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Engine basics => Engine set up tips => Topic started by: steve pagano on February 25, 2007, 04:24:55 PM
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When flying in competition i hear a lot of guys talk about getting there engine to go into a 4/2 break. From what i know a 4/2 break is the best engine run you can get. So what does it take to get the 4/2 break? Can you get it with any engine?
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When flying in competition i hear a lot of guys talk about getting there engine to go into a 4/2 break. From what i know a 4/2 break is the best engine run you can get. So what does it take to get the 4/2 break? Can you get it with any engine?
I guess it all depends on who you talk to as to what is the "very best" engine run. The 4-2 is a "traditional Stunt Run". It is even widely used with the pipe set ups, now, but it's just not as noticeable. My PA 61s are in a deep 4 cycle and just blip at th tops of maneuvers, etc., and that's the way that I see "most" of those set ups working.
Some might say that now it is a 2-2 run..... where the engine just runs in a 2 all the time and then speeds up a touch under load. Either way, it's trying to get the airplane to fly at the most constant speed, not engine speed.
Not all engines will 4-2 in stock form, nor should they. The OS 20FP and the Magnum 36 XLIIS don't, and they work great! The other side is the Fox 35 and it is Classic 4-2. Then you run into the reworked engines..... it is all a matter of the combination of port timing (blow down??), compression, etc., to get the 4-2 run.
To "get" it, you must have an engine that will "do" it. Then it is a matter of adjusting the needle to where you are 4 cycling in level flight and it "breaks" to a 2 cycle under load (like when the nose points up). Then you want it to "shut off" when the nose points down (not quit, just go back to a 4 cycle).
Needle setting, prop load, nitro, compression, all go into chasing that "perfect" 4-2! (and pipe settings if you go that route!)
Bill <><