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Dec 08, 2019, 11:29 AM
Still gassin' it.
You're welcome, and @ Raleighcopter: apologies, did not want to hijack the thread.

Let's get back to the topic of converting this specific Twin…
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Dec 08, 2019, 11:36 AM
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It's alright. I'm still learning new stuff. Proceed.

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Dec 08, 2019, 01:37 PM
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I went back and re-read the thread. My engine is somewhere in Texas, arriving towards the end of this week. When the engine arrives I'll better know what I'm dealing with. The big one is getting muffler pressure. The engine I've acquired has straight pipes. I'm ok with finding an os 4 stroke carb but if I've gotta buy a carb, if I can make one work, why wouldn't I just purchase an rcgf10 carb? Also, can I get a pulse from the crankcase?

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Dec 08, 2019, 01:55 PM
Still gassin' it.
The RCGF10 carb probably has a way wider throat than what the 120 twin wants, and that could lead to carburation issues (too low velocity in the intake, leading to poor atomisation).
Yes, you can get a pulse from the crankcase by just connecting a T in the crankcase drain, lead one leg to the pump of the carb, lead the other leg out to wherever you would normally lead the drain to.

Nobody said it was gonna be easy
It also remains to be seen if the midrange mixture requirements of the RCGF10 match that of your engine. That would determine running behaviour.
Dec 08, 2019, 01:56 PM
Still gassin' it.
Oops… double...
Dec 08, 2019, 03:35 PM
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Alright then. I'll start looking for a carb to modify. Regardless, installing the CDI will happen first so I'll start looking for those parts

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Dec 08, 2019, 04:04 PM
Still gassin' it.
Like others have said before: you can run that engine perfectly fine on methanol and CDI, and you will most likely get good results with 85% Methanol, 15% of a decent synthetic oil.
Better stay away from Castor, but if you have to, then use 80/20

You can always look around for a gasser conversion, and if all else fails, there still is the option of the electronic valve. that will even work with an airbleed carb (simply close the airbleed, and let the electronics take over anything below full throttle).

If you're interested, I can get a set to you after mid Februari. You need a decent programmable transmitter for that option though.
The system is NOT suitable for HV, it is dsigned for 5,5V max.
Last edited by 1967Brutus; Dec 08, 2019 at 04:09 PM.
Dec 08, 2019, 04:05 PM
Still gassin' it.
Oh, you probably allready know this, but for Methanol, use an ignition timing of 34 deg BTDC, for gasoline 28
Dec 08, 2019, 05:15 PM
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I fly OpenTX so my transmitter can do anything I need. I can grab a sensor bracket and magnet ring. I'm good with building the electronics (is it just an Arduino that reads a channel and pulse width modulates a transistor to control the solenoid). I do not have a metal lathe to create the housing out of metal. I could possibly Fab it out of HDPE.

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Dec 08, 2019, 05:40 PM
Still gassin' it.
I can send you a housing only for about 20 bucks plus shipping (I had a run of them CNC-made, 54 pieces, still about 45 left), and that I can do first or second week of January.
I am sure, you can get the solenoid at most Stihl Dealerships, and if you're handy with Arduino, it should be no issue. (although my driver is not Arduino, I do not know what it is exactly, some other type of programmable processor).
Not sure what the valve will cost in the US, over here it generally sells for approx 25 Euro (roughly 30 US$)

What you need is a fixed frequency square wave signal of 25~30 Hz, not critical, but not slower, not faster.
It needs to be able to control dutycycle from 0 till 100% in at the very least 200 steps, but 500 steps would be better (My Taranis has curves adjustable in 200 steps, but the signal itself has better resolution, so aim for better resolution than 0,5%).

The solenoid draws around 130 mA at continuous 5V and taking into account that there might be a bit of induction you need a bit higher switching capability. My driver has 500 mA rating, and that has proven to be OK.

I have so far not noticed any side-effects from the wiring of the solenoid running very close along the ignition box and leads. They don't seem to affect each other, and also no noise coming back to the receiver.

That should get you going.
Dec 09, 2019, 08:30 AM
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the solenoid costs about $43 here (i'm assuming because of the china tariffs). it will also save the cost and time to program an arduino. this makes your fuel metering system very cost effective at $75 since it sounds like all i need (excepting, of courst the CDI, sensor, magnet, plugs, and mounting hardware). i think i'll wait until february and purchase one at that time from you instead.

One question: will i still neeed some sort of heat insulator for the carb or is it basically turn-key for converting the fuel system?
Last edited by raleighcopter; Dec 09, 2019 at 09:06 AM.
Dec 09, 2019, 09:05 AM
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...and i like the solenoid metering method because it sounds like it would work with methanol too. of course, it would require a different curve on the transmitter but seems like it would be very easy to make a dual fuel plane this way.
Dec 09, 2019, 11:34 AM
Still gassin' it.
Quote:
Originally Posted by raleighcopter
the solenoid costs about $43 here (i'm assuming because of the china tariffs). it will also save the cost and time to program an arduino. this makes your fuel metering system very cost effective at $75 since it sounds like all i need (excepting, of courst the CDI, sensor, magnet, plugs, and mounting hardware). i think i'll wait until february and purchase one at that time from you instead.

One question: will i still neeed some sort of heat insulator for the carb or is it basically turn-key for converting the fuel system?
Yes, it is all you need, and (depending on how nice you want to make it) basic installing is the time it takes to solder 2 wires, plug in to the receiver, and split the fuel line and stick the valve in between. Can be done in under 15 minutes. As simple as plugging in a servo and installing an inline filter, literally.
You need to do the soldering yourself, because I cannot predict whether your firewall has a hole big enough to pass the valve through (valve needs to be as close to the carb nipple as is practical). You can solder in connectors, but that you have to provide yourself. Unfortunately, I am not able to get the Original Stihl connectors, or I would have included them. I don't think Stihl sells them separately.
A 2,5 mm hole in the firewall is enough to pass the wiring.

The big time consumer is getting the curves right, that can take anything from 5 minutes to several hours, no way for me to predict that. There's a bit of a learning curve there. I will talk you through it, when you get around setting it up. It's not hard, but you need to "see it". Don't worry, it's not rocket science.

The need for a heat insulator is depending on the specific engine design, so far I saw only the need to insulate remote needles, but not carbs (including carbs that have the HS needle in the carb) on 2-strokes.
On fourstrokes usually you need to heatshield the carb and sometimes the intake header, but NOT on the ASP and OS twins.
Muffler pressure is advised (it greatly helps in compensating for the unloading in the air), and I still have a few straight exhaust headers that I don't use, I can send you one for free for you to braze in a pressure tap if you want to keep yours Original.

Quote:
Originally Posted by raleighcopter
...and i like the solenoid metering method because it sounds like it would work with methanol too. of course, it would require a different curve on the transmitter but seems like it would be very easy to make a dual fuel plane this way.
It actually does work with methanol just as well. Note that in this set-up, the fuel is ONLY metered by the valve, the carb connection is a straight through tube:
Third live test electronic NVA. (3 min 10 sec)


BUT.... that video is 4~5 years old, testing lasted about a month during which the valve functioned flawless, no deterioration of function or adjustment, after which the whole setup was shelved. When I took it out 5 years later, the valve seemed to function (it made the proper rattling noise and I could see the valve disc moving) but did not seal anymore (it passed the full fuel flow regardless of dutycycle).
Now here is the thing: I do NOT know whether that is deterioration because of chemical action of the valve, or just dirt or castor gumming from not using it.
Maybe it would have kept working if it had been in use regularly, maybe it would have failed, I simply don't know.
At 43 dollar a pop, I would suggest to use it with gasoline, after all, it has been designed for that. You can still run the engine on methanol without the valve, after all, the carb was designed for that fuel so that would still work...

OK, just contact me around new year, and I'll send you a metering kit, and throw in a straight header for free IF I manage to get the solenoids in time.
There is a small window (approx. 1 week) that I will be home between travels, and if I can get the solenoid, I can ship it earlier (if not, it will be mid Feb).
The electronics and housings I have on stock, it's the solenoids that I could not get before leaving home.

I have no idea what shipping will be, but I hope it will be reasonable.
Dec 09, 2019, 11:45 AM
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dude, i'm in, and i'll take the exhaust header too. thanks for the offer. i'll assume this happens in february though, and id assume shipping isn't too bad. i've shipped stuff overseas before and it is what it is. let me know when you have a kit ready to ship. i'll be purchasing the ignition components before mid january. will get everything working on methanol and then proceed with converting the fuel system after i'm sure the ignition install is working, the ability to easily switch fuels seems like a plus for this system.
Dec 09, 2019, 12:25 PM
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I might as well send you one of these. A fully programmable, self contained PWM generator.(Freq and Width)
Drives MOSFETs very nicely. Been tinkering with EFI here as well.
PM your address and I can pop one in the mail.


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