Jeffro

I'm returning to my roots in model aviation by getting back to control line! I purchased a nice used Magician and a Fox 35 which I'll use as my primary stunter. I was running this engine on Wildcat 10% which has always been good to my RC engines. This fuel is 16% total oil with a 80% synthetic / 20% castor blend and I felt it was still getting hot even with a very rich setting. I understand the Fox engines like a little more castor and I've also been told to run 5% nitro. Wildcat fuel is about all I have access to in my area and I'm trying to get an idea of how much castor I need to add to these fuels for the best performance. Anyone have any suggestions? I'm not looking for a competition setup, just a reliable engine setup for lots of Sunday morning stunt flying fun!

Thanks for your suggestions,

Jeff

downunder

I'll bet it ran hot . Those engines need around 29% all castor (preferably) so call it 30% to make things easier if you want to mix the fuel yourself. Fox of course make their own fuel to suit these engines.

da Rock

A gallon is 128 ounces.
I think Fox has recommended Fox Super Fuel for their engines ever since they started selling Super Fuel. And they started making Super Fuel because their engines needed what was in it. What was in it was 5% nitro and 29% castor oil.

If you wish to come close to duplicating that, you'll want a gallon of fuel that contains 37 ounces of castor oil. The fuel you now use has about 20 ounces of oil. Adding 18 ounces of castor oil to a gallon would come close. You'd want to actually add that much oil to a partially used gallon, like down about 18 ounces.

Fox's recommendations aren't for "a little more" than 16% oil, they suggest a LOT more oil. If it's an original Fox, you really do want to run more than 18% oil.

BTW, a "competition setup" for a CL precision aerobatics engine like a Fox actually IS just a reliable engine setup that'd work perfectly for weekend stunt flying fun. Those engines weren't made to be tempermental, ultimate horsepower firebreathers. And they actually die rather quickly if they're used that way. The low nitro recommendation is an excellent one. Nitro costs a lot and didn't do much good for those engines. Castor did do good for them however.

There is a slight wrinkle to the oil deal........... There actually isn't much bad about synthetic oils nowadays. The real deal is that castor has a benefit synthetic doesn't. It provides insurance if you screw up the needle setting and get trapped into a too lean run. Keep that in mind.

Jim Thomerson

Fox stunt 35's are low compression engines and can benefit from a bit of nitro. I run 10% and others run 15%. Of course others run 5% and still others 0%. Do get your oil up as advised.

gcb

Jeff,

In addition to needing 25%-29% castor oil in the fuel, if it has a lot of run time on it and it was run with all castor, you may need to avoid synthetic lube. You may want to check with the previous owner and see what he used.

When iron/steel engines have been run a lot and are nearly worn out, using all-castor lube can restore some compression by creating a castor "varnish" seal. Conversely, if an engine has this seal and you use synthetic lube, the cleaning action of the synthetic will remove this varnish and the extra compression will be lost. If this happens, switching to all-castor will restore the seal. This was one of the selling points of Fox Superfuel. It restored some compression to otherwise worn out engines. This does not work with high-silicon aluminum pistons, only porous iron.

I understand that as little as 3% syntheric in your lube will remove the varnish.

If the Fox is fairly new, some like half castor and half synthetic, but still keep the percentage at or above 25%.

Of course this is only one opinion. There is seldom only one way of doing things.

George

PAINLESS

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Here is a handy calculator for figuring out how much oil to add to a gallon of fuel that already has some oil in it.
http://www.nitrorc.com/default2.asp?...orc.com/fuelws
scroll down and click "add oil only"

Jeffro

Thanks to all who have given me some great suggestions on how to provide the best fuel and oil for this engine! I am always amazed at the generous time fellow modelers give to help another. That is what makes this hobby so enjoyable!

Cheers!

Jeff

stg61abc

Hi jeff, please use minimum 25% all castor in your fuel, this engine needs this percentual.
Atachade a pic from a fox 35 from a friend, slighty modified, great running Fox 35
Cheers

stg61abc

sorry, i attached the wrong pic, this is the correct one, thanks

downunder

Seeing this has been brought back again I was asked once if a Fox 35 would run ok with zero nitro. I've got 2 of them, one is a brand new 40th Anniversary, which I bought in a weak moment because the LHS had them on special, and the other is a clapped out old one. I'd never run a Fox before so I figured I'd see what happened with the old one that leaks like a sieve. With 75/25 all castor (the only fuel I had on hand that was close) it started first flick and did so hot or cold from then on. I was a bit surprised . Tuning was dead easy anywhere from a really rich 4 stroke to almost peaked out.

If nothing else it proved that a low compression engine will run perfectly well on zero nitro because I don't know of any other engine that's as low as a Fox 35.

gcb

OK Cubs.

George

lukesp

Some Cubs new have a lot less compression than a Fox 35. [sm=what_smile.gif]

I have personally run Fox 35's without nitro some years back, I intend to again soon. What downunder said is quite correct, I had no problems with them myself. The correct plug needs to be found though, preferably a hot one. There has been a lot of talk in other forums about zero nitro = critical needle settings, super gutless, blah blah blah. It ain't true. People use what they are used to I guess.

BTW, anyone reading this who uses nitro in their Fox engines and feels that they should then please do so by all means. I don't mean to belittle the idea of using nitro at all. Zero nitro is simply another option, particularly for those who mix their own fuels. I do NOT want to start another nitro war.

Hossfly

Jeff, add about a pint of castor to your Wildcat 16% oil and your Fox shoud run very well if you have not yet scored it too much. OTOH, those old iron pistons do sometimes swell and get really tight and then one has to break it in again. Way back when ??? the old speed boys tried to do that frequently. They used up a few pistons but they got results now and then.
Heck I remember a guy, kind of hard up financially, and kept on trying to fly a profile with a worn-out Testors McCoy 35 ( only good for about 25 flights) and one day that thing went rat-race lean on a flight. We all just knew that was the end for him as the thing was smoking on landing. He must have really cooked/tempered something very well because after that flight, he had an engine with good compression and he was still flying that engine every weekend 2 years later when I was getting into RC. None could believe it!

BTW, one version of Wildcat has 18% oil in all the fuels 10% nitro or more. However I have notice that in the last several years, since "Great Pains" got the distribution rights on Wildcat, the exhaust oil is no longer reddish. Methinks there has been a change.

One other little tidbit for you oil/nitro conscious troops that may still play with 1/2 As: I have several Cox .049s of various types including the TDs. I use to think it was nitro that made them run. NAY-Not so, it is the oil content that makes them a piece of cake. I had some 10% nitro, 20% or maybe 22% castor for ducted fans. Those cox babies loved it and they started and ran very well on it. Now I just add a bunch of CASTOR to regular 10% fuel when some grandkids, etc come to fly 1/2A CL in the back yard.

Here is a Fox .35 in a modified Nobler, mostly cosmetics and a tri-gear, that won some trophies along the way. The very bad picture was an original design of mine that was a very fine stunt machine, but used a customized ST .40, yet I still used Fox Superfuel back then.
It's predecessor was good, it was excellent and the third version was total garbage. On to RC!

jeffie8696

Interesting, I have just obtained a nice new Fox .35 CL from an estate. It was a little gummy when I received it but I believe it was from storage oil rather than fuel cause it was squeaky clean. This engine has a very bright shiny finish that I have not seen on other Fox .35s. The compression seems very high also compared to my new OS engines. I couldn't resist the urge and started it up "briefly" just to hear it run. I used Omega 10% (it was all I had available to me) and a somewhat rich setting just to be safe. WOW[X(] this thing makes my .46 and .25 engines look tame. I realize it was just because it has no muffler but it really intimidated me. I am not in to control line except for 1/2A with my daughter so I plan to sell it soon. Could this engine be a special FIA version with higher compression for non nitro use? This thread has been very helpful and I do not mean to "hijack" it. Thanks.

cutaway

Looks like an ordinary Fox .35. Somewhat newer due to the muffler mounting lugs. Older ones won't have those lugs.

One I got from the 70's has a kinda shinyish finish.

lukesp

Jeffie, my new Fox 35's have excellent compression. It's the old worn ones that are loose. []

lukesp

You know what Horrace? That is a fine looking Nobler.

gcb

I think we are having two different discussions about compression. When one refers to "good compression", they are generally referring to the gas seal when turned over. When referring to "high compression" it is usually referencing compression ratio.

A Fox .35 is a low compression ratio engine, in its stock form. A Fox .35 requires a larger oil content to run properly. The design is a maximum displacement in a minimum case size, with small cooling fins. This requires a lot of the generated heat to be carried out with the unburned oil. Using castor as a lubricant does two things for the Fox. First, castor flashes at a higher temperature than most synthetics used in fuels. This provides a margin of safety because if the oil flashes off, it does not carry away heat and you can get overheating and even thermal runaway. Second, the castor oil provides a "varnish" that gets imbedded in the pores of the iron piston and provides extra seal as the piston/cylinder fit wears. This is why, when synthetic is used in a well-worn fit, sometimes you can loose a LOT of compression. If this happens, running with all-castor will restore the lost compression.

Many folks use all or part synthetic in a Fox .35 to keep it running clean. If you do not run it too lean, this works fine. You can switch to all-castor as it ages and starts losing compression from wear and get that varnish seal. I understand that as little as 3% synthetic in the castor will clean the engine of this varnish seal.

Although a Fox .35 can run on zero nitro, I believe most prefer 5%-10%. Depending on where you live, some get better handling by upping to 10%-15% nitro in winter.

Try some variations and see what works for you.

By the way, much of this info is for sport/stunt. If you race it, use whatever works...

George

lukesp

George,
I have personally had several engines improve compression seal from one run on straight castor, no problems there. The only real problem with castor for me has been varnish buildup causing erratic running. Very noticable on 049s and the like, so I run a blend of castor/synth to overcome the problem. It took about 10% synthetic for the varnish to stop forming, but this was with 25% nitro which I believe was contributing to the varnishing problem due to hotter running.
For all my other iron/steel pistoned engines I use straight castor. Once again it's more an issue of preference, I think the synthetics of today are a vast improvement on earlier attempts.

Busher

I am currently using 15% ml70 & 15% castor oil with 15% nitro, rest methanol. This brew has worked fine and the engine seems to work ok in my Boxcar chief.

Hope this is of use

Busher