Engine Run Issue

Everyone,

I am having a small problem with an airplane getting the engine to run in an acceptable manner. My current set up is a Profile Oriental with a Big Art modified Tower 40 swinging an 11x5 APC propeller (at about 8800 rpm) running on either GMA 5-22 or GMA 10-22 with a Big Art tube muffler. The tank is a Brodak 4 oz uniflow with the vent and pick-up tubes both facing forward on the top and bottom of the tank near the outboard side of the tank, the overflow come straight out the bottom on the inboard side of the tank.

My initial runs and tank adjustments up and down suggested that I may have some uneven airflow problems (run ok in the pit and then start really picking up speed as it lifted off). To try and calm this down I made a uniflow pick-up that is located at the center of the fuse just behind the propeller that has 1/8" brass tube with small Prather fuel tubing running back to the tank. This has helped a bit on controlling the speed pick up during lift off.

The problem that I am currently having is that when I pull manuevers in which the airplane slows down (mostly the 8s-all of them and the hourglass and clover are not real pretty either) the engine begins to run rich, almost to the point I think that it will quit. So I am looking for any possible solutions that some of you might have that could help out.

Thanks for any input that you may have.

First thing I would suggest is go to muffler pressure. Second thing is fool with props. The fact that it picks up a lot on take off suggests to me that the engine is overpropped. I'm having a similar problem with an unmodified, de-dieselized Tower 40 on an old time airplane, with 11 x 5 APC. It runs fine through all OTS maneuvers, except that it loads/riches/goes lean/whatever in the top half of the vertical 8's. It's geat in the overheads and horizontals. No obvious difference in inverted flight (havn't timed laps, need to do that).

I'll guess that Art has filled the boost port on the Tower 40 that John Paris is writing about, so his shouldn't run as fast of a two- stroke as your stock Tower 40, or my stock FP. If he thinks varying air pressure affects his engine run, he certainly should try muffler pressure, but I have a suspicion that just popped into my head, as I was writing a too-long response. I think I will re-order the parts of my reply before I post it.

Let's consider whether there's a slight vibration and very slight fuel foaming when the engine is running in level flight and in single element maneuvers, so he's actually going along pretty lean most of the time. Then, when multi-element maneuvers slow the plane, and slow the engine, the vibration is no longer present at the lower rpm's. So there is no slight fuel foaming, which means the engine runs still slower from the richening. It's worth thinking about. And now to switch my trailing two paragraphs from the end to the start . .

>Second thing is fool with props. The fact that it picks up a lot on
>take off suggests to me that the engine is overpropped. I'm having a
>similar problem with an unmodified, de-dieselized Tower 40 on an old
>time airplane, with 11 x 5 APC.

I was getting some break-in time on an FP 40 today (felt funny going that slow for the first time in many months!) Stocker, new when I got it, and only a couple of ground runs before today. With a 10-4, the flight speed was about right for half a flight's worth, flying with no break. But I certainly had forgotten how thirsty an FP starts out -- it went through 4 ounces in about five minutes.

>It runs fine through all OTS maneuvers, except that it loads/richens/
>goes lean/whatever in the top half of the vertical 8's. It's geat in
>the overheads and horizontals. No obvious difference in inverted
>flight (havn't timed laps, need to do that).
>
But this one today would break into a two cycle for the last 45 seconds that reminded me why I got rid of the two I had back in the 1980's, when the FP engine series was still new, and still consisted of an iron piston in a steel liner. When I tested bigger FP's for "slow flying" before, I put them in a 3 pound stunter, and tried to use 11-4's. Even with a 4" pitch, the FP's then and today want to pick up rpm's in a two-cycle until they are bustling along at 60-65 mph. That's a lot of speed for 3 pounds' worth of plane (I have the current FP mounted in a 28 Ounce, gearless 500 square inch foamie profile that was once two different AMA Slow Combat planes).

.
Kiwi

>. I'm having a similar problem with an
>unmodified, de-dieselized Tower 40 on an old time airplane,
>with 11 x 5 APC.

Jim, I can't see how an 11-5 APC would overprop a Tower .40.

For a Big Art modified engine, I would follow Art's recommendation for a starting point. For a stock .40FP, try an 11-3 APC and let it rev. It might not go fast enough for an OTS, however. Then try an 11-4.
Sammy

Hi John:

I know these engines pretty well. Tom Polk REALLY likes his--says its right up there with the his Aero Tiger. I think he might still be running his clipped bolly on it--I'll try to find out.

I also have a couple of these. I run the 11-5 APC as well. pretty much the same set-up you have.

I know Art doesnt like pressure but it might be worth a try. Both Tom and I run tongue mufflers but I would think that would be an issue.

You might try simply tucking the uniflo entry back into the dead cavity under the engine. get it out of the close layer at the fuse.

I have noticed the changes you describe on other set-ups and cleared them up by moving the Uniflow entry to quiet air.

At least its a no pain trial!

Are you guys going to PA next Sunday?

Here is my very successful setup on my Fancherized Twister II for my Big Art Tower 40 FP. Art did block the boost port and replaced the stock head with his customized wedge head. I have a 4.25 oz GMA/Mustain tank with uniflow running on muffler pressure. I have a tongue muffler from Big Art on the Tower with the original holes redrilled to the next drill size with an extra row of 6 holes inbetween the original two rows of 5 holes each. That relieves some of the back pressure. I have a pressure tap on the tongue muffler just inside of the exhaust holes and engine. I run 5% nitro with 11% castor and 11% synthetic oil for 22% total lube. Art recommends no castor, just straight synthetic. I use a Bolly 10.5x6.25 3 blade from Randy Smith for the propeller. I have a 40 size ST NVA with one hole in the Big Art venturi. One thing about this system though, it is very intolerant of air leaks. Make sure the system is tight or you will be experiencing two cycle runaway about 1/3rd of the flight. I recessed the GMA tank into the fuselage by cutting out a tank shaped rectangle slightly oversized in the 1/16 inch doubler and 1/2 inch balsa fuse section in the nose nust behind the engine. So, the tank is 1/2 inch closer to the center of the flying circle than the engine. This helps.

What I have for engine runs, is a nice medium run that is the same from start to finish until the uniflow vent is uncovered. Then I get 1 to 2 laps of high RPM. I get a positive 2/4 break in maneuvers. I do not run the engine like an Aero Tiger, but like a Fox 35. I also use a hot plug, SIG GP003, and this helps too. My lap times on 60 feet 6 inches eye to eye cables is 5.2 to 5.1 seconds. My experience with high RPMs is it is a waste of time. You always are experiencing 2 cycle runaway and only treating the symptons, not the problem.

John,

Lots of good setup detail on your Oriental experiment, but does the engine rich condition seem equal on outsides vs insides? I'm presuming it is equal, obviously some tank height adjustments can be made it there is any inequality. You might try Roy Trantham's trick from the bull session at Brodaks regarding the ten consecutive inside/outside loops and see if any speedup is noticed one way or the other. While not curing the problem entirely, it may help. The nice thing about a profile job is that you can fool with the tank so easily, and replace it just as easily, too. My next suggestion would be to try swapping tanks-I've seen more inconsistiencies regarding Brodaks tanks than GRW's, etc-the internal plumbing may not be just right to make your engine happy, and a different tank may help bring it to light.
The rpm surge on takeoff should not hurt anything, almost everything I've run with uniflo/no pressure does this, and I've built alot of profile jobs with FP and Tower motors. I've never had to move or restrict the uniflo vent on any of them. If the takeoff surge rpm does not drop back down in level flight, then there is a problem.
I have to throw in the obligatory fool with props part, too. On my Brodak warbirds, I seem to gravitate to an 11x5 zinger with thinned blades and rounded tips running in a 2-2-2 mode. These are profiles roughly the same size as your Oriental profile. But on my builtup jobs (Time Machines and Chipmunks) I typically run the FP-35s with 11x6 BY&O or Top flite power props in a 4-2-4. My FPs have never had trouble turning 11 inch props even on 29% oil 5% nitro, although you can tell they are working harder than with the 5 pitches. Also, on a hard corner the FP or Tower will burble rich, usually though most noticable on a hard inside corner.
Wioth your rich dropoff, a plug change might help. Although I normally run glo-devils in an FP, last week a buddy of mine brought my attention to the rpm drop when I was pulling the battery off. Next flight I switched to a thundervolt plug, and besides eliminating the battery rpm dropoff, I noticed the run was smoother with less rich burble in the hard corners. So its worth a try.
At any rate, good luck with it. If the richening up issue makes it unflyable in the maneuvers you mentioned, my money goes on the tank first, with plug/prop tied for second.

great to see you at Brodaks, next time I'm bringing an amphibious plane!

>John,
>
>
> Lots of good setup detail on your Oriental experiment, but
>does the engine rich condition seem equal on outsides vs
>insides? I'm presuming it is equal, obviously some tank
>height adjustments can be made it there is any inequality.
>You might try Roy Trantham's trick from the bull session at
>Brodaks regarding the ten consecutive inside/outside loops
>and see if any speedup is noticed one way or the other.
>While not curing the problem entirely, it may help. The
>nice thing about a profile job is that you can fool with the
>tank so easily, and replace it just as easily, too. My next
>suggestion would be to try swapping tanks-I've seen more
>inconsistiencies regarding Brodaks tanks than GRW's, etc-the
>internal plumbing may not be just right to make your engine
>happy, and a different tank may help bring it to light.
> The rpm surge on takeoff should not hurt anything, almost
>everything I've run with uniflo/no pressure does this, and
>I've built alot of profile jobs with FP and Tower motors.
>I've never had to move or restrict the uniflo vent on any of
>them. If the takeoff surge rpm does not drop back down in
>level flight, then there is a problem.
> I have to throw in the obligatory fool with props part,
>too. On my Brodak warbirds, I seem to gravitate to an 11x5
>zinger with thinned blades and rounded tips running in a
>2-2-2 mode. These are profiles roughly the same size as
>your Oriental profile. But on my builtup jobs (Time
>Machines and Chipmunks) I typically run the FP-35s with 11x6
>BY&O or Top flite power props in a 4-2-4. My FPs have never
>had trouble turning 11 inch props even on 29% oil 5% nitro,
>although you can tell they are working harder than with the
>5 pitches. Also, on a hard corner the FP or Tower will
>burble rich, usually though most noticable on a hard inside
>corner.
> Wioth your rich dropoff, a plug change might help.
>Although I normally run glo-devils in an FP, last week a
>buddy of mine brought my attention to the rpm drop when I
>was pulling the battery off. Next flight I switched to a
>thundervolt plug, and besides eliminating the battery rpm
>dropoff, I noticed the run was smoother with less rich
>burble in the hard corners. So its worth a try.
> At any rate, good luck with it. If the richening up issue
>makes it unflyable in the maneuvers you mentioned, my money
>goes on the tank first, with plug/prop tied for second.
>
>great to see you at Brodaks, next time I'm bringing an
>amphibious plane!
>
>Steve

Steve,
I have been battling the inside outside issue, but think that I have the tank in the right position. What led me to the repositioned uniflow was that I dropped the tank down and started to encounter the richening problem. Before it was out of balance wrt inside-outside, but seemed to run fine. This is the 3rd or 4th tank that I have tried on the airplane, but only the 2nd with this engine.

I will through the plug into the mix if there is enough time, but since this one keeps the fire lit when the RPM is low and running so rich, I am not sure if I would not be asking for trouble.

If you thought Brodak's was damp, should have seen the Nats. When I arrived on Saturday, you could have actually used the floats to take off in many of the areas.

Curt,
There will be three of us heading over on Saturday if the weather looks good (me, Jim and Jay). I almost tried the dead air route last night, but did not have a good way to put it there. Maybe I can get something rigged for tonight. Will also try a tongue muffler with and without pressure. Don't think that it is an engine issue as much as a fuel delivery issue. We will see what happens.

Hi John, Try upping your oil content to 25% or more. Also add one shim to the head.

>Hi John, Try upping your oil content to 25% or more. Also
>add one shim to the head.

Phil,
I have a batch of 10-25 that I can try tonight and some headshims available if they are needed. Given a little time and all of the great suggestions passed along, I am sure that I will get this one going.

Did you get that thing running yet? Hey if it is giving you that much trouble just throw it away and build another one. I have a trash can all ready for it. LOL. Yeah I seen it fly but sure you can do better.
Jay

>Did you get that thing running yet? Hey if it is giving you
>that much trouble just throw it away and build another one.
>I have a trash can all ready for it. LOL. Yeah I seen it
>fly but sure you can do better.
>Jay

Jay,
Why would you want my trash? If I throw it away, it is ready to be thrown away (no good to anyone anymore-I am a master of using stuff until it is unusable).

I did get it running by plugging the uniflow and using muffler pressure in the overflow. Lots of bubbles in the line while running seemed to be the root cause. Still have a little more work to do to be sure.

For those that my be interested, my current set up that seems to be running well is the Tower 40 motor (switched from the Big Art to a Lew Woolard engine-but Lew's ran the same as Art's prior to the vent change-will switch back for confirmation after this weekend's contest) using a 4.25 oz GRW chicken hopper, Len's tongue muffler with a pressure tap, pressure line running to the overflow vent and the uniflow plugged. The engine speeds up a little through the flight, but not to a point where it gets too fast at the end. Still have the APC 11x5 prop and running the PM GMA 10-22 launching around 9300 rpm. 4 ozs of fuel will go just over 6 minutes at this setting. Don't have the exact lap times, but they feel good. Using 63"x0.015" braided-eyelet to eyelet.

Not sure if this is good for anyone, but it is always nice to have some numbers to reference to.

Thanks again for all of the input that I received.

Hi John,

The Weather looks great for the Western PA Stunt Champs. If you come down on Sat. several flyers will be practicing & will be glad to help out in your engine run anyway we can.

Looking forward to seeing you, Jim & Jay again.

>Hi John,
>
>The Weather looks great for the Western PA Stunt Champs. If
>you come down on Sat. several flyers will be practicing &
>will be glad to help out in your engine run anyway we can.
>
>Looking forward to seeing you, Jim & Jay again.

Patrick,
Thanks for the offer. I am hoping that today's practice session will confirm that the set-up works. If it does not, I will pull out another airplane that does and bring it. Already have enough to worry about during a contest, don't need to add the engine run to it.

BTW,we are hoping to be out at the field around 4:00 for a couple practice/tuning flights. See you then.