RC HELICOPTER DYNAMIC ADJUSTMENTS INCLUDING BLADE TRACKINGWelcome to day 2 of how to fly RC helicopters. Blade tracking and engine dynamic adjustments will be sorted out today. First off what is a dynamic adjustment? The easiest way I can explain it is an adjustment that is made while the helicopter is flying or at least running. This is different than the initial set up or static adjustments that we talked about during day 1’s lesson. The two dynamic adjustments we will be focusing on today are engine tuning and blade tracking. Of course if you have an electric RC helicopter you don’t have to tune your motor - you do however have to program your throttle/pitch curves. It will be beneficial if you follow along with the following nitro engine dynamic set up. No matter what powers your helicopter, the power plant has to produce enough energy to get your heli light on the skids at half throttle/collective stick. Programmable throttle curve settings have made this very easy. Nitro Engine Dynamic Setup Most of the engine tuning and setup has already been discussed in the nitro RC helicopter section as well as proper break in procedures and mixture settings. You must understand how your nitro engine works and be comfortable starting and tuning it before you attempt these adjustments. The following dynamic engine setting discussion is to ensure the engine mixture is set to provide the proper amount of power for your first hover exercises. The idea is to set the nitro engine throttle and mixture or throttle/pitch curves to give enough power to lift your helicopter off the ground when the collective/throttle stick is at approximately the half way point on the radio – that is what I mean by “half stick”. On day 1 , we already set the collective pitch to plus 4.5 - 5 degrees of pitch and the carburetor to about 60-70% open at half stick; now we have to make sure the engine fuel mixture or electric motor output is set to provide enough power to get the helicopter very light on the skids at that same half stick setting. The extra weight of your training gear should be just enough to keep your helicopter on the ground during this adjustment. Training gear is discussed during day 3 and you should have them mounted on your helicopter at this time. After you start your nitro engine let it warm up for about 30 seconds at idle speed and then slowly increase the throttle/collective pitch until the helicopter seems to get very light or be close to lifting off the ground – this is called light on the skids. Don’t lift it off the ground! If this is your first time running up your heli or making the switch to a larger RC helicopter, this can be a little scary and intimidating. Just run it up slowly and watch for any large amounts of vibration. Some transitional vibrations are perfectly normal and should go away once your rotor RPM has stabilized. Any remaining vibrations should go away once your blade tracking has been adjusted, assuming your rotor blades are balanced correctly. Now it’s almost a 100% certainty that your cyclic and tail rotor trim will be off and require further trimming (the helicopter will want to drift or turn left and right). This will be adjusted on day 3. If that is the case, just reduce the throttle a bit to keep your bird solid on the ground. Some nice thick grass will also help secure the heli from drifting around as you get light on the skids if you can find some. Just remember, nitro exhaust will leave a small brown dead spot on the grass. If you have a female dog using the same lawn as her bathroom – you won’t even notice the new brown spots. If however you have a prize winning lawn – better perform your dynamic engine adjustments elsewhere. So how did it go? Was there lots of smoke and even at full throttle/collective the helicopter seemed to be glued to the ground? If that was the case, your engine is running too rich. Lean it out by closing your high speed needle valve by ¼ turn and retry. Keep performing the following steps until the engine power is providing enough power to get the helicopter light on the skids at ½ stick. You should be seeing some smoke, but not billowing clouds of it. What if your engine was screaming with hardly any smoke in the exhaust and your heli was very light on the skids before ½ stick? Sounds like you are running way too lean - richen the needle valve setting and keep retesting until you are at half stick before your helicopter gets light on the skids. Running your engine on the slightly rich side will also insure the rotor speed is not too high. A high rotor speed will make the cyclic controls overly sensitive. If you have an electric RC heli, you will have to perform the same dynamic throttle adjustments but you will only have to worry about your programmable throttle curve. Most good quality electric helis perform well for learning with a linear throttle curve from 0% to around 50-55% power up to the half stick point. I find if you start shallowing out the throttle curve after the mid stick point to about 70% power at full stick, this is more than enough power for the exercises we will be doing. This lower power setting will result in lower head speeds making the cyclic not as sensitive and give you longer flight times out of a battery charge. Blade Tracking Dynamic Setup Before we get into blade tracking, you might want to know what exactly blade tracking is right? Let’s go back to our day 1 example where we set the pitch angle of each rotor blade at about 4-5 degrees of positive pitch at half stick. It is all but impossible to get both rotor blades at exactly the same pitch angle by using even the best pitch gauge. Mostly because all pitch gauges rely on a visual reference to the flybar when taking the reading. If the flybar lock doesn’t hold the flybar perfectly horizontal, or you change the angle you look through the gauge, the angle readings will not be the same. The short of this is you will have your main rotor blade pitch angles pretty darn close but most likely not exactly the same – even 1/4 of a degree will cause the blade tracking to be off. 
This picture shows a standard pitch gauge and how you visually level it with the flybar through the "windows" on either side of the gauge. Once leveled, you can get your pitch reading. Now you check the other blade or blades if you have a multi bladed head and it/they should be the same - this will have your pitch settings very close, but not perfect. Now what happens when the helicopter is about to lift off the ground or is in a nice solid hover if one blade has slightly more positive pitch than the other? You guessed it – the blade that has a little more positive pitch will have a little more lift. Because the rotor blades and rotor head have some flex built into them, this blade with a little more lift will actually fly a little higher than the other blade… the blade tracking is off. You can actually see this when looking edge on at the spinning rotor blades as the helicopter hovers or when it is on the ground getting light on the skids – you will see two distinct rotor discs. The blade that has a little more positive pitch will be creating the upper rotor disc and the other blade the lower disc.
A RC helicopter that has out of adjustment blade tracking will vibrate and if the vibration is bad enough may even set up a harmonic oscillation that can be pretty scary. I have purposely set the blade tracking way out to experience this and some RC helicopters seem more susceptible to blade tracking induced oscillations than others. My guess is it has to do with the mass of the rotors or the natural resonance frequency of the rotor assembly – in any case, blade tracking is something you will want to set correctly. Ok, you now know what blade tracking is and why it is important to have set right, let’s go back to your helicopter and check the blade tracking. First off, you need a way to identify each rotor blade so you can tell which one is flying higher and lower. Most RC helicopter kits or helicopter blades will come with two different colored pieces of tape to put on each rotor tip (usually red and black). You can also use red and black electrical tape. Now start up your helicopter and get it light on the skids – you don’t have to be hovering, as long as the rotor blades are producing some lift, out of phase blade tracking will show up. Next crouch down or have an assistant crouch down so you/he/she is looking edge on at the spinning rotor blades (blades at eye level). For obvious safety reasons you should be wearing impact safety goggles just in case. You also don’t have to be close to the helicopter, you will be able to see if the blades are out of track 10-20 feet away. It will be easier to see both different colored blade tips as they are spinning on a sunny day with a dark background such as distant trees or mountains. If your blade tracking is set correctly, both colored blades will be overlapping – flying in the exact same plane. If your blade tracking is out, one of the blades will be flying higher than the other. Say the blade with the red tape is higher than the blade with the black tape. To correct this, stop the engine and adjust the ball link reducing the pitch of the red blade as per your helicopter instructions. You could also increase the pitch of the black blade so it meets up to the red blade. If the adjustment is out a lot, I would recommend doing both – decrease the pitch on the red and increase it on the black. Now start up the engine/motor again getting the helicopter light on the skids and recheck – continue performing these tests and blade tracking adjustments until both blades colors overlap and appear as one blade. Once you learn to hover, it wouldn’t be a bad idea to recheck the tracking again during an actual hover with the rotor blades at eye level. The tracking shouldn’t have changed, but there will be more load on the rotor and this might cause a very slight out of track condition. If so, simply land the bird, adjust the blade tracking as required, and recheck. You will also want to recheck your blade tracking when ever you replace rotor blades or perform maintenance/repairs to your rotor head. After you perform the blade tracking adjustment, the tape can be removed if you wish. This tracking tape will usually start peeling off on it’s own after a while. You will most likely be pretty startled and confused when this happens because the rotor will start making a very strange and scary sound as the tape comes loose. This video shows much of what we have been talking about during day's 1 and 2. I was impressed with the information given and realize it will reinforce some important points. The examples are shown on a small 400 size electric (the smallest I would recommend anyone start with) but much can be applied to larger electrics and fuel powered birds. Ready For Day 3 Now that you have your engine or motor and your blade tracking adjusted, it is time to progress to day 3 – learning the ground hover. Before we start on day 3 this would be a good time to perform a range check on your radio system if you haven’t already done so. There are generally two ways to perform range checks these days with the different radio technologies available. For all standard RC radios (AM, FM, PCM), the general practice is to collapse the telescopic antenna mast down to its lowest position. You should be able to walk about 30m (100 ft) away from your model before loosing radio range. 2.4GHz spread spectrum radios don't have a long telescopic antenna mast of course. The general way to range check them is to hold down the range check button/switch. This reduces the power output of the radio and once again, you should be able to walk about 30m (100 ft) away from your model before loosing radio range. Follow your RC radio's instructions on range checking - these two methods will cover most radios out there, but there are always exceptions. Range checking is something you will do every day from now on when you go out flying, so get in the habit now. Range check ok... onto day 3 .
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