INTRODUCTION PROPELLER GOVERNOR FEATHERING SYSTEM OPERATION LIMITATIONS DIAGRAM PROPELLERS (ATA Chapter 61)..61.1..61.1..61.1.61.2. 61.2 Feathering Oil Supply.. 61.2 Propeller Governor System.. 61.3 PROPELLERS INTRODUCTION The Flagship Detroit DC-3 is equipped with full feathering Hamilton Standard Hydromatic 3-blade constant speed propellers. This chapter provides a general overview of the DC-3 Propeller System as well as normal operations and limitations. PROPELLER GOVERNOR Hamilton Standard Propeller The propeller governor is mounted on the engine nose case and uses oil from the bottom of the engine oil tank to control engine speed from 1200 to 2500 RPM. Levers installed on the left side of the control pedestal operate cables that adjust the governor to the desired RPM. A balance spring in the governor system will stabilize the engine at approximately 2050 RPM if the control cable or governor pulley shaft fails. The prop governor has a range of 18 to 23 degrees, with high pitch (full-feathered) set at 88 degrees. Revised 9/28/12 (send changes to File@FlagshipDetroit.org) Page 61.1
Propeller Levers FEATHERING SYSTEM Feathering Controls Two red buttons are mounted on the overhead panel for operating the propeller feathering systems. Feather Button Depressing the Feather Button energizes the feather pump, located on the engine firewall, and supplies engine oil under high pressure to the aft side of a piston in the pitch changing mechanism, driving it to its most forward stop. The prop blades are mechanically geared to the piston and follow it to their maximum coarse angle, 88 (Full Feather) When the piston can move no further, oil pressure in the prop dome builds above 600 psi and a pressure sensitive switch activates to remove electrical power from the solenoid that holds the Feather Button IN. The button then pops out, power is removed from the pump and the feather cycle is complete. If the feather button fails to snap out after the propeller is feathered, the button may be manually pulled to the OFF position. This will prevent the prop from attempting to unfeather. Unfeathering the DC-3 engine is also accomplished by depressing (and holding IN) the Feather Button for several seconds, during which time hydraulic pressure builds to 650 psi causing the distributor valve to shift and reroute oil pressure to the opposite side of the piston. The button must be held until sufficient RPM is achieved and the engine begins to run on its own power. Feathering Pump Revised 9/28/12 (send changes to File@FlagshipDetroit.org) Page 61.2
The feather pump is 24 VDC 3 HP electric pump capable of producing 1200 PSI. It uses oil from the bottom of the oil tank to feather the propeller. Although the oil tank was designed to reserve 2.8 gallons of oil for the feather pump in the event of an engine oil system leak, this feature may not be available on this particular aircraft. (ABOVE INFO IS IN DISPUTE) If an oil leak should exhaust all engine oil, the propeller will become uncontrollable at the low-pitch stop. In the event that the feather button does not retract automatically, the motor has a 60 second duty cycle limit. The feather pump motors are not protected by circuit protection. OPERATION Set propeller levers for the desired operating RPM. WARNING A propeller may become uncontrollable and overspeed if the Oil & Hydraulic Shutoff Valve Handle is turned OFF before the propeller is feathered. WARNING` If engine oil pressure is lost, the propeller governors will have no oil supply and the propeller will overspeed. Immediately reduce power, reduce airspeed, and feather the propeller. LIMITATIONS Propeller governing range:... 1200 2500 RPM Propeller Governor System Diagram Revised 9/28/12 (send changes to File@FlagshipDetroit.org) Page 61.3
Hamilton Standard Propeller Cutaway View Revised 9/28/12 (send changes to File@FlagshipDetroit.org) Page 61.4
PROPELLER PITCH CONDITIONS Revised 9/28/12 (send changes to File@FlagshipDetroit.org) Page 61.5
ABNORMAL PROPELLER CONDITIONS Revised 9/28/12 (send changes to File@FlagshipDetroit.org) Page 61.6