Has anyone thought or tried to modify the backplate of a nitro 2 stroke to mount a walbro? I was thinking you close off the front and mount the walbro on the back. I know some of the rear mounted walbros use reed valves. I think some others don’t. It’s just a thought.

Yes sir I can get a good idle and top end. It’s everything in the middle that’s giving me trouble. I like the suggestion of “valve leak rate” to keep the line clear of fuel vapors. I’ll give that a try.

My valve orifice is quite fine as I thought it would give me a higher resolution through greater servo travel. In the end it only needs to be the same or greater than the surface area measurement of the tubing ID. I would have thought I had that covered easily.


Step by step. Check with a leak rate….and then open valve orifice some more if that doesn’t work.

I still don’t have a solinoid housing so that option is still in progress.

https://cimg9.ibsrv.net/gimg/www.rcu...fbfe03faf.jpeg
https://cimg8.ibsrv.net/gimg/www.rcu...d2453dd85.jpeg
https://cimg0.ibsrv.net/gimg/www.rcu...fcdebc5f0.jpeg
My crap trap. It’s air tight and yet easy to empty.

It COULD be a possibility, but it will near guaranteed affect pumping efficiency of the crankcase due to additional "dead volume".
This affects scavenging pressure, which in turn will affect engine performance.

Possible, but a lot of metalworking, probably adding quite a bit of weight to the engine, making beam-mounting awkward, and less power,

I cannot think of a single upside. Not even the use of a Walbro, which as I have said more often, does not have a place below 15 cc.

That WILL work.
Minor detail, it will work a touch better, if you bend that tube going to "half height" in such a way that it ends up at half height, in the centreline of the bottle.

As is, there is a theoretical possibility that crud could get into the fuel tank, and it takes just a very tiny bit of crud to turn your fuel into black dirty stuff clogging the feltclunk eventually.

I added a tube to half the depth of the container per your instructions on how to build one of these.

Please don't take it wrong, I am really NOT trying to be pedantic here, but...

You missed something:

It is not a big deal, and depending on intended use of the plane, you can get away with your solution, but for me it is simpler to use only one single principle regardless of flight envelope.

First 3d resin print of solinoid housing curing in the UV light machine. This is just a test fit while waiting for my fuel proof resin to arrive.


https://cimg6.ibsrv.net/gimg/www.rcu...f21f65214.jpeg

I feel like of you're going to load a resin machine it makes sense to print a bunch rather than just one but I don't have a resin printer. How much work is loading resin and then emptying and cleaning it when you're done printing?

Well this was my first print ever so I figured I’d give just one a try. Adding resin was as simple as dumping a little in the tray. I haven’t tried to empty or clean anything yet so I really don’t know. I bought the machine to print solinoid housings as I didn’t have access to any other method at reasonable cost.

Awaiting your results anxiously...

Print results look very good. The dimension check shows measurements are consistently 0.01mm too small. I believe this may be shrinkage during the UV phase. Measurements will be changed in the file to compensate
the offset. The fuel nipple is a good fit on my fuel line and the nipple is much stronger than I thought it would be. I applied a good bit of force to it and it did not break off. With this information I will change the hole in the side of the housing
to be another fuel nipple.

Rev 2


https://cimg7.ibsrv.net/gimg/www.rcu...09747777c.jpeg

not sure about your slicer but the slicer i use for my FDM machine has a setting to increase hole sizes in horizontal surfaces in order to compensate for shrinkage due to temperature change from printing to ambinent. there may be a similar setting in your slicer that will allow you to maintain the correct dimensions in your model and compensate in your print.

If that print is succesful, then you , my good sir, could be the source of housings for North America :D :D :D

Rev 2 getting cured

https://cimg4.ibsrv.net/gimg/www.rcu...e6d0eaedcc.jpg

Soak testing Rev 1 in gasoline. If it still feels hard after 24 hours of soaking I will try Rev 2 on my engine while waiting for the proper gasoline resistant resin to arrive.

https://cimg3.ibsrv.net/gimg/www.rcu...d5cb8f067.jpeg

The good news is that my current resin seems to be no issue with gas.

The bad news is the sharp edges inside the solinoid housing appear to maybe have cut my oring because my assembly seems to be making air bubbles on the test stand when in use.

I went back and redesigned the solinoid housing so that the inside edges are smooth with an edge fillet.

Now I have to order a new solinoid but the good news is that the design should be finished now.

The filletted edges never are a bad idea, but please check whether the bubbles are like a "mist" (extremely fine bubbles dispersed throughout the fluid making the fuel look slightly opaque or "milky") or like clearly distinguisable singular bubbles in otherwise clear fuel, that are large enough to flock together and form larger bubbles...

The "mist" is slight cavitation caused by the oscillating valve, and rarely if ever a problem. Those tiny bubbles usually stay dispersed long enough to not flock together and even if they do, the resulting "combined bubbles" remain small enough to not be an issue. Virtually all my solenoids do it, a bit depending on fuel freshness and ambient temperature, and often times the misty appearance clears up because the vapour recondenses.
What happens is that the energy the solenoid mechanically transfers to the fuel, causes the lightest fractions of the fuel to temporary evaporate, a bit like when you shake a soda can and the CO2 comes out of solution: you definitely do not want to open that can, but if you leave the can resting for a while, it eventually gets back.in solution and you can still safely open it. Not quite the same, but a bit like a miniature version of it.
The singular larger bubbles CAN be a problem if they are allowed to collect somewhere, and they usually are some form of leakage.

Keeping the fuel line between solenoid and carb as short and straight as physically possible minimizes the negative effects (if any) of even minor leakage.

I would also add some fillets to the nipples that the tubing connect to. There's a stress concentration there and that's probably where it'll fail from vibration induced fatigue. Better yet would be to build the resin part so that it has holes where the nipples go and epoxy in some brass or aluminum tubing instead. It may make the housing a bit taller but it'll be vastly stronger.

Possibly also a better seal between tubing and nipples?

Xanaphyst sent a couple of his boards to play with. Don't do what I did which was to solder the display first, then the connector, then the xiao. Each part blocked the next. Start with the xiao then the connector, then the display. Am I correct that this one has the bmp280 sensor on board?

I need to figure out the wiring and make a case now have you designed a case yet?
https://cimg0.ibsrv.net/gimg/www.rcu...e81805e4d8.jpg

My apologies to the group for my "Lack of Input" as of late.. My first big retirement "assignment" is coming up in the form of a major house renovation and the prep is time-consuming - We will be starting soon and I'm doing the majority of the work, so I will be less than productive in the model engine realm. I did however have this Saito 180 almost ready to try on the "bleed system" and decided to give it a try.. Not a 5 minute tune as I had the ignition set up wrong - Not sure what i did but it appears i set it up at TDC rather than 28 Deg advanced. It would start but ran very weird. Once i got that figured it was basically like the other ones i have done and in a short time I had it running fairly nicely. Curve looks like the others with max opening about 1/3 throttle - Closed at idle and top end. This one has a very large 5mm ID on the air path including the tubing and it needs this as Max is almost wide open. It will not run with bleed closed - idles and top ends - but stumbles and dies (choked out) on transition.


Cut the testing short as my test mount was not up to this "Big Shaker". The plywood was not that rigid and the engine really bounced around - not as bad as the video made it look but post run one mount bolt was missing (it was missing in the video too - but i didn't notice.)


PS... for all you spoilt by spring - That is still snow in the background... We had a ton this winter and now we are dealing with all the runoff....:)

As I commented allreadyu on YT, very impressed with this alternative way of doing things, and I am very curious how it will hold up on long term flight testing WRT stability, and atmospheric/flight altitude influences.

it almost seems like we would need/want to add compensation for altitude (pressure) as it would effect the differential pressure on that air valve which effects the flowrate thru it. seems complicated but might be worthwhile.

(this would be independant from the air pressure compensation already programmed to compensate for altitude.)