OS Gemini Twin Rear Walbro Gas Conversion
08-03-2022, 03:09 AM
#151
Ah, yes, I forgot the imbalance.... If I have time, I'll post a pic this evening of what I did to cure that. No idea if it is usable for you, but it's just a thought and fairly easy to execute, also easy to remove if it does not work or adapt to finetune if it does.
08-03-2022, 07:01 AM
#152
Because if it is black and opaque, it means it is polluted, and then you recirculate it to pollute it some more.
08-05-2022, 10:17 AM
#154
As you perhaps know, the ASP has a fairly standard glow carb with lateral moving throttle barrel, as opposed to the OS Gemini, which has a carb where the throttle barrel stays put when opened or closed.
Most likely the OS designers knew what ASP did not or was too cheap to do something about: At low throttle, the opening is slightly offset to the right (when viewing from behind the prop) and that is where I suspect the asymetry in fuel distribution is caused.
I placed a slightly offset and very tiny "scoop" made from an oblique cut piece of 1/8" alu tubing, it protrudes also about 1/8th, or maybe a bit less, into the central intake directly behind the carb, I just drilled a hole, epoxied in the piece of tubing and plugged the tubing also with a blob of Epoxy,
It forms an obstruction that directs any liquid coming from the carb more towards the center of the induction passage.
I overshot a bit, because after this, the left cylinder was favoured a bit more, and now is the "fattest" cylinder, although the differens is much smaller than what it originally was.
At anything above 3500~4000 RPM both cylinders run more or less equally rich and fat, only at low settings there is still this difference. Not perfect, but much better than it was, and if necessary, it can be tweaked.
I have no idea if you can use this exact same idea, but maybe it resonates somehow with your own thought-experiments.
Mind you: the scoop is placed in the T-connector where the intake branches off to each cylinder, this is NOT the carb.
Most likely the OS designers knew what ASP did not or was too cheap to do something about: At low throttle, the opening is slightly offset to the right (when viewing from behind the prop) and that is where I suspect the asymetry in fuel distribution is caused.
I placed a slightly offset and very tiny "scoop" made from an oblique cut piece of 1/8" alu tubing, it protrudes also about 1/8th, or maybe a bit less, into the central intake directly behind the carb, I just drilled a hole, epoxied in the piece of tubing and plugged the tubing also with a blob of Epoxy,
It forms an obstruction that directs any liquid coming from the carb more towards the center of the induction passage.
I overshot a bit, because after this, the left cylinder was favoured a bit more, and now is the "fattest" cylinder, although the differens is much smaller than what it originally was.
At anything above 3500~4000 RPM both cylinders run more or less equally rich and fat, only at low settings there is still this difference. Not perfect, but much better than it was, and if necessary, it can be tweaked.
I have no idea if you can use this exact same idea, but maybe it resonates somehow with your own thought-experiments.
Mind you: the scoop is placed in the T-connector where the intake branches off to each cylinder, this is NOT the carb.
Last edited by 1967brutus; 08-05-2022 at 10:31 AM.
08-05-2022, 10:39 AM
#155
In the radial (also an ASP) I solved the issue with the unequal distribution in a slightly different way, in that there the carb is attached to the distributor via a single 90 degree knuckle,
Here the issue is that in the 90 degree corner, the air can follow the path of the knuckle, but the liquids carried with that air fly on straight through and collide with the opposite side of the passage, then flow along the wall and do not enter the distributor "centered".
So here I drilled three tiny holes that are so small that they do not noticably affect throttleability or fuel draw, but what they do is form 3 tiny airjets that re-atomize the fuel back into the airflow.
More or less the same working principle, but executed differently.
FWIW: I do not think these methods are interchangable, I don't think the scoop would have worked with the radial, and I also don't think the airjets would have worked for the twin, but perhaps in your set-up, which is noticably different than mine, the airjets might find a place. Not in anyway meant as "this is how you do it", much more as "here are some ideas outside the box"...
Here the issue is that in the 90 degree corner, the air can follow the path of the knuckle, but the liquids carried with that air fly on straight through and collide with the opposite side of the passage, then flow along the wall and do not enter the distributor "centered".
So here I drilled three tiny holes that are so small that they do not noticably affect throttleability or fuel draw, but what they do is form 3 tiny airjets that re-atomize the fuel back into the airflow.
More or less the same working principle, but executed differently.
FWIW: I do not think these methods are interchangable, I don't think the scoop would have worked with the radial, and I also don't think the airjets would have worked for the twin, but perhaps in your set-up, which is noticably different than mine, the airjets might find a place. Not in anyway meant as "this is how you do it", much more as "here are some ideas outside the box"...
08-06-2022, 01:16 AM
#156
This is interesting - thanks for posting. I've always suspected the imbalance in my Gemini comes from different length/shaped intake tubes - but who knows!
So you are introducing fresh air into the intake tract after the carburetor? You must've had to richen your mixture quite a bit.
I had thought of putting an adjustable air bleed on the intake pipe of the rich cylinder but that really would be a last resort. I'm going out to fly the Rascal this morning with the iridiums. If the left one doesn't foul all of this will be moot (fingers crossed).
So you are introducing fresh air into the intake tract after the carburetor? You must've had to richen your mixture quite a bit.
I had thought of putting an adjustable air bleed on the intake pipe of the rich cylinder but that really would be a last resort. I'm going out to fly the Rascal this morning with the iridiums. If the left one doesn't foul all of this will be moot (fingers crossed).
08-06-2022, 08:53 AM
#157
Well I did fly a bunch this morning with the iridium plugs and it did oil foul on me. Wouldn’t start and run up the second flight. So I cleared the plugs (it was mostly the right one this time). I also disconnected the crankcase rebreather. I got three more flights after that without a problem.
Bye-bye rebreather!
Bye-bye rebreather!
08-06-2022, 09:17 AM
#158
I would imagine with crankcase oil drops happening at regular intervals rather than continuously, introducing it into the intake drop by drop would cause the engine to go oil rich every time a drop is introduced. Seems like that would be difficult to tune the mixture for a happy engine all the time.
08-06-2022, 09:52 AM
#159
This is interesting - thanks for posting. I've always suspected the imbalance in my Gemini comes from different length/shaped intake tubes - but who knows!
So you are introducing fresh air into the intake tract after the carburetor? You must've had to richen your mixture quite a bit.
I had thought of putting an adjustable air bleed on the intake pipe of the rich cylinder but that really would be a last resort. I'm going out to fly the Rascal this morning with the iridiums. If the left one doesn't foul all of this will be moot (fingers crossed).
So you are introducing fresh air into the intake tract after the carburetor? You must've had to richen your mixture quite a bit.
I had thought of putting an adjustable air bleed on the intake pipe of the rich cylinder but that really would be a last resort. I'm going out to fly the Rascal this morning with the iridiums. If the left one doesn't foul all of this will be moot (fingers crossed).
Before:
After:
The differences are not so much audible (but if you play the vids side by side, there is a few hundred RPM more in the 2nd vid and the throttle response is slightly better), but VERY clearly visible on the temeletry (I have 5 separate cyl temperature readouts, an average temperature, and for each cylinder the deviation from average, and with that info and a trendlog, differences are extremely visible
).I believe the gain in RPM results from 5 cylinders all runing the same (optimal) mixture, instead of 2 cylinders running too rich and 3 cylinders slighly on the lean side but each one on a different mixture.
The Boxer, that is NOT an airjet. No hole, it is plugged off, it is just the piece of tubing sticking out and forming an obstruction, creating a bit of turbulence and deflecting the fuel/oil droplets a bit towards the middle of the T-branch in order to correct the imbalance.
On the underlined: I would not do that, because the airbleed is static while the throttle is moving, making the imbalance shift as a function of throttle movement. Personally, I strive to find a solution that is such that it remains the same regardless of throttle position. With that deflector I did not 100% succeed in that, but it is way better than the standard set-up.
Last edited by 1967brutus; 08-07-2022 at 12:42 AM.
08-06-2022, 10:01 AM
#160
Well I did fly a bunch this morning with the iridium plugs and it did oil foul on me. Wouldn’t start and run up the second flight. So I cleared the plugs (it was mostly the right one this time). I also disconnected the crankcase rebreather. I got three more flights after that without a problem.
Bye-bye rebreather!
Bye-bye rebreather!
(sorry, just pulling your leg a little, Mitch)Just happy to see you solved this, and I am fairly sure you will have good results with the standard plugs now as well, so what's not to like?
Now, I am sure given your metal working skills, you will out-do my hideously ugly valve lube system with some beautifully crafted piping arrangements
(please do so I can in return copy that design...)
Last edited by 1967brutus; 08-06-2022 at 10:23 AM.
08-06-2022, 10:04 AM
#161
I would imagine with crankcase oil drops happening at regular intervals rather than continuously, introducing it into the intake drop by drop would cause the engine to go oil rich every time a drop is introduced. Seems like that would be difficult to tune the mixture for a happy engine all the time.
However, AA5BY on RCGroups introduces his "rebreather" in the velocity stack upstream of the carb, and that appears to work fairly well, at least, he does not report any issues with it. Maybe it also has to do with HOW and WHERE the rebreathing is introduced in the intake. Would not surprise me.
08-06-2022, 11:03 AM
#162
Well I did fly a bunch this morning with the iridium plugs and it did oil foul on me. Wouldn’t start and run up the second flight. So I cleared the plugs (it was mostly the right one this time). I also disconnected the crankcase rebreather. I got three more flights after that without a problem.
Bye-bye rebreather!
Bye-bye rebreather!
Just curious what the possible difference might be.
08-07-2022, 02:34 AM
#163
What I would find interesting, is if you would have a peak RPM reading with, and without the rebreather. I would expect the RPM to rise by about 100 to 200 RPM, since the rebreather introduces not only oil (which should not make a difference wrt RPM), but also exhaust gas (piston ring blow by) which should displace some of the inducted air. More fresh air=more bang per revolution=more power.
Just curious what the possible difference might be.
Just curious what the possible difference might be.
That ASP radial sure sounds good. . . ..
08-07-2022, 03:22 AM
#164
In all fairness, that mainly is the ring-exhaust. Without it I don't like its exhaust note one bit. No bark but a shrill yap like a nest of startled puppies... It's a bit clunky too...
But with the ring collector and double endpipe, it really sounds good. Fairly different from a Keleo ring (which have the reputation of sounding good, but this sounds different, as if it is a larger engine than it actually is..
You should hear it in flight. Goosebumps...
Oh, what the heck....
Last edited by 1967brutus; 08-07-2022 at 03:27 AM.
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TheEdge (08-07-2022)
08-08-2022, 03:40 AM
#166
Thanks... that landing gear was the cheapest piece of servo-operated mechnical crap I have ever seen on a plane, but I managed to do at least 15 or 20 landings with it. Last year I replaced it with a set of decent Electrons but haven't flown it yet due to other priorities.
I hope to be able to take that plane out a few times in the upcoming shore leave.
The cowl is in place in the meantime, and I have flown it with that once. Lot of work getting the baffling under the cowl right, but it now cools better than with the engine fully exposed like in the vid. Plane is faster too, getting more RPM in level flight.
It is my prized posession, that plane and I am extremely careful with it...
I hope to be able to take that plane out a few times in the upcoming shore leave.
The cowl is in place in the meantime, and I have flown it with that once. Lot of work getting the baffling under the cowl right, but it now cools better than with the engine fully exposed like in the vid. Plane is faster too, getting more RPM in level flight.
It is my prized posession, that plane and I am extremely careful with it...
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1967brutus (08-20-2022)
08-20-2022, 08:47 AM
#170
I just bought a Morris motors conversion for my ft-160. Anyone have any recommendations on what plane to put it in? I'm at high altitude so I'm looking for about a .91 sized plane. I'm thinking the H9 carbon cub, but open to suggestions. 
08-20-2022, 05:10 PM
#171
But I hope you will get it to run right, the Morris conversion kit, the metal parts are marvellously made, but carb selection is hit or miss. I have redone a few back to the standard glow carb with the solenoid valve as mentioned here: Electronic solutions to modifying glow engines of all sizes to gasoline and that gives in general way better results.
Not saying those conversions do not work at all, just saying that I have experience with several dissatisfied Morris customers.
08-21-2022, 09:12 AM
#173
TBH, I do not expect any problems...a 160 on gas more or less equals a 120 on output, not a 110. And a plane designed for a 120 will with near 100% certainty fly with an engine that equals a 120 glow, at 5500' altitude.
I fly one of my planes at a corrected 4500 altitude (2100' asl and another 2500 due tropical conditions) and I do not notice any significant loss of performance. The engine appears to be able to handle a slightly larger prop under those conditions but nothing exceptional.
The plane is a 5,5 lbs 60" ws trainer with an engine that at sealevel puts out 0,5 hp, so never overly powered to begin with.
Pretty sure you'll be fine with that FT160 running gas, in planes up to roughly 120 size, unless the plane is a high strung fast and aerobatic plane, then things might get critical. Otherwise I do not expect problems.
The FT160 is a rather bulky and weighty engine, you don't want it in a plane that does not have the wing area to carry weight or in an airframe that tends to be nose heavy on itself. That Rascal that Mitch is using really would not have issues with it.
I fly one of my planes at a corrected 4500 altitude (2100' asl and another 2500 due tropical conditions) and I do not notice any significant loss of performance. The engine appears to be able to handle a slightly larger prop under those conditions but nothing exceptional.
The plane is a 5,5 lbs 60" ws trainer with an engine that at sealevel puts out 0,5 hp, so never overly powered to begin with.
Pretty sure you'll be fine with that FT160 running gas, in planes up to roughly 120 size, unless the plane is a high strung fast and aerobatic plane, then things might get critical. Otherwise I do not expect problems.
The FT160 is a rather bulky and weighty engine, you don't want it in a plane that does not have the wing area to carry weight or in an airframe that tends to be nose heavy on itself. That Rascal that Mitch is using really would not have issues with it.
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RadialWacko (08-21-2022)