bigrcr
07-29-2005, 05:09 PM
On the oil subject;
-Oil in a glow motor has two major functions. The oil lubricates the moving parts (1) and it removes heat from the motor (2). This is the reason glow fuel contains 17-25% oil in it's make-up. The oil is a fluid so it can absorb heat better than a vapor- it carries away excessive heat. There are a few other things the oil does, but that is not part of this discussion. The nitro-methane used also widens the "burn window" for the fuel.
-Oil in a gas motor has one major function and that is to lubricate the moving parts. The oil excess carries little to no heat away, mainly because there is not an excess (at 50:1 there is about 1.9% oil-don't grin guys that use 5 ounces, you only have 3.9% oil). The gas motors don't need the oil amount that the glow motors use since the fuel is not the coolant as well, and cannot be. Gasoline burns in a much tighter window than alcohol as well (air/fuel ratio). That’s mostly why the gas motor needles are more sensitive.
You could add more oil into the mix to aid in heat removal, but the gas motor will not like it, mainly because it operates at a much higher temperature than a glow motor and the oil would start to burn and the excessive oil will foul the plug surfaces. These motors really don't like compressing fluid either so more oil CAN mean more shake and vibration levels.
This is where the oil type and amount comes in.
Petroleum/Mineral based oils: These oils are derived from crude oil or a blend of crude’s and naturally occurring oils . These oils being derived as they are normally would burn along with the temperatures necessary to burn gasoline. HMMMM...not good if you want the oil to lubricate...if it burns up, it won't lubricate and the resultant "ash" would scar your motor. Automobile motors are four strokes and don't use the lubrication oil in the cylinder (it gets wiped off the cylinder to an extent by the rings).
Two strokes pull the lubrication from the motor and compress it along with the fuel contained, using it for fuel. The crankcase in your car does not get hot enough to burn the oil, your 2-cycle motor in your heli brings this oil into the cylinder and tries to burn it. You don't want your oil to burn.
Ashless petroleum oil has been formulated to withstand the temperatures of the 2-cycle motors cylinder temperatures without burning. The flash point has been raised in these oils and impurities that could burn at the temperatures are removed.....Ashless. These oils lubricate well and also allow the cylinder/piston parts to break-in fairly quickly under proper lubrication.
Synthetic oils are not derived from crude oil/naturally occurring oils but are "man-made". These formulations can be specifically tailored (viscosity and flash points mostly) for intended use and temperatures seen in our motors should not affect these oils so that they can do their job.
Too much of these oils and you can foul plugs and raise compression which CAN be detrimental. This can be seen usually as a wet looking plug and can be seen as deposits on the piston and worse on the ring(s) and on the plug as deposits. Reading the plug would include determining if these deposits are from too much oil or the wrong kind or both.
If you are using the right kind of oil, one of the variables is removed and then you are down to looking for too much oil and needle settings.
Air/fuel ratio:
This is NOT the oil/fuel ratio and deals with needle settings, air leaks and to an extent, inherent heat of the motor itself. The 2-cycle motors we use operate at a very specific air to fuel ratio. This is set by the combustion properties of the fuel that we are using (gasoline or Naptha). Gasoline and Naptha burn at VERY close air/fuel ratios (their combustion ratios). The dead on spot within this ratio is where we would like to run, but atmospheric conditions, ignition timing and the motors temperature can effect this. Running the mixture a bit to the rich side will hopefully ensure that the motor is always getting enough fuel in the mixture. When the needles are lean, there is more air than fuel and power goes down and temperatures go up and stuff that would not normally burn, may start to burn. When there is too much fuel in the mixture, power can go down and temperatures can go down (unless there is too much oil- raising compression which could result in temperatures going back up to an extent).
When the temperature gets too low in the motor, it may not be at it's optimum operating temperature which can cause plug fouling, internal scarring (yes- from tolerances not being correct: being lean will do this as well) and needles that are impossible to set correctly due to the motor temperature seeing many changes.
Temperature changes within the cylinder due to a lean condition can be read on the plug as glazing, physical plug damage and a light color on the plug. What you are actually seeing with the white to light grey color is the temperatures burning everything off of the plug and trying to burn the insulator and metal parts as well. The glazing is just that; the temperatures are converting or burning the oil and depositing it as a glaze on the plug. Either way, it's too lean. I could go on about a leak as well, but you should get the Idea.
So reading the plug in our motors is VERY important to do. It is the "check-up" to see "what is really going on" (thanks Beast) inside of the motor and properly reading the plug (and cylinder, piston (exhaust side)) can tell us everything.
There is a very simple and systematic way to read plugs, one day I may have time to put these into easy to understand "layman’s" terms, if I get time. The best practice is to always stay as rich as possible, at least until you really know how to read plugs and such. Tuning by ear is not the best way to do it as it is not a quantifiable measure, the plug is. Even when I tune by ear, I ALWAYS look at the quantifiable evidence (plug, piston, etc) to make sure that the motor is in good health.
-Oil in a glow motor has two major functions. The oil lubricates the moving parts (1) and it removes heat from the motor (2). This is the reason glow fuel contains 17-25% oil in it's make-up. The oil is a fluid so it can absorb heat better than a vapor- it carries away excessive heat. There are a few other things the oil does, but that is not part of this discussion. The nitro-methane used also widens the "burn window" for the fuel.
-Oil in a gas motor has one major function and that is to lubricate the moving parts. The oil excess carries little to no heat away, mainly because there is not an excess (at 50:1 there is about 1.9% oil-don't grin guys that use 5 ounces, you only have 3.9% oil). The gas motors don't need the oil amount that the glow motors use since the fuel is not the coolant as well, and cannot be. Gasoline burns in a much tighter window than alcohol as well (air/fuel ratio). That’s mostly why the gas motor needles are more sensitive.
You could add more oil into the mix to aid in heat removal, but the gas motor will not like it, mainly because it operates at a much higher temperature than a glow motor and the oil would start to burn and the excessive oil will foul the plug surfaces. These motors really don't like compressing fluid either so more oil CAN mean more shake and vibration levels.
This is where the oil type and amount comes in.
Petroleum/Mineral based oils: These oils are derived from crude oil or a blend of crude’s and naturally occurring oils . These oils being derived as they are normally would burn along with the temperatures necessary to burn gasoline. HMMMM...not good if you want the oil to lubricate...if it burns up, it won't lubricate and the resultant "ash" would scar your motor. Automobile motors are four strokes and don't use the lubrication oil in the cylinder (it gets wiped off the cylinder to an extent by the rings).
Two strokes pull the lubrication from the motor and compress it along with the fuel contained, using it for fuel. The crankcase in your car does not get hot enough to burn the oil, your 2-cycle motor in your heli brings this oil into the cylinder and tries to burn it. You don't want your oil to burn.
Ashless petroleum oil has been formulated to withstand the temperatures of the 2-cycle motors cylinder temperatures without burning. The flash point has been raised in these oils and impurities that could burn at the temperatures are removed.....Ashless. These oils lubricate well and also allow the cylinder/piston parts to break-in fairly quickly under proper lubrication.
Synthetic oils are not derived from crude oil/naturally occurring oils but are "man-made". These formulations can be specifically tailored (viscosity and flash points mostly) for intended use and temperatures seen in our motors should not affect these oils so that they can do their job.
Too much of these oils and you can foul plugs and raise compression which CAN be detrimental. This can be seen usually as a wet looking plug and can be seen as deposits on the piston and worse on the ring(s) and on the plug as deposits. Reading the plug would include determining if these deposits are from too much oil or the wrong kind or both.
If you are using the right kind of oil, one of the variables is removed and then you are down to looking for too much oil and needle settings.
Air/fuel ratio:
This is NOT the oil/fuel ratio and deals with needle settings, air leaks and to an extent, inherent heat of the motor itself. The 2-cycle motors we use operate at a very specific air to fuel ratio. This is set by the combustion properties of the fuel that we are using (gasoline or Naptha). Gasoline and Naptha burn at VERY close air/fuel ratios (their combustion ratios). The dead on spot within this ratio is where we would like to run, but atmospheric conditions, ignition timing and the motors temperature can effect this. Running the mixture a bit to the rich side will hopefully ensure that the motor is always getting enough fuel in the mixture. When the needles are lean, there is more air than fuel and power goes down and temperatures go up and stuff that would not normally burn, may start to burn. When there is too much fuel in the mixture, power can go down and temperatures can go down (unless there is too much oil- raising compression which could result in temperatures going back up to an extent).
When the temperature gets too low in the motor, it may not be at it's optimum operating temperature which can cause plug fouling, internal scarring (yes- from tolerances not being correct: being lean will do this as well) and needles that are impossible to set correctly due to the motor temperature seeing many changes.
Temperature changes within the cylinder due to a lean condition can be read on the plug as glazing, physical plug damage and a light color on the plug. What you are actually seeing with the white to light grey color is the temperatures burning everything off of the plug and trying to burn the insulator and metal parts as well. The glazing is just that; the temperatures are converting or burning the oil and depositing it as a glaze on the plug. Either way, it's too lean. I could go on about a leak as well, but you should get the Idea.
So reading the plug in our motors is VERY important to do. It is the "check-up" to see "what is really going on" (thanks Beast) inside of the motor and properly reading the plug (and cylinder, piston (exhaust side)) can tell us everything.
There is a very simple and systematic way to read plugs, one day I may have time to put these into easy to understand "layman’s" terms, if I get time. The best practice is to always stay as rich as possible, at least until you really know how to read plugs and such. Tuning by ear is not the best way to do it as it is not a quantifiable measure, the plug is. Even when I tune by ear, I ALWAYS look at the quantifiable evidence (plug, piston, etc) to make sure that the motor is in good health.