A bit of an ask

[toto]

It would be really good if someone could go to the extreme of posting up an idiots guide to running in a glow engine.

 

It could be either on a bench or in a model. Preferably something reasonably common .... say an OS 56AX or a force .46.

 

Something that would take a layman  beginner from cradle to grave. It could be a wordy type tutorial or even  better.... if in a few parts ..... contain some video footage to make things more obvious.

 

I totally get that this would be a bit of an ask as it could get a bit involved but unless you ask ....... 

 

I have a few glow fuel engines and have tried to run one without consistent success. I don't intend deviating from battery power in the Immediate future but forsee it happening at some point as with my two stinger petrols as well.

 

Cover even the setting up of the unit if its bench or model related and go through the processes from the beginning and try to explain how you get to the point where you have the confidence that things are at a reasonably reliable state.

 

As I said ...... maybe too much of an ask.

 

Toto

Edited January 17 by toto

[Robin Colbourne]

What you are asking represents many hours of work.   A lot of it is already available on the net and in books.  If you do your research first, so you learn the terminology, then you can speak to some experienced modellers who can then guide you further.

Steps to take are:
 

1. Get a good book such as David Boddington's Radio Control Primer  This will cover a lot of the basic information on aspects such as mounting your engine, fuel tank tank height etc.
2. Download the instruction sheet for the engine you have or as close to it as possible, e.g. OS46AX instruction manual
3. Watch some Youtube videos  This is the two I found, I'm sure there are better ones Basics of glow motors  Starting and Tuning a 2 cycle Nitro RC Airplane Engine
4. Go to a club and speak to a few people who have glow models.  Ther may be someone who has a test stand on which they would be willing to run your engine.

 

Edited January 17 by Robin Colbourne

[John Stainforth]

A good a starting point is indeed the manual for the OS46X or 55X. If you do as they say, you really can't go too far wrong. If the engine does not start and keep running there is either a fuel supply problem, or a glow plug/battery starter problem, or you've got the needle valve set very badly out. The tuning of glow engines is pretty straightforward. 

[toto]

No worries,

 

I should have hit Utube first ........ as I have just now done. Found a terrific video on DLE engines where a chap takes you right through setting it up and running it on a test bench...... great video and easy to understand..... invaluable.

 

I may also look at David Boddi grins book as well as long as it covers modern engines. I note some texts seem to reference older units from memory.

 

Many thanks

 

Toto

[PDB]

My approach was to identify a competent pilot at the club who runs IC engines and who was prepared to mentor me through how to safely operate an engine, kept them sweet with the odd bottle of what they fancied and helped them out with cups of tea, take-offs, model recoveries, etc. in return I got the benefit of years of experience and shortcutted the learning process.

 

For me working hand in hand with an experienced pilot meant we focused on my particular engine and it's quirks without having to read and get confused by the mass of information available online and in manuals.

Edited January 17 by PDB

[Rich Griff]

Hi toto,

 

Put your IC hat on when you have a fully working electric foamy.......

 

Did your force engine come with operating instructions ?

 

If not, GG had the instructions for that engine I think. From memory he has the same force engine ?

 

I am sure he will chip in to clarify and help out...all in good time.

 

I know he very kindly supplied the instruction to me as the instruction sheet for the smaller marine engine I purchased were missing....so at least I had something from force to work with. Thanks GG

 

Eventually I got some instructions from force, j Perkins the importer and from an RC boat forum.

 

I think the force websight will also have the instruction sheet etc..for your engine. They may have even by know the instruction sheet for the 20 marine I have ?

 

See advise from Jon at laser engines.....

 

Chase up the instruction sheets for your other engines.....up to date hard copy beats pc every time I feel...

 

You can make up a vice/or similar mounted engine bearer unit ( do not mount the engine in the vice, mount the engine to a wood mounting that is held in the vice. You intend mounting the engine in a slec GRP type mounting that is bulkhead fitted to the aircraft ? ). 

 

Pay particular attention the fuel tank installation and hieght, fuel hieght relative to carb spray bar.....

 

Just to enlighten you, visit PAW model engine site to view engine start up and run vidio...yes it's a diesel ( compression ignition ) but look at were the "fuel tank" is.....

 

Make up a reliable throttle control, reliable tank installation, reliable exhaust ducting, reliable mounting and bench. Reliable glow plug, clip, glow power and electric starter motor.

 

Outside engine runs, exhaust fumes....

 

You have "unreliable niebours" ??!!

 

An engine run at home  will generate noise/interest.....

 

Balanced prop.....

 

As stated, setting up and running a model IC engine is not rocket science, if installed correctly.....

 

Similar safety aspects to electric propulsion, some would say less, some would say  more....

 

Me, being born with greasy fingers etc.. 😁.......

 

Read up on the carb and how it works and it's peculiar particular needle settings.....

 

Clunks have been mentioned some time ago.....

 

Let the forum know when  your "reliable stuff" mentioned above is ready....

 

As a matter of interest, what glow fuel are you using ??

 

You have some petrol engines and well you lucky man 😄

 

My first encounter with a model IC engine would be at the age of about 8, probably a Cox 049.....

[Rich Griff]

Sorry......GG, @GrumpyGnome.....

[toto]

Thanks for the responses.

 

I've been busy watching a load of utube videos, in particular some RGCF stinger 10 and 15cc related videos ( both of which I have ). Also a couple on glow 2 strokes as well. I'm starting to get my head around some of it.

 

I'll respond to some specific points above tomorrow as I can hardly keep my peepers open now.

 

Cheers for now

 

Toto

[Peter Jenkins]

Hi Toto

 

The previous posts have just about covered things.  That having been said, I am always surprised when people who have been running glows for some time express surprise when I ask if they have adjusted the low running needle.

 

The low running needle is usually located on the opposite side from the main needle valve and sunk into the extended throttle barrel.  You need a thin flat head screwdriver to operate the needle.  For a new engine, it will have been set at the manufacturer when they test ran it but it will still need tweaking.  If someone has been playing with the needle then you may have to establish its starting position from the engine manufacturer's instructions.

 

Key thing to remember is that the idle needle controls the engine up to around half throttle before the main needle takes over.  The engine will never run satisfactorily, unless the idle needle setting matches the fuel and conditions it was set at, unless you adjust the idle needle to achieve the optimum mixture.

 

Before adjusting the idle mixture though, get the engine fully warm, run it up to max speed and adjust the main needle for max rpm.  Then open the needle valve to richen the mixture and drop the rpm by 400.  This allows for the engine to accelerate to a faster speed once the model is no longer stationary.  Now, you are ready to adjust the idle needle valve.

 

Be prepared to stop the engine, make an adjustment and restart the engine.  If the idle needle is too lean then when you open the throttle the engine will die.  Open the needle valve a 1/4 turn and try again.  If the mixture is too rich then opening the throttle will be accompanied by an increase in exhaust smoke and a stuttering acceleration.  As you get closer to the ideal setting then bring each adjustment down to 1/8 turn.  A quick way to check if your idle mixture is rich is to check if the engine rpm drops when you remove the glow igniter.  A properly set engine, once warm, will hardly change its note when the igniter is removed.  The reason for the rpm drop is that the plug is cooled by the excess fuel and does not work as efficiently.

 

Sometimes, using a long thin screwdriver you will be able to adjust the idle needle valve while the engine is running.  In this case, turn the screwdriver a 1/8 turn at a time aiming to get the engine to run at the fastest idle rpm as possible.  

 

The acid test is to leave the engine to idle at its lowest sustainable idle speed for 1 minute and then open the throttle briskly.  The engine should pick up quickly and cleanly.  Any stuttering means the mixture is too rich and if the engine dies then its too lean.  Adjust and re-try.

 

Once set, leave everything alone.  Sometimes, if you have set up the engine on a cold day, you may need to tweak the needles on really hot days and vice versa.

 

It's not difficult to do provided you follow the manufacturer's instructions for initial starting.  Once you've made the adjustments I've described above, then do a nose up check i.e. with the engine at idle, point the nose up by about 80 deg and open the throttle.  If you have set the engine up properly the engine will accelerate smoothly.  Thereafter, there is no need to do nose up tests - they are a waste of time if you have set up the engine correctly.

 

Two final points. 

1. If you have an ABC engine (aluminium piston, brass cylinder chrome plated) it must be run in at full throttle and rich for short bursts and allowed to cool off in-between.  Running them slowly will cause them to seize.  Indeed, you may find that they are very tight to turn over and emit squeaking noises as you do so.  That is because the bore is tapered towards the top.  You need to heat the engine up quickly so that the metals expand to give a parallel bore with good tight clearance between the piston and liner.
2. If you have a ringed piston, then the running in is carried out at a lower throttle opening and rpm gradually increased through the running in period until you are at max rpm.

Both engine types will be badly damaged if you get this wrong.

 

 

[toto]

I was happy with that until you got to the end .

 

I'll double check the engine that was run in my Arising Star ( RIP ). I don't know how that was set up as I wasn't involved as such. It certainly had not seized and was still running although not reliably when I uninstalled it from the model. Maybe this will be my practice piece when I'm ready to give it a go on a bench set up.

 

It's something I would need to tinker with at the field as I have dodgy neighbours who are blissfully unaware of what's in my shed and I'd like to keep it that way. 

 

My mentor runs all his models on IC of one description or another and they seem to run impeccably but I think he has enough on his hands just keeping me in the air for now. I'm sure he would be more than willing to keep me straight though as he seems to have the hobby running through his veins ..... very knowledgeable and helpful but one step at a time. 

 

It's like every other part of this hobby I've looked at so far, I am picking things up slowly and in small chunks. I knew nothing about electric models when I started but I'm beginning to get my head around it. Very gradually.

 

Thanks for the above as combined with what I have been disseminating on utube and the likes, it's all helping.

 

Toto

 

 

[David Davis 2]

Morning Toto!

 

There really isn't any mystery about two-stroke glow engines. I believe that you own a Force engine. These have two needles opposite one another which regulate the fuel supply. The low speed needle controls the low to mid-speed running of the engine and is encased within the carburetter. The high speed needle is raked backwards and controls the mid to high speed running. It has a knurled end to make adjustment by hand easier. Having done a quick search on-line I've found out that Force engines are ABC engines, Aluminium piston, Brass cylinder, Chrome  plated. So are most modern two stroke engines.

 

To run it in:

 

Open the main needle valve 3-4 turns from fully closed.

 

It's probably best to leave the slow running needle at the factory setting but if it has been fiddled with, close it it completely, attach a clean piece of fuel tubing to the carburetter, open the throttle 20% and open the needle anti clockwise so that you can just blow through it.

 

Fit the engine securely to a test stand.

 

Fit a propeller which the engine is easily capable of turning, something like a 10 x 6.

 

Fit a glow plug which is appropriate for the engine, an OS 8 or Enya 3 will be fine.

 

Use a fuel containing 15-20% synthetic oil and 5% nitro.

 

Place a finger over the air intake of the carburetter draw up fuel into the engine, turn the propeller backwards against compression, attach a glow igniter apply the starter motor and the engine should start.

 

LET IT WARM UP!

 

Then adjust the main needle to maximum revs at wide open throttle.

 

Keeping the throttle wide open unscrew the main needle so that the engine is running slightly rich. Run two tank fulls of fuel through it. Now re-adjust the main needle for maximum rpm then check the slow-speed running adjusting the needle valve as necessary. DO NOT EXPECT A VERY LOW TICK-OVER AND INSTANTANEOUS THROTTLE RESPONSE AT THIS STAGE.

 

Put the engine in a model and fly it. After half a dozen long flights the engine will be fully run in and you may make your final adjustments of both needles.

 

Edited January 18 by David Davis 2

[Paul De Tourtoulon]

8 hours ago, PDB said:

My approach was to identify a competent pilot at the club who runs IC engines and who was prepared to mentor me through how to safely operate an engine,

The only safe way to start the best advice is in a club, you know the pilot that arrives, flies then cleans ( not obligatory ) then goes home.😇

[Don Fry]

As Paul says. Remember the motors you run need risk assessment. A cooking 40  can get in the car and drive to casualty. A 55 and I can’t.
Competent  includes experience of casualty treatment. Also nice to know for electrics. At least Ic motors stop as they chew into fingers. 
Jon (laser engines)has a load of carb tuning advice, also tank positioning.  

what to do is easy;

Install a motor in good condition correctly with a reasonable prop

tank and pipes ditto
good fuel, and knowing how to look after it.

good air supply

good cooling 

reliable ignition source.

Set the carb for that installation

And there lies a lot of pitfalls. I’m used to motors. I do the above, and I achieve reliability similar but perhaps not quite as good as electric power, but without laying out on new motors after a bit of lawn darting. 

[Brian Cooper]

There is only so far that the process can be put into words. 

A lot of it is done by ear.

 

There is no substitute for doing it for real, ideally with someone who has experience of handling the various engines.  

Edited January 18 by Brian Cooper

[Rich Griff]

Hi toto, wilco....

 

Did you get the instruction sheets you need, and watch the PAW vidio. Fuel tank in vidio ( unless paw has posted a new vidio )

 

Yes it's a diesel, look at the vidio....

 

In the day idle bar glow plugs were available. I have never come across and idle bar come off, but that does not mean others have not.

 

Enya no. 3 is a pretty much go to plug for very general use, and would probably be fine for your application, but, check engine info sheet/engine web site.

 

If you gunna "begin" with the force engine, post pictures of it and the exact model info, it had a rear remote main needle valve ?

 

Mmmmm, paw diesels can be monsters, as can glows.....

 

Just because the prop is mincing your fingers does NOT mean the engine will stop ?

 

What are the exact model petrol engines please ?

 

Have a great day, it's much whiter here today. I expect to see an igloo in the village on the bus ride to town...

[Jon H]

Beware of youtube and club experts. Most of the information from these sources is wrong and simply continues to perpetuate bad advice that has crept into modelling folklore. 

 

There is plenty of good information posted here, some less so but might not be wrong per se depending on the use case. 

 

First piece of information. Engines these days are very hard to kill. One accidental overheat or lean cut will not be the end of the world. The only exception to this rule would probably be the saito radials which love to throw rods. As you do not have one of those, i wouldnt worry. In the old days of steel liners and iron pistons you could kill an engine fairly easily, but still not as easily as was thought. 

 

Running engines stone cold and slobbering rich will be the best way to kill them. You need at good 80'c of temperature minimum in the engine for the thing to work properly. So many people want their engines to be stone cold. No idea why. 

 

1 hour ago, Brian Cooper said:

A lot of it is done by ear.

 

This is spot on. You cannot tune engines by eye, only by ear. Forget counting turns on needles, forget rpm counters and other fluff. Listen to the engine and it will tell you everything you need to know. Yea you need to learn the language of engine farts and wheezes, but its not hard to do. 

 

No1 mistake is always tank placement. Folk install them too high and its game over. For all engines (2 and 4 stroke) without a pump the top of the tank should be in line with the centre of the carb. Not the needle (some have remote needles), not the fuel inlet nipple, the centre of the carb. Thanks to OS for their handy drawing. 

 

 

OS show the tank above the carb in this image, but the fuel level is also shown and there is an air space at the top of the tank. As we never leave air spaces in our tanks just use the top of the tank as a reference. 

 

This needs to be considered if engines are mounted inverted or on their side as the carb position will move with the engine. 

 

With the engine installed correctly fire up the engine, warm up for a bit then wind it up to full chat. keep leaning it off until the rpm begins to sag (might be very sudden). Then open the needle a smidge to restore the revs and its job done. On most engines it should take under 5 seconds to find this setting. Once you have this setting, leave the engine there for 10 seconds at least to make sure it holds on to that setting as it warms up. There is no need to run the engine hundreds of rpm rich of peak power* as this will do nothing for reliability and will simply increase fuel consumption and mess. The engine will unload and go very slightly rich in flight** so there is no need to worry. Waving the nose of the model in the air is also a waste of time. 

 

*some engines on tuned pipes etc will need to be set up differently. This guide is for normal engines with normal exhausts as this is what is being discussed

**some engines (pylon etc) may not exhibit this behaviour due to the extreme change in load/rpm they see from ground to sky. This is especially true if they are also on a pipe. 

 

Slow run tuning is completely ignored most of the time but is very important as all running under about half throttle is controlled by the slow run needle. Setting it is simple if you follow the procedure. Warm engine up, Set main needle, throttle to idle for 5 seconds. Slam throttle full open. Does engine accelerate to full power? if no, and you just get a flame out its probably lean (rare), if yes but you get some coughing and spluttering its rich (extremely common). Lean slow run 1/8 turn and go again. Repeat until the engine will no longer accelerate to full power (lean cut) and then open the slow run again until it does. Reset main needle, check operation, fly. 

 

I have posted this video a bunch of times before but its an old video of me setting up a laser 150 4 stroke. If you want to skip the boring warm up start it about a minute in. The engine is very rich to start, as most are out of the box, and i lean the needles as described. The slow run is leaned a small amount between each acceleration and i very quickly find the lean cut setting. Its then a case of just dialing it in to my satisfaction. I fiddle and faff a bit more at the end as i am too much of a perfectionist, but hopefully it gets the general point across. The biggest takeaway is that the engine went from not running and completely out of tune, to perfectly tuned all within the space of a 4 and a half minute video. Engine tuning is not a week long epic, its very quick once you get the hang of it and the only way to do that is to just keep doing it. 

 

 

 

 

EDIT

 

At one point in the video it looks as though i am tuning the engine with the tacho, which i normally advocate against. I am not, it just happened to be in my hand, but the reason i do not recommend it is made very clear as you can just make out the numbers on the screen and you can see they do not change despite very clear change in engine note. This is why you cant tune with a tach. 

Edited January 18 by Jon - Laser Engines

[Rich Griff]

Nice one Jon....

 

Being a greasy fingered motorcyclist often helps 😃

[leccyflyer]

20 minutes ago, Jon - Laser Engines said:

Beware of youtube and club experts. Most of the information from these sources is wrong and simply continues to perpetuate bad advice that has crept into modelling folklore. 

 

^^^ This ^^^

 

As advised earlier, seek out the guy at you club who brings his model, operates it consistently, with no fuss, doesn't endlessly fiddle with the engine, just starts up, flies, cleans it down at the end of the day and then goes home.  He's the guy that you should be taking advice from, not self-professed "engine whisperers" who never bring a model, never fly, but offer often contradictory and useless "advice" from the sidelines, or make a bee-line for the starting table as soon as they see a newbie, with loads of questions about whether you have the right glow plug, what fuel are you using, where did you get it from, how much did it cost? That's the "club expert" that Jon is referring to, probably hasn't flown in years and he's a complete menace to new flyers.

[Engine Doctor]

11 hours ago, toto said:

No worries,

 

I should have hit Utube first ........ as I have just now done. Found a terrific video on DLE engines where a chap takes you right through setting it up and running it on a test bench...... great video and easy to understand..... invaluable.

 

I may also look at David Boddi grins book as well as long as it covers modern engines. I note some texts seem to reference older units from memory.

 

Many thanks

 

Toto

Toto A DLE is a petrol engine and not quite the same as a Glow engine .If its a glow engine you intend to use then look specifically for setting up a glow engine . Better than that find an experienced member at your club , not t "the club expert fiddler " as already said and  Who often just think they know but someone who really does know to show you . You cant pick up the change of tone etc on you tube as well as you can in real life .

Edited January 18 by Engine Doctor

[toto]

Morning chaps,

 

Just tuned in ....... I'll be reading through all the above later this afternoon ...... on domestic duties first thing today. I have skipped through some of the above briefly but it deserves a proper " second sift " in order to appreciate and understand properly.

 

There are already elements which are staring to " stick " ie high and low throttle needle adjustments which are starting to make sense. Also where about in the running order they are tackled etc.

 

I'm not going to try and post up my " understanding " or attempt to clarify in this post because as I said, I have not had the chance to properly digest all of the above this morning.

 

Have a well earned break as I will be back later today with a myriad of " confirmations of understanding "  of which I'm sure some will need putting straight.

 

Huge thanks for these very detailed responses and the time put into them 

 

I'll be back ........

 

Toto

[john stones 1 - Moderator]

My advice is simple, rig yourself something similar to Jon Harpers set up and get your hands dirty and learn. There's no great mystery to using I.C regardless of some stuff you read.

[GrumpyGnome]

@toto All good stuff above.

 

Be aware that running in (your original question), and tuning, are two separate (albeit linked) topics.

 

Every engine I've ever bought new has running in instructions, which I follow.  Only then do I tune for optimum performance.

 

As Jon said above, fuel tank placement issues are the No1 reason for deadsticks, especially if the engine has been tuned pretty well on the ground.  A surprising number of models currently on the market have sub-optimal tank positions.....

 

Once set up, minimal fiddling is needed and you'll be able to turn up, add fuel, fly, land, add fuel etc. etc. to your hearts content. The only down side being the need to clean your model - but that gives you the opportunity to check the airframe 🙂

[David Hazell 1]

I keep mentioning this fuel tank placement thing to some of the guys at the club - and these guys _really_ know their stuff regarding geometry set up, flight characteristics, etc. But they balk at the "top of the tank, centre of the carb" thing by always saying "What if the plane is inverted?". I'm sure Jon has answered this elsewhere, but I can't find it. I want to be able to answer back with something tangible, help!

[Andy Stephenson]

I've never thought that tank placement was that important. It may have been in the old-days when engines were crude, didn't suck well and were only used in free flight planes that never flew other than straight and level. Have you ever watched someone prop hang a fun-fly model for minutes on end where the tank is hanging inches below the engine, they seem to work just fine.

[Jon H]

23 minutes ago, GrumpyGnome said:

@toto All good stuff above.

 

Be aware that running in (your original question), and tuning, are two separate (albeit linked) topics.

 

Every engine I've ever bought new has running in instructions, which I follow.  Only then do I tune for optimum performance.

 

As Jon said above, fuel tank placement issues are the No1 reason for deadsticks, especially if the engine has been tuned pretty well on the ground.  A surprising number of models currently on the market have sub-optimal tank positions.....

 

Once set up, minimal fiddling is needed and you'll be able to turn up, add fuel, fly, land, add fuel etc. etc. to your hearts content. The only down side being the need to clean your model - but that gives you the opportunity to check the airframe 🙂

 

GG isnt wrong here, but on running in i would suggest you ask yourself a question. 

 

Do you have an ounce of mechanical sympathy and a brain in your head? Most likely the answer will be yes, and if so you can usually amend the running in instructions provided to get the job done quicker and with less faff. 

 

The reason is there is that one guy who will add all sorts of things to some witches brew of trash fuel before firing up his new engine on a prop either miles too small or miles too large, and will then try and wring the life out of it the moment the thing kicks over. As a result, and to protect themselves from a grumpy warranty claim manufacturers tend to be very cautious with their run in instructions. if you arent that guy, you can follow a simple procedure which suits more or less every engine on the market be they 2 or 4 stroke, ABC, Ringed, whatever. 

 

No1. use a good fuel. Cant be bothered to argue about specific brands today, but generally a 5% nitro 15% synthetic oil fuel from a reputable manufacturer will work.

No2. use the right prop and plug. The blurb with the engine will probably be a guide here so... If the instructions are missing, work out the standard prop for your engine (say 11x6 for a 46 2 stroke, 12x6 for a 52 4 stroke, 15x8 for a 120 4 stroke) and knock one inch off diameter to give a lighter load and get the revs up a bit.  I go with os F plugs for 4 strokes and OS no8 for 2 strokes. Personally not a fan of the enya 3, but if you want to try it then fair enough. Just remember your glow clip might not fit it. 

No3. Some engines (ASP for sure) are pretty dry when they arrive from the factory. There is no harm in adding some oil to the thing ahead of time, especially on a 4 stroke. Whip off the rocker cover, a little dab on the rockers. Whip off the cam cover, a little in the crankcase. 2 stroke oil is great for this and there is no need to go mad. 2 strokes just need a little down the carby. Wiggle the engine about to spread the oil round, and leave it to drain if you think you over did it. 

 

No4. mount your engine to the bench/model with respect to tank height etc. 

No5. Start the engine with a rich but not slobbering rich setting on the needles. I would say 2 turns max. Get the glow off and open it up to about half throttle. Run for about 2 minutes and make sure you can feel the head warming up, especially for an ABC 2 stroke. Note that some ABC 2 stroke engines are mega tight when new. If so, get out the heat gun and warm up the head so its north of 60'c before you try and start it. You can even heat it up to 100'c if you want, you wont harm anything. 

No6. Full power, and very rapidly tune for approximately 90% of peak tune. This is a very rough and quick setting, dont loose sleep over it. Run 10 seconds and throttle back. 

No7. Tune the slow run so its not the absolute trash setting it came with. I recently test ran a brand new saito 82 and leaned the slow run nearly 3 full turns in the end so dont be shy. 

No8. Run with this tuning for about 5 minutes or so with varied throttle use right up and down the range. A few 5-10 second blasts at full power between periods of half and idle throttle. Some rapid accelerations from idle to full power are good too. 

No9. Once the time is up or you are bored pinch the fuel line to stop the engine. Allow to cool to stone cold. 

No10. Start the engine, tune for peak on both needles and go fly. Trundle around mirroring what you did on the ground with short bursts at full power. A simple turn around aerobatic routine is great as you use full power on the way up, near idle on the way down, half throttle in the middle, and then the same again. Essentially, just dont thrash it to within and inch of its life. 5-10 minutes of that, land, allow to cool before you go again. 

No11. After about an hour of running (4-6 flights) you can consider the engine run in enough to go to your flying prop and do your final tuning adjustments to suit. After that i recommend you peak the main needle at the start of each new flying day. Just open it so its clearly rich, lean off to peak, past peak, back to peak....hold for 5 seconds...fly. 

 

26 minutes ago, David Hazell 1 said:

But they balk at the "top of the tank, centre of the carb" thing by always saying "What if the plane is inverted?". I'm sure Jon has answered this elsewhere, but I can't find it. I want to be able to answer back with something tangible, help!

 

They should note its not just me saying this. Its in the OS manuals, PAW recommend the same. This information has been recommended by manufacturers for over 50 years and i cant understand why it seems to be such a shock.

 

But, if the plane is inverted the engine will run slightly rich...so no big deal. if the tank is mounted too high rolling inverted will cause the engine to run lean and possibly cause it to stop. 

 

Its all related to the pressure differential between the carb and the fuel and gravity is a component in this. If gravity is assisting, so increasing fuel pressure, you close the needle to compensate. That's great until gravity starts resisting you and you have nearly 20m/s^2 change in acceleration just due to gravity. With the needle closed and a big change loss in fuel pressure the engine will run lean. 

 

5 minutes ago, Andy Stephenson said:

didn't suck well

 

I think its often forgotten that fuel is not sucked into the engine but instead pushed out of the tank. Atmospheric pressure (or exhaust pressure in the tank) is greater than the reduced pressure in the carb during induction so the atmosphere/exhaust pushes fuel out of the tank when the pressure in the carb drops. The problem is, gravity is stronger than both. If the tank is set as i recommend, gravity is always against us and the needle is set accordingly. As fuel is used the gravitational effect increases slightly, but only by a small amount derived from of the mass of the fuel in the fuel line and the head change in question. Say 50mm head change on a medium size model fuel tank and the weight of fuel in 4 inches of 3/32 id fuel line? This is all within the range the engine can tolerate.

 

6 minutes ago, Andy Stephenson said:

Have you ever watched someone prop hang a fun-fly model for minutes on end where the tank is hanging inches below the engine, they seem to work just fine.

 

If the tank was below the needle from the get go, doing a prop hang makes little difference. Yes its lower now than before, but not massively different. Also a model like that will tend to only need 50-60% throttle to prop hang as it needs power/weight well in excess of 1:1. Glow engines all run rich around mid throttle due to compromises needed for acceleration from idle. This will easily cover any increased gravitational effect. Even if you punch the power to zoom out of a prop hang, the model begins to move almost immediately and this movement rapidly unloads the engine. Yes there is an acceleration load on the fuel in the fuel line, but it all works out fine if the engine tank is in the right place. Also, working 'just fine' is very subjective as we all have varying standards of acceptable performance. I want 100% performance all the time, but most modellers are happy if their engine works at all and while it might be fine for them, it will not be living its best life and giving its best performance. This 'its fine' approach also breeds problems for others as explained in the next bit. 

 

What engines cant tolerate is a change from gravity assist to resist. Its easy to spot. Show of hands for those who have owned or seen a model which starts off the flight ok and then gradually goes lean, overheats and quits leaving just under half a tank of fuel in the model. Tank is too high and should be lowered. What usually happens though is the needle is opened a bit to give rich mixture on the ground, and then the model gradually leans off during the flight but will not stop as it has this margin in the needle setting. Thus the myth of setting the needle a bit rich of peak is born, leading countless others down the wrong path. 

 

Yes setting the needle a bit rich 'solved' the problem, but it didnt really, it just masked it. If the tank were lowered the engine would not need to be run rich at all and performance would be better in every way. 

 

Modellers tend to cure symptoms, not problems as the actual root cause of an issue can be tricky to find. It also sounds strange to lower a tank if fuel starvation is the problem, but when you look at the whole system and understand how it all works together it makes total sense. Unfortunately this sort of system wide understanding often requires a reasonable level of technical training which is not available at a club level, and school physics classes are mostly long forgotten. So the best manufacturers can do is make recommendations and write instructions. However, as in your example David modellers who dont know what they dont know, and dont understand the reasoning then go 'nah, that dosent sound right' and we are back to square one with myths and folklore.