yallaair

Hi!
I have done some performance test of various fuels. It seems like that I get more power out of the engine with lower oil percentage.

Example: There is only a marginal difference between WildCat CY30/23 with and a local brand 15/15 synth. But with Wildcat Helimix 15/18, there is a noticeable drop in power.

To get more power from my O.S AX 120, MVVS 91 and ASP 52, how low oil percentage can I use before getting into problems? Car fuels have as low as 9% oil, why can't I use this fuel on airplane glow engines?

rcdude7

My Feedback: (264)

You can, just don't expect a normal service life out of your engine.

The only engines I'm aware of that do well on 10% oil are the giant supertigres. 2000/2500/3000/3250/4500

liquid_TR

Primarily because of plain bushed connecting rods. Where theres no bearing, there is more friction and more need for higher lubrication.

2) there is no oil sump and oil pump in glow engines. The amount of oil in the fuel mix dictates the total amount of lubrication that has to reach all internal part of the engine.

3) methanol is much more dry burning liquid than gasoline - which has its own lubricating properties.

4) the extra - expelled oil works like a liquid heat-sink for the engine. One way or the other, when its expelled it carries heat out of the engine.

asmund

If you load down a car engine, say the HPI 4.6 to about 10000 rpm when running wide open it would not last very long with the same 9% oil fuel as it normally runs in the Savage. In cars the engines are not lugged down like in planes so they spin more freely, thats why they can reach 40 000 rpm`s. I believe there`s alot more forces trying to push the piston sideways into the sleeve in a areo engine running at 11000 WOT than there`s in a car engine running at 35000 rpm WOT, so the aero engine needs more oil to withstand these forces. Also more lugging down means more heat which needs more oil to help cooling and lubricating

jaka

Hi!
Yallair. As you live close to where I live (Sverige) why not use the oils most of the fliers over her use? What I'm talking about is all syntetic oils. It's very common to use 10-15% oil and this without any problems.

I have been into racing (Pylon) and still are and in pylon racing it's practice to use 20% Castor. But 25 years ago a new oil from Nynäs petrolium company here in Sweden came into market (Synex) and this oil was supposed to be used in very low percentages. 5% was the norm then and I personaly tried it on several engines and it worked just fine. One very well known R/C flier over here even used 3%oil in his Rossi .60 engine flown in a military drone project. But I was still sceptical as I had learned (from racing) that there wasn't any oil that could compare to Castor oil when it came to dealing with heat , so I did not do the switch then. I kept running all my engines on 20% Castor oil.

Then approximately 10-15years ago many fliers started to use the then new all syntetic oils from Germany (Aerosynth and Aerosave) and these oils were very fast spreading over Europe. Even I, a reluctant pylon racing advocate tried them and low and behold they worked just fine. 10-15% was the norm to use . As I was a little reluctant I tried 15% and it worked very well.From that day even I did the switch. I still run 20% Castor based fuel but only when I compete due to the rules in our standard Q-500 racing class that doesn't permit syntetic oils.

In Sweden we also run an American a pylon racing class, Q-500 (Super Q-500 in Sweden) and here we run MB, Nelson and Jett .40 racing engines using just 17% all syntetic oil.
Soo...Of course you can use as low oil percentages as 9% all syntetic oil...many fliers over here do just that. But as I said, being a little reluctant I prefere 15% oil myself (I use Motul "Micro" ).

I don't think there any power gain though. But the engines throttle action is a little crispier and the engines don't get any black carbon deposits inside which they always get when running only Castor oil.

asmund

Here`s a thought: a rc-car engine put out its power through a gearbox and two to three differentials, all of which reduces the gear ratio and taking the strain away from the engine making it easier for the engine to rev up and it becomes less stress on the con rod and bushings. Make a car with the engine driving it in the 1:1 ratio as a aero engine and see how long it lasts with low oil content fuel.
When pushing a rc-car too hard the gearbox usually blows long before the engine, there`s no such escape in a plane

jaka

Hi!
Asmund, there is no problem running a car engine in airplane on just 9% oil!
But...remember...a car engine is not perhaps thought to live that long. It's supposed working life is rather short as it is due to the dirt and grime it inhales (despite the air filter used)

asmund

Yes I know. Normal life for a good car engine is somewhere around 6-12 gallons before power drops, but I don`t think it will live that long in a plane with a propeller on it that will only allow it to rev at say 14000 rpm instead of 35000 at WOT, due to more strain and heat. It would take a VERY tiny toothpick of a propeller to allow a car engine to rev to its intended 35-40 000 rpm

liquid_TR

High performance two stroke glow engines used in 1/10 1/8 rc cars are not covered with any warranty. They are always to be used under load, and under no circumstances they shouldnt free wheel.

If the gear box fails and engine revs up without load, the engine is history in that split second 9 out of 10 times. Ive seen many engines blow up - conrod breaks, piston breaks, sleeve gets ruined, crank pin usually doesnt survive even the head bolts get broken.

This is probably true to any engine, any size. They are designed to run under load. Where there is load there is friction. Where there is friction there is heat production. Where theres heat, a proper lubricant is needed for a mechanical system. Not enough lube? Something is gona get worn out - fast.

Lou Crane

To all, best wishes for 2008!

Recent years have seen the engine producing industries develop new clearance standards, materials, and other refinements that work well with very little oil% in fuels. Various internal combustion engine powered gardening tools (lawnmowers, weed-whackers, etc.) are built this way.

Part of the reason is environmental - less oil means less pollution, according to them. Another part of the story is that synthetic oils, for gasoline fuels, have improved a lot. Their abilities are known, and manufacturers can design from that.

For our traditional, methanol fueled engines, many of the new synthetics don't work as well, if at all. An article in the (USA) AMA's monthly magazine I just received has a study of some of these developments in oils. The author didn't bother to emphasize he was talking about gasoline fueled, large (about 200cc and larger) engines as used in Giant Scale and Giant RC Aerobatics, here in the USA, at least.

Even within our methanol-based state-of-the-art engines you will find several which the makers advise run best on ALL synthetic oil blended fuels. I fly CL aerobatics, and a few of the engines designed specifically for that fit this category. Tolerances and operating temperatures are very carefully established, and ANY trace of the 'varnishing' castor oil can produce is unwanted, even harmful to such engines.

MOST CLPA fliers use ABC/AAC type engines, with oil of about 11% each castor and synthetic. CLPA imposes different, probably heavier, loads than racing. Variations in 'drag' load and unload the engine drastically and frequently, at moderate RPMs - a harsh case scenario.

Our older lapped iron pistons in steel cylinders, or iron-ringed pistons in chrome or steel cylinders, still need correct lubrication - which seems to include castor oil in some percentage of the oil fraction.

For racing competition, I can see it would be nice to have one engine last a full season, dependably. But if more successful competing requires a thinner, less drag-producing oil, then winning may mean using up several engines a season. The choice is up to those who intend to win regularly. Challengers must accept the new price of the game, or go elsewhere. I hope it doesn't go that way...

I'll use fuels with oil content in line with the considerations I've mentioned. The ideas work, and are well established. CLPA flights are time limited. (USA 8 minutes, FAI 7 minutes from flier start signal to judges, until the model has rolled to a complete halt.) The oil fraction helps us get very consistent flight times. A more 'economical' fuel - from less oil - can well be less predictable/dependable in that. The penalty for over-running the time limit is very heavy...

jessiej

Interesting post, Lou. I expect that many of the readers here haver never seen a CLPA pattern flown, but for those who have the loads you describe are easy to visualize.

jess

downunder

On the CL aerobatics...I'd read over on SSW that a CL stunt engine has more load on it than a pylon racing engine but I'd always put that down to a bit of one-up-manship. There may be some truth in it though. Certainly the centrifugal and acceleration loads in a pylon engine are way above anything the normal modeller ever sees but in CL stunt the engine is operated right in the max torque area and asked to swing quite large props. Some have even modified an OS 35S to turn a 13" prop!

But because of the way they're run, sometimes it becomes quite evident (in hind-sight...read on ) if there isn't enough oil in the fuel. A case in point is my ST G51 which I began flying it with my usual 20% all castor. It was an absolute dog in that it had an uncontrollable break into a very fast 2 stroke (from the normal 4 stroking in level flight) even just doing a loop. It'd then take about 2 level laps to come back to a 4 stroke. I tried everything imagineable to cure it without success. By chance, one day I ran out of my normal fuel and all I had left was some 25% all castor I'd been using with an iron piston engine so I figured one more flight with that fuel and go home. It totally transformed the engine run to the point where I could do the entire pattern in a continuous 4 stroke.

It took me quite some time to figure out why it transformed it but one day the penny dropped. I always knew that G51 was very economical which meant the flow of oil even with 20% just wasn't enough to stop it from overheating a little when the engine got loaded up more by doing a manoeuvre. This overheating caused the break into a 2 stroke and needed the 2 level laps to cool down. This mild overheating wouldn't be noticed in RC flying or even most other types of CL flying but it brought home to me that every engine needs a bare minimum flow of oil if it's going to last. It's likely that if I were to use maybe 10% nitro (instead of zero) then I could have gotten away with just 20% oil because the much higher fuel consumption would have increased the oil flow.

jessiej

I have wondered what forces are placed on a CL engine due to gyroscopic precession during, say the corners of the hourglass or the abrupt maneuvers of CL Combat.

jess

skiman762

I always wonder how many of the people that post reasons not to run lower oil % do so because they have done it or are just thinking it's bad
In this post the engine has over 80 hours on 12% after running over 300 hours on 20% with not problems at all

http://www.rcuniverse.com/forum/fb.asp?m=6756790

here's another

http://www.rcuniverse.com/forum/fb.asp?m=6765800

downunder

They're not huge because most use either wood or CF props plus the revs are fairly low. However it's there and it does make the nose yaw either in or out slightly. Quite a few use what's called a Rabe rudder (after Al Rabe) which is linked to the elevator so that up elevator (where precession yaws the nose out) moves the rudder slightly inboard and vice versa on down elevator. A reasonable model flying at about 50mph should be able to do a 90 degree (square) turn in about .25 seconds. A good model might do it in under .2 seconds.

NM2K

My Feedback: (14)

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Excisely! <G>


Yamaha realized long ago that the amount of oil needed in their two-stroke motorcycle engines was mandated by the power demand placed upon the engine. Hence, they introduced oil injection for their motorcycles, which worked quite well, most of the time.

If you knew that your engine was going to pull a moderate steady load for a prolonged period of time, you could greatly reduce the oil content and not experience any problems whatsoever. But, if you start varying the throttle, climbing and diving at strenuous rates, etc., you then need more oil than when just maintaining level flight. So, in the end, we calculate how much oil we will need for the most strenuous flight regimens that we will experience, and mix our fuel to that ratio. This means that most of the time, we are running more oil than we really need for a particular low stress flight regime. Without oil injection, this is the best that we can do at the moment.


Ed Cregger

XJet

Well I'm a pragmatist -- which means that in my book, a decent trial and objective observation over-rides theory.

As I mentioned in another thread, our entire club has been running their engines with just 12% lube for over 12 months.

This represents quite an array of engines from OS/TT 46s, SuperTigre 90s, Saitos (82 & 100), a wide range of ASP 2 and 4-strokes, VMAR 46s, etc.

Nobody has experienced *any* mechanical failures and there are no signs of wear. Conrod end journals remain "as new" when an engine that's had 12 months running on this fuel is compared to a "new in box" version of the same engine, pistons are clean with no sign of galling or anything other than the normal ABC wear-patterns. Liners remain pristine, etc.

Now I don't sell oil, I just enjoy getting the most out of the engines I have without risking my sometimes valuable (Saito for example) assets to substandard lubrication.

I don't think I would *ever* dare to run Klotz or Morgan oils at ratios as low as 12% and I was a "20% castor" man for many years (hell most small Fox engines wouldn't even run on anything less) -- but it has to be said that things *have* moved on in the engine and oil world.

Modern engines are made with metals that start off with a lower coefficient of friction for a start (chrome/nickel) and modern synths have vastly superior lubricity and other benefits to bring to the party.

As I've said before -- we used to use 20% castor because that's what engines of the 1950s-1980s needed. The few synth oils that were available were chosen as much for their ability to mix with methanol as their lubricating properties.

But hey folks -- we're in the 21st century now. Most engine manufacturers are using CNC equipment and metalurgies that just weren't around in the early days of model engine design and manufacture.

Using high oil percentages sure won't hurt most motors (but it will hurt some) but I ask you: would you buy a modern high-performance sports car and use straight 30-weight mineral oil in the crankcase?

Probably not eh?

I believe that good engine protection is not just about the quantity of oil being used but the product of oil quantity and *quality* -- you can use more of an inferior oil or less of a superior one.

We run 12% Coopers Plus C and plenty of Europeans seem happy with 10%-14% of their own favorite *advanced* synthetic lube -- yet most folks in the USA seem to run 17%-18% of the somewhat less advanced Klotz or Morgan's oil.

The greater lubricity, film strength and temperature stability of the superior oil means that, even at lower ratios, it's doing a better job of protecting your engine than is the inferior oil at high percentages.

Simply adding more of an inferior oil will *not* necessarily provide more protection or performance than using the optimum amount of a superior oil.

To draw an extreme example of this -- gasoline is a lubricant. It's a very poor lubricant but it *is* a lubricant (it has lubricity and a film strength, although both are very low).

With this in mind, how come a 2-stroke engine run on 100% gasoline (without any other form of oil-injection) will seize up double-quick?

Obviously, if a lube isn't up to the job, even a 100% ratio won't be enough.

So if we assume (and take a few liberties) that a superior oil (such as Cooper's, Aerosynth/Aerosave, Motul, etc) has 50% more lubricity and film strength than a less capable synthetic, you should be able to run it at 2/3 the ratio and achieve the same protection.

Voila -- perhaps that's why you *can* run less (of a superior) oil these days than you could 20 years ago without sacrificing anything.

Of course there's absolutely *nothing* wrong with running 18% of an old-fashioned lube in your fuel, if that's what makes you happy -- just as there's absolutely nothing wrong with running 12% of a superior lube. It's a choice determined by availability and preference I guess.

I remember that my first car used 30-weight mineral oil and this had to be changed every 1,500 miles.

The car I drive now has about 10 times the horsepower and uses Mobil 1 synthetic which gets changed at 10,000 Km (6250 mile) intervals. Despite all this extra power and less frequent oil change, my new car has already done 250,000Kms with no signs of major wear -- my first car was totally worn out (needing a rebore and new rings/bearings) at less than a third that mileage.

So, just as I wouldn't dream of using the same 30-weight mineral oil I used to use 35 years ago (even if I changed it at 1,500 mile intervals), I don't see the point in compromising my nice shiny new model engines by using old-fashioned oils (even if I use 18%-20%). I'll stick to using Cooper's Plus C oil and enjoy the not-insignificant benefits that I get from running a smaller amount of a "better" oil.

But the great thing about a free world (and market) is that we can all make our own choices.

NM2K

My Feedback: (14)

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Your explanation is exactly what I was thinking, Jaka. Reduces lifetime expectation for an engine that is always ran "down in the dirt". Air filters help, but there is only so much that they can do.


Ed Cregger

Lou Crane

Jess, Downunder, and others curious about CLPA loadings... I'm glad to see the interest among those who don't usually think of this mode of flying!

Second, I made an order of magnitude goof in referring to the article in AMA's Model Aviation mag. I meant, of course, 20 or 30cc and up displacement, spark-fired, gasoline burners...

The centrifugal and gyroscopic loads on the engines in CLPA, as Downunder mentioned, appear not crucial - after nearly 60 years! - of long, good service out of such simple engines as the Fox 35 (iron in steel, plain bronze bushed shaft, unbushed rod). The loads I see as key are these:

The model is mixture (and prop, fuel, plug) tuned to a certain "cruising" speed between figures. The engine factors keep that speed (ideally) consistent. Stunter wings can generate enormous lift, and the "cruise" lift is a mere 1.0g, the model's weight. Stunters are almost always very sleek forms, well and prettily finished. There's not a whole lot of skin and form drag; some aver the lines cause more drag than all else, while the wing is unloaded.

An ideal round loop, discounting gravity's 1.0g for discussion, requires about 10 or 11g of wing lift. A 'perfect' square corner, of 5' radius, would require about 50g lift if it could be done. (It can't, but still very tight turns can.) Noted US hobby "aerodynamicist" Wild Bill Netzeband estimates that a rare, but possible, lift load from some stunter wings in a "square" turn may approach 35g.

With Lift comes Induced Drag. IF the wing continues to lift at Wild Bill's 35g, we can follow equations back to find what Lift Coefficient is required. And we can estimate the Induced Drag value that goes with it. Coefficient of Induced Drag is found using the SQUARE of the Lift Coefficient. When we go from 1.0g Lift load, to about 35g, the Induced Drag Coefficient increases by the square of the increase in Lift Coeffcient - around 35^2 or 1,225 times its 1.0g value. Even a few ounces, or dozens of grams multiplied by a number ike that becomes quite a sea anchor.

Where the prop was almost as much freewheeling with the model's velocity (needing only to apply a few ounces to hold airspeed steady) the air suddenly becomes a substantial wall! Far more than gyro or centrifugal loading, I expect the extremely rapid application of load to the prop is most significant. And, yes, we are operating a bit above the engines' torque peak RPMs. Loads drag RPM down to a better torque-yielding bracket in a few thousandths of a second, even allowing for flywheel 'momentum'.

(That loading is also the trigger for the tuned-pipe CLPA mode. The ample power allows acceleration to beyond maximum boost RPM, to where the pipe's resonant boost function goes off phase and actively degrades power. Propellor loads drag RPM back toward max boost, which "comes on" - and off - quicker than the 2cycle/4cycle traditional break.)

With load comes heat, if loads are sustained any length of time. Round figures of about 10g lift requirement (plus and minus the trig aspect of gravity's 1.0g) still mean C(Induced Drag) is about 100 times greater than in 'cruise' flight. With load also comes a wrench of torque from the motor mounts to the fuselage.

A lot is going on... Centrifugal and gyro influences generally do affect the entire model in flight, and as the model is an "almost free-body" (tether restrained) it can diverge slightly in yaw, roll and pitch from these "on-board" variances, as well as execute the commanded paths on the hemispherical surface that is our flight zone. Those minor divergences, are brief and snubbed by other factors that this is not the place to describe. They may act as a cushion, to some extent, to reduce some of the shock of load changes due to violent changes in wing lift required to fly the figures.

At the other end of things, I can see that a light combat model can respond to commanded pitch maneuvering very quickly. That may suggest that the engine can pretty much continue running around its max HP RPM range, AND meet the transient maneuvering loads without great burden. Similarly, Pylon RC racing places a heavy burden to acclerate out from turns - but the RPM band is again in its highest HP output range, and that power, relative to the model's mass and aerodynamic drags, makes for a comparatively lighter load.

Stunt/F2B models often approach 2Kg in weight, and are flown at half the speed of light F2?D? combat models, or a third or quarter of RC Pylon 40 straightline speeds. Both of those events happily call on the maximum of engine power; F2B/Stunt models operate much nearer the torque peak, at which engine's HP is seldom above half of its potential ultimate. Different kinds of loads...

Finally, with few exceptions, engines used in CLPA are detuned, or retuned Sport RC types. There are several, practically hand-made, gems made for CLPA exclusively, but great numbers who enjoy CLPA at lesser levels do not seem to go for the steep prices, parts uncertainties, and expertise expected to be associated with those engines. So, we use living dinosaurs, which still do as well as they ever did, and with mongrelized RC sport engines. They work, reasonably, in the torque peak RPM range, at lower RPM, on larger props, at lower airspeeds, with far less margin of power vs transient loads than in even sport RC flying, much less specialized applications like Pylon RC and F2D. ...and with less sky to use to recapture Kinetic Energy...

Lou Crane

XJet,

An interesting post! Thank you!

Pragmatically speaking, I am a bit reluctant to ditch ALL of recent technology, perticularly those aspects which still work well. If I had a 1950's sports car that required 30 single weight oil, I wouldn't arbitrarily decide to abandon it for the latest 0.5W90 grade with half the alphabet in Service Standards strung after its name, and more detergents than an industrial laundry, more other additives than USA white bread... Without STRONG reason; stronger than just that the trick oil is newer, so therefore must be "better."

However, I have no objection to anyone else making such a jump, if they wish to. I hope we're all agreed that we engage in our hobbies not from external coercion, but because we choose to do so.

As I have confessed to flying control-line, and specifically CLPA, I'd like to inject a thought from that. Nostalgia and Old Time events are very popular in my favorite mode of flying. The aroma of hot castor oil is part of the multi-sensory nostalgia package, and we still have engines that prosper, seemingly without end, on ample castor in the fuel blend. Better still is the aroma of hot petroleum oils, as strewn by old spark ignited engines from the 1940's... Part of the ambience... part of what I and quite a few others enjoy... The rumble and bark of the old engines, even when "muffled' to the satisfaction of neighbors, still harks back to other joyful times.

Enjoy whatever type of flying you do, and please don't expect me to demean what you like.

Jezmo

Lou, that was a very good post. I wouldn't even dream of trying to add anything.

To give a little idea of why I liked the post, I started flying C/L when I was about 7 and the smell of good ole castor glow fuel takes me back in time. (I am 52 now) Also, I went to work for my uncle when I was 9 at his lawn mower shop. We were factory distributors of Lawn Boy power equipment and since they were two stroke, the smell of a small gasoline powered two stroke in a model takes me back in time as well.

XJet

Ah, the smell of castor!

I'm quite surprised that none of those who make fuel scents have bothered coming up with a "castor" scent that can be added to synthetic to give that smell. It'd probably sell better than those fruity scents.

proptop

My Feedback: (8)

That's a great idea [8D]
You could also use it as a (hobby ) room "air freshener"

yallaair

Thanks for all the input folks!
jaka: So, If I understand you correctly, I can buy fuel with 12% oil and adjust the engines to a normal slightly rich setting and be happy? The problem is that very few fuel makers offer a "low oil percentage mix". Today I fly with 15% synth and have not had any problems at all. Perhaps 12-15% is a limit where you can expect getting into some high wear issues on some engines....

jaka

Hi!
Well I'm a bit concervative myself when it comes to oil in fuel so I run 15% all synthetic oil in my fuel (mix myself as many fliers over here do).
American fuels are not sold over here (at least not in the Stockholm region). But Klotz oil has been available over here for decades.

It may seem peculiar though that the Americans haven't tried the all synthetic oils that we have over here in Europe. The trend using low percentage all synthetic oils orginated in Germany 20-25 years ago with the then new Aerosynt and Aerosave oils.

Many fliers over here use 10% all synthetic Aerosave and Aerosynth 2 and 3 oil.
My engines are like new inside with no carbon build what so ever and there is no rust, due to the rust inhibitors in the oil.