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Author Topic: What could be causing this engine to run slower on outside maneuvers?  (Read 3218 times)

Offline Charles Carter

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Listen and watch this Stalker 81RE engine run.  You will notice that above 45 degrees on outside maneuvers only the engine and the plane slow down.  Specifically the vertical figure eight maneuver is most troubling.    I have moved the engine away from the engine mounts because the fuel tank is already resting against engine bearers. I have repeatedly shimmed the engine ultimately as far as 5/8"  from the engine mounts.


Charles Carter



Online Ken Culbertson

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I have had a similar problem on an OS35s when the uniflow may have been too close to the pickup.  I don't know for sure if that was the problem because I swapped out the tank for a clunk.  I have always had better luck with the uniflow "Always out" of the fuel vs the "Always in" but that is just me and others will disagree.  All I am saying is that every time I have had funny things like this happen it has been a uniflow placement issue.

Good luck - Plane sure does fly nice.
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Offline Charles Carter

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Interesting!  At the time being there is a metal clunk tank in place but not a uniflow clunk tank.   Maybe I should try a making a new uniflow clunk tank.  Thanks Ken for your suggestion.

Charles

Offline GERALD WIMMER

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Hi Charles .Nice flight! I did notice that your inverted level laps were a bit faster then uprights ones before the loops, the motor sounding noticeably leaner inverted. By the time of the overheads the motor sounded labored and perhaps even lean as speeds up going back to level flight. Sorry I am not a top stunt guru and cannot offer any new answers, and only really but wish I could help more .  #^ #^
Regards Gerald

Online Ken Culbertson

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Interesting!  At the time being there is a metal clunk tank in place but not a uniflow clunk tank.   Maybe I should try a making a new uniflow clunk tank.  Thanks Ken for your suggestion.

Charles

Something in Gerald's post got me thinking.  How new is that engine?  The faster inverted laps is most likely a tank height issue but that 8, that is something else.  There are only three outside round maneuvers over 45 in the pattern and they are all near the end when your tank is at best half full and your engine is getting hot.  "Back in the day" I had similar problems with power overhead using both Fox 35's and years later with Max 35's.  Both were solved by some real engine people suggesting smaller venturi.   For whatever reason it helped me get the 4-2 kick whenever I went upstairs and let me run a bit richer the rest of the time.  Why yours is doing the opposite baffles me.  Now I am thinking it might be more the engine than the tank but,  adding uniflow is easy and can't hurt so it is worth a try.   Does it do it if you try a v-8 on a full tank?  How about the outside half of the overhead or third leg of the clover?

I hope some of the real engine guru's chime in, you fly too well to be hindered by engine problems.

Ken
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Offline jim gilmore

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let me ask some questions because that way i ca very what i am guess at.
1 engine is mounted inverted or not ?
2 you have shimmed the engine up away from the bearers and the centerline of the tank is where ever it was before moving the engine.
3 what happens if you leave the engine alone and move the tank up/away from the engine bearers ?
Not trying to sound like an idiot but just asking questions to verify that the intended movement is in the correct direction....by test and diagnosis.

Offline Charles Carter

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let me ask some questions because that way i ca very what i am guess at.
1 engine is mounted inverted or not ?
2 you have shimmed the engine up away from the bearers and the centerline of the tank is where ever it was before moving the engine.
3 what happens if you leave the engine alone and move the tank up/away from the engine bearers ?
Not trying to sound like an idiot but just asking questions to verify that the intended movement is in the correct direction....by test and diagnosis.

1 inverted engine
2 correct
3 I suspected it would run even richer if I did that so I never though to shim tank further away from the engine bearers.

Offline Brett Buck

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Listen and watch this Stalker 81RE engine run.  You will notice that above 45 degrees on outside maneuvers only the engine and the plane slow down.  Specifically the vertical figure eight maneuver is most troubling.    I have moved the engine away from the engine mounts because the fuel tank is already resting against engine bearers. I have repeatedly shimmed the engine ultimately as far as 5/8"  from the engine mounts.

   That's backwards from the usual schneurle issue, but I assume it is not a schneurle. If it seems to defy any attempt to fix it (and the obvious is shimming the tank), the only likely path of improvement is to spin it fast, to get higher velocity flow, and maybe cut down on the effects of acceleration. I expect you are using 6" of pitch, might try 5.5 and a leaner needle. Since it's an 81, should have no problem with getting enough poop to do it. That probably won't completely fix it, but it might make it more managable, and you will get better wind performance.

     Brett

Offline Randy Cuberly

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I'm not sure this will help but I will mention it.
The instruction with my new Stalker ST66 RE mentioned the possibility of such a problem, where the tank was against the engine bearers and the engine was shimmed away from them but outside loops still resulted in a rich condition.

The suggested fix was to remove the spray bar and needle valve and drill the single hole in the spray bar through the opposite side with the same size hole as in the first side, resulting in a double hole spray bar.  Replace the assembly in the venturi with both holes diametrically opposite each other directly across from the center of the cylinder formed by the venturi.  According to the direction this results in an approximately .080 inch lower flow of fuel into the engine and will correct the problem.

Again this is in the instructions and I can't personally speak to it's validity.  I would be happy to send you a copy of the instructions if you wish!

I personally doubt that the addition of uniflo will correct this problem in itself.  However the addition of a uniflo tank with an adjustable height uniflo pick up (inside the tank) can be used to effectively change the fuel pressure head and accomplish the same thing as moving the entire tank.  There is a limit of course!

Randy Cuberly
Randy Cuberly
Tucson, AZ

Online Ken Culbertson

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I'm not sure this will help but I will mention it.
The instruction with my new Stalker ST66 RE mentioned the possibility of such a problem, where the tank was against the engine bearers and the engine was shimmed away from them but outside loops still resulted in a rich condition.

The suggested fix was to remove the spray bar and needle valve and drill the single hole in the spray bar through the opposite side with the same size hole as in the first side, resulting in a double hole spray bar.  Replace the assembly in the venturi with both holes diametrically opposite each other directly across from the center of the cylinder formed by the venturi.  According to the direction this results in an approximately .080 inch lower flow of fuel into the engine and will correct the problem.

Again this is in the instructions and I can't personally speak to it's validity.  I would be happy to send you a copy of the instructions if you wish!

I personally doubt that the addition of uniflo will correct this problem in itself.  However the addition of a uniflo tank with an adjustable height uniflo pick up (inside the tank) can be used to effectively change the fuel pressure head and accomplish the same thing as moving the entire tank.  There is a limit of course!

Randy Cuberly

If Stalker is recommending this then it may be the solution but make sure that their solution is not for the generic going rich on outside (negative "G") all the time.  If I had my way I would mount all of my engines "profile".  Relative to internal fuel flow, the engine is in roughly the position upright and inverted.  If you are going to drill the spraybar, please do it on a spare!  If you have the background and a good press then please disregard this - as a former machinist I can tell you that it is nearly impossible to drill through a pipe without special equipment and not enlarge the original hole.  :X

The more I think about it though the more this might make sense. :!  The one factor that is unique in the 8 is the rapid shift from positive to negative "G" forces on the fuel.  This may cause the engine to respond differently when it is hot and the tank is lower on fuel that it does with the engine fresh and a full tank and then I might be just be thinking too much! y1

Good luck - Ken
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Offline Al Ferraro

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   That's backwards from the usual schneurle issue, but I assume it is not a schneurle. 

     Brett
  I agree, my LA 46 breaks into a light two stroke where Charles is having a problem in the vertical eights. I don't know that engine, but if it has a baffle on the top like a Fox 35, then it's probably loading up with fuel, sort of like the Fox burp. The list of things that would help, hot glow plug, less oil in fuel, more RPM (less pitch on prop), open up the exhaust (two restrictive), smaller by pass in the case improving airflow (popsicle stick).
  Charles I personally don't think it is the tank, could you list all the details of your set up ?
Al

Offline Brett Buck

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The suggested fix was to remove the spray bar and needle valve and drill the single hole in the spray bar through the opposite side with the same size hole as in the first side, resulting in a double hole spray bar.  Replace the assembly in the venturi with both holes diametrically opposite each other directly across from the center of the cylinder formed by the venturi.  According to the direction this results in an approximately .080 inch lower flow of fuel into the engine and will correct the problem.

   Or, alternately, it reduces the restriction in the fuel flow and/or creates better atomization. I wouldn't have expect this to matter compared to engines like the PA75 that run large amounts of fuel, but maybe. The problem sounds like it is just for a brief moment at the transition from inside to outside, which is the sort of condition where reducing the fuel flow restriction is going to matter.

     Brett

Offline Balsa Butcher

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To add to what's already been said: The instructions referred to suggest that if the airplane is not new the tank be shimmed 3/32" off the motor mounts. Allegedly this will do the same thing as drilling the case at the expense of a little spinner mis-alignment. As this is an ARF, I'd go that route rather than taking a drill to a $350 plus engine. Worth a try.  8)
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Online Ken Culbertson

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  I agree, my LA 46 breaks into a light two stroke where Charles is having a problem in the vertical eights. I don't know that engine, but if it has a baffle on the top like a Fox 35, then it's probably loading up with fuel, sort of like the Fox burp. The list of things that would help, hot glow plug, less oil in fuel, more RPM (less pitch on prop), open up the exhaust (two restrictive), smaller by pass in the case improving airflow (popsicle stick).
  Charles I personally don't think it is the tank, could you list all the details of your set up ?
Al

Just to confirm, both my OS35s and my LA 46 also break to a "light" 2 at that transition.   I am starting to lean towards Brett's first reaction that this may just be something you learn to live with.  It may be something inherent in the engine design and the 2nd hole in the spraybar solution offered by the MFG tells me it just may be.  I am not sure that adding that hole to fix the one issue might create two new ones.  Not a big fan of trying to make engines better.  I had a Fox35 blueprinted by Duke Fox himself in 1964 and it still burped.  I learned to love the burp.
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Offline Brett Buck

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Just to confirm, both my OS35s and my LA 46 also break to a "light" 2 at that transition.   I am starting to lean towards Brett's first reaction that this may just be something you learn to live with.  It may be something inherent in the engine design and the 2nd hole in the spraybar solution offered by the MFG tells me it just may be.  I am not sure that adding that hole to fix the one issue might create two new ones.  Not a big fan of trying to make engines better.  I had a Fox35 blueprinted by Duke Fox himself in 1964 and it still burped.  I learned to love the burp.

   The burp is a severe defect compared to what Charles is having, fortunately, this was conclusively solved in about 1995 - Fox bypass stuffer. Everything else is just rearranging deck chairs on the Titanic.

    I think a variant on this for Charles is speeding up the engine, but that sort of issue (usually lean, not rich - and it might actually be going lean but not going into a 2-stroke here), specifically, very brief apparent mixture shifts at odd spots, has sometimes been traced to fuel flow restriction somewhere in the system. Very large engines seem to be more prone to this problem, and they don't get a lot bigger than an 81 (although there is or was such a thing as a Jett 88 at one point, I think). I would probably try fuel with either less or thinner oil, and make sure all of the plumbing is as unrestrictive as it can be before resorting to drilling holes. Make sure you can get replacements before you drill anything, since the likely outcome is having to replace the parts that were "improved".

  I wouldn't entirely dismiss the extra spraybar hole (although the explanation doesn't make much sense) but usually it's restrictions before the metering point that matter, not after.

  Note that this sort of thing is *exactly* what Lauri Mallia is referring to in the other posts, and this might be directly analogous, since I think this is a baffle-piston engine instead of a schneurle.

    Brett

Online Ken Culbertson

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   The burp is a severe defect compared to what Charles is having, fortunately, this was conclusively solved in about 1995 - Fox bypass stuffer. Everything else is just rearranging deck chairs on the Titanic.

    I think a variant on this for Charles is speeding up the engine, but that sort of issue (usually lean, not rich - and it might actually be going lean but not going into a 2-stroke here), specifically, very brief apparent mixture shifts at odd spots, has sometimes been traced to fuel flow restriction somewhere in the system. Very large engines seem to be more prone to this problem, and they don't get a lot bigger than an 81 (although there is or was such a thing as a Jett 88 at one point, I think). I would probably try fuel with either less or thinner oil, and make sure all of the plumbing is as unrestrictive as it can be before resorting to drilling holes. Make sure you can get replacements before you drill anything, since the likely outcome is having to replace the parts that were "improved".

  I wouldn't entirely dismiss the extra spraybar hole (although the explanation doesn't make much sense) but usually it's restrictions before the metering point that matter, not after.

  Note that this sort of thing is *exactly* what Lauri Mallia is referring to in the other posts, and this might be directly analogous, since I think this is a baffle-piston engine instead of a schneurle.

    Brett

Brett - wouldn't adding the extra spray bar hole affect the rest of the run as well?  What has me focused on this problem is that it seems to only happen at a part of the pattern that is unique.  I would think that if there was a fuel restriction it would be more random but nothing is lost by making sure you don't have one.  Same with the tank location.  Moving it around should affect a lot of things in pattern and if you get it right for this one it will probably be wrong for someplace else.  I don't think we are changing the right variables to find out what it is.  What is different about that point in the pattern from other outsides?  #1 the engine is hotter, #2 the tank is at least 1/2 empty, #3 it is the only place the plane is going from heavy positive g's to heavy negative g's with the wings level .  My first test would to be to test #1 and #2 by changing #3.  When you get to the V-8 level off inverted at 45 after the inside then fly the rest of the lap inverted at 45 then do the outside.  Knowing exactly where it went "fat" might tell us something.  Now try the same thing with a full tank and fresh engine a couple laps after takeoff.  Having the results of that test should tell us where the problem is and that is where my expertise ends and Brett will tell you how to fix it.

Back to one of your observations that may be the cause.  Why does a fuel restriction have to be something physical?  Why can it not be a sudden change in fuel head pressure that only occurs when the plane is subjected to rapid shifts in g forces at a certain attitude?  At first I sort of chuckled at the going lean without 2 stroke but after replaying the video it does sort of make that sound.  McCoy's used to do that when they got hot.   There is a small chance that Uniflow could impact that...or not.


FYI - I didn't really like the Fox Burp, just lived with it.  Glad they go it fixed.  #^
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Offline Steve Helmick

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1) I can't see any reason to NOT use a uniflow tank, but remember that you can simply raise the wedge in the tank when you build it (asymmetric).
2) Seems to me that Stalker uses a 4mm spraybar, so one can use a Randy Aero NV Assy., which I would recommend anyway.
3) I'm interested in the details, venturi size, fuel, glowplug, fuel burn.
4) Seems like a hotter glowplug might help, along with lower pitch & more rpm.
5) I'm a fan of burning more fuel, which results in more oil flow through the engine.
6) I have a Stalker .76, and got an email from Norm Whittle that he had some run problems and bored the venturi to .330" and fixed it. I would also look at running a wee bit of nitro. He had been burning about 4 oz of no-nitro, so probably increased consumption by 1/2 oz or so.
7) Is your .81 the large crank or small crank? I read that folks with the small crank .76 and .81 can send them in to get refitted with new big crank and bearings. I'd like to know about how to go about that, $, etc.
8) Gordan Delaney has run the Stalker .81 a lot in his Tony, and I'd bet he can help!  y1 Steve


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Offline Charles Carter

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Something in Gerald's post got me thinking.  How new is that engine?  The faster inverted laps is most likely a tank height issue but that 8, that is something else.  There are only three outside round maneuvers over 45 in the pattern and they are all near the end when your tank is at best half full and your engine is getting hot.  "Back in the day" I had similar problems with power overhead using both Fox 35's and years later with Max 35's.  Both were solved by some real engine people suggesting smaller venturi.   For whatever reason it helped me get the 4-2 kick whenever I went upstairs and let me run a bit richer the rest of the time.  Why yours is doing the opposite baffles me.  Now I am thinking it might be more the engine than the tank but,  adding uniflow is easy and can't hurt so it is worth a try.   Does it do it if you try a v-8 on a full tank?  How about the outside half of the overhead or third leg of the clover?

I hope some of the real engine guru's chime in, you fly too well to be hindered by engine problems.

Ken

To answer your question regarding doing a V-8 on a full tank yes it does then also If I remember correctly because it has been awhile.  On the other maneuvers like outside half of the overhead yes but during  the third leg of the clover it isn't noticeable for what I suspect is after the vertical climb it is going down hill.

I am going to try a smaller venturi.

Charles

Offline Charles Carter

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Hi Charles .Nice flight! I did notice that your inverted level laps were a bit faster then uprights ones before the loops, the motor sounding noticeably leaner inverted. By the time of the overheads the motor sounded labored and perhaps even lean as speeds up going back to level flight. Sorry I am not a top stunt guru and cannot offer any new answers, and only really but wish I could help more .  #^ #^
Regards Gerald

Good observation Gerald the engine is a little leaner on inverted flight as a result me tying to fix the problem.   But it didn't make difference.  Thanks

Charles

Offline Charles Carter

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   That's backwards from the usual schneurle issue, but I assume it is not a schneurle. If it seems to defy any attempt to fix it (and the obvious is shimming the tank), the only likely path of improvement is to spin it fast, to get higher velocity flow, and maybe cut down on the effects of acceleration. I expect you are using 6" of pitch, might try 5.5 and a leaner needle. Since it's an 81, should have no problem with getting enough poop to do it. That probably won't completely fix it, but it might make it more managable, and you will get better wind performance.

     Brett

I have switched to a 2 blade 5.5" pitch from a 3 blade prop which had more pitch before and it didn't fix it.  Should I try even a lessor pitch prop?

Charles

Offline Charles Carter

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I'm not sure this will help but I will mention it.
The instruction with my new Stalker ST66 RE mentioned the possibility of such a problem, where the tank was against the engine bearers and the engine was shimmed away from them but outside loops still resulted in a rich condition.

The suggested fix was to remove the spray bar and needle valve and drill the single hole in the spray bar through the opposite side with the same size hole as in the first side, resulting in a double hole spray bar.  Replace the assembly in the venturi with both holes diametrically opposite each other directly across from the center of the cylinder formed by the venturi.  According to the direction this results in an approximately .080 inch lower flow of fuel into the engine and will correct the problem.

Again this is in the instructions and I can't personally speak to it's validity.  I would be happy to send you a copy of the instructions if you wish!

I personally doubt that the addition of uniflo will correct this problem in itself.  However the addition of a uniflo tank with an adjustable height uniflo pick up (inside the tank) can be used to effectively change the fuel pressure head and accomplish the same thing as moving the entire tank.  There is a limit of course!

Randy Cuberly


I already drilled thru the needle valve with no fix.  It might have had the same effect as moving the tank closer to engine bearers but it I did't notice any.    I met you at the SW Regionals this year.  This engine problem was a real problem for me in Az with the thinner air there.  Thanks.

Charles

Online Dennis Toth

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Charles,
One quick thing is to check that the plug is tight and not leaking once the engine is warmed up. The copper washers compress over time and need to be snugged up every now and then. You indicated that the tank is a clunk but not uniflow. It has been my experience that after you rule out the usual suspects plug, fuel, air leaks (around glow plug, back plate, head or NVA) it is the tank. If I had this problem I would replace the tank with a full uniflow, hard tube no more that 1 1/8" thick and 2" wide. I would start with open uniflow with the vent line mounted on the fuse inboard side facing directly into the airstream. If this doesn't fix if try muffler pressure.

Best,   DennisT

Online Lauri Malila

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At least in level flight the engine sounds far too rich.
I’d try a smaller and lighter prop and a hotter plug if possible.
Also, what fuel you use and at what compression ratio?
100% sure that fiddling with needle valve is not going to solve the problem.
One thin that may help a little is a longer venturi, or shielding it completely inside cowling.
Propably you’ll reduce the problem to a tolerable level with these tricks but you won’t get completely rid of it. L

Online Lauri Malila

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If tank is not Uniflow, where is the end of air inlet?

Offline FLOYD CARTER

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Right here, right now, is the first time I have heard of the Stalker running rich inverted.  Is that a problem only with that size Stalker?

I have two Stalker 51 engines.  Both inverted mounting with a metal rectangular, Uni-flow, 1" high tank.  Both engine and tank mounted right on the rails.  I treated this engine just like dozens of other engine/plane combinations I have done.  I use low pitch props, 10-10-10 SIG fuel, and OS #8 glo pug.

I set for a "wet" 2-cycle.  Both engines run at constant RPM, regardless of attitude.

So.  What am I doing wrong?

(One of my Stalker planes, the "TIBURON" took a 1st in Adv. at a recent Fall Follies in Salem.  That would not be possible if the run was not perfect.)
89 years, but still going (sort of)
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Offline Dave Sabon

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Although I rarely post here I have some intimate knowledge about this particular motor I’d like to share.  The saga actually begins some years ago during the 4 Strokes are the best thing ever era.  Bob Brooks built a Gordan Delaney Tony and fitted it with a 4 Stroke motor (don’t remember which one or the size but it was the same as what Gordy was using at the time).  Although when everything was going well the motor ran nicely.  Bob however got frustrated with several internal issues that the motor had that caused the motor to quit unexpectedly.  These issues were repaired both times by the factory (same issue both times).  When the same thing happened a third time he was done.  Again, I don’t remember the details of the motor or what exactly went wrong but I think it had to do with the rocker arms or something.  Anyway, when Bob said he was done with the 4 stroke, he contacted Gordy who said he had moved to the Stalker 81.  With that, Bob bought a brand new one from a distributor who I think was in Canada (anyway, it was not Tom Dixon).  Bob got the motor broke it in and set it up as per instructions from Gordy (same prop, fuel etc.).  As I recall there wasn’t a lot of written info that came with the motor itself.  After the break in, Bob put it in the Tony and right off the bat had the same going rich in outside maneuvers issue that Charles is experiencing now.  Gordy suggested that he move the uniflow tube to solve this issue.  That tube was moved numerous times (in both directions – up from where it started and down from where it started) with no changes in the run.  I don’t recall all of the things we tried but nothing really worked.  Unfortunately, due to pilot error that plane was lost.

Bob then built a P40 that was based on the Delaney Tony numbers.  As an aside, it really is amazing how close in scale those two planes are.  Anyway, during the building process Bob did 2 things.  First, he redesigned the tank compartment of the P40 to accept a more standard shaped tank.  Second, he built the nose so it could accept either the Stalker 81 or my RO-Jett 76 without having to change the spinner etc.  When Bob finished the P40 he asked me to do the test flights and get the plane trimmed to fly.  We started with the Stalker and again right from the git go we had the same problem and virtually nothing we did fixed it. Ultimately, this is what fixed the problem… he pulled the Stalker put it back in the box replaced it with the RO-Jett and all run issues went away. The plane trimmed out very easily and its now basically flip & fly.


Charles in the recent past asked Bob if he could have that motor and although I have no clue about the details of that transaction, I do know that Bob repeated his concern over putting that motor in a plane and the seemingly unsolvable issue that he had.  Charles wanted to give the motor a try in his Strega.   Although he’s more tenacious about trying to fix this issue than either Bob or I could ever be, and he has tried things that did not occur to either of us, the result is that the motor only runs slightly better than what we achieved.  It’s just not right (the motor I mean)

Interestingly, in the past year and a half or so Bob spent an extended period of time in Tel Aviv Israel.  By extended, I mean longer than 6 months. During that time he found a CL club and went to a contest just to watch.  He met a guy from Europe that was running the Stalker 81 and having excellent runs with it.  Bob told the guy of his problems and this gentlemen said that he had exactly the same problems with his motor and was very frustrated.  Here's how he solved it …He went to a contest in the Ukraine (I think) and there was a local guy there running a Stalker 81 and was having great success.  He asked the Ukrainian gentleman if he could buy the motor. A deal was made and the motor put in the plane that Bob saw flying in Tel Aviv.

My theory is this – Something is just wrong with Charles’ motor. I don’t believe that its anything Bob or Charles has done.  I just think it’s a lemon.   I know it’s only anecdotal but two people on opposite sides of the earth having the same issue with the same motor and its fixed it by replacing the problem motor.

Regards,
Dave Sabon

Offline Brett Buck

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I have switched to a 2 blade 5.5" pitch from a 3 blade prop which had more pitch before and it didn't fix it.  Should I try even a lessor pitch prop?

  I am on the same page as Lauri, and there's at least a chance to get it better by running lower pitch. Normal stunt engines in the US have run something around 4" of pitch for about 30 years now.

   Dave may well be right, this particular combination of baffle and liner may just not be quite right just due to tolerance stackup, and there isn't a lot of experience with these sorts of engines here to say otherwise.

     Brett

Offline Steve Helmick

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Was wondering if Lauri might suggest something like adding a glowplug shield to the cylinder head? I'm not sure if adding a shield would do the same thing as just changing to a hotter glowplug or not? I would absolutely try a 4-cycle glowplug, but maybe depending on fuel used.

I recall somebody showed how they did it with a hole drilled through the cylinder head (fore & aft) for a pin with flats milled in it to form a flat blade. The pin was trapped by the cylinder bore, so it couldn't come adrift, and pressed into the head so it couldn't rotate...tho I have also wondered if indexing the "blade" differently might be a way to tune the rich/lean stuff. A "button head" would be useful for experimenting with this sort of thing, except for the baffled piston (yes, it is baffled). But the "button" would also be pinned to the head shell, like the Fox .35 Hemi kit head.  D>K Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

Online Lauri Malila

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It's one of them things that can relieve pain but not give complete cure. Like aspirin.
But certainly worth trying, L

Offline Al Ferraro

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  The first thing I would do is change the tank to uniflow from the pressure setup he is using. You can here the engine go rich and see a smoke trail when he starts the outside loop in the vertical eights, but when he does the hour glass at that intersection the engine seems to run cleaner. The uniflow tank should run leaner when he is going vertical over his currant setup. The best plug I found when running a deep 4 stroke is a Sig idle bar, I tried other recommended plugs that did not work as well. Too much or wrong oil in the fuel would add too his problem when his engine is under a heavy load in a climb. I also notice in the video that the engine is pretty quiet and probably the exhaust is to restrictive, and I would not put a smaller venturi in it.
Al
« Last Edit: May 11, 2018, 05:38:11 AM by Al Ferraro »

Online Lauri Malila

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I recall somebody showed how they did it with a hole drilled through the cylinder head (fore & aft) for a pin with flats milled in it to form a flat blade. The pin was trapped by the cylinder bore, so it couldn't come adrift, and pressed into the head so it couldn't rotate...tho I have also wondered if indexing the "blade" differently might be a way to tune the rich/lean stuff. A "button head" would be useful for experimenting with this sort of thing, except for the baffled piston (yes, it is baffled). But the "button" would also be pinned to the head shell, like the Fox .35 Hemi kit head.  D>K Steve

Steve,

That Would be The master machinist Brian Turner in UK, with his .60 stunt engine. Except that the shield pin was not in fore-aft direction but sideways.
Anyway, I see what you are pondering about creating an asymmetry to compensate running asymmetry but I can guarantee that it does not go like that. I have flown with my heavily asymmetric heads tilted to weird positions, usually by accident but also out of curiosity. Whatever way you make it asymmetric, the result is allways worse.
And to make it even more clear, I have run the engine with heavily asymmetric scavenging, by blocking half of ports on either side of cylinder. The asymmetry only gets worse to same direction, unless I change running direction.
The reason is that there is no asymmetric gasflow that causes the problem, just the fact that engine is operated at too steep part of its power curve, or the engine is sick and peak of power curve is too narrow. When engine is loaded, it goes closer to peak, and when it's unloaded it falls downhill, further from peak. Ideally this kind of engines should produce just enough power so that they reach the top of power curve at top of maneuvre, and not go over it. That is the only way to stop them from accelerating in wind. If you want more grunt and some sort of stability at richer setting, you will need a tuned pipe to limit maximum rpm.

Lauri

Online Ken Culbertson

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Well Charles, if this has not been enough to convince you to never ask another question, nothing will!  I think it is fantastic that we can get access to so much expertise so quickly.  Can you imagine where Stunt would be today if we had this in the 60's?  I sincerely hope one of these suggestions works but I really think you may have a lemon. :-[
AMA 15382
If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline Steve Helmick

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To add to what's already been said: The instructions referred to suggest that if the airplane is not new the tank be shimmed 3/32" off the motor mounts. Allegedly this will do the same thing as drilling the case at the expense of a little spinner mis-alignment. As this is an ARF, I'd go that route rather than taking a drill to a $350 plus engine. Worth a try.  8)

As I read it, the suggestion from Stalker was to drill through the second wall of the spraybar, NOT modify the crankcase. If the Stalkers use 4mm spraybars, which I'm pretty sure they do, it is right close to .157" diameter. At least, my DS .60bb has one, instead of the tiny banjo fitting setup it came with. But if the spraybar is trashed by the modification, it's under $20 for a Randy Aero NV Assy. to replace it with. Another thought tho, this reminded me that GMA drilled the 2 Star .40 spraybar hole to .055", to allow more flow for nitro fuel. Since Charles has gone incommunicado on us and we still don't know what his fuel mix is, I guess we'll remain puzzled. Figuring out what will fix it or did fix it would be nice, so I hope he checks back sometime soon.   D>K  Steve
"The United States has become a place where professional athletes and entertainers are mistaken for people of importance." - Robert Heinlein

In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.  In 2015 18-20 year old's need safe zones so people don't hurt their feelings.


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