Laser 200 Flat Twin

[Ron Gray]

I thought I'd start a new topic based around the new Laser 200 Flat Twin. The intended airframe for this motor is my Wots Wot XL which is currently powered by a Laser 180 but over the past few years it has been powered by a Laser 160v and a Laser 240v so it is a good test bed for the new motor.

 

So this was it as it last flew (minus cowl)

 

 

And after fitting the FT.

 

 

This wasn't that straightforward and necessitated the fabrication of a ply backplate to maintain the firewall / prop driver distance but had the advantage that I could fir the engine to the backplate then bolt the hole assembly to the firewall using the same mounting holes as the 180. As it comes, the throttle arm is on the opposite side to that of the 180 so I just remounted the carb control arm on the other carb but had to raise the throttle control snake as the carbs are much higher on the FT. This then meant that I had to also raise the throttle servo to try and maintain as straight a run as possible (yes I could have used a Bowden cable but I wanted to re-use the existing!). The fuel tank already had provision for twin clunk lines as it was originally configured for the Vs so I just had to fit new, longer fuel tubing to reach the carbs but it gave me the opportunity to check over the tank and to give it a bit of a clean.

 

The next job is to fit the cowl and to do this I'm going to cut it in 2, horizontally (clam shell). I have already found a potential problem in that the carb intakes are right on the line of the cowl sides so it may mean re-forming the cowl in those areas.

[Paul De Tourtoulon]

I did away with bowden cables around 40 years ago, they don't move freely and are not very accurate due to the slop in the outer cables, I still find the best 'snakes' were the white Graupner ones followed by the red and yellow Sullivans,,,

 

 so when will it be in the air ?.

[Ron Gray]

But if you need to they can go round corners (I've got them on my Tigercat for that reason) but you're right, they do need supporting.

 

Flying, well the transplant should be finished over the weekend but the weather for the next couple of weeks is looking 'poor', but it will be as soon as there is a weather opening. 

 

In the meantime, having had a quick chat with Jon, whilst I was going to leave the tank where it is at the bottom of the fuse (to suit the V twins it did have in it) and was prepared to put up with some mixture changes whilst flying, especially inverted, I've agreed with Jon that as I've got the model in a disassembled condition why not raise it. So I am.

[Nick Somerville]

Really looking forward to your feedback on the flat twin Ron. I think a flat 300 will be perfect for when I get around to building my Taylor Corsair 

[Ron Gray]

If the in line twins are anything to go on, they’re going to be good!

 

The good thing is I know how the WWXL performs with various different engines so I have the benchmark. What am I hoping for? Pitts type performance!

Edited April 1, 2022 by Ron Gray

[Ron Gray]

Productive afternoon, 3D printed tank support which positions tank higher up in fuse and together with a 3D printed ‘plug’ which holds the front end, the tank is secure.

 

 

 

[GrumpyGnome]

Nice work!

[Ron Gray]

Thanks GG

[Ron Gray]

No turning back now, the cowl has been cut, 'clam' style.the cut outs for the needles aren't too bad but I will probably 3D print some power bulges to cover them at some point. Happy that I didn't have to cut out for the cylinders or the carbs.

 

 

[john stones 1 - Moderator]

What you cut the cowl with Ron ?

[Andy Gates]

Very neat Ron

[Ron Gray]

Handheld hacksaw blade!

[Ace]

Very neat ?

How are you going to join them together, presumably with a GF lip and what? 

[Ron Gray]

Thanks Ace, the plan is to glass a thin ply strip to the inside of the bottom half and the top half can be screwed to it. I’ve got to glass various cutouts made for previous engines anyway so I’ll do it all at the same time, maybe this weekend.

[Ron Gray]

Couldn’t wait, here’s the first run

 

[GrumpyGnome]

Oooh, that sounds good.....

[Jon H]

Nice Ron. Was that an 18x8 wide?

 

 

[Ron Gray]

Yes Jon, an APC 18x8W - swung it at just under 8K.

[Martin Harris - Moderator]

Do you set the low ends slightly rich at the factory Jon?

[Ron Gray]

Both the 160 in-line and this 200FT are running slightly rich and will need adjusting but they're not wildly out, the pick-up from tick over is quite clean. I put it down to the rarified air we have here on the Norfolk / Suffolk border.

[Jon H]

1 hour ago, Martin Harris - Moderator said:

Do you set the low ends slightly rich at the factory Jon?

 

Yea a little. The flats are richer than most as i do not yet have my test bench properly set up to test them As a result the tank is a bit low and so the needles end up a bit richer than normal. 

 

Generally all manufacturers set their needles rich to guarantee the engine starts as they know most modellers struggle to deal with an engine that will not start or show any signs of life. Its not a criticism of anyone, just a simple fact that people find this hard to deal with. I had this situation in the week where a slow run needle set about 1/4 turn too lean took 3 days and 7 calls totalling probably an hour and a half to rectify. I think it would have been quicker to drive and see the chap, do the work, and then come home! 

 

As detailed on the laser thread, too many try and tune with their eyes or by counting turns on needles. You simply cant do it this way and its all down to your ears to work out the trouble. 

 

As an example i think one cylinder on Ron's FT is running rich as the engine note drops to a single cylinder sound at idle. Both cylinders pick up so its not a lean cut on that cylinder, so it must be rich. This is probably because i used twin clunks for the test run to the T has changed it. That or the camera mic isnt picking up the sound evenly and its actually running fine. 

 

 

 

 

 

 

[Geoff S]

The only flat twins I've had anything to do with have been BMW R50/R60/R69S motorcycles and they were noted for being very smooth, though the torque effects of having the crankshaft in line rather than across the frame took a little getting used to.  I just wondered if the Laser fires both cylinders at the same time or on alternate strokes.  The BMWs IIRC fired on alternate strokes even though the magneto sparked on both cylinders at the top of every stroke, presumably for simplicity.

 

PS Ron's Laser sounds excellent and the easy start impressive.  It did take me a while to work out why the large white building immediately behind the model seemed to sport big catches until I realised it was a trailer ?

Edited April 2, 2022 by Geoff S

[Martin Harris - Moderator]

That's the case with the OS flat twins and their ASP/SC copies using a [one armed?] boxer layout - my ASP 160 is incredibly smooth but my Saito 182 has a common crankpin with consequent uneven firing order which is, if I'm not mistaken, is the Laser layout and despite any static balancing does feel far less smooth.  It has a very distinctive [but certainly not unpleasant] engine note which will probably be the case with the Laser?

[Ron Gray]

Jon is correct and well spotted, the starboard cylinder is running a bit too rich. If you look at the video at about 6.22 you will see the exhaust dripping! The only problem with the configuration of the FT is that the needles are a bit difficult to get at due to the silencers being in the way which means tweaking them with the engine running is a bit difficult. Again, as Jon has spotted, I'm using a T piece for the first time on the FT to see how it runs, I can always revert back to twin clunks if necessary.

[Martin Harris - Moderator]

Another giveaway was the way the revs dropped off when Ron removed the starboard glow plug - a large drop in RPM is an immediate indication that the idle mixture may be too rich.