Laser Engines - Technical questions

[Gordon Whitehead 1]

I used this setup with a Perry pulse pump and Cline regulator when experimenting with petrol on a 4str. If there's a nipple on your carb pump to take crankcase pressure pulses it might work for you, to save adding a second backplate nipple.

Here's where I found the idea: http://saito-engines.info/pumps.html

The last part of the article describes an interesting "pumped tank pressure" system that was apparently sold with the Saito 220.

Gordon

Edited By Gordon Whitehead 1 on 16/01/2018 13:52:30

[Geoff S]

Posted by Frank Skilbeck on 15/01/2018 22:13:02:

Geoff, I was out at the weekend with my 30+ year old Laser 61, problem I had was getting it to stop!

The needle valve on the Super Tigre carb is not very sensitive and I do find a tach makes setting up the top end easier.

My procedure is as follows, tune for top end revs and the richen slightly to drop say 200 rpm, the back to idle and adjust the low end mixture, if it bogs down and splutters on pick up then lean it a bit, once set then check the top end. I must admit I don't really touch my needles, just do a quick rpm check and then fly.

At the weekend mine wouldn't start, plug was showing amps but pulling the plug and it wasn't glowing, new plug and it started first touch of the starter.

This engine hadn't run for years until I 'found' it in the club hut just before Christmas and decided to refurbish it by stripping, cleaning and fitting new bearings. Once I get it set up then I hope not to touch the needles like you.

One of the best glow engines I had is a G34 Super Tigre which just ran and ran, first in the Precedent Fun Fly I used to pass my 'A' and eventually in a Limbo Dancer I built from the plan. So I have some experience with ST carbs. I'm going to set the slow needle by the blow down the fuel pipe with a tiny throttle opening method and then set the main needle using my tacho. I'll then follow your advice and see where it leads - hopefully to a well running engine.

Thanks

Geoff

[Gordon Whitehead 1]

Posted by Geoff Sleath on 16/01/2018 17:20:37:

I'm going to set the slow needle by the blow down the fuel pipe with a tiny throttle opening method

If I remember correctly that's the method Neil Tidey used to recommend for achieving the initial slow needle setting. I think the throttle opening would have been set using 18swg wire. With cheeks puffed out and ear drums popped out too, I always found it a bit difficult to tell when the hiss of escaping air had arrived. I still use the method, though slightly modified. Instead of blowing down the fuel pipe, I squeeze air down it using a disposable syringe. Much easier!

Gordon

[Martin Harris - Moderator]

It was certainly advocated by the legendary Mick Wilshere for those carburettors on their originally intended locations.

[Jon H]

Once I get it set up then I hope not to touch the needles like you.

This is something I hear often and I'm pretty sure its the cause of a great many engine related issues. It is vital that the engine be tuned correctly for the day on which it is being used as factors such as temperature, humidity, air density etc all make a difference to the tune of the engine. In general slow run needles need no adjustment once set but main needles must be checked on the first run of the day. Often little to no adjustment is required but its always worth making sure the engine is spot on before attempting to fly it.

The blowing through pipe trick for the slow run works fine but it is only a base setting to get the engine running. As your engine is already running it wont really help you as it must now be tuned up for its specific installation.

Tuning with a tacho is also not recommended as it leads to excessively lean mixture and 'rpm chasing' in most cases. RPM chasing comes about due to the natural drop in rpm an engine sees once it warms up. If rpm is checked on the first full throttle blast you may see 8500 for example. If you then adjust the needle, are satisfied with the tune, then check again you may see 8400 due to the engine warming up and naturally loosing a few revs. This is usually viewed as the tuning adjustment causing the rpm loss and in our experience there then follows a prolonged period of full throttle operation with leaner and leaner mixes being pushed to try and reclaim 8500rpm or more. During this time the engine gets hotter and hotter, and slower and slower with the user still trying to screw the life out of the needle in search of more rpm.

This video shows me setting up a Laser 150 on the test bench. Both needles are set well rich in the first instance and the engine was given a short warm up. I start with the main needle and tune it as easily as you can see. The slow run is then leaned off slowly, with accelerations in between, until it bogs down. This is a lean cut so the slow run is teased open until I can slap it about as much as I like. as you can see from the video symptoms of a rich idle are a slightly fast idle rpm that is lumpy and wont sit still. Once leaned off you can see the rpm drops and is very stable. Throttle response when rich on the low end is also sluggish and lumpy. Note that setting up the engine takes a matter of minutes only and is not a drawn out process. I hope the video is of use.

[John Stainforth]

This video is really useful. Always great to see how an expert (the expert?) does it!

[bert baker]

Nice

[cymaz]

With the V twin, what indications were there to just only the low end on the right hand carb. Top end was easy to follow but the low end seems a bit of a dark art?

[Chris Walby]

Thanks Jon, That settles it in my book, as mine now needs a little setting up as its running in and the weather is changing (spoke too soon!).

Only thing I noticed with mine is when I pinch the fuel line to stop it the revs pick up then die, but yours didn't, is that any indication of over rich at the bottom end?

[Jon H]

Posted by Chris Walby on 17/01/2018 08:40:39:

Thanks Jon, That settles it in my book, as mine now needs a little setting up as its running in and the weather is changing (spoke too soon!).

Only thing I noticed with mine is when I pinch the fuel line to stop it the revs pick up then die, but yours didn't, is that any indication of over rich at the bottom end?

If you see an rpm rise of more than a 100 or so then its likely a bit rich. When you pinch it off, in general the revs will increase very slightly before it stops. If there is a large rise then you are probably quite rich and could do with a lean off. Tank position can influence this though so the best way is the throttle stabbing approach as its the acceleration load which is the limiting factor on low end tuning. As a consequence, the more gentle you are with the throttle the leaner low end mix you can run. If you were to set a 2 second servo slow/delay on your throttle servo you can run really lean slow run mixes and this is good for fuel economy and in a large engine can also help offset torque swing as the power comes slightly more gradually. Im not suggesting we all go and slow our throttle servos down, its just something to note and you can try it if you like.

Cymaz, slow run settings on the twin are trickier to show on a video but i will try when the weather improves enough. In general the principal is the same as the single with both cylinders being leaned off together until one wont pick up. You then richen that one so its picks up and keep leaning the remiaing cylinder until that bogs down. The sound is also a good indicator and the exhaust note of both cylinders should sound the same. It sounds daft, but you can tell them apart. Its like trying to focus on one instrument in an orchestra. Smoke is not a good indicator as the direction of crank rotation throws oil up one cylinder more than the other. Feeling the exhaust pulses on your hand can be helpful in some cases. 

The video at the bottom is of the 150v that Tartan restored here on the forum. He did a cracking job but was having trouble with the idle so shot the video.

If you listen carefully at the start, and when looking at the left cylinder, you can hear a smooth but muffled thrub in the background. That is the slightly lean right cylinder running happily to itself. The left cylinder is rich as shown by its 'tutt tutt putt pf futt putt' exhaust note that is not in sync with its best mate. As the rich cylinder cools during the long idle ignition retards to the point where firing ceases, all the while load on the lean cylinder rises as the rich cylinder isnt carrying its share of the load. The increase in load causes the lean cylinder to go past its optimum point and ignition again fails causing the engine to stop completely. If the left cylinder was leaner the right would probably keep going. Equally, if the right cylinder was a bit richer it would continue to run on that cylinder even after the left had thrown in the towel.

 

As you are probably starting to see its all about subtleties and really listening to your engine. Most of the time they are telling you what the problem is, its just a case of knowing what to look for.

 

Edited By Jon Harper - Laser Engines on 17/01/2018 09:06:54

Edited By Jon Harper - Laser Engines on 17/01/2018 09:15:49

[Ron Gray]

Not a twin but the first run for my 155 in the re-engined Taylor Craft. Pretty impressive as this is straight out of the box. On the second run I slightly adjusted the top end and am getting 8500 on a 16x8 APC. Good to go! (click on photo to get vid)

Edited By Ron Gray on 17/01/2018 13:10:14

[Jon H]

Video unavailable

8500 is a shade slow, 8700 is what i tend to target. That said its pretty cold and on small props this slows the 155 down a fair bit. On large props it runs faster when its cold. Its all about the mass flow through valves and blah blah...

Anyway, if you have a 17x6 handy try that as it might be better suited to the model than the 16x8

[Keith Berriman]

Followed this thread from start and now covinced my next fuel will be laser 5% just to save the pocket from formula irvine. Just thought I would ask is it better to open a throttle system reasonably slowly more than go full wack in one go. My transmitter has servo slowing in the menu or have I seen expo used on throttle servos? ?

[J D 8]

Opening the throttle in a smooth steady way is best for any engine,you would not stamp the peddal to the floor in your car every time you drive it. [ have known some did but their cars did not last long]

[Jon H]

JD8 is correct, gentle and progressive throttle movement is the best way for any engine.

As i posted in my comment further up the page being gentle with the throttle has a number of advantages. In general, if you aim to move the throttle from idle to full power in around .5-1 seconds you will be doing just fine. If you dont trust yourself to do this in an emergency situation then putting a .5 or 1 second delay on your throttle channel may be helpful.

Another thing to try is only opening the throttle part way in case of an emergency. As an example, if i decide to go around with my large warbirds i rapidly (as fast as i can) open the throttle to around 50% before slowly opening the rest of the way. This helps cover off any cuts on acceleration and reduces the torque swing. This is important as torque swing at low airspeed can be enough to flick the model into a spin, especially if you bump the rudder in your efforts to open the throttle.

Normally half throttle is enough to stop any model from slowing down and give it some acceleration.

[Ron Gray]

Try the vid again, should be ok now. Will try the larger prop tomorrow if it’s not raining.

As a matter of interest Jon, I’ve been using Prosynth fuel in my other 2 stroke glow and have been really impressed with it. So much so that a number of other club members have gone over to it to run both 2 and 4 strokes and all have reported better throttle handling and cleaner running when compared to other, compatible fuels. So last time out I ran my 160v on my usual fuel for the first flight then changed to Prosynth for the second, I have to say that it ‘felt’ better. Another plus for Prosynth is its cost, cheaper than others especially if you buy club quants as I did. I would be interested to know if you’ve tested this fuel?

[Ultymate]

Posted by Jon Harper - Laser Engines on 17/01/2018 15:30:23:

" especially if you bump the rudder in your efforts to open the throttle"

The Joys of mode 2 flying ?

[Ace]

"I would be interested to know if you’ve tested this fuel?"

Ron - a quick search back will highlight quite a previous debate on Prosynth in Lasers with IIRC Jon expressing quite a strong view.

[Martin Harris - Moderator]

I hope Jon doesn't start thinking we're winding him up deliberately!

While I'm here, do you have any approximate fuel burn figures/tank size recommendations for the various engines?

Edited By Martin Harris on 17/01/2018 18:33:55

[Ron Gray]

Did a search for Prosynth but it didn’t return anything.

Edited By Ron Gray on 17/01/2018 18:42:30

[Denis Watkins]

Posted by Ron Gray on 17/01/2018 18:39:55:

Did a search for Prosynth but it didn’t return anything.

Edited By Ron Gray on 17/01/2018 18:42:30

**LINK**

[Ron Gray]

Thanks Denis, I meant the location of where the discussion about Prosynth in Lasers is! I already have the link to Weston as I bought 30 gallons of Prosynth at the end of last year plus have one of their excellent 2 strokes.

[Jon H]

Posted by Ultymate on 17/01/2018 16:55:54:

Posted by Jon Harper - Laser Engines on 17/01/2018 15:30:23:

" especially if you bump the rudder in your efforts to open the throttle"

The Joys of mode 2 flying ?

Could be worse, I mean mode 1 flying... pff

[Jon H]

This is another topic that I am afraid is not up for debate and all I can say is this:

Laser engines do not recommend the use of Weston uk fuels as they are not compliant with our warranty specification.

[Martin Harris - Moderator]

Here