The Care and Feeding of I/C Model Aircraft Engines

Part One - An Introduction

This thread is about the care, repair, tuning and general running of internal combustion model aircraft engines. I am excluding both car and marine engines because they are a specialised subject on their own and my knowledge and experience is almost exclusively limited to model aircraft. I will start off with a general description of the main types - diesel, glow and petrol and their general layout in there most common form - single cylinder motors - both two stroke and four stroke.

If you are going to use I/C engines a general knowledge of what makes them tick is the best starting point. Initially I do not intend to go to deeply into the theory of design and construction - I am assuming that most readers will buy their motors ready made from the local hobby shop, over the internet - or perhaps from a swap meet or a friend. Motors bought from the last two sources are often second hand and I will go into what to look for when buying second hand at a later stage.

So - you've gone and bought your engine - you bring it home in it's pretty new box - the outside of which is festooned with all sorts of letters, number and other assorted signs. Most first time buyers will at least, understand what engine size they have bought. It will probably be somewhere between a "15" and a "61" - either two stroke or four stroke. It might even be as small as an "020" or as big as a "91". these numbers identify the size of the engine in cubic inches. An "020" is 0.02 of a cubic inch and a "91" is 0.91 of a cubic inch. In the early days (back when I was a boy) engines were more likely to have their capacity expressed in cubic centimeters. A "15" was 2.5 cc, a "35" 6cc and a "61" all of 10cc. In a lot of cases these sizes were, and in some cases still are, no more than approximate or arbitary sizes.

The box will probably have mysterious references to "Ringed", "ABC", " Schnurle (or Schnuerle) Ported" and perhaps, depending on make, you will find it is also "FSR", "Pro", "VT", "FA", "FS", "VR", "FC", "P" , "4C" , "AR", "R/C" or just about any other combination of letters and numbers. Your first engine, and probably, most of your engines will be "glow plug" engines. If you become more involved in model building, or if you start to build larger aircraft, then you might change to petrol engines or perhaps become a fan of "Diesel" type compression ignition motors.

BE WARNED! The fascination of model internal combustion engines is addictive and you might find yourself pursuing the ownership of Twin or Multi cylinder engines and even, finance permitting, such exotics as three, five or even seven cylinder radials, Wankel type rotaries, ducted fan engines or, if you become totally hooked, becoming a collector or even attempting to design and build your own!

This is my introductory post so in the next installment we will get down to business and start to look at the basic workings and running of your average two stroke, single cylinder, internal combustion, model aircraft engine. STAY TUNED.

(contents list created and updated by Admin)
Clicking a link will skip to the next relevant section without viewing the comments. Useful for referencing back later.
1) A Bit Of History

I think that's a great introductory post .... it sounds more befitting of an article ... have you considered doing one? .... we'd appreciate it.
I've got loads of questions to ask here .... just give me time to think.
Nice one Grumpy ... I'll forgive you for planting the Feb 29th marriage idea in Ann's mind.

Pol

A Bit Of History:

Single cylinder, two stroke, model aircraft engines have been around in various forms since about the time Adam was a boy. There has even been the ocassional multi cylinder unit chucked in for good measure. In the early days these motors were either petrol or diesel and in a lot of circumstances made at home on a lathe with perhaps a milling machine thrown in. - that is, until the introduction of the glow plug. There were some manufacturers BGP (before glow plugs) but the product was either a some what primitive and cranky diesel or a spark ignition motor. Shortly after WWII some modellers invented a primative glow plug and you can get a good arguement over just who is responsible but it is generally accepted that glow plugs became a reality in about 1947 - 48. Today "glow" motors are pretty much a standard although recent developments have encouraged a resurgence in interest, and a use of, both petrol and diesel motors.




My Enya 35 III TV Special. Model 5224

I'm going to make an assumption - that some readers of this thread will be faced with their very first motor - and possibly their very first R/CTrainer to go with it, therefore we will start with the absolute basics! So - you've bought your motor, brought it home, read all the guff on the outside of the box and, hopefully, had at least a glance at the instructions - go back and read those instructions again - thoroughly! Now you've taken your brand new motor out of the box, wiped the drool of the bench top and are wondering what to do next. You will probably want to start the bloody thing! OK - stop panting, there are a few things you need to do first. You need to make some decisions: - those decisions are - what fuel? - what propellor? - what glow plug? - and do you run it in ( you are going to carefully run it in aren't you?) on the bench or in the air. Oh - one more thing - some new motors come out of the box requiring a small amount of final assembly - usually the carburettor needs to be fitted to the motor and the muffler needs to be attached. Nothing to worry about - read the bloody instructions!

Decision #1:
Unless you have bought a piped ,pumped, 20,000 rpm monster - which means, if you are a beginner you've been sold the wrong motor, you will need a mild (say 5% nitro or no nitro at all) fuel to run it. The subject of fuel can take up several posts and promote screaming arguements among supposedly knowledgeable enthusiasts so for the moment just ensure the fuel you buy is fresh and from a reputable supplier. WATER MOISTURE is the enemy of all methanol based fuels so keep the container tightly sealed when not in use and always use a filter between the container and your tank.

Decision #2:
The size of propellor you use will be dependent on a number of factors so, to start go back and read those instructions - some where in there you will find the engine manufacture's recommendations. It will say something like 8x4 or 10x6 or 11x7 or what ever. the first number is the diameter of the propellor and the second it's pitch. Pitch is the theoretic distance the prop moves forward with each revolution. More about propellors at a later stage but for the moment there are a few things to be aware of - and a few cautions to observe. The propellor should be new, made from wood or a nylon composite, and be COMPLETELY FREE of nicks, scratches and any other imperfections. A new propellor also needs to be balanced and, if a spinner is to be fitted, that should be balanced to. There are a number of effective propellor balancing tools on the market to fit various budgets. Unless you are an expert do NOT attempt to make your own propellor.

Decision #3
Some engine manufacturers do not include a glow plug with a new motor but their recommendation will be included in the instructions. The subject of glow plugs will be covered in detail in a later post but, once again, following the manufacturers recommendation will ensure a safe choice. Glow plugs are graded from hot to cold and the correct choice for ultimate performance can depend on several factors. DO NOT fit a glow plug if you do not know it's heat range or type and DO NOT over tighten it when fitting it to the motor. Use the supplied copper washer and tighten only one quarter of a turn over finger tight.

In the next post I'll examine mounting methods, fuel tank fitting and choice, and how to run a motor in correctly.

Polyphilla wrote: I think that's a great introductory post .... it sounds more befitting of an article ... have you considered doing one? .... we'd appreciate it.
I've got loads of questions to ask here .... just give me time to think.
Nice one Grumpy ... I'll forgive you for planting the Feb 29th marriage idea in Ann's mind.

Pol

Awww come on Pol - lets be honest - you showed her the post yourself! Just a little hint??

An article?? - well maybe but I'm thinking of making an ebook of the posts when I get a fair few sorted out. Free to any Forum members who might be interested.

Im enjoying the New book Grumps,2 authors on the Forum now, marvellous stuff.I remember being introduced to my first IC and how complex it all seemed to be compared to electric.I hadnt considered taking up IC at the time but my instructor of the "alpha "male type arrived at my place of work 1 day with news that "Les wants to sell his trainer with an OS 46LA fitted all in for £100 which of course was cleanly swept from my pocket without touching the sides.It was like someone trying to save me from the devil.My instructor didnt know or want to know about "Electric" he considered it !"Devils Work" and was trying to "Save Me".Now ,Les is an elder statesman of the club and an old school "Engineer" so anything he does is within a 1000th of an inch,"perfection".So my "New trainer" was superbly prepared,no rubber bands holding the wings on cos Les didnt like em,proper plastic bolts and everything lovely and neat.My first day at the field with a fangled IC engined aeroplane was an education in itself and I have to say probably the most daunting part of the hobby to learn and get used to.Being in my sixties and being introduced to such a compicated procedure was a challenge in itself but then on this day when I arrived at the field with my new acquasition all members gathered round to watch as I tried to start it for the first time,all giving me variuos suggestions but none actualyy helping.I admit this thread would have been very useful to me at the time ,so where were you in my moent of need.I became immediately careful and precise with my engines requirements and the procedure of starting my new baby.Everything was placed in a certain position to ensure safety and no possibility of an haccident and continues to this day.It was a very daunting challenge at first and one I will never forget.As a beginner,I carefully went through a list of the start up procedure in my headright from the model restrainer to position of the starter battery,the starter leads,the glow starter,fuel container,fuel pump,Transmitter within reach etc.So, I now have my engine running,the glow start removed ,its ticking over nicely and we are ready to carry it out and take off,NO<NO<NO.The effort and concentration level required by this beginner to go through this procedure was so high that once it was running and sitting there sounding as gorgeous as an IC does in my mind I had achieved all I wanted for the day.I just wanted to sit down,have a rest,and go home.There was no need in me to fly the model,just getting that little engine was enough for me.But then alfa male would walk up to me and in those dreaded words "Come on then Lets fly your model I would surrender to this superior being had him the controller,carry my roaring monster out to the take off area,he would take off,hand the controller to the bundle of nerves by his side and shout various instructions that my frazzled beginners brain totally ignored cos I had enough to do with this super fast monster that had replaced my quiet gentle Brushed 400 Easistar.I was riding an uncontrollable stallion

blimey

we have a new author on the site.

fascinating stuff.

The Beard wrote: But then alfa male would walk up to me and in those dreaded words "Come on then Lets fly your model I would surrender to this superior being had him the controller,carry my roaring monster out to the take off area,he would take off,hand the controller to the bundle of nerves by his side and shout various instructions that my frazzled beginners brain totally ignored cos I had enough to do with this super fast monster that had replaced my quiet gentle Brushed 400 Easistar.I was riding an uncontrollable stallion

Instructions mate - snot Alpha Male - wear ear plugs - throttle back!

Ive a fairly new MDS 61 and the fuel rail appears blocked solid .How do I clear it.Ive had it soaked in paraffin for weeks.Someone suggested the oven,Ive heated it up with the heat gun which has unseized engines at times what do you suggest oh grumpy maestro

Tell us the differences between the crap engines & the good ones.
When I was a lad, OS were just a sport engine. what turned them into world leaders?
Why are MDS classed as garbage? ... is it down to the engineering or the quality of the materials they use?
There are a million questions here Grumpy.... I hope you know what you've started.

Pol.

Grumpy, can you tell us why model car engines are so high revving? ... typical RPM is about 28,000 I believe. They have similar bore & stroke so what are the problems with us using them in aircraft?
I know they have massive heat sinks on the cylinder head..... but is that a problem to an aircraft flyer?

Pol.

The Beard wrote: Ive a fairly new MDS 61 and the fuel rail appears blocked solid .How do I clear it.Ive had it soaked in paraffin for weeks.Someone suggested the oven,Ive heated it up with the heat gun which has unseized engines at times what do you suggest oh grumpy maestro

G'Day Beard. I have a Lincoln 61 which is an American boxed copy of the MDS. It is virtually the same motor. I expect you have completely dis-assembled the carburetor and cleaned it thoroughly. The fuel rail you are referring to is, I expect, the high speed spray bar. If it is completely blocked I'd suggest you soak it in pure methanol if available. Acetone is also effective if the gunk in the spray bar is crystalised. Paraffin is what I think we call Kerosene - bloody useless for this job. I'd advise against using a heat gun but perhaps heating in an oven to no more than 100C. That way the spray bar will be heated evenly and will not be subject to possible distortion. My preference would be to soak it and then blow it through with compressed air. Re-assemble the carburettor using a light "after run" type of oil and PLEASE install a fuel filter between the tank and your motor. I've found using castor oil in this motor does result in a lot of gumming in the motor. I highly recommend using a synthetic oil and the manufacturer's suggested 5 to 15% nitro. I use 5% and an Enya #3 glow plug with an 11x7 prop.

Polyphilla wrote: Tell us the differences between the crap engines & the good ones.
When I was a lad, OS were just a sport engine. what turned them into world leaders?
Why are MDS classed as garbage? ... is it down to the engineering or the quality of the materials they use?
There are a million questions here Grumpy.... I hope you know what you've started.

Pol.

G'Day Pol,
Yep - back when we were both snot nosed little horrors (I still am ) OS were a "sport engine" but over the years they have refined and researched there technology and these days they are righfully considered to be leaders in model engine quality. there are a few manufacturers that stand out from the crowd but you will always find some one (usually the club's self appointed "expert" - definition = ex - as in has been - spurt - as in a drip under pressure) who swears that so and so make or model is a disaster. Choice of make and model depends on what you expect your model to do - are you flying sport, scale, pylon, pattern, what ever. for the average modeller just about every motor on the market these days will do the job required of it. The only exception to that is some of the less well know brands coming out of China and marketed as low cost buys. Conversely there are a few good motors from the same source - ASP comes to mind.

MDS? - hmmm well I have a problem here MDS are my initials and although I have no connection at all with the engine it's hard to shit can something with your own name on it! My understanding is that MDS is a reasonable design but there have been a number of changes in where they were manufactured - from Europe to Tiawan to China. My information is they suffered from quality control issues. I have two MDS motors - a 40 and a 61 (Labelled a Lincoln but actually an MDS) and I've had no problem except that they don't seem to like castor oil as a lubricant - I use synthetic and have had no problems using them as "sports" motors.

Finally - my recommendations? - I use OS, Enya, and YS in most of my builds.

Polyphilla wrote: Grumpy, can you tell us why model car engines are so high revving? ... typical RPM is about 28,000 I believe. They have similar bore & stroke so what are the problems with us using them in aircraft?
I know they have massive heat sinks on the cylinder head..... but is that a problem to an aircraft flyer?

Pol.

G'Day again Pol,
As I've already stated - my knowledge and experience is mostly, in fact almost exclusively, restricted to model aircraft engines. Given that I am no expert there are a number of differences in port design, combustion chamber design and carburation between model car engines and those marketed for use in aircraft. An examination of the relative torque and power curves for each type of motor reveals huge differences in design and purpose. In fact the motors used in cars are so highly developed for that purpose that their use in model aircraft is not even worth considering.