rinkhals01

Hi there fellow modellers.
I have a new in box Avistar 1.80 and I want to convert it to Petrol by using the existing carburetor and a Perry oscillating pump to provide fuel pressure, thereby negating the use of a Warlboro carb in the interest of simplicity. I furthermore will most likely be using an OS-G5 glow plug once again to keep it simple and not using spark ignition which in turn means no complicated engine timing, and obviously less shagging around when at the field. ( As a quick aside, I am a qualified engineer and have taken into account the porting, compression ratio and swept volume, and on paper,I cannot theoretically see why this won't work.)
This set-up, if practical, it will leave me with an easy to operate, lighter engine than what is commercially available while using a much cheaper fuel than nitro.
I am less perturbed about the ignition timing as I can "adjust" this trialing different fuel octanes.
Any thoughts would be so gratefully accepted with many thanks> Smile

1967brutus

I cannot comment on the use of a G5 plug, as I do not have experience with it in converted glow engines, but I do strongly recommend an ignition. Not because of the G5 or its properties, but because changing over to electronic ignition while still running methanol, all the way back in 2013 demonstrated that glow ignition, although fully adequate for methanol, presents a few issues that are much less desirable when running petrol, and in fact improved running and handling of even Methanol burning engines considerably.
Setting the timing is a one time affair and fairly simple, and having a proper timing removes a lot of other issues.

My experience says you are not going to get good results with the stock carb even when using whatever kind of pump, because the fuel metering of a stock glow carb simply is not right for petrol.
You might get decent results with a SuperTigre carb, those are the only glow carbs I am aware of that have the adjustment range to get more or less satisfactory results,

Unless of course you are willing to compromise with rich patches throughout the rev range and black crud from the exhaust.

You might want to look here: Electronic solutions to modifying glow engines of all sizes to gasoline
Admitted, that discussion starts halfway into the subject, because it is a continuation of a discussion that began 3 years ago over on RC Groups but was heavily sabotaged by one or two trolls.
Unfortunately, that discussion was often derailed and has become pretty mutilated because of that, but FWIW here it is: https://www.rcgroups.com/forums/show...convert-to-gas

My personal opinion: any attempts to mess about with different octane ratings to defeat the timing issues from using the G5 plug, basically defeat the purpose of converting to petrol.
I have set up my engines with ignitions (which also brings a few advantageous safety features with it), and set them up for the most common fuel type availlable to me, whioch is over here E10 95RON. I am running petrol now exclusively in all of my engines, which range from a tiny OS FP10 all the way up to the ASP radial, and in that range there also is a .30 fourstroke, and even an OS Wankel. Still have to experience the first mechanical issue (like wear, breakdowns or parts faillures) from the change-over.

rinkhals01

Hi Brutus.
Thank you so much for your reply and I have taken quite a bit from it.
I also apologise for only getting back to you now, but I have been away on a demanding business business trip.... it's truly abhorent how work always interfers with modelling... teehee

1967brutus

Don't worry about it!
Glad to have been of help.

rinkhals01

Hi Brutus.
Here's something I found that relates to this thread and may be of interest tp you. Let me know what you think.

1967brutus

There is not much to think of it... I mean, it is not that engines with a G5 plug won't run or anything.

They just won't run as well as spark ignited engines, and they are, essentially, still glow engines with fairly messy exhaust, and higher requirements for ground-equipment (glow power, electric starters, that kind of thing). Doesn't mean it won't work.
Does mean it is a compromise.

Not one I would be willing to make.

EDIT: maybe I need to clarify myself a bit here: I am a (marine) engineer by profession, and I have different standards for "running well" than most people. For me, it is about optimal burn and minimal wear and fouling. Not maximal power or minimal weight or utter simplicity.

Those factors (minimal weight. maximum simplicity and highest power) are not important to me, and are in general highly overrated, as can be seen here:



That's a simple 60" wingspan Robbe Charter weighing less than 4,5 lbs (and I did not have to use special tricks or exotic materials to keep it that light), running a 5 cc ASP 30, getting 70 minutes of flight out of 6 oz of fuel, and from switching on TX/RX till "cleared for take-off" can be as little as 30 seconds as the first video shows. Yet, more than enough power to safely function as a clubtrainer from first flight up to and including take-off and landing instruction, as well as basic manouvers such as loops, rolls and hammerheads.

If that is possible with a 5 cc fourstroke, I really see no point in using a G5 on a Moki 1.80 "for weightsavings or simplicity"... Any plane big enough to accept that size engine has not only plenty room for it, the reduction in fuel tank size allready more than compensates for both the weight penalty or the space requirements of the ignition system. And about 5 burnt G5 plugs, allready pay for the ignition, so it isn't money that could be the issue either.

rinkhals01

Wow how good is that!!!!!
Now that is impressive and considering how smoothly it runs I agree that this the path worth walking down!
Like you, I too am an ex Marine Engineer and have had to work to standards that most other engineers don't even think about. ( I spent 20 years serving as a "sea going Engineer " on submarines where if it is not done correctly, you die!!!)....

1967brutus

Then you are an entirely different grade of engineer than me (meaning, I think you are a few levels above me WRT both "having a pair" and technical standards, because indeed, consequences of a shabby job are quite a bit different on one of them boats).
Please don't take this wrong, but... I never knew NZ had subs?

FWIW, the vids I posted earlier, that is a sedate low powered trainer, but it does not have to be that way, I do have a few planes in the same wingspan category that do near or full unlimited vertical as well...

Does not require large engines or any high end equipment either t have a bit of fun. This is a clubmate of mine using the same basic principle on an ancient and fairly heavy Robbe Puma, fitted with an also not exactly brand new OS FX46 (with ASP piston/liner setup)
No tuned pipes, no high octane fuel, just plain old E10 95 RON with 1:10 oil content, our standard mix.


But mind you, on the avistar 1.80 you might get good results with a good matched Walbro, for these tiny engines, you are going to either need electronic mixture control, or if you are handy with metalworking, you can modify a glow-carb to get "more or less decent" results. The electronic option is better.

In all fairness, such a project belongs in the "engine conversion" segment, not in the "gas engine" part, IMHO.

kmeyers

Years ago I wrote a little post about the simple idea of weight of fuel savings (glow vs gas). I don't remember much about it right now, but, the premise was very poorly received. I even used the celebrated transatlantic flight of an rc, autonomous then back to rc (TAM used just over a gallon of white gas to fly over a thousand miles on a converted OS .60 ) as an example.
I'm currently converting my float equipped 1/4 scale Cub from a very thirsty Super Tiger 3250 glow two stroke to an old glow Saito 1.80 four stroke that I'm also converting to gas ( with EI ignition and Walbro type carb).
So I have been following this thread and give a + 1 to the Walbro type carb ( purchased on flee bay 13.00 dollars ) EI ignition ( hobby king 25 bucks).
After a one time set up, IMHO, nothing could be simpler or more efficient.

note: I own a lathe and turned a couple of parts for the conversion.

1967brutus

I have an F3A plane, a Wolfgang Matt Saphir, that was originally fitted with a Webra longstroke .60 2stroke, and running a 12 fl.oz fuel tank.
It had a single 2000 mAh NiMH receiver battery.
When I converted it to gasoline, the engine got replaced with an ASP 90 2-stroke, the fuel tank was reduced to 6 fl.oz and the receiver pack got doubled to 2 x 2000 mAh NiMH in parallel.

The conversion turned out to be a smidgen lighter than the original glow fuelled version, by about 30 grammes when fully flight ready.
Empty, it was maybe 75 grammes heavier, but hey, planes never take off with empty fuel tanks, right?

The ASP 90 on gas does by and large about the same performance as the Webra longstroke on 20% Nitro and a tuned pipe.

kmeyers

Just watched the video, pattern planes fly so well. This summer I found a box in the basement that had been there for 12 years, a Great Planes Venus 11 arf. I put it together and it has been my everyday plane for the last two months. Really flies well, seems to do everything I want and more. I put a vvrc 20cc gasser in the nose modified it for tank on the cg and called it a day.
Wish I had opened the box sooner. Best GP arf I have ever had and I have had a few.

rinkhals01

Hi Brutus.
You are correct that in that NZ does not have submarines. I was in the South African Navy for 20 years and then I immigrated to NZ.

1967brutus

I've been to both countries, and they are both beautiful to live in.
Hard to say which one I would like better to retire to. But I'd say Kiwiland...

Merry X-mass (which in your neck of the woods is mid-summer, one of the things I like about NZ... I was there during X-mass and Newyear '89-90 ) and a happy new year to all of you!

Jesse Open

Just a matter of how much simplicity you prefer.
You can pile a considerable mass including peripheral wiring, connectors etci into and on to the plane with one system.
On the other hand, a very simple power source for starting is used with glow ignition . Once running, the aircraft can fly just fine, leaving that power source on the ground. Wear and tear differeces between glow and spark gassers are negligible at best.
BTW, Electric starters for glow ignition are not in the least mandatory.

One must simply weigh the differences honestly and decide.