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A4 - Interceptor
400 - What
is meant by setting it all up with perpendicular links ?
This is the
process you have probably heard about by listening to other
helicopter pilots. What it means is that ALL OF the mechanical
linkages on the helicopter are set absolutely correctly in certain
positions, and after that all levers and mixers follow a
perpendicular position all the way up from the swash plate to the
rotor head and flybar holder and paddles
thing to do is to disconnect at least 2 of the wires going to
your motor to ensure the helicopter cannot start to spool up
when you open the throttle lever. Next get your radio Tx, and
if you have a programmable radio, set one of the PITCH curves so
that 50% stick position gives you 50% pitch. A straight
diagonal line gives this to you automatically.
If you only
have the Esky Radio Tx, you need to switch the IDLE UP switch ON,
which means pulling it forward. Ensure the motor wires are
disconnected before doing this
Now power up
the Tx and the helicopter, and set the throttle stick to mid stick
(so it is giving you a 50% pitch reading) Move the radio to one
side, making sure the stick stays at the middle position and look at
each of the servo horns that go to the swash plate via a linkage
rod. They should all be exactly at a right angle to the servo in
most cases, but this may be towards one end or towards one side,
depending on which helicopter you have. It is relatively
simple to see where it should be by tracing the linkage rod down to
the servo horn. What we are trying to do is to get that servo
horn exactly in the centre of the servos arc of swing.
As can be seen
from the diagram above, each servo horn MUST be as close to
perpendicular to the body of the servo as possible. Most servo
horns have offset splines on them, so sometimes turning a horn
through 180 degrees and retrying it will get a closer
position. It is always a good idea to start off by trying to
get the horns themselves as close to perpendicular as you can, even
if you have a programmable radio. If your radio is not programmable,
then you have to try to do it by trying different horns if possible
to get the best positioning you can.
If your radio
is programmable, then once you have got the horns as close as you
can, go into the SUB TRIM setup in your radio, and use these to
adjust the horn positions until they are dead perpendicular.
This includes doing the rudder servo, and to do this, ensure that
you switch your gyro into RATE mode, NOT Heading Hold.
So far, so
good, all your servo horns are perfectly perpendicular, so now what
You are far
from finished yet. The next thing to look at is the swash
plate. This now needs to be perfectly level. You achieve this
by adjusting the lengths of the connecting rods that go DOWN to the
relevant swash plate servos. You need to be a little careful here,
because if you think about it even briefly, you will realise that
you can end up with the swash plate in a higher or lower position,
depending on which way you adjust the three connecting rods.
Right now, try
to get the swash in as close to centre position of its range of
movement up the main shaft as possible. We may have to revisit this
position later on in the setup process.
So, you now
have the swash exactly level with the servo horns all dead
perpendicular, so move up the main shaft to the next set of whatever
levers you may have on your particular helicopter. Most have a
pair of what are normally called washout levers, and these have drop
links on one end that go down to the INNER swash plate, and another
rod at the other end that goes up towards the head itself. Yet
again you need to get these washout levers as level as you can so
they match the level of the swash plate. However, you CANNOT
DO THIS RIGHT
NOW, so will have to come back to it later on in this process.
Moving on up
the main shaft, we usually find another set of levers running
parallel to the flybar that are called the mixer arms. These
connect to the Main blade holders at one end and to a connecting rod
that goes DOWN to the swash plate at the other end. Check that
the end that connects to the blade holder is connected to the
SHORTER SIDE of the mixer arm. These are usually about a 3 in 12
ratio in length from the pivot point to each connecting ball.
To get the
mixer arms level, you need to adjust the long connecting rods that
go down from the longer end of the mixer arm to the swash
plate. Adjust both of these arms until they are again exactly
level with the swash plate. CAUTION - when doing this, keep the
flybar exactly level as well.
OK, now you
can revist the washout arms halfway up the main shaft. You
will see that there are usually connecting rods that go down to the
washouts from the flybar holder. These are the ones you adjust to
get the washout levers level to the swash plate.
As you do the
previous adjustment, make sure also that the flybar holder remains
level as well.
It's all good
clean fun isn't it ??
The final step
is to fit some main blades, get your pitch gauge out, and get the
main blade pitch to ZERO DEGREES. Yes, I know that means
changing other settings you have just taken so much time over, but
helicopter happens to have adjustable connecting rods that go from
the mixer arm to the main blade holder, you can use these to adjust
the pitch of each blade until you get the pitch set to ZERO
DEGREES. If your helicopter has fixed length connectors, which
is quite common, this is somewhat more difficult.
have two ways to adjust this. The most obvious, and typically the
best way is to change the length of each of the three connecting
rods going from the swash plate servos to the swash plate, changing
the swash plate height which in it's turn will change the pitch of
both blades. If you do choose to go this route, you MUST make
sure that the swash plate remains level throughout the adjustments,
which means adjusting all three the same number of turns.
If you get the
blades to ZERO DEGREES, all is well.
or you don't want to do it that way, you CAN adjust the length of
the long connecting rods between the swash plate and the mixer arms.
You should only do this if the adjustment needed is quite small, say
2 or 3 degrees at most, or else the mixer arms will not be level any
Once you have
the blade pitch on BOTH blades correct. check all the way up from
the servos to the head, ensuring that everything is still level and
perpendicular as appropriate. If not, re-adjust until they
You may well
have to go through this process several times until you get it all
right, but believe me, it is WELL WORTH THE EFFORT.
warning note - most helicopter manufacturers mould the plastic ball
connectors in such a way that there is an ON and an OFF side. You
can see it if you look closely, as the OFF side of the hole is
totally flat, while the ON side has a small curvature inwards on the
inner lip. YOU MUST ALWAYS FIT THESE PLASTIC CONNECTORS TO THE
BALLS THE RIGHT WAY AROUND OR THEY MAY COME OFF AGAIN IN FLIGHT. You
can usually tell because pushing them on the WRONG way is quite a
lot harder. Obviously this also means that every time
you adjust the length of any connecting rod, you must turn it a full
360 degrees, not just a half turn of 180 degrees.
mechanical setup is correct, you can start on setting up whatever
flying curves you want.
AS LONG AS IT NEEDS ON THIS PROCESS - IT IS WELL WORTH THE TIME
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