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Laser Engines - Technical questions

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Jon - Laser Engines21/10/2018 22:22:34
5510 forum posts
268 photos

13x6 or 12x7 will work fine, good to hear its flying well though!

Piers Bowlan22/10/2018 07:40:47
2148 forum posts
53 photos

Going back to your recommendation Jon to fit 'tanks located on or below the centreline of the carb,' I am now planning to fit my Laser 80 to my World Models Midget Mustang (60in span). The question is, inverted or sidewinder fashion? The World Models instructions have the engine fitted inverted and with a little fettling I can lower the tank to the bottom of the cowl but still the top of the tank will be about 1cm above the carb, - any lower and the tank will be dangling in the breeze! Alternatively I could fit the engine at 90 degrees and the tank would not be a problem although the cylinder head would be sticking out of the cowl to the right. I suppose the sensible thing is to try running it on the bench inverted with the tank in the planned position, although it won't be the same as flying it in that position.

So, should I go for the 'safe' position or fit the engine inverted and be dammed?!

Chris Walby22/10/2018 08:13:11
1241 forum posts
303 photos

Piers, Worth considering how you will get to the main needle screw in each orientation. Not much point solving one problem and giving yourself another + access for the glow stick for starting, just depends on whether you like the Laser head visible from one side.

I have one set up where the slow run needle is very close to the exhaust....yep just needs a tweak and as you grip the needle you burn your finger and thumb!! Good news of course as the slow run does not need adjusting very often.

Jon - Laser Engines22/10/2018 08:40:02
5510 forum posts
268 photos

Piers i think you will be ok with the inverted install. If you can use one of the tanks from radio active they are wider than they are tall so you might be able to loose the difference with a different tank.

Piers Bowlan22/10/2018 09:14:40
2148 forum posts
53 photos

Good points Chris. The main needle is no problem in either orientation but I hadn't considered the slow running needle as I thought I could set it up with bench running, although I expect it ill all change once installed. I was planning to use a remote glow as a glow stick looks pretty lethal to remove with the engine running inverted. crook Not too bothered about a bit of the cylinder head showing as it has Laser emblazoned on it. smiley

Thanks Jon, I will check out the radio active fuel tanks for fit. yes

Paul james 822/10/2018 09:49:54
174 forum posts
48 photos
Posted by Jon - Laser Engines on 26/09/2018 14:02:49:

Ron pretty much has it covered to be fair. A single tank with two clunks or two separate tanks are needed. A T piece wont work.

Inverted is fine but just make sure you remember to lower the tank so its in line with the carbies.

No on board glow but twin remote's like Ron suggests are a good idea. That or wire the plugs in series and use a single 2-2.4v battery to power both.

Wooden props are fine if you keep them tight. Menz, fiala, APC, falcon...there are many good props out there. I like wood in the large sizes as they are cheaper, easier to drill for our sleeve nut, lighter (better throttle response and leaner slow run setting) and usually give good downline breaking. They also impose less load on the crankshaft in the event of a prang.

I guess the best advice is to not worry about it too much. Treat it like a single cylinder engine, all of the usual rules apply about tank position, cooling, glow connectors etc. The only difference is that there is two of everything.

Its the same with tuning as well. You essentially have two engines to tune, the fact that they are linked together is not really important. You start both 'engines' and the job is to sync them up. Tune one for maximum power, then tune the other for the same. Double check the first is still ok and you are good to go.

In terms of prop size, i guess 18x8 would be a good start. 17x8 will give more power, but it will rev pretty fast so might give a noise problem. An 18x8 menz wood hits about 7700-8k and that is plenty of revs for an engine that size.

Many thanks to all who have replied and offered information, I picked up a few brand new Menz 18 x 8 props recently so one of them should do nicely by the sounds of it. Next job is to round up all the models that I'm not going to use and get them advertised so I have enough room to swing the proverbial cat before I do any further builds or refurbs .

I will have a look on the website to see what I can find out about the sleeve nut as mine didn't come with one of those fitted.

Paul james 822/10/2018 09:59:59
174 forum posts
48 photos
Posted by Ron Gray on 24/09/2018 10:26:10:

Here you go



If there was enough interest I could make up a few sleeve nuts like this but with a second sleeve extending from the front to take the spinner attachment. That way you would have the best of both worlds, with a better secured prop and a true running attachment point at the front. I'll probably end up making one for my own 200 V twin anyway when I get round to fitting it to the Christen Eagle.

Just a thought.

Don Fry15/11/2018 17:27:23
4557 forum posts
54 photos

I am currently shoe horning an 80 into a ARTF hack designed to take a 53 2st. No room naturally.

I'm using a remote exhaust, the standard one won't fit, and this should be clean in use. But I've never used a remote exhaust system, and offer the solution up for comment.

The clip holding the unit on is flimsy and will break off if stressed, as a bit of insurance in case of mishap. There is no stress on the system, the flexipipe sits in this position naturally.



cymaz15/11/2018 17:40:33
9254 forum posts
1196 photos

Ever thought of a P clip? ( no’s nothing to do with the bladder).

Don Fry15/11/2018 18:40:32
4557 forum posts
54 photos

Yes, and I can soon make one in ali or brass or tin plate, , but metal won't break in a mishap, and I would rather the clip went than a chunk of the head. I've got hundreds of these plastic clips.

trebor15/11/2018 18:43:27
1930 forum posts
216 photos

You might not need a can on the end due to the length of flexi pipe.

ps, you would be better clamping the can. 

Edited By trebor on 15/11/2018 18:45:23

Don Fry15/11/2018 19:35:47
4557 forum posts
54 photos

Trebor, as in clamp the weight, to immobilise it?

Jon - Laser Engines15/11/2018 19:44:42
5510 forum posts
268 photos

depending on how tight the exhaust is in the end of he pipe you might want to hang on to it. You might find it departs the vehicle if you dont!

Don Fry15/11/2018 20:08:53
4557 forum posts
54 photos

Thanks. My site is not noise sensitive.

So I will remove the can, which will prevent loss, and reduce weight.

Ron Gray15/11/2018 21:03:26
2175 forum posts
941 photos

I have a Laser 100 in my Radial Rocket with just a short length of flexi pipe as the silencer wouldn't fit in the cowl. I'm amazed at how quiet it is so you won't have a problem. My pipe is about 2/3rds the length of yours Don.


Edited By Ron Gray on 15/11/2018 21:04:44

Doug Campbell19/11/2018 12:08:56
106 forum posts
2 photos

Why do the crankcases have the bulge above the engine mounts which stop you clamping them in a test stand?

Jon - Laser Engines19/11/2018 12:54:12
5510 forum posts
268 photos
Posted by Doug Campbell on 19/11/2018 12:08:56:

Why do the crankcases have the bulge above the engine mounts which stop you clamping them in a test stand?

On the 70 and 80 it is to support the area below the cylinder head bolts. On the 120, 150 and 155 it is to give clearance to the conrod inside (see photo). Without the bulge the relief for the rod would break through the side of the case.

155 crankcase.jpg

The 100 and 180 do not need either so have no bulge.

Even so, there should not be any trouble clamping the engine in a test stand. I use one of those irvine jobs at home and works well enough. For factory test running i have a bigger version of the irvine stand that we made to suit our longer mounting lugs. If there was a demand i would look into selling them but its not something we have been asked for.

Tim Flyer19/11/2018 12:59:41
1290 forum posts
236 photos

The 80 fits perfectly in my standard test stand . It’s the Irvine one and available at most RC outlets. 7a70f583-396b-49f0-9b26-49992bb4c0ff.jpeg

Edited By Tim Flyer on 19/11/2018 13:08:26

alan p19/11/2018 18:49:17
267 forum posts
7 photos

Nice m/cing John,shows the quality. Hope to have one eventuallylaugh

Doug Campbell21/11/2018 18:20:22
106 forum posts
2 photos
Thanks for the replies and the photo. I have a similar stand and found the top clamps are too wide. It fits now I have filed them down a bit. Never thought to check

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