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Thread: 1/2 A Fuel


  1. #51
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    RE: 1/2 A Fuel


    ORIGINAL: combatpigg

    I think 2 stroke model glow engines are roughly 2/3rds as fuel efficient as the same size 4 stroke..?.
    Some highly tuned engines can exceed the 100% volumetric efficiency mark. I wouldn't be surprised to hear that piped 2 strokes are right at the top.
    Your mathematical breakdown was an excellent read, thanks for taking the time to post that here...!
    It was fun to dig in and work it out, and satisfying to calculate fuel consumption of a Babe Bee and get close to reality with a bunch of assumptions and not too much work. I left out some details in between numbers, but all the density and stoichiometry figures are readily available on the internet. I'll go one step further, maybe this evening, and generate a table of fuel blends and graph total combustibles intake per stroke for a range of fuel blends. The plan is to keep a consistent volumetric (not mass) ratio of methanol to nitromethane of 3:1 and start at zero oil up to 50%. This sounds like a lot of work but with Excel all it takes is getting the initial math right then it does the slug work. I'll plot oil content on the x-axis and total mass of air/fuel mixture (sans oil) on the y-axis, and post it here. That will paint what I hope is an interesting picture of theoretical power loss versus oil content. It may put some to sleep but I find it interesting.

    There's a typo in my post: "0.8cc x 16,000rpm x 0.9 = 10,880cc/minute of mixture"

    It says 0.9 but I actually used 0.85 for 85% VE. Should read "0.8cc x 16,000rpm x 0.85 = 10,880cc/minute of mixture"

    Now I know nobody is reading that closely..
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  2. #52
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    RE: 1/2 A Fuel

    MJD, some of the oil does "burn"...even in an engine that is set to run correctly...but not to a large degree.
    Watch a .049 run at night with open exhaust..it looks like an incinerator in there.
    So, I don't have any idea how much credit oil should be given for BTU value in these tiny engines..but there is a tiny amount. The oil % might actually help modify the pyrotechnical aspects of "the burn" that takes place at just the proper moment in time 400 times per second.
    A good test would be to glue a temp sensor to the bottom of the crankcase and run the engine wide open with various oil contents. You could even skip the nitro, to remove the hassle of trying to maintain it's correct ratio. Just run on straight alky and oil. I would perform the test starting at 25% oil and work down from there towards 8% using a standard size prop for the engine. The engine should be plain bearing, since we are talking about typical 1/2A engine fuel.
    WHO GUNNA FEED MAW KEEEIDS..???

  3. #53
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    RE: 1/2 A Fuel

    I'm sure a bit of it might burn, but for the sake of the theoretical exercise all I can do is assume it does not. I'm not sure I'm about to do the bench stand testing.. although it would be interesting at some point. If nothing else I'd do 3-4 quick tests, thin on oil, normal, high, and stupid high, maybe 10/20/30/40 or 8/16/24/32, something like that. Probably best to start with the high oil in case the low oil tests don't go so well..

    Yeah, a Cox at night looks cool, been a while since I did that. Esp the white flame when you spill fuel all over the engine compartment then touch it off with the exhaust.
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

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    RE: 1/2 A Fuel


    ORIGINAL: MJD

    ..............Now I know nobody is reading that closely..
    Hey!! I knew that, but I just wasn't going to say anything.
    the "other" andrew
    I'm not older than dirt, but I can remember when it was patent pending

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    RE: 1/2 A Fuel

    Thought I would post a bit of my rationale for the statement I made with the following from another forum albeit not a mathematical challenge just another data point to consider. I accept your critism of the low oil content, oil related to needle reliability, and realize that even in my own experience using other fuels with differing ratios of constituants (methanol, nitro, castor/synthectic oils) I had good luck getting the little engines to run reliably. Here it is:

    The following is condensed from a series of letter I wrote to Mr. Don Nix the founder and former owner of Power Master fuels. I wanted to consult with someone who is recognized by the knowledgeable engine authorities as an expert so that I could ask about fuel content suitable for hot humid weather.

    I contacted Dub Jett because I value and respect his opinions and he recommended that I contact Mr. Don Nix.

    The following text is a conversation between Mr. Nix and I on May 15th, 2003. As he notes what he provides are opinions and conclusions from his experience.

    In no way is the following meant to endorse one Fuel Manufacturer over another or as any indication of which fuel is best for a specific application.

    I hope you, as I did, find Mr. Nix’s information enlightening.

    Mr. Nix,
    The Radio Control Combat Association has a very specific class limited to .15 engines, running Master Airscrew 8X3 propellers, with a maximum rpm limit of 17,500. On dry days achieving 17,500 rpm is very possible, but on our first high humidity day we dropped 1,000 - 1,200 rpms. We attributed this to the following:

    1. Humidity in air displaces oxygen. Lack of oxygen limits combustion. Result is power down.
    2. Heat/Humidity cause the air density to go down. This causes less combustible air to go into engine. Meaning fuel is overmatched to air, meaning engines run rich in high heat/humidity.
    3. High engine temperatures caused engines to over-expand, increased friction, making them heat up even more and prevented them from reaching peak rpm.

    Hooray for you! About 9 out of 10 will adamantly argue just the opposite...that humid air is MORE dense. Not so, of course. Any full-scale pilot is taught this almost the first week in training.

    Mr. Nix can you address these specific questions please?
    • Why did the engines run so hot? Is it in any way related to the high oil contents we run (22-23%)? We though oil would carry heat away from the engine, but it didn't work this way last weekend.
    • Why did 10% nitro Byron's fuel run 1,000 rpm more than 15% Red Max in three of the engines? Was it likely due to oil content differences or due to less expansion of piston/cylinder due to lower heat produced by lower nitro?
    • What fuel(s) do you suggest for a .15, running a Master Airscrew 8X3, to approach 17,500 rpms in widest range of conditions. We realize this might be three different fuels and that is fine, but what are they.
    • We intend to test a number of off the shelf fuels in the next couple of months in controlled conditions to get a feel for the characteristics of our engines in different conditions.

    Again, Bingo! When I owned PowerMaster (I assume you know I sold it 5 years ago), I fought a sometimes lonely battle on this subject... the theory that if some oil is good, more is better. Not so. When people used to ask me (as about 9 out of 10 did at trade shows), "What's the oil content?" I would smile and answer, "Just exactly the right amount." Some people would laugh and say, "O.K." but others would get angry.

    I would then explain that the answer wasn't a smart-ass or flippant one, but was precisely accurate. We DID put just exactly the right amount of oil in the fuel. All too frequently, I would have people say to me, "I usually add X amount of oil to your fuel." My response would be, "Why?" Their answer: "Because I figured it needed it." My response: "If it had needed it, we would have put it in there in the first place. Please don't screw up my fuel by adding ANYTHING to it."

    Yes, to a point, oil DOES carry off some heat (but not as much as some seem to think), but when the oil content goes past that "just the right amount" point, performance tends to deteriorate, as you have found out. Yes, I think that's WAY too much oil. Of course, as I always quickly add when people ask, "What's the right amount of oil?" - "Depends on what KIND of oil." The different synthetics differ and sometimes rather dramatically, and castor is certainly different from synthetic.

    Too much oil replaces methanol. Methanol burns; oil doesn't (or shouldn't). Too much oil begins to produce drag, in addition to beginning to glaze the piston and sleeve.

    Certain "respected authorities" usually insist on a much higher oil content that I believe is necessary. Again, it depends on the oil used, but if I were you, I'd try no more than 16% total content, either syn/castor blend (my first choice, or straight synthetic. I think you'll find it runs MUCH better, and if there is ANY more wear than with lots of oil (which I seriously doubt), it will be damned slight.

    Example: Back some 12 years ago, I bought an OS .46 from a friend who could document over 800 flights on it. I might add this guy took almost no care of his engines. He was wealthy, and didn't much care how long an engine lasted. The thing was so encrusted with black crap (on the outside), it looked like the grill on your bbq after a big weekend.

    I also bought a brand new, identical OS .46 and sent the two of them to Dave Shadel, 3-time world pylon champ, and the owner of Performance Specialties. I consider Dave to be one of the smartest engine men in the world. I asked him to compare wear on the very used engine against the new one.

    His report? "There is little to no measurable difference in the wear surfaces on the two engines. Whatever you're doing, keep doing it!"

    I knew that engine had had only one fuel run through it for its entire life: PowerMaster 15%. The total oil content...at that time.... was 15% (10% synthetic, 5% castor).

    I can't think of a more powerful example of my point. Except maybe that a very well known modeler with something like 60 years experience and who has written for countless model magazines all over the world (and no, it ain't Clarence Lee) has for many years used a fuel we made to his specs - 12% straight castor. He uses it in everything he owns - big, little, 2-stroke or 4-banger. Actually, he had been brewing his own with just 10% castor, but I was a little nervous with that, so nudged him to agree to 12%.

    Yes, castor can cause varnish and crud, but little to none if (a) good castor is used and (b) you don't use too much (which most do). He's sent me dis-assembled engines with hundreds of flights that show almost no wear and
    virtually no carbon or varnish.

    Why did 10% nitro Byron's fuel run 1,000 rpm more than 15% Red Max in three of the engines? Was it likely due to oil content differences or due to less expansion of piston/cylinder due to lower heat produced by lower nitro?

    Probably both. Again, your thinking is good....better than most. Back in the days when Formula 1 was a big event, most of the guys who won were using our 65% nitro. On cool, dry days, they'd have me make up some 67-68 or even 70%; on warm, humid days, they'd cut back on the nitro.

    What fuel(s) do you suggest for a .15, running a Master Airscrew 8X3, to approach 17,500 rpms in widest range of conditions. We intend to test a number of off the shelf fuels in the next couple of months in controlled conditions to get a feel for the characteristics of our engines in different conditions.

    Lou, I've been out of the loop for 5 years. I am not current on fuels on the market today. About the best I can suggest would be what you've already decided.....to try several and see.

    And I'll again state the caveat: What I've written is strictly my personal experience and opinion, based on my own tests and feedback from customers who used several million gallons of the fuel we made over the years I owned Powermaster.

    Again, thanks for the nice words. It's definitely an ego boost to know I'm remembered kindly....or remembered at all!!!

    Although Mr. Nix is no longer associated with PowerMaster fuels his series of articles on Oil content, nitro, and fuel tips can still be found in the Information section of the PowerMaster web site. Although written over five years ago we think you will find them quite useful. Please go to www.powermasterfuels.com

  6. #56
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    RE: 1/2 A Fuel

    I think I should stress that all of my gobbledy-gook about extra oil not affecting power.. was strictly countering the premise that it was an effect of dilution of the fuel, i.e. increasing oil % robbed the fuel of the power producing ingredients. What I was trying to say was that this factor alone isn't really a consideration because in the end the dilution effect is miniscule, fractions of a percent - open the needle to admit the right amount of combustibles again and you are almost exactly back where you started. I recognize the potential effects of the oil from other standpoints, and I agree too much is too much, but for other reasons.

    The quote by Mr. Nix is actually perfect because it is exactly what I am talking about! This is is why I set out to figure out if it mattered or not. He says "Too much oil replaces methanol. Methanol burns; oil doesn't (or shouldn't). Too much oil begins to produce drag, in addition to beginning to glaze the piston and sleeve."

    Just because somebody wrote something down once it doesn't make it so. I have no issue with comments about additional drag and glazing. But as far as replacing methanol? Do the math, it's not hard. The dilution issue is not significant. But some fuel makers claim it is.

    Here's a question, and CP alluded to this earlier: of the three main ingredients in model engine fuel - methanol, nitromethane, and oil - which costs the most per gallon?



    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  7. #57
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    RE: 1/2 A Fuel

    I finished a chart showing the effect of oil content. Here, the oil percent is shown on the x-axis, and the total mass of methanol/oil/air mixture (oil excluded) is shown as grams per litre of intake mixture. It's how much you burn per cycle that determines power at any given rpm.

    The oil percent goes from 0% to 50% in 5% steps. The ratio of methanol to nitro methane is kept at 3:1, I thought that was the best way to keep the fuel side consistent.

    Never uploaded a pdf before, lessee how this works..

    Attached Files Attached Files
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  8. #58
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    RE: 1/2 A Fuel

    Wasn't it either Leroy Cox or Duke Fox who ran one of his engines continuously on a 55 gallon drum full of fuel so that he could measure the long term effects of oil content..?
    Has anyone else ever come close to doing a test such as this..?
    I would love to see Mr.8%oil buy a Cyclon .061, equip it with a 4.2x4 APC prop, then proceed to see how far into a gallon of 8% oil fuel it runs at 35,000 rpm.
    AMA Combat flyers used to joke that Powermaster left just enough airspace in the top of each gallon jug so that we could have enough room to dump in enough extra castor to bring the fuel up to standards.
    Anyone who thinks that there is a "one size fits all" ideal percentage of oil content regardless of the application is.....lacking a well rounded background of experience with miniature glow engines, especially in any sort of competition...and I'm not talking about events where "appearance points" matter.
    I'll continue to take the advise of guys who spent the bulk of their modeling careers standing in the winner's circles.
    WHO GUNNA FEED MAW KEEEIDS..???

  9. #59
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    RE: 1/2 A Fuel

    I wonder if the type and percentage of oil required varies with the brand/type of engine. I.E.: Cox p/l set vs. Norvel Revlite vs. ABC, ABN, etc. Do some types require more oil than others to remain healthy? I know a BB supported crank can survive on far less oil than a bushing-type, but what about the top end? The reason I ask is that although I've owned many different types of 1/2A engines over the years, my current stash (10) consists entirely of Norvel .074 RC engines. This means I can get by on ONE "1/2A" fuel mixture. As I mentioned before, I use Wildcat 30% Heli fuel with 4 oz. Sig castor added to each gallon. My engines run fine on this mix, but I haven't been running it long enough to be able to say whether or not the durability/longevity is affected one way or the other.
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  10. #60
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    RE: 1/2 A Fuel


    ORIGINAL: rcguy59

    I wonder if the type and percentage of oil required varies with the brand/type of engine. I.E.: Cox p/l set vs. Norvel Revlite vs. ABC, ABN, etc. Do some types require more oil than others to remain healthy? I know a BB supported crank can survive on far less oil than a bushing-type, but what about the top end? The reason I ask is that although I've owned many different types of 1/2A engines over the years, my current stash (10) consists entirely of Norvel .074 RC engines. This means I can get by on ONE ''1/2A'' fuel mixture. As I mentioned before, I use Wildcat 30% Heli fuel with 4 oz. Sig castor added to each gallon. My engines run fine on this mix, but I haven't been running it long enough to be able to say whether or not the durability/longevity is affected one way or the other.
    I tried running Cox TDs on Cruel Power [substandard oil content] fuel and washed my hands of that mess until I met a 1/2A guru who showed me how to keep them happy. He taught me many things and one of them was to top off gallon jugs of cheap, store bought fuel with castor.
    Norvel AMEs...they benefit from 20% or higher oil, but some could use final polishing on the crank to loosen up the fit with the case. If too tight, you end up with a runaway heat condition that extra oil can delay, but not solve completely. The heat will migrate from the lower end up into the top and cause other problems as well.
    Larry Driskill posted a simple crank mod that reduces surface area contact between the crank journal and the case, but it still leaves enough surface area to support the crank. A pretty crafty mod it is.
    WHO GUNNA FEED MAW KEEEIDS..???

  11. #61
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    RE: 1/2 A Fuel

    CP: I've always followed your advice about ensuring a free-spinning crank-to-case fit. So far, all of my Norvels that I've actually run have been acceptable in that regard. Where they seem to vary the most is in the p/l fit when new, though that's hardly news to you.
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  12. #62
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    RE: 1/2 A Fuel

    Yes sir, My advice is just passing on what others have taught me. 1/2A engines realing suffer from any parasitic drag from too tight of a parts fit and also from varnish build up. I never had varnish form in the Norvels that was noticeable, but the coxes could practically be brought to a dead stop.
    A simple gun cleaning with Hoppes solvent is all you need to clear that hurdle.
    A chance to brag about the Nelson .40 FAI engine. Henry Nelson and Dave Shadel both say that 20% oil is enough for optimum engine life and performance. both these guys had many years of competition trials and customer feedback to get this figured out.
    We're talking about a piped .40 that spins a 7x7 prop @30,000. I decided to "break in" mine on 25% castor and 75% alky. The result was a 202 mph run on a plane that all the "experts" said was not capable of 200 mph.
    It feels good to gloat about that..it always will..
    My point is..even on the 202 mph run the engine always landed cool to the touch. Now that the engine is officially broken in, I might run it 80/20 now..?
    WHO GUNNA FEED MAW KEEEIDS..???

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    RE: 1/2 A Fuel

    ORIGINAL: glowplugboy Give our Rocket Power 24 1/2 A Fuel a try.... 24% nitro, 17% Klotz Benol racing castor... our best selling fuel. You can look for us on ''the Bay'' or order direct from www.gcbmrc.com. Sorry, we no longer take credit cards as the current website shows, new website will be up in a week or so... Thanks, Mike
    Thanks, Mike, I'll keep you guys in mind. No credit cards means you take PayPal?
    George Hostler
    Clovis MADS AMA Club, Vintage R/C Society (VRCS)
    And we know love by this, that He laid down His life for us, and we ought to lay down our lives for the brethren. 1 John 3:16

  14. #64
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    RE: 1/2 A Fuel




    ORIGINAL: rcguy59

    I wonder if the type and percentage of oil required varies with the brand/type of engine. I.E.: Cox p/l set vs. Norvel Revlite vs. ABC, ABN, etc. Do some types require more oil than others to remain healthy? I know a BB supported crank can survive on far less oil than a bushing-type, but what about the top end? The reason I ask is that although I've owned many different types of 1/2A engines over the years, my current stash (10) consists entirely of Norvel .074 RC engines. This means I can get by on ONE ''1/2A'' fuel mixture. As I mentioned before, I use Wildcat 30% Heli fuel with 4 oz. Sig castor added to each gallon. My engines run fine on this mix, but I haven't been running it long enough to be able to say whether or not the durability/longevity is affected one way or the other.
    Only The Lord knows what the best all around solution is until you have seen repeated failure.
    In the general field of mechanical engineering, there must be a specialized area of study called Engine Dynamics, or something like that. This is where the book has already been written about how various metals, surface treatments, shafts loads and shaft speeds interact with various lubricants at different temperatures. Back in the day 100,000 miles on a car was considered pretty darn good and today 250,000+ is considered pretty standard....even on conventional motor oil.
    These improvements came about through lots of destructive testing. Millions of dollars worth of testing over the decades I imagine.
    This is the bottom line and it is the 1st thing that I would ask any model engine fuel dealer who claims that he knows more about what our engines need than the guys who designed and manufactured these engines in the first place.
    The fuel dealers will see how low they can go with oil content to maximize their profits and still be able to keep the public satisfied with their products. I would like to hear from any fuel dealers who also just happened to run Cox engines for sport and in competition for 20+ years to hear what they have to say works best over the long haul.
    I could possibly take a well broke in TD.049 and run it for a short while on low oil content fuel without seeing any problems, but experience has already taught me that there is no point in re-learning what I've already been taught through the School of Hard Knocks.
    WHO GUNNA FEED MAW KEEEIDS..???

  15. #65
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    RE: 1/2 A Fuel

    combatpigg: Only The Lord knows what the best all around solution is until you have seen repeated failure.
    In the general field of mechanical engineering, there must be a specialized area of study called Engine Dynamics, or something like that.
    I'm sure they have a special name for the field, probably more akin to machine engineering. We had a dynamics class in my mechanical engineering studies at the University of Hawaii. We got into the strength of materials, calculating stresses in items such as piston rods given the rotational velocities, etc. The engine is nothing more than another piece of rotating machinery, maintained by internal combustion.

    I never really used it though, first job was working in the structural test laboratory at McDonnell Douglas, doing computer programming and systems administration on minicomputer computer based load servo control and data acquisition systems. We took airframes and airframe components, cyclic fatigued and also did ultimate break tests. Engine tests were done by the engine manufacturer, GE, etc. I watched the C-17 durability test on wing spars, accelerated cycling up and down with million pound hydraulic actuators. It broke with a loud explosive bang you could hear through several walls in the offices next door to the hangar. Also ran one of the smaller data systems on wind tunnel tests. It was interesting experience for a kid just out of college. (Returned to work for them again in the late 1980's.)

    Anyway, makes for interesting talk around a cup of coffee. Doesn't mean I know squat about model airplane engines and flying.

    This is where the book has already been written about how various metals, surface treatments, shafts loads and shaft speeds interact with various lubricants at different temperatures. Back in the day 100,000 miles on a car was considered pretty darn good and today 250,000+ is considered pretty standard....even on conventional motor oil. These improvements came about through lots of destructive testing. Millions of dollars worth of testing over the decades I imagine.
    IMO, much of the improvements in the cars were mandated by US Environmental Protection Agency (EPA) requiring guaranteed reduced pollutants in exhaust emissions. Thus, the engines and components required better metallurgy more akin to commercial trucks, so they could exceed the 100,000 mile mark.

    I know what you are saying about the legacy engines. I remember doing a top overhaul on my father's 1964 Ford Falcon around 64,000 miles, overhauling a 1967 Datsun PL411 Bluebird sedan at around 70,000 miles, and a 1968 Hino Contessa (Japanese Renault) with about the same. The metals in those engines were softer.

    This is the bottom line and it is the 1st thing that I would ask any model engine fuel dealer who claims that he knows more about what our engines need than the guys who designed and manufactured these engines in the first place. The fuel dealers will see how low they can go with oil content to maximize their profits and still be able to keep the public satisfied with their products. I would like to hear from any fuel dealers who also just happened to run Cox engines for sport and in competition for 20+ years to hear what they have to say works best over the long haul.
    I would consider that [/quote]There is another consideration, modelers tend to be thrift motivated. The field of fuels is very competitive. It is not necessarily true that the dealer with the best product wins sales. Those modelers in competition are a smaller minority. However, news of a bad product will also catch people's attention. Those who have had successful usage at a cheap cost will spread to other fliers. So, it in essence is a 2 way street.

    I could possibly take a well broke in TD.049 and run it for a short while on low oil content fuel without seeing any problems, but experience has already taught me that there is no point in re-learning what I've already been taught through the School of Hard Knocks.
    The school of hard knocks is a thorough learner, and I have appreciated other's experiences, so I don't have to repeat them myself. Appreciate your experienced inputs.
    George Hostler
    Clovis MADS AMA Club, Vintage R/C Society (VRCS)
    And we know love by this, that He laid down His life for us, and we ought to lay down our lives for the brethren. 1 John 3:16

  16. #66
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    RE: 1/2 A Fuel


    ORIGINAL: combatpigg

    Wasn't it either Leroy Cox or Duke Fox who ran one of his engines continuously on a 55 gallon drum full of fuel so that he could measure the long term effects of oil content..?
    Has anyone else ever come close to doing a test such as this..?
    That was Fox, I am pretty sure. One of those sidebar reports in a dusty magazine somewhere in one of the boxes of old mags downstairs.

    I would love to see Mr.8%oil buy a Cyclon .061, equip it with a 4.2x4 APC prop, then proceed to see how far into a gallon of 8% oil fuel it runs at 35,000 rpm.
    Even if it made it to the end I'd like to know how much of its life span remained..

    Anyone who thinks that there is a ''one size fits all'' ideal percentage of oil content regardless of the application is.....lacking a well rounded background of experience with miniature glow engines, especially in any sort of competition...
    Even good old common sense says there is no all-purpose answer.. p/l, conrod, crankpin, wristpin metallurgy, fit, plain bearing vs BB, big end/small end surface area, wrist pin vs ball and socket, bla bla, the list goes on. I'm sure it is at least safe to say that the vast majority of off-the-shelf sport engines of average displacement will run fine and deliver an acceptable life span on 16-18% oil content fuel if needled properly. And that experience tells us that shorting small engines on oil content is a recipe for reduced life span.

    I find myself starting to wonder about the real-world effect of viscous drag from the oil. There is such a small amount ingested per cycle I'm not sure about that one. What I find myself thinking about is the fact that the fuel is a solution, it is atomized into tiny droplets, and expected to burn in the space of milliseconds in the combustion chamber. So now I wonder if larger percentages of oil simply inhibit or retard complete combustion of the methanol and/or nitromethane. Then again opening the needle more might compensate for that.. [&:].. my head is spinning.
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  17. #67

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    RE: 1/2 A Fuel

    ORIGINAL: MJD



    I find myself starting to wonder about the real-world effect of viscous drag from the oil. There is such a small amount ingested per cycle I'm not sure about that one. What I find myself thinking about is the fact that the fuel is a solution, it is atomized into tiny droplets, and expected to burn in the space of milliseconds in the combustion chamber. So now I wonder if larger percentages of oil simply inhibit or retard complete combustion of the methanol and/or nitromethane. Then again opening the needle more might compensate for that.. [&:].. my head is spinning.

    I can add a little bit of real world data here MJD-at our operating level. For my sins (which are many) I have since 1992 organised and run the NZ FF World Cup contests, at a great flying site near the small town of Omarama in NZ's South Island. These events obviously centre round the main FAI classes of F1A, F1B and F1C. Anyone with any familiarity with the F1C class will know it is a 'specified fuel' event-80:20 methanol:castor-and has been thus since about 1965 when the FAI banned the use of nitro in this class. Now about a decade ago (I don't recall the exact year and can't be bothered looking it up in the archives) a minor amendment was made-the fuel remains 80:20, but the lubricant no longer has to be castor. Now it was either the 2002 or 2004 events (we run two contests back to back) that were affected by this rule change-which had just come in, and not knowing what the degree of change might be among the competitors, I took the precaution of laying in both castor based and synthetic based 80:20 fuel. These were mixed for us by a local modeller in Christchurch-and the methanol was from the same drum (15 litres of 80:20 castor and 10 litres of the 80:20 synthetic). Well as it turned out, I nearly ran out of the synthetic mix-everyone wanted it. The reason soon became obvious-it was 500-1000rpm faster than the castor mix. And these figures were obtained both with optical and audio tachometers[the latter allowing measurement of rpm in the air]
    Now the only variable was the oil, and the increase in revs (which is quite a % increase in power) can only be attributed to the lower viscosity synthetic oil. The effect was even more surprising because Omarama is 1600ft above sea level (the 500m contour line on the topographical maps meanders right through the middle of the flying site) and F1C engines are notoriously finicky about fuel, head clearance and settings. [the standard advice we usually give to new competitors at Omarama is: 'take one head shim out, and change your HD Nelson plug for a standard one.......]

    We are talking about very highly developed 2.5cc racing engines in this event, turning around 31-32,000rpm here-whether the effect would be repeated with 1/2A sized engines is not clear-and of course if you had nitro in the fuel you'd introduce a second variable, but the experiment would not be hard to do.

    IIRC the synthetic lube in this particular example was Coolpower-the synthetic lube fuel was pale blue in colour.

    ChrisM
    'ffkiwi'

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    RE: 1/2 A Fuel

    No doubt that viscosity has some effect on top rpm and it might not be real noticeable unless you were competing shoulder to shoulder with other guys using similar equipment.
    In competition a lot of guys place all out performance above the engine's long term longevity....especially in the hands of guys who are setting the needle right on the bubble.
    WHO GUNNA FEED MAW KEEEIDS..???

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    RE: 1/2 A Fuel

    ORIGINAL: GallopingGhostler

    We had a dynamics class in my mechanical engineering studies at the University of Hawaii. We got into the strength of materials, calculating stresses in items such as piston rods given the rotational velocities, etc.

    I never really used it though, first job was working in the structural test laboratory at McDonnell Douglas, doing computer programming and systems administration on minicomputer computer based load servo control and data acquisition systems. We took airframes and airframe components, cyclic fatigued and also did ultimate break tests. Engine tests were done by the engine manufacturer, GE, etc. I watched the C-17 durability test on wing spars, accelerated cycling up and down with million pound hydraulic actuators. It broke with a loud explosive bang you could hear through several walls in the offices next door to the hangar. Also ran one of the smaller data systems on wind tunnel tests. It was interesting experience for a kid just out of college. (Returned to work for them again in the late 1980's.)


    IMO, much of the improvements in the cars were mandated by US Environmental Protection Agency (EPA) requiring guaranteed reduced pollutants in exhaust emissions. Thus, the engines and components required better metallurgy more akin to commercial trucks, so they could exceed the 100,000 mile mark.
    Japanese cars and the Mercedes seemed to have already raised the bar during this time, also. Detroit tossed in hardened valve seats and tougher valves to withstand unleaded fuel and higher temps ...but as fas as I know [I'm just a hotrodder] there is no improvement in quality of any of the other moving parts. In fact, some of the earlier forged cranks and rods are more desirable with the engine guys.
    Improving carburetor efficiency and later switching to fuel injection eliminated so much raw fuel washing past the piston rings and diluting the oil in the crankcase. Raising the normal operating temp was also a big step forward after some years where it was a step backwards.

    That is fascinating work you were involved with...! What a great career field that is.
    WHO GUNNA FEED MAW KEEEIDS..???

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    RE: 1/2 A Fuel

    MJD, yep...it had to be Fox and it was typical of the kind of advertising that he did. He loved to get his customers involved in his thought process and he liked to educate his customers.
    I believe oil content effects timing and also the length of the burn. You want a steady push against the piston instead of a sharp hammer blow when the mixture fires.
    This is load dependent engine behaviour that I'm talking about. If the engine has no load, then hammer away.
    This, plus timing is how max power is generated from a given quantity of mixture that's available.
    A knock sensor attached from the engine to an Oscope might reveal what Mr. Oil's role is here.
    WHO GUNNA FEED MAW KEEEIDS..???

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    RE: 1/2 A Fuel


    ORIGINAL: ffkiwi

    I can add a little bit of real world data here MJD-at our operating level...

    ChrisM
    'ffkiwi'
    Real interesting stuff, good to know. 500-1000rpm is indeed a significant difference in power output.

    Good banter all around here. Problem with thinking about one question is that is raises a bunch of others and keeps you up at night. I think about all I was able to establish with crunching numbers on oil content is that strictly in terms of the mass of useful intake mixture ingested per cycle, the oil content has a negligible effect, and therefore other factors must dominate if there is a tangible performance difference.

    - combustion properties (timing, incomplete combustion, ....)
    - oil drag
    - cooling via additional oil mass per cycle
    - probably another dozen bullet points to go here

    Sorry I'm late dear, I had to help my uncle Jack off his horse.

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    RE: 1/2 A Fuel

    I suspect the situation is far more complex than we imagine-with multiple interlinked variables. In the F1C example I gave a few posts back, nearly all the engines involved (and there were 8 or 9) would have been direct drive AAC Nelson 15s, with a couple of geared Hummers and Russian geared ones. So it was a fairly clear cut observation on the effect of changing only the oil nature, using multiple examples of the same engine, similar props and similar rpm bands (even with the geared ones, the engine itself is turning in the low thirties).
    What I don't recall, nearly a decade on, is whether there was any effect on starting and handling. I know historically that Omarama can be tough on F1C fliers, in terms of starting-especially on cold autumn mornings (and since our World Cup schedule is always Apr-May, autumn mornings are a given). I've seen people come to grief in the flyoffs through being unable to get their engine started in the 10-min period, [I've seen this at World Championship level too-the UKs John Cuthbert in Argentina at the 2005 FF World Champs-he was not a happy camper as a result!]

    This segues nicely into the earlier post where someone mentioned the OS recommendation that a small amount of nitro-3-5% can vastly improve starting handling and idling, a position with which I heartily agree. Except that the F1C rules don't allow it! No nitro fuel on a cold morning with a high compression engine can take a lot of lighting up. My solution at Omarama-and we never actually did it, was to warm the fuel-keep it in a 500ml plastic bottle in hot water in a wide neck thermos flask. I'm not sure that the opposite approach-cooling it-on hot days-would show any useful benefit however......................

    ChrisM
    'ffkiwi'

  23. #73
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    RE: 1/2 A Fuel

    Do the rules allow priming with something other than the mandated fuel?
    Sorry I'm late dear, I had to help my uncle Jack off his horse.

  24. #74

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    RE: 1/2 A Fuel


    ORIGINAL: MJD

    Do the rules allow priming with something other than the mandated fuel?

    You raise an interesting point MJD-I don't think there is anything in the rules covering this situation. I suspect if anyone did it, it might result in a protest-and the jury would have to rule. Bear in mind that the use of bladders is nearly universal in this event, and that the engine floods off to stop (assisted by a powerful brake) so priming as we would understand it is not required. The engine is normally primed by briefly releasing the closed fuel line allowing fuel to squirt into the intake [and this only for the first run of the day-after each flight-or even timed ground test run the engine is full of fuel from the flood off process]. The opposite is more usually the case-you see fliers inverting the model to drain fuel out of the engine, leaving it merely sopping 'wet' as opposed to utterly flooded

    In theory you could try priming with a hotter fuel to assist starting..........in practice what you see with F1Cs (because with folding props you HAVE to use a mechanical starter) is the engine turns over splutters a lot and eventually fires-and starts blubberingly rich but when it is very cold won't keep running and often dies. So you repeat the process again and again and eventually it takes, and winds up to peak revs. Of course in a flyoff situation, you only have a 10 minute window to launch-and if the clock is at 8 mins-and your engine decides to go balky on you...................

    ChrisM
    'ffkiwi'

  25. #75

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    RE: 1/2 A Fuel

    Im a RC boater and we Use 65 o 70 % nitro on our motors and we modify them for top performance we also use castor and add extra Klotz KL100 to our fuel. we use in a race about 10 gallons that weekend including testing prior to the race. imagine that LOL
    Feibao Velox-Wren70*Carf Kangaroo-Jetcat P-70*CMP BAE Hawk-Jetcat P-20SE * IMPBA NATIONAL CHAMPION


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