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EASA Part-66 Module17 propeller foundations study materials
EASA Part-66 Module17 propeller foundations study resources

EASA Part-66 Module17 propeller foundations practice questions

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Question 1Blade geometry, loads and construction

In propeller blade element theory, the blade is analysed as a series of small aerofoil sections along its length. Why is the geometric pitch (blade angle) progressively reduced from the root to the tip?

  1. Because the tip moves through a greater rotational distance per revolution than the root, so a smaller angle keeps the angle of attack and advance roughly constant along the blade Correct answer.
  2. Because the root sees a higher relative airflow velocity than the tip and must be unloaded
  3. Because centrifugal force is greatest at the tip and a small angle reduces blade stress
  4. Because the tip operates in compressible flow and a small angle prevents shock formation at all speeds

Explanation

Each blade section advances forward the same distance per revolution but the tip travels a much larger circumferential distance, giving it a higher rotational speed and a shallower helix angle; the blade is therefore 'twisted' with a smaller geometric angle at the tip so each section meets the relative airflow at an efficient angle of attack.

Question 2Blade geometry, loads and construction

Propeller geometric pitch is defined as the distance the propeller would advance in one revolution if it moved through the air like a screw through a solid. The actual distance the propeller advances is the effective pitch. The difference between geometric and effective pitch is known as:

  1. Slip Correct answer.
  2. Blade angle
  3. Helix angle
  4. Angle of attack

Explanation

Slip is the difference between geometric pitch (theoretical advance) and effective pitch (actual advance) and arises because air is a fluid the blade can push backwards rather than a solid; it is usually expressed as a percentage of geometric pitch.

Question 3Blade geometry, loads and construction

For a fixed-pitch propeller, what happens to the angle of attack of the blade sections as the aircraft's forward (true) airspeed increases at a constant engine RPM?

  1. The angle of attack increases because the relative airflow becomes more axial
  2. The angle of attack remains constant because RPM is unchanged
  3. The angle of attack decreases because the forward velocity vector increases the helix angle of the relative airflow Correct answer.
  4. The angle of attack reverses, producing negative thrust

Explanation

The relative airflow at each blade section is the resultant of the rotational velocity and the forward (advance) velocity. As forward speed rises with RPM fixed, the advance component grows, the helix angle of the resultant airflow increases, and because the blade angle is fixed the angle of attack falls - reducing thrust at high speed.

Question 4Blade geometry, loads and construction

Which force acting on a rotating propeller blade is by far the greatest in magnitude and acts to throw the blade outward along its longitudinal axis?

  1. Thrust bending force
  2. Centrifugal twisting moment
  3. Centrifugal force Correct answer.
  4. Aerodynamic twisting moment

Explanation

Centrifugal force, caused by rotation, is the largest single load on a propeller blade and tries to pull each blade radially outward from the hub; it can reach many tonnes of pull at the blade root and dominates blade and retention design.

Question 5Blade geometry, loads and construction

The centrifugal twisting moment (CTM) acting on a rotating propeller blade tends to rotate the blade toward which pitch position, and how is this exploited in many propeller designs?

  1. Toward low (fine) pitch; used to drive the blades to fine pitch on oil-pressure loss Correct answer.
  2. Toward high (coarse) pitch; used to assist feathering
  3. Toward feather; used as an overspeed stop
  4. Toward reverse; used to assist ground braking

Explanation

The centrifugal twisting moment always tries to rotate the blade toward the plane of rotation, i.e. toward low (fine) pitch. Single-engine constant-speed propellers use this natural tendency, often with a spring, so that on loss of governing oil pressure the blades go to fine pitch (high RPM) as a fail-safe.

Question 6Blade geometry, loads and construction

The aerodynamic twisting moment (ATM) on a propeller blade in normal forward thrust acts to rotate the blade toward:

  1. Low (fine) pitch
  2. High (coarse) pitch Correct answer.
  3. The reverse pitch stop
  4. The plane of rotation

Explanation

The aerodynamic twisting moment results from the centre of pressure of the blade aerofoil being forward of the blade's pitch-change axis; this tends to rotate the blade toward high (coarse) pitch. It is smaller than the centrifugal twisting moment, which opposes it toward fine pitch.

Question 7Blade geometry, loads and construction

P-factor (asymmetric blade effect) on a single-engine aircraft at high power and high angle of attack causes the propeller's resultant thrust line to move. For a conventional clockwise-rotating propeller (viewed from behind), the descending blade is on the right side and the aircraft yaws:

  1. To the left, because the descending right blade produces more thrust Correct answer.
  2. To the right, because the descending right blade produces more thrust
  3. To the right, because the ascending left blade produces more thrust
  4. There is no yaw because thrust remains symmetric

Explanation

At a high angle of attack the descending (down-going) blade meets the relative airflow at a greater effective angle of attack and higher resultant velocity, producing more thrust than the up-going blade. For a clockwise propeller the descending blade is on the right, so the extra thrust on the right yaws the nose left.

Question 8Blade geometry, loads and construction

Propeller torque reaction tends to roll the aircraft in which direction, and why?

  1. In the opposite direction to propeller rotation, as a Newton's third-law reaction to the torque driving the propeller Correct answer.
  2. In the same direction as propeller rotation, because of conservation of momentum
  3. Toward the descending blade, because of asymmetric thrust
  4. It produces a pitching moment, not a rolling moment

Explanation

By Newton's third law, the engine torque that spins the propeller produces an equal and opposite reaction on the airframe. A propeller turning clockwise (viewed from behind) therefore produces a torque reaction that tends to roll the aircraft to the left (anticlockwise).

Question 9Blade geometry, loads and construction

A propeller blade section is identified by reference points. The portion of the blade that mates with the hub is the root or shank; the leading-edge side that faces forward in flight is the:

  1. Blade face (the cambered side toward the cockpit)
  2. Blade back (the cambered, lower-pressure side toward the front) Correct answer.
  3. Blade station
  4. Blade shank fairing

Explanation

The blade back is the cambered (curved) side that faces the direction of flight and develops lower pressure, analogous to the upper surface of a wing; the blade face is the flatter side facing aft toward the pilot. The pressure difference between back and face generates thrust.

Question 10Blade geometry, loads and construction

A propeller is described as a 'constant-speed' propeller. The defining feature of a constant-speed propeller is that it:

  1. Has its blade angle fixed at manufacture and cannot be changed
  2. Has two selectable blade angles, one for takeoff and one for cruise
  3. Automatically varies blade angle to hold a selected RPM constant over a range of power and airspeed Correct answer.
  4. Holds a constant blade angle while the engine RPM varies with airspeed

Explanation

A constant-speed propeller uses a governor/constant-speed unit that continuously adjusts blade angle to keep the engine RPM constant at the value selected by the pilot, regardless of changes in power, airspeed or attitude within the governing range.

Question 11Blade geometry, loads and construction

Modern composite propeller blades commonly use a foam or low-density core wrapped in fibreglass/carbon and bonded to a metal shank. Compared with solid aluminium-alloy blades, a key advantage of composite blades is:

  1. Lower weight and the ability to repair surface damage and erosion, with metal shanks retained for hub attachment Correct answer.
  2. They cannot suffer any fatigue and so have no life limit
  3. They eliminate the need for any balancing after manufacture
  4. They are fully conductive and need no separate lightning/static protection

Explanation

Composite blades are lighter than equivalent metal blades, can be designed with thin efficient sections, and minor surface and erosion damage can often be repaired; a metal shank or ferrule is retained to take the centrifugal retention loads at the hub.

Question 12Blade geometry, loads and construction

On older wooden propellers, a thin metal sheath (tipping) is fitted to the leading edge near the tip and small holes are drilled in it at the tip. The primary purpose of these drain/breather holes is to:

  1. Allow trapped moisture to escape and prevent the wood swelling or the tipping lifting Correct answer.
  2. Reduce the propeller's weight at the tip for balance
  3. Bleed off static electrical charge from the blade
  4. Provide attachment points for de-icing boots

Explanation

Wooden blades absorb moisture; the metal leading-edge tipping is drilled with small holes near the tip so that any moisture collecting under the sheath can drain or evaporate, preventing the wood from swelling and the metal tipping from lifting in service.

Question 13Blade geometry, loads and construction

A blade station is used to specify blade angle and to locate measurements along the blade. A blade station is defined as:

  1. A specified distance, in inches or millimetres, measured from the centre of the hub along the blade Correct answer.
  2. The point of maximum blade thickness
  3. The angle between the blade chord and the plane of rotation at the tip
  4. The location of the blade's centre of pressure

Explanation

A blade station is a reference position measured as a distance from the hub centre along the blade radius (for example the 30-inch or 42-inch station). Blade angle is normally quoted at a specified reference station, often around the 75% radius.

Question 14Blade geometry, loads and construction

A two-position controllable-pitch propeller differs from a constant-speed propeller in that it:

  1. Provides infinitely variable blade angles automatically held by a governor
  2. Allows the pilot to select one of two fixed blade angles, with no automatic RPM regulation between them Correct answer.
  3. Can be feathered but not reversed
  4. Has a fixed blade angle set during overhaul

Explanation

A two-position controllable-pitch propeller lets the pilot select either a fine (takeoff/climb) or coarse (cruise) blade angle, but unlike a constant-speed propeller it does not have a governor automatically varying the angle to hold a set RPM.

Question 15Blade geometry, loads and construction

A 'left-hand' propeller is one that, viewed from behind (from the cockpit), rotates:

  1. Clockwise
  2. Only in reverse
  3. Anticlockwise (counter-clockwise) Correct answer.
  4. In either direction depending on power

Explanation

By the usual convention, a propeller's hand is defined by its direction of rotation viewed from the rear (cockpit side). A left-hand propeller turns anticlockwise; a right-hand propeller turns clockwise. On counter-rotating twins this convention identifies which engine takes which propeller.

Question 16Blade geometry, loads and construction

Why are the thick, structurally strong but aerodynamically inefficient blade root/shank areas sometimes fitted with blade cuffs (shank fairings)?

  1. To add weight for balance
  2. To act as de-icing fluid reservoirs
  3. To improve the airflow over the inboard sections and increase cooling airflow into the engine cowling/nacelle Correct answer.
  4. To stiffen the blade against centrifugal force

Explanation

Blade cuffs are aerofoil-shaped fairings fitted over the thick, near-cylindrical shank region. They convert the inefficient inboard sections into useful aerofoils, improving airflow and helping to scoop additional cooling air into the engine nacelle.

Question 17Blade geometry, loads and construction

Propeller blade vibration and resonance are influenced by the natural frequency of the blade. A first-order (1P) vibration occurs:

  1. Once per second regardless of RPM
  2. At twice the engine firing frequency
  3. Once per propeller revolution, often linked to aerodynamic or mass imbalance Correct answer.
  4. Only during feathering

Explanation

A 1P (first-order) vibration occurs once per revolution of the propeller and is commonly associated with imbalance, an out-of-track blade, or aerodynamic asymmetry; it is the vibration that dynamic balancing primarily targets.

Question 18Blade geometry, loads and construction

A fixed-pitch propeller selected for an aircraft used mainly for high-speed cruise (a 'cruise prop') compared with a 'climb prop' will have:

  1. A finer (lower) blade angle for better climb and takeoff
  2. A variable blade angle
  3. A coarser (higher) blade angle, giving better cruise efficiency but reduced takeoff/climb thrust Correct answer.
  4. A shorter diameter to spin faster

Explanation

A cruise propeller is given a coarser fixed blade angle so it is efficient at cruise speed; the trade-off is reduced thrust at low speed, giving a longer takeoff run and poorer climb than a finer 'climb' propeller of the same diameter.

Question 19Blade geometry, loads and construction

The 'blade angle' of a propeller is correctly defined as the angle between the:

  1. Relative airflow and the chord line of the blade section
  2. Chord line of the blade section and the plane of rotation Correct answer.
  3. Blade leading edge and the blade trailing edge
  4. Resultant airflow and the longitudinal axis of the aircraft

Explanation

Blade angle (pitch angle) is the angle between the chord line of a given blade section and the propeller's plane of rotation. It must be distinguished from angle of attack, which is measured between the chord and the relative airflow.

Question 20Blade geometry, loads and construction

Geometric pitch and effective pitch differ. If a propeller has a geometric pitch of 60 inches and an effective pitch of 50 inches at a given condition, the slip is:

  1. 10 inches, or about 17% of geometric pitch Correct answer.
  2. 10 inches, or about 20% of effective pitch only
  3. 110 inches
  4. 0 inches because the propeller is efficient

Explanation

Slip is geometric pitch minus effective pitch: 60 - 50 = 10 inches. Expressed as a percentage of geometric pitch it is 10/60 = 16.7%, i.e. about 17% slip.

Question 21Blade geometry, loads and construction

A windmilling propeller (engine failed, blades not feathered, prop driven by the airflow) creates a large amount of drag. This drag is greatest when the blades are at a:

  1. Feathered (edge-on) angle
  2. Coarse (high) blade angle
  3. Reverse angle
  4. Fine (low) blade angle, presenting a large flat area to the airflow Correct answer.

Explanation

An unfeathered, windmilling propeller produces the most drag at a fine (low) blade angle because the blades present a large frontal area and act like a disc; this is why a failed engine's propeller is feathered to coarse/edge-on to minimise the drag.

Question 22Blade geometry, loads and construction

When the relative airflow at a propeller blade section is constructed, it is the vector sum of two velocities. These are:

  1. The aircraft's forward (advance) velocity and the section's rotational velocity Correct answer.
  2. The aircraft's forward velocity and the wind velocity
  3. The rotational velocity and the slipstream velocity only
  4. The induced downwash and the freestream

Explanation

Each blade section meets a relative airflow that is the resultant of the forward (advance) velocity of the aircraft and the rotational (tangential) velocity of that section. The angle of this resultant to the plane of rotation is the helix/advance angle, and the blade angle minus this gives the angle of attack.

Question 23Blade geometry, loads and construction

Propeller efficiency is defined as the ratio of the:

  1. Engine power input to the thrust power output
  2. RPM to the forward speed
  3. Geometric pitch to the effective pitch
  4. Thrust power output (thrust x forward speed) to the shaft power input from the engine Correct answer.

Explanation

Propeller efficiency is the useful thrust power produced (thrust multiplied by the aircraft's true airspeed) divided by the shaft (brake) power delivered to the propeller by the engine. Typical maximum efficiencies are around 80-90% at the design condition.

Question 24Blade geometry, loads and construction

At very high forward speeds, fixed-pitch propeller efficiency falls off rapidly. The main reason a constant-speed propeller maintains higher efficiency across a wide speed range is that it:

  1. Always uses a very fine blade angle
  2. Adjusts blade angle to keep the blade sections at an efficient angle of attack as forward speed changes Correct answer.
  3. Increases RPM continuously with speed
  4. Reduces its diameter at high speed

Explanation

A constant-speed propeller varies its blade angle as forward speed and power change, keeping each blade section near its most efficient angle of attack. This avoids the efficiency loss that a fixed-pitch propeller suffers when its single blade angle is no longer optimum for the new speed.

Question 25Blade geometry, loads and construction

Tip speed is a limiting factor in propeller design. As the helical tip speed approaches the local speed of sound, the consequences include:

  1. Increased efficiency and reduced noise
  2. No effect, as propellers are unaffected by Mach number
  3. Automatic feathering of the blades
  4. Compressibility effects, shock formation, a sharp rise in drag and noise, and loss of efficiency Correct answer.

Explanation

When the helical (resultant) tip speed nears Mach 1, compressibility produces shock waves at the tips, causing a steep rise in drag and noise and a loss of efficiency. This limits practical propeller diameter and RPM, and is why tip speed is controlled in design and operation.

Question 26Blade geometry, loads and construction

A wooden propeller is constructed from several laminations of selected hardwood glued together, rather than from a single block, primarily to:

  1. Make it heavier for balance
  2. Allow the blade angle to be changed in flight
  3. Make it electrically conductive
  4. Improve strength, reduce the tendency to warp, and balance internal stresses Correct answer.

Explanation

Laminating several layers of selected, seasoned hardwood and bonding them with the grain arranged appropriately gives a stronger, more dimensionally stable blade that resists warping and distributes internal stresses better than a single solid block.

Question 27Blade geometry, loads and construction

On a constant-speed propeller, the relationship between selected RPM and blade angle in level cruise is such that, for the same power, a higher selected RPM corresponds to a:

  1. Coarser blade angle
  2. Finer blade angle Correct answer.
  3. Feathered blade
  4. Reverse blade angle

Explanation

To run faster at the same power, the governor holds the blades at a finer (lower) angle so each blade takes a smaller bite of air per revolution; a lower selected RPM at the same power is achieved with a coarser angle.

Question 28Blade geometry, loads and construction

The plane of rotation of a propeller is:

  1. The plane containing the longitudinal axis of the aircraft
  2. The plane of the relative airflow
  3. The plane tangent to the blade tip path at one point
  4. The plane perpendicular to the propeller shaft in which the blades sweep as they rotate Correct answer.

Explanation

The plane of rotation is the disc-shaped plane, perpendicular to the propeller shaft axis, swept out by the rotating blades. Blade angle is measured between the blade chord and this plane.

Question 29Blade geometry, loads and construction

Thrust bending force on a propeller blade in normal operation tends to:

  1. Pull the blade radially out of the hub
  2. Bend the blade forward (in the direction of thrust) about its weakest section Correct answer.
  3. Twist the blade to fine pitch
  4. Twist the blade to coarse pitch

Explanation

Thrust acts forward along the propeller axis and, distributed along the blade, tends to bend the blades forward. Centrifugal force, being much larger, partly offsets this bending by tending to straighten the blade radially.

Question 30Blade geometry, loads and construction

A propeller's 'activity factor' is a design parameter that broadly indicates the:

  1. Number of de-icing cycles per minute
  2. Number of blades
  3. Maximum RPM the propeller may turn
  4. Power-absorbing capacity of the blade, related to its planform (chord distribution) and area Correct answer.

Explanation

Activity factor is a non-dimensional measure of a blade's power-absorbing capability derived from its chord (planform) distribution along the radius. A higher activity factor (wider blades) absorbs more power, allowing a given power to be handled with fewer or smaller-diameter blades.

Question 31Blade geometry, loads and construction

Multi-blade (e.g. four-, five- or six-blade) propellers are increasingly used on modern turboprops mainly to:

  1. Reduce manufacturing cost
  2. Eliminate the need for a governor
  3. Allow the propeller to run without balancing
  4. Absorb high engine power while keeping diameter and tip speed (and hence noise) within limits, and to reduce vibration Correct answer.

Explanation

Adding blades lets a propeller absorb more power without increasing diameter or tip speed, which keeps tip Mach number and noise down and can smooth vibration. This is why high-power turboprops often use four to six (or scimitar) blades rather than a larger two-blade propeller.

Question 32Governing, feathering and ground pitch control

In a typical single-engine constant-speed propeller (e.g. Hartzell compact hub without counterweights), the governor directs engine oil under pressure to the propeller piston to move the blades toward:

  1. Coarse pitch; with oil pressure released, a spring and the centrifugal twisting moment drive the blades fine Correct answer.
  2. Fine pitch; with oil pressure released, a spring and the centrifugal twisting moment drive the blades coarse
  3. Feather; with oil pressure released the blades go to reverse
  4. Reverse; with oil pressure released the blades go to feather

Explanation

In a non-counterweighted single-engine constant-speed propeller, governor oil pressure moves the piston to drive the blades toward coarse (high) pitch; if oil pressure is lost, the internal spring assisted by the centrifugal twisting moment returns the blades to fine (low) pitch / high RPM as a fail-safe.

Question 33Governing, feathering and ground pitch control

A propeller governor maintains a selected RPM using three main elements. Which set of components correctly describes the governing mechanism?

  1. Speeder spring, flyweights, and a pilot valve, with an engine-driven gear oil pump Correct answer.
  2. Accumulator, slinger ring, and a feathering latch
  3. Synchrophaser, magnetic pickup, and a stepper motor
  4. Beta tube, reversing lever, and a low-pitch stop

Explanation

A propeller governor balances the speeder spring (set by the prop control) against the centrifugal force of rotating flyweights; the flyweights position a pilot valve that ports boosted oil from the governor's gear pump to or from the propeller to change pitch and hold the selected RPM.

Question 34Governing, feathering and ground pitch control

A constant-speed propeller is governing at the selected RPM (the 'on-speed' condition). In this state, the governor flyweights and the speeder spring are:

  1. In equilibrium, so the pilot valve neither ports oil to nor from the propeller and the blade angle is steady Correct answer.
  2. In a state of imbalance, with the flyweights overcoming the spring
  3. Both fully extended, holding the pilot valve fully open
  4. Disconnected, because the governor is inactive when on-speed

Explanation

At the on-speed condition the centrifugal force of the flyweights exactly balances the speeder-spring force; the pilot valve sits in its neutral position so oil is neither added to nor drained from the propeller, holding the blade angle and RPM constant.

Question 35Governing, feathering and ground pitch control

During a descent at fixed throttle, the engine of a constant-speed propeller installation tends to speed up, creating an 'over-speed' condition. The governor responds by:

  1. Decreasing blade angle to reduce load and recover RPM
  2. Increasing blade angle (toward coarse) to add aerodynamic load and bring RPM back to the selected value Correct answer.
  3. Holding blade angle and signalling the pilot to reduce throttle
  4. Feathering the propeller to prevent over-speed

Explanation

In over-speed the flyweights move out, raise the pilot valve, and oil is ported to drive the blades toward a coarser angle. The increased aerodynamic load slows the propeller back to the selected RPM, restoring the on-speed condition.

Question 36Governing, feathering and ground pitch control

Moving the propeller control lever rearward in the cockpit changes the speeder-spring tension in the governor. Reducing speeder-spring tension causes the governor to select:

  1. A lower RPM, because the flyweights overcome the reduced spring force at a lower speed, driving the blades coarse Correct answer.
  2. A higher RPM, because less spring force lets the flyweights overcome it sooner
  3. The same RPM, because the spring only affects oil pressure
  4. Feather, because the spring is fully relaxed

Explanation

Pulling the prop control back reduces speeder-spring force, so the flyweights reach equilibrium (fly out) at a lower rotational speed; the governor therefore drives the blades toward coarse pitch until the engine settles at the new, lower selected RPM.

Question 37Governing, feathering and ground pitch control

The governing range of a constant-speed propeller is bounded by mechanical stops. When the blades reach the low-pitch (fine) stop and the propeller is still under-speeding, the propeller effectively behaves as a:

  1. Fixed-pitch propeller, with RPM then varying with power and airspeed Correct answer.
  2. Feathered propeller
  3. Reversing propeller
  4. Two-position propeller

Explanation

Once the blades are against the fine-pitch stop the governor can no longer reduce pitch further, so the propeller acts like a fixed-pitch propeller. RPM then varies directly with throttle and airspeed until conditions return the engine within the governing range.

Question 38Governing, feathering and ground pitch control

On a feathering constant-speed propeller fitted with counterweights, the function of the blade counterweights is to:

  1. Increase the centrifugal twisting moment toward fine pitch
  2. Provide a centrifugal moment that drives the blades toward coarse pitch / feather, opposing the fine-pitch tendency Correct answer.
  3. Balance the propeller statically only
  4. Damp torsional vibration in the crankshaft

Explanation

Counterweights are fitted at an angle to the blade so that, as the propeller rotates, their centrifugal force generates a moment driving the blades toward coarse pitch and feather. This works with feathering springs to overcome the natural centrifugal twisting moment that wants fine pitch.

Question 39Governing, feathering and ground pitch control

Why is feathering a propeller after an engine failure on a multi-engine aircraft so important?

  1. It aligns the blades roughly edge-on to the airflow, stopping the propeller windmilling and greatly reducing drag Correct answer.
  2. It increases the windmilling drag to slow the aircraft down
  3. It keeps the dead engine turning so it can be restarted
  4. It provides reverse thrust to assist directional control

Explanation

Feathering turns the blades to a high angle (approximately 80-90 degrees) so they lie almost edge-on to the airflow. This stops the propeller windmilling and minimises drag, which is critical for climb performance and controllability after an engine failure.

Question 40Governing, feathering and ground pitch control

On many piston-twin feathering propellers, what prevents the propeller from feathering automatically every time the engine is shut down normally on the ground?

  1. Spring-loaded anti-feathering (centrifugal) latches engage below a certain RPM and lock out the feathering springs Correct answer.
  2. The governor pilot valve mechanically blocks the feather oil line at low RPM
  3. The de-icing slinger ring holds the blades in fine pitch
  4. Residual oil pressure in the hub holds the blades fine

Explanation

Centrifugally operated anti-feathering latches (start locks) engage as the propeller slows below a set RPM (commonly around 800 RPM), mechanically holding the blades at a fine/start position so the feathering springs cannot drive the blades to feather during a normal ground shutdown.

Question 41Governing, feathering and ground pitch control

A turboprop's 'beta range' refers to the regime of operation in which:

  1. The governor alone schedules blade angle to hold a constant RPM (the flight/alpha range)
  2. Blade angle is controlled directly by the power lever (ground operation), covering ground-fine, flight idle and reverse, rather than by the governor holding RPM Correct answer.
  3. The propeller is feathered and the engine is shut down
  4. Only the synchrophaser controls the blade angle

Explanation

The beta range is the ground-operation regime in which blade angle is set directly by the power lever position (ground-fine through reverse) instead of being scheduled by the constant-speed governor. The alpha (flight) range is where the governor holds the selected RPM.

Question 42Governing, feathering and ground pitch control

On a Hartzell/McCauley style feathering propeller, the feathering force that drives the blades to feather when governing oil pressure is released is provided primarily by:

  1. Internal feathering springs assisted by the blade counterweights' centrifugal moment Correct answer.
  2. Engine oil pressure boosted by the governor
  3. The centrifugal twisting moment of the blades
  4. A slinger ring pressurised by de-icing fluid

Explanation

In these designs governing oil holds the blades against feather; to feather, the oil is dumped and the feathering springs together with the counterweights' centrifugal moment drive the blades to the feather position. This is why pulling the prop control to feather (or a feather solenoid) releases the oil.

Question 43Governing, feathering and ground pitch control

An accumulator is sometimes fitted in the propeller feathering/unfeathering system. Its purpose during an in-flight restart is to:

  1. Store oil under pressure that can be released to drive the blades out of feather (unfeather) so the engine can be restarted Correct answer.
  2. Store de-icing fluid for the slinger ring
  3. Damp pressure pulses in the synchrophasing circuit
  4. Provide emergency electrical power to the feathering pump

Explanation

An unfeathering accumulator holds a charge of pressurised oil. When unfeathering is selected, this stored oil is released into the propeller to move the blades out of feather toward fine pitch, allowing the engine to windmill and restart.

Question 44Governing, feathering and ground pitch control

In a Hamilton Standard Hydromatic propeller, both fine-pitch and coarse-pitch movement are achieved using oil pressure on opposite sides of the piston (a double-acting design). The dome piston motion is converted into blade rotation by:

  1. A slinger ring and feed shoes
  2. Cam tracks (a fixed cam and a rotating cam) that translate axial piston movement into blade rotation Correct answer.
  3. A direct rack-and-pinion on each blade root only
  4. Centrifugal counterweights acting alone

Explanation

In the Hydromatic, the dome piston moves axially under oil pressure and engages a fixed cam and a rotating cam; the cam-and-roller arrangement converts the axial motion into rotation of the blades, giving positive control to both fine and coarse pitch and to feather.

Question 45Governing, feathering and ground pitch control

In a constant-speed system, what is the effect of selecting a lower RPM with the propeller control during cruise (engine power unchanged)?

  1. Blades go finer, the engine speeds up, and fuel flow rises
  2. Blades feather and the engine stops
  3. Blades go coarser, the engine slows to the new RPM, and, for a given power, propeller efficiency at cruise often improves Correct answer.
  4. Nothing changes until the throttle is also moved

Explanation

Pulling the prop control back lowers the governed RPM; the governor drives the blades coarser to absorb the same power at the lower speed. Within limits this is a normal cruise technique that can improve propeller efficiency and reduce noise at the lower RPM.

Question 46Governing, feathering and ground pitch control

A constant-speed propeller is observed to 'hunt' (RPM cycles up and down) and surge. A likely cause within the propeller/governor system is:

  1. Correctly adjusted governor and clean oil
  2. An over-tightened spinner
  3. Air or contamination in the governor oil, a sticking pilot valve, or an incorrectly set governor causing unstable governing Correct answer.
  4. A correctly tracking propeller

Explanation

Hunting (cyclic RPM surging) usually indicates unstable governing - air entrained in the oil, contamination, a sticking pilot valve or worn governor parts, or an out-of-adjustment governor. The governor cannot settle on the on-speed point and continually over-corrects.

Question 47Governing, feathering and ground pitch control

A 'feathering pump' (auxiliary oil pump) is fitted to many turboprop and large piston feathering systems. Its main role is to:

  1. Supply de-icing fluid to the slinger ring
  2. Lubricate the governor flyweight bearings
  3. Provide an independent supply of high-pressure oil to feather (and sometimes unfeather) the propeller even if the engine and its oil pump have failed Correct answer.
  4. Pressurise the spinner against ice

Explanation

A feathering pump is an electrically driven auxiliary oil pump that can supply high-pressure oil to the propeller to feather it (and on some systems unfeather it) independently of the engine-driven pump, which may be unavailable after an engine failure.

Question 48Governing, feathering and ground pitch control

Why is a low-pitch (fine) stop and a separate latch arrangement provided so that a turboprop cannot enter reverse pitch in flight?

  1. To save oil
  2. Because selecting reverse (negative) blade angle in flight would produce dangerous loss of thrust/control and possible structural overload; a flight-idle stop must be deliberately unlocked for ground use Correct answer.
  3. To reduce noise in the cruise
  4. To prevent feathering

Explanation

Entering reverse pitch in flight would create sudden negative thrust and severe handling and structural hazards. A flight-idle/low-pitch stop, released only by a ground interlock (for example weight-on-wheels or a lifted gate), prevents the power lever from selecting reverse while airborne.

Question 49Governing, feathering and ground pitch control

The beta tube (or feedback/follow-up rod) in a turboprop propeller pitch-control system provides:

  1. De-icing fluid metering
  2. Electrical RPM signals to the synchrophaser
  3. Mechanical feedback of the actual blade angle to the control unit so the system knows the blade position in the beta (ground) range Correct answer.
  4. Oil scavenge from the hub

Explanation

The beta tube is a feedback element that follows the piston/blade position and reports actual blade angle back to the propeller control. This closed-loop feedback lets the control accurately set ground-fine, idle and reverse angles in the beta range.

Question 50Governing, feathering and ground pitch control

A constant-speed propeller installation shows a steady RPM that is too high and will not reduce below the governed maximum even with the prop control fully back. A probable cause is:

  1. The blades are stuck against the coarse-pitch (high) stop
  2. The de-icing system is on
  3. The spinner is loose
  4. The governor is not porting oil correctly, the pitch-change mechanism is jammed at fine pitch, or the prop control linkage is disconnected, so the blades cannot coarsen Correct answer.

Explanation

If RPM stays high and the blades will not coarsen, the pitch-change system is failing to move the blades toward coarse - a governor fault, a jammed mechanism stuck near fine pitch, or a disconnected control linkage. The fault must be found before flight, as RPM cannot be controlled.