Aircraft Propeller Systems

The engine and propeller combination have a resonant frequency problem in which excessive vibration can occur in a certain range of RPM. The tachometer for an aircraft with this limitation is marked with a red arch. When it is necessary to pass throuhg this range it must be done as quickly as possible

Toward a lower pitch

Toward a higher pitch

The accumulator stores oil under pressure when the engine is operating normally. This oil is used to help the propller blades move toward a lower pitch when the blades are unfeathered.

This is the in-flight mode of operation from takeoff to landing.

In low pitch.

Install a spacer behind the rear cone to move the propeller forward on the shaft.

The relationship between the propeller and the crankshaft is determined to reduce vibration.

The snap-ring allows the propeller to be pulled off of the shaft when the retaining nut is backed off.

Fixed-pitch, ground adjustable, constant-speed non-feathering, and constant-speed feathering

Wood, aluminium, steel, composite construction.

The comperssion of the speeder spring

Oil is allowed to drain out of the propeller.

A spring-loaded latch mechanism prevents the blades from moving into the feathering position when the engine is shut down on the ground. When in the air, aerodynamic forces keep the propeller rotating fast enough that centrifugal force holds the baldes unlatched so they can move to the feathered position when oil pressure is taken out of the propeller.

High-pressure engine oil is directed into the propeller through the governor.

The pilot moves the propeller pitch control. This changes the compression on the speeder spring inside the governor which moves the pilot valve. The pilot valve directs oil into or out of the propeller to change the pitch of the blades. THe changes in pitch changes the air laod on the propeller which changes the RPM.

Basically, it is the control system. A controllable-pitch propeller uses a manually operated oil valve to control pitch, and a constant-speed propeller uses a goveror to control the valve.

Propeller control should be in the low-pitch, HIGH RPM position.

This is the mode of ground operation, and it includes starting, taxiing, and ground reverse operation.

When operating in the beta range, blade angle is determined by the power lever.

In the Maintenance Manual for the propeller

Only minor repairs or minor alterations.

AC 43.13-1C Chapter 8 section 4 and in the propeller maintenance manuals

No, this could cause hidden damage that may render the balde nonrepairable.

This would be a Major Repair

No, a transverse crack of any size is reason for rejecting the balde

Small roughness, nicks, and scrratches in the leading edge of the blade.

File them out with a fine file or stone, leaving a smooth contour.

Clean the damage out to a sasucer shape depression and spray the area with a dye-peretrant liquid. Allow it time to seep into the crack (if one is present), wipe away all of the liquid. Spray the area with a developer. If the damage is actually a crack, the developer will pull the penetrant out and form a visible line.

The manufacturer or a repair station aapproved by the manufacturer (FAA-approved)

- Check the track of the propeller blades
-Remove small nicks and scratches in the blades
-Check the dynamic balance of a propeller
-Lubricate the propeller

Adjust the Maximum RPM stop

A universal propeller protractor

At a distance from the center of the propeller hub. This distnce is specified in the propeller maintenance manual in therms of propeller blade stations.

1. Remove the spinner and remove the safety wire from the mounting bolts (if they are drilled heads)
2. Support the propeller with a sling and mark the alignment between the propeller hub and the engine flange with a felt-tip pen
3. Unscrew the mounting nuts and protect the threads of the mounting studs or bolts as the propeller is removed
4. Place the propeller on a cart for transport

Special studs or dowel pins align the propeller to the engine in the proper orientation.

An FAA-approved propeller repair station with approval for the particular propeller.

The Aircraft TCDS specifies which propellers are approved for installation.

This is the engine in a multi-engine airplane whose ROMs follow those set on the master engine.

- The propeller governor of the mster engine is set to the desired RPM.
- A signal from the master engine governor is sent to the control box which sends a signal to a stepping motor.
- This motor adjusts the propeller governor and fuel control of the slave engine causing it to maintain exactly the same RPM as the master engine.

-A chemical ant-icing agent system is used.
-A mixture of isopropyl alcohol and ethylene glycol is pumped into a slinger ring on the back of the propeller hub.
-From there centrifugal force slings it out along the blades. Ice cannot from on the resulting slick surface.

-An electrothermal deicing system is used.
-Electric heating elements are embedded in rubber boots that are bonded to the leading edge of the baldes and slip rings to the heating elements.
-The timer sends current to one propeller for about 90 seconds and then to the other for the next 90 seconds.
-This allows the ice to form and then break loose and blow away.

-Observe the loadmeter or ammeter to see if the proper current is flowing.
-Follow the sequence of boot heating by feeling with your hands to see which one is heating.
-The boots should all have similar heat rise in the same length of time.

-Propellers become nearly invisible when spinning rapidly and may not be visible to those close to the airplane.
-Measures must be in place to prevent people from approaching the airplane when the engine is running.
-Propeller blast is also a potential danger that can cuase damage to equipment or other aircraft behind the running engine. Before starting an engine, the aviation mechnaic must use caution and understand what is behind the operating engine.
-Areas below and in front of the propeller should be checked for gravel, rocks, and other FOD what could damage the propeller while operating.