Stuka Stunt Main Forum · 31 of 31 known posts recovered · the forum listed 33 replies
Dennis Parsley
What goes up hopefully keeps going round and round.
Duke Fox never liked to do anything the same as others. Come to think of it, he never even liked to do things the same as himself. So he did little odd quirks with different engines, one of which was the flat end on the Fox 35 needle valve. It helped to spawn the following saying:
"The are three settings on a Fox engine:
1) Too rich
2) Too lean
3) Won't run."
Well, the Fox 35 has proven to be the longest production engine in existence--sort of like the old Volkswagen Beetle. People either love them or hate them, but, aside from a few outward cosmetic changes and different attempts at muffler mounting "gizmos", Fox left it pretty much the same as always. Thus when they finally decided the round needle worked better, they couldn't include it with the engine. You get the flat one with the engine but can buy the round, pointy one on the side.
If you have a choice use the round one. The threads on these needles are still to coarse, but it should be easier for you to get a good setting with the round needle over the flat one.
Leonard is being kind. Replace the NVA with a ST version and you'll be much happier. Some will chime in and say that the Super Tigre stem is slightly bigger then the Fox and should be slightly thinned to keep the same venturi size so you don't lose power. Truth is there is not enough power loss to worry about. Given the power output of the 35 if that little bit is going to affect the way your plane performs then you really need another motor.
Dennis
I never did figure the Physics of that... but I do like a good Theory.....
And I think this is just that... ONLY a theory.
I tried to use the flat sided Fox NVA's and found that I could set the engine and make three flights at three different needle settings without touching the needle! All my Foxes quickly sprouted ST NVA's and life became good.
Jim
If you want the grand-daddy of Fox motors, contact Larry Foster and get one of his 35's. Terrific motor with buckets full of power!!!!
Bill (Love those Fox 29's and 35's) Hodges
Bruce H
Well this is interesting, Duke Fox tried everything but you need to go to Sig to get parts to make it work. Sounds like Duke was his own problem. Imagine being the manufacturer of a product that is flawed and someone else offers the fix for it, and you just keep making the same flawed product. Makes you kinds wonder why there are Fox bashers in the hobby.
My question is. if this oddball stock needle works better, then why wasn't its design ever used in another engine in the followimg 50 some years?
And I guess I could also ask, didn't the people at the Fox factory know how to put them in right? It wasn't like we were changing venturis or anything on this engine. Although one may on occasion remove the needle, outside of breaking a needle off, there was never a reason to remove the spraybar. The round needle replacement that Fod, themselves, has come up with does improve things, so I don't see any reason to keep making them with the old needle design. I just wish they would go to a finer thread as well.
I still maintain that the Fox haters either have not flown a Fox in several years or have gotten their information second hand.
Bigiron
The reason these needles became problematic was Duke's characteristice 'cheapness'. He insisted on using cutting tools far beyond their useful life. The tools got dull, thus the NV assemblies suffered from sloppy fits.
Anyone else hear this explanation????
Fred
Bigiron
That's the story I heard as well, and it does make a certain amount of sense. I actually had reasonable luck with the stock Fox parts, aside from breaking them off by the dozen as the result of the outside burp/quit on profiles.
I have only seen pictures, but I understand that an even earlier Fox needle was tapered, but with a + shaped thing attached to the pointy end that rode in the other side of the spraybar. That's an excellent design, since it's held from both ends. The cylindrical needle with the flat is a much more economical variation on it. If the threads fit better, it would be darn near bulletproof.
While I find the ST to work acceptably well, they are known for vibration issues in some engines. That skinny needle is just cantilevered out from the end of the collet, and can vibrate like a tuning fork. The Nelson/PA and Jett/RO are much stiffer and of course fit tighter and they are much less prone to this. The OS is even better in this regard, as it fits tightly to the smooth bore of the spraybar and is very well supported.
I use the PA and RO-Jett and they work well. But it is kind of nice to have a "click" adjustment like on the OS and Fox.
Brett
And a hearty "amen" to De and Bigiron here too. I used to have several profiles with Fox engines and needle valve assemblies on them. I generally cut the needle valves off just beyond the point where they were retained by the clip (less likely to bend or break the needle in the event of pilot error). One or 2 "clicks" one way or the other and I pretty much had my setting for the day, so the long "handle" on the needle really wasn't needed ...
Dennis
Tom
Some of these had the holes that were not quite straight across. In that case install with these facing down (so you can't see either hole.) I think this was more of a manufacturing goof as not all of the needles showed this characteristic and sometimes it is difficult to see.
Basically, turn the needle so the holes are side-to-side and look down the venturi. Then turn the needle over so the holes are again side-to-side. If they are less noticeable one way over the other, that is the way to install it.
The Max NV Assy.has a tapered needle and finer threads when compared to a stock Fox NV and IMHO are a bit more linear when adjusting the engine speed.
Duke was in fact a pretty clever guy. He had some character flaws, one of which will forever keep me away from any Duke Fox fan club, but only the petty will ever deny his creative, many times unique, solutions to various design challenges.
There was mention of no other manufacturers copying his flat-needle idea. How weak! ST didn't copy the O.S. clicker, or vice versa, and there are adherents to both methods of retention.
For myself, several years ago I quit using stock Fox needle valves and assemblies, switching to remachined (.130 diameter) ST NVAs.
It wasn't because the Fox pieces didn't work. I just got tired of the mindless unsolicited input that said they didn't work, questioned about why was I using them, blah, blah, blah. This was especially notable because at the time I was getting real good runs, which was generally what prompted other fliers to look at my motors, only to reverse field, telling me what didn't work on an engine they had only moments before been praising as to the run quality and consistency from flight to flight, contest to contest. Sheeeesh!
Reminds me of a good friend who quit using the 40VF in Expert PA due to the whining sounds. Not from the pipe. From the lips of his fellow fliers complaining about the exhaust note of the 40VF.
Dan
Currell
The ones that followed give no mechanical advantage. It's like: you are Willie Sutton or someone who wants his fingerprints ground off.
Just buy a Fox Stunt.
Currell
You misunderstood my question, Dan. In the 50 some years since this flat needle design was introduced by Fox, I wasn't asking about other manufacturers. I was asking about Fox. If this needle design was so great, why didn't Fox ever use it on any of the other engines that they produced in the following 50 plus years? It seems to me that Duke Fox, himself, disowned it on every following design, while doggedly sticking to it with the 35.
>Leonard Neumann
Well, here's the question:
>My question is. if this oddball stock needle works better, then why wasn't its design ever used in another engine in the followimg 50 some years?
Pretty easy to "misunderstand" a statement like that.
>And I guess I could also ask, didn't the people at the Fox factory know how to put them in right? It wasn't like we were changing venturis or anything on this engine. Although one may on occasion remove the needle, outside of breaking a needle off, there was never a reason to remove the spraybar. The round needle replacement that Fod, themselves, has come up with does improve things, so I don't see any reason to keep making them with the old needle design. I just wish they would go to a finer thread as well.
>Leonard Neumann
Don't have much manufacturing background, do we? Nor a clear idea of tooling costs.
Admittedly, Duke was cheap and a number of his products show that. On the other hand, we still have ready access to an iconic engine from our youth, and that in itself is a small miracle, not to mention being a big boost to period-correct OTS and Classic models.
I'm really glad the Fox 35 is still around. Gives me interesting motors to play with. And the all-knowing critics have something to play with as well.
Dan