Too windy to fly today, but temperature is down to 70 and low humidity.

I bench ran a couple of ounces of 16% nitro 20% oil (50-50) just to make certain the break-in was complete. My Hangar 9 tach showed a peak RPM of a hair over 25,000. I dialed the needle back and ran the tank out at 24,600, +/- 150 RPM. Cylinder was not even close to smoking hot.

Setup was unmodified stock. APC 5-3. Kudos to Rockin' Rusty for all his work on these when he was still around.

Dave Mo...

What ship are you planning to use the Big Mig in, Dave?

-Chris

I've got a Pinto waiting to be finished off.

Dave Mo...

Tee heee...I got a Pinto waiting to be started!

Mr. Dave, I'll be watching. It is good to see Rusty's name...he is missed on CEF.

Jim

Whatever you do, watch how much weight you build into the tail end. Also maybe push the engine forward a bit. I put all the parts into their proper locations this eve and did a quick balance check with the CG as shown in the plan. She pointed almost straight up.

Not sure what to think here. I kick myself now in looking at the design as it should have been obvious when I was building it.

Dave Mo...

A follow-up to my note above. Lead weight of .4 oz in the front end brings the ship into close balance. So there you have it.

Dave Mo...

Well, I'd like to say that this project has worked out but I can't so far. Been out with it four times and still no dice. It'd make a great hangar Queen, but I'm not giving up yet.

First I had to learn how to start an inverted engine. I'm getting better after multiple floods. Then I got a great run but only because (in spite of) a loose engine. Now I can't find that needle setting if my life depended on it. I get a nice 20K on the tach, launch and it dies out without catching air. After a few such attempts, I likely opened the needle a few clicks too much and it blasted raw fuel out the exhaust. It's trying my patience, but my sensitivity to excess sun and heat on a baseball diamond doesn't help. The saga will be continue.


Dave Mo...

Mr. Dave,

I know holding the plane is, well, inconvenient. Have you tried holding it and starting the engine with the plane upside-down? Then flip back upright to tune and launch.

I ran a Scientific P-40 with an AP .061 and a Jan Haluzko NVA/venturi. The plane was built around a traditional wedge tank and I ran the plane on muffler pressure. I should be up front...all I ever expected was Roundie-Roundie with wing-overs.

I need to review your build...
How did you rig the tank? Muffler pressure or Uni-flow? This plane was designed around the Tee Dee or Medallion if I remember right. The Norvel .061 is a slightly heavier engine, so I'm surprised you needed a bit of extra nose weight. If this is the case, then I may build mine around a Norvel .074.

Oh yeah, Jim. The ship turned out very tail heavy, thus the added weight. In addition, I lengthened the front end by 1/4" to accommodate the tank and shift the Norvel engine forward. The tank is standard vented with muffler pressure.

I'm starting to become leery of the Norvel .061 for this full fuse plane. Unless I missed something, the only people who've run these do so on bladder and plank models. Hoping somebody can correct me if I'm wrong. At any rate, I'll keep at it and let you know. I do have an .051 Tee Dee in the inventory if some drastic change needs to be made.

Dave Mo...

Are you sure your Norvel is the Big Mig version?  Or could it be the AME version?  About the only way you can get a "happy" run with the AME version is to run on pressure.

The Big Mig has 5 relatively small intake ports.  The AME has 3 relatively HUGE intake ports compared to the Big Mig.

Keith

Keith

I just checked and found the Norvel has five nice little ports. I still have high hopes for this ship as I did get a semi-decent run and I'm still convinced the problem is operator malfunction. A starting and running session under controlled circumstances is in order (not at the hot, dusty field). So might try that in my basement for a short run today.

Dave Mo...

I have run several of these engines (Big Mig's) since the Tucson 1/2A Scale contests around 2010.  I know the instructions say to use 15% nitro for break in.  Then the instructions say to use 25% nitro for flight operations.  For me, that helps, but they are happier with 35% nitro.  Problem is that plug life is reduced.

Keith

MUFFLER PRESSURE WORKS VERY GOOD ON THE NORVELS

Keith

I think you're really on to something here. I'd been running 15% nitro (20%) oil. I just mixed up a batch of 25N-20O. What a huge difference starting it in the basement just now. At least with further flight tests I can perhaps look forward to better starting and needling. Will consider higher nitro as needed. At least the glow heads and plugs are still available.

Many thanks.

Dave Mo...

Thanks, Bob!

D...

Mr. Dave,
If you start running low on OEM glow plugs KamTechnik makes interchangeable heads that take Nelson or Turbo plugs. He does great parts! NFI...
https://kamtechnik.com/product-category/norvel-aftermarket/

Nice link, Jim. Looks like good product and very fair prices!

Thanks.

D...

The dilemma continues. After boosting the nitro to 25%, it starts very well. But I get runs of only 3-4 seconds, regardless of needle settings. A few large bubbles appear in the fuel line and then she shuts down, even on a full tank. Looks like a cowl teardown is in order unless you gents think fuel line bubbles originate elsewhere.

Much obliged.

Dave Mo...

I'd take some time with a syringe and hose just to map.out the lines to check they are doing what you think inside the tank.

What happens when you plumb the muffler to the other vent tube instead?

Good suggestion, Jim. Per the building plans, the tank has only one vent. And I've tried using it with and without muffler pressure.

In the back of my mind lies a concern about the tank I built (an extra quarter inch of length to accommodate the Norvel). It could be the Norvel doesn't like that extra length, or maybe the tank sprang a leak after installation. Will check as you suggest. Thanks.

Dave Mo...

Have you tried  balloon tank?

Mark

I've not given that a shot as this is a full fuselage model. If I stay with the Norvel engine, that'd be worth a try. I'm also considering a mill with better fuel draw, e.g., Medallion.

Thanks.

D Moe...

I have trouble believing that another 1/4" added length to the tank would be the cause. There is a bigger issue somewhere. If you haven't already, I would suggest plumbing an external tank at the same height and running the engine. (I assume the tank is built in and has no access?) If the engine will start and run SMOOTHLY thru a full tank with a "same height" external tank, then it is time to do the remote diagnostics on the built-in tank. All the usual stuff and nothing left out just because it is a PITA....

--Pressure test with the syringe and some "no foolin' pressure?"  If the tank was not thoroughly soaked, flushed and rinsed with lacquer thinner after soldering things, the flux may have plugged a pinhole (or three) but once it has had fuel in it for a while you are back to leaks. I still wouldn't expect the drastic symptoms you describe even with pinholes on pressure. But, if you double-check this (triple?) then guys can stop asking about it and you can get after the more likely problem(s).

--Did you pull the fuel line at the NVA and see if the fuel flows out when the plane is level? Does it flow out when the outboard wingtip is 60 degrees down?

--Because of the unique single-vent design of the Mathis tank, are you absolutely sure that you are filling the tank to the top? Getting a syringe measurement going in that matches your increased-volume tank? Can you draw the FULL amount out when connecting the syringe to each tube? When the plane is tilted to the angle you expect would submerge the plumbing for a "good to the last drop" test?

--Are you positive that the pickup is in the center? If the tank will free-flow at the needle end of the tubing when full, will it stop flowing after you have captured half the fuel? And what about inverted? Half volume flow and then stops?

--Did you use 3/32" copper tubing on the tank or did you use 1/8"?

--If you can remove the tank, does it pass the "rattle test?"

--Did you have to squeeze the tank to get it into the plane? Did you cut an angle on the vent tube on the inside so that it cannot be obstructed by contact with the top of the tank?

--Do you have flex line that can kink in the bends and stop the flow? Is there ANY flex line inside the fuselage where you can't see it?

Of course, you can take the engine out and put it on the stand, but recognize all the additional things that are slightly--even if unintentionally--altered during the process.

A possible thought regarding the case where you had it needled on the ground but it died immediately after launch:  This is a classic symptom of an engine without enough fuel draw, and/or a needle that is set too lean. We look for this setting intentionally on CL glow-engine racing planes, then richen up just a tad.

I have built two of these Pinto tanks so far. One of them has not been flown yet. A friend has one that I believe was run on a balloon tank. It occasionally had issues.

Dave: Many great questions, so I've got some work to do! I'll give it all a go in the next few days and will report back. Thanks for your thoughtful consideration.

Dave Mo...

Hello All:


Back with a report. I put in a couple hours with diagnostics & attempts at running.

1) No leaks in tank or lines. Verified with serious bulb pressure tests in a quiet room.
2) With a full tank and ship at the level, I pulled the fuel line at the needle and could only get flow if I lowered it a half inch below needle.
3)The tank holds 1-3/4 ounce when full. It is plumbed with 1/8" pipes. No trouble getting it to fill completely.
4) When I installed the tank, it was a loose fit in the compartment. Loose enough so that I could pad it all around.
5) I did find that the needle was partially blocked, so cleared that out to great effect.

So, I attached an external 1-oz. uniflow tank with rubber bands. After many attempts to get the needle right for starting, I managed to get a run of less than a minute that left much fuel in the tank. I forgot to check if the exterior tank passed the flow test at the needle. I might try substituting a non-uniflow tank next if it doesn't.

I got a little burnt out, so that's where I left it. Will try again.

Dave Mo...