I wish that I had a Rand for every time I have helped a new chopper pilot set up his heli and ask the question “have you checked your tracking”. Every time I get goggled at as if I am the monster from Mars. Well, today I aim to explain to those new guys what is blade tracking, why it is important and how do you fix it.
One thing that you new guys have to understand is that a heli works on balance. If something is longer, short, heavier, lighter or set differently the chopper will begin to become unstable and/or develop an extreme vibration. It is for this reason that blade tracking is important.
So, what is blade tracking? Well, quite simply blade tracking is when the blades are moving in a circular motion and the second blade tracks the first on the same level and plane. Almost like walking in a narrow foot path where you have to follow the person right in front of you in the same path.
So, why is it so important for the blades to track perfectly? As you at this stage will know, the helicopter flies by changing the pitch on the main rotor blades. This changing of the pitch on the main blades causes the blades to start generating lift. This lift causes the chopper to lift into the air. As I said earlier, the chopper is a device that works on balance. In the event that the tracking should be out, blade A’s pitch will be more than blade B’s pitch. This causes blade A to generate more lift than blade B. Because lift causes drag you in effect make blade A’s aerodynamic “weight” more. So now you have the situation where blade A and blade B aerodynamically “weighs” different. What you have done now is unbalanced the main rotor blade and the result is vibration. For those who don’t know. Vibration is BAD for a chopper. Bad vibration can destroy a chopper. I also have seen where bad tracking has made the chopper almost impossible to fly.
So, how do you recognise bad tracking? WORD OF WARNING HERE!! RC helicopter blades are dangerous. Always bear in mind that a blade could break or splinter and hurt you, badly. Ask a friend to help you hold the chopper while you stand back to look at the blade from the side. Spinning blades can appear invisible so be careful not to come to close.
If you spin up the rotor and you see the same as in picture A, your tracking is correct and you can go and fly. On the other hand, if you see what is in picture B, setting will be necessary on the rotor head to correct the tracking.
Most choppers uses the same Bell Hiller control system and should therefore be almost the same to set up.
Firstly what you need to do is get blade tracking stickers (normally supplied with the blades) and paste them about two to three centimetres from the blade tip. This is for you to be able to see which blade is which.
Next, you spin up the chopper, view the rotating disk from the side and see if you can distinguish which colour blade runs high and which blade runs low. OK, now you know which one runs low and which one runs high. Normally you would set the link between the Bell Control Arm and the Blade Grip. On some choppers you set it by changing the length of the link between the Bell Control Arm and the Swash Plate. Your helicopter manual will tell you which one to set.
To set the tracking, set the top running blade’s link to so that the pitch decrease. Use half turns if unsure. On the bottom running blade, set the link to increase the pitch of the blade. Try and keep the amount of turns the same on both the A and B blade’s links. Spin up the rotor and check you tracking. Continue this until your tracking looks like picture A.
So, now you know what tracking is.