A lot of people have emailed me since the last newsletter asking what tips I learned from Curtis in respect to engine tuning. Now I must begin by declaring that I am by NO MEANS an engine expert, but since enough people have asked, I'm going to write how I setup an engine. Take this not as gospel, but as another point of view.
What I had been doing wrong:
You see, you should use a mixture of listening to the engine, looking at the helicopter for shakes and smoke as well as feeling the temperature of the engine. All of these methods will give clues as to what the engine is doing at the current fuel mixture setting.
How I tune now
I tune this engine according to the instructions provided by OS for the 60B carb as well as looking at heli for visible vibrations and the quantity of smoke. I also listen to the tone of the engine as well as any other noises and finally, I test the temperature of the engine by touching the backplate.
Tuning the needles:
I then hover the heli at about 50% power for a couple of minutes to let the engine warm up. Most likely the heli will be running very rich (rough running, fins vibrating, canopy shaking, slow headspeed, slow in throttle response, lots of smoke). I will confirm this by landing the heli and feeling the backplate of the engine. It's most likely that with the heli running so rich, that the backplate will be stone cold. If that's so, then the heli is definately too rich.
To rectify this, I lean the top needle about four clicks. This will be enough to make a noticeable difference. Again, I hover the helicopter for about one minute to allow time for the mixture change to show results. Now, we should notice the engine should be four-stroking less (it will still be four-stroking to some extent), we should also notice that the vibrations in the heli (canopy, fins, etc) will have lessened, but probably not vanished. The engine should also feel a bit more responsive to throttle inputs and the headspeed should have increased slightly from the first hover. Smoke will have lessened a little bit, but will still be flowing in copious amounts. Confirm that the engine is warming up by landing the heli and placing the index finger on the backplate. You should now start to be feeling some warmth, but it is unlikely that it will be very hot.
Again, lean the high end needle 3-4 clicks and hover the helicopter again.
You should see a noticeable difference from the previous flight. The vibrations
in the heli should have settled down now to either none, or very minimal. The
engine should also have reduced it's four-stroking behaviour to either none
at all, or very infrequent. The headspeed should be close to normal and the
throttle should be quite responsive now. The smoke content shouldn't be as copious
as before, but should be constant.
Now, it's time to set the needles for full throttle. I always do this by flying
the heli backwards down wind climbing at about a 45 degree angle. The reason
for this is that if the heli has a flame out, it is easy to autorotate the machine
back down again. I do this by slowly and smoothly feeding in collective (not
stabbing it which may flood the engine and quit it) and listening to how the
engine reacts to the throttle and watching both the headspeed and the smoke.
Ideally, what you want is for the engine to take the throttle input smoothly with the headspeed not decaying and the smoke output should be consistent. If this is the case, then I fly the machine around at full throttle for a couple of minutes seeing if the engine loads up (if so, it is most likely too rich on the high end) and then land and check the engine temperature. Again, you should be able to comfortably hold your finger to the backplate, it not, then it's too lean, richen the high end needle.
Now, I then hover the helicopter again for a couple of minutes and watch the helicopter again. Now it's most likely to be a fraction lean now that we have set the high needle for full throttle. The heli is likely to run a little rough here and vibrations may have returned. The headspeed is likely to be pretty high and the throttle will be very responsive. The smoke however is likely to be quite low. Land the heli and test the engine temperature. You're likely to find that the engine is quite hot. Now I adjust the mid-range needle to achieve a nice smooth hover. I open this needle four clicks and hover the heli again to ensure that the vibrations have lessend, the engine has smoothed out and the smoke has become consistent. Land the heli and check the temp. Continue to open the mid-range until you have a nice smooth hover.
Again, fly the heli round to ensure that you are happy with the engine settings and that's pretty much it.
Tuning your throttle curve:
Different carb styles:
Remember, this is just a guide, it's by no means gospel. There are many people out there who know much more about engine tuning than I, but this is what I have used to tune my engines and it seems to work for me.