Setting idle speed with tachometer
 

A buddy of mine brought a tachometer to work yesterday and said I should use it to set my idle speed...he's new to R/C flight as well. My manual doesn't mention doing that. Is it something I should do and if so, what do I set it to?

RE: Setting idle speed with tachometer
 

You could I guess but I never have. I don't see the point in it. If your buddy whips out a temp gauge, then you'll have me "concerned":eek: Simple logic here, if the idle is set to high, the plane will roll away. If the idle is set to low, it won't.

Where do we come up with this good stuff?:D

RE: Setting idle speed with tachometer
 

they come in handy when you are tweaking a propeller to an engine ,but i always go by ear.

RE: Setting idle speed with tachometer
 

Let me guess... he didn't give you any specifics as to the whys and hows. Don't take for granted that which another beginner tells you, particularly if he starts suggesting you do things such as setting an idle with a tachometer. You set the idle as low as you can reliably get it while still providing good acceleration into the midrange without sagging.

RE: Setting idle speed with tachometer
 

Your engine isn't even broken in yet which means it won't reach it's best idle. However slow it will go now, it will go slower/smoother later. Good chance your idle mixture will be too rich out of the box too as this is the way OS tends to ship them to protect from lean running at idle. This MAY need to be adjusted too. You need to get under the tutelage, in person, of a competent/experienced pilot/instructor and NOT the guy who told you synthetic oil was bad.

No tach needed.

RE: Setting idle speed with tachometer
 

We have a guy at our field that is ALWAYS trying to get his engine running "perfectly". He will spent hours trying to get the top end and idle set just right, only to have them die in flight. If you want to know who to get tuning advice from find the guy at the field that goes out, starts his plane, taxis out, flies, lands, taxis back, kills the engine, and then heads for the stands to shoot the breeze with his buddies. You want him because he has learned to tune his engine correctly and then LEAVE IT ALONE, and just flies. You really need to make a decision, you can spend all of your time tinkering and worrying about getting the engine set correctly, or you can just set it and fly-- and have more time to spend with your flying buddies!! :D

Ken

RE: Setting idle speed with tachometer
 

I am a gadget guy. I like toys and toys that I can use with my toys. So I have a tach and temp gauge. I do not use these to tune my engine. I use them to see the results after having tuned my engine or switched propellers. Think of them as the instruments in your car. They simply give you feedback of the operation of your engine and statistical data.

RE: Setting idle speed with tachometer
 

old saying if not broken don't touch it

RE: Setting idle speed with tachometer
 

easy way to set idle: If it sounds good (like its not dieing) then leave it, if it sounds like its going to die then trim it up a couple of clicks until it sounds good.

RE: Setting idle speed with tachometer
 

A tachometer has its uses. I keep one in my flight box, and use it to set the high speed needle on the first flight of the day. When I set the idle, sometimes I'll just check to see where it's idling (2500-3000 is usually a good target, but it varies).

For most trainers, a very low reliable idle makes landings easier. As you move up into planes with heavier wing loading, you'll find its not so critical, since the planes tend to land with a little more speed (again, this is plane dependent). In those cases, I'll set my idle a little higher, as it makes the overall tuning a little easier (I'm talking a couple hundred RPM, as in 3000-3500 at most).

But Ken is right. Set it (once a day for me) and forget it. As for the low end mixture, once my engines are broken in, I've never had to make any low end adjustments after I've got it set where I want it. If the low end is getting saggy, check your glowplug.

Brad

RE: Setting idle speed with tachometer
 

I use a tachometer to "perfect" my tuning, whether for idle or high speed needle adjustement.
I only do this once and when I change plug, propeller, or fuel.
It is not something I do commonly on the field, I rely mostly on my ear for these small weather related adjustments :)

For Idle:
I set my engine in such a way to pick up instantaneously when transiting to full throttle; and for this I need to let in the correct amount of fuel/air mixture that will be burnt completely at idle without leaving any accumulated fuel in the piston head. I am not afread of lean mixtures, bcs at idle the engine fins are able to cool it properly without any extra help
When I set the idle, let's say at 2500rpm on my OS 46AX MAX, I then "clean" it by doing some full throttle revs, and then drop it back to idle and watch the speed with a tacho.
If the engine idle is set accurately, the tachometer should read 2500rpm all the time with minimal variations, and you can idle forever until the tank is empty. What you will often notice is that as you idle, the rpm tends to drop when the needle is not set correctly :) and it eventually dies!
Of course we are assuming that the tank to carb position is correct and the issue is only due to needle setting!

For Full Throttle:
I use the tachometer to detect the highest peak in RPM and then I drop it down towards the rich side by 500rpm. This depends a lot on the weather, and I often play with that setting and adjust it by ear after the initial tuning with the tacho.

RE: Setting idle speed with tachometer
 

I assume this is the same guy who told you not to use cool power fuel. Sounds like he has been flying 2 or 3 months and is already an expert.

You really don't need a tachometer. Tune the high end for peak rpm, idle down and tune the low end until it trasitions fairly smoothly and won't die at idle, run it back up and richen the high end
until you hear the rpm start to drop (200-300 rpm). Stop right there and leave it alone.

As the engine continues to break itself in the idle will become more and more reliable. Trying the tune the low end perfectly when the engine isn't fully broken in is a waste of time.

Regards,
doubledee

RE: Setting idle speed with tachometer
 

The best way to set idle needle is, AFAIK, by pinching the fuel line. Let the engine run idle for some time (>30 seconds) and then pinch the fuel line shortly. If the engine speeds up, it's too rich. If it dies, it's too lean. If you don't get any change, it's ok. After having done this, reduce throttle as far as possible. No tachometer needed for this, just listen to your engine. After having done this, redo the pinch method again. Once you think you got it right, let the engine run idle for some time (>30 seconds) and then quickly advance throttle to full. It should gain RPM without any hesitation. If it quits immediatly, it's probably too lean. If it stalls for a second and then picks up again, it's probably too rich. If it does this, let the engine run idle again (>30 seconds) and then advance throttle to full quickly. The second it stalls, pinch the fuel line. If that helps, it's too rich. If not, it's too lean.

Using a tachometer for idle is nonsense. Sure you can say 'I want an idle RPM of 2200', but if your engine won't run reliable at those speeds, you can use all the tachometers you want, it won't help.

A tachometer is usefull to see the max RPM an engine gets with a certain prop. For instance; I'm using a Saito 82a fourstroke and had a 13*7 prop on it. After adjusting the needles, I measured top RPM, which turned out to be around 11500 RPM. Considering this is on the ground and the RPM will be higher in the air, this is an indication this prop is slightly too small. I replaced it with a 13*8 prop and now i'm getting like 10500 RPM, which will translate to around 11500 in air (max RPM for this engine is about 12k).

Also remember to run the engine slightly rich on the ground, or else it'll die on you in the air.

RE: Setting idle speed with tachometer
 

I've only owned a tac for one season but I find it best for finding highest RPM at max throttle so I can then back off two or three clicks. Knowing the leanest mix is nice but knowing I'm not destroying my cylinder sleeve and piston is nicer.

As far as idle, I can't much fault Cyclic Hardover's description. I might say it's the lowest speed that allows the engine to continually run.

The 9C radio (others too, I'm sure) has a great feature in the throttle end-points that allows a throttle cut switch AND a switch that flips between very low idle (landings, spins) and not quite so low an idle (taxi, downwind legs). Nothing worse than taxing out, yelling "TAKING OFF" and then having it die before you throttle up. The "Idle-Down"

RE: Setting idle speed with tachometer
 

I have one and I like it for testing props and new fuels. A tachometer isn't required to properly tune an enginge. I just like it to see what effect different props and fuel have on the engine. Its also fun to know the exact numbers.

LT-40

RE: Setting idle speed with tachometer
 

Hey, there's much more where that came from![X(]

RE: Setting idle speed with tachometer
 

That applies to two-stroke engines. A two-stroke can be tuned by ear pretty easily for most people. Most people can't, however, tune a four-stroke by ear. That's why many people buy tachs. They're handy for some things, but the only place they're really a necessity is with a four-stroke.

RE: Setting idle speed with tachometer
 

I guess I have to confess that I do use a tach for a fourstroke. If you don't you could ruin the engine. I don't mind blowing up a 2 stroke but a 4 stroke makes a big mess:D Oh yeh and $$$$$$ and world peace!

RE: Setting idle speed with tachometer
 

I agree here too. When dealing with a 4-stroke you'll need to use a tach until you get the hang of tuning it by ear, which can take quite some time.

Ken

RE: Setting idle speed with tachometer
 

Ok i am not very experince but how can our model engines idle all tank long..I mean the oil will accumulat after some time and end up pooling there and the rpm will drop.. are you saying we shoudl adjust to the point were we are burning ALL the oil as nothing will accumulat...

RE: Setting idle speed with tachometer
 

They are handy, but not a necessity.. at least, not in my limited experience. I have owned a Saito 82a for about 4 months now, so I'm by no means an expert. However, I do not own a tach and have flown approximatly 7 gallon of fuel with it, without any problems besides the ones I created myself. It seems you have to actually fill a fuel tank before take off. No one ever told me.. Duh! ;)

I did however use a tach (lended) for comparing props and I am planning to buy one. I have no doubt a fourstroke will be better tuned using a tach, but I wouldn't call it a neccesity.


The oil will accumulate where?

He's talking about the oil/fuel mixture. Oil is the lubricant, methanol/nitro/gas/whatever is the fuel ;)

RE: Setting idle speed with tachometer
 

The excess oil will blow out the muffler even if it's uphill and at idle. Some MAY pool in the muffler but as it builds up it will blow out and when you rev up it will also clear.