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Page 7 - 24 Rev. 5 15-Nov-2007 Doc. No. 7.01.05-E
DA 42 AFM Airplane Description
7.9.2 PROPELLER
Two mt-Propeller MTV-6-A-C-F/CF187-129 hydraulically regulated 3-bladed constant speed feathering propellers are installed. Each propeller has wood composite blades with fiber-reinforced plastic coating and stainless steel edge cladding; in the region of the propeller hub the leading edge is coated with adhesive PU foil. These blades combine the lowest weight whilst minimizing vibration.
Propeller control
The propeller pitch control system is integrated into the engine. The pitch is controlled automatically by the ECU. To change the blade pitch angle gearbox oil is pumped into the propeller hub. The oil pressure is regulated by an electrically operated valve, the governor valve, which is controlled by the ECU. Increasing the oil pressure leads to a decrease of pitch and a higher RPM. Decreasing the pressure leads to higher pitch and a lower RPM.
Depending on the power setting the propeller pitch is adjusted such that the required RPM will be obtained as shown in the following diagram.
Doc. No. 7.01.05-E
Rev. 5 15-Nov-2007
Page 7 - 25
Pressure accumulator:
The pressure accumulator is a nitrogen oil type. It is connected to the gearbox oil circuit via an electric valve at the accumulator, which is operated with the engine master switch.
When the engine master switch is set to ON the valve is opened. When the engine is running, the accumulator is filled with oil at a pressure of approximately 20 bar (290 psi). During engine operation the accumulator makes sure that enough oil pressure is available even if the oil feed by the gearbox oil pump is decreasing due to negative acceleration. The hydraulic pressure keeps the propeller pitch angle below the start lock position, or moves the propeller blades beyond the start lock position.
Feathering:
To feather the propeller the engine must be shut down with the appropriate engine master switch. This will open the electric governor valve. All oil will flow back from the propeller hub, allowing the blades to move into the feathered pitch position. At the same time the electric valve at the pressure accumulator closes, and the oil pressure is restored in the accumulator.
Feathering is only possible at propeller speeds above 1300 RPM.
CAUTION
If the engine is shut down below an RPM of 1300 the propeller pitch remains below the start lock position. In this case the speed must be increased to increase the propeller RPM.
Unfeathering:
To unfeather the propeller, the associated engine master switch must be set to ON. This will open the electric valve at the pressure accumulator. The pressure stored in the accumulator will move the propeller blades into a low pitch position. As soon as the propeller starts turning and the gearbox oil operates, the accumulator will be refilled.
Ground operation:
CAUTION
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