Is this right? I am now using a tac meter to help set my engines. One of the engines is the O.S.46LA. The specs. say the range of rpms are from 2000 - 16000. So I have set this engine at 11000 rpm by the tac. I should say that I am not looking to get the max speed/power from any of my engines, but I am trying to get my engines to fly for many years. So I am thinking that I am running on the rich side since I am below the max rpms. Does this setting sound right for my purpose which is a good running engine that will run for a long time. It is running real good and does leave a "smoke" trail you can see.

Hi Brooke,

I'm certainly not an expert in this area, so I'm sure others will chip in.

An important factor is the prop you put on your engine, also you have to take into consideration that once airborn the engine will probably run ~1000rpm more then on the ground (this is what I am told, please correct me if I'm wrong).

I have an OS .40LA with 11x5 prop and a Webra .60 with a 13x6 prop and both run around 10200 on the ground.

Johan

11,000 sounds a bit low, I would look for around 12,000 if you are running a MAS 11-6 prop. To be sure you would have to supply prop info such as 2 or 3 blade, size and pitch such as 11-5 and also the brand such as APC or Master Airscrew. For info, you will never see high rpms like 16,000 unless you are using a prop that is too small to be practical for most airplanes. For OS 46 FX series engines I conistantly read 14,200 for reliable running. Other engines such as the Thunder Tiger 42 turn an MAS 10-6 prop around 12000 rpm. Hope this helps.

It's really hard to adjust a motor so it's running rich using a tachometer. What you need to do is adjust the motor so it's running a close to top speed, and then turn the needle valve 2-4 clicks out. This will richen it back up. If you can see a smoke trail from the exhaust you're good. If you run your motor like that it will last you a lifetime.

Ken

Hi!
You must have missunderstood this rpm thing with engines!
A certain rpm is not what is important. And certainly not aiming for what the manufacturer says is the rpm where the engine deliver it's peak hp.
All our glow engines can be run at a wide rpm spectrum. Your OS .46 LA for instance can cope with props that load the engine from say ...8000-17000 rpm without hurting the engine in any way...as long as you set the highspeed needle right (a little rich).

But for most sport models a 11x5, 11x6 or 12x4 APC is the best prop for your OS.

Regards!
Jan K
Sweden

Thanks for the info. I am running a MAS 11x6 prop on it now. Also Rc Ken you say to run it at top speed and then back it down. Do you mean top speed being top of the rpm range? I understood the rpm range as the max rpm being the lean side and the lower the rpm setting the richer it would be. It sounds like I am wrong, so can anyone tell me what the rpm range is for or what setting the rpm with a tac is good for?

You are right, high RPM=lean, low RPM=rich. When you read the OS Manuals they say that to find the optimum needle-valve setting, to close the vavle until you hit peak RPM, and then open it slightly from there. I don't have my manual here, so I can't recall how far. Most folks on here seem to bring the engine to peak RPM (which is lean) and then drop it by about 300rpm opr so. What Ken said with the 4 clicks open on the needle valve should accomplish that. And like he said, if it smokes, your ok.

An just to make sure, max rpm in this case is whatever your tac shows you when the engine is at its leanest with the given prop, not the theoretically max possible rpm in the engine's manual.

OK now I am confused,
I understood low and high RPM data to be idle and full throttle speeds not rich or lean.
In the example above.
2000 rpms at idle
16000 rpms at full throttle
Is that wrong?

Let's see if I can avoid talking us further into a hole . Do you take your example from the manual (e.g. rpm range for the engine between 2000-16000)? My understanding is that those #s represent the theoretical range the engine can run at without something bad happening (and yes the 2000rpm won't be at full throttle).

The actual rpms you will be able to achieve can be quite different as they depend highly on which prop you use, atmospheric circumstances etc. So using a tac to try to get your engine as close as possible to 16000 rpms and then leave it there is probably not a good idea.

Also I think tacs are more used to tune 4 strokes, they're almost mandatory for 4 strokes as right mixture setting is very important and running your 4 stroke too fast (too high rpm's) is surely going to break something and they are more difficult to tune just based on listening.

If the above didn't help surely folks more knowledgeable than myself can provide more detail.

O.K., I am not trying to confuse things here. But if one can't depend on the tac readings to set the engines for max performance then how do you know it is running to lean, should that happen. I am just trying to figure this out because I did have someone "tune" one of my O.S.46Fxi's and now it is dead, it was ran way to lean. Now I know it was ran to lean, but at the time I did not have any experience with it. Not that I am experienced now either.

Hi!
OK! You see we modelers don't usually set our engines by any gadgets like tachs...we simply use our ears to listen to how the engine sound and set the engine accordingly.
This is very easy when you know how. The human ear is a very reliable instrument if you know how to use it right.

You seem to think that the manufacturers recommended max rpm is what you should get (aim for) with every prop you use on your engine ...like if the OS LA. 46 you have got should be able to rew 16000rpm with every prop...Nothing could be further from the truth. An OS .LA .46 engine will only rew around 10000-12000rpm with a 11x6 APC ...or MA (Which is the worst prop you could use)...but with a 9x6 it will rew around 13500-15000 rpm. So which prop is the best then?...In your case definitely the 11x6.

What we seek when we choose a prop for an engine /airplane is to get as good performance as possible. Different props perform differently. But we never try to prop the engine to the manufacturers max teoretical rpm as this would be useless and require a much too small prop for most airplanes which would not give us any performance at all.

So just listen to what your ears tells you, and set the high speed needle accordingly!

Regards!
Jan K
Sweden

After break in (following the manufactures recommendations) I use my tac to find the highest rpm that the engine will turn with the prop that is mounted. On my OS 91 I hit 11600. As I go leaner the engine drops off so I quickly come back to the highest point then richen the high end a until I lose a couple hundred RPM (about 11400). Now i am sure that I am not to rich and it allows for engine unloading when in the air. If the plane is small enough, I hold the plane nose high when the engine is running and have some one run the throttle up to max just to be sure it does not go lean. Thats it.. high speed is set right. Now low end is another story.

Once the engine is broken in and the high speed set where I want it, I set the engine to its lowest steady idle.. lets say it is 3000 RPm. I pinch the fuel line near the carb and listen to the engine.. If it starts picking up rpm it is too rich on the low end, I turn the engine off and I turn the idle mixture screw in a 1/16" I then start the engine run it back up to full throttle, then back down to the lowest steady idle. It should be getting lower.. say 2800 RPM now. Keep repeating this untill when the fuel line is pinched the engine increase very little or holds steady for a second before fall off and dying. If the engine is broken in, the idle should be around 2000-2200 RPM and steady with no signs of dying. Some engines will hold much lower idles, and the bigger the engine, typically the lower the idle due to the heavy prop acting as a flywheel.

If you do the pinch test and the engine dies immediately you are too lean.. richen up and try again. When set correctly the transistion from an idle to high RPM should be steady and almost as fast as you can move the transmitter stick. If it is too lean it will falter or die, if too rich it will lag behind the stick movement and will be rough. You will learn to recognise the difference quickly.

Once you have a good steady idle you go back to the high setting and reset according to my first paragraph as it will like be affected by the idle mixture if you had to change it very much.

It is good idea to change the glow plug after it has been broken as new engine has oils and metal shavings that will adhere to the platinum wire. While the engine may start and run ok.. it can make the idle hard to set and the plug usually fails early in any case.

Once the idle mixture is set you seldom have to mess with it, but weather etc can affect the high speed need so it should be checked prior to each days flying, just takes a second, run it up to where it falls off, back off to highest rmp then richen a few hundred RPM more and your good to go. I never have to play with the high speed more than once in a given day unless I start early in the morning when it is cold and the weather changes significantly later in the day

O.K., the way I understand what bluestratos is saying is that when you use the tac the rpm's will keep going up, as you turn the high end leaner, until you hit lean, or max rpm's, then if you keep going leaner the rpm's will start to drop. So once you find the high rpm end then go back a couple hundred and you should be real close if not good. This makes since to me. Is this right?

I am not trying to get max rpm's from all props, I am sorry if that is how it sounds. I am just trying to find a better way for me to set my high end on my engines. As for props I am still using what that manuel says to use for that engine as far as the break-in prop and then once I have several flights on it I will go one size bigger. If I am still way off I will just stick with making sure I see smoke while flying until I can get back with the experienced flyer's in person.

As far as just going by ear, well I can hear however I do have a good amount of hearing lose in one ear. Going by what others tell me, I hear things different than others so I am just trying to find another method if their is one. Or I should say if I can understand this.

I have a tach, but I do not use it for tuning my engines. The only time I get it out is to compare peak RPMs for different props or when I'm adjusting the length of a tuned pipe. Here's what I do to ensure the engine is at a needle setting that will give it long life and few deadsticks.

While holding the plane with a firm two handed grip, have someone else run the engine up to full throttle. Then point the nose of the plane straight up. If the engine slows immediately, it's too lean. Lower the plane to the ground, richen it and try again.

If the engine speed doesn't change, it's still a bit too lean. Lower it, richen, and try again.

If the engine speeds up a bit and holds that speed, you've got it at a good spot.

If the engine speeds up significantly, it may be too rich. Lower it, lean it out a bit and try again.

This method has worked well for me for years. While it might be possible to squeeze a bit more performance out of an engine, the occasional deadsticks I get are not due to a lean engine.

BTW, that 16,000 RPM thing is because there are some people who put ducted fans on their engines instead of propellers (What some people won't do to ruin an engine!)

Follow Chuck's advice. You don't need a tach to tune an engine.

Thanks for the help! I guess Jaka was right, "I misunderstood this rpm thing with engines." Well at least I already said I am still trying to learn. I guess in about another five years or so I will know alot more than now, but still be learning. I will try out piper chuck's way, it sounds easy. Thanks again.

brooke,
You can use your tach to set your engine, but you don't start out with it being the deciding factor. Matter of fact, you merely use it to record the "correct" setting and then later to repeat that setting.

Our engines are dependent on the correct fuel/air ratio being set for them. And that's what we do and do the initial setting with all the tests and twiddles that bluestratos and chuck and a few others have mentioned. You really are discovering what needle setting works for your engine with the prop that is on the airplane that day. THEN.....

After you've got your good needle setting, tach it. And keep that in mind for next time.

Next time out, you use the tach to help repeat that good needle setting.

If you don't work out the optimum fuel/air needle setting (with all those tricks just mentioned) your engine will probably never run dependably nor with much power. It'll probably always give you fits. You gotta set it by the way it runs, not by any rpm numbers. And then you can record that rpm for that make and diameter and pitch of prop for later use.

Tachs are BIGTIME helpful for 4strokes. They're rather "flat" running engines and will sound about the same when a bit rich or when too lean. But they won't be turning exactly the same rpm, and a tach will tell you what you can't hear. And they're helpful with 2cycle engines too, just not as important.

They're a secondary tool, not a primary. But the guys who know how and when to use them are miles ahead of the guys who don't.

There is also a useful technique with a tach that a newbie can use to learn what rich and lean and too lean sound like.

Crank the engine and open the throttle.
Open the needle valve until the engine starts to run obviously rich. There will be lots of exhaust and it might even have raw fuel in it. The engine will have obviously slowed down as you get it into "obvious" rich. It may even sound like a 4cycle engine. Tach the sucker.

Now, start to slowly lean it out.
Watch your tach readings as you lean it out.
The rpm will increase as you continue to lean it out.
The engine will continue to turn better and better rpm.
Turn the needle in slowly. Don't hurry.
At some point, as you continue to lean the needle out, the rpm will begin to fall off.
You've just discovered the max rpm of that engine and the too-lean needle setting.

The max rpm needle setting was your too-lean needle setting.
Somewhere richer on the needle is your optimum setting.
Back the needle out a few clicks and note the tach reading. Now, with that setting, hold the airplane with the nose pointed up. If the engine sags after 10-20 seconds, click the needle out a couple more clicks. If you can't get the needle rich enough that the engine will hold it's rpm with the nose up, you've got a tank problem that you need to solve. If you can, you're good to go.

Let's look at that statement.
The max rpm your engine will turn on the ground gives you a needle setting that is going to be too lean in the air.
When the airplane is free to move forward, the engine has an easier time turning the prop. So the rpms in the air will be greater than on the ground.
When an engine turns easier, it turns faster. When it's turning faster, it actually needs more fuel going into it. Why? Because it's getting more air and you've not adjusted the needle to give it the extra fuel to match the extra air.
So you adjust the needle on the ground to give the engine more fuel that it's going to need in the air.

So your max rpm needle setting on the ground is going to be a too-lean setting in the air.

Thanks a lot guys! I can't say it enough. I know it has been said over 1,000,000 times already, but it really is great to get so much information from a variety of people so quickly here. It is a big help.

Also I think I am starting to get the idea of this now that I have been applying what you guys have told me and I can really see how it works.

You have received some good advice. Once you get things working to suit you leave them alone. Leave your tach in the box unless you make some sort of change and need to find the sweet spot again.

The LA 46 should turn at about 11,000 with an 11X5 APC prop, give or take a few hundred rpm depending on altitude, humidity, temperature, etc. I always use a tach to set the high speed needle at the beginning of the day, setting it to peak rpm -300 rpm to the rich side. Been running it for 3 years without a dead stick.

When it unloads in a dive at full throttle, you'll probably approach the 14k-16k range. The 11x5 is my prop of choice for the LA 46, as it gives a good optimum for thrust and speed. Its actually faster at full throttle than my SPAD Debonair likes.

Good Luck.

Brad

With a MAS 12-6 prop ou should be able to get a touch over 12000 rpm. If you get the extra 1000 rpm over the 11000 you get now you will see a big difference in getting the plane up to take off speed. When I first bought my new tach I tached different engines on trainer planes to see what kind of rpms the props were turning with the different engines. What I found was that if the engine was turning a MAS 10-5 prop at 10,500 rpm on a 40 engine. The plane barely had enough speed to get airbourne. 11,000 was a bit better. 12,000 was quite good and was obtainable with engines such as the Super Tiger 42 size. At higher rpms (just over 14,000) such as you would expect to get out of a OS FX or AX engine the take off was short and fast! These take offs are all off a rough grass field. Hope this info helps. [8D]

I want to make it clear that there is no number that you should be shooting for. You are looking to get the fuel mixture correct. That may give you one RPM setting today, and a different one tomorrow depending on weather conditions, or the numbers may change from one location to another.

Use your tach for info only. Don't use it to tune your engine.

In other words... You SHOULD:

"Ok, engine sounds right, and "Noses Up" correctly... Let's see what the RPM is"

But you SHOULD NOT:

"I'm getting 500 RPM less than yeasterday. Let's see if I can bring that up"