tsmithh
Posts: 13
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Joined: 2/12/2006
Last Login: 4/21/2013
From: layton,
UT, USA
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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
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All Forums >> RC Airplanes >> "1/2 A" & "1/8 A" airplanes >> RE: 1/2 A Fuel 
RE: 1/2 A Fuel - 
.. my head is spinning.