Laser Engines - Technical questions

[Artto Ilmanen]

On 22/06/2021 at 00:33, Jon - Laser Engines said:

Engines will always need a retune when changing fuels. I really dont recommend this tune and forget idea as things change day to day. It only takes a few seconds to tune the engine before the first flight of each flying session and even if it ends up exactly where it started you at least know its set exactly right

 

Jon, do you tune your aerobatic models with Laser engines on max power on the ground, too? 

 

From what I remember of our discussions you tune the engine to max power on ground and leave it there  - at least your warbirds.

 

I just refer to the matter that in my experience an aerobatic model tends to have more power on vertical maneuvers if set a tad rich on the ground? As example, this seems to be the case with my Yak54 / 300V. I'm running a Menz 20x7 and I have tested an APC 20x8, too.

 

 

Tuning the main needles to max power before first flight of each flying session is easy. Setting the main needles in balance but a tad rich is a bit more complex, though..

 

Edited September 2, 2021 by Artto Ilmanen

[Don Fry]

I tune to max, as in lean off, and you get to a flat bit. And I leave on the rich side of the flat bit. Lean it off from there and it does not seem to go faster, it’s flat. So I can’t say it’s rich.

My hooligan stuff does vertical at half throttle. (When not broken)

[Martin Harris - Moderator]

This, to me, is where the nose up check is of benefit.  I believe Jon's antipathy to it is based on use of Lasers in scale models primarily although he may disagree.  What works with a correctly located fuel tank with an extended level high power test doesn't always give the same result when dragging fuel from several inches below the carb from an unpressurised fuel tank in extended vertical operation...

 

Tin hat on...?

[Martin McIntosh]

Yes, quite.

[Chris Walby]

Sorry I don't agree, if the tank is in the correct position there is no need to do the nose up test. Tune for max RPM and get on with it, the caveat is that the engine must be fully warmed up up before the setting up is carried out.

 

Finally from I have seen people struggling to hold a medium/large model at WOT nose up with the TX in the other hand or worse leave the TX on the ground while doing the test, this is just plan dangerous. At WOT the model will be the most difficult to hold onto, most likely to shed a prop or spinner and flying debris arc likely to cover the pit area. 

 

My largest model is a 180 single or 100 twin and there is no way I will do a nose up test in the pits on my own and I wound be extremely concerned if someone turned up with a larger engined model and tried a nose up test. If you always need a helper then its over complex or if you only do the test once in a blue moon then what's the point? My understanding is that the tuning process recommended by Jon (Laser Engines) is comprehensive for reliable operation and no other tests are required based on following the guidance given regarding correct installation of tank/cooling etc.

 

As for extended vertical operation...with our height limit an interesting comment unless this means extended periods of prop hanging - how exciting ?

 

[J D 8]

  When I first joined my club many moons ago everyone was doing the nose up test. I had never heard of it having been a lone or just one mate flyer up to then.

I was encouraged to do it as part of the start up routine, not to hard to do with 40size models which most were at the time but as models grew bigger it seemed a dodgy thing to do and went back to doing a thirty second run up in the stocks so to speak. Which is much like what full size light aircraft do.

[Ron Gray]

My Great Planes U-Can-Do is powered by a Laser 100 and had a bit of work done to the nose so that I could fit the fuel tank as per 'Laser guidelines' (Jon). The engine is tuned for max revs, exactly the same as my other Lasers but as this 'plane is supposed to be 3D capable it certainly isn't flown like my others. In answer to Martin's comment above, I can say that from personal experience long vertical climbs are not an issue neither are my useless, but sustained, attempts at prop hanging. So I do believe that there is some truth that the nose up check is not necessary when an engine has been tuned (correctly). However, I can attest to one circumstance where it would have saved me a lot of time and worry. I was having problems with my 240v fitted to my Wots Wot XL, the engine would run perfectly in the pits and was tuned for max revs but every time I took off and it was in a nose up attitude one pot would cut out, sometimes I could manage a take off but as soon as I climbed out one pot would cut. Cutting a long story short, I took the engine off and fitted it to my test stand and it ran fine even when I lifted the front of the stand up (nose up test???!!!). I put it back in the 'plane, took off and one pot cut. Back in the pits I enlisted help and whilst tethered I raised the nose and sure enough one pot cut. I traced it back to a very small air leak (hole) in one fuel feed line to that cylinder. Replaced the line and all was well.

 

I can't see that there is any downside to a nose up check as long as the engine has been tuned beforehand and the model is held in a safe manor and away from people (apart from those assisting in the test of course). I certainly won't be doing it on my 2 x Laser 160v powered Tigercat though!

Edited September 3, 2021 by Ron Gray

[Jon H]

The nose up test is such a waste of time. I know i bang on about it but it really is pointless and, as JD8 points out, flippin dangerous with bigger models. 

 

Although i fly mostly scale and usually with unpressurised Lasers, i also have a Satio 45, Enya 53, Enya 155, OS 40, OS 240 and soon an ASP 160 twin all in service as well. The saito, os40 and enya 53 are pressurised, the rest are not. The saito and enya 53 are in scale models, the rest are not. My hangar 9 pulse modified into a twin uses a pair of laser 70's non pressurised. Incidentally the enya 155 in my H9 pulse 125 used to be pressurised, but the muffler fell off and i flew the rest of the day without it (holy cow it was loud!). Anyway it ran so much better without pressure that it now runs without it all the time. 

 

I never nose up test any of them and all of them run perfectly. I never worry about it, just tune for max power, hold for a good 10-15 seconds(apart from the saito, its got an overload prop on it), and then fly. The OS 240 flat 4 in my AWXL is awesome and i can do anything i want with the model. I dont spin/snap it, as the engine is very heavy and the firewall decidedly flimsy, but other than that it does the lot. My scale models also probably spend more time in vertical climbs than my sport/aerobatic models do. I am sure i can do a 1000ft loop with my sea fury if i try hard enough and i love doing a massive quarter clover with the sea fury and La7. 

 

However. As Don suggests, there is a range of tuning that can be considered optimum and if flight performance suggests you need a little richer mix in vertical's then fine, open it a smidge when you land. After a while you may have a mental list of one plane being leaned off and open 2 clicks, most being left alone, another being leaned off and then slightly past the peak so its really right on the edge of too lean. This is all fine as it comes from direct experience with the engine in the air doing its thing. Just pointing the nose in the air might be a bodge fix that gets around problems sometimes, but it also is a bodge and most of the time will mean your engine is just running rich. As we all know, a rich engine chews up fuel, makes a mess, is unreliable, and more likely to go rusty. 

 

It has to be said though, that most problems with engines boil down to bad tank placement, bad tuning, bad cooling. These are the 3 main issues and i think 90% of engine problems can be traced back to these 3 issues. 

 

Another thing to consider is the changing engine note due to doppler shift and the reducing RPM as the model looses speed in the climb. Is the engine actually sagging, or is it just a sound illusion caused by these two factors. Very often its a sound illusion, but without onboard RPM sensing that might be difficult to prove. 

 

So my advice will always be the same. Top of tank, middle of carb. Tune for max power, fly. See how the engine behaves, tweak accordingly if needed. 

 

Also the position of the carb, the position of the outlet on the tank, the orientation of the engine etc. none of it matters. Top of the tank, middle of the carb. That's literally all there is to it. 

 

[Martin Harris - Moderator]

JD8, I don’t believe there are many full sized aerobatic aircraft that use simple suction fed non float chambered carburettors…

 

There’s no argument from me that you can get away without a nose up check with many models by doing a proper extended power test but in the real world of poorly designed ARTFs and less than ideal locations on plans then it is a simple check which can save a model. 
 

My argument is that with any model where it’s practical to do so, why wouldn’t you?

 

Chris, I’ve seen propellers coming off under power - not one has ever gone backwards so unless a test is done pointed in an unsafe direction then where is there any safety issue over and above the same thing happening on a level power check - especially at a site like ours where a power check against the safety fence must surely be safer than extended running at full power on a start up bench. 
 

 

[Martin McIntosh]

From my experience this only really applies to four strokes which seem to draw fuel much better. Many two strokes had/have a very large intake to squeeze out more power and unless left very rich will die when the nose is raised. I used to fly F3A using OPS`s with Kavan so called pressure carbs which were like dustbins and could only be run on crank case pressure with a TK regulator, thus allowing the motors to be leaned to the extreme, in fact I could get two continuous schedules from only 12oz of fuel.

Two of my Lasers need silencer pressure, one because the tank has to be very high to fit in at all so the motor otherwise fails with the slightest negative g, the other because I cannot get my finger in to choke prime it so instead can now do it by blocking off the silencer, an old trick.

[john stones 1 - Moderator]

Very simple for me, if flyers see value in a nose up test, why do you care ?

Tune your engine correctly ??? There you have it folks, you all fly, you all see how many fail at this, matters not how many times you show/help some they get it wrong, nose up when they take off it cuts, advise em to richen it they fly and don't break their model. How many times you watched a pilot fiddle with the needle ? You're sat there knowing it's too lean, what happens when he takes off ? It goes sick, if you're telling me you ain't seen it, I don't believe you.

Bigger models it's potentially dangerous ? Yep, hobbies fraught with danger, be careful.

[Chris Walby]

57 minutes ago, Martin Harris - Moderator said:

My argument is that with any model where it’s practical to do so, why wouldn’t you?

 

I’ve seen propellers coming off under power - not one has ever gone backwards so unless a test is done pointed in an unsafe direction then where is there any safety issue over and above the same thing happening on a level power check - especially at a site like ours where a power check against the safety fence must surely be safer than extended running at full power on a start up bench. 
 

 

 

Perhaps you were not at the field, but Phil's big warbird 2 stroke spinner and prop came off when I was starting it (on a bolt so not double nutted), the prop dropped however the spinner/backplate went backwards and nearly reached the access road. I have had a couple of spinner failures one of them (a couple of people on site obeying safety guidelines) and bits ended up near the clubhouse patio! The test was not prolonged WOT either.

 

Alost everything can be dangerous, its the things you do to reduce the risk of an accident happening is what's important. Waving a screaming model above your head just does not seem like a safe thing to do if it can be avoided (and is not recommended by the manufacturer).

Edited September 3, 2021 by Chris Walby

[Martin Harris - Moderator]

A failed spinner will eject backwards of course and likely be given energy by the propeller - but tuning issues will not cause the failure. 
 

 

[john stones 1 - Moderator]

Bit OTT for me, waving a screaming model above your head, nose up can be done in a much calmer way, communication with others is a benefit as well.

[Jon H]

1 hour ago, john stones 1 - Moderator said:

Very simple for me, if flyers see value in a nose up test, why do you care ?

Tune your engine correctly ??? There you have it folks, you all fly, you all see how many fail at this, matters not how many times you show/help some they get it wrong, nose up when they take off it cuts, advise em to richen it they fly and don't break their model. How many times you watched a pilot fiddle with the needle ? You're sat there knowing it's too lean, what happens when he takes off ? It goes sick, if you're telling me you ain't seen it, I don't believe you.

Bigger models it's potentially dangerous ? Yep, hobbies fraught with danger, be careful.

 

 

The reason i care is because it is usually a bandage on a broken leg and is, for the most part, totally unrepresentative of conditions the engine will see in flight so means nothing anyway. There is also the assumption that it will reveal a lean mixture, which it wont as the whole lean mixture thing is wrong in the first place. You cant run engines lean. if they are generating full power, they are not lean. If lean, power will drop sharply, it will overheat and then stop very quickly. 

 

If engines stop in flight due to overheating or mixture change as fuel is used, the tank placement is wrong, or the cooling or whatever. running the engine rich to bandage that is not the right solution as it does nothing to fix the actual problem. Lower the tank, baffle the cowling etc. 

 

If the cooling and tank placement were correct it is far easier to tune the engine as there is no variation during the flight. That way, even if the tuning isnt 100% it wont get any worse during a flight. 

 

What i am trying to do is suggest people look for the actual root cause of the problem and solve that rather than using hacks to hide the problem. I appreciate that fixing the actual problem can be more work than tuning the engine a bit rich, but you only have to do it once instead of fighting your engine every day. if you do it when you build the model in the first place you can fly safe and happy without a 2nd though. 

 

Another example of this 'bodge it' mentality would be retracts. Gear wont go up...so you roll inverted and shove negative g on it to get them up. Or, perhaps you could land and fix the problem? I know which one i would choose. If they wont go up, there is fair chance they wont come down either. 

 

I just get irritated by bodge job fixes to simple problems with simple solutions.  Especially when the rewards for this small effort are very significant. I never even consider that an engine will quit on me. It just never even enters my head and that means i can focus on flying. 

 

I appreciate that some will never learn, dont want to be told, etc. That's fine, they can live in ignorance all they like and run 30% castor in their fuel. But for the majority who do want to learn and improve their standards the continued repetition of modelling folk lore does little but continue the myths and prevent actual progress long term. So that is why i get wound up ?

 

 

 

 

[Martin Harris - Moderator]

I agree with everything you say above Jon, with a couple of small exceptions. 

 

In an ideal world you're quite right but the fact remains that people don't always get things right and although a properly engineered, maintained and set up model should only require a level check, a nose up check will make the engine work harder to draw fuel - simple physics...  This easy check shows up any error that has been missed with a level power check...or you can wait until it's 30 feet in the air and the engine quits!

 

Secondly, I really can't agree with taking off assuming nothing will go wrong - that's against every edict of airmanship that I was ever taught.  Even the crew of the most reliable airliner practice engine failure drills regularly and are fully prepared for the eventuality.  Have a plan...the old truism of needing any two out of height, airspeed and ideas at all times is rarely challenged...

 

We've agreed to differ on this in the past so I'd better make this my last word for the time being.

[thebluemax]

1 hour ago, Jon - Laser Engines said:

I appreciate that some will never learn, dont want to be told, etc. That's fine, they can live in ignorance all they like and run 30% castor in their fuel. But for the majority who do want to learn and improve their standards the continued repetition of modelling folk lore does little but continue the myths and prevent actual progress long term. So that is why i get wound up ?

 

 

 

 

Some people learn by listening

Some learn by watching others

Then there is always those that need to pee on an electric fence to find out for themselves

 

 

[Artto Ilmanen]

4 hours ago, Jon - Laser Engines said:

 

 

However. As Don suggests, there is a range of tuning that can be considered optimum and if flight performance suggests you need a little richer mix in vertical's then fine, open it a smidge when you land. After a while you may have a mental list of one plane being leaned off and open 2 clicks, most being left alone, another being leaned off and then slightly past the peak so its really right on the edge of too lean. This is all fine as it comes from direct experience with the engine in the air doing its thing. Just pointing the nose in the air might be a bodge fix that gets around problems sometimes, but it also is a bodge and most of the time will mean your engine is just running rich. As we all know, a rich engine chews up fuel, makes a mess, is unreliable, and more likely to go rusty. 

 

Top of the tank, middle of the carb. That's literally all there is to it. 

 

Gents,

 

Thanks for for the comments. I personally have never done the nose up test.

 

I think Jon said it well: tune it to max, then, based on the performance in the air small tweeks can be done once landed. I suppose this means tweaking one carb at a time: flying and repeating the process of small adjustements after landing (again) once best performance is reached. Then moving to the other carb and doing the same thing.

 

Another thing: "top of the tank middle of the carb" -> I think I misunderstood this somehow earlier when installing the engine. Now it's more like "middle of the tank, middle of the carb" -> maybe I need to check if I can lower the tanks (see picture)

 

 

[Martin McIntosh]

You all seem to have missed my point about the difference between four and two strokes. They need to be treated in a different way completely. Even under some sort of pressure (other than crankcase) it should be tank centre and spraybar on the same plane. Of the very many two stroke glows I have had I would not even think about running one without pressure of some kind.

On a safety note, the above photo shows a motor above a car mat. I tried that once and the 60 sucked the similar mat into the prop!

[Ron Gray]

Martin, if you read the post where the question was asked, which prompted the discussion on nose up testing, it was specifically about Laser engines, hence, I would guess, why your comments about 2 strokes have been 'ignored'. From Artto

 

21 hours ago, Artto Ilmanen said:

Jon, do you tune your aerobatic models with Laser engines on max power on the ground, too? 

 

From what I remember of our discussions you tune the engine to max power on ground and leave it there  - at least your warbirds.

 

I just refer to the matter that in my experience an aerobatic model tends to have more power on vertical maneuvers if set a tad rich on the ground? As example, this seems to be the case with my Yak54 / 300V. I'm running a Menz 20x7 and I have tested an APC 20x8, too.

 

 

Tuning the main needles to max power before first flight of each flying session is easy. Setting the main needles in balance but a tad rich is a bit more complex, though..

 

[Artto Ilmanen]

Another thing regarding fuel filters:

 

If I recall it right the fuel filter between the tank and the carburettor is not recommended ? I think I read Jon having written something like this..? Jon, would you mind either confirming or correcting me on this matter.

 

p.s. thank you all for your comments

 

Martin: your remark on car mat is noted! I will switch to something else, such as plywood ?

Edited September 3, 2021 by Artto Ilmanen

[john stones 1 - Moderator]

I quite like the World and it's imperfections myself, yet to meet anyone on 30% castor, or the retract juggler, as to the fence peeing, whatever turns you on.

It's a bandage, for less than perfect installation  ? o.k, and there are model flyers galore out flying imperfect models, always will be.

Learn by listening and watching ? Yep, me too listened to many many people and developed my opinion from experience, seems we simply disagree, is that not permissible ?

[john stones 1 - Moderator]

38 minutes ago, Artto Ilmanen said:

Another thing regarding fuel filters:

 

If I recall it right the fuel filter between the tank and the carburettor is not recommended ? I think I read Jon having written something like this..? Jon, would you mind either confirming or correcting me on this matter.

 

p.s. thank you all for your comments

 

Martin: your remark on car mat is noted! I will switch to something else, such as plywood ?

 

Ply could move as well, peg the mat down.

[Jon H]

6 hours ago, Martin Harris - Moderator said:

I agree with everything you say above Jon, with a couple of small exceptions. 

 

In an ideal world you're quite right but the fact remains that people don't always get things right and although a properly engineered, maintained and set up model should only require a level check, a nose up check will make the engine work harder to draw fuel - simple physics...  This easy check shows up any error that has been missed with a level power check...or you can wait until it's 30 feet in the air and the engine quits!

 

Secondly, I really can't agree with taking off assuming nothing will go wrong - that's against every edict of airmanship that I was ever taught.  Even the crew of the most reliable airliner practice engine failure drills regularly and are fully prepared for the eventuality.  Have a plan...the old truism of needing any two out of height, airspeed and ideas at all times is rarely challenged...

 

We've agreed to differ on this in the past so I'd better make this my last word for the time being.

 

I know we have covered this in the past and i dont want to fall out over it, but the thing is a nose up test will not reveal a tuning issue that is not apparent with a level power check. 

 

Engines go slightly rich in flight due to unloading. yes there are exceptions, but in general normal engines with standard exhausts go slightly rich as they unload. This will easily offset the gravitational effect on the fuel in a climb once the model is moving forward at the 20+mph our models fly at. The nose up test is done at zero forward speed, and i am sure that most of my engine would fail it, and yet they all run fine in the air. 

 

Chris made a good point a few posts back about engine temperature and its impact on tuning. Its very true and cold engines need a richer mixture to keep singing. This is where the 10-15 second full power blast comes in as it gives the engine a fighting chance of being nicely warmed up and it makes a big difference to takeoff performance. 

 

Again, i have not had an engine quit on takeoff in over a decade so i must be doing something right. 

 

On the 2nd point, you are right of course. But to clarify, i dont expect to an engine failure. It really never crosses my mind that i am going to loose an engine or have any sort of problem. However, i do still plan for such an eventuality. This came in handy when some debris blocked the needle on one cylinder on my 300v equipped P39. 2 feet off the ground, just off the edge of the runway over a ploughed field with a 12ft hedge to clear and a now 150 single cylinder engine turning a 20x10 prop and trying to haul a 21lb warbird over said hedge. It was close, but i was able to get away with it. My plan for such an incident is simple. Gear up, throttle back to around 80%, climb as best i can until high enough to level off, gain speed, turn...etc. 

 

Just because something is not expected dose not mean it should not be planned for ? 

 

 

[Jon H]

Not a fan of fuel filters. They can leak air when the seals go. 

 

Its not a big issue mind, and in some cases they are needed. Our petrol engine needs one as the carb is super sensitive to dirt and its the only way. 

 

John, i know not every model is going to be perfect, but i think everyone should strive for as close to it as they can. I always work on the basis that i can always do a better job, and each model i build is better than the last in some way. Its been 20 years? Im still building and my models are still not perfect. They never will be, but each is better than the last and one step closer. 

 

I just cannot deal with the british leyland 'that will do' mentality. Its the same with 'but we have always done it this way' mentality as well. It takes such a tiny effort to do something better than you did it before. I dont see why its so hard. 

 

maybe im the odd one out.