UKIE 35 Break-In

Thank you, Ken. There was a 9" prop in the box...time to switch it out.
I'm also going to re-plumb the fuel system with fresh line and a scrubbed clunk, and mix up some fresh fuel. I think the manual said something like 5% nitro, and 25-28% oil-heavy on the castor oil.
Oh, and get new lines. I picked up some 60 lb stuff, but am reconsidering after your suggestions.

OK...second day of work attempting to break in this new engine. After last week's work with it, I spent some time Googling information about this engine. This obviously isn't a small Cox engine!

Since fuel draw was suspect,  anew fuel tank was plumbed up...no more recycled tank and lines. The second prop was replaced with a 10x4, and I may go one smaller yet for the next break-in period.

I now have pushed about 20 ounces of fuel through it.
My arm and shoulder are sore from flipping this thing so much today. The first thing I did was to replace the original glowplug because it behaved as though it is flaky. Even bench-testing the plug showed an iffy-glow. I plan on ordering a couple of new plugs tonight or tomorrow.

Today's efforts went a little easier AFTER I put a piece of fuel line on the needle. The needle is sloppy loose in the NVA body. It is also in a horrible spot, and has already gotten bent a bit from flipping the prop with a chicken stick. I already sought out Randy (from Stunt Hanger) for a PA NVA, but he no longer markets them. He did indicate an OS .15 NVA should work fine. Since I have a spare one, that will be tested next.

I will mount it and fly the plane once I can easily hand-start it. If that doesn't happen soon, then I will resort to carrying a 12V battery and starter. Right now, it spits and backfires through the venturi. I have never seen that happen on my Norvels/APs/Medallions! And, man, is this thing thirsty! But when it runs, it blows the bushes 25 feet down my front walk!

Anyway, here is a picture and short YouTube video:


https://youtu.be/2Zs1sGI7G5I

Jim, I mentioned to you about clipping the needle valve, this would've avoided the issue you just experienced. There's no straightening a Fox needle valve as it will instantly break. Your current prop choice is better but it can still prefer a smaller diameter like the 9x6 I mentioned. The Fox needs a load and a 4 pitch won't offer that. It needs the smaller diameter for slightly more rpms which offer more cooling but the 6 pitch keeps the rpm's at bay. Your engine is spitting through the venturi due to having too much fuel within it. Either your over priming it or your needle is open too much to begin with. Your tank could also be siphoning into the engine. This causes the engine to run backwards thus spitting fuel out of the venturi. Keep your tank slightly below the centerline and offer 1-2 revolutions to the prop with your finger over the prop and watch the fuel come up the fuel line. Then a you just need a slight prime to the venturi or exhaust stack and smack the prop BACKWARDS when the prop is TDC. Backflipping prevents fingers from getting smacked and if the engine is loaded it will start far easier. Do your engine a favor and reconsider the electric starter on a Fox .35. It will do damage to it as it will grind the nose of the case and also grind the rod into the backplate. There's absolutely no need for a chicken stick as they can do more damage than good as well. Learning the backflip technique takes a little practice but it prevents all that unwarranted flipping your mentioning.

A Fox needle valve is turned down to .127" in the center portion of the spraybar, The ends though where it passes through the case is the same size as a Super Tiger assembly. While I'm a fan of original Tiger setups, Eric Rule from RSM offers Hobby Fasteners clone of the Tiger. I'm certain Randy offers this needle as well and I don't know why he didn't mention it. A Tiger spraybar is .156" all the way across it. This fits the Fox but it reduces the power slightly but increases fuel draw. I generally file a flat on one side of the spraybar if I feel that power is down. The only thing the Tiger assembly requires is spacers to center the hole in the spraybar in the center of the venturi. I typically use the red fiber washers from a Perfect Bellcrank or I make shims.

Hi Ken,
I appreciate the tutelage! Next prop will be 9x6. Tank will get lowered too. Can you recommend any one particular glow plug?

Randy mentioned the other spray bars, but says "I use  either the  Fox  or best one is the  OS 15 NVA, it works well with a tin washer on each size, and is  very close to the same diameter,  using  ones like  ST  NVA and  Enya are  too thick and cut down power"

The real beauty of the OS set up is that I have a couple of spray bars and a broken needle valve body from my OS LA .15. This makes for a really cheap test with a remote needle valve too. I do intend to try that AFTER the smaller prop and lowered tank, but only if the engine is still finicky. Hopefully my tach will work (I'm dying to know what rpms it is turning).

I desperately want this engine to work without doing a whole lot of "upgrades," which is my default answer to difficult hardware (like my cars, motorcycles, and house). Having said that, I already know I can replace the slant-tip needle with a fairly easy-to-source OEM one.

Thanks for popping in and guiding me.

FredVon,  I'm giving all I've got! Even just bench-testing makes me smile. Thanks!

A Fox .35 doesn't need all the upgrades your reading or being told about. They will work as is if certain guidelines are followed. Will a better quality needle valve improve the run? Yes, but if the tubing placed on the needle valve is cut square and the correct length, the needle will perform as intended. This means DON'T cut the tubing with side cutters or a X-acto knife on a a table. Get a piece of music wire about 2" long, slide a piece of fuel tubing onto it. Chuck the music wire into a drill press or Dremel tool and cut the tubing with a single edged razor blade. You cut various sizes and you can cut it square.

The OS needle valve or most any needle valve will work. However, the problem is that dimension of the choke area within the venturi is going to differ from the stock Fox setup. I have a OS assembly here in my box which has the larger knob on the spring end. If memory serves me correctly the .15 size utilizes a smaller sized knob. This tells me that my larger knob assembly is for the .20-.46. The spraybar dimension on this unit is .125". This is smaller than the .127" stock unit. This could diminish fuel draw but could offer more power. It may not and could be totally fine. I never used a OS assembly on a Fox as I have no desire to do so and I prefer a Enya needle valve over a OS anyhow. The OS is out of production and Enya offers them through Bob Brooks at a lesser cost than anyone on the internet.

Glow plugs are just as important than fuel. Thunder Bolt R/C plugs are the best plug for this engine hands down. The idle bar improves the run not to mention it shields the element from fuel in the maneuvers. Yes a non idle bar plug will work but this is the plug for this engine. Available through Mike Goes Flying.com. They're the most reliable and the hottest available. A Fox plug is the absolute worst choice and I would refrain from using them other than breaking the engine in. Others will chime in and tell you I use them. The posts loosen, the insulation blows out, the coils also break free which can fall into the cylinder and will instantly cause a catastrophe.

I'm not a fan of a remote needle valve setup other than on my combat related engines that are on bladder pressure. Why, well for one when you use a remote needle on suction with a Fox .35 you need the tank as close as possible to the engine spraybar as you can get. Adding another piece of hardware mid line into the equation results in 3-4 additional or possible air leaks not too mention it increases the length of the fuel tubing. In addition, regardless of tank height, the fuel line at some point is going to rise up and then loop down. This is a big no no and will cause a delay in needling when the needle is moved possibly doing so in a maneuver. It also causes the fuel to want to gravitate back to the tank during startup causing even more of a headache to start.

If you clip the needle valve as I have mentioned in my prior post, this reduces the need for one to grab the knob. If your going to get bit by the prop, it's going to happen when you go to adjust the needle. Bending the needle as I have mentioned, allows you to hold the model and with the same hand extending your index finger to the needle. You can push the needle or easily unscrew it with one simple swipe of your fingertip while still retaining a tight hold of the model with the same hand thus keeping your other hand free and away from reaching over a spinning prop.

I can provide pictures of anything I have mentioned and very good tank installation methods. I can also offer you tank choices. The internet can offer good information but at the same time it can be engine overload.

Jim
the ancient Fox 35 is about a bare bones simple engine there ever was....Like a Cox .049 reed engine.....once you learn that engine all others are just too easy.....

I apologise for the disservice I did you...not thinking I sent you a raw new engine with muffler and selection of props....
neophyte learning the care and feeding of Fox 35 is hard enough without fighting a new engine break in

ditch the muffler on your bench...neighbors can deal with chain saws every now and then...they can listen to a Fox sing for a few minutes
prop as Ken been telling you...the 9 x 6

wet 2 stroke....pinch line to make lean n scream for 5 10 seconds...back to wet 2...if too wet 4 stroking lean it out a bit to wet 2 pinch n scream a few times....now good n warm...let cool back to room temp.......breakin is like ARO and fuel blends oil content and ratios....a religion folks will infinitely argue about

I am a many heat cycles with lots of oil breakin guy.....once parts are worn together and wear metal is reduced...I reduce oil to what I think is needed

fredvon4 wrote:

I apologise for the disservice I did you...not thinking I sent you a raw new engine with muffler and selection of props....
neophyte learning the care and feeding of Fox 35 is hard enough without fighting a new engine break in.

Mr. Fred, no disservice at all.
I consider it an honor and a privilege that you allow me the opportunity to learn how to Fox! I started on Cox decades ago, and took a decades-long hiatus. Coming back I've learned Norvel, then AP, and soon I'll know Fox well enough to fly the UKIE.

As long as I have you and Mr. Ken guiding me, I'll do just fine. My next break-in cycle will be next weekend. I do intend to lower the tank to see if maybe I was flooding it. The smaller prop will be in the engine. I still need to make my .015x58' lines (I think that is what I read on SH). Only once the engine is broken in will the plane be flown.

And I hope I'm not coming across as complaining. If I am, then I apologize. I only mean to document the process. I really am having fun. Even my wife indicated I was smiling more than I had been the last few weeks!

Thanks much...really!

Ok...time to kick in another gear!

I went so far as to build a mounting plate to hang the 4 oz tank inboard. It really looked ok too! Then I listened on a Friday night StuntHanger virtual meeting. Several more "seasoned" builder/fliers said I would have to launch really lean in order for the engine to richen up to "normal" under G-force pressure feed.

Then I remembered the headaches I had learning fuel system basics on the BHM Mossie.

Researching hotwire cutters, and seeing no real NiChrome wire near me, I settled I to buying the mini bow/cutter at Hobby Lobby. With 40% off coupon loaded on the phone, I picked up my new tool and began testing it in scrap styrofoam.

Then I cut a notch into the outboard wing of the UKEY so the tank would still fit behind the engine and inline. A bit of JBS Industries epoxy over the raw foam, and then a quick fiberglass tape over that. I think I'm getting close to flying this beast!

I would be very concerned about your hardware cutting into your tank. And it will do it because I've had it cut right through metal tanks.  Putting a piece of ply onto the backside of the tank would be helpful. In truth, it would be best to put some hardwood behind your landing gear slightly wider than than the wire and clamps to cant the rear of the tank outboard. With the tank sitting as is, the engine could surge for several laps at the end of the run which is annoying. You will also probably find your going to need the tank slightly higher. You will know that when you go into a outside maneuver or inverted. Fox's generally prefer the tank at least 5/16" higher than centerline. If the engine is richer inverted vs upright, raise the tank. One thing I see with those style tanks is it's taller in height than in width. What this does is provide a lot of head pressure which offers a very rich run and then leans way out towards the middle of the run. The ideal tank for the UKIE is a chicken hopper. This insures a constant fuel draw and is governed by the small hopper which regardless of how much fuel is within it, it runs generally the same start to finish. It's not that your tank won't work, pay attention to your engine run.

Jim re read all of Ken's advice you are in good hands as he has forgotten more about Fox motors than you or I will ever know