Fox run

Stuka Stunt Main Forum · 16 of 16 known posts recovered

John B. · Nov 23, 2000 09:04 PM

Got a Banshee w/ Fox 35 with Fox needle and tongue muffler. 3.5 oz unifolow 3/16 above the center of venturi. I admit to being too imptient to go through a long break in. Got about 10 tanks of fuel through it.

Now the problem is that it just doesn't want to keep running inverted. I'm new at this, so I'm looking for any advice any one can give me.

Thanks,

The Kiwi · Nov 23, 2000 09:39 PM

#1 source

LAST EDITED ON Nov-23-00 AT 09:39 PM (EST)

An eighth of an inch is a lot more typical amount of offset, and you haven't said how it runs in your hands when you flip it upside down while running on the ground (in other words, what made you decide on the amount of offset you are using?)

G. Man · Nov 23, 2000 11:09 PM

#2 source

You should locate your tank feed in line or lower than c/l of
spray bar, sounds like you may be force feeding the way you have it. This applies to inverted mills more so.
Check your spray bar, venturie, is it pointing
down but sideways (I find sideways works best when running inverted).

LNeumann · Nov 24, 2000 12:26 AM

#3 source

You got me confused now. John has a Banshee, so the engine is side mounted. The center of the tank should be a bit higher than the needle, but, perhaps, not as high as John has it.

John, when you start your engine, set it so it is running a lean 4-cycle whille level, but breaks into a 2-cycle when you point the nose up at about a 45 degree angle. Now, while you are still holding the plane, flip it over upside down and see if it still holds the lean 4-cycle. If it breaks into a 2-cycle and stays while inverted (or goes even leaner) then the tank is too high. If it gets too blubbery rich while inverted, the tank is too low. You can adjust the height this way while the plane is still on the ground, and, when close, then fly it and check lap times. Lap times should be the same right side up and upside down.

Also, it is never good to short circuit the break in process. If the engine is not fully broken in and goes lean in the air, with the too tight fits of a not broken in engine, it may go even leaner and hotter and leaner and hotter. Well, you get the idea. One bad run could cook the engine permanently. Spend a little extra time with the engine on the bench, and you can look forward to years of happy and productive service.

Leonard Neumann

lsg3240 · Nov 27, 2000 12:39 AM

#4 source

I am having the same problem with mine. Today I swapped a O.s N.v. assembly for the fox one. It seemed to help a lot. Next week I am going to lower the tank as per the instuctions given earlier. (one change at a time!) Let us know what works for you because I ame really interested! Thanks

The Kiwi · Nov 27, 2000 01:24 AM

#5 source

>I am having the same problem with mine. Today I
>swapped a O.S. N.V. assembly for the fox one.
>It seemed to help a lot.

Although I also prefer the operation of an OS NVA on the old Foxes, the ones available today are rather "fat" compared to a stock Fox NVA. If your plane was leaning out too much flying inverted, the NVA could worsen the condition by shutting off some of the potential air volume available.

> Next week I am going to lower the tank as per the
>instuctions given earlier.

Until you make the various ground tests mentioned, wait on any offset height changes. Uniflow tanks do run differently inverted than upright compared to standard stunt tanks, and some offset is required. A high-rpm setup on a slow combat model with a Chicken Hopper sometimes needs a quarter inch of upward offset to run the same in both directions. My Max-H 40 runs more slowly than a hot 36, but with that type of tank also wants a lot of offset.

> ... Let us know what works for you because
>I am really interested!

Well, I still am perplexed by Crapshoot's Enya running symptoms he wrote here about. I'm quite certain we'll get to the bottom of John B's difficulties running inverted. I'm not so sure we can adequately diagnose that Enya by electronic correspondence!

Kiwi

Jim T. · Nov 27, 2000 04:21 PM

#6 source

Kiwi, I havn't run anything but uniflows in so long that I don't remember how a standard stunt tank runs, so you lost me there. How a uniflow tank runs is determined by the position of the uniflow, not the position of the tank. The easiest way to move the uniflow is to move the whole tank, of course; however, if the tank cannot be moved, moving the uniflow to the right place inside the tank will solve the problem. I've never used a commercial uniflow tank so I don't know how they are plumbed inside.

Jim Thomerson

LNeumann · Nov 27, 2000 06:41 PM

#7 source

The Taffender and now Brodak uniflow tanks are plumbed with the uniflow even with the pick up tube, and just to the inside of it.

Leonard Neumann

Larry F · Nov 27, 2000 08:09 PM

#8 source

But what about the needle valve question? I you have a good tank set-up, is the Fox .35 government issue needle valve OK? I know they snap like toothpicks if you "land" inverted. I know they don't look right, with one flat side.

If you substitute, is the O. S. the way to go, or others? Seems like the Oliver was also a favorite back when.

Larry F

LNeumann · Nov 27, 2000 08:25 PM

#9 source

Some like the stock Fox needle. I was never too fond of it. Fox has a new needle to replace the original in the engine that has a tapered tip that, for me, is easier to set for a good run. The Fox spray bar is .125 in diameter. The Old (no longer available) OS needle assemblies for the 20 and 25S engines (the engine before the FP) were of the same diameter. The present ones are .135-.137. You can use these on the Fox, and if you do without modification, you will get a bit more choke and better fuel draw, but lose a bit of power. You can, on the other hand, file the sides of the spray bar to narrow it up slightly and you will get the choke area back. I have always liked the OS needle valves because I like the positive "click" that you get with them. Some like the ST type needles, and, although these are thicker yet (.157) you can, again, file each side of the spray bar to an approximate .125 width and maintain the original choke area on the Fox.

Pick the one you like, and go with it.

Leonard Neumann

peabody · Nov 28, 2000 10:48 AM

#10 source

I am of the opinion that anything built with a Fox 35 for power ought to incluse a fuse! At least the pyrotechnics can be simple!

See Ya

Peabody

mrwhizkers · Nov 29, 2000 03:02 AM

#11 source

John B- Before trying to "fine tune" your run with tank height and brand/type/style of NVA, I'm curious to know what your basic powertrain components are as pertains to fuel-prop-plug combinations. Until these are right, everything else is just "spittin' in the wind".

John B. · Nov 29, 2000 07:57 AM

#12 source

Thanks to everyone for the help on this one.

Broke in engine with a 9-4 master airscrew plastic prop.

Needle valve is standard Fox, but I did file back the needle keeping the ramp angle the same so as to get more thread engagement. In stock configuration it was running 4 stroke just as the last thread disengaged. I have a piece of fuel tubing on the needle to seal air leaks coming down the threads.

For flying I'm had an APC 10-6. Now have a Top Flite old round tip 10-6, and have various other 10-6 props in the box.

Fuel is Sig Champion 15% with added 7 oz castor per gallon to up the castor content. Uniflow tank, no pressure.

Plug is a Fox rc long with bar.

Tongue muffler

Since my inquiry Ii've done some bench running. With this setup I can get a 4-2 change as I raise the nose and see no difference when I invert it.

Again thanks for the help.

John B.

lsg3240 · Nov 29, 2000 09:17 PM

#13 source

I looked at the fox needle valve that I removed and it is very loose where it enters the internal threads. I placed it back on the engine with a short piece of fuel tubing over the needle portion. The engine started on the second flip and ran much better and when held inverted ran fine. Seems like I read this in a mgazine but do not remember. I am going to hold off on any change untill this weekend. Why do some spraybars have two holes and some only have one? I am using a fox glow plug with no idle bar, 5%fuel with 25%oil, 10x6w zinger prop and a comercial uniflow tank. Any ideas for improvements would be greatly appreciated. Not many control line folks here. Two of us actually, and both of us are new guys.

The Kiwi · Nov 29, 2000 11:02 PM

RE: Fox run, Fox NVA's#14 source

LAST EDITED ON Nov-29-00 AT 11:45 PM (EST)

> (snip!)
>... Why do some spraybars have two holes
>and some only have one? (...) Not many
>control line folks here. Two of us actually,
>and both of us are new guys.

Here and at Isky's, you can connect with beaucoup C-L folks who have many decades of experience among them. This includes George Aldrich, my friend of about 40 years, and the designer of the Nobler stunt plane, if you follow the URL below for occasional visits to Iskandar's forum (he is also a regular at another C-L forum whose owner seems to me to encourage rudeness and unpleasantness as his administrators' behavior, so I never go there and recommend that anyone who appreciates good manners should also boycott the place).

The first Fox 35's came with a spraybar made by Austincraft, with a single hole in it. When they began making one of their own, it had two holes to match the unusual shape of the needle, which is wedge-ended, not pointed. The recently offered pointed needle won't work as well with two holes, I suspect (but I don't like either one very much because the threads are too coarse) .. and yet I really can't recall seeing a "one-holer" from Fox since that old Austincraft.

"(P.S. I forgot the URL that I'd promised!

http://bigwig.geology.indiana.edu/scripts/cl-messages/cl-messa.html

so THERE it is, now!)"

Kiwi

Bigiron13 · Nov 29, 2000 11:21 PM

RE: Fox run, Fox NVA's#15 source

At first, I would run a 5 pitch. 10 X5 APC or some other brand because your engine is fairly new and may try to heat up a little. The 5 inch pitch won't load it quite as much because of unloading in flight. After you start getting some good flights, then go up to the 6 inch pitch. Regardless of what prop you use, BE SURE IT IS BALLANCED.
Kiwi, I bought out an old hobby shop the other day, and found several NEW stunt 35 needle valve assemblies, The old BRASS, bodies, and found that the needles were much tighter in those than the new ones. I tried the new tapered needle in the old brass seat and it was still tight. I am going to set up all my engines with old seats and new needles.
Bigiron