Laser Engines - Technical questions

[john stones 1 - Moderator]

I would think your being yourself Jon, as are others and they settle for what keeps em happy,

Never owned a Leyland, Japanese for me.

[Martin McIntosh]

I feel that I must comment on the fuel filter or not issue. Other than those lousy Sullivan Crap Trap ones I have never had one leak in 60 odd years of usage experience. My fuel is filtered at least twice in the bottle, a simple gauze type to remove the dead spiders and bits of grass then a really fine one. A quality filter is fitted to the fuel line in the models because of the chance of dirt entering the fueling lines when filling and in the case of silencer pressure it would be bits of carbon. YS instructions say to fit another between the none return valve from the motor to the tank so that any unwanted bits will not interfere with the complex delivery system.

Someone I know only uses the simple gauze ones to their motors and has no end of trouble with blockages.

[Don Fry]

Jon, calm. You are an Engineer, note the capitol. Us lesser mortals expect you lot to get it right, (Hey ho, the nuclear reactor has just melted, the lift shaft brake has failed, what can I do in 30 seconds).
I expect a bit of sharp, it’s a machine, but the rest of us think they have a bit of soul, and a prayer will fix it.

The above, aided by a St Émilion, is not an insult.

[Rich Griff]

Even the Japanese make Friday cars etc., Ask me how I know...but in an other thread....titled "Fridays Production" or similar...

Edited September 4, 2021 by Rich Griff

[EarlyBird]

13 hours ago, Jon - Laser Engines said:

maybe im the odd one out. 

No you aren't there's another one here. Engineer and perfectionist that is. 

'that will do' is not a phrase I ever use. It's either right or wrong, for me it's that simple. 

[Gary Manuel]

Just to add my tu'pence worth about the nose up test.

 

Jon is obviously an expert at setting up and tuning models, so it's natural that he should have a high success rate. Others will have a lesser rate of success. The nose up test is simply that. A final test before take off that the model is running in such a way that it should be able to tolerate the actual nose up, low speed attitude it will encounter after rotation into take-off. If Jon were to carry out the nose up test, he would probably pass it 100% of the time due to his experience and "ear". Other will not pass it 100% of the time. The times when they fail it and the engine cuts has probably just saved them an engine cut at take off.

 

My message here is simple. The test does no harm, so why wouldn't you do it?

[Andy Stephenson]

For me it is the closest approximation to the effect of acceleration on take-off, which is when there is always a possibility of a lean cut if not tuned to perfection.

[Artto Ilmanen]

I think the point what Jon is saying is:

 

• One should learn how to tune a model airplane engine so you do not have to do the dangerous nose up test. As if you know what to do the nose up test is worthless as in anyways it does not simulate the real flying condition..

 

Edited September 4, 2021 by Artto Ilmanen

[Ron Gray]

Just collected an old 150v, doesn't look too bad but want to check the timing, does anyone (Jon?) have the photo showing this please?

[J D 8]

Nose up test. What those with pusher planes do ??

[Martin Harris - Moderator]

This any use Ron?

 

https://web.archive.org/web/20160316212702/http://laserengines.co.uk/Camtiming.htm

[Ron Gray]

Thanks Martin, that’s what I wanted.

[Jon H]

Ron, the timing on the page listed is wrong for the 150v. Its a half tooth different (tooth in the middle of the lobe lobe not a space) so you need a count of 6 not 7 on the inlet cam. Call me if you like, it might be easier to explain. 

 

Last effort on this nose up thing. 

 

It does not revel tuning errors. It simply does not do this, anyone saying so is incorrect. im not trying to be rude, its just a fact. If the engine is running flat out in a level condition and holding power (good long blast to check it), it is tuned correctly. If it stops for some reason, the problem is not the tuning. 

 

Most of my models will fail the nose up test. I have tried it out of idle curiosity and got bored after they all failed or at the very least faltered. As all of the failed models fly perfectly, it again demonstrated the pointlessness of the whole thing. 

 

To everyone saying engines are hard to tune...they arent. Yes i tune mine to the last ounce of their performance, but getting an engine to 98% peak is easy for anyone. I forget who posted saying it, but there is a band where you can go rich or lean on the needle with no effect on the engine. Anywhere in this range is fine and its very easy to find it. Setting slow runners is easy too if the proper method is used. I have even considered doing a video of a tuning speed run. Main and slow run needles removed from the carb and sat on the bench. How long to install them, start the engine and tune for max power with no factory settings to work from. I think it can be done in 2 minutes just by listing to the response of the engine and making adjustments as we go. If i can do it in 2, everyone else can do it in 5 surely. 

 

takeoff fuel surge. I used to hand launch one of my models. Got more acceleration than a normal roll and didnt quit. Usually failures connected to fuel surge are not that at all and its back to slapdash tuning done on a cold engine. Engines take time to warm up and they cannot be accurately tuned when cold. Tank placement can also be another root cause. 

 

The test does no harm...other than running engines rich all the time, making them messy, prone to rusting, less economical and less reliable. All the things people moan about when it comes to glow engines. Also, and this is not intended as an insult to anyone, the level of understanding of engine operation within the hobby seems to be at rock bottom and i have noticed a sharp drop in the 10 years i have been at laser. Some of the questions i get at work blow my mind. It seems a great many people got either very poor, or no instruction on model engine operation when they were being taught to fly. All they got was the modelling folklore lecture just passing on the same bad advice the instructor was given way back when. If there is to be any hope of raising this level of knowledge we must weed out these old and incorrect assertions regarding model engine operation. Every time they are repeated the whole thing just keeps going. Please dont be afraid to ask questions, im not judging people who dont know, but please follow the advice given and not run everything past the 'club expert'. After all, if he had all the answers why ask me in the first place ? 

 

I am an expert and posses skills beyond those of mortal men...no, just no. Nothing i do is beyond the ability of anyone else armed with the right knowledge and operating practices. Yes i have great experience, but none of what i do is hard and there are shortcuts you can take to get the result without having to know all the in's and out's. Getting the thing installed correctly, with the tank right, the cooling etc. Get all that done and you are 90% there. 

 

Its not black magic, just simple steps. 

[Gary Manuel]

6 hours ago, Jon - Laser Engines said:

 

 

Most of my models will fail the nose up test. I have tried it out of idle curiosity and got bored after they all failed or at the very least faltered. As all of the failed models fly perfectly, it again demonstrated the pointlessness of the whole thing. 

 

 

I'm confused Jon.

 

If your models fail a nose up test, how can you confidently launch them? The flight might involve varying degrees of nose up, low / no velocity flight, which the model would find indistinguishable from the nose up test. If the engine cuts when being held nose up on the ground, how will it not cut when in a slow vertical climb / stall / prop hang / tail slide? These are varying degrees of nose up, slow forwards to slow backwards movement. How can the model know whether it is being held back by the modellers hands during a nose up test or by gravity during this kind of flight?

Edited September 6, 2021 by Gary Manuel

[Jon H]

2 hours ago, Gary Manuel said:

 

I'm confused Jon.

 

If your models fail a nose up test, how can you confidently launch them? The flight might involve varying degrees of nose up, low / no velocity flight, which the model would find indistinguishable from the nose up test. If the engine cuts when being held nose up on the ground, how will it not cut when in a slow vertical climb / stall / prop hang / tail slide? These are varying degrees of nose up, slow forwards to slow backwards movement. How can the model know whether it is being held back by the modellers hands during a nose up test or by gravity during this kind of flight?

 

Because the test does not replicate the forces and loads the engine will see in flight. This is the whole point. 

 

On the rest, speed is the main reason. With the engine moving forward it unloads, when it unloads its runs rich. I know everyone has been told they go lean, but they dont. yes there are exceptions to this rule when you get into tuning exhausts or extreme rpm changes and so on, but for normal engines with normal mufflers they go slightly richer and this offsets any gravitational related fuel flow issues. In a hand launch the model is accelerating hard, but the engine is also unloading just as quickly. The model in question was powered by an OS15 2 stroke, and it would tolerate a nose up just about, but i never had it go soggy on me on a launch. If it did, i would just launch it at 80% of full power and that would sort that out. 

 

When you come to 3d type flying like the prop hang/tail slide etc, you dont do those at full power. 3d is not my thing, but im told generally prop hanging is done at around half throttle to allow sufficient excess power to climb out and this makes sense. I doubt many tail slides are done at full power! If you are at or below half throttle your fuel is being metered as much but the slow run needle as the main needle so main needle settings are not really that important. When you come to climb out, the model accelerates rapidly and we are back where we started with the engine being unloaded so offsetting the gravitational tug.

 

Crucial to all of this though is having the fuel tank in the right place. If tank placement is wrong the whole thing falls apart as the engine will be set too 'lean' in the first place. It isnt actually lean, just the needle is set to assume a certain amount of assistance from gravity and this assistance is no longer there. 

 

If tanks were installed correctly, everything would be so much easier. Its why i bang on about it so much. 

 

[Chris Walby]

Around and around "we" go steadily winding Jon up! 

If you have a question then ask Jon

If you choose to ignore him than that's your decision, but can you let him get on with the job he has building and developing Laser Engines

 

In the limited 6 years of flying I have had many electrical and IC problems. Only one was a mechanical issue with a Laser engine and although technically out of warranty Jon provided fast and quality service getting it repaired (it took me longer to get the engine out and back in the air frame then him to fix it). I don't see that level of service anywhere else.

 

Jon - Thanks for all of your assistance (Laser Engines and non Laser Engines) over the years.

[Jon H]

Whenever i am asked for advice, especially on the forum, this sums up how i think about answering. 

 

 

 

 

[Ron Gray]

At the risk of prolonging this part of the thread (maybe it needs its own ' To nose up or not' thread?). Back in the day I always used to carry out the nose up test after 'tuning' an engine (look at my 1982 video of me starting the OS15 on my Spatman), but when I came back into modelling and started flying I/C again I queried the logic of this with more established flyers. Their response was always "you've got to do that to make sure you've tuned the engine correctly and that it won't lean out on take off", my thoughts were very much like Jon has stated, if I've tuned the engine correctly when it's in the pits then it is tuned, if that tune changes then something else is affecting it, most commonly running lean as a result of a poorly positioned tank. So I have continued with that approach, tune it in the pits and by all means hold its nose up but don't retune for that situation as that is compensating for an issue elsewhere that needs to be addressed, just my view.

 

However, I do not think that anyone is winding Jon up by asking questions or indeed questioning his reasoning, that is what a forum is for. It is entirely up to Jon if he does or doesn't provide an answer and only he can decide if he has the time to visit this forum and do so!

[Gary Manuel]

1 hour ago, Jon - Laser Engines said:

When you come to 3d type flying like the prop hang/tail slide etc, you dont do those at full power. 3d is not my thing, but im told generally prop hanging is done at around half throttle to allow sufficient excess power to climb out and this makes sense. I doubt many tail slides are done at full power! If you are at or below half throttle your fuel is being metered as much but the slow run needle as the main needle so main needle settings are not really that important. When you come to climb out, the model accelerates rapidly and we are back where we started with the engine being unloaded so offsetting the gravitational tug.

 

I'm not deliberately trying to wind you up Jon, I promise. I'm just trying to make sense of what you are saying versus what my brain is telling me and what I have seen during take-off many times with my own eyes.

 

I take your point about prop hanging etc at half throttle partially using the slow run needle, but what about when the throttle is opened fully to climb away. It doesn't climb immediately. There is a time when the throttle is fully open, the nose is high and there is no forward movement. The engine is fully loaded, so how is this different to a nose up test?

 

 

Edited September 6, 2021 by Gary Manuel

[Jon H]

Im not accusing anyone of deliberately being a pain. There are those out there who like a bit of a trolling, but i dont see that here. The frustrating part for me is its the same old discussion again and again year after year. Broken record and all that. 

 

Gary, yea i see what you are getting at but if we have our prop hanging model chilling out at a half ish prop hang, its not just sat at half throttle. The throttle is moving up/down below this mid point exactly as it would when hovering a helicopter. So we are sometimes on main needle, sometimes on slow run, but mostly on the transition depending on how it is set. 

 

If we take half throttle as our base point for thrust=weight, anything over half will accelerate the model. If we open the throttle the model accelerates instantly and even 5mph is enough to start unloading the engine at a given throttle setting. More importantly, our slow run needle withdraws and allows unrestricted fuel flow to the engine. Certainly continuing to wind the throttle up keeps adding load but we also keep accelerating and as we reach full throttle we are fully on the main needle, which we set for max load on the ground with a stalled prop. Sure we are nose up now, but we have a little load relief from the forward speed. Depending on how fast the servo moves, the speed at which the engine accelerates, and the speed the model accelerates the various issues cancel out. 

 

Its all a balance to be sure, and its possible to topple the cards here but again we are into the granular detail of a specific use case rather than general tuning advice for normal sport, scale and aerobatic flying. This all comes back to an earlier point. Listen to the engine in the air. If it protests in a prop hang climb out, fine, open it up a bit, perhaps 1 click. This is a better option as the engine is in its normal working environment, at its normal temperature/load and so on rather than the NUT which is basically crude guess work based upon no actual information on performance in the air. 

 

Tuning is not a ground only thing. Most of the time how its set on the ground will be fine in the air, but sometimes it might need a tweak. One big thing that helps other than tank placement is throttle stick discipline. Dont slam the throttle open. Wind the power on smoothly. If you dont trust yourself, setting a throttle curve or even a 1 or 2 second delay on the throttle channel can really help as it has zero impact on small movements but will make a difference if the throttle is thrown open in a panic. 

 

 

 

 

[Nigel R]

36 minutes ago, Gary Manuel said:

I take your point about prop hanging etc at half throttle partially using the slow run needle, but what about when the throttle is opened fully to climb away. It doesn't climb immediately. There is a time when the throttle is fully open, the nose is high and there is no forward movement. The engine is fully loaded, so how is this different to a nose up test?

 

Quite. My take, 3d model, tune so it runs when pointing vertical, it's within normal conditions.  Most of my more normal aerobatic airframes will (just) prop hang at or close to full throttle. They will also get a nose up test. I don't know about everyone else's 3d efforts, but mine don't accelerate vertically away fast enough to ever unload *. And, whilst you might hang level at around half throttle, you also need throttle response, and it needs to be good. So the whole shebang has to work with nose up. It is conceivable (e.g. large throat carb on 2 stroke) that it may not be achievable to tune for this case and also maintain good tuning for level flight. You may need a pump & reg to get consistency. Another can of worms!

 

edit:

* "noticably unload"

Edited September 6, 2021 by Nigel R

[Gary Manuel]

Thanks Jon. That makes sense.

 

Moving away from the subject of nose up testing and I promise that this is not an attempt at Jon bashing or Laser bashing but a genuine technical question about Laser engines that I have puzzled about for some time. I have great respect for both Jon and Laser engines, but the issue of tank positioning, particularly with inverted engines always seems to raise it's head.

 

The correct fuel tank placement is with the top (or arguably centre) of the tank level with the centre of the carburettor spray bar. Most manufacturers make allowances for this in the design of their engines by porting the intake to a position where the carb is closer to the model centre line. This allows the engine to be mounted in any orientation without significantly changing the carb position and therefore the tank mounting position. Is there any reason why this has not been done with laser engines as it seems to me to be an obvious design consideration with a simple fix?

 

Laser - inlet at top of cylinder (bottom when engine inverted)

 

OS - ported towards centre line.

 

Saito - ported towards centre line.

Edited September 6, 2021 by Gary Manuel

[Martin Harris - Moderator]

Long inlet tracts are inefficient and can lead to fuel atomisation problems where fuel and/or water droplets form on the cold pipe - perhaps even causing carburettor icing in extreme cases (not sure how methanol compares to petrol in this context?) which would probably go undetected during any post mortem.

 

I was watching water almost pouring off the external surfaces of the inlet tubes of my Saito twin the other (bright sunny) day when I was doing some setting up....

[Gary Manuel]

I did wonder whether the longer inlet ports might have an adverse effect on performance. OS / Saito (for example) have judged it as worth while though, so why not Laser?

[John Stainforth]

20 minutes ago, Gary Manuel said:

I did wonder whether the longer inlet ports might have an adverse effect on performance. OS / Saito (for example) have judged it as worth while though, so why not Laser?

Has anyone heard of any problems with OS and Saito 4-strokes caused by the positions of their carbs? (I haven't.) Having a more centralised carb generally makes it easier to place the tank in the correct position.