Answers - Propellers (Part 2) | Aircraft Systems

Answers - Propellers (Part 2)

61. a
Dye-penetrant inspection is normally used to detect cracks or other defects that are open to the surface.

62. c
Mechanical stops in the propeller hub limit the constant-speed range of a constant-speed propeller.

63. c
To allow an engine to develop its rated takeoff power, a constant-speed propeller is normally set in the low pitch, high rpm position. This places the lightest load on the engine, allowing it to develop maximum power.

64. b
The high and low pitch stops of Hamilton Standard propellers are located in the counterweight assembly. However, in some of the more modern constant-speed propeller assemblies, the pitch stops are located in the dome assembly.

65. a
The two-position and the constant-speed counterweight propellers both use hydraulic force to decrease blade angle and centrifugal force acting on counterweights to increase blade angle. The major difference between the two is that the constant-speed propeller utilizes a governor to boost the oil pressure to a higher level and automatically control the oil flow to and from the propeller, while the two-position propeller operates at engine lubrication system pressure with the oil flow controlled by a manual selector valve.


66. a
Propellers are subject to aerodynamic vibrations when the blade tips travel at near sonic speeds. In addition, mechanical vibrations are transmitted from the engine to the propeller. At certain combinations of airspeed and engine rpm these vibrations can create harmonic stresses that could lead to metal fatigue and eventual propeller blade failure. Therefore, the Type Certificate Data Sheets for engine/propeller combinations identify any critical rpm ranges that are to be avoided to prevent severe vibration. Regulations require that these ranges be marked on the tachometer with a red arc.

67. b
Oversize or elongated bolt holes on a wooden propeller are typically cause for rejection. However, some oversize or worn bolt holes may be repaired by the use of metal inserts to restore the original diameter. This is a major repair and must be performed by a certificated repair station.

68. a
Beta range refers to a reversing-type propeller that can operate in a zero or negative thrust range. During operation in beta range, propeller governor operation is locked out and all propeller control is accomplished with the power lever.

69. c
A blade cuff is a metal, wood, or plastic structure that is attaches to the shank of a propeller blade. The cuff surface transforms the round shank into an airfoil section and is designed primarily to increase the flow of cooling air to the engine nacelle.

70. a
A three-way propeller valve is a selector valve used in a two-position propeller control system. The three-way valve directs oil from the engine lubrication system to the propeller to control a propeller blade's pitch angle.

71. b
The primary purpose of a propeller is to convert engine horsepower to useful thrust. Modern propellers can convert up to 85 percent of an engine's brake horsepower to thrust horsepower.

72. b
A constant-speed propeller achieves maximum efficiency by allowing the pilot to adjust the propeller blade angle as necessary to produce the most efficient blade angle for most conditions encountered in flight.


73. c
The centrifugal twisting force, sometimes called centrifugal twisting moment, acting on a propeller is greater than the aerodynamic twisting force and tries to decrease a propeller's blade angle.

74. b
A propeller's geometric pitch is the theoretical distance that the propeller will move forward in one revolution. Effective pitch, on the other hand, is the actual distance that the propeller moves forward in one revolution. The difference between geometric pitch and effective pitch is called slippage. Therefore, effective pitch plus slippage is equal to geometric pitch.

75. c
Propeller blade angle is the acute angle formed by the propeller blade chord line and the rotational plane of the propeller.

76. c
Torque bending force, in the form of air resistance, tends to bend cause a propeller's tips to lag in the direction of rotation.

77. c
Thrust bending force tends to bend the propeller tips forward as the propeller pulls an aircraft through the air. This force is comparable to the coning action of a helicopter rotor blade, except that the thrust bending force acts forward instead of upward.

78. b
During takeoff, a constant-speed propeller is set for high speed and a low pitch angle so the engine can develop its maximum rated power.

79. c
A certificated mechanic may perform minor repairs or alterations to propeller blades. Deep scars, nicks, and dents on aluminum propeller blades and the straightening of propeller blades are major repairs. These repairs may be performed by a properly certificated repair station or the propeller manufacturer.

80. a
During takeoff, when maximum power and thrust are required, the propeller blades are set to a low blade angle that allows the engine to turn at a high rpm.

81. b
Federal Aviation Regulations require that the longitudinal clearance between the propeller blades or cuffs and stationary parts of the airplane be at least one-half inch measured with the propeller in the most adverse pitch position.

82. a
Most non-counterweight propellers use oil pressure to increase the propeller's blade angle.

83. a
On constant-speed propellers equipped with counterweights, centrifugal force acting on the counterweights is used to increase a propeller's blade angle.

84. c
Hartzell propellers have two grease fittings (zerks) on their hubs. When lubricating these propellers, one zerk should be removed while grease is pumped into the other zerk. This prevents pressure buildup in the grease chamber and helps avoid damaging the blade seals.

85. c
When an engine is shut down in flight, the propeller blades create a substantial amount of drag which decreases aircraft performance. Feathering propellers eliminate this drag by driving the propeller blades to a 90 degree angle.

86. b
Hartzell Compact propellers utilize a latch stop called the automatic high pitch stop to hold the blades in a low angle when the engine is shut down on the ground. The latch mechanism is comprised of springs and lock pins that prevent the propellers from feathering once engine rpm falls below a predetermined value.


87. b
During the first run of a newly installed hydromatic propeller it is necessary to bleed any air that may be trapped in the propeller dome. This is accomplished by several full travel movements of the propeller piston, which forces air back to the engine sump where it is vented through the breather line.

88. c
Front cone bottoming occurs during the installation of a spline shaft propeller when the apex of the front cone contacts the ends of the shaft splines. This happens when the rear cone is too far back on the propeller shaft. When this occurs, neither front nor rear cone can be tightened into the propeller hub's cone seats. The only way to correct this is to move the rear cone forward.

89. c
Front cone bottoming occurs during the installation of a spline shaft propeller when the apex of the front cone contacts the ends of the shaft splines. This happens when the rear cone is too far back on the propeller shaft. When this occurs, neither front nor rear cone can be tightened into the propeller hub's cone seats. The only way to correct this is to move the rear cone forward.

90. b
When the feather button is pushed in a full-feathering hydromatic propeller system, a holding coil keeps the button in the depressed position. The feather button energizes the feathering pump motor which takes oil from the engine supply tank and directs it to the propeller governor. The propeller governor ports this oil to the propeller piston and drives it to the full feather position. When the propeller is fully feathered, pressure in the inboard piston increases rapidly and the electric cutout switch automatically opens. This deenergizes the holding coil which releases the feather button.

91. a
The purpose of the cones for a spine shaft propeller installation is to support and align the propeller hub on the shaft. This is similar to the action of tapered bearings which position and support a wheel on an axle.

92. c
AC 43.1 3-1 B specifies that when a fixed pitch wooden propeller has been installed, the bolts should be checked for tightness after the first flight, after the first 25 hours of flying, and at least every 50 flying hours thereafter. This is because the moisture content of the wood fibers can cause shrinkage after exposure to heat, causing the bolts to become loose. The fibers can also swell from humidity, which will cause the bolts to be too tight.

93. b
A loose retaining nut on a spine shaft propeller installation allows movement between the propeller cones and the hub cone seats. If not corrected, this movement can lead to galling or wear on both the front and rear cones and the cone seats.

94. a
Hydraulically operated constant-speed propellers should be placed in the high rpm, low pitch position for all ignition and magneto checking. This causes the propeller to operate as a fixed-pitch propeller and provides a standard rpm for determining the operating condition of the engine.

95. b
In a hydromatic propeller, the spider shaft oil seal prevents oil from leaking between the spider and the propeller shaft and out around the rear cone.

96. a
Bearing blue color transfer, sometimes called Prussian blue, is used to determine the amount of surface contact between a tapered propeller shaft and the propeller hub. At least 70 percent surface contact is required.

97. c
Propeller blade tracking is the process of determining the blade tip positions relative to each other. A propeller out-of-track condition may indicate a bent propeller shaft or a blade that is bent.

98. c
The three small holes (No. 60 drill) in the metal tipping of a wooden propeller serve to ventilate and release moisture formed by condensation between the tipping and the wooden blade.

99. c
Correction of an out-of-track condition on a fixed pitch wooden propeller is made by inserting paper or brass shims between the inner flange of the metal hub and the propeller boss. On flange type shaft propeller installations, the shim should be placed between the propeller boss and the propeller shaft flange.

100. c
To manually feather a hydromechanical propeller, the propeller control lever is pulled into the feather position. This action ports governor oil pressure from the cylinder in the propeller hub assembly back to the engine and allows the force of springs, counterweights, or compressed air to drive the propeller to the feather position.

101. c
Hydraulically operated constant-speed propellers should be placed in the high rpm, low pitch position when conducting any ignition or magneto checking. This results in a set blade angle that provides a standard rpm for determining the operating condition of the magneto.

102. b
A flanged propeller shaft with dowel pins allows propeller installation in only one position on the crankshaft.

103. a
The shank, or base of an adjustable pitch propeller is subject to more stress than any other portion of the propeller blade. Therefore, no repairs are permitted to the shanks of aluminum alloy adjustable pitch propeller blades.

104. c
An aluminum alloy propeller blade should only be straightened in accordance with the propeller manufacturer's approved procedures. When blade straightening is allowed, it's cold worked only.

105. b
Rotating propellers are constantly subjected to high centrifugal loads and severe vibration. Therefore, any scratch, nick, or gouge can create a stress concentration that could develop into a crack and lead to fatigue failure.

106. a
Repairs of minor defects on aluminum propeller blades should be made parallel to the length of the propeller blade.

107. a
Repairs on the face or back of a propeller blade are made with a spoon-like riffle file, which is used to dish out the damaged area.

108. b
To make sure that all minor scratches or file marks are removed after a repair is made to an aluminum propeller blade you should polish the affected surface with very fine sandpaper. The sandpaper should be moved parallel to the length of the blade and, once the sanding is complete, the repaired area should be treated with an appropriate protective coating.

109. a

110. c
Of the choices given, dye-penetrant inspection is the most effective method of detecting cracks on an aluminum propeller blade. Although a bright light is a valuable tool for assisting in visual inspection, it is not a reliable means of detecting small cracks.

111. b
According to FAR Part 43, Appendix A, shortening propeller blades, or retipping wooden blades, is a major repair. All propeller major repairs must be performed by an appropriately certificated repair station or the propeller manufacturer.

112. a
After performing a dye-penetrant inspection on a propeller, all penetrant residue should be removed using a solvent approved by both the penetrant and propeller manufacturer.

113. b
Dye penetrant inspections allow a properly trained technician to differentiate between cracks and scratches on aluminum propeller blades.

114. c
Rotating propellers are constantly subjected to high centrifugal loads and severe vibration. Therefore, any scratch, nick, or gouge can create stress concentrations that could develop into a crack and lead to fatigue failure.

115. c
A transverse crack is a crack that is parallel to a propeller blade's chord. Transverse cracks of any size are not repairable and render a propeller unairworthy.

116. b
Cold straightening a bent aluminum propeller blade is considered a major repair and, therefore, can only be performed by an appropriately rated repair station or the propeller manufacturer.