STEMME S12, Maintenance Manual

Page: 59 / 290

DOCUMENT NUMBER:
L500-912.820 ISSUE JUL 20, 2016
AMENDMENT: 00
DATE: --
CHAPTER- PAGE 3-25
MAINTENANCE MANUAL STEMME S12
WARNING
Balancing the variable pitch propeller or its assemblies may only be performed by the manufac-
turer or by authorized and licensed maintenance facilities according to the specific instructions
and using appropriate equipment.
The positions, number and weights of the balancing weight washers of the individual propeller
must be entered in the maintenance form »Propeller Adjustment Report« (Annex D).
3.4.10.5 EXPANSION ELEMENT AND CONTROL SYSTEM
The thermo expansion actuators are heated electrically and cooled by convection and heat dissi-
pation. Electric energy is transferred to the propeller blades by slip rings. The expansion elements
actuate only towards the high pitch angles. The propeller blades are rotated in the direction of
lower pitch position by the return spring at the lever mechanism assisted by mass and aerody-
namic forces on the blades.
When the propeller switch in the cockpit is in „cruise“-position, the expansion elements are heated
with about 50 Watts (with the engine running). The elements are heated until a temperature of
55º C is achieved and the element expands. As soon as the stop is reached propeller blades are
in cruise position and are held in this position by the two-point control system. If the propeller
switch is set to T/O position, the heating elements are switched-off and the expansion elements
cool down. By duplicating any essential elements and realization of logic-OR the control system
is fully redundant.
Heat insulation of operating elements is optimized to insure that the time for full change of pitch
in either direction will not exceed 5 minutes under any operating conditions (from idle to full
power). Typical actuating time for full change of pitch is about 2 ½ min.
The electrical energy to the expansion elements is interrupted (blade pitch automatically to T/O)
as soon as the propeller switch is set to T/O or when the nose-cone handle is not locked in OPEN
position (engine master switch is OFF).
If the nose-cone is closed, electrical energy to engine and propeller is isolated to save energy
when soaring.
In order to check the pitch range mechanism, a push-button that can be operated from outside
is provided on the right hand side (in flight direction) of the front gearbox frame. With the mas-
ter switch “ON” and the button pushed and held, the expansion elements are heated and the
propeller is brought into the cruise setting. When the cruise setting is achieved, the stop switch
disconnects the electrical current to the heating elements. For this check, the push-button must
be activated for about 3 to 4 minutes to heat the expansion elements. On releasing the push-but-
ton, the elements cool down and the propeller returns in the start position.