Petrol or Glow

[Jon H]

Posted by john stones 1 on 03/10/2016 18:43:49:

Don't set him off on nose up one again

Sorry John, its one of my pet hates as it tends to mislead people into running overly rich wasting fuel, making the model messy, and on occasion causing the engine to stop.

I would however recommend a nose up test with a petrol engine though as it tests the pump. If you do an idle nose up test and the rpm rises significantly there is a fair chance your pump diaphragm is not happy

[Don Fry]

Posted by Donald Fry on 03/10/2016 12:04:48:

This talk of diluting fuel with methanol intrigues me. I have a batch of 10% nitromethane, 18% oil (4gallons) which is not of great use, and getting 8 gallons of fuel for the lasers is good.

What grade of methanol does the job?

Gentle budge, do I need the anhydrous stuff, or is the 99.85% stuff OK.

[Martin Harris - Moderator]

Posted by Jon Harper - Laser Engines on 03/10/2016 19:12:06:

Sorry John, its one of my pet hates as it tends to mislead people into running overly rich wasting fuel, making the model messy, and on occasion causing the engine to stop.

I don't really follow that logic - if the model is too lean, from many personal observations, it sags or cuts when nose up but may go unnoticed until take off or mid-flight if the test is not done. Correcting this condition potentially avoids a dead stick or prevents engine damage. If it is too rich, I agree that it may not show up with the nose up (a perceptive pilot may well realise though) and the consequence is slightly reduced power, slightly higher fuel consumption and a bit of mess on the side of the model. Engine cuts from excessive richness are rare except during extended idling and unlikely at wide open throttle during the critical take off phase.

Not doing a nose up exposes the model to the consequences of being too lean (or in some circumstances, too rich). Not everyone is capable of or sufficiently well trained to detect the correct setting from the engine sound or response while on the ground.

Doing a nose up is a simple check for the average pilot and an extra layer of safety for even the best of us.

Edited By Martin Harris on 03/10/2016 19:59:19

[Jon H]

This is where the whole thing falls over. The idea that an engine running too lean will actually keep running. An engine that is too lean will not run at full power while flat on the ground so the nose up test is useless for testing that as 'too lean' refers to a condition where there is insufficient fuel to maintain combustion or the excess of temperature created by the mix causes the engine to overheat and slow down/stop within a very short period of time. So if the engine maintains full power for 15-20 seconds without significant drop in rpm then it cannot be considered to be too lean. Also if the engine gets half way through a flight and stops then its not too lean, at least not in its original setting. If the mix has gone lean due to the tank level dropping then the tank is probably not quite in the right place (as I mentioned in my earlier post). So If you were to do a nose up test now it has passed the 20second flat power check the engine would likely die off after a few seconds, which is what it should do. If you were to fly this engine and do a loop it would not die off and would pull the model round quite happily

The reason the engine would work in the air is the change in engine tuning that occurs in flight due to airspeed and the unloading of the engine. Contrary to popular belief most engines go rich in flight as they unload (there are exceptions) so the engine described above will be just fine in the air until it hit a certain airspeed while in the vertical position. Remember also that cooling is generally improved in the air due to the higher velocity flow around the engine.

My flying in the past 10 years has proven to me without doubt that the nose up test is a waste of time. If it were as valid as people claim then all of my models would have suffered engine failures all over the place. As it happens, I have had so few engine failures that I can more or less remember each one, and in each instance it was due to some unusual occurrence, usually related to fuel supply but not to the needle setting. That is apart from my La7 when I knew the tuning was a bit off but thought it would be ok and it was not, and my Sea Fury when the slow run needles touched the cowl and every open/close of the throttle leaned them off a bit until the engine stopped. Remember also that most of my engines are totally unpressurised and still, with no nose up test, they work just fine and all of my trainees, as well as some of my flying buddies, no longer bother with it and between them we have not had single mixture related engine failure in over 3 years.

[Jon H]

Sorry Donald you keep getting forgotten. Go for the best grade available, Model Technics sell it in gallon cans and, according to a customer of mine who did a spectrothingybob analysis of their methanol, its as pure as you will ever get.

[Martin Harris - Moderator]

We've maybe wandered a bit off topic Jon, but I (at least?) am finding it interesting and thought provoking.

I think that you are absolutely correct in what you're saying, in that a correctly tuned engine will not respond adversely to a nose up check, but not everyone seems capable of basic engine tuning. Once you introduce bottom end/mid range tuning, so many people just seem to glaze over and give up on trying to understand what are really very simple procedures. Maybe we need some presentations by experts with a talent for teaching as you seem to have managed in your club?

In the meantime, I still believe that the nose up check provides a quick and simple (15 seconds at full power as an alternative is actually an awful long time) indication that an engine is too lean - certainly my own experience is that an over leaned engine will reveal itself to the most insensitive operator in a matter of a couple of seconds. Actually, scrub that - I've heard engines going obviously lean during a cursory nose up and the pilot then start towards the flight line intent on flying the model - usually followed by it dying on initial acceleration or fifteen feet off the ground if someone hasn't been able to offer words of advice in time!

There's nothing like some challenging hypotheses to promote understanding though - maybe an article or two from you in the magazine would not be such a bad idea?

Edited By Martin Harris on 04/10/2016 01:15:30

[Jon H]

I hear what you are saying and its fair to say that perhaps i have a better ear than most when listening to engines but i still think that a long full power blast is far better. For a start it gets the engine well up to temperature and is more likely to reveal any tuning specific issue as opposed to a tank related issue like the NUT. The extra engine temperature can help fend off the dreaded engine cut just as you pop it down on the runway, although again that usually suggest naff slow run tuning.

I also am all to aware of people going through the motions of setting their engine without the faintest clue what is happening. I was at old warden a little while ago and a chap had a small PAW diesel powered model that was so over compressed i was wincing at the sound. The chap in question however seemed blissfully unaware and duly cranked on a bit more compression before turning it back to the original setting. Needless to say his flight was not very successful.

And again i agree that folk often glaze over when talk turns to tuning and setup of engines but i have no idea why. Its so much easier than the maths needed to really work out the correct electric powertrain for a model, and as the rewards are so great i dont quite know why people give up so easily. I am often surprised here at Laser by the number of calls asking for carb setup advice, or more specifically, the 'factory settings'. We have no factory setting, i take it to the bench, run it, and thats it. I have no clue where the needles are in terms of number of turns as its totally irrelevant information as you need to listen to the engine not count turns.

Now i fully understand and respect that non everyone has a high level of experience and in many respects the simple operation and handling of our engines makes them quite good for beginners as they are not as fussy as some, but it still surprises me that even long time modellers struggle and i wonder how many modellers would be able to get an engine going if i gave it to them with both needles fully closed and asked them to set it up. i am not criticising someone who couldnt do it, i am just surprised and would then teach that person how to do it and what to look for.

The biggest hurdle for me when trying to advise people is modelling folklore. So much misinformation is banded around on forums/internet/the club 'expert' and even, on occasion, the modelling press. Its noones fault, its not malicious, but a great deal of the information is either out of date (running in procedures, use of castor oil etc) or was never correct in the first place (the engine overheated it must be too lean, 4 strokes need special 4 stroke fuel etc). The problem with fighting this stuff is im on my own vs an entire hobby set in their ways. Other people with model manufacturing/distribution i have spoken to about this have basically told me to not bother and just let everyone get on with it, but it frustrates me to see people struggle needlessly with the simplest of engine operation tasks just because they have been either lead astray, or just do not know what to look for when setting their engine because noone ever told them

 

Edited By Jon Harper - Laser Engines on 04/10/2016 09:00:26

[Martin Harris - Moderator]

I also understand what you're saying Jon, but I remain to be convinced that your method would necessarily give better results - although I intend to do some comparative testing! There's scope for errors in both methods due to people rushing the check and even failing to recognise symptoms obvious to the more sensitive ear. How many times have you seen someone poking the nose of their Model at the sky for less than a second and pronouncing themselves satisfied with the result? Would they do an extended power check for long enough to indicate a lean engine?

[Jon H]

If folk are too lazy to bother checking their settings/model properly then they wont get anywhere and nothing will save them. Thats not something any procedure or test can do anything about. And is 15 seconds really that long? it takes half that to do a thorough control check (done with the engine flat out) anyway.

The flat full power check should be easier though as they dont even have to pick the model up, and if we are worried about peoples ears they could even watch the rpm with a tacho although i wouldnt recommend it as it might lead them to tinker in search of more revs.

Next time i fly my escapade i will do a nose up test to see if it passes. I know it will prop hang in the air so logically it should but for some reason i suspect it wont. I might see if i can get someone to video the whole thing.

[Don Fry]

I must admit I have always been in the run it a bit rich club. And I have had few problems. Lately I have sorted a couple of engines to run as Jon specifies. Problem count does not seem to increase.

[Rich too]

I must admit when I took up modelling 38 years ago, holding the nose up is how you were taught, and I rarely had engine problems.

Back to the original question, petrol all day for me, no mucking about with needles once its been set up. and no need for all that starting equipment. (although I do have glow for smaller models)

[john stones 1 - Moderator]

Used glow for years without problems 4 strokes are my favourites i love the sound and way the powers delivered, price and availability of fuel means i'm petrol and lecky now though. Nose up ? yep me too, mostly O.S and Y.S for me, followed instruction book and never had an engine fail yet, whatever method others follow, if it works for you jobs a good un

John

[Jon H]

Posted by Rich2 on 04/10/2016 13:11:13:

I must admit when I took up modelling 38 years ago, holding the nose up is how you were taught, and I rarely had engine problems.

Back to the original question, petrol all day for me, no mucking about with needles once its been set up. and no need for all that starting equipment. (although I do have glow for smaller models)

I know this is what is expected of petrol engines, but i have to confess i rarely find it to be the case. The very few who fly petrol at my club spend more time flicking and faffing than they ever did with glow, and from my own tests on the Lasers (and others) i find petrol engines fussy intolerant things that simply do not work unless everything is perfect. I appreciate that i am in the middle of a development project, and our engines require very accurate fuel metering due to their efficiency, but still, its a nightmare to get it right.

All of that said however, i am looking for optimum performance all of the time. Listening to petrol engines flown at shows they are nowhere near that with burbles and gurgles all over the place. The same is true of all the conversion videos i see online. Yes it runs, but it sounds really dreadful in the mid range and its not right. But folk seem to think its great :\

[Jon H]

Posted by john stones 1 on 04/10/2016 13:44:45:

followed instruction book and never had an engine fail yet

John

I am the instruction book, why is everyone arguing with me? I know i am right

[Tim Flyer]

No comments from me on the tuning argument . I love the 4 strokes, but 2 stroke glow motors still have a very good place in smaller models. Cheap to buy and very easy to set up and run . I'm putting an OS 55AX with tuned pipe into a Wot 4 Mk 3 trad kit I'm building for my son and hopefully he will let me have a go too. The engine is a proper little hornet and starts on the first flick too just like it should! One chap at our club is a real commited electric only flyer , he keeps suffering a big dead stick problem at the end of the day . Every time he tries to leave the club it seems he has flattened his car battery!! And has to beg a jump start from other members😊 Maybe a generator should be added to cost of electric flying?

[Robert Welford]

I am the instruction book, why is everyone arguing with me? I know i am right

What about Mr Tidey?

[Don Fry]

Merely God

[Jon H]

Posted by Robert Welford on 04/10/2016 14:31:11:

What about Mr Tidey?

Retired 4 years ago and now the lucky devil spends all his time playing with aeroplanes.

[Manish Chandrayan]

Posted by Robert Welford on 04/10/2016 14:31:11:

I am the instruction book, why is everyone arguing with me? I know i am right

What about Mr Tidey?

He is V 1.0

Jon is V 1.1

[Rich too]

Posted by Jon Harper - Laser Engines on 04/10/2016 13:48:18:

Posted by Rich2 on 04/10/2016 13:11:13:

I must admit when I took up modelling 38 years ago, holding the nose up is how you were taught, and I rarely had engine problems.

Back to the original question, petrol all day for me, no mucking about with needles once its been set up. and no need for all that starting equipment. (although I do have glow for smaller models)

I know this is what is expected of petrol engines, but i have to confess i rarely find it to be the case. The very few who fly petrol at my club spend more time flicking and faffing than they ever did with glow, and from my own tests on the Lasers (and others) i find petrol engines fussy intolerant things that simply do not work unless everything is perfect. I appreciate that i am in the middle of a development project, and our engines require very accurate fuel metering due to their efficiency, but still, its a nightmare to get it right.

All of that said however, i am looking for optimum performance all of the time. Listening to petrol engines flown at shows they are nowhere near that with burbles and gurgles all over the place. The same is true of all the conversion videos i see online. Yes it runs, but it sounds really dreadful in the mid range and its not right. But folk seem to think its great :\

Jon, I understand what you are saying, but I think you are getting the last 5% out of the engine, and most of us tune to 95% and everything works fine - touch wood I have not had a deadstick with my petrol motors yet. There is no need to tune garden machinery, mower, chainsaw, hedge trimmer - why is that?

You're too much of a perfectionist Jon.

[john stones 1 - Moderator]

Lads i see at field don't faff with their petrol motors either and there's a good variety of brands there, get your plumbing right use good fuel/oil, store it correctly, stop fiddling...go enjoy your flying.

[bert baker]

I fitted an old MAC 10cc with tuned pipe to a plane and when done the install forgot that I had converted the carb to use a remote needle,, turned up a field and found it would not start,,,,so cable tied the fuel line down until it ran ok,, I did have to remove the tank pressure pipe..athough Idle was a bit chewy ,it flew ok,,engine, had four flights..

So do we need a fuel needle to be so adjustable,, would a fixed jet sort out the needle fiddlers..

[Jon H]

Posted by Rich2 on 04/10/2016 17:37:49:

Posted by Jon Harper - Laser Engines on 04/10/2016 13:48:18:

Posted by Rich2 on 04/10/2016 13:11:13:

I must admit when I took up modelling 38 years ago, holding the nose up is how you were taught, and I rarely had engine problems.

Back to the original question, petrol all day for me, no mucking about with needles once its been set up. and no need for all that starting equipment. (although I do have glow for smaller models)

I know this is what is expected of petrol engines, but i have to confess i rarely find it to be the case. The very few who fly petrol at my club spend more time flicking and faffing than they ever did with glow, and from my own tests on the Lasers (and others) i find petrol engines fussy intolerant things that simply do not work unless everything is perfect. I appreciate that i am in the middle of a development project, and our engines require very accurate fuel metering due to their efficiency, but still, its a nightmare to get it right.

All of that said however, i am looking for optimum performance all of the time. Listening to petrol engines flown at shows they are nowhere near that with burbles and gurgles all over the place. The same is true of all the conversion videos i see online. Yes it runs, but it sounds really dreadful in the mid range and its not right. But folk seem to think its great :\

Jon, I understand what you are saying, but I think you are getting the last 5% out of the engine, and most of us tune to 95% and everything works fine - touch wood I have not had a deadstick with my petrol motors yet. There is no need to tune garden machinery, mower, chainsaw, hedge trimmer - why is that?

You're too much of a perfectionist Jon.

ok so if I sell engines that fail my test running as they are 95% ok everyone is happy with that? Didn't think so

And its not about perfection, its about getting what I paid for. Why spend out on an engine then not use its full potential? If its not set up to give you its best then you have to live with 'good enough' and that's not really what we should be aiming for.

As for chainsaws, most are hopelessly rich as shipped so that they are more or less guaranteed to work. Mine however are not as far better cutting performance can be had by leaning the needles off. My hedge cutter and strimmer have been similarly adjusted.

As for a fixed jet I don't think it would work too well for model engines. The differing loads from prop changes would require mixture changes. I went through all that with walbro and they agreed a fixed jet wouldn't do it

[john stones 1 - Moderator]

Ooooh gardening i do that for a living

Same set of Stihl hedge cutters for last 12 years never tweaked it n it's never missed a beat, i do buy new blades now n again though that's where cutting performance comes from. Chainsaw, had it longer same story, get a good chain keep it sharp.

John....off topic dept

[Former Member]

[This posting has been removed]