Glowgeek

I am VERY interested in seeing the temp differences between cylinders at idle, mid and full throttle. I've seen what Bert mentioned about cylinders swapping temps. On my Saito 200Ti and other twins I've had it's not unusual to see one cylinder move from the coolest to the hottest based on rpm.

I suspect that the diverter will cause the greatest difference between cylinder temps, that is, idle compared to wot. Just a guess really.

mitchilito

My Feedback: (6)

I had a chance to run the experiment yesterday. In a nutshell it didn't work well. It definitely did not like the full biased-to-the-right position. Both high and low needles were hard to get set - and really weren't happy anywhere!

I'm not really surprised as I suspected that full bias would be too extreme. I have turned it down to around half bias and we'll see what happens there. I have a feeling it's going to be very sensitive to bias position so it may take a lot of experimenting.

Stay tuned!

Jesse Open

Another route:

Glowgeek

Glowgeek

Glowgeek

Mitch, CH and MMM used very similar intake manifold designs for their gas conversions i.e. straight up carb mounting, no 90° turn. May be the route to take if your design doesn't pan out as expected.

As far as recirculating crankcase oil? Saitos and OS 4 strokes are both known to run hundreds of hours running methanol or gas with proper maintenance, without recirculating oil. There are plenty of folks recirculating oil running methanol with no apparent I'll effects. There is one guy who has run hundreds of flights on gas while recirculating oil through the velocity stack. With only those examples to go by I lean towards the belief that oil recirculation is probably ok but personally I wouldn't begin recirculation until the engine was fully broke in. Just my thoughts.

Jesse Open

Far from recent, oil recirc via velocity stack is a very old trick. The fellow at RCG's main innovation was that he used shrink tubing.

I have never noticed any negatives to implementation during the break in rituals, nor any long term problems whatsoever.


Had one of the Saito dual carb FA-300T in a Smith Miniplane. Great running engine, very easy to tune.

1967brutus

Does your set-up allow for tuning the bias during operation? Just wondering. That would allow for to dial it in within a few minutes...

Glowgeek

Would love to see pics of the two gas carbs on your FA-300T. Or were you running gas through the factory glow carbs?

Jesse Open

It was a standard Saito 300 dual carb engine.
Saito methanol carbs.
Regarding implementation of dual carbs, fuel choices aside. Arlyn has done quite well with Saito carbs and gasoline.


Like this:
https://m.youtube.com/watch?v=QKJ9BvKDKLk

Sounds like this:
https://m.youtube.com/watch?v=GD8gDAUsJBc

Turn up the audio

mitchilito

My Feedback: (6)

First off - keep those comments coming. These threads are a big part of what makes this hobby fun for me.

With regard to Adrian's (C&H Ignitions) gas conversion: it's going to suffer from the same fate as the stock engine or my conversion: one cylinder is going to be leaner than the other.

With regard to the dual nitro-carb setup on the Saito 300: it does not have a fuel pump or fuel regulator like the Walbo. These shortcomings are two of the things I wanted to address with my conversions.

With regard to my diverter barrel being readily adjustable: I WISH! But alas, it's not going to happen. I have a sneaking suspicion that it's not going to work out as I'd hoped and I'll be going to some kind of defuser setup like Brutus suggested. Maybe a screen setup or some such. But who knows, maybe my diverter will pan out.

1967brutus

WRT the thing about "fuel pump"or "pressure regulator", I can ASSURE you from meanwhile longterm experience, that these items are not only highly overrated, they also are totally obsolete! Can't stress this enough.
The vid below is 5 years old and stems from before the electronic fuel control I use nowadays, and things have only gotten better since.

We all know to test our glow engines at WOT with the nose vertical in order to check WOT mixture settings, and we also all know, that it is NOT a given that a glow engine can accelerate from idle to WOT while the nose is vertical. You're lucky if they do, most won't accelerate with the nose up, unless you richen idle mixture such that throttle response becomes hesitant in level flight. So we don't do that, and accept that it won't accelerate, because it never presented a problem, right? Now hold my beer:

This is nothing but a modded glow carb and muffler pressure, and it accelerates from idle to full regardless of whether the nose is level or vertical. And ALL my engines do that...

There is a compromise in that the fuel tank cannot be located in CoG, but I am wondering how significant that is with an 8 oz tank on a 13 lbs plane, and 45 minutes of flight from that tank (1 oz weight change per 5 minutes). So in all fairness, I consider all efforts related to moving the tank towards CoG as a bit of a waste of time.

As for the uneven mixture distribution: the ONLY thing that REALLY works 100% of the time throughout the full throttle range, is to make sure ALL fuel evaporates before the split into the individual headers. Vapour distributes equally, oil does not. As long as there is fuel still in solution in that oil, nothing is going to get it right. All you can hope for is "as good as it gets".
For my own FT160, I have achieved equal cylinder temperatures within 2~3 degrees Celsius from roughly 15% power (corresponds to about 3000~3500 RPM) upwards to about 90% power (corresponds to äbout 400 RPM below peak). Below that one cylinder drops away about 15~20 deg C, and at WOT I see roughly 10 deg C difference. This is as measured in flight. Ground figures differ, because due to the rotating motion of the propwash, both cylinders get far from equal cooling as well: Richt cylinder receives air coming from below, where muffler and pushrod tubes hinder airflow a bit, left cylinder receives air from above, where it hits the fins unhindered. Left cylinder tends to run cooler because of that.
I am not interested in ground behaviour, qas long as it is acceptable enough to taxi out to the runway and get the plane in the air.
A side note here: I fought larger temperature differences for a long time until I spent some time locating the temp probes in exactly identical places. The location itself is not that important, but the fact that left and right are located the same IS important. Really makes the difference between chasing your own tail and getting consistent results when making a change.

Unfortunately the radial is a bit less consistent, but here too, the thing with evaporation (the solenoid creates that purely as a side-effect) reduced the temperature differences from well over 100 deg C to less than 30, which I think is acceptable for a radial.

Now please don't get me wrong: I am NOT saying that you or anybody else should abandon pumper carbs. They are working, and working well. It is NOT that. It is just that it is a bit of a waste of time thinking that a gasser conversion HAS to have such carb. It doesn't. It really doesn't, and anything previously running glow fuel and glow carbs, does not need it. (Yes, I think Saito took the wrong turn here).
What I AM saying is that you have to look for ways to promote evaporation of fuel. Be that intake air heating, introduction of turbulence, whatever, I don't know, but that evaporation is ALL important on multicylinders with a single carb.
Singles less so, because there is nothing to get out of sync, in those situations it is only efficiency and cleanliness of combustion, which on this scale is rather unimportant. But multies with a single carb, evaporate evaporate evaporate

Jesse Open

Mitch
I understand your points regarding the lack of fuel supply, regulation etc.
The point being, Arlyn and others have been using the Saito carbs with gasoline reporting good results. (Without pumps, regulators.)

As a side note, the 300 Saito twin, dual carb was running valve operated, tank pressure as supplied from the crankcase.

Tony Hallo

What did the autos do back in the carb days? Exhaust cross over, might try warming your aluminum block and insulating the carb from the heat.

mitchilito

My Feedback: (6)

Sounds like what the YS engines used. But that would require a regulator, no?

Jesse Open

"Require" is a key word. What some folks seem to require,others can do quite well without

The Saito case pressure source was fairly rudimentary. It worked best at minimal pressure. They used an adjustable needle valve to relieve excess pressure. The system was really of limited use for most folks, Probably of little use for gasoline applications.

mitchilito

My Feedback: (6)

As I mentioned before I'm building a giant scale (50%) Bucker Youngmeister and it's now springtime outside so I can finally start the paint process. This will take weeks and weeks so you may not hear from me for a while. I just didn't want you all to worry about me

See you after a while for the continuing Gemini gas conversion fuel mixture saga. . . .

Yes, it's big. Will be Moki 300 powered.

Jesse Open

A real beauty !
Keep us posted.

1967brutus

wow!

mitchilito

My Feedback: (6)

You'll find my build here:

JW Büker Jungmeister build

mitchilito

My Feedback: (6)

I wanted to check in here to let all you guys that have been following along know that I'm waving the checkered flag on this project.

In a nutshell: I did not like the way the engine was running with my "inlet charge diverter" drum. I gave it a good try then decided to center it once and for all. Along the way something got in the Walbo and caused it to misbehave. SO: I centered the diverter drum, disassembled/cleaned the carb and put a new gasket set in it and test ran it one final time. It starts and runs great.

I did do one final modification to the diverter drum. In this picture the outlet of the drum (which leads to the intake pipes) is on top. I opened/smoothed the sharp edges of that port and installed it centered. Yes, there are still minor differences between the cylinder mixtures but I'm so happy with the running characteristics and power output that I'm calling it done.

One day not too long from now I will build an aircraft specifically for this engine and at that time I will return to this thread and update. Kind of like I did with the little Gemini 160 project. Until then, see you all later -


The edges at the sides of the hole (on top in this pic) are now opened up smoothly leading to the intake pipes left and right

1967brutus

COOL!

Glad to hear you are happy with how it runs now...

All that leaves to be desired, is a vid of it...

kmeyers

This to me is more evidence that a simple rotation of the carb 22 degrees may have been a solution.
Did this drum setup loose you any rpm?

mitchilito

My Feedback: (6)

No loss of rpm. I'm getting 6750 with a Xoar 20x8. Not a powerhouse but quite adequate. To me the loss of power compared to when they are nitro-powered is well worth it. I just can't stand the internal corrosion and unreliability of glow plugs on these engines.

1967brutus

Hear hear!