Laser Engines - Technical questions

[Jon H]

Quite right Paul, although you are assuming an airtight crankcase and they arent.

We tested running for many hours with the breather closed and there were no negative effects on the engine in terms of its operation. Long term however i suspect that its better to vent the crankcase to try and expel some of the nasties that can accumulate down there. There was also a tendency for the front bearing seal to blow out and then the engine just made a mess!

An ideal solution would be a short pipe to a catch tank that can be drained after the flight, but its a bit of a faff. ED is also quite right when he says that with modern thin oils, and with low oil fuel, the whole conversation is becoming less and less relevant.

[Mike T]

I use a small plastic T piece on my breathers. Short stub of fuel tube to connect the breather nipple to the T, one leg of which points up to the carb. The other, downward leg vents via tubing through the bottom of the cowl.

The idea is that the air vents up through the short stub and the oil drains down the longer tube. I've no idea whether this is technically effective, but the top of the engine bay stays relatively clean and an awful lot of oil splatters the bottom of the fus... Here's my J60:

[Paul james 8]

Posted by Jon - Laser Engines on 01/09/2020 14:55:54:

Quite right Paul, although you are assuming an airtight crankcase and they arent.

We tested running for many hours with the breather closed and there were no negative effects on the engine in terms of its operation. Long term however i suspect that its better to vent the crankcase to try and expel some of the nasties that can accumulate down there. There was also a tendency for the front bearing seal to blow out and then the engine just made a mess!

An ideal solution would be a short pipe to a catch tank that can be drained after the flight, but its a bit of a faff. ED is also quite right when he says that with modern thin oils, and with low oil fuel, the whole conversation is becoming less and less relevant.

Interesting re. crankcases not being airtight. I'm guessing that the likeliest place for leakage is the front bearing which, as you say can end up with the seals blowing out, just goes to show how much positive pressure can build up. I'm sure that it is possible to run engines without crankcase breathers (I've a fair few OS without) but can't see that having a breather is ever going to be detrimental.

As you mention; as far as mess is concerned the more modern fuels with lower viscosity oil and lower oil content should run cleaner but I like the idea of having the venting so the oil can move around and replenish as well as possible.

[Nigel R]

"I'm sure that it is possible to run engines without crankcase breathers (I've a fair few OS without)"

I think OS have internal re-circulation on anything without a crankcase breather. The alpha four strokes, for instance. All eventually vent crank - via cam chamber and then valve area - on into the inlet manifold.

[J D 8]

Enya 90 needs a crank case vent, one of mine bought S/H as new would start with ease and run fine in the air for 4 to 5 minuets and then bog down and stop. First thought was leaning out in the air but opening the needle shortened the run time.

To cut the story short after much messing about and much dead stick practice the engine was removed and as I put it down I noticed the breather nipple had only a pin sized hole in it, enough to let some oil out but not enough flow to prevent a build up in the case. Once on the ground the oil would drain and we would be good to go again. Pic shows nipple next to it's replacement .

[ken anderson.]

many moons ago,people used to fit a 35mm film canister to their models and have the breather tube going in to it to collect the expelled stuff..

ken anderson...ne...1..memory dept.

[Martin McIntosh]

With you on the plugs Jon, they are the only types I keep in my box other than Enya 3 which is virtually the same as the OS 8.

I started to fit breather tubes to my Lasers a while ago and there is hardly any mess on the models now.

[Jon H]

Posted by Nigel R on 01/09/2020 16:24:56:

 

The alpha four strokes, for instance. All eventually vent crank - via cam chamber and then valve area - on into the inlet manifold.

Very true Nigel, it was such a good design the abandoned it for the Alpha MkII, reverted to a normal breather, and promoted it as a better solution! gotta love marketing people. They are worse than lawyers

 

Edited By Jon - Laser Engines on 01/09/2020 20:00:51

[Solly]

My Alpha 81 Mark 1 would run erratically in the cold weather due to the small oil passage being blocked with cold oil. Once the engine got hot the problem disappeared. I solved the problem by drilling and tapping a hole for a breather nipple in the backplate, as per the Mark 2. It now runs perfectly.

[Nigel R]

I thought the story went that was put back in order to add after-run?

Certainly ain't no way of doing that with the mk1 alpha, just run it hot and dry says the instructions. And it goes on, if you fancy it you could pull the glowplug and squirt some oil in.

[Jon H]

no idea. if it was for after run oil it was, like after run, a bit of a waste of time. Unless you brim the crankcase, really fill it up and get all the air out and then drain it adding after run does little to nothing. Even if you do flood the case, if the oil you use is not able to blend with the fuel/oil you use then again, its not helping you very much

[Richard Harris]

Thanks for the info Jon and all, I've passed it onto my friend.

Rich

[Martin Arnold 1]

Posted by Jon - Laser Engines on 01/09/2020 22:02:08:

no idea. if it was for after run oil it was, like after run, a bit of a waste of time. Unless you brim the crankcase, really fill it up and get all the air out and then drain it adding after run does little to nothing. Even if you do flood the case, if the oil you use is not able to blend with the fuel/oil you use then again, its not helping you very much

Totally agree with you Jon on the "ARO" as some people call it, they seem to go mad with pages of posts on another forum about the stuff !!

Gave up trying to use it years ago on my four strokes, the bearings still will rust as you say, think it just makes people feel better pumping some oil in the crankcase !!

[Daniele deg]

Jon,

your tec tips are very instructive, I'd like to make some questions of general interest (sorry if I missed in the previus posts):

fuel: I'm using Motul micro 18% and 5% nitro on my saito 180, in an old post you say it's safe to run with 10% oil an 5% nitro, this is true for your Lasers or can be done also with others?

spark ignition: a spark ignition (alcohol) can produce better results in term of fuel consumption and power? I'ts a wast of time?

Corrosion: spray gun oil through the vent nipple could be an option for buried cowl engines, with little fly time (10 fly per year ex.).

Laser 300V: I hope you can restart the production of the twins, before the brexit will be complete? (I live in Italy).

Thanks again for this precious support to the rc community,

cheers

Daniele

[Jon H]

Yep, its another one in the modelling folk lore book in my view. You will stand a much better chance of preventing rust if you choose the right fuel, and then take the time to tune the engine properly. For some reason everyone burbles their engines round half a turn too rich complaining about high fuel consumption, cost, mess, rust, and reliability problems. All the while the flee to petrol and electric to rid themselves of the problems of a glow engine.

Little do they realise that actually, if they tuned it right and used a fuel than was less than 20% slime most of their problems would go away instantly. But nooooo, you cant run an engine 'lean' (ie, tuned for peak performance) as it will overheat! ok..fit the cowl properly and baffle it to direct the air..you know, make an effort?

Nope, that is all way too much like hard work. Lets just complain about stuff on forums instead

Sigh.

[kevin b]

Hey folks, Jon had a rant !

Maybe it was caused by the stress of working late nights on multi-cylinder engines and gearboxes ?

[Martin Arnold 1]

Yep Jon with you again !! I always tune mine to the max..... Non of this a few clicks rich for me, as you say the motor is not giving it's best set like that.

Been running all my four strokes as above apart from YS on MT Dynaglo 5% for years with a total oil content of 10% (8% EDL 2% castor), with no ill effects and you get a 85% methanol content, which is after all is the fuel !!

Edited By Martin Arnold 1 on 03/09/2020 19:23:48

Edited By Martin Arnold 1 on 03/09/2020 19:24:45

[Martin McIntosh]

Is after run mineral or vegetable? Tried the stuff once and it took me ages to start the motor again. I once bought a s/h YS and the guy stated that it had been treated with after run which if it was mineral would have dissolved the silicone regulator.

I have not as yet found a solution to rusted bearings on a laid up engine.

[Jon H]

Posted by Martin Arnold 1 on 03/09/2020 19:22:20:

MT Dynaglo 5% for years with a total oil content of 10% (8% EDL 2% castor), with no ill effects and you get a 85% methanol content, which is after all is the fuel !!

ditch the 2% castor and its a winner

[Jon H]

Posted by Martin McIntosh on 03/09/2020 19:48:23:

Is after run mineral or vegetable? Tried the stuff once and it took me ages to start the motor again. I once bought a s/h YS and the guy stated that it had been treated with after run which if it was mineral would have dissolved the silicone regulator.

I have not as yet found a solution to rusted bearings on a laid up engine.

I tend to give any engine going into storage a good battering on the bench. First i blast it with the hose to clean it off, then fire it up. Small prop, loads of revs and get it as hot as i can. All the needles get reset and after a good thrashing i pinch the fuel off and turn it to TDC. Once cool enough i wrap it in a plastic bag and it then lives in a box under the bed. As yet i have not had engine rust up on me even after 5 or more years of snoozing.

[tigerman]

I have Seagull Gypsy Moth power by a Laser 80 I have a APC 14X7 prop on it but want to go for a more scale look and fit a wooden prop .I can only find a 14X6 wooden prop which I think will be fine but just wonder if I would notice any difference in the flying going from a 14X7 to a 14X6 prop .Any with a technical brain out there explain to me what the difference ,if any there would be flying a 14X7 prop to a 14X6 prop

[Martin McIntosh]

My Super Aeromaster with a Laser 80 had a 14x7 APC but have just changed to a Falcon wood 15x6 in an attempt to get a better climb. Not bothered to measure the revs but the more efficient type of prop seems to overload it so I may well try a 14x6 wood if I can get one. Yours being a much slower model should be fine. You would get less speed and more pull.

[tigerman]

Martin I brought my 14X6 wooden Prop from " The Prop Guy " .It is £10.60 + £8 postage but the prop is a really good quality prop

[Nick Somerville]

Props definitely not all the same! I had a Aerostar 18x8 in my Extra 330sc on a Laser 180 and changed to a Menz of the same size and pitch. Quieter and a tad more pull going vertical. Today I changed the Smart 20x6 on my Stampe, also Laser 180, to a Menz 20x6 today and performance was hugely improved. On the Stampe I had started off with a 18x8 as the engine was new but changed to the Smart prop as I had bought it cheap. It is a lot clumsier looking that the Menz and it is now just going to be an emergency spare. Looping with the Smart was always a bit of an effort requiring a paced entry, whilst the Menz You can be pootling along at half throttle and go straight into a loop opening up as you start the climb.

[Robert Welford]

Propeller choice appears a little ad hoc / experimental at times.

I have a Graupner Taxi 2400 (2.4m high wing) powered by 3W 28i. Prop used Biela 19 x 8 and is/was a good match - noise/climb/speed.

I transferred the 3W 28i with the Biela 19 x 8 into an Acro Wot XL and it exhibited lacklustre performance. I changed the prop to a Mejzlik 18 x 11, which I thought would be too much and model came a live - unlimited vertical, reasonable noise level etc.

Wednesday evening this week I flew my CARF Extra 2.3m (3W 55 Xi) with Biela 23 x 8. Great all round performance, but sounds like a Harvard at times. As an experiment I changed the prop to a Mejzlik 23 x 8 and the performance was not as good - the vertical was reduced.

The trial and error approach works well for a 10cc glow models as props of this size are affordable. However, propeller experimentation gets a bit expensive for 30cc and above engines.

Edited By Robert Welford on 16/09/2020 16:22:40

Edited By Robert Welford on 16/09/2020 16:23:05