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Propeller

Piaggio Avanti

SimsAir

Propellers The aircraft's five-bladed constant speed, full-feathering, reversible propellers are manufactured by Hartzell. The propeller blades are attached to a hub, which has a servo piston, low pitch stop rod(s), low pitch stop collar, feathering spring, and beta yoke. The servo piston moves the blades to change pitch in response to oil pressure supplied by a primary governor. Counterweights on each propeller blade assisted by the feathering spring move the blades to the feathered position with loss of controlling oil pressure. In response to propeller lever setting, the constant-speed primary governor hydraulically controls propeller (Np) RPM by changing the propeller's pitch. The primary governor range is from 2,000 to 1,600 RPM. The primary governor maintains selected propeller speed by decreasing or increasing blade angle respectively. Decreasing blade angle speeds the propeller while increasing the angle slows it. If the primary governor fails to limit propeller speed, the over-speed governor acts at approximately 2,080 RPM to reduce oil pressure to the servo piston. Reduced oil pressure reduces propeller speed by moving the blades to a higher blade angle. A mechanically monitored hydraulic stop sets the propeller's low pitch stop to prevent inadvertent propeller reversing. Raising the power lever aft past the normal idle stop allows the propellers to move toward the reverse thrust setting. Oil pressure to the servo piston then drives the propellers through the zero thrust angle (beta range) to the full reverse blade angle. Pulling the power levers further aft increases engine power to the maximum reverse thrust range. The primary governor's fuel topping mode reduces engine thrust to limit propeller RPM to 95% RPM of selected RPM (1,900 RPM when selected RPM is 2,000). Fuel restriction by the fuel topping function prevents propeller over-speed. Place the AUTO FEATHER switch in ARM position with both power levers above approximately 85 to 90% N1 setting arms the auto-feathering system. As engine torque increases, that engine's high-pressure switch energizes the opposite engine's arming-light-out relay and illuminate its AUTOFEATHER light. This interlock between the two engines prevents system arming until both engines are above the mentioned power setting as well as both engines auto-feathering if a malfunction occurs. If an engine fails and torque drops, the respective high-pressure switch at 650 ft-Ibs. de-energizes the opposite engine's arming-light-out relay, de-activates its auto-feather system, and extinguish its AUTOFEATHER light.

Rev 1

For Training Purposes Only Copyright Š 2006, Donald W. Sims, All rights reserved

16-1


SimsAir

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Piaggio Avanti

Propeller

As torque continues to fall, the low-pressure switch energizes its auto-feather control relay at 200 ft-lbs to route power to the respective over-speed governor's solenoid dump valve. Oil pressure is dumped back to the gearbox case and the feathering spring and centrifugal weights rapidly move the propeller to the feathered position. Holding the AUTO FEATHER switch in the TEST position with Ng RPM below 90% bypasses the power lever switches to verify operation of the pressure switches, control relays, and solenoid dump valves. The propeller control system comprises the single-acting hydraulic propeller governor, which combines the functions of constant speed unit blade pitch control and fuel reset valve (beta), and the coordinating system, which includes the beta lever, the beta cam and the related cables and rods. Primary Governor

Beta Block, Slip Ring and Over-Speed Governor

On the propeller synchro-phase system, magnetic pickups generate an AC current proportional to propeller RPM. The control box compares waveforms of the AC inputs from each propeller's pickups and attempts to superimpose the waveforms (match propeller RPM) by varying propeller RPM. With propeller RPM within the 25 RPM authority range, the control box sends correction signals to increase the slower prop.

16-2

For Training Purposes Only Copyright Š 2006, Donald W. Sims, All rights reserved

Rev 1


Propeller

Rev 1

Piaggio Avanti

For Training Purposes Only Copyright Š 2006, Donald W. Sims, All rights reserved

SimsAir

16-3


SimsAir

16-4

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Piaggio Avanti

For Training Purposes Only Copyright Š 2006, Donald W. Sims, All rights reserved

Propeller

Rev 1


Propeller

Rev 1

Piaggio Avanti

For Training Purposes Only Copyright Š 2006, Donald W. Sims, All rights reserved

SimsAir

16-5


SimsAir

16-6

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Piaggio Avanti

For Training Purposes Only Copyright Š 2006, Donald W. Sims, All rights reserved

Propeller

Rev 1


P-180 PTG - Section 16 - Propeller