Informative article on aircraft engine oil

[Guest deanfi]

Quite a good article regarding oil

 

https://www.kitplanes.com/engine-theory-6/?fbclid=IwAR23PYK53-VXm5eyHQ2E-6T4_1yujdPL2425w-uJqprO6xQCzafeWfDyncw

 

 

[facthunter]

Might be better if he knew the difference between tolerance and clearance. He is not alone but they are two entirely different things.. Lots of words and not a lot of real information. The sort of "advertising oils" material common ground with" OUR OIL" does al this (Actually hard to prove).. Cooling your motor with air by running lean of peak is stretching things. I actually wonder what that contentious topic has to do with what oil you use.  Oil doesn't cool things very well. You need a lot of it and special oil jets in turbocharged motors are common to universal.. The main reason for larger running "clearances" on some bearings is to achieve higher oil flows with SOME bearing materials that don't have the best friction co-efficients so need to control the heat build up somehow.. Clunking noises in some larger engines are because of dynamic counterweights on the crankshaft. not CAVERNOUS clearances )not Tolerences)  A tolerance is a max allowed dimensional variation A clearance is what's designed into the motor intentionally as a required to allow for oil flow or metal expansion when running.. Most sludge formation is because of short runs and water contamination where the engine doesn't fully warm up. This WAS covered in the article as far as temps needed was addressed. Longer trips are easier on engines and sitting idle is just what they don't need.. Oil doesn't contain MAGIC. It's formulated for the job it's designed for and all aviation grade oils have to meet a standard so you have some assurance of quality in a world where that is mostly not available. (unfortunately). Nev

 

 

[onetrack]

You might want to rethink that, "Oil doesn't cool things very well" statement, facthunter, if you take a look at the Rumely OilPull tractors, built from 1909 to 1930.

 

These tractors utilised oil for the engine cooling medium, and the oil-cooling of these engines was quite successful. Corrosion is totally eliminated, and the boiling point of oil is much higher than water.

 

https://en.wikipedia.org/wiki/Oil_cooling

 

https://tractors.fandom.com/wiki/Rumely_Oil-Pull

 

I recently purchased a 2005 model Atlas-Copco trailer-mounted compressor for an associate. This unit is powered by a 4 cyl Deutz engine - and the Deutz engine cooling system uses oil as the cooling medium.

 

Engine cooling via oil allows higher engine operation temperatures, for increased efficiency, but the engine must be designed to handle the higher temperatures of oil cooling.

 

Water cooling is simply cheaper for manufacturers, and this design provides a steady income stream in parts and repairs, as it's reported that around 60% of engine problems are cooling-system related.

 

 

[facthunter]

Tractors have notoriously low outputs in the early times for their capacity so what they did 100 years ago is not quite relevent to the aero engine of today.. I did qualify the statement b y saying it works with oil jets etc but you can't rely on the small splash effect to do much on a continuous heavily loaded engine..OIL in your radiator instead of water or good coolant certainly would not work. Also in heat treatment of metals oil is not used for the peak Hardness( quenching)  required, Water  or brine(nitrates) are even molten (Low melting point) metals are used then. Some engines are part oil cooled which helps to get the heat out when a lot of parts are under covers. . I didn't JUST say the bit you quoted. It was meant IN CONTEXT. As you say water isn't perfect as it's boiling point it too low for optimum engine efficiency. Engines operate better at say 120 C+ head temps. Nev

 

 

[John Robert]

I am surprised that Evans coolant has not been mentioned in the discussion of cooling. It fits in between oil & water.

 

I have used Evans in my 914 since fitting it in a Jodel in 2006. I have also changed my Rotax powered  CT to Evans. Down side is higher engine temps on take off & climb. But the advantages are that when cooling is really essential at 110degrees plus . Evans will continue whilst water looses all effective cooling as it start to boil. The other advantages  as with oil cooling corrosion is almost eliminated. The system no longer requires a pressurised system. Water requires pressure to increase the boiling temps usually about 12PSI at ground level, for those more academically minded than me I am sure they would be able to quote the pressure at 10,000 ft. My guess is that the figure would be quite scary. John

 

 

[facthunter]

ALL true..  Especially important if magnesium is used .Glycol also reduces the rate of heat extraction but raises the boiling point. I recall in the tropics a lot of the earlier two strokes ran just pure water or  bigger radiator(s). Glycol leaks easily and can cause corrosion.  There's a minimum recommended % to use in the water mix IF you buy it concentrated.. Some of todays coolants are tested with  a strip. (like litmus paper).   Generally don't mix them . It's not recommended and there's so many different types  it's hard to know what's going on. Record the type in your engine log book. Nev

 

 

[Guest deanfi]

I found the article informative which is why I posted the link , hopefully some others may get something out of it

 

I found it  interesting to read about fully synthetic oil and why its not used .

 

I got interested in the oil issue after reading about  vernatherm and there use on Hurricanes which had to scramble up to meet the attacking bombers and the oil was not up to temp ect.

 

some quotes from J Mac McClellan on the oil/engine  are also interesting and informative ,

 

Because the airplane engine functions over such a large range of temperatures, the tolerances must be very loose compared to the car engine to allow for expansion. Those loose tolerances, and high pressures in the cylinders, actually shear, or cut up, the molecules in the oil. Also, the tolerances of the aircraft engine allow combustion byproducts such as carbon to get past the piston rings and into the oil, which eventually contaminates it and reduces its lubrication properties.

 

Oil is also an essential part of the cooling process in an airplane engine. The cooling air flows over the cylinder heads and barrels and does a good job of carrying away heat in those areas. But air can't reach the heart of the engine, where heat forms at bearings, on lifters and in pistons, so it's the function of oil to carry that heat to an external oil cooler, where the heat is transferred to the atmosphere.

 

whole article is here

 

https://www.flyingmag.com/safety/maintenance/piston-engine-essentials/

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[onetrack]

Oil definitely does play a big part in engine cooling, and this is a well-known fact. I agree, the comparison between vintage tractors and aircraft engines wasn't a good comparison, but I was simply pointing out that oil as a coolant is quite a viable idea, as evidenced by the current model Deutz diesel stationary engines, that use lube oil as a coolant.

 

There's also the oil cooling advantage of no cavitation, as compared to utilising water as a coolant, where cavitation is common.

 

https://www.deutz.com.au/2011_engine_series_deutz/

 

 

[facthunter]

Oil can froth .  Water can form steam pockets As far as I know both can cavitate. Perhaps the word cavitate is used incorrectly?

 

      Please lookup the DIFFERENCE between a clearance and a tolerance. IF one doesn't know that he/she shouldn't be talking about anything mechanical. Oil CAN cool but a few drops splashed now and again won't do much. You need a specific fairly high FLOW to get a reliable  and quantifiable effect. Certain plain ( higher) frictional co efficient bearings Copper -lead, Alutin) NEED extra clearance to allow more oil to cool the bearing. That's WHY the extra clearance. Oil has a maximum sheer velocity after which it won't work reliably as a lubricant The parts have to be in relative motion  to provide an oil film also. At rest there's no film and the parts may be in contact so there's an initial resistance to movement DRY starts are not good . An engine should be pre pressurised ideally and certainly not loaded or revved until oil has circulated to all critical parts.

 

   An alloy piston running in a steel or iron cylinder, when cold will have excess clearance but when running at full power and stabilised temps will have minimum clearance  when it's new. The  stipulated (Manufacturers) wear limits in aero engines are not that large as they have to make rated power till the day they are removed and be reliable also. You don't "wear them out" in the normal sense.  Bit like a race engine in that respect. Nev

 

 

[skippydiesel]

I found the article informative - do wish the Yanks would adopt the metric system of measurement.

 

No mention of pre lubricating the engine - I was taught to hand turn the engine (LyCons)  befor the first flight/start of the day , to check for consistent compression "feel", clear any oil reside in the combustion chamber and to pump a small amount of oil through the system. I still do this with my "burpy" Rotax 912  with the additional check on engine oil quantity - if nothing else it gives me that warm glow of satisfaction that I have done all that I can to prepare the engine for first ignition.

 

 

[Guest deanfi]

regarding oil and cooling, there a so many articles stating oil is a coolant ,

 

Oil also serves as a vital coolant for engine components that can’t be air-cooled. Pistons, for example, are exposed to just as much heat of combustion as cylinders, but they don’t have cooling fi ns or expo-sure to airfl ow. The only thing that keeps them from melting is the large quantity of oil that is splashed and squirted onto the bottom of the pistons to carry away the heat.

 

https://www.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2011-01_all-about-oil.pdf

 

from Lycoming

 

the flow of oil through the engine is completely pre-determined by the designed engine-running clearances and by the passages which are drilled in the crankcase and accessory housing during engine manufacture. This flow of oil serves three purposes. First, it lubricates, but cooling the engine by carrying away the heat generated by combustion is a second purpose, which is often just as important

 

https://www.lycoming.com/content/understanding-oil-flow

 

 approximately 30 percent of a radial piston engine’s cooling occurred in its oil cooler which is interesting ,

 

https://www.cycleworld.com/is-air-cooling-better-than-liquid-cooling/

 

 

 

 

 

 

 

 

 

[facthunter]

 Some of those statement are INCORRECT .The top of the piston's area is much less than the head which also has exhaust ports to deal with.  and heat also gets to the cylinder as the piston moves down. ALL oil Companies list what numerous functions their oil does but the main one is to keep rubbing parts from destroying themselves  by maintaining a thin film of oil separating the parts., Most of the heat getting out of the piston is by way of the cylinder walls.  If you look at most radial  engine oil cooler s they are quite small compared with the area  and amount of airflow over and around the rest of the engine. They are also designed to have a progressive area of oil flow as they have a tendency to get oil thickening in the cooler parts of the honeycomb matrix so at any time except when they would be very hot  The oil cooler is only working in a small % of the core and pressure loss is reduced across it.as the hot oil flows better.. You might be able to look up OIL COOLER CORING and there may be something on it there. I have lot's of time operating these engines and these facts are from my training and experience.  Nev

 

 

[skippydiesel]

I am sure BMW promoted their legendary boxer engine as being "oil cooled" - yes I know the head have cooling fins and this may have just been a marketing ploy.

 

 

[facthunter]

They were actually quite reliant on a large oil flow and designed to have one as the 4 valve heads were under covers and 4 valve heads do have a "cooling between the exhaust ports" problem. Where you have cam chain runs and covers,  you can't get a direct heat flow to the fins so the fins are useless in those areas, and are just for LOOKS. A lot of modern bike engines rely on oil  for heat transfer as they are inadequately finned but do run very hot and are somewhat notorious for it and require synthetic oils almost universally for that reason.

 

  In the early days( 20"s). a fellow called Bradshaw made an oil cooled engine that had only the head aircooled which was almost instantly nicknamed the Bradshaw Oil Boiler and wasn't very successful. Note He didn't even attempt to cool the head  by anything other than air but it was very OPEN as all the designs of the period were...

 

     Heat transfer is  a direct function of temperature difference. ALL other things being equal. .  If there.s NO difference there's no heat transfer.  It flows from hotter to less hot  An engine with head temps at 230 C (the usual upper limit) has a largish temp difference with an ambient of say 26C than a liquid cooled engine with an average radiator temp of less than110 degrees max  to the same ambient.  The aircooled motor has less % difference in heat transfer rate as the comparison is 230/26 and 110/26  (difference 204 compared to 74 )  Aircooled motors work better in temperature extremes than liquid cooled motors. Lots of war tanks used in the desert were powered by radial air cooled engines .Nev