Jim.Thompson

Very interesting!

Understood!
I don't expect the bolt pattern to be too much of a problem as my carb insulating block(s) is/are hand made; I can simply make another one with carb bolt spacing to suit..
I have OpenTX transmitters that will solve that.

Thanks for the good replies.

Jim.

1967brutus

Excellent!

John_M_

It's been a while since I've done anymore work on the wt walbro, been side tracked with a couple projects.

[In reply to the bold]
It's definitely not easy to modify the wt to accept the solenoid valve. I've screwed up two carb bodies in the process of figuring out where all the fuel passages are.

I have one bored out to the correct depth to fit the solinoid, and the fuel passages at the bottom of where the hi/lo needle seats are, once you bore down to the seat tappers, the fuel passages that feed the main jet, and idle / intermediate jets are large enough for the solenoid to modulate fuel delivery correctly, just like the m-carb does.

The issue is plugging the original fuel passages under the welch plug in the metering chamber that feed both needles, and then drilling a new passage from the welch chamber to feed the solenoid valve chamber. Once that is done the carb will operate just as the m-carbs do.

The other thing I would like to achieve, is to relocate the hi/lo needles to the side of the carb body to intersect the main and idle/ intermediate fuel passages to fine/trim the fuel delivery from the solenoid as needed (if needed?). After ruining one carb body, I know where those passages are, so relocating the needles is not as difficult as milling the solenoid chamber and relocating the fuel feed passages.

It's not easy to do for sure, and you need an endmill, or a decent drill press and a solid means to hold the carb body to the mill table. It's not something anyone can do.

Fitting an original m-carb to the engine would be the way to go, but for me, the m-carb is too big to fit in the location inside the cowl without having to move the engine forward, and that's not something I really want to do. So for now, I'm going to just persist and try to finish modifying the walbro.

1967brutus

It is imperative to have at least SOME form of "calibrated orifice", adjustable or not, because the solenoid itself has a full flow capacity sufficient to feed (estimated) a 30 hp engine.
Which means that in ordr to modulate the fuel for, say, a 3 hp engine, the solenoid has to operate in the lower 10% of its dutycycle. In itself not too bad but it would require custom calibrated electronics or it would go at the cost of resolution in the curves.


I'd expect the original M-tronic carbs to have a fuel orifice tailored to the engine range it is intended for.
I was not aware that the M-tronic carb is that much larger than the equivalent Walbro. But I would think that building a suitable header between engine block and carb would allow for relocation to any more suitable location?

John_M_

That's what I figured, why I wanted to relocate the needles, if I can intersect the fuel paths. I can cut up the buggered up carb and take some measurments if I need to.

They do, there is a fixed orifice on the lo / intermediate fuel circuit at the bottom of the solinoid chamber. There are two orifices actually, one feeds the main jet, the other feeds the idle / intermediate jets.

The m-carb body is quite a bit bulkier than a walbro wt series carb, even after removing the choke lockout mechanism, and the choke position switch. I don't have an image available to show you the gaui f50r installation in the Super cub, it's a shoe horn fit to begin with, with the wt carb. To fit the m-carb I would have to move the engine forward about 3/4" (19mm). I like scale apperence, and moving the engine that much forward, would make the cub way too long in the nose. I'll get something sorted out.

Anyway how you doing mate? I haven't seen much activity from you for a while. Hope things are going well with you.

I had a bad experience with the J3, one of the receivers failed, just shut down, and left me with half the control surfaces working, shut down making a left turn. The right aileron, and elevator half were stuck in a downwards position, about 20% of their travel. Rudder and throttle still active. Ended up forcing a landing with a bad approach, stalled and bellied in on the gear, caught the right wing tip on the edge of the rwy. Fortunately minor damage to the wing tip and collapsed the gear. She's good as new, but I switch over to jeti for the J3, still using the 18sz for the SC.

Cat 1

My Feedback: (1)

Here are some videos of the 30CC Gasser conversion fitted with the stock M tonic carb - the carb bore is slightly big for the 30cc but I got it to work by keeping the choke fitted even though its unused or by using a 3D printed "restrictor"

The discussion starts around page 350 of the "other" forum mentioned above and goes for many pages.

Glowgeek

Purrs like a kitten! No midrange burble, just as expected, Fantastic!

John_M_

I've seen those videos back when you first posted them, it's what made me look into adding it to the 50cc. The 201 m-tronics carb is designed for their 35cc chsinsaw, it's does have a larger venturi, but there is a black plastic restrictor, a turbulator of sorts behind the throttle plate.

1967brutus

For now, I'm again sold out. 4 kits went to 3 different buyers in France, one kit reserved for one of my own to be commissioned planes, the remaining 5 kits went to 3 dutch buyers.

Just requested 10 new controllers to be made, and tomorrow I'll ordeer 10 solenoids.
Still 13 housings in stock, so before the end of the year I'll have to ask my buddy to fire up the CNC once more...

1967brutus

On another note: today a glider&tow meeting, I did not count them, but I think I.ve done about 25 tows, gliders ranging from 700 grammes and slightly over 1 metre WS to 4kilo and 4 metres wingspan, release heights 200 to 250 metres (600 to 750 ft).
The Boxer's getting thirsty when it has to work hard, and I went through 700 ml (23 oz) of fuel...

It was a lot of fun.

Cat 1

My Feedback: (1)

Sounds like a great time Bert.. aerotow is not a "thing" here but I would love to try it.

BarracudaHockey

My Feedback: (11)

It's an awesome way to wreck two planes for the price of one

1967brutus

It was, and you definitely should try it. Especially on the thermal days, its very fulfilling, because nothing says "power" any better than a towplane hauling a majestic glider upwards. Real fun when for example there are two or three towplanes and a whole bunch of gliders, each tow trying to get as many gliders in the air in the shortest possible time.

Actually, I still have to witness the first "dual crash" in now about 5 years that I am doing this... With a suitable plane, it's a lot easier than it looks, so much so that even my very first tow, with the line rigged improperly (forgot to use the ropeguide behind CoG) and thus my tug tracking like a wet rag, went otherwise uneventful albeit a bit all over the place...

Back then:

More recent:

BarracudaHockey

My Feedback: (11)

I was joking, I've done hundreds of tows as both the glider and tow pilot

1967brutus

Awww... dang it... Stepped right into that one with both feet, didn't I?

BarracudaHockey

My Feedback: (11)

An article I did on the subject if you're bored
https://www.modelaviation.com/horizonhobbyaerotow2015

Glowgeek

Great article, Andy. Very inspiring.

At one time we had a few older gentlemen at our field with gliders. Their tow pilot moved away so the next year I volunteered for tow duties with my Senior Telemaster. It was fun while it lasted. One of the pilots moved away and another passed away that year. The third pilot had no interest in flying without his other two buddies. How often have we seen that happen?

1967brutus

Very well put! Nothing to add...

1967brutus

Just checked my logfiles, It seems I did 21 pulls, highest release altitude 277 metres (in approx 65 secs), highest CHT over the day was 125 deg C, but that was at a slightly lower altitude, probably with a larger and heavier tow...

mk13

Hi!

​​​I am one of the French people to whom Bert sent a conversion kit a few days ago.
Thanks again Bert the kit and your kindness!

This is the first time I do this mod and the first time I run a glow engine 😅
I did the mod on an old training plane (Taramis) with an old OS max 25RC engine.
I put Billy603's (Guillaume) setting for the curve. The engine runs, but I have a bubble problem between the valve and the carb. I don't understand how these bubbles can appear in this hose because I don't have bubbles before the valve (between the tank and the valve). Do you think it is possible that there is an air leak between the valve and its support?
I will try to put a video of the first run.

1967brutus

I have seen extremely fine bubbles (almost like a dust or mist) that are no problem. They are usually caused by vibrations (like a form of cavitation). These very seldom cause issues.
If however the bubbles are large enough for them to be visibly round in shape, and are stagnant in the line when you hold the nose down (the bubbles stay in the line and do not flow with the fuel), it is probably heat (valve housing touching the engine) or very hard vibration (the housing swinging to and fro and hitting something). Best is to relocate the solenoid to a place with less vibration. Although in general, te closer to the carb, the better, the position of the solenoid is not very critical and up to 10 cm distance I have used succesfully.


Since you have a very small engine, it can be of help to select a smaller diameter fuel tubing between valve and carb nipple. This helps maintaining a bit of "velocity" in the fuel line, and this helps with carrying away any bubbles. The smallest size availlable is 1,8 mm inner diameter. It is a bit hard to get that on the connections, but it can be done when the tubing is carefully heated a bit (for example a hot air blower or hot water).

Mind you, most likely it is necessary to fine tune the curve you took from Billy. It usually is a good starting point, but it is extremely rare that an existing curve 100% suits a different engine, EVEN if the two engines are identical.

Looking forward to a video.

1967brutus

A general word of warning, that was not included in the "manual": Hans (the guy that makes the drivers) warned me, that he tested with some safety items in the circuitry, but they make the valve response less accurate.
Therefore, there is NO protection against short-circuit of the valve output. Please make sure that whatever happens, the connection on the solenoid is arranged in such a way that wire breakage cannot lead to the wires accidentally touching each other, it will burn out the switching transistor.

mk13

Hi!

The video from yesterday and today. (I put an old oil can for the video to avoid too much noise for my neighbors &#128517





Yes, I see in the hose round bubbles (~2mm diameter), and a lot micro bubbles than came from the valve and they make the big bubbles bigger.

So, I replaced yesterday all fuel hose by the smallest than I found, there is less bubbles but there are always some. I put this morning some sealant between the valve and the body (without dismounting the valve), I hope it will solve the problem (I only see bubbles after the valve, not before).
I put my solenoid on a foam square, and it doesn't touch the engine so it's cold during running.

All my electric cables from the ignition and the valve are in a sheath.

I will give you some news when I will try again.

1967brutus

As long as the bubbles won't interfere with the engine behaviour, it's OK... If the bubbles keep moving and dissapear into the carb without causing the engine to hickup or burp, it's not a real problem.


How is the full throttle behaviour?

Oh... I nearly forgot: Your engine has a cast iron piston in a lapped cylinder. If you followed the advise, you are now running 10 parts gasoline and 1 part synthetic oil.

Cast Iron pistons benefit from a bit of castor in the fuel... Does not have to be much, lie 2% of the total fuel, or 20% of the total oil should be more than enough to maintain a good piston seal.

mk13

The full throttle is not too bad, I must set the points of the curve.

But in low and mid range the bubbles go in the carb and the engine have missed fire or sometime stop.

Thank for your advice Bert, I will add some castor oil in my fuel.

​​