Noblarf engine woes

OK here is where it stands. When the engine runs, it drags the Noblarf around like a scalded cat. But, it only runs dead lean. The exhaust is coming out BLACK. Try to richen it up, and it dies after a half minute or so.

I haven't had this problem running Norvel .06s on backplate pressure, and am wondering if I have a compression ratio problem, pressure vent size problem, "don't do this, it won't work" problem, or what.

I will say, that when it runs a full flight, there is NO variation in the performance in level flight. However, it won't run rich enough not to be over-lean in maneuvers and overheads.

Colder plug? Lower Nitro? Less compression? Lower pitch prop (10x4 modified Zinger, currently) Screw-it, go to muffler pressure and restrict the venturi a bit? Hey you combat dudes, I could use a little help here.

BTW, Keith Trostle flew it and liked it enough to do a series of square 4-leaf clovers. First time he has done that with one of MY planes! Also, he made some comments that he suggests going to a lower flap elevator ratio than 1:1 as spec'd by the instructions. Who am I to argue??? I will try to swap the flap and elevator rod positions on the flap horn! He says that the old 1:1 setup has been proven to be too much. You get a lot of drag, and can turn as tight with less flap, but not slow down as much. Keith, pitch in and let us know if I got this right?

Finally, I did check out the pushrod flex, and I think there was a little. I made up a brace for the middle fuselage former to tightly trap the pushrod. If anyone needs a small patch of Sapphire blue Monokote, let me know, I have a whole roll......

>Lower pitch
>prop (10x4 modified Zinger, currently) Screw-it, go to
>muffler pressure and restrict the venturi a bit?

Try a 9-4 APC and a fine air filter.

Larry what motor do you have in the Nobler. I flew my #2 first flight New Years Day with wind ,It was fast but it was real windy . GMA OS 35 S powers mine, And its 44 oz with all the modifications.

OS 25 FP, standard venturi, backplate pressure into a Hayes 4 oz. clunk tank. When set to run the full flight (too lean) it runs flawlessly and consistent. However, it clearly is running at peak level, and slightly overlean in maneuvers. When I richen it up to be at a rich 2 cycle in level in hopes of hitting peak in the maneuvers, it dies.

My goal is to get the performance I currently have in level flight when I am in maneuvers, and slightly richer in level. It won't at present do that.

Fuel draw isn't the problem, Brett. It is running backplate pressure, and drips fuel out the venturi for a while if it dies. There is a LOT of pressure in the tank.

I know I can get this to run perfectly with a restricted venturi and muffler pressure, I had this engine on my Flite Streak ARF with this setup for a long time with great success. Unfortunately, that reduces the power output significantly.

What I want to know, is how to re-tune the engine to run at full power on the high pressure setup. It isn't overheating, it isn't failing to draw fuel, in fact, it dies rich if not set overlean. If set dead lean on the ground, it will fly the entire flight, but obviously way too lean on maneuvers and overheads, but carrying through. When I richen it up to where it would be right in maneuvers, it won't keep running. When set so it will run the full flight out, the exhaust residue is BLACK. If it was a diesel, I would say it was overcompressed. Does the same apply to glow?

I tried some lower nitro fuel with more oil, and when the exhaust ran clear, the engine quit.

I would prefer to get the full power out of the engine that it has shown it can produce, and go to longer lines rather than detune the engine and shorten the lines.

Obviously there is something I don't understand about high pressure systems that the combat boys probably solved eons ago. As I say, I suspect it is something in the compression, nitro, plug combo that I hope someone can give me a clue on.

>Fuel draw isn't the problem, Brett. It is running backplate
>pressure, and drips fuel out the venturi for a while if it
>dies. There is a LOT of pressure in the tank.
>
<< snip>>

>I know I can get this to run perfectly with a restricted
>venturi and muffler pressure, I had this engine on my Flite
>Streak ARF with this setup for a long time with great
>success. Unfortunately, that reduces the power output
>significantly.

If it ran OK on a regular setup, but doesn't on pressure, then the compression/timing/plug etc. is not the problem. I think you may be experiencing the same problem that Howard and Paul ran into on the B-17. If I recall correctly, Howard reported that the pressure vs rpm had a negative slope above some RPM. This was on the 15FP, of course, but it's perfectly consistent with your observations. Maybe a little time on the test stand with a manometer is in order.

You are ad inexplorata on this and I have no idea what to do to fix it, aside from the obvious.

I might also point out that may be getting over the top on power. These are economy motors, and they're only going to put out so much before they self-destruct. Even if you get the engine to run and needle properly, you might still destroy it by overstressing it. The black stuff may not be the result of running too lean. But I suppose there's only one way to find out. At least they are inexpensive.

My experience with the LA25 was that it was happy only with an APC 9-4 or a 10-3 prop (from Brett B. suggestions). Anything like a 10-4 caused the engine to sag in the latter half of the pattern, That was with a Ukey 35.

I came away with the impression that it (LA25) was ok for very light 35 size planes (~35 oz?), but perhaps a bit too weak for a "normal" 35 type plane. So even though the Nobler Arf is pretty light, I went with a Brodak 40. Pretty happy with that combo, which comes out at approximately 40oz. I have been interested in hearing about people's experience with the LA/FP/TT 25 sized engine in the NoblerArf.

I tried to run a Fox 35 on case pressure with a uniflow tank on a Twister with the same results you mention. I was flying off a stooge and I set the Fox as rich as I could and it leaned out overlean in the air as you describe. I tried it for a couple of very frustrating hours and went back to muffler pressure with no problems. The Fox 35 was a bit the worse for wear and I did eventually replace its piston and liner.

>My experience with the LA25 was that it was happy only with
>an APC 9-4 or a 10-3 prop (from Brett B. suggestions).
>Anything like a 10-4 caused the engine to sag in the latter
>half of the pattern, That was with a Ukey 35.
>
>I came away with the impression that it (LA25) was ok for
>very light 35 size planes (~35 oz?), but perhaps a bit too
>weak for a "normal" 35 type plane. So even though the Nobler
>Arf is pretty light, I went with a Brodak 40. Pretty happy
>with that combo, which comes out at approximately 40oz. I
>have been interested in hearing about people's experience
>with the LA/FP/TT 25 sized engine in the NoblerArf.

I am pretty well convinced that the FP and the LA are significantly different in this regard.

Brett

p.s. But, I would note that if it's going "like a scalded cat" right now, it has more than enough power - too much, in fact, which is why he wants to back off on the needle.

Another thought- if all else fails, try a Sullivan ss-4 clunk tank set up for suction, and put muffler pressure into the vent. My diagnosis (and this has happened on some 25's I have seen) is that there is inadequate fuel suction. bb

Larry,

One of the neat things about you is your absolute committment to build your own envelope!

Who else would ever have thought to use crankcase pressure on a sport engine in a stunt plane. You are in a class by yourself my friend. Of course, you've got to be both the student and the professor since you're emulating Cristopher Columbus here. (Well, Rich Porter might well have been an alumnus, although he could well be getting his doctorate as we speak...er...type)

One of the things that concerns me is your comment about *black* exhaust. Black usually means ugly things like "bits of embedded metal" in the oil. This generally comes from something relatively benign like a loose muffler and too much vibration causing an abrasion of metal. It can come from an overlean needle setting on engines without ABC type metallurgy. In that case what you are seeing is bits of piston cluttering up your oil viscosity This is generally to be avoided.

This is just a suggestion (I know, it runs counter to the general "Designman" philosophy but, what the heck, you could wear a paper bag over your head and with the NobleARF nobody will recognize you), you could, 1.remove the engine from the plane, 2.Remove the pressure tap from the crankcase, 3. replace the tap with a screw (conventional variety sans hole through the middle), 4. replace the engine in the NobleARF, 5. put on a 9 X 4 prop, 6. Richen the needle enough to compensate for suction delivery, 7. See if it runs OK in a configuration known to work for the commoners, 8. make future changes based on how it works in that condition.

Ted Fancher

P.S. for those unfamiliar with Mr Designman, those "smilies" mean this message is intended to be delivered with tongue firmly implanted in cheek!

p.p.s. Just for chuckles, try running the engine in the prescribed manner and seriously evaluate a shorter set of lines in terms of how well you fly the pattern (as opposed to how slow you can make your lap times ... a challenge for which there are no trophies).

Hint, hint, Larry

Happily, the black is actually a really dark brown, a color with which I am very familiar from running diseasled engines. I plan to try an extra head gasket and then lower nitro. If it is overcompressed, that may cure it. Any engine should be runnable on backplate pressure if you do it right. (I think...)

The next thing to try is a smaller hole in the pressure vent. Since the engine dies rich when I attempt to run it at less than ultimate maximum, I may be generating too much pressure in the tank.

I would think that if the engine was overstressed, it would die lean, especially in maneuvers. Instead, it just keeps churning on.

Where is Sir Dirt when you need him? As a combat flier, he must have a few ideas!

>Happily, the black is actually a really dark brown, a color
>with which I am very familiar from running diseasled
>engines. I plan to try an extra head gasket and then lower
>nitro. If it is overcompressed, that may cure it. Any
>engine should be runnable on backplate pressure if you do it
>right. (I think...)

Not if the pressure goes down as the rpm goes up. That would make it unstable, since as speed up, it would get leaner, and as it slowed down, it would get richer - which, curiously enough, is exactly what it's doing...

It doesn't leap out at me why running more overall power would make you need to reduce the compression, and in general, lowering the compression and/or reducing the nitro just makes it run hotter because you will need to run it leaner to get the same power.

Ad Inexplorata - or maybe terra incognita.
>I would think that if the engine was overstressed, it would
>die lean, especially in maneuvers. Instead, it just keeps
>churning on.

Not overlean, just overstressed. Hot may be caused by items other than too lean. It might be richer the stoichiometric, but still unable to get rid of the heat that is generated. ABC engines don't necessarily get leaner as they heat up.

I did tach the engine, it was turning about 11.5K on the 10x4 modified Zinger. Oddly, it takes quite a while (5 or so laps) to decide to go into the richen-up and die mode. Perhaps it is heating up on the ground, then cooling off in the air. Perhaps I'll try a flight with the cowl off. I have what looks like a big hole in the front, and more than double that behind the engine, but who knows.

On the ground, I can't get a stable rich two cycle, and not a prayer of a 4 cycle. It just won't run anything but dead lean without quitting. Very unusual. I could see it being unstable in the air or such, but this is VERY strange.

Hmm, could it need MORE nitro or a hotter plug to stay lit rich? Maybe I am looking at this backwards.

Ok, I know this is a stupid question to ask you, especially given your engine experiennce, but are you sure the engine is going rich in the air? The ABC/N engine can begin to sag when it overheats, and the rpm will drop. Sometimes it isn't completely obvious that the engine is overheating and sagging.

I will say that in the beginner pattern, I had no trouble with 10-4 props on a LA25. It was only when I tried the Intermediate pattern did I have trouble with sagging.

When it is dead lean, it will fly the pattern. It only dies if I go richer from there. Having it go lean from the richer position is just too wierd to handle! Plus, it is drooling fuel out of the venturi due to tank pressure when it lands.

To repeat, I can not get a stable rich run in the air or on the ground. I can get a stable lean run, but too lean when I hit the maneuvers.

The ABC/N engine can begin to sag
>when it overheats, and the rpm will drop. Sometimes it isn't
>completely obvious that the engine is overheating and
>sagging.

I think Alan is right! I had the same symptoms with an OS.32F, and it just didn't get ruined because of the 50%castor in the fuel.

No one has mentioned what fuel is being run in the OS 25FP. I made the mistake of grabbing the wrong fuel for mine, and it was awful! Poor needling and it would quit in the middle of a flight for no good reason.

I discovered I was using Fox 35 fuel with 28% castor! These things seem to run best with a mix of synth and castor, and not too much of either one.

The first flights were with 15% nitro, 18% oil Powermaster (synth/castor mix). I did try running it with 10% nitro 28% castor, and it didn't change.

Just out of curosity, how big is your pressure tap hole? Dia ?
Bigiron

It was my smallest drill, I think about .013 diameter.

One bad/good thing about running case or bladder pressure is that the engine will keep going even if lean, whereas it would die if it was on suction. Larry, are you running a one-way valve in the pressure line? Might help (or hurt). Also try a larger pressure hole. Sounds like you may not be getting enough pressure to the tank when the engine unloads in the air. Do not give up (as I did with the Fox 35)!

I do have a check valve in the pressure line, as that vent line doubles as the fuel filler. I guess it is time for some serious bench testing. A larger pressure hole is certainly easy to do compared to making a smaller one. BTW Jim, thanks a lot for the forward swept articles, I never saw those before! I love that glider!

Hmm, I could bring the pressure line outside the cowl and run it to the top vent hole, Pull it off for fueling, cap the filler line and re-attach the pressure line for flight.

Yup, definitely gonna do some bench work here, far better than fiddling around with it in the plane!

Does anyone know if the 25 fp and 25 LA use the same head gaskets?

I'm thinking that the Hayes tank might not seal well enough for CC pressure use. I recall that they have a plug in the front and two molded-in vent/fillers. It's been MANY years since I used crankcase pressure, but I seem to recognize those run characteristics as signs of leaks. To my way of thinking, a plastic tank is ok, if you limit pressure to muffler-type, which is about .25 psi, from memory. For sure, the tank is trying to expand from the pressure, and why the fuel continues to pour out the venturi for some time, after the engine quits. How big is this stock venturi? I'd rather run a Bruline black or even green filter and 20% nitro, on suction. Steve

Have you checked the right half plane thoroughly? I think you might discover a pole there.

>Have you checked the right half plane thoroughly? I think
>you might discover a pole there.

Is my recollection above correct? Does the pressure go down as the revs go up (on the 15)?

That's what I measured, both with a backplate tap and a "timed" tap on the other side of the crankshaft hole from the air intake.

>That's what I measured, both with a backplate tap and a
>"timed" tap on the other side of the crankshaft hole from
>the air intake.

Hence the poles in the right-half plane.

For what it is worth... Just some ideas, no real solutions

Working with the Cyclon 049 I've found that over compressed makes for a running combination that sounds very much like what you are seeing. Basically an insensitive needle on the ground that either seems to go from "it dies" rich to "sounds right" lean to "way over" lean with lots of turns on the needle but very little change between those three settings. Back the head off some or drop the nitro and things seem to get better.

You might try one of the Novel pressure fittings. They only have about an .008" hole. However, you will probably have to allow some time on the ground for the tank to "pump up" before setting the needle.

Since the engine is only turning roughly 12,000 rpm, you might want to try a check valve in the pressure line. Depending on how your tank is plumbed, you might be getting back flow through the pressure line so that you have a metering jet on one fuel source (the pressure tap) and an adjustable valve on the other fuel source. I've found that a check valve in the pressure line often helps. I've been using the reed valve one from Fourmost

http://www.fourmost.com/auto_plg.htm

a 9/4 is too much prop for the stock LA 25 if you are trying to run it at top rpm. They are much more tractable on an 8/4 using pressure fuel. It keeps running because OS has done such a good job selecting materials for the piston and liner, so it can take the abuse, at least for awhile. An iron piston motor would be toast in a couple of runs.

You need to open up the venturi and use a smaller prop so the needle valve can work. Then you can richen it up a bit. The LA 25 should be able to pull a Nobler at 80 mph or better.

I think Ted is right, why the backplate pressure?'

Just plug the hole, use *regular* muffler pressure and a uniflow adapted dubro or sullivan tank.

I never hd trouble with this setup.

God bless,

Ion, you are familiar with following the rhythm of the drummer. So does Larry, but not the same one.

Come to think of it, I won my first stunt trophy with a Fox of some sort on crankcase pressure. That was in 1961.

Well, maybe I'm listening to Elvin Jones and he's listening to Tony Williams...

God bless,

>Well, maybe I'm listening to Elvin Jones and he's listening
>to Tony Williams...
>
>God bless,
>
>Ion

I never heard of either one. Oh, well, as long as we are happy.

I never heard of either one either. I am more into Tom Lehrer, Flanders and Swan, and Anna Russel.

1. I am using a check valve
2. The engine is a FP not LA
3. It ran the 10x4 perfectly on suction with the venturi blocked down to .218 diameter
4. I have the Hayes 4 oz clunk tank (which, BTW only holds 3.5 oz) and it doesn't center on the needle.
5. Yes, I should have adequate power with a conventional setup, but I want to make this work, because I want to make it work!!! I REALLY hate it when there is something I don't understand.

>I never heard of either one either. I am more into Tom
>Lehrer, Flanders and Swan, and Anna Russel.
>
>1. I am using a check valve
>2. The engine is a FP not LA
>3. It ran the 10x4 perfectly on suction with the venturi
>blocked down to .218 diameter
>4. I have the Hayes 4 oz clunk tank (which, BTW only holds
>3.5 oz) and it doesn't center on the needle.
>5. Yes, I should have adequate power with a conventional
>setup, but I want to make this work, because I want to make
>it work!!! I REALLY hate it when there is something I don't
>understand.

It seems pretty well solved to me - if the pressure goes down as the rpm goes up (as Howard found was the case with the 15), you're sunk. And it would appear that the symptoms match this scenario to a tee. It does close to max out the RPM almost regardless of the needle setting, (if it runs at all) since it effectively sets itself (runs away lean until "too leaner" slows the motor and thus increases the pressure). Once again, the burning oil is a pretty good symptom that it's maxed out on temperature.

BTW, I would expect that a .218 venturi is *way* smaller than you could run on suction. It's about 50/50 whether it will run reliably with the stock .257 venturi and a 10-4. Experience suggests that a few hundred feet of density altitude makes a big difference. So it's right on the edge. Slightly smaller would make it a slam-dunk. .257 to .218 with a stock spraybar is almost a factor of 2 in terms of cross-sectional area. Somewhere in between would provide much more power and still be reliable, without the obvious problem with running crank pressure.

Or, go get some bladder tubing, and you can run any venturi you want.

The engine ran beautifully on the .218 venturi and muffler pressure with a uniflo tank. Totally controllable and reliable, plenty of power with the 10x4 on a Flite Streakarf.

That plane now sports a .19 size Indian Sharma diesel, driving a 10x5. On a 3.5 oz tank, I can do the pattern, unwind the lines, do another pattern, unwind the lines, practice a couple of more maneuvers and have laps left over.

Is there a possibility of overcooling combined with too much oil? Larry, what was the air temperature?

My OS 25FP's have given me good results with 5 to 10% nitro and 20% oil (50/50) on a profile, no muffler, uniflo suction, stock venturi, props 9-6, 9-7, or 10-4 --air temp 50 to 85F.

Below 50F, I get symptoms similar to yours. Then I try to get the engine up to operating temp by raising the methanol in the mix, by reducing both the nitro and castor content of the fuel. Seems to work, but by then both the air temp and fuel temp have warmed.

Observation at flying field: Befuddlement level is inversely proportional to air temperature.

Randy Bush

That's really cool. Good for you. I would look for a way to get the fuel flow to increase with RPM. I have been wondering how to do this for the B-17, which had the same problem. One notion is to squirt fuel directly into the crankcase and take advantage of the negative pressure gradient with RPM. That requires a higher pressure in the tank, though.

Please tell us what you come up with.

It just occured to me that Bill Atwood designed that side pressure tap into the Tee Dee and Medallion series engines. He must surely have known about backplate pressure, and that would have been easier to do. Somehow, I think he had a good reason to do it the way he did. I know that the engines where I used the side tap were perfectly docile, and the hole size wasn't all that important. Also, you didn't need a special, fine-thread needle valve!

Perhaps I'll buy a 25 LA to sacrifice to the cause and try a tap out the side of the case on it.

BTW, if you want to use that side tap on a C*x engine, take a 2x56 Tee nut, and grind the flange into a nipple shape. Thread that onto the existing nipple on the engine, and your fuel hose will stay on! If you are the nervous type, Goop adhesive is totally fuelproof and will guarantee a perfect seal.

>>Well, maybe I'm listening to Elvin Jones and he's listening
>>to Tony Williams...
>>
>>God bless,
>>
>>Ion
>
>I never heard of either one. Oh, well, as long as we are
>happy.

Elvin Jones was John Coltrane'a drummer, and Tony Williams was a "discovered" by Miles Davis.

You certainly heard about Miles Davis, the trumpet player.

Here are some links for John Coltrane and Miles Davis:

http://www.johncoltrane.com/automat/swf/main.htm

http://www.milesdavis.com/home.htm

God bless,