Skylark ultralight engine.

[Eatherbreather]

Personally, I think 30 is too advanced. Heading into methanol engine timing. 26 to 28 will see your engine run on the RCEXL. Go from there.Converted methanol engines are generally small and higher revving (10 000+) so 30 is perhaps OK there. Done a few Super Tigres. G51 petrol, G90 petrol, 2300 (on meth). These days the Chinese make small petrols cheaply so it's easier to buy.....

Not sure I would ever run a RCEXL in a manned vehicle. Had a couple fail. At the very least I would use duel ignition, duel plugs including duel sensors.

 

3W or DA would probably be better quality.......but still very EXPERIMENTAL.

 

Don't worry about the plugs. Just get it running and "read" them later.

 

I like the "half-moon" sensor holder....

 

Have you looked at the reeds? Wouldn't surprise me if they were cracked.....Carby kitted?

 

Being "Eatherbreather" I take it you’re a diesel fan too?

I reckon 30 deg would be too advanced too. I will reset mine to 26 deg and start from there. I had quite forgotten about the prospect of using DA or 3W ignition and hadn't thought of doubling up the systems - are much better arrangement I'm sure.

 

The spark plugs. Yes that's exactly what I was going to do - I don't imagine this engine will be run very often and the heat range of the plugs I have is pretty well in the middle so I can't see any horrors like holed pistons happening. I will keep an eye on it though.

 

The sensor holder - with age comes some brains apparently. I thought ahead a bit and deliberately machined a "tail" on it to accomodate a zip tie to prevent the sensor wire being strained at the sensor. Also (not shown) I drilled and tapped a 3mm hole right through the magnet disc under the 4mm diameter magnet before fitting the magnet. This way if I need to I can remove the magnet by screwing a 3mm bolt into the disc under the magnet and effectively press it out.

 

The reeds looked ok no cracks that I could see. I don't think this engine has done a lot of work. I haven't kitted the carby. I am going to "suck it and see" on that one but I fully expect it will need kitting. I have had it apart and thoroughly cleaned it all. The various rubber bits and diaphragms that typically dry out looked ok - I have seen worse but running it will be the only way to really know if they're any good or not. I contacted Tillotson some time back and as I recall they said this carby was REALLY old - made well before 1980. They didn't have a kit specifically for it any more but had a "generic" kit that would probably do.

 

"Eatherbreather". Yes I am mad for a bit of model diesel engine action! They smell bad (read "awesome"), are harder to start and run, are messy, noisy and are often odd looking things. What's not to love! My user name was meant to be "Etherbreather" but I accidentally typo'd it when I was setting up my Youtube account? For whatever reason I couldn't change it and the typo stuck and now I use it everywhere. Well spotted

 

 

[Eatherbreather]

Twin carbs would still flow to the same case giving it's own balance/syncro issues. Single carb and reeds seems to be the "modern" way....Having said that, I've often thought about making a piston ported Zenoah flat twin. I've got a few stuffed, 2mm stroked cranks and 36mm barrels.....30CC singles..

Great minds! The twin ignition I'm now using on the "Skylark" (Skylaugh?) engine was to be used on a homemade twin using whipper snipper pistons, cylinders etc. If the twin carbs didn't solve the problem I was going to maybe make an intake manifold to both ports with a single carby or just blank off the intake ports and put a single carby on the crankcase.

 

I expect that twin carbys might at best just be swapping one problem for another i.e. may or may not help with fuel/air distribution but at the expense of syncro hassles. My understanding of the poor mix distribution in flat twin two strokes is caused by the rotating engine innards favouring one cylinder over another by sort of pumping the mix in the direction of rotation? Or in the case of rear induction as with my glow twin the cylinder nearest where the mix enters the crankcase is "favoured".

 

 

[riverduk]

Hi just found this blog looking for other info, but hey, with regard the motors origin, I did read here that the engine was made of hand made cases (???) + victa parts. Might be worth contacting the Holbrook Ultra light Museum via the Holbrook UL club (President, Bryan Gabriel: (02) 6036 2601) I was at a fly in there about 5 years ago and recall hearing of such a beast powering some early ultralight aircraft, some of which, I think, may be on show at the museum, not totally sure but maybe. I do know however that they are very knowledgeable and keen to pass on any info they might have as they are very proud of their museum which is a treasure chest of all things early ultralight here in Oz.

 

cheers, Ross

 

 

[Eatherbreather]

G'day riverduk!

 

Thanks for the info lead, I may very well contact them soon.

 

An update: Got the beast mounted, costing more time and money than it did to get the engine complete and of course, it doesn't run. I am now gonna try kitting the carby but I suspect the problem is in the piston/bore fit. I took the cylinders and heads off to see if the rings were free and they are but the compression still feels soft. Doesn't appear to have any cylinder base or head gaskets but it's not leaking either. I will make and fit some anyway just to be sure. No obvious bore wear or damage however. It may just be that the tolerances were bad to start with?

 

The pull start worked very well! As suspected the inertia of the prop carried the engine past compression - albeit not great compression. The cord has since broken though. It was a bit shabby to begin with. The engine would run for a second or two if I dried the plugs. Fuel is getting into the cylinders (and dribbling out the exhausts) but not wanting to fire. The spark is good.

 

A spot of crankcase porosity was found and subsequently sealed. Doing so has made no difference.

 

Pics shown use of whipper snipper fuel tank and throttle and model plane tacho and battery voltage meter.

 

Throttle assembly was useful for having a fail "safe-ish" spring loaded throttle lever. That is when released it goes to idle and not flat out as a simple friction system might. Also the stop switch is used. The "run" and "stop" positions are in fact reversed as the switch is used to close and complete the circuit to run instead of closing only to short out what would have been magneto ignition. Another feature I hoped would be useful is the throttle lock that hold the throttle at about 1/4 throttle for starting. All these things have been quite useless so far, time will tell though.

 

If it doesn't run after carby kitting and gaskets a rebore/piston/rings may be needed. Not sure I want to spend that kinda money and the cylinder walls look pretty thin to me already.

 

 

 

[Downunder]

Did we discuss the reed valve petals ? Are they cracked, flexing OK? Sealing.....

 

Nice set up, by the way....

 

 

[pylon500]

"Here's one I prepared earlier"

Love the little twin Cox, how did it run?

 

 

[Eatherbreather]

I haven't looked at the reeds recently but when I did previously they looked ok - no cracks, stting flat. Having said this I had chats with a mate of mine and he told me of a 125 moto-x/trailbike he had years ago. He said that when it came time for a rebore he did this and it of course ran great afterwards, much better than before as expected. When asked if he had replaced the reeds too he said "no, they looked fine". They were fine in that they worked but that is all they did. At someone's insistence he replaced the apparently "ok" reeds and the bike was again massively improved.

 

Makes sense to me now that I know this. I guess reeds by their very nature and the job they do in their working enviroment are going to fatigue and change with age/use. This is what I like about projects like this, especially this Skylark twin that I'm messing about with. I have been wrong about several aspects of it already and have learned a great deal about engines from it. It's probably better that this engine continues to throw challenges at me. If it had worked and run properly from the outset I would have learned little or nothing.

 

Now to source new reeds. If I can't find any I can make them.

 

 

 

[Eatherbreather]

It ran ok - I wouldn't say great but as you probably know Cox problems are often solved with more nitromethane in the fuel. I should re-visit it sometime and give it a damn good thrashing with some different fuels and maybe try different glow heads. It seemed to favour one cylinder more than the other as I recall (the one that's offset slightly to the rear closer to the intake?). I think this condition may also be because the rotating innards of the engine tends to pump the incoming fuel air mix towards one cylinder more than the other.

 

It's because of this I am considering retaining the carbies mounted on the cylinders for my "flat twin whipper snipper parts engine" project. Two carbies will be harder to tune doubtlessly and make for a heavier and bulkier engine. My thinking being that if one cylinder is a bit weak I can hopefully correct (optimize) the fuel air mix for that side of the engine - this hopefully being possible by the piston ported carby enabling the incoming fuel/air mix being placed more or less directly under the piston and filling the transfer ports of that cylinder rather than having the fuel air/mix pass through the bottom end of the engine so much. If this doesn't work I can blank off the intake ports and mount a single carby on the crankcase (offset if need be to position the carby nearer whichever cylinder is weaker) with reeds.

 

If this doesn't work I will have a beaut paper weight.

 

 

[Eatherbreather]

Woohoo! Shelley beach! Just up the road from me! - Just checked out your hang gliding pics : )

 

 

[Eatherbreather]

Are you related to Len per chance?

 

 

[pylon500]

My fathers name was Len if you're asking me...

 

I've done some modelling in the past as well.

 

Yes, I'm an ex-Sandgroper.

 

Some of my modelling stuff in the google link below.

 

 

[Eatherbreather]

I see! If we're talking the same "Len" (and I suspect we are) then I have couple of things here that he used to own. I never had the pleasure of meeting him myself unfortunately. One of the items is a letter opener made from an old bit of streamline section flying wire? It has some numbers stamped around the threaded end (metric M5) but I have no idea what they mean or what aircraft this came off. I made a brass handle for it and use it every day

 

I can fire off some pics to you of what I have if you like. Is there some way of sending private messages om here or do I need an email address?

 

 

[planedriver]

Just click on members name from members list at top of page and you should be able to easily send them a private message.

 

Hope this helps.

 

Planey

 

 

[pylon500]

Are you related to Len per chance?

Sorry about the slow reply (forgot which post this was in..)

Finally found a picture of my father in his 'Hey Day', as Western Australian 'Champion of champions' circa 1963?

 

At the time he held WA control line speed records in class B (5.0cc), and class C (10.0cc), as well as state champ for control line stunt, and I think A2 free flight glider.

 

 

Was flying models into the '90s, but was also getting back into full size gliding and setting state and national records there.

 

Held Australian height gain record of 25,462ft (remember, that is gain, not absolute) around 1987, off the Stirling Ranges.

 

Sadly, he passed away back in 1994.

 

 

[Eatherbreather]

Woohoo! Look at them trophies! I have here his pulse jet starter and some engine mounts that appear to be for a "Dynajet" pulse jet. It is my understanding that he used to do night flying demos of pulse jet control line at the Perth Royal show. He certainly seem to have been a very keen and capable guy.

 

A wee update for the Skylark twin - I fully re-kitted the carby a couple of days ago when the parts arrived from Tillotson - in Ireland! They moved their operations there some years ago. They had no record of my particular model of carby but true to their word the kit they sent fitted perfectly. I have removed and re-examined the reeds. They appear to be completely fine just as I recalled but I will replace them anyway. Once I have these sorted and I have repaired the pull start cord I will have another go at blowing the fence over (hopefully)

 

Coming up after the break a look back at the stories still to come....

 

 

[Dick61]

The Skylark was built in Melbourne, Berwick actually and the one you have looks to be a fairly early one as it has the Victa twin flywheel on it. I can't tell from the pictures but if it has cast iron barrels then it is definitely early. There were over 400 produced and most were sold to the USA, the later units had a specially wound coil, with the flywheel off the early Victa 125 as it gave better spark, these had their fins machined off as there was no need for the cooling fan. The were 320cc and the only parts from Victa were the ignition flywheels and some ignition internals, the pistons were Yamaha and the con rods from Kawasaki, the reed valve is also Yamaha. The carbie is a Tillotson pump type from a Ski-Doo. The crankshaft was purpose built for the engine and there was a very small batch that had breakage problems as the incorrect steel for the shafts were supplied and the problem wasn't discovered until they failed in service. They were rated at 18hp with a weight of 25lbs, they were originally conceived due to the inventor buying a Skycraft Scout from Ron Wheeler in about 1975/76 and finding that the Pixie engine which WAS a converted Victa engine couldn't get the aircraft off the ground. The Skylark Aero Twin was the first purpose built Ultralight Aircraft engine in the world, what you have is a piece of history from the early days of the Minimum Aircraft movement in Australia. The Victa twin ignition system was replaced with a specially wound coil and 125cc flywheel because the Victa twin system was a piece of crap.

 

 

[Methusala]

Yes Dick, you can see from my earlier post that it was a brave attempt but dangerous in the air. Mine was "equipped" with pressed steel mufflers from an early Victa mower engine and one split into pieces flying through the prop and wrecking it. The motivation seemed to be to make a quid rather than to be a responsible aviation enterprise. I replaced my Skylark with a Fuji Robin EC 44 and had no further power plant related problems.

 

 

[Dick61]

You stated earlier that you had a crankshaft failure and now you're saying that you had a prop strike when your muffler system went through the prop. Obviously you haven't made the connection between the two and have just blamed the engine for your troubles. The explanation from the maker does not sound correct and maybe your memory is faulty after 35 years, if your engine was "equipped with pressed steel Victa mufflers then you put them on yourself, they were not an original fitting on the Skylark. Oh, BTW when you had your crank fail at 100 feet was that at the Pakenham Airstrip?

 

 

[Methusala]

The prop strike occurred while the engine was fitted with a toothed belt reduction unit. This I later removed because it was so poorly manufactured the belt would run off its cogs and there was no way to align it. I don't think that the shock transferred to the crank indirectly via toothed belt should account for failure of the crank. You stated that some crankshafts were manufactured from crook steel - ergo the failure in my engine. I am not sufficiently in my dotage not to recall the frightening events of this time. It was probably on Ron Lang's advice that I fitted the exhaust seeing that he did not have an exhaust system supplied with the engine. I don't wish to open old wounds or criticise the guy for what happened so long ago. I accept that, in those days, we were all experimenting and that this was the way it was. I never flew at Pakenham and was fortunate, as were a lot of others, to come through those days alive. However I don't want anyone to remain under the illusion that this was a fit device to power any ultralight. I recall that Ron Firth, from around Bowral, had a Skylark with cast iron barrels and direct drive on his Scout and I never heard that he got anything but good service from it. Regards, Don

 

 

[facthunter]

The Scott company made a good twin cyl aircooled two stroke in the early 30's and Enfield McCulloch. as well. the second ended up in a lot of Autogyro's. Both used in Flying Flea's at times. Nev.

 

 

[Eatherbreather]

G'day all!

 

Thanks for the info! Yes mine has cast iron cylinders (with steel liners?) and a Tillotson carby. Some time back I kitted the carby with genuine parts still being made (in Ireland now). It also had the disgusting (useless) Victa twin ignition that I have removed including the fin-less Victa flywheel.

 

Previous attempts to get this engine running have failed to produce more than a few consecutive coughs - the compression felt pretty low as I recall. When the weather improves I hope to re-visit it to get it running. I have got new head gaskets to fit (Victa 160cc same bolt spacing) and need to make and fit some lower cylinder gaskets and fix the pull start that died. Also need to replace at least one of the reed sets as some bored f*#kwit thought it would be good to make origami out of one of it when I had them out of the engine to try to find replacements - I am reliably informed that new reeds work much better than old ones even if they aren't damaged in any way.

 

I don't like my chances but I will try to get it going anyway. If none of this sees it running I may get it off to someone more knowledgeable it may need a bore/pistons/rings rebuild? It is such a simple engine there really so little in it to prevent it from running otherwise. The notion of fitting a "Scout" propeller to it and having it work is encouraging though as that is the propeller I have been using and the only "loose" propeller I have!

 

The Jimbo.

 

 

[pylon500]

If you are planning to run direct drive, the old Scout prop would be way too big.

 

I was playing with a couple of Kirby (Tecumseh) 144cc motors back in the beginning, running direct drive props.

 

My last set were 32x16, and could have been maybe a little bigger?

 

 

Yes, it's a pusher, I was using two of them on a home made trike.

 

 

[Eatherbreather]

Oh! I was going direct drive - any suggestions what size might be ok? The prospect of carving my own horrifies me, I need something "off the shelf". Doesn't have to be awesome, just safe and permit the engine to run.

 

 

[Methusala]

Sorry, correction.... Russel Firth was the guy with the Scout

 

 

[facthunter]

If you just want a test prop, it's pretty easy to knock one up. It needs to be balanced and a bit of extra weight won't hurt. Do it for the experience. I doubt you will just "find" anything suitable. Nev