1967brutus

Good info, Lonnie!

Thanks!

Cat 1

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Thanks Guys.. You confirmed what I understood so far - I do see that the carbs are different and a couple versions have been used - The latest has a unique low speed adjustment and the early ones seemed to have an air bleed.. Wait to see what this one looks like when it arrives.

On rings - I had some RMJ rings in the cart for my 160 but the shipping on small orders kills the pricing to me - I have used their rings with great success but ordering one set nearly doubles the price here. I think I might make a set or two - Have made rings before for gassers with great success.

Cat 1

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Look at this cutie - If they weren't so rare (and expensive) I sure would like one. Microwings FX-10S - 1.6CC - Don't think it would be a great conversion candidate but I thought you "engine heads" would like it.

Cat 1

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So... A bit of shop time today sorting out the fuel system on the Boxer test mule. The tank position (high) troubles me a bit and got thinking (which is always dangerous) so I spent a bit of time playing with a theory.

Some of you might know what a "Uniflow" set up is and its basic function.. I have used a Dual clunk uniflow on an RC plane before with an odd high mounted fuel tank and it worked well apart from an issue that plagues this setup for RC. When you Back off power the drop in muffler pressure causes a back flow down the "pickup level" vent and floods the muffler.. A check can be used but then the tank pressure stays high for quite a while and causes very rich low power mixtures.. Playing with how to incorporate this concept into an "air pump" system had the same issue - When the pressure would decay (pump slows down) it would flood the supply line and dump fuel out the air bleed in the air pump supply line. I thought a catch (and return) can might work (sort of like a crap trap but set to return the fuel when the pressure returns. Did some math and found that a throttle cut in a near empty 16 oz (500ml) could return over 1 oz (30ml) at 1psi decay.

I set up a test rig and confirmed this could be the case - Playing with plumbing I found a solution (I think) and it worked in the test rig - Also confirmed - using pressure differentials - the Uniflow would help with the high mounted tank.

One issue remains - And it is an issue with the crap trap setup - If you pull power when inverted - you can still flood the "fuel trap" (similar to a crap trap) but in this case the fuel can be returned to the tank.

I KNOW this is not a Simple solution as the plumbing is looking like a rocket motor - But have a look and see what you think. The theory is (proven on my bench) that the Check valved vent at the top of the tank will dump the pressure on decay but keeps the Uniflow as the primary pressure supply in the system.

I think this system could also be used for a Muffler pressure setup - But the can would have to be set to eliminate return to the tank (as it does in the current config)

1967brutus

Oh, WOW! What a cutie! Is that engine still in current production? If so, I want one if only for the cutie-factor and bling value.
It's got supercharging YS-style, it seems.

Only issue I see with gassifying it, is the clearance between prop and plugcap. That is going to be tight if at all possible, but then again, I have one Runtronic Ignition, which has a way smaller plugcap and much thinner and more flexible HT-lead.
Dang... now I HAVE to go and try to find one...

1967brutus

Just to bring things in perspective: a 500 ml tank is twice what you would need for the Boxer. 250 really is large enough for all purposes, even my BigLift can do 4 to 5 safe tows to 600 ft on that. So that reduces the amount of "regurgitation" by half. 15 ml of max reflux on a near empty tank (where you preferrably won't fly much) 7,5 ml on a half empty tank, and less than 4 ml on 75% tank capacity.
Any decent throttle management will make reflux a non-issue.
The only plane where for me reflux is a minor issue is the F3A plane, where sudden power cuts from full power to abrupt idle are regular and happen in negative G conditions (tank vent immersed).

I am a bit confused though why it is not possible to mount the tank lower or the engine a touch higher. Next to my BigLift, there is an OS twin in my club, admitted, the planes are high wing "floaters" but we do both not have real issues with tank placement. My Big Lift can be fuelled to the max without the fuel syphoning out, as it is a tail dragger, and the stance of the plane lowers the tank sufficiently. In flight the level attitude really is a non-issue, the engine consumes enough for it not to flood.

My suggestion: use a 250 ml tank, and test what the set-up does with needles as set for running, but engine stopped and the plane in its normal tail-down stance it would have on the ground. If it does not syphon with the engine off, you're good to go in the air.

Mind you: Even IF there is minor syphoning going on, it will only "flood" the headers, but not the cylinders, because fuel does not flow upwards. The excess will leak out of the carb.
Two or three vigourous reverse flips with the throttle full open will clear the headers.

IMHO, the uniflow style tankvent is not needed to get a good running engine.

But I absolutely HAVE to say: your system layout with the checkvalve for immediate pressure relief and a "pushback" line for any regurgitation is pretty clever, and it took me quite a bit of thinking before I got its workings. It can work with the airpump, but not with muffler pressure, because the craptrap is not supposed to return any backflush-fuel as it will be contaminated with muffler crap.
Then again, I still have to experience my first issue with a full craptrap. Even the F3A plane at best has about half of its fluid-capacity used after a flight.

Cat 1

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Here is a link Bert.. I think the article mentioned only 300 were made and they are out of production.. seems to be for sale here though.
https://www.okmodel.net/microwings-f...w-motor-fx-10s

Its rated at a decent power for being a tiny 4 stoke - no doubt in part to the case supercharging - Looks like someone with some spare time could create this layout with a 2 stroke case, A 4 stroke head and some custom parts. Some videos of it flying too if you search Fx-10S

Cat 1

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Your quite correct Bert, I may have been overestimating tank size - I think it was a "leftover" from when I was planning the 25cc two stroke on this airframe.. will see it this helps - The issue was the length of the 500 ml tank and a former in the way prevented getting it low in the airframe. I actually re-did the firewall to get the engine up a bit. I might retain a small "regurgitation tank" as it would also be easy to fit and on a smaller tank I can probably do away with the extra vent and check.

1967brutus

Did you allready check if a 250 ml tank would fit lower? Because that would basically solve the issue completely, and eliminate the need for a uniflow system, and thus most of the regurgitation issue. I about 10~15 cc of free space in the tank, which is enough to keep the vent fluid-free during ground runs.

Since I use double muffler pressure ( the pressure taps of both mufflers are connected via a straight T, and the alternating pressure pulses shoot the crap back and forth between the mufflers with virtually none of it going to the tank. The Boxer is the only plane in my fleet where I have so far never needed to empty the craptrap, like, ever...
It serves its purpose because there most definitely IS some black crap and crud in it, but in all those years maybe not even 5 ml (the trap is 60 ml of volume and "passes on" at 30 ml).

Aerobatics might cause some regurgitation though, but I have never done any form of that with this plane.

1967brutus

Aouch! That comes down to 650 Euro or thereabout...

Cat 1

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I'm "up north" with work right now Bert so can't verify until i'm back. I think the issues I'm trying to solve might go away with a smaller tank - I do want to try the "air pump" setup though as I have had good success and a bit of extra tunability on the bench. It would be easy to simplify and convert back should I run into issues with it in a real world application.

I did close the deal on the 2nd boxer (OS 1.60) too. It might be here late this week. Can wait to see how it looks. I got it for "parts" pricing - So it its rebuildable I'm a happy dude..

1967brutus

Oh, I did not mean it like "why not muffler pressure?" or anything like that, the controlled tank pressure as you have it seems to add an extra dimension of accuracy and consistency. And above all I am really curious whether it will also work out in the airlike it does on the bench.

Cat 1

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Yes Bert I realize that.. I did respond a bit oddly and didn't think you were questioning the air pump setup. It would just be nice to substitute the air pump for muffler pressure and compare both "in Air". I will try and fly both for comparison.. One thing I know is I can run a less restrictive Exhaust with the air pump - Best case with muffler pressure would require chambers like you run I think - I could not get the pressure my carb "likes" with the straight pipes unless I restricted the ends.

I am hoping the uniflow can go away as it was only a solution for the siphoning I thought would be an issue. I had another plan in place in the form of a Robert Ultra Fueler (Part 205) - I ordered one as I thought the 4 port setup could act as a fuel shutoff to prevent siphoning - But The plastic construction and multiple o-rings doesn't sit well with me - Looks like a air leak generator - I never have had good luck with any of the fancy fueling ports - They all end up leaking and causing trouble for me.

1967brutus

That REALLY would be educational. Especially comparing the "tunability" of the pump versus the "natural stability" of muffler pressure.

Unrestricting exhausts IMHO is not desirable. At least, NOT when that means "wider than standard". Restricted headers also are not desirable: Not enough volume and length. Ideally one wants the inertia in the exhaust tract to provide the backpressure, not the cross section. And for that you need volume and length.
I never have tested side by side to make sure, but I have the distinct impression engines run better with an exhaust "system" (a header, a muffler volume and a tailpipe). Not so much in absolute power, but more in "behaviour throughout the throttle range". Something to do with valve overlap and the inertia in the gas stream. Now that might be just me and my imagination (although some effects noticed with the Wankel seem to confirm that simply adding length to the exhaust system, regardless of "tuning that length" significantly improves that Wankel's performance), but at least my clubmates agree that those mufflers really do a nice job on the engine.

Mind you, the ones I used are the "baffled mufflers" as JustEngines from England sold them (I think they still do, by the way), but I am 100% sure that with your machining skills, you'll be able to turn out a set within a single afternoon, not even breaking a sweat...
What JustEngines did, was make two muffler halves, leaving the external diameter a bit wider than final dimension, TIG-weld the two halves together with the baffle inbetween, then turn down to final diameter, with that last cut removing all visible traces of the weld and making the mufflers appear as being made out of one solid piece of barstock.

Jesse Open

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Jesse Open

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1967brutus

Jesse Open

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Jesse Open

1967brutus

This a kind, respectful and ONE TIME ONLY request to PLEASE leave us alone, Gary.
Your muffler designs are VERY WELL known to all of us here, because all of us ARE (either former or current) RCG members.
Those designs also are not in any way, shape or form of any extraordinary benefit to the subject of this thread.

There really is NO need for you to remind us of why we relocated this thread from there, to here.
None of us here have made ANY references to you, your person or any of your work, we did to the best of our knowledge, nothing to trigger your contribution.
I would have expected that our mutual positions were pretty clearly defined since your last contribution in this thread.
I think, the moderator also made his position very clear, and I would really ask you to respect that.

We did not touch you, PLEASE stay away from us.

Jesse Open

Bert,
The pics were posted as a follow up to your comments regarding mufflers and straight pipes. They were posted without comment one way or the other.
Straight pipe increased volume, reduced tip.
Baffled muffler, extended tip, welded construction.
Standard Saito cast with extended, larger diameter outlet and increased outlet port area in baffle.
Not about you. Although you have seen the pics, there are others stopping by who may not have.

No need to take offense, none intended.
I won't post any further.

1967brutus

Appreciated.

Cat 1

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Got a Box with a Boxer in it today...

For what I paid I'm a Happy Clam. It did have a compression issue but I could quickly see that the Exhaust valve on one side was not moving - Dave called it - stuck lifter. Had to carefully drill the valve cover bolts off as someone stripped out the socket heads. Compression is very good now. Bearings are very done and I have some internal clean up to do but its all very good apart from one Intake tube has a dent in it. Its an older one with the Air Bleed carb but I did confirm has the "latest" connecting Rods.

Quite a few differences between the ASP and the OS..
Cylinder fins are different
4 head bolts vs 6 on the ASP
3 bolt valve covers. Different Shape
Manifold center and carb are different mounting.

Even got a Pretty Gemini 160 Box

1967brutus

Yeah, the ASP/Magnum, although clearly visible a clone, does to my knowledge only share the conrods as direct interchangable parts.

Raleighcopter

Nice. Looks like a winner once you clean it up. Those head covers are jewelry.