Engine Break Fundamentals?

[Kafin Noe’man]

Hi all,

After having discussions with other fliers, I was often told to set the engine to have break such as 4-2-4 or 2-2-2 or 4-4-4. At this point, I’m starting to get to know how the 2 or 4 sounds, but how do I achieve one and know if it’s going to be 4-2-4 or 2-2-2 or 4-4-4 on the ground? By playing around with the needle-valve and tilting the nose up and down and hear the engine?

Is it safe to say 2 is going toward the “lean” and 4 is going toward the “rich”?

Please correct me if I’m wrong.

I also hear a lot about setting it wet 2-2-2, does this mean aiming for 2 stroke sound without going too lean?

And what’s the use of pinching the fuel line to see/hear a change in speed? Is it to make sure the engine is not going too lean?

One last question, how important is the launch RPM? Because sometimes I have set the RPM to meet the required RPM but soon after it takes off, it kinda loose its power and going slow. Is it because of too lean?

Looking forward to hearing more advice from you guys!

Thank you so much, and Merry Christmas!


Best,
Kafin

[Dan McEntee]

Hi all,

After having discussions with other fliers, I was often told to set the engine to have break such as 4-2-4 or 2-2-2 or 4-4-4. At this point, I’m starting to get to know how the 2 or 4 sounds, but how do I achieve one and know if it’s going to be 4-2-4 or 2-2-2 or 4-4-4 on the ground? By playing around with the needle-valve and tilting the nose up and down and hear the engine?

Is it safe to say 2 is going toward the “lean” and 4 is going toward the “rich”?

Please correct me if I’m wrong.

I also hear a lot about setting it wet 2-2-2, does this mean aiming for 2 stroke sound without going too lean?

And what’s the use of pinching the fuel line to see/hear a change in speed? Is it to make sure the engine is not going too lean?

One last question, how important is the launch RPM? Because sometimes I have set the RPM to meet the required RPM but soon after it takes off, it kinda loose its power and going slow. Is it because of too lean?

Looking forward to hearing more advice from you guys!

Thank you so much, and Merry Christmas!


Best,
Kafin

     Hello Kafin;

        How an engine runs depends on how it's timed and what kind of porting it has. A lot of guys make comments about an engine break but do not realize exactly what that means given the engine they are talking about  and how it is ported and timed. Older engines like the Fox .35 and McCoy Red Heads had the classic 4-2 break that you can really hear, and that means it runs mostly in a four stroke ,(and that can be a wide range of RPM,) and when the nose goes up, gravity and physics takes affect and the engine leans out and "breaks" into a two stroke run, and that run depends on things like airplane weight, drag, prop pitch and basic needle setting. You can set a needle so rich that if the model is light enough, it may go through the whole flight and not break into a 2 stroke because it is so rich and can't burn the excess fuel.  How hard and engine breaks can depend on several factors that I mentioned before , and if the model is sort of heavy and draggy, it will need a more lean needle setting in order to perform, so that when the model is on the air, you won't hear that much of a difference some times. Modern engines like the LA.40 and .46 series can have a break, again, depending on the factors I mentioned before. On these engines, a needle setting that is 200 RPM higher or lower can make a difference, but be very hard to tell by ear some times. Some guys count clicks. I like to use a tach just as a tool to find what base RPM and engine likes to run at. The actual RPM doesn't mean too much, you just need to know what it is so you can find that point again. Pinching the fuel line and listening to the RPM change can give you an idea of where you are at. But if you have a full fuselage airplane you can't do that. Raising the nose is a more gentle way of achieving the same thing, When you raise the nose, gravity restricts the fuel feed a bit and makes the engine lean out. When you go back to level, the RPM should go back to the same point. And you are correct, a "2" is more to the lean side, and "4" is more to the rich side of adjustments.  One thing to keep in mind when making adjustments is that if everything about your fuel system is correct with no leaks and vented to atmosphere, centrifugal force that comes from the model reaching flying speed will increase the fuel head pressure in the tank and  will make the engine richen up a bit when in the air. The engine may be in a full 2 stroke sitting on the ground, but when launched, by the time it makes one lap you make hear the difference and see the model slow up a bit. It may act the same way even on muffler pressure. Test flying in the only way to fine tune this. You may get a pretty close initial set up from past experience, but fine tuning sometimes requires you to use a tach so you can repeat your setting  more easily. Model size and weight affects this also. you can have an LA.46 on a heavy Twister (45 to 50 ounces) like a lot of guys like to use, and have a good set up for that airplane. But then you can take that same engine and set up and put it in a heavy Legacy .40 (60 ounces and heavier) and it won't work. The LA.46 may break while flying the Twister, but it will have to run closer to the 2 stroke mode all the time to fly the bigger and  heavier model. It may actually be breaking a tiny bit, but you can't hear it. Several other parameters can affect how much and how hard and engine breaks, such as compression, what kind of muffler it has, prop pitch, nitro content in fuel, oil content in fuel, atmospheric conditions and a host of other things. The biggest thing you could do is learnt to keep notes or a log on what you are using on a specific airplane and engine as far as prop, fuel, plug and such and experiment with those more simple factors and pay attention to the results. Changes may work, but if they don't, you know where you need to go to put things back where you started. Keep thing simple at first, and if you make changes, only make on at a time, so if the changes does not work, put it back where it was. Ad far as launch RPM, it is just a reference number. If the model launches at 9000 RPM but richens up and slows down too much in the air , then set the launch RPM at 9300 RPM next time and see what happens. Again, the RPM figure really doesn't mean anything, it's just a reference. If your tach breaks down and you get a new one, you may have to alter that a bit if the new tach does not read the same as your old one, and I have seen that happen. Just make the necessary change and record it.  To do all that I have covered above can take a LOT of flying! But don't take short cuts or skip over things.
  MERRY CHRISTMAS!!
    Dan McEntee

[Kafin Noe’man]

Hi Dan,

Thank you so much for your thorough response.
I get a lot to learn from your post alone. I’m grasping more and more knowledge everyday.

Another follow-up question, let’s say I wanna do the 4-2-4, one of the things to make sure or check is when I’m raising the nose up, I need to hear the pronounced change in sound of engine leaning out, meanwhile when I want to have the wet 2-2-2, I still need to hear the engine leaning out a bit when nose is up. Do I get that right?

In order to get that wet 2-2-2, can I close the needle up to the peak RPM and then go open it few clicks back (1/4 turn)? This, I assume the engine will still be on the 2 but on the richer side.

One last question, if I don’t hear any lean out sound when I raise the nose, does that mean the engine is already too lean?

Thank you!


Best,
Kafin

[Dan McEntee]

Hi Dan,

Thank you so much for your thorough response.
I get a lot to learn from your post alone. I’m grasping more and more knowledge everyday.

Another follow-up question, let’s say I wanna do the 4-2-4, one of the things to make sure or check is when I’m raising the nose up, I need to hear the pronounced change in sound of engine leaning out, meanwhile when I want to have the wet 2-2-2, I still need to hear the engine leaning out a bit when nose is up. Do I get that right?

In order to get that wet 2-2-2, can I close the needle up to the peak RPM and then go open it few clicks back (1/4 turn)? This, I assume the engine will still be on the 2 but on the richer side.

One last question, if I don’t hear any lean out sound when I raise the nose, does that mean the engine is already too lean?

Thank you!


Best,
Kafin

        The "2" or two stroke mode, like the four stroke mode, can run a range or RPM and is not a certain "point" or setting. The 2-2-2 that you refer to is what some might call a "wet-2" where the engine is solidly in a two stroke mode from take off, through the maneuvers, to landing. It's not quite peak RPM. When you get to the very peak of the needle setting, any more lean and it slows down and can quickly die. You will hear the engine slow down and sag whenever it gets to this point and you should not push things and just fly level and ru8n the tank out, which may take a lot longer that usual. Again, you won't get every engine to run in this manor and it is a type of run most modern engine will put out peak power. The other variables I mentioned, especially prop size and pitch affect this. There are RPM changes going on but because of the very minor RPM changes and engine noise, you just can't hear them.

    On setting the needle for the 4-2-4, you will get close by setting it on the ground, but the proof of the setting will be in the air and in your lap times. Keep in mind that if your entire fuel system is sound with no leaks, your engine should slow down a bit when it gets into the air. When setting it on the ground, it may be in that "wet -2" mode that I described, but when it gets into the air and centrifugal force gets into the picture, the extra pressure in the tank will richen things up and then if everything else in the equation is working, it will do the 4-2-4, depending on the model weight, drag, prop pitch, type of muffler and all the other little variables. Listen top your engine every flight. The knowledge of what to do will come from experience as you build time. This is why I encourage people to stick with one engine and one model while going through this process to keep things simple.

  MERRY CHRISTMAS!
   Dan McEntee

[Steve Helmick]

I would only add that it is hopeless to start the engine, set the NV to your launch rpm and head for the handle. The engine will take a short while to warm up to the point where the NV setting will hold steady. I think that is why you are finding the engine sagging lean after takeoff. If you hear the engine change rpm just as you pick up the handle, that's why.

What I do is start the engine, and either pinch off the muffler pressure line or block off the uniflow air inlet several times, while taching the engine. When the engine sags a little, stop pinching/blocking. When the engine then returns to the same rpm setting twice, it's warmed up and time to set the NV for launch...with a tachometer! I think you'll find this will work well.

I see some guys start their engine and never touch the NV, but I also see a lot of them have problems that could be avoided by warming up the engine. At contests especially, it may be some time between rounds, and the air temperature may have changed significantly.    Steve