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A4 - Interceptor
400 - What
are the various lever arms on the head called ?
something that seems to confuse most new pilots, and even some more
of the more experienced pilots as well.
the bottom of the main shaft where it sticks out from the top of the
frame, the first thing you see is the SWASH
PLATE. This is a crucial part of every helicopter, as
it is the mechanism that allows us to transmit control commands all
the way up the rotor blades, despite it rotating quickly. The
swash plate has 2 parts to it, the outer swash and the inner
swash. You can see that the outer swash is connected to
the servos by connecting rods of one form or another, and therefore
it cannot possible rotate. To ensure that it cannot do so, there is
a locating rod that sticks out of the back of the outer swash
plate that engages in a slot in a bracket immediately behind the
mainshaft called (unsurprisingly) the Anti
|On the right is a picture of an
INT400 swash plate and the locating peg going back to
the right in the picture into the AR bracket.
This picture shows very clearly the
connecting rods going to the servos are connected to the swash
plate at the connectors on the outer swash plate ring
The inner part of the swash plate does
of course, rotate at the same speed as the main blades, and
that is why, as you can see in these pictures, all the
connections going upwards toward the top of the head start
from the INNER
ring of the swash plate. On the picture above, only
the two RADIUS ARMS are
actually in the picture connected to the inner swash
plate. Note that these arms are "bent" and
that the bent part always faces toward the direction of
rotation of the head.
|As we move upwards form the Swash
plate, we find what are called the washout
arms. These are linked to the INNER swash
plate by the Radius arms mentioned above, while
the other end of each washout lever arm goes up to the head
|This is shown more clearly in
the picture on the right, where the connecting rods going
upwards can be seen connected to the flybar
|Here is a fuller picture of the
top of the head. You can see that the large rectangular
frame is the Flybar control cage.
Also visible here are the Mixer
arms, which run alongside the flybar holder,
through which the flybar can be seen coming out at each end.
|A clearer picture of the mixer
arms sitting INSIDE the Flybar control cage, with
one end connected to the main
blade grips by a short connecting rod.
It is very important to note that if you
ever remove the flybar holder and mixing arms to
repair the helicopter, the mixing arms MUST be
replaced the correct way around.
That is with the short end of each arm
(measured from the pivot screw) being "behind" the
rotation of the main head (which is clockwise), so that the
short connector arms shown here are ALWAYS connected to that
the order upwards is Swash Plate, then washout arms, then mixer arms
and flybar control cage, finally comes the Blade grips themselves.
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