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Old 07-07-2014, 08:54 AM
  #3501  
1QwkSport2.5r
 
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I was under the impression he meant to make them behave better. I know there were modifications to some of the engines like the .40 and .50 to make them more tractable. There is a newer head button for the .40s that allows more nitro beyond the 5% maximum for many Fox engines. I also know the midrange was a bit lean in some of the .40s and there was a needle modification in the .50 among other things. There were other "projects" mentioned for other engines like the 1.20 twin as well. Of course I could be completely wrong which wouldn't surprise me.
Old 07-10-2014, 12:53 AM
  #3502  
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A bit off the main direction of this Club...

I fly mostly CL Stunt - properly called Precision Aerobatics, or CLPA. Precision, yes. When you fly between 5' above ground and the length of the flying lines + your reach height, you are never three mistakes high.

The 'figures' almost all include segments that use that ~5' altitude. With no carb, airspeed is not flier-controllable, but does vary from drag loads in tight cornering, and from progress up and down.

Carbs may be a chore to set, but it can be done. It is more 'interesting' to set a fixed-choke engine to perform consistently and correctly, for a g-exposure range from 1g in level flight to over 25g in sharp turns, and to handle the effects of gross load angles (the resultant of gravity, maneuver radius load momentary directions, and model roll attitude at various 'heights.') There is also the roughly 3g outward from centrifugal force at most modest altitudes.

The Fox 35, still in occasional production, if the most hopeful word from Fort Smith is correct, became the essential engine for the early decades of CLPA. Newer designs outdid the Stunt 35 in various ways, but where are they now? Of course, today, we DO have better made, better designed engines that are less particular in use. Progress, after all, since 1948 cannot be denied. Still, it seems to be a shifting environment - new engines appear and become de rigeur for a season or three, then fade away somewhere.

The Fox 35 Stunt, for all its warts, quirks and age related liver spots, STILL does what it did when it laid out the basic definition of stunt engine performance. The most significant change is that the 4/2 cycle break is no longer held in awe. Newer engine designs have a very broad RPM range in 2-cycle mode, so prop, plug, fuel and setting can be studied to get the optimum flight performance.

Why the Fox Stunt 35? Iron (Meehanite) piston in leaded steel sleeve (don't know if the sleeve is still 'leaded' - sounds poisonous!) Plain bearing shaft and rod. Specs that hit a wonderful middle ground range - almost all Fox 35s, unless brutalized criminally, run much the same. The combination of metals benefits from a high% castor fuel...

I've "cleaned up" and "modified" Stunt Fox engines for over 30 years, mostly for my on use, but also for a few dozen friends. At times in the past, Fox QC was not the most effective. That has improved enormously since the introduction of schneurle ported Foxes in the 1970's...

My mods are to make an optimum engine out of the parts in the box. I mike the parts to determine how much, if any, production tolerance 'this one' has. Oddly, these engines are match-fitted so that the spec deviations are compensated to a great degree. An undersize sleeve is matched to an undersize piston, for example. They still run very much the same!

Cumulative spread of spec variances can cause significant results. I've reworked some that measured under 0.350 displacement, and some that were near 0.360. Design specs would result in 0.352 cu in... The accumulation of spec variances can change sleeve timing drastically. E.g., cylinder flange thickness, casting shaft center to deck height, crankpin radius, cylinder port (opening) distances from flange, piston height, piston head distance above piston pin center, rod length on centers.

I've measured stock-in-box samples from the worst years with port timing variances of 10° to 30° from intended spec! Again, this is much improved in recent decades...

I developed spreadsheets to allow me to analyze what a sample is, and how it needs adjustment to my preferred numbers. E.g., 'blowdown' - the total difference between shaft degrees of exhaust port open and bypass port open - relates to the RPM for best efficiency. The greater the 'blowdown,' the more it suits higher RPM. I prefer to think of the lag between exhaust and bypass port opening - i.e., half the blowdown duration. THAT lag time governs whether flashback of burning charge may obstruct bypass flow, or at the other side, whether useful 'time' is forfeited from bypass flow.

I've settled on EX=115°/ BY=120° B/ or A/TDC port openings/closings, and can almost always achieve that despite cumulative tolerance errors. I also partial-balance the shaft:- its mass is a bit eccentric - metal removed for the shaft inlet port is 'to one side.' Judicious 'carving' on the crankdisk almost always allows the shaft to balance on knife edges with the crankpin vertically above the shaft centerline. THAT eccentricity is reduced significantly. As stock, the tendency would be to 'wipe' around the main bearing...

"MY" Fox Stunt 35s, if I'm satisfied with them, vibrate noticeably less, are a bit more economical of fuel, and have slightly more power than stock. They start and run dependably. I admire some other modified Fox 35s - notably the L&J Foxes my friend Larry Foster turns out - but if I've seen them honestly. they clearly produce more power, consequently consume more fuel, and vibrate noticeably more. Personal preferences...

Not all Fox engines are RC. This is a review of the engine that started the successful history of the Stunt 35 and all the other great Fox engines over the past 66 years. Consider: - the Fox 40 Schneurles are based on a Fox Combat Special of the 1970s. The Fox 15BB Schnuerle has been and still is a powerhouse in production since the early 1970s. The 25BB Schneurle is a fabulous engine, dismissed as a Fox by those who dislike the brand. Only an ABC version could spread its excellence beyond this Club's circle.

Oh, by the way, if you hadn't noticed, I DO like Fox engines. I don't have enough fingers and toes to count how many I have, and use...
Old 07-10-2014, 02:56 AM
  #3503  
1QwkSport2.5r
 
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There has been a BUNCH of stunt .35's on eBay recently. I've been trying to acquire some smaller Foxes and Enyas but the prices got pretty high towards the end, much more than a used engine should be worth. There's a NIB .40bb std. that I'm vying hard to get my hands on. I've learned to not bid super high up front, hopefully it doesn't hit a ridiculous $$$ amount.

On a different note, I'm learning the huge curve that is the Fox 1.20. A beast of an engine to say the least. If my hands and arms survive break-in, it should be a fine running engine.
Old 07-10-2014, 05:52 AM
  #3504  
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dang... Lou, looks like you've been doing your homework!!!
Old 07-10-2014, 03:07 PM
  #3505  
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We used to run the Fox .35 in the Foxberg races. They would shake the fuselage to pieces without a cheek cowl. We have since gone to LA .25 motors, and they run very smooth and just as fast or better than the old Fox .35. I think maybe the Fox could restart a bit better if they were not run too lean though. I was kind of mad when we were forced to go to the LA .25 because I had to buy another motor, but they are pretty good. I am still stuck with the old Foxes that will not accept a muffler. The stunt guys around here are using the LA .40 and .46s now to still give the 4-2-4 cycle run and still run slow enough to give the 5 second laps. Because this is the Fox club, I will affirm my love for my Fox .15 BB. Runs fairly fast for an iron piston, and idles down to nothing consistently. Kind of a shame Fox manufacturing is winding down. Old Duke was full of quirky and great ideas, and acted on them. Always a leader not a follower like the others. Not a whole lot of development went into new designs since his demise. Just tweaking IMHO.
Old 07-10-2014, 04:17 PM
  #3506  
1QwkSport2.5r
 
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What's a realistic price for a NIB 40bb std. (Lapped iron/steel)? I have an older 40bb std that I got with my 1.20 that runs okay, wouldn't mind adding a brand spanking new one to my collection.
Old 07-10-2014, 04:52 PM
  #3507  
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They are about $100 new from Fox, if you can get one from there. $111 for the Deluxe. Maybe there is a super deluxe too? From -bay, I would pay less because of warranty, shipping, lies etc.
Old 07-10-2014, 05:09 PM
  #3508  
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Originally Posted by aspeed
They are about $100 new from Fox, if you can get one from there. $111 for the Deluxe. Maybe there is a super deluxe too? From -bay, I would pay less because of warranty, shipping, lies etc.
I was figuring $50-55 to be max that I'd pay. It has the box and such, looks nice and shiny.
Old 07-11-2014, 04:31 AM
  #3509  
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Sounds about right. Half of new is standard for pretty much everything.
Old 07-18-2014, 01:27 PM
  #3510  
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I hope this is the correct group for this question.

I'm trying to find some information about an odd Fox C/L engine I have. It has a fairly large, square intake and the front housing and rear cover are held on by four bolts, each. The rear cover has a pressure tap.

Unlike my other Fox engine (a .35), there is no number visible in the small raised circle beneath the word FOX on the case.

What's confusing me is that the exhaust port is on the left side, like my Torpedo C/L engines. I'm not sure if a previous owner swapped the front and rear or if it came that way from Fox. A search of the internet did not provide an answer. I do know that the engine just screamed when I tested it. It's definitely working well.

Thank you,
Richard
Old 07-18-2014, 06:01 PM
  #3511  
earlwb
 
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Sounds like you have a Fox .36X combat engine. They made numerous versions of the engine over the years for control line combat competition.
Fox combat .36X engine history: http://www.clcombat.info/foxhistory.html
More about them here too http://www.clstunt.com/htdocs/dc/dcb...opic_id=331805
and we discussed them some here too http://www.rcuniverse.com/forum/glow...ox-engine.html
Old 07-18-2014, 06:19 PM
  #3512  
rg1911
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Thank you for the links. I had read the history page, but it didn't have any pictures that looked like mine. I'll try to take a couple clear pictures to post.

Cheers,
Richard
Old 07-18-2014, 11:02 PM
  #3513  
Lou Crane
 
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Richard,

Hi, again!

Follow he link in earlwb's post above. It describes your mystery engine very well as a 1960 type. With the center block separate from front and back ends, it is easy to swap the exhaust port from side to side. I doubt that the baffle piston would allow putting the exhaust to the rear- the six-bolt head wouldn't likely line up in any useful way.


To complete the swap, the piston and head would need to match the stock fit - baffle to the bypass side, head fitting on.

Also, if you are really adventurous, and if the front end bolt-pattern permits, you could reverse the rotation direction. Why? No idea, but it could be possible...

Remount the front end rotated 90° to either side. That makes up the needed 180° change. The intake is advanced or retarded 90° and meets the shaft port similarly advanced or retarded. However, the bias of port timing for high speed use would probably be reversed, defeating the purpose... Where the port opened early and closed late turning CCW, that could be reversed when turning CW.

Cheers to you , too...
Old 07-20-2014, 03:10 AM
  #3514  
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Here is a copy of the magazine review that was done for the Fox .35 Combat Special engine. One point to remember is that the engines were designed for a fuel pressure feed. Either using a bladder or crankcase pressure. They did make a venturi intake restrictor that was used for special events that required it.

http://sceptreflight.net/Model%20Eng...20Special.html
Old 07-20-2014, 04:10 AM
  #3515  
1QwkSport2.5r
 
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For its day, the Combat Special .35 is quite impressive. .87bhp is crazy high for a .35 of the era, eh?
Old 07-20-2014, 11:27 PM
  #3516  
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First, earlwb, thanks for the link to Sceptreflight. Since the Elmore sites deactivated, this looks very good. Host first page comments indicate the Elmore site was source for many of the tests indexed. Regret only that many are reduced to initial page, but understand the reasons given.


1QS2.5r - The (unnamed) author spells out that max power test figures were on 30% nitro. Not scary for US fliers, but rare in UK due to cost . That's an interesting test report!

18K to 20K RPM on the props named is quite good power. Fox's quoted comment that the engine was built strong enough for quite a bit more nitro also fits the reported Max HP value. Remember, too, back about then, Fox also sold BLAST fuel, rumored to be well above 50% nitro. (Someone here may have a "better" number for that.)
Old 07-24-2014, 06:51 PM
  #3517  
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Yes Fox Blast and Fox Missile Mist fuels were the fuels to get back in the day.
Here are some Fuel can pictures to salivate over.

Well I do';t know what happened to the Missile Mist fuel can, in the attachments, I thought I had added it.
But here it is:

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Last edited by earlwb; 07-25-2014 at 09:11 AM. Reason: typo correction
Old 07-24-2014, 09:09 PM
  #3518  
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Missile Mist sure was a good name! Loved the purple can as well.
Old 07-25-2014, 04:12 AM
  #3519  
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I think the Missile Mist had some perfume in it to improve the ambiance at the field. Old Duke had great ideas.
Old 07-27-2014, 06:55 AM
  #3520  
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So yesterday my friend and I made the new heads for low nitro glow fuel for my Fox 1.20 twin. The factory heads (center 2) are setup for 25% nitro fuel. New heads are aimed at 5-10% nitro. Compression has gone up considerably, so much so that it will have to be hand flipped only now. I don't think my starter will turn it over even at 24v.

Old 07-31-2014, 06:19 PM
  #3521  
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I have a Fox 35 Stunt 40 th aniversary edition. Beauntifull
Old 08-03-2014, 05:54 AM
  #3522  
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I am adding a couple more Foxes to my collection; another .40bb std. and a .50bb. Both are like new but with some runtime. I've heard the .50 makes a good diesel conversion?
Old 08-08-2014, 05:38 PM
  #3523  
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And I came across an estate sale of a late aero modeler. I picked up a NIB Fox .46BBRC ABC for $30, and a Fox .19 for $10 factory test run only. The QC test run tag is in the 46BB box. The .19 is missing the exhaust baffle and linkage, though I'd probably want to find a muffler that will fit it instead. The guy also had an Irvine .25 Mk II Dykes ringed engine for $10 very gently test ran that I grabbed for a buddy of mine. For $50, I don't think I came off too bad.
Old 08-08-2014, 08:57 PM
  #3524  
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You got robbed. But I'll do you a favor and buy that Fox .46 from you for $40. LOL
Old 08-08-2014, 09:12 PM
  #3525  
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Originally Posted by Sport_Pilot
You got robbed. But I'll do you a favor and buy that Fox .46 from you for $40. LOL
LOL! I have a good dose of oil sitting in the .46 overnight, it was pretty stuck from sitting. Heated in the oven for a short time got it at least moving. It needs to get pulled apart though. I want to make sure the bearings are gritty from oil and not rust. I'm sure it's fine as-is though. It's going into my pile of "engines to run". I think my pile has 5 or 6 in it now which will include the engines I'm still waiting for; the new .40bb and .50bb.

So my Fox pile now consists of a .19RC, .40BBRCStd. (X2), .46BBRC ABC, .50BBRC, and the 1.20 twin. Love the Made In USA on the box!

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