Tanks? General questions.

[Matt Brown]

I’ve been back flying CL now 3 years. I flew combat competitively throughout the ‘80’s.  On my slow combat planes I ran GRW chicken hoppers and they generally ran great. I’m now back attempting to fly stunt but I can’t get a decent engine run out of half dozen planes. Currently, everything I am flying is a profile. All have some form of metal tank mounted on outboard side of fuselage. Most have a fuel filter in the feed line. All are uniflow. Fuel is the same that the rest of the club runs without issues.
Does a particular style/shape tank work better than others? My latest is a Fox 35 stunt on the nose of a Novaclone. I got the tank pictured because it looked to hold the most fuel in the space I had to work with. I took it out last week but couldn’t get through a full tank. It would die just a couple minutes into the flight if it even lasted that long! The tank is airtight and I can easily empty it through the feed line so it doesn’t seem to have any internal issues. It was new for this plane so it has no history. I cleaned it internally with fuel and then rinsed it well with alcohol. Engine seem to run fine and then just cuts off. It doesn’t sound particularly rich or lean and it runs fairly similar through insides and outsides.
I have these and other issues with all my CL engines. For the most part, I virtually never have operating issues with any of my RC engines.
Not sure what the problem is???

Matt

[kenneth cook]

            Matt, I have never had success with that style tank. They always had a tendency to act funny just about into the second loop of the overhead 8. The fuel gets pinned away from the pickup and the engine would hiccup. I just stopped using that style.  Actually, I have but it had a fair amount of rework to it. I have to say that since your familiar with Chicken Hoppers, I would slap one of those right on there, the Fox .35 does quite well using them. Just get clean air to the uniflow pipe. I just place a piece of fuel tubing on the uniflow vent and extend it onto the cylinder head and let it lay on it. The cylinder just makes for crazy turbulence into the uniflow if the extensions aren't in place.

[Mike Haverly]

I could be wrong, but this might be more representative.  It looked backwards to me.

[Matt Brown]

Wish I had a chicken hopper that would fit! Never heard of getting the vent in clean air but it makes sense. I’ll give that a try tomorrow. A few other guys are using Hayes 3oz tanks but can’t buy those anymore.

Matt

[Dave_Trible]

Just to clear all bases I'll ask or suggest the following;

The engine looks like its been around. 

1. If it's been stored awhile it's a good bet there is corrosion inside making havoc and could be about to die.

2. The plug looks rusty and the same age.  Try a new plug (NOT that old Fox-a good plug)

3. What fuel?  With 1.and 2. above especially if it's not 28-30% castor then ...it better be.

Good Luck!

Dave

[Dan McEntee]

    This may be reaching a bit, but that tank is , like REALLY close to the back of the engine.  I like to keep my fuel line run as short as possible, but you gotta have some air gap between the engine and tank. Alcohol has a really low boiling point, and there is plenty of heat coming off the engine to get the fuel hot and change it's viscosity. Try a flight with a piece of raw balsa shoved in there and see if anything changes. Make the balsa big enough to insulate as much of the tank as possible.  I have seen funnier things happen! You can check it out another way, and that is to just use a smaller tank, have a bigger gap between the engine and tank, and see how it runs in that configuration. The fact that you say the engine seems to be running OK until it quits leads me to believe that as the fuel load goes down, and the engine gets hotter, it takes a smaller amount of heat to cook the fuel, and that's when it leans out suddenly and quits. Just a theory but possible.
   Type at you later,
  Dan McEntee

[Gary Dowler]

It's a Fox engine. What fuel are you using?  What you are describing is classic results of trying to run a Fox 35 on modern fuel with 18-20% oil, of which only a portion is castor. This causes them to over heat and quit. And they frequently not restart until they cool down.  Add castor and try again.

I fly with exactly the same tank, which I've used with both a Fox 35 and a OS 20FP. The tank is flawless, as long as the right fuel is in it.

Gary

[bill bischoff]

Wish I had a chicken hopper that would fit! Never heard of getting the vent in clean air but it makes sense. I’ll give that a try tomorrow. tanks but can’t buy those anymore.
A few other guys are using Hayes 3oz
Matt

By the way, MECOA sells Hayes tanks.

[Peter in Fairfax, VA]

Is the engine broken in?

[Matt Brown]

In this instance, engine history is unknown. It has excellent compression cold and pretty decent after it quits. I picked it up at a swap meet several years ago sans NVA. I club member had this NVA that he gave me. Fuel is Sig 5% nitro, 29% castor mix for Fox .35 Stunts.
I’ll see if I have anything to make an insulator between engine and tank. Everything is already loaded in my truck and heading straight to the field after work. I just recently learned that Randy has a Fox replacement NVA. Will get one ordered. I will check with MECOA at Toledo on Friday for more tanks. I’ve used Hayes tanks exclusively in my RC stuff the last 20 years.

Matt

[BillP]

Might try changing the tank. The pickup inside the tank could have a pinhole that sucks air after a little bit of fuel is used. I had it happen to an old Perfect #11 tank. I took the end cap off and found a totally corroded tube. A new tube fixed the problem.

[Dennis Toth]

Matt,
I have been running the Fox 35 with a muffler in my OTS El Diablo for several years. It first, I was having funky runs, changed NVA's (Randy, ST), tanks (round plastic double clunk, tin pinch corner, straight V), fuels (5%N 29% C; 10%N 27% 50/50), props 10x6, 9x6 (APC, wood), muffler pressure. None of these had any solid impact.

When I built the ship I wanted to use the round tank as it seemed to be a clean install and would hold the amount of fuel I needed. This had the plumbing coming through a 3/4" hole in the firewall. I set the uniflow vent up in back of the engine block thinking it would be in a dead zone and reduce the upwind/downwind effects. Sometime last year I remembered some advice that was given at a GSCB stunt forum many years ago (by who I don't remember) to locate the uniflow on the circle inside side of the fuse about 3/16" off the fuse side and pointing directly into the free airflow stream.

I made up a small bracket out of strip brass to hold a piece of copper tubing about 3/4" and installed it under the rear engine bolt. Hooked up the uniflow line to this and instant success! I can now set the engine anyplace I want and it just holds the setting. I went back to the full RMS 10x6 prop, 7%N, 27% 50/50 fuel.

I was having similar issues with my OTS Ringmaster that has an OS Max 25 (steel/baffle, ST NVA, muffler) in it. It has the typical profile stub uniflow tank that has the uniflow vent coming out to the top of the tank on the V. After the success with the El D I made up a similar fitting to mount off the back mount bolt of the engine pointing straight into the airstream about 3/16" above the fuse profile. Again, instant success. Solid run, 9x6 RevUp prop, set it where you want no fluctuations. It seems that the profiles have turbulent air flow over the fuse side and with the standard uniflow vent location straight out of the tank get pressure fluctuation all over the map, give it a try on the profiles it is cheap to try and should help the run.

One last thought is if you intend on using the Fox NVA you can seal the threads between the NVA body and tension ring with a piece of fuel tubing, it really helps. Also make sure the NVA to the case is sealed, I use black silicone gasket sealant. One last thing for the Fox 35 stunt on a profile if you run it in a 4-2-4 is the stick in the bypass modification, this eliminates the outside corner burp. You can search this forum it has been detailed many times.

Best,   DennisT

[Matt Brown]

Between many of the suggestions here and a bit of guidance from one of my club members, I got this Fox running fairly decent. It really difficult to needle as you don’t hear much change on the ground but definitely noticeable in the air. Biggest issue now is going very rich on outsides. Outside squares are really tough to do as it nearly dies on the second corner but it cleans up and pulls decent through the second outside square loop. Also goes very rich on the second corner of the wingover but cleans up and pulls okay through the third corner. I don’t think it is a tank height adjustment as it runs very similar during the level flight laps and the inverted flight laps.
For such a simple,quick building plane, it flies great! I need to tame it down a bit with maybe a spinner nut for nose weight and maybe reduce elevator throw. It turns better than my Fancherized Twister , and nearly as good as my SV-11.

Thanks for the help!

Matt

[Matt Brown]

I currently have a Merlin 2005 red plug in it now. Not sure of its heat range. I’ll be looking for new NVA at Toledo. If I don’t find one there, I’ll get one ordered from Aero Products.
Hopefully I can get this one sorted out completely in the next week or so.

Thanks, Matt

[Glen Peterson]

You could try setting your tank height by doing lazy 8's and listening to the sound of the engine. When it sounds the same on both sides, the tank should be set right. In the picture it looks as though the tank is a bit low for a fox 35. Is it glued on or not attached when the picture was taken? You should make it adjustable. The back end of the pickup tube inside the tank usually ends up 1/8 to 1/4 inch above the glow plug for the fox 35. And is your propeller balanced.

[BillP]

If its not showing much rpm change on the ground it sounds like it's over propped. My fox 35s adjust ok with 10x6 props  but are more needle friendly with 9.5x6 or 9x6 props. I know almost everyone on the planet flys 10x6 but the smaller props dial in easier and they are my go to props. Stock fox needle valves work fine...flat or tapered as long as you use tubing to stop air leaks.

[Glen Peterson]

10 X 5'S are my go to. George Aldrich confessed that he used 10" dia. but less than 5" pitch. The old Top Flite Props had less than advertised pitch. 

[Matt Brown]

I started with a 10-6, dropped to a 10-5. Broke that one when the engine stopped out of position on landing. Last try was an APC 10-4. It felt pretty good with the APC.
In the pic I posted, it was just laying there. It was actually from a post I did on facebook asking for cleaner looking tank mounting methods on profiles.


Matt

[Dennis Toth]

Matt,
Which picture has the tank position you are using? The first picture that you posted has the tank below the plug center. The second is in the correct position for the Fox (pickup lined up with the fin above the plug centerline). Also the second picture has the vent above the fuse side and pointing into the free air stream. Did you do the stick in the bypass for the Fox? This mod is simple and will make the Fox perform much better in the outside corners. For props, the 10x5 BYO is a real good fit. 10%N 27% oil (I get a qt of Brodak 10%, 29% castor with a qt of 10%N 23% synthetic plus 1/2oz if Aero One from Randy). I have used Enya No.3 plug with good results. As far as vibration, as lone as the engine does not have any binding and the mounts are solid the vibration will be minimal. Do check the prop balance. Also don't use a heavy prop nut to balance the ship. Add a muffler or bolt on weight to the nose. The Fox bearing will wear excessively with this weight. It is OK to get the initial balance point but should be changed out once you know were to balance the ship.

From one of Brett Bucks posts here is the Fix - http://stunthanger.com/smf/engine-set-up-tips/the-fox35-'fix'/


Best,   DennisT