Model Diesel Engines - Page 19 - RC Groups
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Aug 23, 2009, 09:52 PM
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E-Challenged's Avatar
Davis Diesel and Tower Hobbies sell diesel fuel by the gallon. Davis also sells special 1/2A diesel fuel as well as diesel conversion heads for 1/2A to .60 glow conversions.
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Aug 24, 2009, 05:55 AM
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vintage1's Avatar
Originally Posted by earlwb
Wow, they were serious about lubrication back then. 1/3 castor oil, 1/3 ether and 1/3 kerosine. 33% oil percentage.
Castor oil is not the ideal lubricant. Synthetics are MUCH better.
Aug 24, 2009, 07:16 AM
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earlwb's Avatar
Actually nothing is more ideal than Castor oil.
Synthetics offer absolutely no protection from lean runs, the oil simply burns up providing no lubrication. Then synthetics do nothing to protect against corrosion either. I am always seeing people complaining about the ball bearings going bad on ball bearing equipped engines. But then that is in nitro/methanol glow fuels, maybe with diesels it would be less of a issue. Castor oil doesn't simply evaporate in a lean run, it develops longer chain molecules that still lubricate, although it ultimately leads to varnish. But the engine doesn't sieze up.

Plus the engines don't really have a lot of cooling fins on them to help cool the engine. The oil actually helps to cool the engine and removes heat from the engine as it passes through. If the engine passes a certain point in temperatures the synthetics get burned up instead of helping to cool the engine. Thus the synthetics actually wind up contributing to engine failure by creating more heat.

Most of us are running diesel engines using old technology of lapped pistons in a iron liner or even iron pistons as well. Those types of engine designs were developed before synthetics even became known.

Now for the guys that say, they don't have lean runs. If you are flying control line or a simple two channel RC plane (no throttle). Or even a RC model and you forget and it runs the tank dry. You have to wait for the engine to run out of fuel to make a landing. So you have a rather vicious lean run at the very end when the fuel tank runs out of fuel. Usually the engine starts sucking some air for a few seconds before it actually runs out of fuel too.

But then there are some reasons to run all synthetic oil, maybe in a competition, if you used a modern ball bearing ABC engine, you could get a little more power as the oil would burn yeilding a little bit more power. Which of course could make the difference between winning and losing.

But maybe a compromise is better still, use some mix of synthetic and castor oil. Then you combine the best of both types of oils.


and Model Airplane News (October 2009) has a article about it in their current issue.
Last edited by earlwb; Aug 24, 2009 at 07:31 AM.
Aug 24, 2009, 07:54 AM
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When I mixed my own diesel fuel I used auto engine oil (can't remember the grade) as it was a lot cheaper & more easily available in the right quantity than castor. Also because it's a mineral oil it mixes with the paraffin but would be no good in glow fuel as it doesn't mix with methanol. Castor can only be used in model diesel engines because of the ether content.
Aug 24, 2009, 09:02 AM
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vintage1's Avatar
synthetic 2 stroke oils are designed NOT to burn up. They have very high temperature tolerance. Also, once in the combustion chamber, it doesn't matter if they do. The lubrication is all done in the crankcase little end and the piston cylinder interface. As long as the oil doesn't degrade once it hits the combustion chamber (diesels run cooler than glo, mostly) the oil will do its work on the compression stroke: the rest is fine. Of course if you go down from 30% oil to the sort of 5% or less that is possible with synthetics, then there is more actual fuel in the mix, so you probably can lean out more..and leaned out ebgines can fail even with a load of castor.

I don't think anyone has really investigated what is or is not the best oil to use.
Aug 24, 2009, 09:30 AM
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I looked into oils a couple of yrs back when trying different lubes,and found that most vegitable oils offer better extreme pressure qualities to either mineral or synthetic oils , this is by vurtue of the polerised molecules that cause them to cling like hairs rather than just lay about in a jumbled fashion.
As a result i tried mixes with several diffent vegitable oils with mixed results as other properties of some interfered with combustion.
Olive oil and Caster are stand out lubricants and I now use a mix of the 2 with a greater volume of olive oil as it gives easier starting and better throttling - this maybe due to the fact it mixes with kerrosine without ether and its lower room temp viscosity. further on viscosity olive oil has a higher viscosity than castor at elevated temps and is more temp stable - ie: it has a high combustion temp , prolly why its favoured as a cooking oil.
Aug 24, 2009, 09:57 AM
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Gluehand's Avatar
Originally Posted by vintage1
I don't think anyone has really investigated what is or is not the best oil to use.
When reading this, I tend to agree with most of what's said above (however that is possible...), but personally, I choose to stick ( ) to the Castor in my diesels due to its supreme sealing properties, which is essential for "well used" engines.....either Mineral or Synthetic oils could beat the Castor in that game....

Aug 24, 2009, 02:27 PM
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earlwb's Avatar
The synthetic 2 stroke oils do burn up. which is why they use them in the gasoline engines. it reduces the pollution emissions. But you can't run low oil percentages in our model engines unless you can use needle bearings on the rod small and big ends and ball bearings on the crankshaft. without the needle bearings and ball bearings, you can't get the oil percentages down too low.
The model fuels simply use the same oil they use in weedeaters, chainsaws, blowers etc. of course with the exception of castor oil.

vintage1, they have been analyzing the oils and their lubricating properties for many years. I think you simply missed the studies and articles about it. Reference Model Airplane News Oct 2009 issue for example. Several of the old model airplane great model engine designers and engineers of the modeling world (George Aldridge, Clarence Lee [ ], et cetera) went into detailed studies of different oils and which ones worked better or not.
here is one magazine article as published in model Airplane news around 5/15/2008.
Model Airplane News has been around for ages, and some of their old back issues have some of these studies written up in them.

We have been benefiting from the studies done many years ago by the oil companies. I think for the last 20 years or so, we really haven't had any new kinds of oils come out, everyone has been using the older formulations for many years now. I suspect that the oil companies, for motor oil, have been simply repackaging the oil and claiming new features.

clipclop, interesting info on the olive oil. I like it. Any specifics about which olive oil would be better, extra virgin olive oil, dark color or clearer color, and single source or blended from multiple sources maybe? or would it matter?
Last edited by earlwb; Aug 24, 2009 at 02:42 PM.
Aug 24, 2009, 10:02 PM
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earlwb's Avatar
I thought I would bring the subject back in line again.

Here is a pic of one of my Russian Replica Elfin .09 (1.5cc) diesel engines. I am thinking about putting one on a scratch built Q-Tee 1/2a plane to see how it does. Just two channels, rudder and elevator. Does anyone think a old design .09 diesel is too much power for a Q-Tee? I figure I can lower the compression a little bit and not tune it for max RPMs as needed.

I have one of the Russian Marz 2.5cc engines (15) here too:

I find the two small engines the .09 and .15 interesting in that they both seem to be all exhaust port and no intake ports. It has me wondering how they did it. I surmise the intake ports are just below the edges of the exhaust ports.

I also have a old NIB Aurora K600 RC throttle equipped .36 diesel engine too:

Aug 25, 2009, 12:54 AM
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Warren B's Avatar
Hi Earl,
I was not familiar with Q-Tee, but a quick search filled me in.
36" span x 7" chord, will go like a rocket with an Elfin.
I'd be going for something a little milder (maybe a 1cc like a Frog 100, DC Spitfire, AM10), but as you say tyou can always back off the comp (but my Elfin doesn't slow down that much, still likes to make the "Elfin bark").
Looks like one of the Russian ABC's have you started it? I've heard some are not runners.
Good luck!
Aug 25, 2009, 05:34 AM
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Just something I missed with reference to useing Olive Oil, I dont recomend it in well used engines as the Olive oil will strip out the varnish and carbon deposits which a well used engine may be useing to maintain compression. But in new engines there will be no such deposits. Also due to Olive oils higher combustion temperature the exhaust will be much cleaner with the added benefit of being more pleasant smelling.
I use extra virgin olive oil as the light pressing(first press) used results on lower gum levels in the oil = to first press (degummed castor)
I have run a well used but still in good nick diesel on all Olive Oil lube @ 22% , this resulted in an extremely black exhaust for the first 5-6 minutes as it cleaned out the carbon/varnish deposits after which the exhaust went clear even with the compression maxed. The fuel mix used was 22% olive,20% ether,58% kero, the engine was just as easy to start as a regular old english mix useing castor oil, but yeilded more power with a clean exhaust( the old english mix runs very black when set for max power), no ill effects have been seen from running on all olive oil , but I er on the safe side by running a mix of olive/castor for regular use.
Aug 25, 2009, 07:55 AM
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earlwb's Avatar
Thanks clipclop, good stuff.

warren_b, yeah I was trying to decide if the 09 diesel would be all that much more powerful or not. The COX .049's are hard to beat for their power and power to weight performance. But I did get two of the Elfin Replica engines a while back, with the thoughts that one of them ought to work. But these Russian Elfin replicas look really good, really nice castings and machining on the outside.

I flew many a Q-Tee with different .049 engines. From Cox .049 Black Widows to the Cox .049 Tee Dee's and Cox .049 RC engines. At the time though nothing developed as much power as a small Cox engine. The other .049 size engines were pretty anemic in comparison, plus they usually weighed a lot more too.

I have plans for the Q-Tee, I think I have all the balsa I need and spruce for the struts, I just need to finish cutting out the parts and band sawing out a bunch of wing ribs. The planes go together fast with CA glue. Throw some iron on covering and they are pretty much done. Maybe this weekend.
Last edited by earlwb; Aug 25, 2009 at 04:15 PM.
Aug 25, 2009, 11:47 AM
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JackHiner's Avatar
Here is a photo of a Russian Elfin .15 iron and steel diesel I got from Aerodyne a few years back. Legal for SAM events and some day I will build a model for it for SAM Class A LER event. I have run it some and easy to start and adjust. Jack
Aug 25, 2009, 11:59 AM
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TLyttle's Avatar
Seems to me the old Elfin weighed about 5 times more than the Cox, so balance would be a problem.

My PAW80s seem to pull as hard as any Cox reedie I ever owned, without too much weight penalty. (I'm kinda stuck with diesels, glow fuel is very difficult for me to get; besides, I haven't owned a large-displacement glow engine since 1968!)
Aug 25, 2009, 04:18 PM
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earlwb's Avatar
At the time I was flying the old Q-tee planes we only had things like a old McCoy O49, old Testors 049, et cetera to compare too. I vaguely remember a .06 engine of some sort. and the Cox pretty much out did them all. I did have a Mills .75 replica I had bought, but it was bad right out of the box with a defective connecting rod, so I never got to try it. When I decide to get up the energy I plan on seeing if I can make a new rod for it. I have sort of been waiting more than 30 years to do it though.

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