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Laser 200 in line twin - retro fit


Ron Gray

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Im going to take my multimeter in on monday and have a look at the earth issue. Its something we have seen before but not to this degree. It will sort itself out over time as the plugs going in and out just wear the anodising a bit, but i might be able to do something when i assemble the engines that will make life easier. 

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9 hours ago, Ron Gray said:

I used to use the ones from South Herts Models, brass tube with ball bearing surrounded with wire coil, but as they’re no longer available I use these Fastrax . However whilst they stay in place and are fine, they are a little bit too long so I’m going to try these Traxxas. The problem I’ve found with this engine is that due to the anodising I can’t get a good connection so my ‘usual’ setup for twins, one remote plug connected to both glow plugs, just doesn’t provide enough current, hence why when I first ran the in-line it only fired up on one. So now I have 2 separate remote plugs, one for each.

 

I love the South Herts ones - they are sadly missed.  Sometimes the grip was a little too good!

 

The old front plug Lasers might have precluded the use of glow sticks and plunger fittings but the plugs were a lot more accessible than the modern deep set ones.  Does Jon recommend any particular type?

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Having now got the Sportster into a ‘ready for flight’ state I thought I’d better check the CG.  So out came ‘Vanessa’ and much to my surprise I need to add nose weight even with the flight battery as far forward as I can have it. If you had asked me about the CG before I started on the fit I would have said that it would need tail weight, or at the very least the flight battery moving towards the tail, I even chatted to Jon about it and said I may cut an access hatch in the rear of the fuse to get to the battery.

 

When I think about it, a largish chunk of the engine is now sitting behind where the original engine was due to me moving the firewall back.

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  • 1 month later...

Nice work Steve. From your photo i was a little worried about the cooling but if you say it flew fine then i guess its ok! I hope to get my own engine in the air on Friday if the weather holds. 

 

You got any video of the beast in action?

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On 20/02/2021 at 09:32, Ron Gray said:

@Jon - Laser Engines Following our discussions I can only think that it is the anodising causing the problem as my twin plug setup works fine on the 160vs and the 240v.

Yes anodising will greatly reduce or possibly even insulate electrical conductivity . It's not unknown for it to build up during the anodising process and stop the anodising due to the insulating effect  . Try earthing the engine with a bolt that screws into the crankcase like a  back-plate bolt possibly . If the heads are heavily anodised  Then there may be resistance between the Cylinder and Cyl-head. worth checking .

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Three more good flights today!

1679453215_AcrowotXLLasertwin(1of1)-2.thumb.jpg.bb101ffa622e9a64a250523371013754.jpg

 

1487738676_AcrowotXLLasertwin(1of1)-7.thumb.jpg.60db71f4b84e47ca8c6ed488b9a28cb1.jpg

 

Jon - you are correct, there is a cooling problem. I am running richer than I should, getting only 7800 on a Menz 18x8. On two of the flights, after about 5 minutes, when performing a tall stall turn, the engine cut on the down line. It landed ok both times, but the engine was very hot. I think some much better baffling is in order before the next outing...

And sorry, no-one to take video yet.

 

Graham - this is the first engine for the AWXL - I didn't have anything suitable in the hangar!

 

E.D. - I too had the anodise problem, in the glowplug screw hole. Held the engine upside down, carefully ran a plug tap held in my figers a few times up and down, and everything worked ok. Please don't tell Jon...?

 

Steve.

PS Thanks to Nigel Castle for all the flying photos!

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ah ok Steve, that answers that. 

 

Looking at your photos you need to seal off the cold side (carb side) of the engine. The front cylinder must also be baffled to prevent ram air passing down its right side (exhaust side, see photo at the bottom of what i mean) and all of the air coming in must be deflected into the top of the cowl. With a baffles installed to prevent the air escaping out the back/top/sides etc the air will flow down, through the fins, and then ideally out the bottom of the cowling. You will need to cover up most of the hole in the cowl to keep the air where it needs to be. 

 

I use this system on the OS flat 4 in my AWXL and it works perfectly. As your installation is basically half a flat 4 the same system should be used. Its the same for an upright or inverted engine, high pressure on the cold side, low pressure on the hot side. 

 

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Thanks, Jon.

Your suggestions are different to what I had planned...

I was going to block off the entry point at the front of the port side of the cowl, and the port exit. That restricts the airflow to the starboard side of the cowl.

Second - baffle the whole port side of the cowl, so that no air gets below the mounting lugs.

Third, deflectors to guide the incoming air around underneath the front cylinder, then up around the rear cylinder to exit past the top of the cylinders.

I was trying to cool the top part of the cylinders? There is currently no exit for air at the bottom of the cowl - all airflow exits past the cylinder heads etc.

 

I'm not sure how I can apply your illustration to my installation, but I will study it for a while.

See "final fitting" photo above.

Your comments would be greatly appreciated...

 

Many thanks,

 

Steve.

 

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 Along/through the fins is the way the air needs to go not across them. I have an RCV 60sp in a tight cowling in the SNJ of my profile pic.. Baffles direct air along the fins which in the RCV's case is across the crankcase. The 60sp was not popular with many flyers I recon because many did not take in the cooling/baffle instructions 

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3 hours ago, J D 8 said:

 Along/through the fins is the way the air needs to go not across them. I have an RCV 60sp in a tight cowling in the SNJ of my profile pic.. Baffles direct air along the fins which in the RCV's case is across the crankcase. The 60sp was not popular with many flyers I recon because many did not take in the cooling/baffle instructions 

 

The RCV would cool in the same way as this inline, my OS flat and the full size equivalents. 

 

As modellers we only deal with single cylinder engines most of the time and any twins tend to be flat or V. All of these configurations can be cooled by, essentially, blowing air in their faces. 

 

With cylinders inline (including flat 4 or 6) cooling by blowing air in their faces is no longer an option and the engine must be cut in half. Cold high pressure one side, hot low pressure the other side. The same is true for the RCV with its unusual layout. All of the cooling air flow through the fins is then at 90' to the direction of travel of the engine. This splitting in half can be left/right like in an upright or inverted inline engine, or top/bottom like the flat 4/6, the RCV or in inline twin on its side. 

 

In the case of the AWXL Steve, the hold in the cowl over the cylinder heads needs to be sealed up, at least on the cold side of the engine as you need that wide of the deal to be sealed up tight so that the only escape for the airflow is through the cylinders. 

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Thanks for the good advice, Jon.

I'll block off the port side of the cowl completely, so the only airflow is into the orifice at the starboard front of the cowl, down under the front cylinder, then up around the rear cylinder past the exhaust side. I'll shroud around the needles, above the carbs, to try to keep the airflow more to the hot/exhaust side of the cylinders.

I'll also put baffles to keep the airflow nearer to the lower (hot) cylinder side (currently rather open!).

 

There is no exit for airflow either at the base of the cowl or at the rear of the port cheek, the air can only exit via the side around the cylinder heads - see picture..

The exit hole is about 2½ times the inlet hole area - I don't want to close it up too much more...?

 

Also - I have a Spektrum telemetry receiver (AR6600T), which I haven't used for temperature sensing before.

Questions for Jon (or others more knowlegeable than I):

Where is the best place to mount the sensor (bead thermister) to read the cylinder temperature?

What is the best method for mounting the sensor?

At what temperature should I start to panic? ?

 

Thanks for all the help, and sorry for all the ignorance...

 

Steve.

 

1214485363_AWXLcheek.thumb.jpg.015bcfcb1b7b9a5f32db35f74f58688a.jpg

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Sorry Steve thats not going to work. Leave the port side open as that is not your issue. You just need to blank off the empty space so the air cannot escape around the engine. 

There is clearly still confusion on this so i have made a quick video to try and explain it better. 

 

 

 

I can help with the temp sensor too...throw it away ? The temperature range of an engine is pretty broad, but the limit depends on a number of things like quality of the oil, how long does it operate at a given temperature, what is the load etc. I cant give you a number so just dont bother with it . 

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Well the Giant Super Sportster came out today and despite the strong wind (horizontal windsock) I managed 4 circa 8 minute flights. No overheating and no mishaps and the engine behaved through big loops and rolls. My only concern is some mechanical noise noticed by all present, I need to have a closer look to see if anything is amiss. I’ve got some vids of the flights which I’ll publish later and I apologise beforehand as they were taken with a cap mounted Runcam so the ‘plane soon disappears into a dot and the wind roar largely blankets the engine sound. 

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Hi Jon

On the full scale Zlin 526with its inline engine one can see that the airintake is on the hot side of the engine and the outlet is on the cold side. Why do you recommend it on the 200twin the other way round. Is it because of the curburators must be on the high pressure side and the temperture regime in the small cylinders, compared the the full scale, is of no concern. Thanks for your explanation.

 

Regards Aldo

 

zlin-526f-sp-emb-for-sale-by-plane4you-aircraft-sales-center-100.jpg

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Model engines tend not to suffer from carb icing but on full size this is a problem. To save fitting a carb heat many full size aircraft have their carbs situated so they only draw warm air that has been heated by the engine. This caused major carb issues on the B36 bomber as it used radial engines designed for standard operation (carb on the back of the engine) in a pusher configuration and the carbs protested as they dangled in the freezing air. 

 

In our models drawing cool air into the cylinder aids overall cooling, helps with tuning stability and is generally better for the engine. Due to the very small mass of our engines vs the heat they make, cooling is always the first priority and blasting hot air from the exhausts over the engine is not likely to help it out. 

 

 

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