23. MODULE 17A (B1) — PROPELLER
32 multi-choice. Time allowed 40 minutes.
1 / 32
Which tapered propeller installation cone is split into two halves and carries serial numbers?
The front (forward) tapered cone is manufactured as two matching half-shells with serial numbers so that matched halves are always kept together to ensure proper fit.
2 / 32
What is the correct policy for propeller securing plate circlips after removal?
Circlips are subject to fatigue from the snap-fitting process; they must be used once only and replaced with new circlips whenever they are removed.
3 / 32
What material are metal fixed-pitch propellers typically manufactured from?
Duralumin and aluminium alloys are used for metal fixed-pitch propellers because they offer a good strength-to-weight ratio, workability and resistance to fatigue.
4 / 32
What does preloading propeller blades before installation achieve?
Pre-loading introduces a compressive stress into the blade root that counteracts the vibratory tensile loads encountered in service, preventing the resonant oscillation known as blade flutter.
5 / 32
As a propeller blade moves through the air, which two aerodynamic forces are produced?
The total aerodynamic force on each blade resolves into thrust (perpendicular to the disc plane, propelling the aircraft forward) and torque (tangential to rotation, opposing the engine’s turning effort).
6 / 32
What angle of attack characterises a windmilling propeller?
When windmilling, the relative airflow meets the blade from the front, giving the blade a small negative angle of attack, which is why a windmilling propeller absorbs energy from the airstream rather than generating thrust.
7 / 32
When the force on the governor speeder spring is increased and RPM rises to match, what adjustment does the governor make to blade angle?
Compressing the speeder spring raises the set-point RPM; the governor responds by porting oil to reduce blade angle (fine pitch), which allows RPM to rise to the new set point.
8 / 32
At what spanwise intervals are measurements normally taken along a propeller blade section?
Propeller blade inspection and measurement is standardised at 6-inch intervals along the span, providing sufficient resolution to characterise the blade aerodynamic and structural profile.
9 / 32
A constant-speed variable-pitch propeller is running on the ground facing into a headwind. What effect does the headwind have on propeller RPM?
The constant-speed unit (governor) automatically adjusts blade angle to compensate for the headwind effect, so RPM remains at the set value.
10 / 32
What does a propeller pitch lock system protect against?
The pitch lock prevents the blades from moving toward fine pitch (fining off) in the event of a governing or pitch change mechanism failure, avoiding an uncontrolled runaway condition.
11 / 32
Why are regular resistance checks performed on electrically de-iced propeller slip rings?
Resistance testing identifies open circuits within the heating elements embedded in the blades, ensuring each element will function when de-icing is selected.
12 / 32
What blade angle is associated with a feathered propeller?
When feathered, the blade chord is aligned approximately parallel to the aircraft flight path, giving a blade angle close to 90° to the plane of rotation, minimising windmilling drag.
13 / 32
When are blade angle adjustments carried out on a variable-pitch propeller?
Blade angle adjustments to a variable-pitch propeller require the engine to be shut down and the propeller stationary; no adjustments are permitted with the engine running.
14 / 32
On an aircraft fitted with a propeller brake, what system is the interlock connected to?
The propeller brake interlock is wired to the HP (high pressure) fuel cock to ensure the fuel supply is cut before the brake can be applied, preventing engine damage.
15 / 32
Which of the following statements about propeller blade angle is incorrect?
On a fixed-pitch propeller, blade angle is set and does not change with RPM; on a constant-speed propeller, blade angle is actively changed to maintain RPM. The statement that blade angle changes automatically with RPM (implying it is a passive/direct relationship) is incorrect.
16 / 32
In a windmilling condition, what effect does the aerodynamic twisting moment (ATM) have on the centrifugal twisting moment (CTM)?
During windmilling the aerodynamic forces produce an ATM in the same rotational direction as CTM; ATM therefore assists CTM in moving the blade toward fine pitch.
17 / 32
Which methods are acceptable for marking blade stations on a propeller blade during inspection?
Only non-damaging methods may be used; masking tape and non-permanent marker are acceptable because they can be removed without leaving marks or stress concentrations on the blade surface.
18 / 32
If the true airspeed of an aircraft increases, how does the constant-speed unit respond?
Higher airspeed increases the apparent pitch of each blade, tending to load the engine and reduce RPM; the CSU responds by increasing blade angle (coarsening) to maintain the selected RPM.
19 / 32
How should a wooden propeller be wrapped during storage?
A wooden propeller must be wrapped loosely to allow the wood to breathe and equalise with ambient humidity, preventing moisture trapping, warping, or splitting.
20 / 32
Under which flight condition does an offset fin most effectively counteract propeller slipstream effect?
The slipstream from a propeller imparts a sideways force on the fin; this effect is greatest at high power combined with low airspeed, which is why the fin offset is designed for those conditions.
21 / 32
On a free turbine turboprop, how can propeller RPM be adjusted while keeping gas-generator RPM constant?
The PCU control lever varies the governor set point for the free turbine shaft, allowing propeller RPM to be changed independently of gas-generator speed.
22 / 32
What range of blade angles does the Beta operating range encompass?
The Beta range extends from maximum reverse pitch up to flight idle pitch, covering the ground operation regime where the pilot has direct blade angle control.
23 / 32
At which blade angle setting does a propeller blade absorb the greatest amount of power?
Power absorbed by a propeller blade is proportional to the total aerodynamic work done; in practice the blade absorbs equivalent power across all blade angles because pitch and thrust trade off equally.
24 / 32
When a reversing propeller moves toward maximum reverse blade angle, through which sequence of positions does it pass?
The blade rotates from fine pitch, through the plane of rotation (zero pitch), then into fine reverse pitch and finally to maximum (coarse) reverse pitch.
25 / 32
What happens to engine RPM when a fixed-pitch propeller aircraft is ground-run with its tail into wind?
With the tail into wind, the relative airflow over the propeller is from the front but reduced in total; the prop blades experience a higher effective angle of attack from the reversed wind component, increasing resistance and causing RPM to decrease.
26 / 32
How is the operation of a propeller electrical de-icing system monitored from the flight deck?
An ammeter (or current indicator) in the flight deck shows the current draw of each de-icing heater circuit, confirming that elements are energised and functioning correctly.
27 / 32
In an on-speed (correctly governed) condition, how does oil behave in the governor pilot valve tube?
When RPM matches the governor set point the pilot valve is centred, blocking oil ports; oil neither enters nor leaves the tube and blade angle remains constant.
28 / 32
How does a multi-engine aircraft synchronising system maintain equal RPM across all propellers?
One designated master propeller control unit (PCU) is the reference; all other engines (slaves) are automatically trimmed to match the master’s RPM.
29 / 32
If a continuous line of indentations is found across more than 25% of the chord at one blade section, what is the correct disposition?
Damage extending across more than 25% of the chord represents a structural hazard; the blade must be declared unserviceable and removed from service.
30 / 32
On what operating principle is the hydromatic variable-pitch propeller based?
The hydromatic system uses servo oil pressure applied to a piston within the propeller hub to drive a rotating cam and gear mechanism that changes blade pitch.
31 / 32
What happens to the centrifugal twisting moment (CTM) acting on propeller blades as rotational speed increases?
CTM is generated by the centrifugal force acting on the blade mass distributed away from the pitch-change axis; as RPM increases, centrifugal force rises and so does CTM.
32 / 32
Along the span of a propeller blade, where is thrust produced most effectively?
The inner portion of the blade from the root to approximately 50% of the radius generates the greatest thrust because the chord is widest and the section camber is most effective in that region.
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