full In subsonic aerodynamics, the theory of lift is based upon the
stall, power-off landing in order to ensure minimum landing forces generated on a body and a moving gas (air) in which
speed in emergencies. A tailwheel-type aircraft loaded it is immersed. At speeds of approximately 260 knots, air
excessively nose-heavy is difficult to taxi, particularly in can be considered incompressible in that, at a fixed altitude,
high winds. It can be nosed over easily by use of the brakes, its density remains nearly constant while its pressure varies.
and it is difficult to land without bouncing since it tends to Under this assumption, air acts the same as water and is
pitch down on the wheels as it is slowed down and flared classified as a fluid. Subsonic aerodynamic theory also
for landing. Steering difficulties on the ground may occur in assumes the effects of viscosity (the property of a fluid that
nosewheel-type aircraft, particularly during the landing roll tends to prevent motion of one part of the fluid with respect
and takeoff. To summarize the effects of load distribution: to another) are negligible, and classifies air as an ideal fluid,
conforming to the principles of ideal-fluid aerodynamics such
• The CG position influences the lift and AOA of the as continuity, Bernoulli’s principle, and circulation.
wing, the amount and direction of force on the tail,
and the degree of deflection of the stabilizer needed In reality, air is compressible and viscous. While the effects of
to supply the proper tail force for equilibrium. The these properties are negligible at low speeds, compressibility
latter is very important because of its relationship to effects in particular become increasingly important as speed
elevator control force. increases. Compressibility (and to a lesser extent viscosity) is
of paramount importance at speeds approaching the speed of
• The aircraft stalls at a higher speed with a forward CG sound. In these speed ranges, compressibility causes a change
location. This is because the stalling AOA is reached in the density of the air around an aircraft.
at a higher speed due to increased wing loading.
During flight, a wing produces lift by accelerating the airflow
• Higher elevator control forces normally exist with a over the upper surface. This accelerated air can, and does,
forward CG location due to the increased stabilizer reach sonic speeds even though the aircraft itself may be
deflection required to balance the aircraft. flying subsonic. At some extreme AOAs, in some aircraft,

4-39

the speed of the air over the top surface of the wing may be the boundary between subsonic and transonic flight and is
double the aircraft’s speed. It is therefore entirely possible largely dependent on the wing and airfoil design. Critical
to have both supersonic and subsonic airflow on an aircraft Mach number is an important point in transonic flight. When
at the same time. When flow velocities reach sonic speeds at shock waves form on the aircraft, airflow separation followed
some location on an aircraft (such as the area of maximum by buffet and aircraft control difficulties can occur. Shock
camber on the wing), further acceleration results in the onset waves, buffet, and airflow separation take place above critical
of compressibility effects such as shock wave formation, Mach number. A jet aircraft typically is most efficient when
drag increase, buffeting, stability, and control difficulties. cruising at or near its critical Mach number. At speeds 5–10
Subsonic flow principles are invalid at all speeds above this percent above the critical Mach number, compressibility
point. [Figure 4-56] Wing airflow effects begin. Drag begins to rise sharply. Associated with
the “drag rise” are buffet, trim and stability changes, and a
M = 0.50 decrease in control surface effectiveness. This is the point
of “drag divergence.” [Figure 4-57]

Maximum local velocity is less than sonic
Critical Mach number

M = 0.72 S
M = 0.77 CD (Drag coefficient)
Maximum local velocity equal to sonic Force divergence Mach number
CL= 0.3 Critical Mach number
upefrlsoownic Normal shock wave

Subsonic Possible separation

Figure 4-56. Wing airflow. 0.5 1.0
M (Mach number)
Speed Ranges
The speed of sound varies with temperature. Under standard Figure 4-57. Critical Mach.
temperature conditions of 15 °C, the speed of sound at sea
level is 661 knots. At 40,000 feet, where the temperature is VMO/MMO is defined as the maximum operating limit speed.
–55 °C, the speed of sound decreases to 574 knots. In high- VMO is expressed in knots calibrated airspeed (KCAS), while
speed flight and/or high-altitude flight, the measurement of MMO is expressed in Mach number. The VMO limit is usually
speed is expressed in terms of a “Mach number”—the ratio associated with operations at lower altitudes and deals with
of the true airspeed of the aircraft to the speed of sound in structural loads and flutter. The MMO limit is associated with
the same atmospheric conditions. An aircraft traveling at operations at higher altitudes and is usually more concerned
the speed of sound is traveling at Mach 1.0. Aircraft speed with compressibility effects and flutter. At lower altitudes,
regimes are defined approximately as follows: structural loads and flutter are of concern; at higher altitudes,
compressibility effects and flutter are of concern.
Subsonic—Mach numbers below 0.75
Adherence to these speeds prevents structural problems due
Transonic—Mach numbers from 0.75 to 1.20 to dynamic pressure or flutter, degradation in aircraft control
response due to compressibility effects (e.g., Mach Tuck,
Supersonic—Mach numbers from 1.20 to 5.00 aileron reversal, or buzz), and separated airflow due to shock
waves resulting in loss of lift or vibration and buffet. Any of
Hypersonic—Mach numbers above 5.00 these phenomena could prevent the pilot from being able to
adequately control the aircraft.
While flights in the transonic and supersonic ranges are
common occurrences for military aircraft, civilian jet aircraft For example, an early civilian jet aircraft had a VMO limit of
normally operate in a cruise speed range of Mach 0.7 to 306 KCAS up to approximately FL 310 (on a standard day).
Mach 0.90. At this altitude (FL 310), an MMO of 0.82 was approximately
equal to 306 KCAS. Above this altitude, an MMO of 0.82
The speed of an aircraft in which airflow over any part of always equaled a KCAS less than 306 KCAS and, thus,
the aircraft or structure under consideration first reaches
(but does not exceed) Mach 1.0 is termed “critical Mach
number” or “Mach Crit.” Thus, critical Mach number is

4-40

became the operating limit as you could not reach the VMO the earlier discussion that the speed of sound is decreasing
limit without first reaching the MMO limit. For example, at with the drop in temperature as the aircraft climbs. The Mach
FL 380, an MMO of 0.82 is equal to 261 KCAS. number is simply the ratio of the true airspeed to the speed
of sound at flight conditions. The significance of this is that
Mach Number Versus Airspeed at a constant Mach number climb, the KCAS (and KTAS or
It is important to understand how airspeed varies with Mach KIAS as well) is falling off.
number. As an example, consider how the stall speed of a
jet transport aircraft varies with an increase in altitude. The If the aircraft climbed high enough at this constant MMO
increase in altitude results in a corresponding drop in air with decreasing KIAS, KCAS, and KTAS, it would begin to
density and outside temperature. Suppose this jet transport approach its stall speed. At some point the stall speed of the
is in the clean configuration (gear and flaps up) and weighs aircraft in Mach number could equal the MMO of the aircraft,
550,000 pounds. The aircraft might stall at approximately and the pilot could neither slow up (without stalling) nor
152 KCAS at sea level. This is equal to (on a standard day) speed up (without exceeding the max operating speed of the
a true velocity of 152 KTAS and a Mach number of 0.23. aircraft). This has been dubbed the “coffin corner.”
At FL 380, the aircraft will still stall at approximately 152
KCAS but the true velocity is about 287 KTAS with a Mach Boundary Layer
number of 0.50. The viscous nature of airflow reduces the local velocities on
a surface and is responsible for skin friction. As discussed
Although the stalling speed has remained the same for our earlier in the chapter, the layer of air over the wing’s surface
purposes, both the Mach number and TAS have increased. that is slowed down or stopped by viscosity, is the boundary
With increasing altitude, the air density has decreased; this layer. There are two different types of boundary layer flow:
requires a faster true airspeed in order to have the same laminar and turbulent.
pressure sensed by the pitot tube for the same KCAS or KIAS
(for our purposes, KCAS and KIAS are relatively close to Laminar Boundary Layer Flow
each other). The dynamic pressure the wing experiences at The laminar boundary layer is a very smooth flow, while
FL 380 at 287 KTAS is the same as at sea level at 152 KTAS. the turbulent boundary layer contains swirls or “eddies.”
However, it is flying at higher Mach number. The laminar flow creates less skin friction drag than the
turbulent flow, but is less stable. Boundary layer flow over
Another factor to consider is the speed of sound. A decrease a wing surface begins as a smooth laminar flow. As the flow
in temperature in a gas results in a decrease in the speed of continues back from the leading edge, the laminar boundary
sound. Thus, as the aircraft climbs in altitude with outside layer increases in thickness.
temperature dropping, the speed of sound is dropping. At
sea level, the speed of sound is approximately 661 KCAS, Turbulent Boundary Layer Flow
while at FL 380 it is 574 KCAS. Thus, for our jet transport At some distance back from the leading edge, the smooth
aircraft, the stall speed (in KTAS) has gone from 152 at sea laminar flow breaks down and transitions to a turbulent flow.
level to 287 at FL 380. Simultaneously, the speed of sound From a drag standpoint, it is advisable to have the transition
(in KCAS) has decreased from 661 to 574 and the Mach from laminar to turbulent flow as far aft on the wing as
number has increased from 0.23 (152 KTAS divided by 661 possible, or have a large amount of the wing surface within
KTAS) to 0.50 (287 KTAS divided by 574 KTAS). All the the laminar portion of the boundary layer. The low energy
while the KCAS for stall has remained constant at 152. This laminar flow, however, tends to break down more suddenly
describes what happens when the aircraft is at a constant than the turbulent layer.
KCAS with increasing altitude, but what happens when the
pilot keeps Mach constant during the climb? In normal jet Boundary Layer Separation
flight operations, the climb is at 250 KIAS (or higher (e.g. Another phenomenon associated with viscous flow is
heavy)) to 10,000 feet and then at a specified en route climb separation. Separation occurs when the airflow breaks away
airspeed (such as about 330 if a DC10) until reaching an from an airfoil. The natural progression is from laminar
altitude in the “mid-twenties” where the pilot then climbs at boundary layer to turbulent boundary layer and then to
a constant Mach number to cruise altitude. airflow separation. Airflow separation produces high drag
and ultimately destroys lift. The boundary layer separation
Assuming for illustration purposes that the pilot climbs at a point moves forward on the wing as the AOA is increased.
MMO of 0.82 from sea level up to FL 380. KCAS goes from [Figure 4-58]
543 to 261. The KIAS at each altitude would follow the
same behavior and just differ by a few knots. Recall from

4-41

Turbulent boundary layer

Transition region
Laminar boundary layer

Laminar sublayer

Figure 4-58. Boundary layer. Whenever a shock wave forms perpendicular to the airflow, it
is termed a “normal” shock wave, and the flow immediately
Vortex generators are used to delay or prevent shock wave behind the wave is subsonic. A supersonic airstream passing
induced boundary layer separation encountered in transonic through a normal shock wave experiences these changes:
flight. They are small low aspect ratio airfoils placed at a 12°
to 15° AOA to the airstream. Usually spaced a few inches • The airstream is slowed to subsonic.
apart along the wing ahead of the ailerons or other control
surfaces, vortex generators create a vortex which mixes the • The airflow immediately behind the shock wave does
boundary airflow with the high energy airflow just above the not change direction.
surface. This produces higher surface velocities and increases
the energy of the boundary layer. Thus, a stronger shock wave • The static pressure and density of the airstream behind
is necessary to produce airflow separation. the wave is greatly increased.

Shock Waves • The energy of the airstream (indicated by total
When an airplane flies at subsonic speeds, the air ahead is pressure—dynamic plus static) is greatly reduced.
“warned” of the airplane’s coming by a pressure change
transmitted ahead of the airplane at the speed of sound. Shock wave formation causes an increase in drag. One of
Because of this warning, the air begins to move aside before the principal effects of a shock wave is the formation of a
the airplane arrives and is prepared to let it pass easily. When dense high pressure region immediately behind the wave.
the airplane’s speed reaches the speed of sound, the pressure The instability of the high pressure region, and the fact that
change can no longer warn the air ahead because the airplane part of the velocity energy of the airstream is converted to
is keeping up with its own pressure waves. Rather, the air heat as it flows through the wave is a contributing factor
particles pile up in front of the airplane causing a sharp in the drag increase, but the drag resulting from airflow
decrease in the flow velocity directly in front of the airplane separation is much greater. If the shock wave is strong,
with a corresponding increase in air pressure and density. the boundary layer may not have sufficient kinetic energy
to withstand airflow separation. The drag incurred in the
As the airplane’s speed increases beyond the speed of sound, transonic region due to shock wave formation and airflow
the pressure and density of the compressed air ahead of it separation is known as “wave drag.” When speed exceeds
increase, the area of compression extending some distance the critical Mach number by about 10 percent, wave drag
ahead of the airplane. At some point in the airstream, the air increases sharply. A considerable increase in thrust (power)
particles are completely undisturbed, having had no advanced is required to increase flight speed beyond this point into the
warning of the airplane’s approach, and in the next instant the supersonic range where, depending on the airfoil shape and
same air particles are forced to undergo sudden and drastic the angle of attack, the boundary layer may reattach.
changes in temperature, pressure, density, and velocity.
The boundary between the undisturbed air and the region Normal shock waves form on the wing’s upper surface and
of compressed air is called a shock or “compression” wave. form an additional area of supersonic flow and a normal shock
This same type of wave is formed whenever a supersonic wave on the lower surface. As flight speed approaches the
airstream is slowed to subsonic without a change in direction, speed of sound, the areas of supersonic flow enlarge and the
such as when the airstream is accelerated to sonic speed shock waves move nearer the trailing edge. [Figure 4-59]
over the cambered portion of a wing, and then decelerated
to subsonic speed as the area of maximum camber is passed. Associated with “drag rise” are buffet (known as Mach
A shock wave forms as a boundary between the supersonic buffet), trim and stability changes, and a decrease in control
and subsonic ranges.

4-42

Shock waves

upersonic flow Normal shock wave

S

M = 0.82

Normal shock wave

Supersonic flow

M = 0.95

M = 1.05 Bow wave Spanwise flow Airspeed sensed by wing Mach 0.70
Subsonic airflow
True airspeed Mach 0.85Figure 4-60. Sweepback effect.
Figure 4-59. Shock waves. the effect of persuading the wing into believing that it is flying
slower than it really is; thus the formation of shock waves is
force effectiveness. The loss of lift due to airflow separation delayed. Advantages of wing sweep include an increase in
results in a loss of downwash, and a change in the position of critical Mach number, force divergence Mach number, and
the center pressure on the wing. Airflow separation produces the Mach number at which drag rises peaks. In other words,
a turbulent wake behind the wing, which causes the tail sweep delays the onset of compressibility effects.
surfaces to buffet (vibrate). The nose-up and nose-down pitch
control provided by the horizontal tail is dependent on the
downwash behind the wing. Thus, an increase in downwash
decreases the horizontal tail’s pitch control effectiveness
since it effectively increases the angle of attack that the tail
surface is seeing. Movement of the wing CP affects the wing
pitching moment. If the CP moves aft, a diving moment
referred to as “Mach tuck” or “tuck under” is produced,
and if it moves forward, a nose-up moment is produced.
This is the primary reason for the development of the T-tail
configuration on many turbine-powered aircraft, which
places the horizontal stabilizer as far as practical from the
turbulence of the wings.

Sweepback The Mach number, which produces a sharp change in drag
Most of the difficulties of transonic flight are associated with coefficient, is termed the “force divergence” Mach number
shock wave induced flow separation. Therefore, any means of and, for most airfoils, usually exceeds the critical Mach
delaying or alleviating the shock induced separation improves number by 5 to 10 percent. At this speed, the airflow separation
aerodynamic performance. One method is wing sweepback. induced by shock wave formation can create significant
Sweepback theory is based upon the concept that it is only the variations in the drag, lift, or pitching moment coefficients.
component of the airflow perpendicular to the leading edge In addition to the delay of the onset of compressibility effects,
of the wing that affects pressure distribution and formation sweepback reduces the magnitude in the changes of drag, lift
of shock waves. [Figure 4-60] or moment coefficients. In other words, the use of sweepback
“softens” the force divergence.
On a straight wing aircraft, the airflow strikes the wing
leading edge at 90°, and its full impact produces pressure and
lift. A wing with sweepback is struck by the same airflow at
an angle smaller than 90°. This airflow on the swept wing has

4-43

A disadvantage of swept wings is that they tend to stall at the descending flightpath with no change in pitch attitude, further
wingtips rather than at the wing roots. [Figure 4-61] This is increasing the AOA. In this situation, without reliable AOA
because the boundary layer tends to flow spanwise toward the information, a nose-down pitch attitude with an increasing
tips and to separate near the leading edges. Because the tips of airspeed is no guarantee that recovery has been effected,
a swept wing are on the aft part of the wing (behind the CL), and up-elevator movement at this stage may merely keep
a wingtip stall causes the CL to move forward on the wing, the aircraft stalled.
forcing the nose to rise further. The tendency for tip stall is
greatest when wing sweep and taper are combined.

Prestall

Intitial stall area

Stalled

Figure 4-62. T-tail stall.

Figure 4-61. Wingtip stall. It is a characteristic of T-tail aircraft to pitch up viciously
when stalled in extreme nose-high attitudes, making
The stall situation can be aggravated by a T-tail configuration, recovery difficult or violent. The stick pusher inhibits this
which affords little or no pre-stall warning in the form of type of stall. At approximately one knot above stall speed,
tail control surface buffet. [Figure 4-62] The T-tail, being pre-programmed stick forces automatically move the stick
above the wing wake remains effective even after the wing forward, preventing the stall from developing. A G-limiter
has begun to stall, allowing the pilot to inadvertently drive may also be incorporated into the system to prevent the pitch
the wing into a deeper stall at a much greater AOA. If the down generated by the stick pusher from imposing excessive
horizontal tail surfaces then become buried in the wing’s loads on the aircraft. A “stick shaker,” on the other hand
wake, the elevator may lose all effectiveness, making it provides stall warning when the airspeed is five to seven
impossible to reduce pitch attitude and break the stall. In percent above stall speed.
the pre-stall and immediate post-stall regimes, the lift/drag
qualities of a swept wing aircraft (specifically the enormous Mach Buffet Boundaries
increase in drag at low speeds) can cause an increasingly Mach buffet is a function of the speed of the airflow over the
wing—not necessarily the speed of the aircraft. Any time that
too great a lift demand is made on the wing, whether from too
fast an airspeed or from too high an AOA near the MMO, the
“high-speed” buffet occurs. There are also occasions when
the buffet can be experienced at much lower speeds known
as the “low-speed Mach buffet.”

An aircraft flown at a speed too slow for its weight and
altitude necessitating a high AOA is the most likely situation

4-44



















sideward lift that moves the tail to the right and yaws the nose When both rudder and elevator controls are moved by the
of the airplane to the left. Rudder effectiveness increases with pilot, a control mixing mechanism moves each surface the
speed; therefore, large deflections at low speeds and small appropriate amount. The control system for the V-tail is
deflections at high speeds may be required to provide the more complex than that required for a conventional tail. In
desired reaction. In propeller-driven aircraft, any slipstream addition, the V-tail design is more susceptible to Dutch roll
flowing over the rudder increases its effectiveness. tendencies than a conventional tail, and total reduction in
drag is minimal.
Yaw
Secondary Flight Controls
Secondary flight control systems may consist of wing flaps,
leading edge devices, spoilers, and trim systems.

CG Left rudder forward Flaps
Flaps are the most common high-lift devices used on aircraft.

These surfaces, which are attached to the trailing edge of

the wing, increase both lift and induced drag for any given

AOA. Flaps allow a compromise between high cruising speed

and low landing speed, because they may be extended when

needed, and retracted into the wing’s structure when not

needed. There are four common types of flaps: plain, split,

slotted, and Fowler flaps. [Figure 5-17]

Left rudder Aerodynamic force The plain flap is the simplest of the four types. It increases
the airfoil camber, resulting in a significant increase in the
FFiigguurree55-1-151. .TThheeefeffefcetctoof fleleftftrruuddddeerrpprreessssuurree.. coefficient of lift (CL) at a given AOA. At the same time,
it greatly increases drag and moves the center of pressure
V-Tail (CP) aft on the airfoil, resulting in a nose-down pitching
moment.
The V-tail design utilizes two slanted tail surfaces to perform
the same functions as the surfaces of a conventional elevator The split flap is deflected from the lower surface of the airfoil
and rudder configuration. The fixed surfaces act as both and produces a slightly greater increase in lift than the plain
horizontal and vertical stabilizers. [Figure 5-16] flap. More drag is created because of the turbulent air pattern
produced behind the airfoil. When fully extended, both plain
and split flaps produce high drag with little additional lift.

Figure 5-16. Beechcraft Bonanza V35. The most popular flap on aircraft today is the slotted flap.
Variations of this design are used for small aircraft, as well
The movable surfaces, which are usually called ruddervators, as for large ones. Slotted flaps increase the lift coefficient
are connected through a special linkage that allows the control significantly more than plain or split flaps. On small aircraft,
wheel to move both surfaces simultaneously. On the other the hinge is located below the lower surface of the flap, and
hand, displacement of the rudder pedals moves the surfaces when the flap is lowered, a duct forms between the flap well
differentially, thereby providing directional control. in the wing and the leading edge of the flap. When the slotted
flap is lowered, high energy air from the lower surface is
ducted to the flap’s upper surface. The high energy air from
the slot accelerates the upper surface boundary layer and
delays airflow separation, providing a higher CL. Thus, the
slotted flap produces much greater increases in maximum
coefficient of lift (CL-MAX) than the plain or split flap. While
there are many types of slotted flaps, large aircraft often
have double- and even triple-slotted flaps. These allow the
maximum increase in drag without the airflow over the flaps
separating and destroying the lift they produce.

5-8

Basic section Leading Edge Devices
Plain flap High-lift devices also can be applied to the leading edge of
Split flap the airfoil. The most common types are fixed slots, movable
slats, leading edge flaps, and cuffs. [Figure 5-18]

Fixed slot

Movable slot

Slotted flap Leading edge flap

Fowler flap

Leading edge cuff

Slotted Fowler flap

Figure 5-18. Leading edge high lift devices.

Figure 5-17. Five common types of flaps. Fixed slots direct airflow to the upper wing surface and delay
airflow separation at higher angles of attack. The slot does
Fowler flaps are a type of slotted flap. This flap design not not increase the wing camber, but allows a higher maximum
only changes the camber of the wing, it also increases the CL because the stall is delayed until the wing reaches a
wing area. Instead of rotating down on a hinge, it slides greater AOA.
backwards on tracks. In the first portion of its extension, it
increases the drag very little, but increases the lift a great deal Movable slats consist of leading edge segments, which move
as it increases both the area and camber. As the extension on tracks. At low angles of attack, each slat is held flush
continues, the flap deflects downward. During the last portion against the wing’s leading edge by the high pressure that forms
of its travel, the flap increases the drag with little additional at the wing’s leading edge. As the AOA increases, the high-
increase in lift. pressure area moves aft below the lower surface of the wing,
allowing the slats to move forward. Some slats, however, are

5-9

pilot operated and can be deployed at any AOA. Opening a
slat allows the air below the wing to flow over the wing’s
upper surface, delaying airflow separation.

Leading edge flaps, like trailing edge flaps, are used to
increase both CL-MAX and the camber of the wings. This type
of leading edge device is frequently used in conjunction with
trailing edge flaps and can reduce the nose-down pitching
movement produced by the latter. As is true with trailing edge
flaps, a small increment of leading edge flaps increases lift to
a much greater extent than drag. As greater amounts of flaps
are extended, drag increases at a greater rate than lift.

Leading edge cuffs, like leading edge flaps and trailing edge Figure 5-19. Spoilers reduce lift and increase drag during descent
flaps are used to increase both CL-MAX and the camber of and landing.
the wings. Unlike leading edge flaps and trailing edge flaps,
leading edge cuffs are fixed aerodynamic devices. In most tabs, balance tabs, antiservo tabs, ground adjustable tabs, and
cases leading edge cuffs extend the leading edge down and an adjustable stabilizer.
forward. This causes the airflow to attach better to the upper
surface of the wing at higher angles of attack, thus lowering Trim Tabs
an aircraft’s stall speed. The fixed nature of leading edge The most common installation on small aircraft is a single
cuffs extracts a penalty in maximum cruise airspeed, but trim tab attached to the trailing edge of the elevator. Most trim
recent advances in design and technology have reduced this tabs are manually operated by a small, vertically mounted
penalty. control wheel. However, a trim crank may be found in some
aircraft. The flight deck control includes a trim tab position
Spoilers indicator. Placing the trim control in the full nose-down
position moves the trim tab to its full up position. With
Found on many gliders and some aircraft, high drag devices the trim tab up and into the airstream, the airflow over the
called spoilers are deployed from the wings to spoil the smooth horizontal tail surface tends to force the trailing edge of the
airflow, reducing lift and increasing drag. On gliders, spoilers elevator down. This causes the tail of the airplane to move
are most often used to control rate of descent for accurate up, and the nose to move down. [Figure 5-20]
landings. On other aircraft, spoilers are often used for roll
control, an advantage of which is the elimination of adverse If the trim tab is set to the full nose-up position, the tab moves
yaw. To turn right, for example, the spoiler on the right wing to its full down position. In this case, the air flowing under
is raised, destroying some of the lift and creating more drag on the horizontal tail surface hits the tab and forces the trailing
the right. The right wing drops, and the aircraft banks and yaws edge of the elevator up, reducing the elevator’s AOA. This
to the right. Deploying spoilers on both wings at the same time causes the tail of the airplane to move down, and the nose
allows the aircraft to descend without gaining speed. Spoilers to move up.
are also deployed to help reduce ground roll after landing. By
destroying lift, they transfer weight to the wheels, improving In spite of the opposing directional movement of the trim
braking effectiveness. [Figure 5-19] tab and the elevator, control of trim is natural to a pilot. If
the pilot needs to exert constant back pressure on a control
Trim Systems column, the need for nose-up trim is indicated. The normal
Although an aircraft can be operated throughout a wide range trim procedure is to continue trimming until the aircraft is
of attitudes, airspeeds, and power settings, it can be designed balanced and the nose-heavy condition is no longer apparent.
to fly hands-off within only a very limited combination of Pilots normally establish the desired power, pitch attitude,
these variables. Trim systems are used to relieve the pilot of and configuration first, and then trim the aircraft to relieve
the need to maintain constant pressure on the flight controls, control pressures that may exist for that flight condition.
and usually consist of flight deck controls and small hinged Any time power, pitch attitude, or configuration is changed,
devices attached to the trailing edge of one or more of the expect that retrimming will be necessary to relieve the control
primary flight control surfaces. Designed to help minimize pressures for the new flight condition.
a pilot’s workload, trim systems aerodynamically assist
movement and position of the flight control surface to which
they are attached. Common types of trim systems include trim

5-10

Elevator Nose-down trim stabilator moves up, the linkage forces the trailing edge of the
Trim tab tab up. When the stabilator moves down, the tab also moves
down. Conversely, trim tabs on elevators move opposite of
the control surface. [Figure 5-21]

Tab up—elevator down

Nose-up trim

Elevator Stabilator
Pivot point
Trim tab

Antiservo tab

Tab down—elevator up

Figure 5-20. The movement of the elevator is opposite to the FFiigguurree55--2117. .AAnnaanntitsiesrevrovotatabbaatttetmemptpsttsotostsrteraemamlinlienethtehecontrol
scuornfatrcoelasundrfiascuesaedndtoismuaskeedthtoe smtaabkielatthoer lsetsasbsileantsoitrivleesbsyseonpspiotisvieng
dFiriegcutiroen5o-f1m6o. vTehmeemntoovfetmheenelteovfattohreterliemvatatobr. is opposite to the tbhyeofoprpcoeseinxgerttheed fboyrctheeexpeilrotet.d by the pilot.

Bdairleacntiocne oTfambosvement of the elevator trim tab. Ground Adjustable Tabs
Many small aircraft have a nonmovable metal trim tab on the
The control forces may be excessively high in some aircraft, rudder. This tab is bent in one direction or the other while on
and, in order to decrease them, the manufacturer may use the ground to apply a trim force to the rudder. The correct
balance tabs. They look like trim tabs and are hinged in displacement is determined by trial and error. Usually, small
approximately the same places as trim tabs. The essential adjustments are necessary until the aircraft no longer skids
difference between the two is that the balancing tab is coupled left or right during normal cruising flight. [Figure 5-22]
to the control surface rod so that when the primary control
surface is moved in any direction, the tab automatically
moves in the opposite direction. The airflow striking the tab
counterbalances some of the air pressure against the primary
control surface, and enables the pilot to move more easily
and hold the control surface in position.

If the linkage between the balance tab and the fixed surface is
adjustable from the flight deck, the tab acts as a combination
trim and balance tab that can be adjusted to any desired
deflection.

Antiservo Tabs Figure 5-22. A ground adjustable tab is used on the rudder of many
small airplanes to correct for a tendency to fly with the fuselage
Antiservo tabs work in the same manner as balance tabs slightly misaligned with the relative wind.
except, instead of moving in the opposite direction, they move
in the same direction as the trailing edge of the stabilator.
In addition to decreasing the sensitivity of the stabilator, an
antiservo tab also functions as a trim device to relieve control
pressure and maintain the stabilator in the desired position.
The fixed end of the linkage is on the opposite side of the
surface from the horn on the tab; when the trailing edge of the

5-11

Adjustable Stabilizer
Rather than using a movable tab on the trailing edge of the
elevator, some aircraft have an adjustable stabilizer. With this
arrangement, linkages pivot the horizontal stabilizer about its
rear spar. This is accomplished by use of a jackscrew mounted
on the leading edge of the stabilator. [Figure 5-23]

Adjustable stabilizer

Nose down Jackscrew
Nose up

Pivot Figure 5-24. Basic autopilot system integrated into the flight
control system.
Trim motor or trim cable
The autopilot system also incorporates a disconnect safety
FiFgiugruer5e-523-1. 9So. mSoemaierpaliarpnleasn, einsc, ilnucdliundginmgosmt ojestttjreatntsrapnorstpso, rutsse, an feature to disengage the system automatically or manually.
adujsuesatanbaledsjutasbtailbizleersttaobpirliozveirdteotphreorveidqueitrheed rpeiqtcuhirterdimpiftocrhctersi.m These autopilots work with inertial navigation systems,
global positioning systems (GPS), and flight computers to
forces. control the aircraft. In fly-by-wire systems, the autopilot is
an integrated component.
On small aircraft, the jackscrew is cable operated with a trim
wheel or crank. On larger aircraft, it is motor driven. The Additionally, autopilots can be manually overridden. Because
trimming effect and flight deck indications for an adjustable autopilot systems differ widely in their operation, refer to the
stabilizer are similar to those of a trim tab. autopilot operating instructions in the Airplane Flight Manual
(AFM) or the Pilot’s Operating Handbook (POH).
Autopilot
Chapter Summary
Autopilot is an automatic flight control system that keeps an
aircraft in level flight or on a set course. It can be directed by Because flight control systems and aerodynamic characteristics
the pilot, or it may be coupled to a radio navigation signal. vary greatly between aircraft, it is essential that a pilot
Autopilot reduces the physical and mental demands on a pilot become familiar with the primary and secondary flight
and increases safety. The common features available on an control systems of the aircraft being flown. The primary
autopilot are altitude and heading hold. source of this information is the AFM or the POH. Various
manufacturer and owner group websites can also be a
The simplest systems use gyroscopic attitude indicators and valuable source of additional information.
magnetic compasses to control servos connected to the flight
control system. [Figure 5-24] The number and location of
these servos depends on the complexity of the system. For
example, a single-axis autopilot controls the aircraft about the
longitudinal axis and a servo actuates the ailerons. A three-
axis autopilot controls the aircraft about the longitudinal,
lateral, and vertical axes. Three different servos actuate
ailerons, elevator, and rudder. More advanced systems often
include a vertical speed and/or indicated airspeed hold mode.
Advanced autopilot systems are coupled to navigational aids
through a flight director.

5-12

AChaiptrerc6 raft Systems

Introduction

This chapter covers the primary systems found on most
aircraft. These include the engine, propeller, induction,
ignition, as well as the fuel, lubrication, cooling, electrical,
landing gear, and environmental control systems.

Powerplant

An aircraft engine, or powerplant, produces thrust to propel
an aircraft. Reciprocating engines and turboprop engines
work in combination with a propeller to produce thrust.
Turbojet and turbofan engines produce thrust by increasing
the velocity of air flowing through the engine. All of these
powerplants also drive the various systems that support the
operation of an aircraft.

6-1

Reciprocating Engines
Most small aircraft are designed with reciprocating
engines. The name is derived from the back-and-forth, or
reciprocating, movement of the pistons which produces the
mechanical energy necessary to accomplish work.

Driven by a revitalization of the general aviation (GA)
industry and advances in both material and engine design,
reciprocating engine technology has improved dramatically
over the past two decades. The integration of computerized
engine management systems has improved fuel efficiency,
decreased emissions, and reduced pilot workload.

Reciprocating engines operate on the basic principle of Figure 6-1. Radial engine.
converting chemical energy (fuel) into mechanical energy.
This conversion occurs within the cylinders of the engine In-line engines have a comparatively small frontal area, but
through the process of combustion. The two primary their power-to-weight ratios are relatively low. In addition,
reciprocating engine designs are the spark ignition and the the rearmost cylinders of an air-cooled, in-line engine
compression ignition. The spark ignition reciprocating engine receive very little cooling air, so these engines are normally
has served as the powerplant of choice for many years. In limited to four or six cylinders. V-type engines provide
an effort to reduce operating costs, simplify design, and more horsepower than in-line engines and still retain a small
improve reliability, several engine manufacturers are turning frontal area.
to compression ignition as a viable alternative. Often referred
to as jet fuel piston engines, compression ignition engines Continued improvements in engine design led to the
have the added advantage of utilizing readily available and development of the horizontally-opposed engine which
lower cost diesel or jet fuel. remains the most popular reciprocating engines used on
smaller aircraft. These engines always have an even number
The main mechanical components of the spark ignition and of cylinders, since a cylinder on one side of the crankcase
the compression ignition engine are essentially the same. “opposes” a cylinder on the other side. [Figure 6-2] The
Both use cylindrical combustion chambers and pistons that majority of these engines are air cooled and usually are
travel the length of the cylinders to convert linear motion mounted in a horizontal position when installed on fixed-wing
into the rotary motion of the crankshaft. The main difference airplanes. Opposed-type engines have high power-to-weight
between spark ignition and compression ignition is the ratios because they have a comparatively small, lightweight
process of igniting the fuel. Spark ignition engines use a crankcase. In addition, the compact cylinder arrangement
spark plug to ignite a pre-mixed fuel/air mixture. (Fuel/air reduces the engine’s frontal area and allows a streamlined
mixture is the ratio of the “weight” of fuel to the “weight” installation that minimizes aerodynamic drag.
of air in the mixture to be burned.) A compression ignition
engine first compresses the air in the cylinder, raising its Horizontally opposed engine
temperature to a degree necessary for automatic ignition
when fuel is injected into the cylinder.

These two engine designs can be further classified as:

1. Cylinder arrangement with respect to the crankshaft—
radial, in-line, v-type, or opposed.

2. Operating cycle—two or four.

3. Method of cooling—liquid or air.

Radial engines were widely used during World War II and Opposed cylinders
many are still in service today. With these engines, a row or Figure 6-2. Horizontally opposed engine.
rows of cylinders are arranged in a circular pattern around
the crankcase. The main advantage of a radial engine is the
favorable power-to-weight ratio. [Figure 6-1]

6-2

Depending on the engine manufacturer, all of these Intake valve Cylinder
arrangements can be designed to utilize spark or compression Piston
ignition, and operate on either a two- or four-stroke cycle. Exhaust valve
Spark plug
In a two-stroke engine, the conversion of chemical energy
into mechanical energy occurs over a two-stroke operating Crankcase
cycle. The intake, compression, power, and exhaust processes
occur in only two strokes of the piston rather than the more
common four strokes. Because a two-stroke engine has a
power stroke each revolution of the crankshaft, it typically has
higher power-to-weight ratio than a comparable four-stroke
engine. Due to the inherent inefficiency and disproportionate
emissions of the earliest designs, use of the two-stroke engine
has been limited in aviation.

Recent advances in material and engine design have
reduced many of the negative characteristics associated
with two-stroke engines. Modern two-stroke engines often
use conventional oil sumps, oil pumps and full pressure fed
lubrication systems. The use of direct fuel injection and
pressurized air, characteristic of advanced compression
ignition engines, make two-stroke compression ignition
engines a viable alternative to the more common four-stroke
spark ignition designs. [Figure 6-3]

Forced air Exhaust valve Fuel injector

Connecting rod Crankshaft

Piston Figure 6-4. Main components of a spark ignition reciprocating
engine.
1. Intake/compression 2. Power stroke
and exhaust In a four-stroke engine the conversion of chemical energy
into mechanical energy occurs over a four stroke operating
Figure 6-3. Two-stroke compression ignition. cycle. The intake, compression, power, and exhaust processes
occur in four separate strokes of the piston.
Spark ignition four-stroke engines remain the most common
design used in general aviation today. [Figure 6-4] The 1. The intake stroke begins as the piston starts its
main parts of a spark ignition reciprocating engine include downward travel. When this happens, the intake
the cylinders, crankcase, and accessory housing. The intake/ valve opens and the fuel/air mixture is drawn into the
exhaust valves, spark plugs, and pistons are located in the cylinder.
cylinders. The crankshaft and connecting rods are located
in the crankcase. The magnetos are normally located on the 2. The compression stroke begins when the intake valve
engine accessory housing. closes and the piston starts moving back to the top of
the cylinder. This phase of the cycle is used to obtain
a much greater power output from the fuel/air mixture
once it is ignited.

3. The power stroke begins when the fuel/air mixture is
ignited. This causes a tremendous pressure increase
in the cylinder, and forces the piston downward away
from the cylinder head, creating the power that turns
the crankshaft.

6-3

4. The exhaust stroke is used to purge the cylinder of of a diesel-fueled reciprocating engine lies in the physical
burned gases. It begins when the exhaust valve opens similarity of diesel and kerosene. Aircraft equipped with a
and the piston starts to move toward the cylinder head diesel piston engine runs on standard aviation fuel kerosene
once again. which provides more independence, higher reliability, lower
consumption, and operational cost saving.
Even when the engine is operated at a fairly low speed,
the four-stroke cycle takes place several hundred times In 1999, Thielert formed Thielert Aircraft Engines (TAE)
each minute. [Figure 6-5] In a four-cylinder engine, each to design, develop, certify, and manufacture a brand-new
cylinder operates on a different stroke. Continuous rotation Jet-A-burning diesel cycle engine (also known as jet-fueled
of a crankshaft is maintained by the precise timing of the piston engine) for the GA industry. By March 2001, the first
power strokes in each cylinder. Continuous operation of the prototype engine became the first certified diesel engine
engine depends on the simultaneous function of auxiliary since World War II. TAE continues to design and develop
systems, including the induction, ignition, fuel, oil, cooling, diesel cycle engines and other engine manufacturers such as
and exhaust systems. Société de Motorisations Aéronautiques (SMA) now offer
jet-fueled piston engines as well. TAE engines can be found
Intake valve Exhaust valve on the Diamond DA40 single and the DA42 Twin Star, the
first diesel engine to be part of the type certificate of a new
original equipment manufacturer (OEM) aircraft.

Piston Spark plug These engines have also gained a toehold in the retrofit
market with a supplemental type certificate (STC) to re-
Crankshaft Connecting rod engine the Cessna 172 models and the Piper PA-28 family.
1. Intake 2. Compression The jet-fueled piston engines technology has continued to
progress and a full authority digital engine control (FADEC,
discussed more fully later in the chapter) is standard on such
equipped aircraft which minimizes complication of engine
control. By 2007, various jet-fueled piston aircraft had logged
well over 600,000 hours of service.

Propeller
The propeller is a rotating airfoil, subject to induced drag,
stalls, and other aerodynamic principles that apply to any
airfoil. It provides the necessary thrust to pull, or in some
cases push, the aircraft through the air. The engine power is
used to rotate the propeller, which in turn generates thrust
very similar to the manner in which a wing produces lift.
The amount of thrust produced depends on the shape of the
airfoil, the angle of attack of the propeller blade, and the
revolutions per minute (rpm) of the engine. The propeller
itself is twisted so the blade angle changes from hub to tip.
The greatest angle of incidence, or the highest pitch, is at the
hub while the smallest angle of incidence or smallest pitch
is at the tip. [Figure 6-6]

3. Power 4. Exhaust The reason for the twist is to produce uniform lift from the
hub to the tip. As the blade rotates, there is a difference in
Figure 6-5. The arrows in this illustration indicate the direction of the actual speed of the various portions of the blade. The tip
motion of the crankshaft and piston during the four-stroke cycle. of the blade travels faster than the part near the hub, because
the tip travels a greater distance than the hub in the same
The latest advance in aircraft reciprocating engines was length of time. [Figure 6-7] Changing the angle of incidence
pioneered in the mid-1960s by Frank Thielert, who looked (pitch) from the hub to the tip to correspond with the speed
to the automotive industry for answers on how to integrate produces uniform lift throughout the length of the blade. A
diesel technology into an aircraft engine. The advantage

6-4

There are two types of fixed-pitch propellers: climb and
cruise. Whether the airplane has a climb or cruise propeller
installed depends upon its intended use. The climb propeller
has a lower pitch, therefore less drag. Less drag results in
higher rpm and more horsepower capability, which increases
performance during takeoffs and climbs, but decreases
performance during cruising flight.

ModeFigure 6-6. Changes in propeller blade angle from hub to tip.ots The cruise propeller has a higher pitch, therefore more
Short trapropeller blade designed with the same angle of incidence259 knotsdrag. More drag results in lower rpm and less horsepower
throughout its entire length would be inefficient because as capability, which decreases performance during takeoffs and
airspeed increases in flight, the portion near the hub wouldspeed climbs, but increases efficiency during cruising flight.
have a negative angle of attack while the blade tip would
be stalled. nots —129 k The propeller is usually mounted on a shaft, which may be
an extension of the engine crankshaft. In this case, the rpm
Greater travel distance—very high speed—389 kn of the propeller would be the same as the crankshaft rpm. On
rate travel distance—moderate speed— some engines, the propeller is mounted on a shaft geared to
vel distance—slow the engine crankshaft. In this type, the rpm of the propeller
is different than that of the engine.
20 in.
2,500 rpm In a fixed-pitch propeller, the tachometer is the indicator of
engine power. [Figure 6-8] A tachometer is calibrated in
hundreds of rpm and gives a direct indication of the engine
and propeller rpm. The instrument is color coded, with a green
arc denoting the maximum continuous operating rpm. Some
tachometers have additional markings to reflect engine and/or
propeller limitations. The manufacturer’s recommendations
should be used as a reference to clarify any misunderstanding
of tachometer markings.

Engine r.p.m. is indicated on the tachometer

40 in. I5 20
2,500 rpm I0 25RPM

60 in. HUNDREDS
2,500 rpm

Figure 6-7. Relationship of travel distance and speed of various 5 30I
portions of propeller blade. 3
I0
Small aircraft are equipped with either one of two types
of propellers. One is the fixed pitch, and the other is the HOURS 35
adjustable pitch. AVOID
CONTINUOUS
Fixed-Pitch Propeller OPERATION
A propeller with fixed blade angles is a fixed-pitch propeller. BETWEEN 2250
The pitch of this propeller is set by the manufacturer and AND 2350 RPM
cannot be changed. Since a fixed-pitch propeller achieves
the best efficiency only at a given combination of airspeed Figure 6-8. Engine rpm is indicated on the tachometer.
and rpm, the pitch setting is ideal for neither cruise nor
climb. Thus, the aircraft suffers a bit in each performance The rpm is regulated by the throttle, which controls the
category. The fixed-pitch propeller is used when low weight, fuel/air flow to the engine. At a given altitude, the higher
simplicity, and low cost are needed. the tachometer reading, the higher the power output of the
engine.

When operating altitude increases, the tachometer may not
show correct power output of the engine. For example, 2,300

6-5

rpm at 5,000 feet produces less horsepower than 2,300 rpm angle is within the constant-speed range and not against
at sea level because power output depends on air density. Air either pitch stop, a constant engine rpm will be maintained.
density decreases as altitude increases and a decrease in air If the propeller blades contact a pitch stop, the engine rpm
density (higher density altitude) decreases the power output will increase or decrease as appropriate, with changes in
of the engine. As altitude changes, the position of the throttle airspeed and propeller load. For example, once a specific
must be changed to maintain the same rpm. As altitude is rpm has been selected, if aircraft speed decreases enough to
increased, the throttle must be opened further to indicate the rotate the propeller blades until they contact the low pitch
same rpm as at a lower altitude. stop, any further decrease in airspeed will cause engine rpm
to decrease the same way as if a fixed-pitch propeller were
Adjustable-Pitch Propeller installed. The same holds true when an aircraft equipped with
The adjustable-pitch propeller was the forerunner of the a constant-speed propeller accelerates to a faster airspeed. As
constant-speed propeller. It is a propeller with blades whose the aircraft accelerates, the propeller blade angle increases to
pitch can be adjusted on the ground with the engine not maintain the selected rpm until the high pitch stop is reached.
running, but which cannot be adjusted in flight. It is also Once this occurs, the blade angle cannot increase any further
referred to as a ground adjustable propeller. By the 1930s, and engine rpm increases.
pioneer aviation inventors were laying the ground work for
automatic pitch-change mechanisms, which is why the term On aircraft equipped with a constant-speed propeller, power
sometimes refers to modern constant-speed propellers that output is controlled by the throttle and indicated by a manifold
are adjustable in flight. pressure gauge. The gauge measures the absolute pressure of
the fuel/air mixture inside the intake manifold and is more
The first adjustable-pitch propeller systems provided only correctly a measure of manifold absolute pressure (MAP). At
two pitch settings: low and high. Today, most adjustable-pitch a constant rpm and altitude, the amount of power produced
propeller systems are capable of a range of pitch settings. is directly related to the fuel/air flow being delivered to the
combustion chamber. As the throttle setting is increased,
A constant-speed propeller is a controllable-pitch propeller more fuel and air flows to the engine and MAP increases.
whose pitch is automatically varied in flight by a governor When the engine is not running, the manifold pressure gauge
maintaining constant rpm despite varying air loads. It is the indicates ambient air pressure (i.e., 29.92 inches mercury
most common type of adjustable-pitch propeller. The main (29.92 "Hg)). When the engine is started, the manifold
advantage of a constant-speed propeller is that it converts pressure indication will decrease to a value less than ambient
a high percentage of brake horsepower (BHP) into thrust pressure (i.e., idle at 12 "Hg). Engine failure or power loss is
horsepower (THP) over a wide range of rpm and airspeed indicated on the manifold gauge as an increase in manifold
combinations. A constant-speed propeller is more efficient pressure to a value corresponding to the ambient air pressure
than other propellers because it allows selection of the most at the altitude where the failure occurred. [Figure 6-9]
efficient engine rpm for the given conditions.

An aircraft with a constant-speed propeller has two controls: 25 30 35
the throttle and the propeller control. The throttle controls MANIFOLD
power output and the propeller control regulates engine rpm.
This in turn regulates propeller rpm which is registered on 20 PRESS 40
the tachometer. 15 45IN Hg

Once a specific rpm is selected, a governor automatically ALg.
adjusts the propeller blade angle as necessary to maintain
the selected rpm. For example, after setting the desired rpm 10 50
during cruising flight, an increase in airspeed or decrease in
propeller load will cause the propeller blade angle to increase Figure 6-9. Engine power output is indicated on the manifold
as necessary to maintain the selected rpm. A reduction in pressure gauge.
airspeed or increase in propeller load will cause the propeller
blade angle to decrease.

The propeller’s constant-speed range, defined by the high
and low pitch stops, is the range of possible blade angles for
a constant-speed propeller. As long as the propeller blade

6-6

The manifold pressure gauge is color coded to indicate the Two types of induction systems are commonly used in small
engine’s operating range. The face of the manifold pressure aircraft engines:
gauge contains a green arc to show the normal operating
range, and a red radial line to indicate the upper limit of 1. The carburetor system, which mixes the fuel and air
manifold pressure. in the carburetor before this mixture enters the intake
manifold
For any given rpm, there is a manifold pressure that should not
be exceeded. If manifold pressure is excessive for a given rpm, 2. The fuel injection system, which mixes the fuel and air
the pressure within the cylinders could be exceeded, placing immediately before entry into each cylinder or injects
undue stress on the cylinders. If repeated too frequently, this fuel directly into each cylinder
stress can weaken the cylinder components and eventually
cause engine failure. As a general rule, manifold pressure Carburetor Systems
(inches) should be less than the rpm. Carburetors are classified as either float type or pressure type.
The float type of carburetor, complete with idling, accelerating,
A pilot can avoid conditions that overstress the cylinders by mixture control, idle cutoff, and power enrichment systems is
being constantly aware of the rpm, especially when increasing probably the most common of all carburetor types. Pressure
the manifold pressure. Conform to the manufacturer’s carburetors are usually not found on small aircraft. The basic
recommendations for power settings of a particular engine to difference between a float-type and a pressure-type carburetor
maintain the proper relationship between manifold pressure is the delivery of fuel. The pressure-type carburetor delivers
and rpm. fuel under pressure by a fuel pump.

When both manifold pressure and rpm need to be changed, In the operation of the float-type carburetor system, the
avoid engine overstress by making power adjustments in outside air first flows through an air filter, usually located
the proper order: at an air intake in the front part of the engine cowling. This
filtered air flows into the carburetor and through a venturi, a
• When power settings are being decreased, reduce narrow throat in the carburetor. When the air flows through
manifold pressure before reducing rpm. If rpm is the venturi, a low-pressure area is created, which forces the
reduced before manifold pressure, manifold pressure fuel to flow through a main fuel jet located at the throat. The
will automatically increase, possibly exceeding the fuel then flows into the airstream where it is mixed with the
manufacturer’s tolerances. flowing air. [Figure 6-10]

• When power settings are being increased, reverse the The fuel/air mixture is then drawn through the intake manifold
order—increase rpm first, then manifold pressure. and into the combustion chambers where it is ignited. The
float-type carburetor acquires its name from a float, which
• To prevent damage to radial engines, minimize rests on fuel within the float chamber. A needle attached to
operating time at maximum rpm and manifold the float opens and closes an opening at the bottom of the
pressure, and avoid operation at maximum rpm and carburetor bowl. This meters the correct amount of fuel into
low manifold pressure. the carburetor, depending upon the position of the float,
which is controlled by the level of fuel in the float chamber.
The engine and/or airframe manufacturer’s recommendations When the level of the fuel forces the float to rise, the needle
should be followed to prevent severe wear, fatigue, and valve closes the fuel opening and shuts off the fuel flow to
damage to high-performance reciprocating engines. the carburetor. The needle valve opens again when the engine
requires additional fuel. The flow of the fuel/air mixture to
Induction Systems the combustion chambers is regulated by the throttle valve,
The induction system brings in air from the outside, mixes which is controlled by the throttle in the flight deck.
it with fuel, and delivers the fuel/air mixture to the cylinder
where combustion occurs. Outside air enters the induction The float-type carburetor has several distinct disadvantages.
system through an intake port on the front of the engine In the first place, imagine the effect that abrupt maneuvers
cowling. This port normally contains an air filter that inhibits have on the float action. In the second place, the fact that its
the entry of dust and other foreign objects. Since the filter fuel must be discharged at low pressure leads to incomplete
may occasionally become clogged, an alternate source of vaporization and difficulty in discharging fuel into some
air must be available. Usually, the alternate air comes from types of supercharged systems. The chief disadvantage of
inside the engine cowling, where it bypasses a clogged air the float carburetor, however, is its icing tendency. Since
filter. Some alternate air sources function automatically, the float carburetor must discharge fuel at a point of low
while others operate manually.

6-7

FUEL/AIR MIXTURE Float-type carburetor FUEL INLET
The blend of fuel and Fuel is received into
air is routed to the FLOAT CHAMBER the carburetor through
combustion chambers Fuel level is maintained the fuel inlet.
to be burned. by a float-type device.

THROTTLE VALVE FUEL
The flow of the fuel/air
mixture is controlled by MIXTURE NEEDLE
the throttle valve. The The mixture needle
throttle valve is adjusted controls fuel to the
from the flight deck by discharge nozzle.
the throttle. Mixture needle position
can be adjusted using
VENTURI the mixture control.
The shape of the venturi
creates an area of low AIR INLET AIR BLEED
pressure. The air bleed allows air to be mixed
Air enters the carburetor with fuel being drawn out of the dis-
DISCHARGE NOZZLE through the air inlet. charge nozzle to decrease fuel density
Fuel is forced through and promote fuel vaporization.
the discharge nozzle
into the venturi by
greater atmospheric
pressure in the float
chamber.

Figure 6-10. Float-type carburetor. from excessive carbon buildup on the plugs. Carbon buildup
occurs because the rich mixture lowers the temperature
pressure, the discharge nozzle must be located at the venturi inside the cylinder, inhibiting complete combustion of the
throat, and the throttle valve must be on the engine side of the fuel. This condition may occur during the pretakeoff runup
discharge nozzle. This means the drop in temperature due to at high-elevation airports and during climbs or cruise flight
fuel vaporization takes place within the venturi. As a result, at high altitudes. To maintain the correct fuel/air mixture, the
ice readily forms in the venturi and on the throttle valve. mixture must be leaned using the mixture control. Leaning
the mixture decreases fuel flow, which compensates for the
A pressure-type carburetor discharges fuel into the airstream decreased air density at high altitude.
at a pressure well above atmospheric. This results in better
vaporization and permits the discharge of fuel into the During a descent from high altitude, the mixture must
airstream on the engine side of the throttle valve. With the be enriched, or it may become too lean. An overly lean
discharge nozzle located at this point, the drop in temperature mixture causes detonation, which may result in rough
due to fuel vaporization takes place after the air has passed the engine operation, overheating, and a loss of power. The
throttle valve and at a point where engine heat tends to offset best way to maintain the proper mixture is to monitor the
it. Thus, the danger of fuel vaporization icing is practically engine temperature and enrich the mixture as needed. Proper
eliminated. The effects of rapid maneuvers and rough air on mixture control and better fuel economy for fuel-injected
the pressure-type carburetors are negligible since their fuel engines can be achieved by use of an exhaust gas temperature
chambers remain filled under all operating conditions (EGT) gauge. Since the process of adjusting the mixture can
vary from one aircraft to another, it is important to refer to
Mixture Control the airplane flight manual (AFM) or the pilot’s operating
Carburetors are normally calibrated at sea-level pressure, handbook (POH) to determine the specific procedures for
where the correct fuel-to-air mixture ratio is established a given aircraft.
with the mixture control set in the FULL RICH position.
However, as altitude increases, the density of air entering the Carburetor Icing
carburetor decreases, while the density of the fuel remains As mentioned earlier, one disadvantage of the float-type
the same. This creates a progressively richer mixture, which carburetor is its icing tendency. Carburetor ice occurs due
can result in engine roughness and an appreciable loss of
power. The roughness normally is due to spark plug fouling

6-8

to the effect of fuel vaporization and the decrease in air Relative humidity 100% High carburetor
pressure in the venturi, which causes a sharp temperature 90% icing potential
drop in the carburetor. If water vapor in the air condenses 80%
when the carburetor temperature is at or below freezing, ice 70% Carburetor icing possible
may form on internal surfaces of the carburetor, including 60%
the throttle valve. [Figure 6-11]

To engine Fuel/air mixture

50% 70°F/21°C 100°F/38°C
20°F/-7°C 32°F/0°C

Outside air temperature

Ice Figure 6-12. Although carburetor ice is most likely to form when
Ice the temperature and humidity are in ranges indicated by this chart,
Venturi carburetor ice is possible under conditions not depicted.

Ice by a decrease in manifold pressure, but no reduction in rpm.
Propeller pitch is automatically adjusted to compensate for

loss of power. Thus, a constant rpm is maintained. Although

carburetor ice can occur during any phase of flight, it is

particularly dangerous when using reduced power during

a descent. Under certain conditions, carburetor ice could

build unnoticed until power is added. To combat the effects

of carburetor ice, engines with float-type carburetors employ

a carburetor heat system.

Incoming air Carburetor Heat

Figure 6-11. The formation of carburetor ice may reduce or block Carburetor heat is an anti-icing system that preheats the air
fuel/air flow to the engine. before it reaches the carburetor, and is intended to keep the
fuel/air mixture above the freezing temperature to prevent
The reduced air pressure, as well as the vaporization of fuel, the formation of carburetor ice. Carburetor heat can be used
contributes to the temperature decrease in the carburetor. Ice to melt ice that has already formed in the carburetor if the
generally forms in the vicinity of the throttle valve and in the accumulation is not too great, but using carburetor heat as a
venturi throat. This restricts the flow of the fuel/air mixture preventative measure is the better option. Additionally, the
and reduces power. If enough ice builds up, the engine may use of carburetor heat as an alternate air source can be used
cease to operate. Carburetor ice is most likely to occur when if the intake filter clogs such as in sudden or unexpected
temperatures are below 70 degrees Fahrenheit (°F) or 21 airframe icing conditions. The carburetor heat should be
degrees Celsius (°C) and the relative humidity is above 80 checked during the engine runup. When using carburetor
percent. Due to the sudden cooling that takes place in the heat, follow the manufacturer’s recommendations.
carburetor, icing can occur even with temperatures as high
as 100 °F (38 °C) and humidity as low as 50 percent. This When conditions are conducive to carburetor icing during
temperature drop can be as much as 60 to 70 °F (15 to 21 °C). flight, periodic checks should be made to detect its presence. If
Therefore, at an outside air temperature of 100 °F (37 °C), a detected, full carburetor heat should be applied immediately,
temperature drop of 70 °F (21 °C) results in an air temperature and it should be left in the ON position until the pilot is
in the carburetor of 30 °F (-1 °C). [Figure 6-12] certain all the ice has been removed. If ice is present, applying
partial heat or leaving heat on for an insufficient time might
The first indication of carburetor icing in an aircraft with aggravate the situation. In extreme cases of carburetor icing,
a fixed-pitch propeller is a decrease in engine rpm, which even after the ice has been removed, full carburetor heat
may be followed by engine roughness. In an aircraft with a should be used to prevent further ice formation. If installed,
constant-speed propeller, carburetor icing is usually indicated a carburetor temperature gauge is useful in determining when
to use carburetor heat.

6-9

Whenever the throttle is closed during flight, the engine cools Usually, the face of the gauge is calibrated in degrees Celsius,
rapidly and vaporization of the fuel is less complete than if with a yellow arc indicating the carburetor air temperatures
the engine is warm. Also, in this condition, the engine is more where icing may occur. This yellow arc typically ranges
susceptible to carburetor icing. If carburetor icing conditions between -15 °C and +5 °C (5 °F and 41 °F). If the air
are suspected and closed-throttle operation anticipated, adjust temperature and moisture content of the air are such that
the carburetor heat to the full ON position before closing the carburetor icing is improbable, the engine can be operated
throttle and leave it on during the closed-throttle operation. with the indicator in the yellow range with no adverse effects.
The heat will aid in vaporizing the fuel and help prevent the If the atmospheric conditions are conducive to carburetor
formation of carburetor ice. Periodically, open the throttle icing, the indicator must be kept outside the yellow arc by
smoothly for a few seconds to keep the engine warm; application of carburetor heat.
otherwise, the carburetor heater may not provide enough
heat to prevent icing. Certain carburetor air temperature gauges have a red radial,
which indicates the maximum permissible carburetor inlet
The use of carburetor heat causes a decrease in engine air temperature recommended by the engine manufacturer. If
power, sometimes up to 15 percent, because the heated air present, a green arc indicates the normal operating range.
is less dense than the outside air that had been entering the
engine. This enriches the mixture. When ice is present in an Outside Air Temperature Gauge
aircraft with a fixed-pitch propeller and carburetor heat is Most aircraft are also equipped with an outside air
being used, there is a decrease in rpm, followed by a gradual temperature (OAT) gauge calibrated in both degrees Celsius
increase in rpm as the ice melts. The engine also should run and Fahrenheit. It provides the outside or ambient air
more smoothly after the ice has been removed. If ice is not temperature for calculating true airspeed, and also is useful
present, the rpm will decrease and then remain constant. in detecting potential icing conditions.
When carburetor heat is used on an aircraft with a constant-
speed propeller and ice is present, a decrease in the manifold Fuel Injection Systems
pressure will be noticed, followed by a gradual increase. In a fuel injection system, the fuel is injected directly into
If carburetor icing is not present, the gradual increase in the cylinders, or just ahead of the intake valve. The air
manifold pressure will not be apparent until the carburetor intake for the fuel injection system is similar to that used
heat is turned off. in a carburetor system, with an alternate air source located
within the engine cowling. This source is used if the external
It is imperative for a pilot to recognize carburetor ice when air source is obstructed. The alternate air source is usually
it forms during flight because a loss of power, altitude, operated automatically, with a backup manual system that
and/or airspeed will occur. These symptoms may sometimes can be used if the automatic feature malfunctions.
be accompanied by vibration or engine roughness. Once a
power loss is noticed, immediate action should be taken to A fuel injection system usually incorporates six basic
eliminate ice already formed in the carburetor, and to prevent components: an engine-driven fuel pump, a fuel/air control
further ice formation. This is accomplished by applying full unit, fuel manifold (fuel distributor), discharge nozzles,
carburetor heat, which will cause a further reduction in power, an auxiliary fuel pump, and fuel pressure/flow indicators.
and possibly engine roughness as melted ice goes through the [Figure 6-13]
engine. These symptoms may last from 30 seconds to several
minutes, depending on the severity of the icing. During this The auxiliary fuel pump provides fuel under pressure to the
period, the pilot must resist the temptation to decrease the fuel/air control unit for engine starting and/or emergency
carburetor heat usage. Carburetor heat must remain in the use. After starting, the engine-driven fuel pump provides
full-hot position until normal power returns. fuel under pressure from the fuel tank to the fuel/air control
unit.
Since the use of carburetor heat tends to reduce the output
of the engine and to increase the operating temperature, This control unit, which essentially replaces the carburetor,
carburetor heat should not be used when full power is required meters fuel based on the mixture control setting, and sends it
(as during takeoff) or during normal engine operation, except to the fuel manifold valve at a rate controlled by the throttle.
to check for the presence or to remove carburetor ice. After reaching the fuel manifold valve, the fuel is distributed
to the individual fuel discharge nozzles. The discharge
Carburetor Air Temperature Gauge nozzles, which are located in each cylinder head, inject the
Some aircraft are equipped with a carburetor air temperature fuel/air mixture directly into each cylinder intake port.
gauge, which is useful in detecting potential icing conditions.

6-10

Fuel tank

Auxiliary fuel pump

Engine-driven fuel pump

Fuel/air control unit

Fuel lines Fuel manifold valve

Figure 6-13. Fuel injection system.

A fuel injection system is considered to be less susceptible to the power supply. A supercharger relies on an engine-driven
icing than the carburetor system, but impact icing on the air air pump or compressor, while a turbocharger gets its power
intake is a possibility in either system. Impact icing occurs from the exhaust stream that runs through a turbine, which in
when ice forms on the exterior of the aircraft, and blocks turn spins the compressor. Aircraft with these systems have
openings such as the air intake for the injection system. a manifold pressure gauge, which displays MAP within the
engine’s intake manifold.
Advantages of fuel injection:
• Reduction in evaporative icing On a standard day at sea level with the engine shut down,
• Better fuel flow the manifold pressure gauge will indicate the ambient
• Faster throttle response absolute air pressure of 29.92 "Hg. Because atmospheric
• Precise control of mixture pressure decreases approximately 1 "Hg per 1,000 feet of
• Better fuel distribution altitude increase, the manifold pressure gauge will indicate
• Easier cold weather starts approximately 24.92 "Hg at an airport that is 5,000 feet above
sea level with standard day conditions.
Disadvantages:
• Difficulty in starting a hot engine As a normally aspirated aircraft climbs, it eventually reaches
• Vapor locks during ground operations on hot days an altitude where the MAP is insufficient for a normal climb.
• Problems associated with restarting an engine that That altitude limit is the aircraft’s service ceiling, and it is
quits because of fuel starvation directly affected by the engine’s ability to produce power.
If the induction air entering the engine is pressurized, or
Superchargers and Turbosuperchargers boosted, by either a supercharger or a turbosupercharger,
the aircraft’s service ceiling can be increased. With these
To increase an engine’s horsepower, manufacturers have systems, an aircraft can fly at higher altitudes with the
developed forced induction systems called supercharger advantage of higher true airspeeds and the increased ability
and turbosupercharger systems. They both compress the to circumnavigate adverse weather.
intake air to increase its density. The key difference lies in

6-11

Superchargers accelerates the fuel/air mixture outward. Once accelerated, the
A supercharger is an engine-driven air pump or compressor fuel/air mixture passes through a diffuser, where air velocity
that provides compressed air to the engine to provide is traded for pressure energy. After compression, the resulting
additional pressure to the induction air so the engine can high pressure fuel/air mixture is directed to the cylinders.
produce additional power. It increases manifold pressure
and forces the fuel/air mixture into the cylinders. The higher Some of the large radial engines developed during World
the manifold pressure, the more dense the fuel/air mixture, War II have a single-stage, two-speed supercharger. With
and the more power an engine can produce. With a normally this type of supercharger, a single impeller may be operated
aspirated engine, it is not possible to have manifold pressure at two speeds. The low impeller speed is often referred to
higher than the existing atmospheric pressure. A supercharger as the low blower setting, while the high impeller speed is
is capable of boosting manifold pressure above 30 "Hg. called the high blower setting. On engines equipped with a
two-speed supercharger, a lever or switch in the flight deck
For example, at 8,000 feet a typical engine may be able to activates an oil-operated clutch that switches from one speed
produce 75 percent of the power it could produce at mean sea to the other.
level (MSL) because the air is less dense at the higher altitude.
The supercharger compresses the air to a higher density Under normal operations, takeoff is made with the
allowing a supercharged engine to produce the same manifold supercharger in the low blower position. In this mode, the
pressure at higher altitudes as it could produce at sea level. engine performs as a ground-boosted engine, and the power
Thus, an engine at 8,000 feet MSL could still produce 25 "Hg output decreases as the aircraft gains altitude. However, once
of manifold pressure whereas without a supercharger it could the aircraft reaches a specified altitude, a power reduction is
produce only 22 "Hg. Superchargers are especially valuable made, and the supercharger control is switched to the high
at high altitudes (such as 18,000 feet) where the air density blower position. The throttle is then reset to the desired
is 50 percent that of sea level. The use of a supercharger in manifold pressure. An engine equipped with this type of
many cases will supply air to the engine at the same density supercharger is called an altitude engine. [Figure 6-14]
it did at sea level. With a normally aspirated engine, it is not
possible to have manifold pressure higher than the existing Two-speed supercharged engine
atmospheric pressure. A supercharger is capable of boosting
manifold pressure above 30 "Hg. Low blower High blower

The components in a supercharged induction system are similar Brake horsepower Normally aspirated engine
to those in a normally aspirated system, with the addition of
a supercharger between the fuel metering device and intake
manifold. A supercharger is driven by the engine through a
gear train at one speed, two speeds, or variable speeds. In
addition, superchargers can have one or more stages. Each
stage also provides an increase in pressure and superchargers
may be classified as single stage, two stage, or multistage,
depending on the number of times compression occurs.

An early version of a single-stage, single-speed supercharger Sea level Density altitude
may be referred to as a sea-level supercharger. An engine
equipped with this type of supercharger is called a sea-level Figure 6-14. Power output of normally aspirated engine compared
engine. With this type of supercharger, a single gear-driven to a single-stage, two-speed supercharged engine.
impeller is used to increase the power produced by an engine at
all altitudes. The drawback with this type of supercharger is a Turbosuperchargers
decrease in engine power output with an increase in altitude. The most efficient method of increasing horsepower in an
engine is by use of a turbosupercharger or turbocharger.
Single-stage, single-speed superchargers are found on many Installed on an engine, this booster uses the engine’s exhaust
high-powered radial engines and use an air intake that faces gases to drive an air compressor to increase the pressure of
forward so the induction system can take full advantage of the the air going into the engine through the carburetor or fuel
ram air. Intake air passes through ducts to a carburetor, where injection system to boost power at higher altitude.
fuel is metered in proportion to the airflow. The fuel/air charge
is then ducted to the supercharger, or blower impeller, which

6-12

The major disadvantage of the gear-driven supercharger––use shaft. By directing different amounts of exhaust gases to flow
of a large amount of the engine’s power output for the amount over the turbine, more energy can be extracted, causing the
of power increase produced––is avoided with a turbocharger, impeller to deliver more compressed air to the engine. The
because turbochargers are powered by an engine’s exhaust waste gate, essentially an adjustable butterfly valve installed
gases. This means a turbocharger recovers energy from hot in the exhaust system, is used to vary the mass of exhaust gas
exhaust gases that would otherwise be lost. flowing into the turbine. When closed, most of the exhaust
gases from the engine are forced to flow through the turbine.
A second advantage of turbochargers over superchargers is When open, the exhaust gases are allowed to bypass the
the ability to maintain control over an engine’s rated sea- turbine by flowing directly out through the engine’s exhaust
level horsepower from sea level up to the engine’s critical pipe. [Figure 6-15]
altitude. Critical altitude is the maximum altitude at which
a turbocharged engine can produce its rated horsepower. Since the temperature of a gas rises when it is compressed,
Above the critical altitude, power output begins to decrease turbocharging causes the temperature of the induction air to
like it does for a normally aspirated engine. increase. To reduce this temperature and lower the risk of
detonation, many turbocharged engines use an intercooler.
Turbochargers increase the pressure of the engine’s induction This small heat exchanger uses outside air to cool the hot
air, which allows the engine to develop sea level or greater compressed air before it enters the fuel metering device.
horsepower at higher altitudes. A turbocharger is comprised
of two main elements: a compressor and turbine. The System Operation
compressor section houses an impeller that turns at a high rate On most modern turbocharged engines, the position of
of speed. As induction air is drawn across the impeller blades, the waste gate is governed by a pressure-sensing control
the impeller accelerates the air, allowing a large volume of mechanism coupled to an actuator. Engine oil directed into
air to be drawn into the compressor housing. The impeller’s or away from this actuator moves the waste gate position.
action subsequently produces high-pressure, high-density On these systems, the actuator is automatically positioned to
air, which is delivered to the engine. To turn the impeller, produce the desired MAP simply by changing the position
the engine’s exhaust gases are used to drive a turbine wheel of the throttle control.
that is mounted on the opposite end of the impeller’s drive

TURBOCHARGER THROTTLE BODY INTAKE MANIFOLD
The turbocharger in- This regulates airflow Pressurized air from the
corporates a turbine, to the engine. turbocharger is supplied
which is driven by ex- to the cylinders.
haust gases, and a com-
pressor that pressurizes
the incoming air.

EXHAUST GAS DISCHARGE WASTE GATE AIR INTAKE EXHAUST MANIFOLD
This controls the amount Intake air is ducted to the Exhaust gas is ducted
Figure 6-15. Turbocharger components. of exhaust through the turbocharger where it is through the exhaust man-
turbine. Waste gate compressed. ifold and is used to turn
position is actuated by the turbine which drives
engine oil pressure. the compressor.

6-13

Other turbocharging system designs use a separate manual Ignition System
control to position the waste gate. With manual control,
the manifold pressure gauge must be closely monitored to In a spark ignition engine the ignition system provides a
determine when the desired MAP has been achieved. Manual spark that ignites the fuel/air mixture in the cylinders and is
systems are often found on aircraft that have been modified made up of magnetos, spark plugs, high-tension leads, and
with aftermarket turbocharging systems. These systems the ignition switch. [Figure 6-16]
require special operating considerations. For example, if the
waste gate is left closed after descending from a high altitude, A magneto uses a permanent magnet to generate an electrical
it is possible to produce a manifold pressure that exceeds the current completely independent of the aircraft’s electrical
engine’s limitations. This condition, called an overboost, system. The magneto generates sufficiently high voltage
may produce severe detonation because of the leaning effect to jump a spark across the spark plug gap in each cylinder.
resulting from increased air density during descent. The system begins to fire when the starter is engaged and the
crankshaft begins to turn. It continues to operate whenever
Although an automatic waste gate system is less likely the crankshaft is rotating.
to experience an overboost condition, it can still occur. If
takeoff power is applied while the engine oil temperature is Most standard certificated aircraft incorporate a dual ignition
below its normal operating range, the cold oil may not flow system with two individual magnetos, separate sets of wires,
out of the waste gate actuator quickly enough to prevent an and spark plugs to increase reliability of the ignition system.
overboost. To help prevent overboosting, advance the throttle Each magneto operates independently to fire one of the two
cautiously to prevent exceeding the maximum manifold spark plugs in each cylinder. The firing of two spark plugs
pressure limits. improves combustion of the fuel/air mixture and results in
a slightly higher power output. If one of the magnetos fails,
A pilot flying an aircraft with a turbocharger should be aware the other is unaffected. The engine will continue to operate
of system limitations. For example, a turbocharger turbine normally, although a slight decrease in engine power can be
and impeller can operate at rotational speeds in excess of expected. The same is true if one of the two spark plugs in
80,000 rpm while at extremely high temperatures. To achieve a cylinder fails.
high rotational speed, the bearings within the system must be
constantly supplied with engine oil to reduce the frictional The operation of the magneto is controlled in the flight deck
forces and high temperature. To obtain adequate lubrication, by the ignition switch. The switch has five positions:
the oil temperature should be in the normal operating range
before high throttle settings are applied. In addition, allow 1. OFF
the turbocharger to cool and the turbine to slow down before
shutting the engine down. Otherwise, the oil remaining in 2. R (right)
the bearing housing will boil, causing hard carbon deposits
to form on the bearings and shaft. These deposits rapidly 3. L (left)
deteriorate the turbocharger’s efficiency and service life. For
further limitations, refer to the AFM/POH. 4. BOTH

High Altitude Performance 5. START

As an aircraft equipped with a turbocharging system climbs, With RIGHT or LEFT selected, only the associated magneto
the waste gate is gradually closed to maintain the maximum is activated. The system operates on both magnetos with
allowable manifold pressure. At some point, the waste gate BOTH selected.
will be fully closed and further increases in altitude will
cause the manifold pressure to decrease. This is the critical A malfunctioning ignition system can be identified during
altitude, which is established by the aircraft or engine the pretakeoff check by observing the decrease in rpm that
manufacturer. When evaluating the performance of the occurs when the ignition switch is first moved from BOTH
turbocharging system, be aware that if the manifold pressure to RIGHT, and then from BOTH to LEFT. A small decrease
begins decreasing before the specified critical altitude, the in engine rpm is normal during this check. The permissible
engine and turbocharging system should be inspected by decrease is listed in the AFM or POH. If the engine stops
a qualified aviation maintenance technician to verify the running when switched to one magneto or if the rpm drop
system’s proper operation. exceeds the allowable limit, do not fly the aircraft until
the problem is corrected. The cause could be fouled plugs,
broken or shorted wires between the magneto and the plugs,
or improperly timed firing of the plugs. It should be noted

6-14

Upper magneto wires Upper spark plugs Lower spark plugs
Lower magneto wires
� �
4 �

Left magneto Right magneto

Figure 6-16. Ignition system components.

that “no drop” in rpm is not normal, and in that instance, the Reciprocating engines use either a wet-sump or a dry-sump
aircraft should not be flown. oil system. In a wet-sump system, the oil is located in a sump,
which is an integral part of the engine. In a dry-sump system,
Following engine shutdown, turn the ignition switch to the the oil is contained in a separate tank, and circulated through
OFF position. Even with the battery and master switches the engine by pumps. [Figure 6-17]
OFF, the engine can fire and turn over if the ignition switch
is left ON and the propeller is moved because the magneto The main component of a wet-sump system is the oil pump,
requires no outside source of electrical power. Be aware of the which draws oil from the sump and routes it to the engine.
potential for serious injury in this situation. After the oil passes through the engine, it returns to the
sump. In some engines, additional lubrication is supplied
Even with the ignition switch in the OFF position, if the ground by the rotating crankshaft, which splashes oil onto portions
wire between the magneto and the ignition switch becomes of the engine.
disconnected or broken, the engine could accidentally start
if the propeller is moved with residual fuel in the cylinder. An oil pump also supplies oil pressure in a dry-sump system,
If this occurs, the only way to stop the engine is to move the but the source of the oil is located external to the engine in a
mixture lever to the idle cutoff position, then have the system separate oil tank. After oil is routed through the engine, it is
checked by a qualified aviation maintenance technician. pumped from the various locations in the engine back to the
oil tank by scavenge pumps. Dry-sump systems allow for a
Oil Systems greater volume of oil to be supplied to the engine, which makes
them more suitable for very large reciprocating engines.
The engine oil system performs several important functions:
The oil pressure gauge provides a direct indication of the oil
• Lubrication of the engine’s moving parts system operation. It ensures the pressure in pounds per square
inch (psi) of the oil supplied to the engine. Green indicates
• Cooling of the engine by reducing friction the normal operating range, while red indicates the minimum
and maximum pressures. There should be an indication of
• Removing heat from the cylinders oil pressure during engine start. Refer to the AFM/POH for
manufacturer limitations.
• Providing a seal between the cylinder walls and
pistons

• Carrying away contaminants

6-15

Oil filter cap and dipstick

Sump oil and return Engine
oil from relief valve and
Pressure oil from
oil pump Accessory
Bearings
Low pressure oil screen
Oil pump Oil sump
Oil pressure relief valve
High pressure oil screen
Oil cooler and filter 245 II5

T 200 6I00200SPI P
E °F I50 R
M I00 E
P S
S

75 OIL 0

Figure 6-17. Wet-sump oil system.

The oil temperature gauge measures the temperature of oil.
A green area shows the normal operating range and the red
line indicates the maximum allowable temperature. Unlike
oil pressure, changes in oil temperature occur more slowly.
This is particularly noticeable after starting a cold engine,
when it may take several minutes or longer for the gauge to
show any increase in oil temperature.

Check oil temperature periodically during flight especially Figure 6-18. Always check the engine oil level during the preflight
when operating in high or low ambient air temperature. High inspection.
oil temperature indications may signal a plugged oil line, a low
oil quantity, a blocked oil cooler, or a defective temperature to loss of power, excessive oil consumption, detonation, and
gauge. Low oil temperature indications may signal improper serious engine damage.
oil viscosity during cold weather operations.
While the oil system is vital to the internal cooling of the
The oil filler cap and dipstick (for measuring the oil quantity) engine, an additional method of cooling is necessary for the
are usually accessible through a panel in the engine cowling. If engine’s external surface. Most small aircraft are air cooled,
the quantity does not meet the manufacturer’s recommended although some are liquid cooled.
operating levels, oil should be added. The AFM/POH or
placards near the access panel provide information about Air cooling is accomplished by air flowing into the engine
the correct oil type and weight, as well as the minimum and compartment through openings in front of the engine
maximum oil quantity. [Figure 6-18] cowling. Baffles route this air over fins attached to the engine
cylinders, and other parts of the engine, where the air absorbs
Engine Cooling Systems the engine heat. Expulsion of the hot air takes place through

The burning fuel within the cylinders produces intense
heat, most of which is expelled through the exhaust system.
Much of the remaining heat, however, must be removed, or
at least dissipated, to prevent the engine from overheating.
Otherwise, the extremely high engine temperatures can lead

6-16






















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