If i start with a fuel that is 1/2A fuel that is25% nitro 20% castor and added enough castor to bring the oil to 50% total which drops the nitro to around 17%, would this be ok to run in my fox 15, 19, 35?</p>

It doesn't quite work like that.

You would need some methanol in there somewhere. If you have a fuel that is 25% nitro and 20% oil that would leave you with 55% methanol.
You also need to keep in mind that the nitro ratio that is important is between the nitro and methanol. This is what is burned for energy. The oil, no matter what kind, does not burn. It's purpose is to lubricate and to help cool the engine. By adding oil, you don't change the nitro to methanol ratio.

Also most folks would not run 25% nitro in one of these engines. 10% nitro would be plenty. At the same time, 50% oil would be far more than you would need. 22%-25% should be fine.

Robert

You  do not want 50% oil!  Actually adding oil does not lower the nitro content, which seems to violate the laws of physics.  Look at it this way.  Your engine is adjusted to run well on a certain amount of alcohol and nitro finding their way into the cylinder.  The oil is just along for the ride.  If you add more oil, you have to open the needle so you can get the same amount of alcohol and nitro into the cylinder, along with more oil. 

I would suggest you buy some fuel with 10% nitro, whatever kind of oil, then add castor to get the total oil up to 25 % and go fly. 

jayseas,

I don't think ANY glow engine will run with 50% oil.

You can run your .15 and .19 with the fuel as is, but it would last longer with about 22%-25% oil. I like 22%.

The Fox .35 is another story. As I mentioned in the other post, it likes 25%-28% oil.

Unless you are racing, you do not NEED 25% nitro. It will run in the .15 and .19 (never tried that much nitro in the .35) , but you are wasting your money. You could add both castor and methanol to bring the nitro percentage down to your 17% range.

George

You do not need more than 25% oil in your fuel even for the iron/steel technology in the older Fox motors. Most of them will run well on fuel that has some synthetic oil in the mix as long as at least half the oil is castor. Fox Superfuel (which can be ordered from Fox Manufacturing in quart containers) is 5% nitro, and 29% castor. Sig Mfg makes a good all castor fuel with 25% castor. You can run a synthetic mix but one lean run can cause damage in the older style motors. That said even cool power and omega fuels thatare very low in oil contentare okay in aFoxif you add at least 8 oz of castor oil to a quart of their fuel and avoid lean engine runs.There should be a visible cloud of oil coming out the exaust when the engine is running... the smoke trail when flying on a calm night is impressive.Castor by not burning pulls heat from the engine and if you do get a lean run it thickens casing the motor to slow down without being badly damaged. Most synthetics will vaporize at high temps leaving very little to lubricate the motor. Synthetics also remove the glaze that forms on the iron piston in old style engines... that glaze helps protect the moving parts. An old Fox may have great compression and with one lean run on all synthetic fuel loose compression so badly as to be hard to start.
Bob

Actually, I believe a relatively small percentage of synthetic will remove the castor seal just from normal running. The varnish seal can be restored by using all castor fuel.

One of the selling points for all-castor Fox Superfuel was to form a varnish seal on iron/steel engines in order to regain some compression on "over the hill" engines.

In another thread Jayseas referred to the Foxes as old. I'm not sure if he meant years, run-time, or both. Also, this castor varnish seal forms on porous iron but not on modern engines with high-silicon aluminum pistons.

Or at least I think that's the way it works.

George

Jim I think by adding oil to your fuel does lower nitro content.That is why i was asking if i started with 25% all caster oil by adding enough castor oil to bring the nitro content into acceptable levels to run the fox 35.And yes theses engines are all old , 50's 60's 70's era.
So would 10% nitro be fine to run in all my Fox engines 15, 19, 35 with all castor?Problem is nobody around here sells all caster fuels except the all castor 1/2A fuel which is 25%nitro and 20% castor.I see sig sells fuel that is all castor 10% nitro. But it is like $45 a gallon and they don't sell quarts.I have heard and read that any synthetic oil in the fuel will burn away the seal that is created by the castor fuels, taking away compression, which would be no good.Does the fuel need to have methanol?

Here is a site i found. for blending fuel.

<font color="#ffb903" size="2">http://www.nitrorc.com/default2.asp?Introduction=http://www.nitrorc.com/fuelws</font><font size="2"> </font>

Jim is a lot smarter than I am, but;
Larry Foster suggests that one use 25% castor and 3% klotz in his new Fox engines along with 15% nitro. I use this in southern California and it makes all of my old Foxes, K&amp;B's and McCoys sing. They are all old and well run, gummy and all with old castor, except one L&amp;J Fox 35 and one T&amp;L McCoy 40. I thought I might lose some compression on the older jobs with the 3% klotz but it didn't come to pass.

I would try to add enough oil to bring the total oil content to 28% and run them at a nice four cycle and see how they run.

Chris...

Tucson has a large group of CLflyers and Iam fairly sure they could point you to a nearbyshop that carried fuel suitable for the Fox engines. Maybe the best way to connect with them would be through www.stunthanger.com and there are a lot of CLguys there with a ton of experience running Fox motors (along with some that think they belong in a "Fox Toss" contest....
Bob

I sort of feel bad every time I post this because it is not anything like what the experts say.  I am running a Fox stunt 35 I bought back in 1977.  The only things I did to it were to lap the piston and cylinder and put in a Super Tigre NVA.  Back in the day, it had well over 1000 flights on it with (probably) all castor fuel.  I've been flying it for about three years now, well over 200 flights.  I am running Sig Champion 10% nitro, 20% oil-half castor, half synthetic.  During this period, I put one lean run on the engine.  It got hot enough to stop in flight.  No damage was done that I can see.  The engine has excellent compression and gives one flip starts.  I have no intention of changing fuels. 

Jim, can you explain on how you lap the piston and cylinder on the fox 35?Also can you tell me if altitude makes alot of difference in the amount of nitro?I lve at 5000 Ft.

Jim and others were quite correct that adding oil does nothing as far as changing nitro (or methanol) percentages because you tune the needle to get the correct flow of methanol/nitro into the engine.This is all the engine wants to know about. A simple example is a fuel with just methanol and oil. No matter how much oil you add the engine is always tuned to accept a certain flow of the methanol through it. The engine always runs on 100% methanol and the oil just gets carried in with it. Now mix a blend of 50/50 methanol/nitro with no oil. This is the fuel for the engine although it wouldn't run for long . now add any amount of oil and the fuel part of that blend will still be the same 50/50 mix of methanol/nitro. You just have to open the needle more to allow for all that oil.

The last part of that fuels link is incorrect when it comes to calculating percentages by adding oil because it's treating the entire fuel blend as one thing, the way it's normally done. What's generally not recognised is that a fuel blend is just that, a blend of oil and fuel.

Downunder, I still beleive you are incorrect.If you are correct , then there would be only 100 % nitro fuels.they would all be the same nitro content.Explain why a fuel that has 10% nitro , and another that has 15% nitro..If oil doesn't lower the nitro content then what does? Nitro is nitro.I don't beleive there is different octane levels.If there is then that would explain it to me.

<ul>[*]<font face="verdana,arial,helvetica,swiss" size="2">Adding any component to fuel will automatically decrease the percentage of other components already in fuel. If you have 10 ounces of Substance A and 10 ounces of Substance B in a glass, for example, you have a 50/50 mixture. Let's say you then go and add 10 more ounces of Substance B. You've increased you percentage of Substance B, right? Well, yes, but you've also decreased your percentage of Substance A. You still only have 10 ounces of Substance A, but you have a total of 30 ounces of mixture, and only 1/3 of it is now Substance A. You've decreased Substance A's percentage from 50% to 33% and increased Substance B's from 50% to 66%. Sound complicated? Well, not really, that's why we're here to calculate this for you.</font>[/list]
<font face="verdana,arial,helvetica,swiss" size="2">
</font>

Also tunning the needle valveand nitro % is two different things..
Jim</p>

You are right as far as overall content is concerned.

Be aware that no combustive energy is derived from the oil content in a two stroke engine. All oil that goes into a two stroke engine comes out of the exhaust. It is there only for lubrication and the hot oil that is expelled from the exhaust carries with it heat from the combustion which means that the cooling fins have less work to do in keeping the engine cool.

The only combustive energy derived would be from the actual fuel, not the oil.

The lubricative oil does not burn.

Imagine a roll of newspaper rolled up and thrown in a fire. The fire would consume the paper as fuel.
Now take a similar amount of paper and wrap it around some rocks that will not burn. What will happen is that the paper will burn but the rocks will not. The rocks even though added to the fuel do not change the amount of energy that the paper will give to the fire. The rocks will only get hot.

Nitro is not a fuel but an additive that gives the fuel mixture more oxygen an important component to make the burn hotter and therefore gives more energy to the methanol.

Check around and see who burns 100% nitro.

Quote from Wikipedia:
" nitromethane is used as a fuel in racing, particularly drag racing, as well as for rockets and model airplanes and commonly referred to in this context as "nitro" or "top fuel". The oxygen content of nitromethane enables it to burn with much less atmospheric oxygen in comparison to hydrocarbons such as gasoline:

4CH3NO2 + 3O2 → 4CO2 + 6H2O + 2N2
14.6 kg of air is required to burn one kilogram of gasoline, but only 1.7 kg of air for one kilogram of nitromethane. Since an engine’s cylinder can only contain a limited amount of air on each stroke, 8.7 times more nitromethane than gasoline can be burned in one stroke. Nitromethane, however, has a lower energy density"

Robert

Robert, I understand how fuel burns in an engine. I know the oil is only there for lubrication and cooling.And your point is?

Perhaps so however very closely relatedand a change in one will have have a direct effect on each other and germain to the discussion.

You would need to add methanol to the overall mix in order to lower the effective nitro content of the fuel.
Adding oil does not lower the effective nitro content.

Fox engines, as has been pointed out do like all castor and lots of it although some have used oil blends that have some synthetic and have enjoyed success.

Sorry about the long post last, I did not mean to confuse.

Robert

Robert no need to be sorry i appreciate you taking the time .
Take care
JIm

So areyou sayingwhen you purchase fuel that is 10% nirto by volume it will produce the same power no matter what the oil content? Or since the nitro is not 10% of thefuelmix but 10% of the total does this really hold?
If I buy brand X fuel with 10% nitro and 20% oil with the remainder alcoholit is not the same blend of nirto and alcohol asbrand Y fuelwth10% nitro and 25% oil with the remainder alcohol. In the second case there is 5% actual less fuel and the higher oil content fuel should get poorer economy. (Which Ihave seen inGoodyear racing.) Of course all that misses that some synthetic oils do burn atthe temps model engines reach(which is one reason that they do less to cool an engine).
The easiest way around all this for someone wanting to run a Foxor other old style iron piston engineis to buy whatever fuel is available at the hobby shop and add enough castor oil to bring the total oil up to at least 25% of the mix. If it is a fuel where you cannot find the oil content listed anywhere assume it has only 18% and all synthetic oil. In that case I would add 16 oz of castor to a gallon of fuel and be pretty close. If I could I would stay away from fuels that do not already claim to be a castor blend.
I think we have beat this horse to death....
Bo

Your right we don't need anymore discussion on this.
Everyone have great day.
jim

Nitro content is lowered from 15% to 10% by increasing the percent of methanol. Let's say you have two fuels, both with 20% oil. The label for one will say it has 15% nitro so that one has 15% nitro plus 20% oil leaving 65% for the remainder which is the methanol. The label for the other will say it has 10% nitro so it has 10% nitro plus 20% oil leaving 70% methanol. "Nitro" fuel is a bad name for it because it's more properly a methanol fuel. Nitro is just an additive to the base fuel and any engine will run just fine without any nitro in the fuel. I haven't used nitro in over 50 years. Well, once in a racing competition.

I buy gallons of Powermaster 20% Nitro, 18% Oil(2/3 synth &1/3 Castor) I then add Castor to bring it up to approx 23% oil. Makes my old Cox engines sing!(very economical also)

Jim,

Sorry you are backing out on this.

As I see it, several of us are speaking of the same thing in slightly different ways.

If I understand Downunder's point, the flammables in the fuel provide the power. To get the same power, you have to burn the same quantity of methanol (and nitro, if it's part of the blend.) The oil content doesn't affect that, but in a low-oil% fuel, more of the methanol (and nitro) are in the mix drawn in by the engine in each revolution - presuming that all the fuel ingredients are vaporized or atomized to the same degree as they go into the engine. With a higher oil percentage fuel, you need more total fuel to enter to keep the same quantity of the flammables available for burning. Richer needle, in other words, and often more fuel consumed per minute.

And oil absorbs heat from the engine metal and from combustion. Burning is supposed to produce heat, and that heat is our power. By reducing the heat released, in proportion to how much the oil absorbs, and by taking up space that could otherwise have been filled with the combustibles, the oil content damps down the combustion and thus the power production. We live with that, since without oil, our engines would quickly become expensive, funny-looking, welded-solid paperweights...

These ARE definite effects on how a fuel runs. Adding more of any one of the main ingredients, without changing the others in the same proportion, also has effects...

To compare: If a fuel is 20% Nitro and 25% oil, the rest is the methanol - 55%. If it is 20% nitro and 15% oil, methanol makes 65% of the fuel. It is an interesting algebra exercise to find how much oil to add to bring its % up from 15% to 25%, because the oil added increases the total fuel volume.

Example: If you start by adding 10% of the original volume as oil, think of it this way. You started with 100 "%-units" of blend. That means 20 units of nitro, 15 units of oil and 65 units of methanol. Add 10 units of oil. Total volume of the blend is now 110 units. Nitro units don't change. Methanol units don't change. Their percentages do, however.

The 20 units of nitro in 110 total units of volume isn't 20%; it's 18.2%.
The 65 units of methanol in 110 total units of volume isn't 65%; it's 59.1%.
Even the oil % changes: 15 units + 10 units is 25 units in 110 total units of volume, which is not 25%, but 22.7%

Add up the new percentages: they equal 100% of the new total volume. And, you have that extra 10 units more than the original total fuel volume to deal with...

You can doodle out a few more guesstimates of how much oil to add to make 25% of the new total volume in a few more runs with the same procedure, and also figure the effective nitro and methanol % that result...

And, Bob, Hi! There may be a fallacy about the synthetics leaving the engine unprotected/unlubricated if they burn away during combustion... Sure, some part of the synthetic % does burn, but only WHILE it is exposed to the burning methanol and nitro. The power stroke of the piston, in other words. ...When the piston is moving down, uncovering the sleeve where nothing is sliding in it. The next bypass charge sprays the interior of the sleeve with a fresh dose of cool oil for the piston to ride up on during the compression stroke. Part of the reason synthetic blended fuels are popular, may be that many sport RC fliers prefer that their models do not become so oil-coated as we CL fliers are very used to putting up with.

The synthetics are excellent oils, but not for all uses. Similarly, all-castor as the oil% is not ideal for certain aluminum piston ABC/AAC/or ABN engines. Castor's tendency to form a varnish coating on cast iron pistons helps those stay lubricated and sealed; tapered-fit brass or aluminum sleeves have no room for such a coating...

Finally, if all else fails, re-read the engine manufacturer's instructions. Mfr's certainly won't tell you to do something that will make their engines look bad...

If fuel is 15% nitro and 18% oil, how much castor would you add to a gallon to bring it to 20% oil?

2 1/4 oz, I use three and 1 oz of Aerolube in all of my gallons of 18% Powermaster. I does the trick.
Chris...