With all due respect to Bigiron, I think there are better nostalgia .35 engines than Foxes available. A good Fox .35 is a great engine... the problem seems to be sorting through enough of them to find the nugget in the pile. It seems to be the norm to add a stuffer backplate and a hemi-head and if you have any money left, buy a balanced crankshaft to get the desired performance. At his point you now have a $140.00 Fox.

IMHO,  better choices are OS Max .35s or Enya .35 (5224). Smoother with more power than a stock Fox. Enya's don't seem to ever wear out.

Let the flames begin.

Thanks for your responses.

My aim is to get back into some CL flying, after being away from it, flying RC for some 30 years.
The idea is to fly CL in parallel to flying RC, and mainly for sport and probably hardly any competition, if at all.

Are there any "special" requirements e.g. some special fuel for the Fox?

Fuel wise - Powermaster makes a GMA blend that's 29% all castor.  A good choice and readily available.  Set up tank old style, ie:suction.  Every one I have set up on uniflow goes lean during the flight.  (my experience only, others may differ)  Sure there are more competitive, powerful etc engines out there but Fox 35's still work well and you can't beat the built in nostalgia factor.

The Fox gets a lot of bad press about special needs, finicky setup, etc but if you look at the special needs, and finicky setup of any of it's comparable competitors suddenly it doesn't look so bad.  The only bad aspect of the Fox is that the power available is limited.  As long as it's on a plane about the size of a Nobler or smaller and fairly light, it's content.  It requires "special" fuel (5 or 10% nitro, 25-30% all castor), and they do take a while to break in.  Pretty easy issues to work around.  All the hop up parts are not needed.  They give a minimal improvement but the engine runs fine without them.  Once in a while it's possible to get a bad Fox, but the majority work fine as long as you use a proper fuel, and break it in correctly.  They are still available new, but there's also a never ending stream of Fox 35's through ebay.  Many have never been mounted, or run.  Later engines with muffler lugs usually bring $40-50, ones without can often go for under $20.

Try 10-5 or 10-6 props and see previous posts regarding fuel.  20% castor/synth blend is a  for fox 35s.

Hi EZ,

The Fox 35 became "THE" stunt engine mainly after George Aldrich became famous with his 4-2 run in his Nobler.  The Fox 35 set the standard for the 4-2 run.

The power deal is largely relative.  The first "foam wing" model to win the US National Championship in stunt was Bob Lampione's Sabre in 1969.  It used a Fox 35 and was in the 50 oz. range.  Bob used a 10-6 Rev Up Extra Wide prop to get enough "bite".

A Fox 35 is very thin walled i the crankcase (very light!) and doesn't cool itself well which necessitates the heavy castor oil content.  The Fox 35 also likes high doses of nitro.  15% is just fine to run in them as it also helps to cool the engine in a round about way.

Thousands of stunt contests have been won with Fox 35s and they still win.  Not the strongest, but still able to do a very good job.

Oh...high nitro and castor oil contents equates to expensive fuel doesn't it?
Hmmm, will have to think about it...prices here are more than what you're used to in the U.S...

Don't know about the cost of "castor oil" in Israel, but I wouldn't think it would be very high.

You don't *have* to use over 5% nitro.  Fox Superfuel (expressly for the Fox 35) is 5% nitro.  I don't know how well a Fox 35 runs on no nitro (FAI fuel).  But, you DO need 25% or more castor oil in your fuel.

Hi Doc,

I am glad you have been lucky with your Fox 35s.  The very design nature of the Fox makes it want to run hot.  It is a very thin casting for the crankcase, and not designed to cool itself well at all.  The bushing, crank, and piston will not react to heat for long periods of time and not show wear or failure. 

I have heard stories of people running their Fox 35s "for years" on "no oil" and no problems.  Of course I never hear exactly how many flights they are putting on each specific engine per year or session, even.

Simple truth is, I have not heard ANY of th established Fox 35 gurus ever say a thing but that the Fox needs at least 25% castor in the fuel.  So I pass that along since they know a lot more than I do, and I like to have an engine that still runs like new after several hundred flights.  Randy has posted his "Fuels" article, and I believe him 100% when it comes to engines since his track record with engines is beyond all others right now.

No disrespect meant, just a differing opinion.

Cost - wise I'm not worried about the Castor oil content, it's the high nitro I don't want however, if a Fox can be run well on 5-10%, should not be a problem at all, that's what I usually use (apart from FAI fuel for my ASPs)

It will run just fine on 5%-10% nitro.