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Laser Engines - Technical questions

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bert baker26/12/2017 09:02:07
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1524 forum posts
317 photos

Planes under the hammer

David P Williams28/12/2017 15:03:02
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879 forum posts
292 photos

Hi all, I'm struggling with the same old inverted laser/tank height problem. It's made worse by an angled cooling tunnel where I really need the tank to be. Anyway, I understand that the centre line of the tank should be level with the centre line of the carb spraybar/venturi. Does the style of tank make any difference, eg I have one of these Dubro tanks

Dubro DB414 14oz. Fuel Tank

If mounted upright the fuel feed comes out of the top of the tank and if mounted inverted (any reason why you can't mount these style tanks inverted?)the fuel feed comes out of the bottom. Does any of this matter? I can't get my head round it.

Should I just get a tank where the feed comes out of the centre?

Thanks for any help and advice

Bob Cotsford28/12/2017 15:16:49
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8258 forum posts
454 photos

It's the centreline of the tank that matters David, where it feeds from shouldn't matter. On my Provost I hacked the tunnel so that I could drop the tank by an inch or so. There's still plenty of airflow, at least the engine hasn't complained.

Duct top dropped to lower the tank.jpg

Laser 100 fits ok.jpg

Jon - Laser Engines28/12/2017 15:21:33
5209 forum posts
237 photos

What Bob said

Which model are you working on? got a photo of the installation? might help work out the best plan of attack

Edited By Jon Harper - Laser Engines on 28/12/2017 15:22:31

David P Williams28/12/2017 16:16:24
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879 forum posts
292 photos

Thanks chaps.

Jon - it's a 150 that I bought second hand from (I think) a deceased modeller's estate, DP M02 stamped on the mounting lug. It appeared to have had very little running.

It's fitted in a SLEC/Apache Chipmunk, that I flew for the first time earlier this year. Four flights, four deadsticks. Seems to run fine on the ground, holds full throttle, idles fine, but take off and fly for a minute or two, and the engine either dies or it will run at low throttle setting but not throttle up. I was worried about overheating so the last couple of flights were without the cowl, with the same result. After the last one I restarted it on the ground - same thing, wouldn't throttle up then slowed and stopped with big puffs of smoke. Very disappointed and didn't want to further risk the model I had spent a ot of time on, so it went in the naughty corner.

After seeing all your stuff on the forum about tank position, I though I would use the winter workshop season to try lowering the tank. The centreline is currently about 25mm above the carb, and I thought this might be part of the problem.

Or is it just my rubbish engine tuning skills?

Edited By David P Williams on 28/12/2017 16:17:13

Jon - Laser Engines28/12/2017 16:23:05
5209 forum posts
237 photos

nope that sounds like the tank. As the fuel level reduces so does the fuel head and that effectively leans the mixture and that is the cause of your issues.

Lowering the tank shouldn't be too back on the chippy, we have had many lasers fitted to that model without issue.

If it helps, you might be able to use a smaller tank as you shouldn't need more than 12oz for the 150. This might help squeeze it into the space if you have other stuff in the way that cannot be removed with some hacking.

David P Williams28/12/2017 17:01:59
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879 forum posts
292 photos

Thanks Jon. It would have been easier to do it while building, but I should be able to lower the tank without too much trouble. I have a nice sliding battery tray below the tank, just need to swap it to above the tank plus find another 10mm or so- plenty of room to do that with the 14oz tank I have. Won't get out flying for a while now though, I'm becoming a fair weather flyer as I get older and the model is too nice for the muddy lengthy grass on the field at this time of year.

trebor28/12/2017 19:09:20
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1926 forum posts
216 photos

My pair of engines are making what I think are loud clicking noises after I've given them a good clean. I don't think it's the valves but more like the cams or push rods. I had a bit of trouble getting the valve adjusters to seat on the push rods once the rockers were in place but I cannot pinpoint what's causing the noise. Any tips appreciated. Can you hear clicking going on on a new engine ?

bert baker28/12/2017 19:26:47
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1524 forum posts
317 photos

Sounds normal to me,

trebor28/12/2017 19:52:27
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1926 forum posts
216 photos

I'm thinking that the followers are sticking maybe then clicking free.

trebor09/01/2018 12:13:34
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1926 forum posts
216 photos

Would it improve the fuel supply if I made a fuel tank air vent that pointed forwards behind the prop, for prop air pressure dont know

Ron Gray09/01/2018 13:18:44
1701 forum posts
474 photos

Jon advised me to do exactly that, point the vent tube forward where it comes out of the fus.

Jon - Laser Engines09/01/2018 13:54:38
5209 forum posts
237 photos

What Ron said

and the valve springs tend to click as they are compressed/decompressed. Its pretty common on all model 4 strokes and nothing to worry about.

And Ron your 155 is about to fly the nest. Sorry for the delay. 

Edited By Jon Harper - Laser Engines on 09/01/2018 13:55:19

trebor09/01/2018 14:19:30
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1926 forum posts
216 photos

I've never had a open vented fuel pipe before it's always been on the exhaust pipe. Should I loop the pipe to prevent spillage ?

Merco 6109/01/2018 15:07:16
54 forum posts
19 photos

Hope this question is not interrupting the flow too much.I am about to swap out a much longer engine and replace it with my Laser v200.It will entail a1.5 inch spacer of some sort.Ive made up ally standoffs and long bolts in the style of many modern petrol engines,but it looks rather ungainly and I,m a bit concerned that I might be putting the Laser mounting lugs at risk in the event of a noseover into the rough.Would appreciate your views.Thanks.

Jon - Laser Engines09/01/2018 16:03:30
5209 forum posts
237 photos
Posted by trebor on 09/01/2018 14:19:30:

I've never had a open vented fuel pipe before it's always been on the exhaust pipe. Should I loop the pipe to prevent spillage ?

No need. Once the engine fires it starts drawing fuel and this suction keeps everything where its supposed to be.

Merco, no problem at all. Just laminate some ply to the required thickness and seal with epoxy. Once thats done drill though the block and use long bolts through the engine, block, and firewall into captive nuts. These will pull the whole lot together and be nice and secure.

Ron Gray09/01/2018 16:12:08
1701 forum posts
474 photos

@Merco61

standoff ring.jpg

standoff ring mounted.jpg

Ron Gray09/01/2018 16:13:47
1701 forum posts
474 photos

@ Jon, thanks and hope you're feeling better!

G194009/01/2018 16:28:23
3523 forum posts
1 photos

Is this fuel tank installation OK? Like Trebor I've always used a pressure feed from the silencer. Here I've put a piece of soft aluminium tube through the firewall . If I need to put the tank any higher then the feed to the carb will get progressively longer which I assume should be kept to a minimum.

installed 1.jpg

You can just see the forward tip of the tank over the top of the bay.

installed 2.jpg

The vent/pressure pipe is just near the carb and exits alongside the engine bearer just forward of the throttle linkage.

I'm hoping to test fly the Laser 62 some time this week. Just got to set up the throttle servo and check the CoG.

Geoff

trebor09/01/2018 17:10:21
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1926 forum posts
216 photos

The top of the tank just looks higher than the carb intake, I would think that's ok. Mine carb is about 3/4" higher than the centre of the tank and outlets.

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