"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

Mixing Cox Fuel

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Old 11-18-2012, 01:12 AM
  #1
Chikokishi
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Default Mixing Cox Fuel

I was reading though the 1/2A fuel post and i saw mention of using regular gasoline. Is it possible to use regular gasoline, or regular diesel, mixed with a bit of caster oil, in a little cox engine? Im not going for spectacular performance.. its only going onto a foam plane for control line flight. We do not have a hobby shop in this area at all, so stuff like nitro is out of the question. I can probably get kerosene at Walmart, and Castor oil there also.

Thanks!
Chiko
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Old 11-18-2012, 06:32 AM
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Default RE: Mixing Cox Fuel

Chiko,

Glow fuel is normally Methanol (alcohol) nitro methane and a lube of either castor, synthetic, or a combination of the two. An exception is FAI fuel which is 80% methanol and 20% castor.

The methanol causes a catalytic reaction with the platinum alloy in the glow plug to sustain combustion after the battery is disconnected. Gasoline will not do this.

Although additional ingredients have been tried for a specific run, the alcohol/nitro/lube is still the best.

Model "diesel" engines do not use pump diesel, they use kerosene, ether, and castor. The ether can be obtained from "starting fluid".

I'm guessing that the article you read recommended 15%-25% nitro, ~20% lube half castor, half synthetic (or all castor), and the rest methanol for your Cox engine. Forget the experimental stuff for now and enjoy some store-bought fuel.

George
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Old 11-18-2012, 11:14 AM
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Chikokishi
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Default RE: Mixing Cox Fuel

So if i were to get Kerosene, Starting fluid (Grill..? Car...?) and caster oil. This should be a good mix? What would be the ratio?

Chiko
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Old 11-18-2012, 11:39 AM
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Default RE: Mixing Cox Fuel

If you try to convert a Cox .049 to diesel, better stock up on lots of spare parts.
Diesels are really easy to hydraulic lock since the dead air space above the piston is practically nil and the high compression is right at the internal parts breaking point..
I've washed my hands of trying Cox diesels, I've never seen a Cox diesel make it through a gallon of fuel for sure...maybe not even 2 quarts before it either snapped a rod or broke the crank. The so called diesel cranks don't really solve the problem because the engine will snap or bend the rod anyway.
You will be money ahead if you buy a purpose built diesel engine, like PAW, Sharma, MP Jett, etc.
I have mixed 1/3 lamp oil, 1/3 castor oil and 1/3 John Deere starting fluid to fly a PAW brand .15 diesel control line. I don't know if these ratios are optimum or not, I just picked up the recipe from hearsay. Compared with the fuel that I used to get from Erik Clutton [Dr Diesel], it probably wasn't as good but it ran good enough.
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Old 11-18-2012, 12:05 PM
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Default RE: Mixing Cox Fuel

Good inputs, combatpigg, I didn't realize that dieselizing the Cox engines had pitfalls, sound advice to use a manufactured diesel instead of conversion. Also good inputs on improvised alternate fuel that works. Given that a quart of Half-A glow fuel from the likes of SIG and other companies is cheap and lasts nearly a season of flying, I agree. The OP is better off using glow fuel on the Coxes.
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Old 11-18-2012, 12:30 PM
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Default RE: Mixing Cox Fuel

Quote:
ORIGINAL: Chikokishi

So if i were to get Kerosene, Starting fluid (Grill..? Car...?) and caster oil. This should be a good mix? What would be the ratio?

Chiko

And you'll be utterly wasting time and money-UNLESS you also buy a diesel head for it. Cox engines are designed to run on a methanol fuel with an appropriate amount of lubricant (at least 18% minimum), and variable amounts of nitromethane, depending on engine model, intended usage and prop size. By variable nitromethane I mean anything from a practical minimum of about 10%, right up to 65%. That latter % will kill your engine in very short order-but before it does you'll get about as much power as that particular engine could ever produce. Very very few people ever run that much nitro, but a few competitors are prepared to write off an engine per event in the interests of winning. The practical minimum nitro % figure represents a compromise between loss of power, ease of needle setting, load and atmospheric tolerance.
It IS possible to run a Cox on a straight methanol: oil mix but they usually sag when the battery is removed, are tricky to set the needle on, and require quite a lot of warm up to get even an adequate run. A low % of nitro improves starting, makes them easier to set, more tolerant of load variations and the weather-and gives a bit more power.

You can't just run them on any old inflammable liquid you happen to have handy..................

FORGET gasoline, pump diesel, lamp fuel, fried yak butter or any of the other things you might conceivably be able to put into a Cox engine-they don't work! Pure and simple. Hydrocarbons won't mix with castor oil, (unless other compounds are added to the mix), and the glowplug self energising catalytic effect only works with methanol. In the unlikely event you could actually start the engine on some of your proposed mixtures you would find that the battery would have to remain connected to sustain combustion.


The 'diesel' fuel mix GCB mentioned:-kerosene, ether and oil-requires the use of a special cylinder head, which you'd have to buy-you can't just use this fuel in a standard Cox. CP's 1/3-1/3-1/3 mix is a very old formula and has stood the test of time for more than 60 years. It's also generous in the lube department, but works perfectly well-and is often used as a 'running-in' fuel mix for diesels. Most of us use a bit less oil and a bit more kero-but 1/3-1/3-1/3 is safe!

As CP has also pointed out, while you CAN run Coxes with this form of ignition, the operating stresses are much higher and crankshafts in particular are prone to breaking-not to mention rods being bent. Whilst it can be done-you need to know what you're doing, understand fully the idiosyncrasies of diesel operation, and have a good reason for doing it. Simply for the sake of being 'different' is not a very good reason..............and be careful about the economy aspect-which is often overstated! Diesels DO have a lower specific fuel consumption than glow engines-BUT the fuel is more expensive-even if you mix your own-and you had to buy the diesel head in the first place! From an economy point of view, converting a Cox to diesel will not generate any great savings (if any) in operating costs compared with operating that same Cox on low (10-15%) nitro fuels-which for most people's purposes are perfectly adequate.

ChrisM
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Old 11-18-2012, 12:35 PM
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Default RE: Mixing Cox Fuel


Quote:
ORIGINAL: Chikokishi

I was reading though the 1/2A fuel post and i saw mention of using regular gasoline. Is it possible to use regular gasoline, or regular diesel, mixed with a bit of caster oil, in a little cox engine? Im not going for spectacular performance.. its only going onto a foam plane for control line flight. We do not have a hobby shop in this area at all, so stuff like nitro is out of the question. I can probably get kerosene at Walmart, and Castor oil there also.

Thanks!
Chiko
Short answer: no. You need glow fuel with suitable specs for those engines.
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Old 11-18-2012, 12:43 PM
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Default RE: Mixing Cox Fuel


Quote:
ORIGINAL: Chikokishi
So if i were to get Kerosene, Starting fluid (Grill..? Car...?) and caster oil. This should be a good mix? What would be the ratio?

Chiko
I think you missed the point that kerosene is for model DIESEL fuel. For model diesels, automobile/truck starting fluid can be used for its ether content. I believe grill "starting fluid" is Naptha. Model diesel engines do not have a glow plug but get their combustion from compression. Adding Ether to the fuel (~30%-35&) allows it to fire on a lower compression setting which provides less stress to moving parts.

For your GLOW engine I would suggest you mail order some commercial 1/2A glow fuel such as SIG. Many folks live where there are no hobby shops. Just do a search on 1/2A glow fuel to find lots of mail order shops. Buy it in quarts to avoid "HAZMAT" charges. A couple of quarts should last you for many flights.

Again, you need methanol based fuel for the catalytic reaction with the glow plug so it will run when you disconnect the booster battery.

It appears that you have little experience with model engines so be sure to ask questions.

George
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Old 11-18-2012, 04:25 PM
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Default RE: Mixing Cox Fuel


Quote:
ORIGINAL: Chikokishi

I was reading though the 1/2A fuel post and i saw mention of using regular gasoline. Is it possible to use regular gasoline, or regular diesel, mixed with a bit of caster oil, in a little cox engine? Im not going for spectacular performance.. its only going onto a foam plane for control line flight. We do not have a hobby shop in this area at all, so stuff like nitro is out of the question. I can probably get kerosene at Walmart, and Castor oil there also.

Thanks!
Chiko
Just order a quart from Sig. Something that small does not require the haz mat fee and it has a proven record. Sig 25%.

John
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Old 11-18-2012, 06:02 PM
  #10
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Default RE: Mixing Cox Fuel

Thanks for all the replies! I was totally getting confused trying to read forums where everyone says they used all these fuels. I have 4 engines. a really small red cox, the cylinder is about 5/8" from the crankcase to the glow plug. a slightly larger silver one with a 13/16" cylinder, then i have the motor that came with the old cox pt-19, and finally i have a larger motor with an exhaust and such that i havent given much thought to.

Ill do a search for the 1/2a fuel. thanks again!
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Old 11-18-2012, 09:24 PM
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Default RE: Mixing Cox Fuel

Good luck..! I have an old friend who grew up on a rural farm in Idaho and he had to learn to improvise at an early age. He did experiment with gas / oil in model plane engines and was able to keep them running with a battery connected to the glow plug. A glow plug can draw a couple amps or more, so unless the engine ran real strong...there might be a good reason why you don't here about this model engine fuel alternative more often.
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Old 11-20-2012, 06:55 AM
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Default RE: Mixing Cox Fuel

Heh Chiko, you can find 99.9% pure methanol (lacquer thinner or wood alcohol) at hardware / paint suppliers. Castor oil you might find at drugstores although it might not be as pure (degunked) as that from R/C hobby suppliers. The nitro is not absolutely necessary especially if you're not seeking performance. I mix 4 parts methanol with 1 part castor oil. If your engine has good compression and the plug glows bright it will start and run properly.

A small addition of acetone (1% of total fuel volume) available at hardware / paint suppliers could substitute as nitro if you want to improve needle sensitivity. See this article: http://www.rcuniverse.com/forum/m_61...tm.htm#6116311. WARNING: use glass or metal containers when handling acetone because it disolves most plastics.

My best mix is 4 parts methanol, 1 part castor oil, and 1 part R/C car racing fuel (which contains 30% nitro and 12% synthetic oil blend). The resulting fuel mix is 5% nitro and 19% oil blend (predominantly castor).

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