424 break without having a Fox motor

1. Almost any engine will "break" at least once from a 4 to a 2 cycle, no matter its timing, compression ratio, or inability to dispose of heat.

2. The Max-S, Max-H, Merco 35/40/49, ST 46, Veco Series 100 29/35, and GH 29S will all perform the "right kind" of 4-2-4 (I now own a Johnson "S," but haven't run it, however my friend GMA has reported that it can do the perfect type of "stunt run," so I believe that one is among the specials). Other engines may have a break, but with too much of a power jump when shifting to the two- cycle, so it's not as useful for stunt.

I have owned and still do own examples of all of the engines in my list. I've never noticed any particular loose fit between the cylinder and case in the Maxes or the ST, NOR any serious heat- retention problems. The GH 29S and Johnson CAN'T have anything in the way of a similar complaint because the cooling fins and the cylinder are all one piece. I haven't had my Merco or Veco engines apart in order to know about the interaction between case and liner.

3. I've had Fox 35's that had rather snug fits between the case and cylinder.

4. It's my opinion that while I may agree that certain aspects of the Fox 35 design owe a lot to the legendary cheap attitudes of Duke Fox, the main contributor to the heat problem has always been the minimal bulk/weight of the case compared to the basic engine displacement. For its own time, it was the Chevy 265 of its day, compact, light, and comparatively powerful.

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P.S. Playing at word games with insults aimed at inanimate objects doesn't say a lot in favor of the gamer's level of maturity. But more to the point, I have almost always hated those goofy Fox NVA's, ever since they replaced a perfectly good Austincraft NVA that worked a great deal better.

But yesterday I was visiting with Don Martin, who is involved with a teaching program in the school system he works for that uses model planes as a sort of bridge to reach between troubled young people and the support staff of the schools. Don has several Fox 35's he's been using, but one of the newer ones was not running in typical Fox fashion.

A year ago, when I spent quite a lot of time with Don at the last Houston Memorial Contest, he had a Fox with a "straight" needle. There was no way to adjust anything with it. I don't like Fox's needle valve stuff, usually, but did have a spare wedge-cut needle, and gave it to him. We got that Fox 35 to run well enough (for a new Fox engine, at least) once we yanked that unmachined needle out.

I was busy in the pits and in the circle for much of the time that Don was at the field this time around, but late in the day did have some time I could spend with him again. I found it interesting that he was having more troubles of various kinds with still more Fox 35's; he told me of asking someone among the stunt-flying contingent about a Fox that seemed to want to stick in a four-cycle, and never to break at all, no matter how many break-in runs it had on it.

Whoever it was, if he named him, it was unfamiliar to me. But it seems that this particular someone turned the Fox NVA sideways so its two holes pointed up and down, started the engine, and tuned it, and then "Voila," the two-cycle operating mode was suddenly available. Odd little story, isn't it?

The K.

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>However since the 4-2-4 break
>seems to have an almost
>mystical appeal to everyone and
>it is so sought after
>it is an interesting pasttime
>to try and capture the
>methodology of the motor.

Almost any 2-stroke model motor will do a 4-2 break. There is nothing remotely mystical about it, just a simple matter of applying the right load.

Whether or not it's at a usable RPM, or the boost is the right amount of power, are other matters. Lots of typical baffle piston motors from the late 50's-60's like the ST46 and 60, OS35S, etc, are excellent low-rev 4-2 break motors just like they come. The rev range of these motors (8500 ish on the ground) drives you to relatively high pitches like 6" or so to get the right level flight speed at the 4-2 break point. More modern motors like the 20FP can be made to do a reliable 4-2 break motor at much higher revs (11000 or so) that requires about 3-4" of pitch to get a decent lap time.

One of the old skills, quickly being lost since traditional baffle-piston 4-2 break motors disappeared from competition, is the art of adjusting the 4-2 break correctly. There is at least as much to know about fiddling the venturi, compression, nitro, and backpressure to get the breaks to happen exactly when and to the degree you want as there is to tuning a tuned pipe system. Everybody who was competitive in the 80's had to know all this stuff, and spent many happy hours diddling around with head shims and bolts in the muffler holes. . The fact that the power was marginal made the need to get it exactly right vital.

I was thankful for the tuned pipe as much for the lack of all this fiddling as I was for the added performance.

Brett

An aside: One point brought home with a vengance this very weekend- if anyone tells you that you need to do anything of consequence to the guts of a STg21/46 or ST60 to make it a good stunt motor, run away in the other direction as fast as you can possibly go! It's completely unnecessary and undesirable. In particular, if the mods involve machining, make sure that all changes are easily reversible in the field. That way, once you come to the conclusion that the whole idea was a big mistake, you can get it back to the excellent stock configuration!

It is not going to help, and it is going to hurt. And, as for the 4-2 break, that comes from other considerations (timing, compression, etc.) not a loose fit of the cylinder to the case.

> Duke mustov lucked into the timing, compression
>and heat dissapation for a favorable break. I 'm
>pretty sure that the 4/2 was developed some time
>after the engine had been out

The Orwick .64 engine was timed very similarly, according to GMA, and would also run the 4-2-4. Duke apparently copied a lot from Orwick. The early fliers didn't trust engines that changed speeds the way that the Fox 35 would, and George tells lots of stories about how people reacted with disbelief to his preference to run engines that way.

The Fox design has changed only very slightly from its 1947 start, and the use of the 4-2-4 with it by Aldrich began two to four years after it came out.

If the first statement were true, Fox would have a rep for overheating, rapid wear, etc. This is not the case. (True, when you look at the case, the surface area is minimal, especially the area reserved for the cooling fins). But this was a deliberate tradeoff vs. weight. And it turned out to be the right call, design wise. Fox (Stunt) is not the most thermally stable engine, of course. But remember: you can overcool a model motor as well as undercool it. (All of the newer CLers that use too cool plugs or not enough nitro would have yet another issue to confront).

Fox was one of the first, if not the first, engines to use a monoblock construction. This rarely is pointed out. No separate sleeve/finned cylinder arrangement. This simplified the design, and eliminated potential leak sources. Most contemporary engine makers have continued this approach. This, interestingly, roughly parallels automotive engine design development. In the early days, cylinders often were cast individually, and bolted to the block. Also, blocks could come in two separate pieces. As time progressed, all of this became a single unit.

As far as building to a price is concerned: practically every manufacturer has this challenge (well, maybe not Rolls Royce or Bentley, but now that BMW and VW have them...Maybe the Million Dollar Bugatti coming out, perhaps...). Remember that Fox was not the price leader at $14.95 and $15.95 in the '50s. Duke had the luxury of using quality parts and relying on R & D, at this price. If you want to talk building to a price, then look no further than McCoy (.35). At $5.95, they were indeed successful, despite some shortcomings!

Fox liners seem to fit more or less the same as other competing makes...Someone please correct me if I'm wrong.

This is about as emotionally detached as I can get it. I hope it partially answers the mail. I did my best, Dennis.

Although change in load will affect the engine run (which you can readily see in high wind conditions as the airplane turns into and out of the wind) the major factor on the 4-2 break is the fuel head. When the engine is set correctly, it will run 4-cycle when the plane is sitting level, and if you point the nose up to a 45 degree angle it will break into a 2-cycle. There is no load factor affecting this at all. It is all fuel head, and that is what is working on the engine in normal flight.

It would be nice if the change in load explaination were correct, as the break would then come just when you need it.

If you try what George suggests on a Fox 35 (change to a 12 x 6?), it won't even run. But, yes, putting a significantly larger club on an engine with the needle set for a smaller prop will change the needed needle setting even if the engine is capable of turning the bigger prop. (And with a pipe ship, it can affect where you now need to set your pipe.) But if an airplane is significantly slowing down while going uphill, you don't have enough engine or prop or something just isn't set up properly.

My example of the airplane turning into or out of the wind shows the affect of load on the airplane in that the inertia of the tethered plane turning around a point tends to maintain a more constant ground speed while the actual load on the engine changes when turning into or out of the wind. Thus is slows going up wind and speeds up going down wind--just exactly what we don't want.

But we don't have nearly that type of load affect on a properly sized and set up engine/airframe combination when wind is not a factor. (The dreaded "wind up" in the wind is another factor that I am not going to address here.) Going back to my Fox 35 example, and in zero wind conditions, if you have the engine set properly for the break, you will be able, while the plane is still on the ground, to point the nose up and have it break into a 2-cycle, and return the plane to level and have it go back to a 4-cycle. This is how I have learned to set the engine and know that the needle is correct before launch. And that shows the affect of fuel head on the engine, not load.

My McCoy .35 Red Heads, OS Max-S .35's and OS Max-H .40's all do a very satisfactory 4-2-4 stunt run stock. They might indeed run the break better with some tweaking by an experienced engine man, but they do well as it is.

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