Laser Engines - Technical questions

[Rocker]

Now Laser have stop production of the 120 ,how close performance wise is the Laser 100 compare to the 120 .Saving my pennies to find a engine for a Seagull Spacewalker 120 .I am sure the Laser 100 should fly the Seagull Spacewalker OK ,just need to make sure .No hurry I see the the Laser 100 is out of stock so is the Seagull Spacewalker 120 (The Spacewalker 120 is due in about August not sure when the Laser 100 will be available no doubt Jon will let me know the answer to both these questions

Edited By Rocker on 14/07/2018 14:17:44

[Former Member]

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[Former Member]

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[Jon H]

Trebor, im not sure of the size. I was only 10 when laser stopped using them! Im sure M+R can help you.

Rocker, the 100 would be plenty. As Percy says the 100 is a long stroke motor with plenty of grunt. The spacewalker is not a high performance model, a 15x8 would be my choice of prop and im sure it would putter around quite happily.

[Alan Hilton]

Hi Jon

My next build is a chilton dw1 GAESZ it would make producing an accurate cowl much easer if the front bearing housing and prop driver were anodised red .Would this be possible on a new 155 .Have you got piston rings for a 150

Alan

[Joespeeder]

Hey Jon,

Flew the Storch !! Flew great. But I’m having trouble keeping the right side cylinder lit. It seems to load up and I’m getting a good amount of oil from the rocker cover.

My current thought is my drain is too small and loading that cylinder with excess oil.

I’ll swap the drain. Would a drain that’s too long, too small, or both load the right cylinder with oil and cause it to go out?

I ran the drain down the long landing gear struts to try to keep the fuse cleaner. But I think the lines I used were too small for the distance.

It’s going to be awesome once I get the cylinder to stay lit. 20lb plane 40lbs thrust and I as seeing about 7500rpm on a 22x6 Xoar. Once I get things settled I’ll report the final tune numbers. With both cylinder lit the Storch felt great on the sticks.

Joe

[Jon H]

Alan, sorry i missed your post. In theory i can get them done red but as we never anodise anything that colour it would have to be a special. If so, it wont be cheap.

Joe, good to hear the storch has flown. You will have to remind me which engine you have as i have forgotten! Usually cylinders dropping is due to the tuning being out, most likely the slow run. The breather should not cause any running issues and the rocker covers should be full of oil if the engine is inverted so that is normal too.

Edited By Jon - Laser Engines on 18/07/2018 08:50:16

[Joespeeder]

Hi Jon,

It’s the 300v running 10 & 10 with Klotz. Ok, I’ll keep tuning and replace my breather pipe. It’s the only thing I can see that’s out of the ordinary.

I used standard fuel tank tubing brass tube along the strut with new black Nitro fuel line since it looked good. The length of my drain is about 1 1/2 feet, maybe a little more. As I think about this, that black line is very thin and flexible compared to standard silicone line I’ll check for pinching.

The left side cylinder never dies and the right side it really wet around the back of the head and started to leak dark oil from the rocker cover. The engine is still breaking in. I looked to see if the carb was seated or I had some other issue. Everything seeems tight. I lost the cylinder in flight at about 1/2 throttle cruising and trimming the Storch.

I’ll keep tuning, the one cylinder gave me fits and I never trust myself.

Thanks Jon.

Joe

[Jon H]

Hi Joe

The left cylinder (right when inverted and viewed from behind) lends to run slightly leaner on the slow run than its best mate. Its just to do with the firing order and its why we use two carbs.

Its likely that as you have installed the engine inverted its slightly richer than it was on my test bench which is why that cylinder is now protesting. Anything at or below half throttle is slow run needle territory so its likely that is where the trouble is.

also at idle you should be able to hear the cylinders individually if you listen carefully. I suspect that the good one is idling with a relatively constant tutt, tutt, tutt, note where as the one that stops is not running so smoothly. If it sounds more tutt, pff, phutt, tut and lacks the constant and obvious exhaust pulses of the good cylinder then it is likely too rich and the slow run should be leaned off.

Before that, make sure both main needles are set for maximum rpm by leaning them off in turn until the cylinders loose power. This is the only way to set them accurately. I have added a video at the bottom showing me testing a 300 and setting the tuning. Its not the best video but its all i have got at the moment. Listen very carefully at 2.20-2.25 and you can hear the right cylinder drop out slightly. It was still firing, but you can hear its missing quite a bit where as the other cylinder is still thrubing along nicely. After i lean it off you can hear from 2.35-2.39 its firing evenly on both pots. 

18 inches is very long for the breather. Its unlikely anything will escape from there but that said it shouldnt cause the engine any problem. I have run my engines with breathers blocked off before now and it makes no difference.

 

Edited By Jon - Laser Engines on 18/07/2018 12:22:36

[Joespeeder]

Thanks Jon,

I’ll revisit it in the next day or two. I hate having to ask questions you’ve gone over and over. Thanks for the video, I wasn’t sure about the breather.

I know an 1800rpm idle is really well tuned. I was shooting for 2,500-2,600 since I’m still breaking in. What do you target for a new 300v idle range?

Joe

[Jon H]

1800-2000 is fine for idle. The performance of the engine will not change much during the run in. TO be honest, they give about 99% of their performance from the word go

[Joespeeder]

One last question, I'm running the flexible extensions. Would I do better with the mufflers? I would put them about 4inches away from the head by using the flex extensions and some silicone tubing as connectors.

Would the back pressure help my idle?

Joe

[Jon H]

nah, the exhausts wont make much difference at idle. Also, the 300 will melt silicone in about 5 minutes so don't waste time with that!

[Manish Chandrayan]

Does that mean, that a 150 will also melt a silicone exhaust joiner or extension? Given that a 300 has two 150 pots.

Edited By Manish Chandrayan on 19/07/2018 04:03:18

[Jon H]

Posted by Manish Chandrayan on 19/07/2018 04:02:03:
Does that mean, that a 150 will also melt a silicone exhaust joiner or extension? Given that a 300 has two 150 pots.

Edited By Manish Chandrayan on 19/07/2018 04:03:18

Any 4 stroke over about a 90 will make short work of silicone tube. Once you are above 120 its really getting into a per flight rate for consumption!

A friend and i both have Enya 155's and the exhaust on those is so hot it might as well be the depths of hell itself. They run so hot in fact castor oil wont even burn onto the exhaust as it just turns to ash! Brutal engine mind, its only let down by the old school air bleed carb so i updated mine to a laser carb and its much better

[Tim Flyer]

My 155 threw away its silicone exhaust outlet last Sunday. It was just one of the short grey cranked pieces that help deflect exhaust away from the body to save a bit of mess. It’s the second one it has rejected. I hadn’t expected it to last more than a few flights anyway. It had lasted a number of flights though. I do agree that silicone is useless on 4s engine exhausts. My OS 4s exhaust is super hot too. My new Laser 180 has a rather nice threaded tube on the manifold. It would be nice if we could buy them as an accessory and buy adapters to fit a short bit of steel flex tube on the end..

Edited By Tim Flyer on 19/07/2018 09:53:41

[Jon H]

Posted by Tim Flyer on 19/07/2018 09:02:10:

It would be nice if we could buy them as an accessory and buy adapters to fit a short bit of steel flex tube on the end.

We used to do them but it was a kit of parts and you sort of had to make it all work yourself. As metalwork skills seem to be in the decline, many people were not able to make the best out of it so we needed a more 'finished' solution.

Alas, the company that supplied us with the flexi pipe changed their order setup and would only supply a minimum of 300m of pipe. this was about 20 years supply for us and needless to say we didnt take them up on the offer so its pretty much all finished now.

I can do a straight extension for the exhaust though

[SR 71]

Hi Jon, what is the equiverlant petrol cc to the Laser 300, I have a bibe with a petrol engine in it, just thinking a nice fs would be better

[Manish Chandrayan]

Looks like I have either been very lucky or I have a very special silicone exhaust deflector that is mounted on my OS 95V. Haven't given me a bother ever since it went on and I must have had close to 40-50 flights on the setup.

[Jon H]

Manish my comments are meant as a general rule of thumb. A great deal depends on the cooling available to the exhaust as well as other factors. If the exhaust is buried in a cowling the whole lot gets quite a bit hotter than it would outside dangling in the breeze.

SR71, our 300v is 48cc and is similar in performance to something like a zenoah 45. APC 20x8 will do near 8000, 7300 or so for 20x10, that sort of thing. I personally use 20x8 menz wooden props and see mid-high 7000's. We get similar rpm from 22x6 props and that would be suited to a slower model that needs thrust as opposed to speed.

Which model is it specifically that you are trying to power? If you can let me know its current engine, its weight and size we can work it all out.

[Manish Chandrayan]

Jon, From what I have read, silicone can retain it's properties up to around 300 Celcius. Do the exhaust gases at the end of a typical four stroke muffler are that hot? And if they are, I even cringe to imagine what would be the EGT temperature at the exhaust valve/outlet?

I have experienced four stroke exhaust run much hotter than a two stroke. I had an instance where the exhaust gases burnt through a layer of epoxy, charred the underlying balsa, melted couple layers of tape and Rx battery shrink wrap. Luckily I had a reason to open the cowl before the gases melted through the wire insulation. Maybe one more flight and the inevitable would have happened.

The deflector I am referring to is on a Great Planes Super Skybolt. I discarded the original muffler on the OS 95 (as that meant butchering the cowl) and used a muffler from ASP 91 four stroke. Entire muffler is under the cowl with only the last bit of the deflector almost flush with the cowl bottom. But the deflector has worked fine till now. Maybe later today I will take a picture and share

Edited By Manish Chandrayan on 19/07/2018 13:25:59

[Jon H]

while i have never measured the EGT accurately my infrared thermometer reads overload if i point it at an exhaust on a running engine. As it overloads at 250'c clearly the muffler body is hotter than that. If you have ever had the misfortune to touch a 4 stroke exhaust you will note the distinct 'sizzle' your flesh makes upon contact. It takes a fair bit of heat to do that. 

I am not sure if anyone has done this, but if you were to remove your exhaust and run the engine at night you will see blue flame thrown out of the exhaust port so im quite prepared to believe the EGT is well over 1000'c (or whatever temperature it is methanol burns at) as it leaves the cylinder. It then cools as it expands in the exhaust and heat is also conducted away through the engine. OS even have cooling fins on their exhaust which may help keep it cool.

If i had a decent thermal probe i would check it but i dont have one.

Edited By Jon - Laser Engines on 19/07/2018 13:47:51

[Don Fry]

Constant pressure flame temperature for methanol is just under 2000 ° C. Very complicated subject,

[Chris Walby]

One thing to remember it the difference between the melting point of aluminium and the temperature methanol burns at...best not to run your 2 stroke too lean at full throttle

Perhaps why I stick with 4 strokes

[Jon H]

Posted by Don Fry on 19/07/2018 14:12:33:

Constant pressure flame temperature for methanol is just under 2000 ° C. Very complicated subject,

Complicated it sure is, which is why i have not really bothered to study it as its not something we really need to worry about.