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Laser Engines - Technical questions


Jon H

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3 hours ago, Jon - Laser Engines said:

Its why i dont recommend Steve Dunne's pressure isolated header tank setup

I think this is what Jon is referring to. A chicken hopper system will and does work, I’ve tried one after seeing the sketches for it on the forum, but you have to ensure that it is built correctly and there is more potential for errors due to the additional plumbing required, hence Jon’s reticence to recommend it. In the end I decided against continuing to use it and chopped the model about instead, which worked! 
I will also hold my hand up and admit that I had an irregular running 155 on one of my models, exhibiting exactly the symptoms Jon has described, lean and rich. In the end I chopped out bits of the internal fuse structure and lowered the tank, problem solved! The only disadvantage with the lowered tank is that it is now more difficult to prime the engine, before I lowered it I used to prop the tail up and that was enough to flood the carb, now it takes several seconds with the electric starter to get the fuel through. As this is only for the first flight of the day I’m not really concerned.

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35 minutes ago, kevin b said:

Excuse my ignorance, but If you need a lower fuel level is it not possible to use a hopper tank system with a smaller tank as low as possible ?

 

To elaborate on Ron's post, yes, but you need to pressure isolate it. If you dont, all of the head pressure from the top tank simply pressurises the bottom tank and its the overall system head pressure which is what causes the problem. 

 

So, you need a setup which allows the top tank to feed the bottom without adding any pressure to it. Steve's setup works, but you need tanks with 4 or 5 pipes in them, multiple drain and fill lines and all the rest of it. Once you start drilling holes in fuel tanks to add all the fittings you need and dealing with an octopus of pipes, the chances of something going wrong are very high. 

 

So, we are back to square one. Lower the tank. A bit of wood chopping is not the end of the world and even if its fairly complicated like on my DB Hurricane, i only have to do it once. On the maiden flight the engine was utterly faultless from the off giving me great confidence in the model after only 2 circuits. Loops, rolls, half cuban 8's were all performed comfortably with no pressure, no pumps and no problem. 

 

 

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Personally, I would try the plumbing octopus first, before hacking away at an airframe to accommodate a very low tank position. I have manage to get a "chicken hopper" system to work well. It's not that difficult to get the whole thing thoroughly checked out and tested on a test bench before installing it in the plane. 

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4 hours ago, John Stainforth said:

Personally, I would try the plumbing octopus first, before hacking away at an airframe to accommodate a very low tank position. I have manage to get a "chicken hopper" system to work well. It's not that difficult to get the whole thing thoroughly checked out and tested on a test bench before installing it in the plane. 

 

John, i know you mean well but with respect mate this isnt about what you would do. The official recommendation is not to use chicken hopper tanks and that is more or less the end of the discussion.

 

Just because you managed to make it work it does not mean that everyone else will and i cannot offer technical support on some random setup that is working to your standard of acceptable and not mine. i have never seen it operate so it might be perfect, but i dont know that so how can i recommend it? I know it will be perfect with the tank lowered so i will recommend that. 

 

Anyone calling with a problem and a non standard tank setup will simply be told to move the tank as i have no hope of dealing with it if i have no benchmark in the hardware. There is also a more than fair chance the tank is the problem anyway. 

 

 I explained all of this in the earlier posts and have to admit i am more than a little frustrated that i have to explain it again only a few hours later. 

 

The thing that baffles me the most is that it takes so much more time/effort to dream up and build some of these fantasy solutions than it would do to just move the tank. I am genuinely at a loss to explain it and really at my wit's end with the whole discussion. 

 

If moving a tank is really that difficult a task just buy a different engine. 

Edited by Jon - Laser Engines
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I apologise: I had no idea that your official recommendation was not to use hopper tanks. 

 

The hopper tank system is not the least bit random, but it is confusing. This is why it has to be thoroughly checked out on the bench. All I was advocating was trying this out first, before putting a saw to a model airframe. I have only used the hopper system once in a model, which had an unimpressive structure (i.e., weak looking), so the last thing I wanted to do was to start removing parts of that rather inadequate looking structure to accommodate the tank.

 

BTW, I did not dream up a hopper system: I used a very useful sketch that was provided by someone on this forum, and found that their set-up worked remarkable well - even though (it has to be confessed) it was quite difficult to see how it was working with the engine running!

 

I highly appreciate your expert views and have been careful to place the tanks generally as you have suggested. I have found (as you say) that it is essential with Lasers not to have the tank too high; but rather low doesn't seem to present problems. (In my S6b, the tanks are slightly low, but I tested the running of the engine with the tanks in that position, very thoroughly on the bench, before committing the rather low position to the design.) 

 

My own approach is to test thoroughly first, cut later.

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Quote

 

I was very surprised at the tirade against me, having had 60+ years of using model engines of every type. Rather more time than some.

As a former F3A British Champion and twice a team member I could not afford a motor problem of any description so I was very careful to ensure that whatever tank/pressure system was 100% reliable. I still apply this to my five Lasers and use whichever is most suitable for the model design, for instance, my Super Aeromaster was meant for an upright two stroke but it has an inverted Laser 80 on silencer pressure which got round the problems. The tank could only go in one place. My Stampe has a simple system of a 9oz feeding a 6oz below it.

I fully understand Jon`s concern with ensuring that a new user will get the best from their motor.

Regarding Spits, yes, I could get the tanks a little lower but the space is already occupied by the three battery packs.

 

With that I shall sign out of this forum.

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@Martin McIntoshI really don't think that there has been anything directed personally at you, as Jon has said, Laser's recommendations are what they are, if we 'disagree' or have a different approach that we think works then there is room for discussions around those (which I would welcome )but maybe not in this thread! 

 

And just to set the record straight, despite owning quite a few Lasers I don't necessarily agree with everything Jon says (he knows that!).

 

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Zflyer, sadly i cant just let it go as someone new to the thread might assume everything here is official advice when its not. While i appreciate the input from everyone, there are times i have to just say 'no, it has to be this way' 

 

John, yea i know Steve posted the sketch and that's fine but as i have covered many times, its not recommended as it can work, but its not guaranteed it will. 

 

Martin, F3a models on piped 2 strokes are nothing to do with a 4 stroke with no pressure. Their requirements are very different. Exhaust pressure is also not required and nipples should not be fitted. The exhaust can is not designed to take one and it will fall out in time. The engine will then stop. If the fuel tank was correctly located there would be no need to drill holes in the engine. Looking at the aeromaster plan (assuming i have the same one) fitting the engine and tank inverted or upright looks easy enough, and i didnt know your spitfire was electric. 

 

Ron, yea its fine. I just reserve the right to be really sarcastic whenever anyone disagrees with me and it bites them in the bum. If you are ok with that its all good ? 

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Oddly a technical question, I have a Laser 65 (ish, as I am not picking it to bits just to find out its a 62!) as in forward facing plug and old style carb. Jon has already said its no longer a supported engine with spares and use it until let gets to the end of its life which is perfectly acceptable as it cost me nothing.

 

Not had any real bother over the last couple of years, but it dead sticked on me a few months back resulting in pilot error and an argument with a fence and not the runway.

 

Fuselage repair complete and 4 flights today with increasing tuning success until the final dead stick, had to take both needles out to remove the congealed oil. And although cold there seems to be something else going on as I followed the standard tuning process.

  • Warm up and set up, all ok apart from the pick up is a bit sluggish, WOT is ok although it seems quite tolerant to a turn or two on the main needle. From memory this is usual for this type of carb
  • In flight it just sounds a bit rough at the bottom end and after a bit of thrashing the idle picks up a bit (first three flights) prior to landing
  • What was odd was the need to retune it before it each flight, I did it anyway as I wanted to fine tune, but it was the fact that it was well off tune once started

Anyone had experience with this engine/carb arrangement (has a twin spring pincher on the main needle) as I think it could be the needle rotating with revs/in flight or the O rings are cream crackered and sometimes letting air in. Not sure what the top hat seal does or the impact if its in a poor state.  

 

Advice as to what to do next please?

 

 

 

 

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Hi Andy, I'll take a couple of photos and post although it does look like the one you have posted which might explain the odd running. Nothing has fundamentally changed and once its dead sticked and is back on the bench it starts and needs a retune so I don't think its rubbish in the tank (once wiped another tank out and left fibers in it ?).

image.png.868563122566585c66a9ea4c37371244.png

 

I have a couple of OS LA 46's which have a similar main needle locking (spring thing) and they have a small cable tie fitted. I can slide the tie along the needle to tune and slid it back to lock the needle and stop it rotating. While an o ring might do the same job I am just wondering if you have come across this issue and whether bending the spring or cable tie/o ring is the "standard" solution.

Its in a Nova 40 and its all well old but flies really nice, everything from ultra slow slow/stable circuits when teaching to loops, bunts and inverted circuits.....and of course sounds nice!   Might even convert it to a steering nose wheel....but then again it spends so little time on the ground ?

image.png.627fc4ddf5ec083a1f9b5286f873458f.png

 

 

 

 

Edited by Chris Walby
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  • 2 weeks later...
  • 2 weeks later...

Already posted this but posted it in the wrong Thread

Will my Laser engines run OK using Optimix 12% fuel instead of using Model Technics Laser fuel .I am finding every time I try a buy some Model technic Laser fuel it is always out of stock ,So thought I would run my Laser engines on the Optimix 12 % instead 

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29 minutes ago, Ron Gray said:

MT fuel is now produced and sold by Opti - MT fuel and is available from many outlets including Model Shop Leeds

Hi Ron - look at Model Shop Leeds website, or Optifuel website, and you will see that there is only a very limited range of MT fuels available so far.

They only have "full fat" Laser fuel - Jon thinks that low-oil Laser 5 Pro should be available soon.

There is doubt in the shops whether or not Techpower  and some other MT fuels will be produced at all by Optifuel, due apparently to "limited demand".

We can only wait and see, or wait and hope...!

 

If anyone knows better (Optifuel spokesman??) we would be delighted to hear it.

 

Steve.

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Optiful 12 will not damage or do any harm to a laser (apart from the 180 where you risk knocking) but it has excessive oil/nitro/cost. Basically you are paying more for increased fuel consumption, more cleaning, and no additional performance. 

 

As the other guys have pointed out Optifuel are now making the laser fuels for us and full fat laser 5 is available. Both laser 5 and laser 5 pro are going to be changed to a new oil (for ease of production reasons) soon but they are waiting for my thumbs up on the test gallons i have here in stock. I cant do as much testing as i would like as the weather has been rubbish at weekends and my club field is rather boggy. 

 

There was always going to be a transition period after MT closed its doors and we are at the tail end of that now. 

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