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 Post subject: the difference a plug makes
PostPosted: Sun May 20, 2012 1:02 pm 
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Joined: Sat Oct 27, 2007 3:44 pm
Posts: 376
Going over data that I've collected over a short period of running a lot of engines..so it's not talking about something new and revolutionary. But from running and flying a few engines and I came to realize how much a simple plug can make such a difference.
Case in point is the OS LA 46, a great out of the box engine that everyone usually bolts in and flies. Even so a change of venturi and an additional head gasket are standard changes in many situations I found that the plug can be a major factor in getting a great repeatable run on these engines.
I had 2 of the LA46's that while they were good as the temperature outside went up even fuel changes did not make the run settle down. Even had the standard 12.25x3.75 prop on it. Talking it over with a few friends one said what plug are you using. Told him the Thunderbolt hot that I generally use in all of my engines. he said did you try an OS A-3 which is a medium length plug, I said no.
Ok, so you just know that I got one into the engine and like magic it settles down and runs like a well tuned sedan, Boring, but that is what we need for our purposes. So to the point. Long hot plugs on some engines really do advance the timing and make the engine run hot and run away. So I've done this little test and tried it on the notoriously fickle LA/40 and while not a cure did make the engine more useable. While on the subject, the Evolution 36 has awakened my interest in alternative fuels for our engines and I firmly believe that more then a few of them could run on slightly less oil then we are using now with more favorable results. I'm using a few larger ball bearing engines on Powermaster 10/18 with very good results, and no they are not Ro jett's. This fuel is almost a standard with the R/C crowd. I guess that i'm doing this just to see if these old standards fuels that are recited as a mantra are really relevent to todays superior metalurgy
The end point of this little thread is take a few different plugs even,shudder, a less then hot variety, definitely a medium length plug and try them. Also with less oil I'm firmly convinced that the hot plug can be replaced with a normal. I'll let you know during the flying season how the testing is going and if there is any interest a report at the end of the season.

Dennis


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 Post subject: Re: the difference a plug makes
PostPosted: Wed May 23, 2012 9:38 am 
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Joined: Wed Apr 06, 2005 10:41 pm
Posts: 538
Location: Clio, MI
Dennis,
You are right about plugs making a difference. My most notable experience was trying to find a plug that would survive a Fox outside burp in a profile airplane. I had gone through a number of needles before I started cutting them down so I could survive an inverted landing on my Sig Twister, but it still bothered me that unless the needle was exactly perfect, the engine would quit when I pulled an outside loop. Fortunately I developed a good method of testing on the ground and was able to sort through plugs rather quickly before settling on a final version. For what it is worth, it is the plug that Tower Hobbies sells under their name which I suspect is made by the same people that manufacture the OS plugs.

Speaking of finding things out on engines, we need to consider many things when it comes to an engine run. You have mentioned the plug, but things like fuel type (not all are created equal), nitro percentage, oil type, oil percentage, spray bar hole position, NVA type, venturi size, prop size, prop material/weight, pressurized system, tank type, muffler type and muffler exit size all have a huge impact on how the engine runs. Best thing to do is start with a known good set up and then experiment from there. Run performance, power, heat and fuel consumption are all impacted. It is important to be patient and methodical as you go through the motions to find what the engine likes.

FWIW,
John


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 Post subject: Re: the difference a plug makes
PostPosted: Wed May 23, 2012 10:56 pm 
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Joined: Sat Oct 27, 2007 3:44 pm
Posts: 376
John,

Of course you are right about all of the other variables but to keep it simple it pays to deal with one thing at a time. Even on a discussion on a forum if too much is out there it can get muddied fast.
That said if you use a constant on every engine and change only one thing in this case the plug and you get an improvement then you know definitely that you are on to something and then you can fine tune the others.
But, after a lot of running and playing with engines I run only 2 fuels both powermaster on plain bearings and add a 3rd lower oil for BB engines also Powermaster.
same for props. I only use 2 props for each displacement for comparative purposes an they are the same 2 that go on every engine being tested in that displacement. It isn't fully scientific but it get's me into the ballpark more often then not.

Dennis


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 Post subject: Re: the difference a plug makes
PostPosted: Thu May 24, 2012 11:34 pm 
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Joined: Wed Apr 06, 2005 10:41 pm
Posts: 538
Location: Clio, MI
Dennis,
You are right about having a starting point and then changing only one thing at a time being a good way to keep things in sight. At work here there are all sorts of techniques that we use to evaluate multiple changes in a matrix and then extract the impact of each change to come up with an optimum design. It is a great concept and works well, but I don't use it for my hobby.

Excellent point about the fuel. I generally will use 2 different brands and different flavors depending on the application within the brand. You can get a lot of trouble if you don't have a good fuel source and will be chasing problems for a long time. Some guys like to save a buck or two a gallon, but for me it is just not worth it. Powermaster and Sig are my baseline fuels and I have a few others that are okay, but these two are generally what you will see me using when it comes time to be judged. Just one less thing to worry about.

John


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