Diamond DA 42 NG, Maintenance Manual

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AIRCRAFT
DA 42 NG AMM Propeller
Doc # 7.02.15
Rev. 4
61-20-00
Page 3
15 Mar 2018
2. Description and Operation
The DA 42 NG has two MTV-6-R-C-F/CF187-129 or two MTV-6-R-C-F/CF190-69 (if MÄM 42-600 is
installed) variable pitch and feathering propellers. A counterweight is fitted to each propeller blade.
When the propeller is rotating the counterweight overcomes the centrifugal twisting moment and
causes the blades to move towards coarse pitch. The propeller uses oil pressure to decrease the blade
angle (pitch).
The constant speed governor is an mounted part of the engine control system. The engine control
system measures many engine parameters. The propeller blade angle is adjusted automatically. The
pilot has only one lever for each engine to control the engine performance. Figure 1 shows the
propeller RPM as set by the engine EECU system for a given load.
As with other constant speed propeller control systems, the EECU senses engine performance and
sets the governor to regulate oil pressure to the propeller to change blade angle as necessary.
Depending on the power setting the propeller pitch is adjusted so that the required RPM will be
obtained as shown in Figure 1.
Figure 2 shows the propeller control system schematic diagram.
The oil pressure at the governor is 22 bar (320 PSI). If the engine speed is too high, the constant
speed governor operates the governor so that the oil flows out from the propeller. The counterweights
on each blade moves the blades to a coarse pitch and increases the blade angle. This reduces the
RPM.
If the engine speed is too low, the governor increases oil flow into the propeller. The piston moves to
reduce the blade angle. This increases engine RPM.
For further information of the governor's working principles refer to the mt-Propeller Operation and
Installation Manual, latest revision.
During normal operation a preset coarse-pitch-stop prevents the propeller blades from moving past
a preset blade angle. A centrifugal latching mechanism disengages the coarse-pitch-stop when the
propeller is rotating at speeds greater than 1300 RPM. If the engine fails in flight, or if the propeller oil
supply fails in flight, the blade counterweights will increase the blade pitch angle. If the engine is
rotating faster than 1300 RPM the centrifugal latching mechanism will be disengaged and the propeller
blades can move to the feather position. The propeller pitch angle in feather position is 81° ± 1°
(80° ± 1° if MÄM 42-600 is incorporated).