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Interceptor 400 answers

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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

The first 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 don't panic......

If your 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.

Basically you 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.

If  not, 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 more.

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 are.

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.

One final 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.

Now the mechanical setup is correct, you can start on setting up whatever flying curves you want.

SPEND AS LONG AS IT NEEDS ON THIS PROCESS - IT IS WELL WORTH THE TIME

 

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