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Laser Engines - Technical questions

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bert baker11/01/2018 11:05:08
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1087 forum posts
228 photos

It's his Veiw,

I am a member of many clubs, and at no point so far has any one or a safety officer ever asked me to display that my fail safe is working.

Perhaps this needs to have its own thread

bert baker11/01/2018 11:09:34
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1087 forum posts
228 photos

Getting back to technical stuff,

I have a 150 that was original fitted with a straight cylinder it came to me as a rebuilt engine but using the barrel shaped cylinder, so would it remain as a 150,

David Holland 211/01/2018 11:13:35
156 forum posts
7 photos

Bet that hasn't got much compression!! (sorry)

Jon - Laser Engines11/01/2018 11:48:35
3586 forum posts
144 photos
Posted by bert baker on 11/01/2018 11:09:34:

Getting back to technical stuff,

I have a 150 that was original fitted with a straight cylinder it came to me as a rebuilt engine but using the barrel shaped cylinder, so would it remain as a 150,

The external barrel shape was purely cosmetic so nothing will have changed

Ron Gray12/01/2018 21:19:21
769 forum posts
200 photos

Is there enough space between the carb on my Laser 155 and the bulkhead? Hopefully there is otherwise I’m going to have to cut and build an air channel.

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Chris Walby12/01/2018 22:17:37
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406 forum posts
65 photos

Jon will be able to give a definitive answer, but my 2p is it will be okay (might not get the absolute maximum last fraction of full power) but if you look at the K&N filter web site they supply engine air filters (all be it for much larger engines) pan head filters that are shorter than their inlet diameter.

at least it won't be sucking a load of dust and runway debris if its tucked away.

PS in theory I think you need about 5 diameters to get close to laminar flow, but I haven't see an inlet tract that long as its not really practical plus that's assuming you are at full throttle most of the time!

Jon - Laser Engines13/01/2018 16:23:48
3586 forum posts
144 photos

you might just get away with that one Ron. If you find the engine is slightly erratic in flight then you likely have some turbulence over the intake and will need to make a small mod. Its up to you if you want to try it in the air or just mod it now and be done with it.

if you do it now don't go mad, just take a small section out about the dia of a 2p. you can then back fill with either a balsa block or use the cardboard inner from a roll of covering. Once done paint it up with thinned epoxy and you are good to go

Ron Gray13/01/2018 16:30:19
769 forum posts
200 photos

Thanks Jon, I was thinking of using a half section of a bit of plastic pipe epoxied in position making an air channel to the underside.

Jon - Laser Engines13/01/2018 20:45:05
3586 forum posts
144 photos
Posted by Ron Gray on 13/01/2018 16:30:19:

Thanks Jon, I was thinking of using a half section of a bit of plastic pipe epoxied in position making an air channel to the underside.

yup, that will work nicely

Chris Walby14/01/2018 17:38:59
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406 forum posts
65 photos

Now with half a tank of fuel run through the Speed Air (Laser 70) I have really started to explore the flight envelope and had a couple of problems this morning (one self induced so does not count!).

First up after a number of successful stall turns, the next at full throttle and then as I eased it to 1/4 throttle it seemed to momentarily "cough" and as I turned to vertical down it slopped. Dead stick back on the runway although the hedge did look a bit taller than normal.

Based on the need to make it richer by 1/3 of a turn to get it through the noise test and stop it dying at full throttle I backed it off 1/2 a turn (leaner) went for another fly. All seemed okay until I did a long slow low fly pass and throttled up and it died, this time I had no option but land in the adjacent field (very soft mud). Thus I went back to previous setting plus another 1/4 turn richer.

Flew ok but did cough once on another vertical climb. Most flying at 1/4 to 3/4 throttle with short duration at full say 5 seconds max. Throttle response seems ok and issues appears in latter part of flight time (land with 1/4 tank left).

Okay question time!

1/ In the vertical position the fuel level is furthest from the carb by about 6 inches (with tank 1/4 full) would this be pushing my luck (especially if I progressively back the throttle off to idle for the stall turn)?

2/ I have a nice loop from the tank to the carb, should this be ?as short as possible as it just adds effective negative head as the fuel has to go higher than the carb

3/ As the temperature was 10C today which is about 10C warmer than most of the other flights, which way does the mixture drift with temperature? The higher ambient air temperature the leaner its runs or is it richer?

Just so I am ready for when it warns up!

Current flight score for 2018 IC flights = 10 Electric = 4

Ron Gray14/01/2018 17:57:54
769 forum posts
200 photos

Air feed to 155

Rather than use a bit of plastic pipe I decided to use a length of steel as this would give me the opportunity of forming mounting lugs. This is the result, which I’m quite pleased with plus I can now forget about the air feed to the carb.

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trebor14/01/2018 21:07:08
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1481 forum posts
174 photos

Do you think this installation will work if the carb is 1 1/4" higher than the centre of my fuel tank but level with the top of the tank ? I fitted vent with a flared end outside the engine bay hoping for some ram air effect dont know and the tube lifted up to prevent spillage.

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Martin McIntosh14/01/2018 21:24:08
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2340 forum posts
928 photos

Those tubes look overly long. Can you not shorten them quite a bit? Cannot see exactly which one goes to the carb.

Chris, sounds like the mid range, not the top end, needs sorting to me. Does it pick up instantly on the ground or hesitate (too lean) or need to clear its throat a bit (too rich) ?

Martin Harris14/01/2018 22:00:00
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7439 forum posts
186 photos
Posted by Chris Walby on 14/01/2018 17:38:59:

Now with half a tank of fuel run through the Speed Air (Laser 70) I have really started to explore the flight envelope and had a couple of problems this morning (one self induced so does not count!).

First up after a number of successful stall turns, the next at full throttle and then as I eased it to 1/4 throttle it seemed to momentarily "cough" and as I turned to vertical down it slopped. Dead stick back on the runway although the hedge did look a bit taller than normal.

That's either a big tank or perhaps you mean half a gallon?

ARTF fuel tanks are often mounted directly to the formers which can encourage fuel foaming, especially as the tank starts to get emptied and bubbles can be sucked through the fuel lines - have you packed foam around the tank? This can reduce the effects.

Chris Walby14/01/2018 22:07:35
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406 forum posts
65 photos

Martin,

Its faultless on the ground with slow or rapid throttle opening it revs up a treat. All the previous flights in colder weather have been no problem, although I have been running the engine in and relearning its characteristics so rolls loops and inverted flying are no trouble at all.

Only difference today was not blowing a gale, freezing cold and big vertical climbs with reducing throttle (stall turns) previously I would roll 180 and pull over the top + it has less in the tank but still lands with 1/4 in it. Hence my question as it seems to be running lean so is that right in warmer weather it may need to made richer?

trebor14/01/2018 22:11:38
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1481 forum posts
174 photos

Posted by Martin McIntosh on 14/01/2018 21:24:08:

Those tubes look overly long. Can you not shorten them quite a bit? Cannot see exactly which one goes to the carb.

I've shortened the carb one, just left enough to pinch when the flying is finnished for burning off fuel.

Martin McIntosh14/01/2018 22:39:16
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2340 forum posts
928 photos

Chris, I would think that in colder weather you may need to richen it a bit due to the fuel being less viscous but this should not make enough difference for the motor to quit when throttling up. Lasers are very tolerant of high or low end settings and I have not needed to touch my 80 in the cold. One old trick is to add a capfull of petrol to a 5l fuel can. It keeps the plug alight better for some reason, although I no longer do this.

Adding a silencer pressure tap to my 80 cured it from stopping in negative G (high tank, inverted motor).

Martin Harris14/01/2018 23:22:52
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7439 forum posts
186 photos

Always worth checking that the clunk hasn't folded forwards - especially if one of the previous landings was less than perfect. The vertical climb would allow air to be sucked into the fuel line in this case.

Colder air is more dense than warmer air, hence the occasional need to richen the mixture if temperatures drop significantly.

Jon - Laser Engines14/01/2018 23:46:10
3586 forum posts
144 photos

Chris, its possible your tank is a shade high and you are having a change in fuel head. If you can lower it a touch do so and try again.

Trebor, I think you will be ok. If not then its time for a pressure tap.

Ron, that should do fine

Chris Walby15/01/2018 08:22:31
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406 forum posts
65 photos

Cheers guys,

For info its a 10oz tank and is a tight fit in the fuselage so padding might be tricky, but it can be lowered as its sitting on a balsa block.

There were no bubbles in the fuel line so no indication plus it flies in other orientations okay and the clunk is in the right place, all be it I think it might be a bit long as it can just touch the back of the tank (the clunk does not seem that heavy either (one supplied with SELC tank).

I'll take the tank out add a bit of padding, lower it a bit, shorten the clunk line and feed to the carb and try that.

Perhaps I need to fiddle with it a bit more!! Martin, That's what I thought when I leaned it off (as it was warmer) but it made it worse.

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