One on my flying buddies is having issues with a plane which is driving us all crazy. It is a scratch built Tom Warden Trophy trainer.

Front end is of excellent engineering, glued with epoxy. Engine LA .46  ( tried two different ones that worked well in other planes)

tried two different tanks, different glow plugs including new Thunderbolt RC Long. Different fuels including All Castor Sig with extra oil

added. He has filled the tank box with balsa and added an adjustable ply tank mount, with foam for vibration dampening. He  tried a Hayes

Plastic Clunk tank that has worked well in other planes.  He tried three different props  Xoar 12x4  balanced, Xoar 11x5 balanced and

APC  12.25x3.75 balanced.  He has checked the NVA and used silicone to seal it. I believe he is using a ST NVA with .287 Venture.

It works well until about half the pattern.  This is crazy as the front end is excellent for a profile. He has checked the back plate head bolts

etc. He has Armour All in the fuel also. Almost out of ideas tomorrow he will try a Brodak .40 on this plane to see if the same problems

exist. Both the LA .46 motors were used successfully without issue in other planes??? Both LA .46 have The Metal backplates, and one

LA .46 has a Randy Smith NVA. One LA has a venture smaller than the .287  . One LA .46 was fairly new but broken in well.

I have never seen anything like this. Again not my plane but really crazy. What say you all?

He has used this set up in a plane that was way over 65 oz. This plane is 55 oz.  615 sq in . I will give him the thunder Tiger 11x4.5 worked well on my LA .46

Another  tip  that can help is to start the motor, put your finger over the  vent tube so the  RPM increase, then set the  needle, that takes about 4 seconds  and most times results in a better needle setting

That's how I do mine -- it seems to take forever to settle on an RPM from the rich side, but it's fairly prompt coming down from lean.  Dunno why -- I've decided that it's just a little blue knob of aluminum with a shaft sticking out and magic on the inside.

Well no luck with Brodak .40, different  prop. etc. Our resident expert flyer thinks that it has a strange resonant noise that can be felt when holding the
plane. We told our friend to put an electric motor in it!!!!!!( He is headed in that direction anyway)  Thanks for all the replies.

    Is this unflow or suction, and does it have muffler pressure or open intake to the tank.

    If suction and open:  the answer is obvious - at some point the fuel pressure drops too low (which is much more common on a profile) and it can't get enough fuel. Adding castor probably makes this worse, since the ability to suck fuel depends on several items, only one of which is generally considered. Everybody more-or-less understands the effect of the venturi diameter, but most miss completely the fact that the fuel viscosity also has a huge effect - the thicker the fuel, the more difficult it is to draw through the needle/spraybar/fuel lines. One of the things David and I have found over the recent years when we have been experimenting with the fuel system is that even the 75 with its tiny venturi can have occasional "funnies" that can be changed or eliminated by using oversize fuel lines, reduced-viscosity fuel, and/or counterboring the spraybar. The average flow rate is of course higher on the 75 since it's burning *8.5* ounces a flight, but the real problem is not the average flow rate, it's the peaks. If you watch the fuel line you can't see it and it looks like a continuous flow, but in reality it goes in spurts, and that raised the peak velocity in the lines.

    Even the regular fuel line makes some difference but the biggest difference by far was made by counterboring the spraybar. We were trying to understand a few things one day, and we ended up comparing the PA spraybar to the Jett spraybar, and noticed that the cross-sectional area on the Jett was about 2x-3x as large. David took a PA and bored it out - which was a complete failure since it removed the needle valve seat! On the next try, he bore it almost to the seat. Then like magic, all the occasional random blips of 2-stroking were gone. Same thing happens when running low-vis oil and a standard spraybar.

       I would hasten to point out that it ran pretty darn well even with the stock spraybar and normal fuel tubing - well enough to win the WC and several NATs. It just ran better and better as restrictions in the fuel system were removed.   

     I tried the larger line, larger feed line in the tank on the Jett 61, but it didn't make much difference, probably because the peak flow was much lower due to the longer intake timing, less suction, and of course, 6.7 ounces instead of 8.5. However, it was markedly different depending on the oil  content of the fuel. I wasn't sure if it was really just the viscosity or some combustion or cooling effect from the oil. So I tried an experiment - I took some copper fuel tubing and wrapped it tightly around the header, and then JB-Welded it in place. I ran the fuel from the tank, to the copper coil, and then from the other end of the coil to the filter and spraybar. This created a fuel pre-heater much like the regenerative cooling for a rocket engine, except intended to heat the fuel instead of cool the engine. Nor surprisningly this made for a massive needle change,  and bit of lag when starting, but the engine ran even better than normal. Same fuel, no heater, ran much different even when the needle was reset to get the same speed. It greatly reduced the boost in the corners, and the engine ran substantially smoother, almost to the point it was *too* smooth for anything but perfect conditions. It also fell apart in a few flights - jb-weld is OK for fixing leaks in the back end of the pipe, but right off the header seems to be a little too hot.

    If uniflow and pressure:  I don't know why, but I have had something very similar to what you describe several times happen to me, both on the ST46 and 30 years later on the Skyray/20FP. It would go about halfway, right after the square 8, and take off. I figured it might have something to do with heating up the fuel and causing it to foam. but that's a little bit if a stretch. It didn't matter where I put the vent outlet inside the tank. I ran many flights with uniflow and pipe pressure on the PA61 and never had an issue, but it does happen occasionally.

    Suction and pressure - I would be surprised of this worked less well than suction and no pressure and for sure the mechanism would be different. In this case, maybe the needle opening has to be so small to handle the extra pressure that it starts vibrating like the ST needle used to,. I can't run the Jett on pressure (suction or uniflow) because the needle opening is so tiny with some needles that it was impossible to adjust.

    Uniflow and open: no idea.

    In any case I would suggest just trying it in a different configuration than it is now, and see if the problem changes, which might give you a clue. Another alternative is to put a 1/2 ounce of stick-on weight *on the tank* (clean well first!) - if it is a resonance issue with the tank, that will certainly change. We found a problem on the original/prototype "Doctor" that responded much differently when we tacked some weight to the tank.

    I am actually amazed we don't have more problems with resonance than we do.

     Brett

The  281  venturi is  good for a  PA  NVA in an  OS LA 46 , or  a  .255 for the  OS 20  Needle assembly that OS sells for it

Randy

Nothing was said about the muffler, or spinner, for that matter. Mufflers can clog up, and spinners can be out of balance. And of course, a needle nose spinner has more potential to misbehave. Further, I've never believed in adding Armor All to perfectly good fuel.

Was the same muffler used on both OS .46's per chance?    Steve

Good mustard is available and relatively inexpensive, Mike! I'm good for now...half a bottle. 

Have you tried running stock fuel in your .46LA? I've only run one .46LA, and have run it on everything from a Humongus to a Lark to a 4-Runner, on .271" to .285" restrictors (.157" spraybars), PM 10-29 and 10-22, Wildcat 10-18 Premium with 2 oz of Aero-1 added, and probably some SIG 10-20, somewhere along the line.

For other things to try, I'd suggest trying an APC 10.5 x 4.5, perhaps change the launch rpm. Oh, how much fuel are you consuming? I'm NOT a fan of being a miser and trying to get by with the least possible.  Steve 

Pull the head off and check to make sure the cylinder flange notch is engaged to the tiny split pin they use to index the cylinder. Randy Powell had a problem with his SSW OS .35FP and discovered this was the culprit. Ya never know!  Steve

Walter Hicks OP indicated that there were aluminum pads under the engine, on top of 3/8 x 1/2 maple mounts. It's Sunday, but it's also Mother's Day, so I don't expect flying reports from today, but maybe yesterday?  Steve

    Is this unflow or suction, and does it have muffler pressure or open intake to the tank.

    If suction and open:  the answer is obvious - at some point the fuel pressure drops too low (which is much more common on a profile) and it can't get enough fuel. Adding castor probably makes this worse, since the ability to suck fuel depends on several items, only one of which is generally considered. Everybody more-or-less understands the effect of the venturi diameter, but most miss completely the fact that the fuel viscosity also has a huge effect - the thicker the fuel, the more difficult it is to draw through the needle/spraybar/fuel lines. One of the things David and I have found over the recent years when we have been experimenting with the fuel system is that even the 75 with its tiny venturi can have occasional "funnies" that can be changed or eliminated by using oversize fuel lines, reduced-viscosity fuel, and/or counterboring the spraybar. The average flow rate is of course higher on the 75 since it's burning *8.5* ounces a flight, but the real problem is not the average flow rate, it's the peaks. If you watch the fuel line you can't see it and it looks like a continuous flow, but in reality it goes in spurts, and that raised the peak velocity in the lines.

    Even the regular fuel line makes some difference but the biggest difference by far was made by counterboring the spraybar. We were trying to understand a few things one day, and we ended up comparing the PA spraybar to the Jett spraybar, and noticed that the cross-sectional area on the Jett was about 2x-3x as large. David took a PA and bored it out - which was a complete failure since it removed the needle valve seat! On the next try, he bore it almost to the seat. Then like magic, all the occasional random blips of 2-stroking were gone. Same thing happens when running low-vis oil and a standard spraybar.

       I would hasten to point out that it ran pretty darn well even with the stock spraybar and normal fuel tubing - well enough to win the WC and several NATs. It just ran better and better as restrictions in the fuel system were removed.   

     I tried the larger line, larger feed line in the tank on the Jett 61, but it didn't make much difference, probably because the peak flow was much lower due to the longer intake timing, less suction, and of course, 6.7 ounces instead of 8.5. However, it was markedly different depending on the oil  content of the fuel. I wasn't sure if it was really just the viscosity or some combustion or cooling effect from the oil. So I tried an experiment - I took some copper fuel tubing and wrapped it tightly around the header, and then JB-Welded it in place. I ran the fuel from the tank, to the copper coil, and then from the other end of the coil to the filter and spraybar. This created a fuel pre-heater much like the regenerative cooling for a rocket engine, except intended to heat the fuel instead of cool the engine. Nor surprisningly this made for a massive needle change,  and bit of lag when starting, but the engine ran even better than normal. Same fuel, no heater, ran much different even when the needle was reset to get the same speed. It greatly reduced the boost in the corners, and the engine ran substantially smoother, almost to the point it was *too* smooth for anything but perfect conditions. It also fell apart in a few flights - jb-weld is OK for fixing leaks in the back end of the pipe, but right off the header seems to be a little too hot.

    If uniflow and pressure:  I don't know why, but I have had something very similar to what you describe several times happen to me, both on the ST46 and 30 years later on the Skyray/20FP. It would go about halfway, right after the square 8, and take off. I figured it might have something to do with heating up the fuel and causing it to foam. but that's a little bit if a stretch. It didn't matter where I put the vent outlet inside the tank. I ran many flights with uniflow and pipe pressure on the PA61 and never had an issue, but it does happen occasionally.

    Suction and pressure - I would be surprised of this worked less well than suction and no pressure and for sure the mechanism would be different. In this case, maybe the needle opening has to be so small to handle the extra pressure that it starts vibrating like the ST needle used to,. I can't run the Jett on pressure (suction or uniflow) because the needle opening is so tiny with some needles that it was impossible to adjust.

    Uniflow and open: no idea.

    In any case I would suggest just trying it in a different configuration than it is now, and see if the problem changes, which might give you a clue. Another alternative is to put a 1/2 ounce of stick-on weight *on the tank* (clean well first!) - if it is a resonance issue with the tank, that will certainly change. We found a problem on the original/prototype "Doctor" that responded much differently when we tacked some weight to the tank.

    I am actually amazed we don't have more problems with resonance than we do.

     Brett

Interesting experiment with heating the fuel... funny we did the same thing but the other way around to cool fuel on an racing bike I experimented on sometime back (Copper tuning coiled up in the Air Filter box. When you get right down to it the fuel delivery systems in model airplanes is down right stone age. It is a wonder get any consistency at all. Heating a alcohol based fuel most likely helped the fuel atomize. Fuel atomization has been a hot topic in performance engine building for decades. Some insist that polishing the intake manifolds to a mirror finish improves performance by reducing drag on the airflow to the engine, others insist that a rough intake helps the fuel atomize (mix) better with the air. But I agree with you and Randy high castor content will not help the situation. I do not think there has ever been a CL flier alive who had not had engine runaway issues at some point. Less so with 2-2 engines used today but it still persists. One thing to try would be to run a full tank out on the ground and watch the fuel in the fuel line and see if anything changes, maybe it will do it on the ground as well.

At Last!  I am now getting good engine runs.  Here is a recap of the saga.
Just before the Regionals contest in Roseburg, Oregon this past May, I was trying to solve an engine running away in a new Trophy Trainer.  I tried numerous “fixes” but nothing was working.  I believed that the problem was due to a resonant vibration in the plane.  Very unfortunately, just after the Regionals, I developed a pinched nerve in by back and could not walk, let alone fly for the next few months.  But with some physical therapy and frequent exercising, I am on the mend and back at it.  So here are the steps that got me to the fix.
Since I was convinced it was vibration related, I stiffened the fuse.  I have attached a few of the pictures but essentially I made a 1/8” x ½” x (about)17” piece of 6 ply plywood strip, then laminated a .010 thick piece of carbon fiber on that.  I then used a balsa stripper to strip off (approximately) a 3/8” thick section of the bottom part of the fuse.  I then epoxied the plywood, carbon fiber side to the fuse body at the “notch” in the bottom of the fuse, glued the cut out piece of balsa back onto the plywood piece in the fuse, then finished.
First test flight, the engine still ran away but more in the middle of the flight rather than a few laps into the flight as before.  Thus the characteristics seem to have changed.  So I took the plane back home and “sandwiched” the fuse with two pieces of approximately 3/32 balsa.  I wrapped the balsa with masking tape to hold it in place without damaging the finish.
Yesterday was the next test flight.  Again the engine ran away about half way through the flight.  So now it now seems that the engine runaway was more related to “time into the flight” as opposed to “amount of fuel in the tank” as before.   That coupled with the now very stiff fuse, seemed to confirm the problem was, at a minimum, no longer related to the vibration.
With that in mind, went back to the basics and looked at what else could cause the problem.  Since it now seemed like time into the flight and engine leaning out, I started looking for related causes.  The fuel filter was tucked neatly under the muffler.  So I removed the fuel filter entirely and ran a new piece fuel line around the engine so as to insure it did not touch the engine.  (During the earlier trouble shooting procedures, I had checked the filter for leaks, cleaned it and replaced the tubing.)
With that change, the plane almost made it through the pattern without running away.  Up to now, I had been running a uniflow tank on pressure.  Given the improvement but incomplete “fix”, I decided to take the uniflow tank off of muffler pressure.  I did that and got a complete flight.
I finally got a full flight without a runaway.  After celebrating, I removed the taped on fuse stiffeners and it again flew without a runaway.  So it seems to be fixed, but…here is the larger question however.  This motor is a well-used  LA46.  It came from another airplane.  In the other airplane, its fuel consumption was in the area of 4 ½ oz.  Now it is slightly less than 4 oz.  Why so much less than before?  It wants to run much more lean than before, hence the propensity to run away,  and I don’t understand why.  It is the same N/V and venturi as before.  I don’t remember if this is the same tank as before, just not sure.  Was the fuel filter too close to the engine and heating up the fuel?  That is my theory.  I will replace the filter but make sure it is well away from the engine.
I have included a picture of the nose of the plane (please ignore the gunk build up on the motor, I need to clean it up now that it runs).  The only thing I see that is questionable is the proximity of the venturi to the fuse.  The reason I have not pursued that is because back in the earlier stages of trouble shooting this problem, I had tried a Brodak 40 in the plane and its venturi sat well above the nose ring area.   I wanted to give an update to the problem and its probable fix because of all of the help I got from everyone and to share some of the trouble shooting their outcomes.
Tx.  Mike

Hi Michael,

Believe me I'm no engine expert, but I have an OS 46LA that I'm really pleased with how it runs. Because I'm no engine expert I have to keep everything as simple as possible. The engine is on a 56 oz. profile, running an APC 12.25x 3.75 prop and a 5 oz. uniflow metal tank with muffler pressure. Everything is stock including the muffler with the exception of a CNC aluminum backplate to replace the nylon one. I used a very thin bead of clear silicon sealant to seal the backplate to the case. I am also using the stock remote needle valve assembly and venturi. Have you tried the stock remote needle valve?

Also, how does the engine quit at the end of the flight? Does it "surge" for a couple of laps before it quits or does it cut off cleanly?

Dennis

Hi and thanks for the thoughts. 
I agree with both of you and your thoughts and ideas.  The part that really complicates this is the fact that I have had 3 different motors in this plane.  Two LA46's and one Brodak 40.  I have tried a metal uniflow and a plastic (Hayes) clunk.  I have played with different props, fuels, venturi's, tank isolation's (not oscillations), and air frame stiffening.  The motor  mounts are maple with 1/8th aluminum pads glued and screwed.
That covers most of the experimentation.  The result is always the same, with some slight variations.  The best I have ever gotten is a reasonably decent run with some erratic running.  Most are total runaways after a few laps, sometimes more than a few but still unpredictable. 
So I have already cut the motor mounts and I am fashioning an electric set up primarily because the plane flies well when it is not running away.

For what its worth I had a LA46 on a Cardinal profile. Took off and flew perfect the first half of the flight and then ran away. After trying everything I pulled the tongue muffler off and drilled out the existing holes .003 each. Never ran away again. Ran the same from the start to end of plastic tank. APC 12 1/4 X 3 3/4, mostly a strong 4 cycle with a slight break into 2 cycle at the top of maneuvers. Good luck with yours.

Look how much balsa, ply, and fiberglass I have on the nose of my Twister. The fuse is laminated with a veil sandwich and covered with fiberglass and silkspan from nose to tail. The doublers and triplers are on both sides of the nose. It makes the tank and engine look recessed, but it's stiff as a rock.