RadialWacko

Ooo, I love this idea. The sig four star was my first ever nitro plane over a decade ago. I think I might just do this.

RadialWacko

We get density altitudes of 8-9000+ feet almost daily in the summer. Your reasoning makes sense on paper but I think you would be surprised how drastic of a difference it is here.

1967brutus

I have to honestly admit that I have no hands-on experience with the density altitudes you mention, but I still would be surprised if that Twin would not fly that Rascal at your locale. It might perform a bit different, that I readily believe.
My reasoning bases on how horribly overpowered RC planes generally are. The plane I told you about, the one that I fly in indonesia? In its last iteration by the manufacturer, a .40 2-stroke was advised, which is well over 1 hp.
I have a spare one that is still at home, and the plane is perfectly fine with 0.25 hp. I use it as clubtrainer even, and it is not critical in take off or corrective manouvres as happen frequently when instructing.
I am not claiming that tiny engine will fly it at your locale, just indicating how badly overpowered manufacturers recommendations generally can be.

RadialWacko

I one hundred percent agree with all of that. I learned and grew up at a field at 1/5 the elevation I am at now. I will never forget trying to fly a plane that I brought with me at my new location. I knew it was going to be a performance decrease, but it didn't even get off the ground... This engine would certainly fly the Rascal, I'm not saying that. But I do think it would struggle with even a .91 aerobatic plane, it's that significant. But with that said, I agree that most planes are way over powered. For the most part, I enjoy scale flying a lot more so I think it will work out well. Indonesia sounds like a nice place to fly, and that's cool that you are involved in the club training program. Good on you!

mitchilito

My Feedback: (7)

RW,
If you look at the flying vids of my Rascal with the gas twin in this thread you'll see that at sea level where I fly it has lots of power. But with the reduction in performance you are describing it's quite possible that you would not be satisified with it's performance where you fly. However, there are things you could do to mitigate that loss. If it was me I might consider continuing to run methanol which would negate a large portion of your density altitude power loss. I, personally wouldn't run nitro tho - its just too corrosive.

With that said, you would have to change some of the seals/diaphrams in your walbro carb to accommodate alcohol. The Moris conversion comes with a WT962 carb (or at least did when he filmed the vid I posted earlier in this thread - and then purchased for my conversion) and works GREAT with gasoline. I'm not sure how it would work with alcohol, since you have to pass more than twice the volume of fuel while running methanol. I'll bet it would work tho.

I'll bet Jesse OPEN would know that answer tho. He described a background in this exact area.

Jesse?

mitchilito

My Feedback: (7)

Hello world!!

It took three months for something worth mentioning to happen with regard to my wonderful Rascal/Gemini. The norm is I go out, gas her up and fly fly fly. But yesterday after starting her up I noticed an aileron twitching badly on taxi out. It seemed worse at different (lower) throttle settings. Then I noticed that ALL the controls were twitching. Badly. What the heck?? I taxied in and shut her down.

I come from the days of 72mhz radios where this kind of behavior was an every day occurrence but I've NEVER experienced this with 2.4ghz. The communication link is just too good. Or so I thought.

I could only think of one thing that could possibly cause this: an ignition leak. So I wiggled the spark plug caps and reseated them firmly. They did seem a little loose - one in particular reseated inward about a millimeter or two - not much really. But that did it: no more twitching.

Like I said, I've never had an interference problem of any kind with modern radios - but it can happen. So be sure to check your plug caps from time to time. . . .

Hope you all have the best of the holiday season! Till next time. . . . . .

kmeyers

So fly fly fly and periodic maintenance.
Great pic!
Thanks for the update.
Happy holidays

1967brutus

If you still have the same ignition you had in the beginning of this thread, if you ONLY pushed the plugcaps down, that issue will re-occur, and sooner or later cost you that pretty Rascal... And that is preventable...

You have the twistlock plugcaps, they should lock 100% by pushing down hard on them, then twisting them about 30 degrees (half of a hex) clockwise, and releasing them should be "pushing down hard, twist 30 degrees counterclockwise and release"

Also, this specific type of plugcaps should come with contactsprings that go into the cap to ensure a good electrical connection between plugbase and cap-shell. They are thin gauge conical springs and go in with the small end facing the engine.

mitchilito

My Feedback: (7)

No, I don't have the "twist lock" plug caps anymore. I'm now running the RC excel style caps that are just a force fit. Not sure what the friction mechanism is but they are generally VERY hard to remove (just like on my Saito FG-60 radial).

I actually made a nifty little slide hammer to remove these style plug caps. Very handy!


When used carefully this baby is also much less abusive to the equipment

1967brutus

Ah, OK, I did not know that of course.
I have so far not yet had one of those new styple caps come loose, but I do not trust them as much as I do the twistlock caps, with which I have never had a single problem (once I discovered that they were twist-locks... before that I thought they were the worst possible design )

EDIT and PS: That slide hammer is a good one, Going to steal that from you

kmeyers

I believe that a flat screwdriver at the base prying up with a twist while wiggling and a slight pull upward is in my opinion the least likely to cause any damage.
Seeing your tool gives me the idea that a purpose built tool is a better way to go (can you see the smoke coming out my ears?).

mitchilito

My Feedback: (7)

I LOVED the ease of installation/removal of the twist locks but could never get them clocked right i.e. one was always noticeably higher than the other. Just bugged me.

Then I got the Saito FG 60 with the push locks and had a hell of of time trying to get the caps off. The slide hammer is a MUST. Maybe I should manufacture a couple hundred ☺️

1967brutus

I have basically the same with my ASP radial.
For the twistlock caps, I have always "indexed" the plugs (more like "index the hex") so the caps would be on in more or less proper alignment, has never been an issue. Most of the times it was no more than tightening one plug a bit stronger, very rarely I had to flatten the washer a bit.
Nowadays the single and twin ignitions from RcExl all come with the pushlocks and I do not particularly like them. But what can we do?

I have so far managed without a cap pulling tool, but I am going to try it.

mitchilito

My Feedback: (7)

I think you'll find you really like the ease of removal with the slide hammer. One just has to be careful using it. Wouldn't want to yank on the leads. . . .

1967brutus

I am gonna find out when I am home again (at sea till early January)

mitchilito

My Feedback: (7)

So I always said I was going to do it and it's finally time. I'm beginning the process of converting my 50cc Gemini to gasoline. You'll find the thread here:

OS 50cc Gemini Twin Gasoline Conversion

Hope to see you regulars there!

A little teaser. . .. .

kmeyers

You tease. you got me.

mitchilito

My Feedback: (7)

Several fun things to talk about this time. I took her out to fly yesterday and it didn't want to start. Started on left cylinder but the right one didn't want to fire. I took out the plug and cleaned it and eventually got it to run on both. But during flight it just wasn't right. Full power was okay but the transitions weren't good.

At home, while spinning the prop on the bench, I noticed one cylinder had ZERO compression! I'm not sure I've discussed this in this thread (I think I have) but the right cylinder exhaust valve had carboned up and was extremely sticky! This happened one time before (maybe an hour of flight time ago?) and that's when I learned how good Sea Foam fuel additive is. I put a scant drop on of it on that exhaust valve and it INSTANTLY melted the carbon. Since that happened I've been running at least an ounce of Sea Foam/gallon of gas. But apparently that's not quite enough to get to that right valve chamber so I added another 1/2 oz.

On a side note, I also found that the iridium plugs will foul oil foul very easily. It's nothing but the standard plugs for me from now on -

1967brutus

Strange... You're running 20:1, if I'm not mistaken? Forgot which oil though.
I run 10:1 Castrol PowerRS 2stroke with regular E10 pumpgas, and I haven't had any sticking valves. When mine was still only running the "modded glow carb" there was a fair bit of tar like crud in the combustion chamber and valves, but nothing that ever led to issues with either valves or sparkplugs. That went pretty well for at least about 30 runhours (counter, not estimated).
Since I have been using the electronic-controlled fuel metering, the plugs are basically dry, the black crud has gone and the valves remain clean. Currently close to 60 hours total (IIRC 58 and a bit, but not sure, can't check it right now).

I do mix in a common "carb cleaner" additive bought at the petrol station: Wynn's Wynn’s Petrol Treatment - Voor 22.00 uur besteld, morgen in huis! (werkenmetmerken.nl) but I doubt if that stuff has anything to do with keeping exhaust valves clean.

I can't think of a reason why your engine fouls up that quickly, but it sure is strange.

mitchilito

My Feedback: (7)

I am running 20:1 - Redline Racing oil, Brutus. I had been running 15:1 but with the amount of sludge blowing out of the exhausts and the regular fouling I reduced it to 20:1. I had thought it was oil fouling this past problem but I'm pretty sure it was mostly the sticky valve. I do know that the non iridium plugs work fine so I'll be sticking with them.

Also: I feel very safe running 20:1 in this engine for this reason: after a flight session, say 10 minutes after flight I will pull the crankcase drain plug (remember, my crankcase drain is normally connected directly to the intake Venturi) and I get a LARGE drainage of collected oil in the case. Also, every time I take the valve covers off it's nice and wet in both sides. Unlike my Saito radial which the top cylinder runs pretty dry and the bottom two are slightly oily - but not drenched that's for sure.

Apparently the Moki 300 has this same carbon stick problem so I've added some Seafoam to my valve lube oil for both these engines.

1967brutus

I also only use the common plugs, never even tried the Iridium ones, never saw a reason to. in almost 8 years and several hundred runhours, I have had exactly ONE occasion where a fouled plug was the proven cause of an engine flame-out. All other cases it was either a plug cap issue or a bad ignition battery.

I have heard of the redline oil, but am unfamiliar with it, it is not a common oil here in Europe, so I have no idea whether the type or brand of oil is a possible cause of what you encounter.
Seafoam is also an unknown here, does not even pop up in a google search, so I can't comment on that either,

I do know that engines do not break down mechanically from 20:1, I have seen too many people using that ratio to claim otherwise. Possible wear is not why I run 10:1 Reason is that up til now, I seem to encounter fewer problems like the ones you mention (sticking valves and/or fouling plugs) than people using lower oil ratios. And I prefer "less problems" over "less crud". ( I know: if I wanted less problems I should have stuck to meth and glow, but hey, I dislike problems but welcome a challenge )

I opted not to recirculate the crankcase effluent: it is used oil, and whichever way you turn it, used oil contains dirt. I see no point in re-introducing dirt coming from the engine, a 2nd time into same engine. Come to think of it, that recirculation can very well be one of the possible reasons for your fouling issues, because that oil inevitably contains combustion residue that normally would be expelled and be done with it, but now gets a 2nd opportunity to cause trouble.

Just general info I picked up along the past 8 years:
If there is (black) sludge coming from the exhaust, oil content of the fuel mix has nothing to do with that. Fuel/oil ratio affects the volumetric amount, but not the colour or blackness. If the crud is black, the engine is still burning a rich mixture. You would be surprised how little of the oil actually burns off INSIDE the engine. That percentage is negligable, oil burns way too slow for that. Normally oil burns off in the exhaust system but our systems are way too small for that too.
Ditto for blue exhaust gas: it is excess fuel, not excess oil.
There is very little one can do about that rich burn using a conventional carburettor, regardless of the type/brand of carb, because it is caused by the properties of the principle of carburation itself. All carburated engines big or small do it to s certain extent,
That excess fuel causes soot forming, and the oil washes away that soot because deterging soot is one of the oil's functions. More oil=>better washing=>less problems. Sounds counterintuitive, but is fact (assuming a decent oil quality of course).

Rich running mainly is caused by poor atomizing and/or poor mixing of fuel and air, and is not really a function of needle settings: the ignitability of the fresh charge is not determined by the overall fuel/air ratio, but by the fuel/air ratio of the evaporated part of the fuel, because liquids do never burn: it is always only the vapour that burns. That is some stupid law of nature someone once invented, but unfortunately for us engine-whisperers, it is true nonetheless: a liquid cannot take part in a combustion reaction unless it evaporates first.
Poor atomising forces the needles to be opened more in order to maintain ignitability, but once the vapour is ignited, the liquid fuel evaporates due to the heat, and also takes part in combustion, causing it to go rich and form soot. That is why you can set the needles on the brink of fuel starvation (the engine cutting out because the mixture falls out of its ignitable range) and STILL have a rich burn once firing. Some people say that a fine mesh wiregauze downstream of the carb promotes evaporation, thus allows for leaner needle settings and reduced sootformation, but I have never tested with that (too much machining involved, and such a mesh can clog up).

mitchilito

My Feedback: (7)

Wow, that is a lot to unpack, Brutus. I'll have to chew on this for a while! Thanks for all the input.

kmeyers

1967brutus
Are you typing or using voice recognition?
just kidding
As always, you bring a lot to the conversation.
Thank you

Jesse Open

LOL!

To listen to some folks, you may have thought that methanol fuel and glow plugs were extremely challenging. Those glow drivers alone seem to baffle so many folks.
Then again,must admit that I never considered spark plugs and gaspoline difficult either. Not now, not even forty years ago.
Your newest project looks great. Running well is a good thing. Having a neat, clean installation is always a worthwhile undertaking.
Keep up the fine work.

mitchilito

My Feedback: (7)

Thanks guys. For a quick update, I took her out the day after the stuck valve incident, adjusted the mixture a tad and flew like a madman all day long. It really is the coolest toy on earth (okay, I might be a little biased).