This is how it works ...
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2. HEIM
In HEIM systems the COLLECTIVE PITCH and ROLL
functions are mixed electronically (i.e. in the transmit-
ter). As a result the swashplate moves UP/DOWN
(COLLECTIVE PITCH) and right/left (ROLL).
PITCH-AXIS is mechanically de-coupled and is con-
trolled by a separate servo.
For a helicopter with HEIM mechanics the servos
should be assigned as follows:
HEIM-MIX for servos 2 and 3
PITCH-AXIS for servo 4
If the swashplate is to be tilted forward (direction of
flight) (PITCH-AXIS movement) only servo 4 carries
out this action. This means that only the inputs
ROLL and COLLECTIVE PITCH are present in the
HEIMHEAD mixers for servo 2 and servo 3.
If the swashplate is to be tilted at right-angles to the
direction of flight (ROLL), then only servos 2 and 3 are
required to move. These two servos also move to
provide COLLECTIVE PITCH control (swashplate
up/down).
3. CPM-head
Over the last few years helicopters with a CPM rotor
head have developed to become by far the most
widely used type of control system.
In the CPM rotor head all three control signals
(COLLECTIVE PITCH, PITCH-AXIS and ROLL) are
mixed. Depending on the position of the servos rela-
tive to the swashplate it may be the case that the
PITCH-AXIS or ROLL input must not apply to one
servo. In this case the unwanted input must be
switched off for the servo concerned. This is always
true in arrangements where servos are connected to
the swashplate at 0°, 90°, 180° or 270° relative to the
direction of flight.
The following diagram of a 90° rotor head shows just
such a case.
3
6
2
5
Incidentally: the 90° arrangement can also work with
only three servos. In this case the front servo (here
No. 3) is simply not present.
The servo assignment for this type of rotor head is
simple:
Assign HEAD-MIX to all servos
When the swashplate is to be tilted in the direction of
flight (PITCH-AXIS) only servos 3 and 5 have to
move. This means that the PITCH-AXIS input must
be switched off in the mixers for servos 2 and 6.
When the swashplate is to be tilted at 90° to the direc-
tion of flight (ROLL) only servos 2 and 6 have to
move. This means that the ROLL input must be
switched off in the mixers for servos 3 and 5.
Direction of
flight
Direction of
flight
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