Constant Speed Propeller

RENGINES/N-301

QUIOC, DARYL L.

ORENZO, RONDON CYRIL

PROPELLER BASICS

PROPELLER

-consist of two or more blade connected together by a hub attach to

the engine shaft.

-converts rotational power from the engine into thrust.

PROPELLER

• A propeller blade is designed similar to a wing but it

must work while rotating about a center hub.

COMPONENTS

COMPONENTS

CONSTANT SPEED PROPELLER

• Is a device which allows us to efficiently convert power from the engine into thrust.

• Adjusting propeller pitch allows for better efficiency (more engine power converted into thrust) in a variety of flight attitudes (climb, cruise, etc)

• Greater pitch demands greater torque from the engine, thus for a given power setting, the result is lower RPM’s

• Pitch is controlled by the (blue) pitch

control lever

PROPELLER CONTROL

• Oil is supplied through the propeller

piston to a piston head, which is

pushed down due to the oil

pressure, pushing it against a spring

and holding it into a high-pitch

position

INCREASING PITCH

• The pressure is maintained in the

system to hold the pitch on the

propeller

MAINTAINING PITCH

• Oil is allowed to drain from the system,

allowing the spring to “win” against the

oil, forcing the pitch to high pitch

DECREASING PITCH

THE GOVERNOR

• Governor controls

the oil pressure to

the propeller (thus,

controlling pitch)

THE GOVERNOR – CONTROLLING PITCH

• The propeller control

lever tightens a

threaded shaft that in

turn tightens the

speeder spring, which

increases resistance

against spinning

flyweights, which are

mechanically

connected directly to

the engine…

CONTROL OF THE GOVERNOR

Speeder

Spring

To Prop Lever

Flyweights

Prop Lever Forward Prop Lever Back

• When engine RPM is slower than

the propeller control setting, the

speeder spring holds the pilot

valve down and oil flows from the

propeller…

• This is called “underspeed”

GOVERNOR UNDERSPEED

Speeder Spring

To Prop Lever

Spinning

Flyweights

• As engine RPM increases, the

tops of the weights are thrown

outward by centrifugal force; the

lower legs then pivot up, raising

the pilot valve against the force of

the speeder spring so no oil can

flow to or from the propeller…

GOVERNOR ON SPEED

Speeder Spring

To Prop Lever

Spinning

Flyweights

• The faster the flyweights spin, the

further out they are thrown,

causing the pilot valve to be

raised (against the spring) and

allowing more oil to flow to the

propeller…

• This is called “overspeed”

GOVERNOR OVERSPEED

Speeder Spring

To Prop Lever

Spinning

Flyweights

PUTTING IT ALL TOGETHER

• On Speed condition results when the

RPM is constant. Movement of the

cockpit controls have set the speeder

springs at the desired RPM. The

flyweights have positioned the pilot

valves to direct oil to or from the

propellers. This, in turn, has positioned

the propeller blades at a pitch that

absorbs the engine power or RPM

selected. When the moment of RPM

balance occurs, the force of the

flyweights equals the speeder spring

load. This positions the pilot valves in

the constant RPM position with no oil

flowing to or from the propellers.

ON SPEED

• At constant speed, an Overspeed

condition results and airspeed

increases when the airplane begins a

descent or engine power is increased.

Since the pitch of the propeller blades

is too low to absorb engine power, the

engine RPM begins to increase. At the

instant this happens, however, the

flyweights move out and raise the pilot

valves, causing oil to flow to the

propeller, increasing the pitch of the

blades in both cases. Engine speed

then slows to the original RPM setting.

OVERSPEED

• If the airplane begins to climb or

engine power is decreased, an

Underspeed condition results.

Airspeed is reduced and, since the

pitch of the propeller blades is too

high, the engines begin to slow down.

At the instant this happens, the

flyweights will droop, causing the pilot

valves to move down. Simultaneously,

oil flows from the propeller, reducing

the pitch of the blades. This

automatically increases the speed of

the engines to maintain the original

RPM setting.

UNDERSPEED

OTHER INFORMATION

• The governor boosts the oil pressure sent to the propeller by 3 to 6 times (e.g. to 300 PSI)

• The governor range sets the limit on maintaining a constant speed propeller

• Beyond these limits, throttle has a direct control on the RPM’s

• Within these limits, the propeller pitch adjusts for any given throttle setting to maintain the RPM’s

• In general, maintain propeller setting (RPM) higher than throttle setting (manifold pressure)