Quick Engine Tuning Question

[Brady Longmore]

Ok this is for you engine pros out there.

About a week ago I flew my heli for the first time since last fall. It flew flawlessly. No vibes that I could see. Then a few days ago I flew again, and noticed some vibes in the tail fin. I flew again today, and now no vibes again.

Sorry, but I can only rely on my nitro experience with RC cars. So, I can say that a big difference was temperatures. On the day it had vibes I was flying in warmer weather than the other two days, without vibes.

My nitro experience tells me that I need to lean out a bit in the warmer weather, and richen as the weather cools. Am I correct about this?

[cbergen]

Absolutely correct.

[Piton]

Would one also richen the high needle when carrying a payload?

[cbergen]

That is also correct, though it may require richening both needles to make the transition smoother.

[Brady Longmore]

Good question Piton....Good info Chris.

Thanks!

Any other tuning tricks and common knowledge for some of us newbies?

Like, what is the difference in the High and low needles? What exactly are you adjusting? Air intake?

What situations do you adjust one or the other or both?

[cbergen]

Hmm, Ok.

The difference between the high and low needles.....Think of it this way. Did you ever have a chevy V8 with a 4 barrel carb? When you stomped on the gas, the secondaries opened up to give you more fuel and more air into the engine.

The low needle is generally in use at idle up to normal hovering engine RPM (the primaries). Going to higher engine RPM's (idle up for instance) draws more fuel through the high needle as well as the low. Not instead of the low, IN ADDITION to the low(the secondaries).

This is why we typically tune the engine in a hover using the low needle, but depending on rpm's you may be right in that transition point where the high needle is also coming into play. The trick is knowing the difference...

What you're adjusting is how much fuel is being mixed into a given amount of air going through the carb. Closing down the needles lessens the amount of fuel (leaning it out), opening the needles increases the amount of fuel (richening it up).

It takes time to get an "ear" for tuning these engines, but if you always remember to richen the needles first, test it to see if that improved the response, THEN lean it if necessary, you should not run into ruining your engine.

If you think about what is happening with the air around you, it may give you an indication of which way to go with the needles. For instance, if you go higher in altitude, the air gets thinner. Less air means you need less fuel. So you lean the needles a little bit. Same thing occurs when the temperature rises. The air gets thinner, so leaning the needles slightly is necessary.

Now as you get closer to sea level, or the temperature drops, the air gets denser (actually the oxygen molecules are packed closer together), so more fuel is needed to maintain the proper air/fuel mixture.

Just some thoughts.

[Piton]

My experience, limited as it is, has seen me flying at elevations from 4,000 to 9,500ft above sea level, changing day to day, hauling about 6 pounds on the EB. Temps at 4k ranging from 25-60 deg F, and temps at 8-9,000ft being about 20-32 deg F.

At higher altitudes I first experimented with needle tweaking, and not head speed. I leaned ever so slightly on the high needle as I was hovering just a bit above half throttle at higher elevations. But what I found helped the most flying at higher elevations in cooler temps was a slight bump up in head speed. I have since bounced between high and low elevations and just changed the head speed. Figuring if I'm a little rich at altitude, so be it. So now I have my radio set up for three elevations essentially. One for 4k, one at 7k, and another for above 9k. Seems to work. Although flying at 9,500k with 6 pounds is something to get used to. Things happen alot slower. Sort of like flying with huge expo I guess.

Again, I make no claims to be an expert. Just trying to work out the kinks of multi elevation, and primarily high elevation flying. As that is what I am most interested in at this point.

Eventually I'll let you know how the Bergen handles 10.5k and 11k in cool temps. Not sure I'll ever fly it at those elevations on a warm summer day with really low air density.

[Brady Longmore]

Great explanaition Chris. That would explain why sometimes in the past when I've been in Utah and had Gary tune my engine to perfection, and then drive back up to Idaho where the elevation increases, it's got a little vibe when I get back, when before at Gary's it did not. :? I probably just needed to lean it just a tad after the elevation increase.

So, let me make sure I've go this straight. The low needle is the primary, and the high needle is the secondary? The secondary isn't really going to come into play until I have reached hovering speeds and above, depending on my head speed at hover? Or I'm guessing when carrying a payload too.

[MarkWebber]

Time for fuel injection :wink:

Brady

Right, if the payload's heavy enough, you'll need to work on your tuning to keep up with the extra weight.

[Piton]

Time for fuel injection :wink:



Yeah, fuel being amps. :lol:

[cbergen]

Brady, I think you got it!!

[MarkWebber]

Yeah, fuel being amps.

Yeah...need to sneak a camera under one of Greg's e-Magnums. :wink:

No way I'll give up my gasser though!