Laser Engines - Technical questions

[Jon H]

Nigel -  Expecting a model to prop hang at full power is not really an optimum situation. Pushing a model to the limits of its performance envelope like that will reduce all of the margins and you may end up with problems and/or compromises as a result. I look at it like this. If you want to prop hang, buy that sort of model and engine it accordingly. If you do, the situation changes dramatically and performance is as described previously. Asking a model to do something which it essentially cant do, making a compromise that just about allows it to do the thing it really isnt capable of, then recommending the compromise as a one size fits all solution to a non problem in other models...ehh its not exactly ideal is it? 

 

Carb placement - Martin more or less nailed it. In the dim and distant past OS style intakes were tested, but performance was somewhat degraded and they suffered with fuel accumulating in the u bend and causing the cough and splutter on acceleration we sometimes see from other brands. It is something i am considering looking into again mind you as ARTF's have changed the map a bit. Its pretty low on my priorities list mind you. 

 

Gary - Detention for you. Top of tank, middle of carb! 1000 lines for you after school ? 

 

 

[Nigel R]

I think you misunderstand a little Jon, I'm thinking standard sport aerobat, I don't know, an Acrowot with an 80 for instance, just at end of vertical climb, they can hang for a bit before kicking over with rudder.

 

I don't recall stating the nose-up is a one-size-fits-all though?

 

BTW I do get that ground tuning is only a starting point, and that in-air performance is the ultimate truth.

 

[Manish Chandrayan]

In defence of the straight through inlet, Weston used to sell four-strokes that were labelled 'tuned by West' or similar and featured straight through intakes. 

[Jon H]

9 minutes ago, Nigel R said:

I think you misunderstand a little Jon, I'm thinking standard sport aerobat, I don't know, an Acrowot with an 80 for instance, just at end of vertical climb, they can hang for a bit before kicking over with rudder.

 

I don't recall stating the nose-up is a one-size-fits-all though?

 

BTW I do get that ground tuning is only a starting point, and that in-air performance is the ultimate truth.

 

 

I see what you are saying but we are still into edge case's here and are bordering on deliberate attempts to break things. In this specific example, i would expect an 80 to give an acrowot unlimited climb anyway so throttle needs to be reduced to get the thing to stop, and then we are back where we started as the engine is now no longer at full power and the NUT has no relevance as a result. But assuming a thrust-weight ratio of less than 1:1 you could try and stall turn the way you mention, but really its only if you are trying to break something or prove a point. Would you really stall turn that way normally or would you throttle back a bit on the way up to slow it down? If you want to stall turn your acrowot, its not exactly common to climb vertically until it totally runs out of puff, then try to prop hang on to it while flat out, and then rudder it over just before it flops out of the sky. I would consider this approach to be pretty unusual. Not that its a guarantee of the engine stopping anyway.

 

And i know you didnt say it was the one size solution, its just commonly seen that way. A bit like expo... 

 

 

 

 

 

 

 

 

 

 

 

[J D 8]

 Both the OS Pegasus flat twin and flat 4 are known to suffer icing if conditions are right. Read about it some where.

Edited September 6, 2021 by J D 8
not sure what happened here but someone asked about long inlet tube icing.

[Jon H]

I have never had mine ice up, but it is possible i am sure under the right circumstances. If the engine is in a cowl i would say less so though as the hot air from the cylinders will pass the carb on its way out the bottom. 

 

FAO Ron. Further to our chat on the phone these are the updated cam timing diagrams http://www.laserengines.com/cam-timing/ 

[Ron Gray]

Thanks Jon, all timed up now, just got to mount it and see if it runs!

[Gary Manuel]

5 hours ago, Jon - Laser Engines said:

 

Gary - Detention for you. Top of tank, middle of carb! 1000 lines for you after school ? 

 

Will 1000 lines on this forum do?

 

P.S. I only said arguably centre of the tank - maybe I can write a 1000 line argument on that subject? I also never said that I do the nose up test myself. I'm actually not a great needle twiddler but I do see a lot of other people's models fading away after take off.

 

Edited September 6, 2021 by Gary Manuel

[john stones 1 - Moderator]

Anyone every heard the phrase "Agree to disagree" turning into a picking of nits and highlighting of minor comments.

The Carb position on Lasers ? Something I'd wondered  about myself, now I know, owned quite a number of various makes, never come across icing on mine nor anyone elses, but maybe it has happened but I was unaware. Engines ? I find them quite easy and pleasurable to use, installations the same, baffles me why it's such a chore for some, but that's true of lecky flying in my case, I find it a chore and to others it's a breeze.

[Tim Flyer]

One important advantage I believe in the short and straight carb inlet tube on lasers is that it avoids fuel accumulation particularly in an inverted engine.
 

This reduces risk of prop throwing or severe spluttering and hydraulic lock when starting. It’s easy for a laser to spit out excess fuel which can happen just after  tank filling. 

[Nigel R]

12 hours ago, Tim Flyer said:

fuel accumulation particularly in an inverted engine.

 

if you turn the engine backwards, the exhaust valve opens up and allows you to drain any fuel, I think?

 

why would the engine need to spit out fuel after tank filling?

 

Edited September 7, 2021 by Nigel R

[J D 8]

Many use an electric fuel pump to fill and it takes a second or two to switch off, in that time fuel floods everywhere including in the engine and over the ground.

[Nigel R]

I'm missing something JD8, I don't see how you flood fuel into the engine when filling?

 

on a 3 line tank, where fuel could conceivably go up the feed line, if you close the throttle then fuel doesn't go into the carb

on a 2 line tank, you're pulling the carb feed off anyway to fill the tank

on a setup with a fuel dot in the feed line, the fuel is only going into the tank

 

 

[Martin McIntosh]

Mine problems are usually the other way round. After filling, I need to get a prime into the carb especially if it is the first start of the day, hence the silencer pressure on my Tiggy since I cannot get my finger near it.

[Ron Gray]

Interesting that Martin. None of my Laser engine installations allow me to choke with finger over the carb intake, all I do is put the throttle to max, turn the prop over about 10 (ish) times, usually with starter, throttle back to idle, glow driver on then start. Engines usually fire up shortly after.

[Martin McIntosh]

That is what I would normally do too on other motors but for some reason I find Lasers difficult to initially prime.

[Ron Gray]

Still if the pressure nipple works then all’s good. ?

[J D 8]

3 hours ago, Nigel R said:

I'm missing something JD8, I don't see how you flood fuel into the engine when filling

 

 

  Has to be a 3 line tank, the most common and throttle will not be  closed it will be in the slow [ tickover ]position but open enough to let fuel in. At the rate electric pumps go it only takes a short delay on the switch off and fuel is flooding from the exhaust and some gets in the engine. I much prefer a hand pump, much more control.

[Chris Walby]

Hand pump for me, why?

• Every time I fill a tank I count he number of handle rotations, say forty to fill it, Then each time I fly I then refill it, say 25 rotations. That way I can judge with the aid or the TX timer how long I should fly. Some I run closer to empty and others (warbird twins) I want plenty of safety margin.
• Most I fill and drain from the carb fuel line, firstly I know it empties right to the bottom of the tank, secondly any debris/dirt gets washed into the tank when filling + I check the filter gauze after emptying the tank to see if anything been picked up

Regarding starting, most of the time is just spin it over until it self primes or failing that flick the TX to throttle cut for a couple of seconds, then back to idle if its very cold ambient air temp.

 

PS for the OS LA46's in the Extra Slim Twin  (as the carbs are above the tank when sitting on its tail skids and self drain) is to fill the tank before flight, open throttle to 1/4 and then pinch the exhaust/vent line + 1/2 turn on the pump and I can see the fuel run up to the inlet and dribble out. Glow plug on and then fire them up.

[Artto Ilmanen]

Gents,

 

Can someone provide me with instructions on how to adjust valves on Laser engines, twin and single, please? 

 

-Artto

[Nigel R]

Chris

 

I find the easiest way to prime two strokes, much as Martin described... if you have exhaust pressure, just block off the exhaust outlet with a finger, turn the motor by hand a few times, and pressure will force fuel up the tube to the carb.

[Chris Walby]

Nigel,

 

I have to have the noise reducing flexible things on the ends of all exhausts so its hard getting a decent grip + its all oily. 

 

And while I am filling the tank the exhaust vent line is off to indicate when the tank is full so its easy to do it then as part of the filling/pre-flight operation + holding my thumb over any of my Laser won't work as the tank vent is not connected to the exhaust.

 

Artto,

 

Would be worth checking to see if the valve clearance is correct before adjusting? 

Rotate crank until piston is at top dead center on the firing/power stroke (both rockers should have some slack/clearance. Check valve clearance and adjust if necessary. I would be quite surprised if they actually needed adjusting in normal operation unless the engine has been in use for many hours.

[Ron Gray]

Another thing I have done to choke the carbs on Laser engines is raise the tail of the model so that the fuel tank is higher than the carb then open the throttle and turn the engine over. Only works if you have sufficient ground clearance! But does also work if your tank is too high (sorry Jon). On the Tigercat I temporarily close off the tank vents after filling the tank and then continue to fill (couple of turns)with the throttles open, bit messy but also seems to work.

 

Anyway, off to fly the Sportster to test the 200 in-line in hot weather to check for overheating.

[Nigel R]

Chris, ok, makes sense, end of day if the pump method works, its all good.

[Jon H]

The egines should draw fuel without any trouble when cranked with an electric starter. If its not drawing, something is wrong. This could be tuning, gloopy oil in the carbs (a problem in very cold weather) or a blockage of some other kind. 

 

If slow run needles are set too lean the engine will draw fuel but not fire when cold. Once it warms up it will keep going even if the slow runners are too lean for a start. 

 

I dont bother priming engines if they are going to be electric started. Hand started engines get a heavy prime and then the backwards flick method to get them going.