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Norvel .061 Big Mig for Semi-Serious St

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Dan McEntee:
   I have been playing with some smaller models for a while and recently acquired a Doodlebug stunt model , designed by Wild Bill Netzeband and this model was built by the late Jim Wilson, who was a local modeler here in St. Louis and had several small models published in the magazines over the years. Jim was very good at operating diesel engines and I'm betting that is what he had on the model, but I wanted to try a Norvel .961 Big Mig for the extra power, since it is a large model and I had hopes of flying it on longish lines.

   I have been having mixed results with the effort and have trouble getting consistent runs. Some flights are great, then a simple refuel and launch with out changing anything results in a flight that has the engine lean out and speed up, go rich and too slow, run along time on a measured amount of fuel , all over the place as far as performance. The engine has been broken in, and I have tried numerous props, fuel, and tanks. Sometimes it will go through 1 1/2 ounces of fuel , run like I want it to, and then keep running for 8 to 10 minutes. Lots of run away runs. I have tried standard tank, like a perfect #8 I think it is, and modified one with a better arranged pick up tube but still standard vent, and another one with a relocated pick up to better feed the engine with a shorter fuel line and a uniflow vent. This tank has shown the most promise but still no repeat consistency and have tried venting to atmosphere and muffler pressure. The muffler tend to work loose and wobble, since it's retained with a simple wire bale,  and thinking this might be the source of the problem, I glued the muffler to the flange with a small amount of red silicone to seal it and replaced the spring wire bale with some safety wire attached in the grooves front and back and then twisted on the back side to really secure the muffler and the silicone to seal it. The first flight today was VERY promising and performed exactly as I had hoped, but the next flight went astray again!! Fuel has been experimented with ranging from 10% SIG type fuel to 15% all synthetic and 15% SIG type fuel but at 18% total oil. I planned on trying some 25% nitro fuel but forgot the bottle this morning. I know the more nitro I have will allow the needle to open more and hopefully a consistent run but results still vary. I have two head gaskets in the engine and wonder if I have to add more?? 

   I have run these things for many hours on the TuffBaby trainers at Oshkosh, but that was just round and round training flights. My next thought with this is to get some supplies for bladder pressure and try a bladder on it and see what happens, and also go up the nitro ladder with 20% and 25% being in the que for the next flying session. So far, prop hasn't made a huge difference, but I'll keep experimenting. Does anyone have a set up that works well for them that I can try? One of my big problems is hearing the little booger!! I can't tell most time if it's slowing down because it's too lean or too rich?? Too rich will generally keep running. Too lean will usually quit. When things work correctly, this airplane flies pretty nice for a small model and my intensions are to just fly it like i do my other sport airplanes, but I gotta get a consistent run first.

    Any suggestions for a set up for the Norvel Big Mig .061??

   Type at you later,
    Dan McEntee
   

Motorman:
I tried 10-15% nitro and the engine just ran too cold. I went to 20% nitro with 20% castor and it came to life. 1/2a engines like castor, helps them seal or something.

Using an APC 6-2 with good result but have made some 6-2.5 carbon props based off a Rev Up 6-3 wood. Big clunky props like mas or grish just drag the engine down too much.

A suction venturi and a fine NVA are critical on 1/2a and it's good to keep the vent tube far away from the pick up in the tank.

I think if you get the engine hotter it will run better. I run mine in a pretty good 4 stroke but the extra nitro keeps it lit.

Hope that helps,
MM 8)

ray copeland:
I mostly run balloon tanks if possible, if not, the brodak bh-528b and bh-508 work well on profiles. I also run Sig 10%most of the time with the exception of the ame 's  that i have on combat planes they get 25%. Make sure the feed line from the tank is as short as possible. The cox 5x3 prop works great along with the apc 6x2 if the plane is too fast or the apc 5.5x2.5.. Maybe try a new or different plug, Nelsons work as well as the Kamtechnik turbo. Vibration can effect 1/2a's too. Norvel made a cold plug and head early on, took me a while to figure this out as the plug size and hole in the head are smaller and they needed a lot of nitro.
Maybe Ken Cook will see this and chime in with his experiences.

Dan McEntee:

--- Quote from: ray copeland on June 28, 2024, 12:53:36 PM ---I mostly run balloon tanks if possible, if not, the brodak bh-528b and bh-508 work well on profiles. I also run Sig 10%most of the time with the exception of the ame 's  that i have on combat planes they get 25%. Make sure the feed line from the tank is as short as possible. The cox 5x3 prop works great along with the apc 6x2 if the plane is too fast or the apc 5.5x2.5.. Maybe try a new or different plug, Nelsons work as well as the Kamtechnik turbo. Vibration can effect 1/2a's too. Norvel made a cold plug and head early on, took me a while to figure this out as the plug size and hole in the head are smaller and they needed a lot of nitro.
Maybe Ken Cook will see this and chime in with his experiences.

--- End quote ---

   I didn't know about the cold plug. I'll have to check what I have. I have what I think are stock factory plugs and some Merlin plugs from Al Kelly. I'll have to check those. I may have a Galbreath head for the Nelson plugs that would fit also. Now that I think about it, I started out with a Merlin plug and head, and then installed a stock Big Mig head and Norvel plug. The last session flights tended to slow down like the engine was getting more rich, an indication of the plug being too cold?  I've run these on 10% nitro many time before in a trainer mode and don't recall ever having this uneven run but those were mounted on a tank mount. Engine is sidewinder on a profile fuselage, and custom tank to put the tank as close as possible with a pretty short fuel line path. I'm gonna go look at some heads and plugs Thanks for the feedback.

 Type at you later,
  Dan McEntee

kenneth cook:
             One thing to keep in mind in regards to Perfect tanks is that they're far from perfect. The pickup is NEVER soldered in the rear of the tank. It's anyone's guess as to where it is in the tank. In addition, the tubing is not seamless and the type of brass used has a tendency to split. Therefore , regardless if the tank is new or used, it's certainly worth taking it apart.

       I have to ask what style Norvel are you running? Is this a Rev-Lite version with the round cylinder head or is it the older nickle plated square style head? I ask this because the Rev-Lite version uses a bolt in venturi. The fit and the o-ring totally blows which can leak air causing very erratic running. I find better thickness o-rings to replace them and I also if needed use a bit of JB weld to insure it seals.

          Anytime I try and run a tank on a 1/2A profile, I do my best to sink the tank into the fuse to assist in aligning the pickup tube with the venturi. The Norvel needs to run at high rpm's to sustain fuel draw and it doesn't take much to upset this. Therefore, if your using a wedge tank the chances are your pickup tube is too far outboard and your engine is already suffering a lean condition.

            Dan, while you mention the engine is broken in, it's not uncommon for these engines to pick up aluminum from riding in the case and it essentially gets burnished onto the shaft at the nose. Usually, this becomes quite noticeable when the shaft won't just fall out of the case. I polish them up and remove this. It's a remedy for the shaft but it really doesn't repair the case. This can act like a brake when the engine is running and this too can essentially make the engine run all over the map.


          One thing I've experienced with Norvel's is that I can run them on 10% stunt fuel and achieve the same performance as I do on Cox TD's running 25% nitro. I only run as much as I need. I also use Nelson /Galbreath setups. Greg from Kamtechnik is the only person producing Nelson head buttons for Cox/Norvel. He also produces them in turbo plug varieties. If your running two gaskets and haven't taken out a plug with the lean runs you've been experiencing, I personally wouldn't add anymore.

          I have to agree 100% with Ray's comment about the 5.5x2.5, this prop is not the same as the 5.5x2  so don't confuse them. You mention that the muffler is coming loose which I find a bit alarming as if the engine is vibrating. Could you place some aluminum pads under the engine? This will not only give the engine some footprint preventing vibration but it will also shim the engine further off of the fuse moving it closer to the pickup in the tank.

        One thing I discovered with the Al Kelly plugs are that the red hot plug is TOO HOT and it causes pre ignition. Obviously, using additional head gaskets circumvented this but just turning the prop to clock it into position would cause a aggressive backfire.
       


           

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