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One thing that is common to almost all models in this club is that they have an internal combustion motor powering them. Whether it be a two or four stoke, petrol, glow or diesel, you will find at least one of these powerplants at the field most days of the week.
A Foot & Mouth consideration (still) for Coombes is that you don’t want an unreliable engine on the field – the last thing you want is an unplanned out of field ‘dead stick’!
So, I thought I would put together an article on my version of how to setup, store and run the average model engine. My method is valid for both two and four strokes, and to a degree, can be used on petrol motors. (I haven’t much current experience with petrol – ask Chris Merry instead!)
The starting point is to make sure you run-in your engine before you try seriously to setup the engine – if it’s still a little stiff the settings WILL change as the flight goes on and the motor warms up. I am lucky to have a garage to run my engines in (removing my car first, of course) so I have invested in a Mick Reeves engine stand and mounted this on a lump of wood that is suitably shaped to support a fuel tank and throttle linkage. This whole contraption then fits a Workmate so that the propeller is at a comfortable height – I hate bending down & grovelling in the dirt trying to get an unknown engine to go.
R.T.F.M !
Always read the instructions before doing anything! The suppliers know their engines a lot better than even the average ‘club expert’ so by following what the instructions say for running-in will save a lot of hassle & heartache and can even lengthen the useful life of the engine!
I have two fifteen-year old engines in regular use. One, a Super Tigre 61 is from a target drone that I acquired after the aircraft was shot down. The other is an O.S. 45 FSR that originally came out of a Baron 50 helicopter that I bought from Bob the ex-chairman when he was running the Kalt helicopter concern for Harry Brooks models. Both engines are perhaps a little short of breath nowadays, but they both still flick start.
As an example, ABC engines from Irvine, ASP & SC all require short, sharp runs – run the engine slightly rich until it gets hot to the touch & then stop and allow to cool. O.S. on the other hand, tells you to run their ABC engines exceedingly rich, leaning out occasionally to a ‘clean’ two stroke. This may be because they are not true ABC construction, using a nickel-like plating not Chromium.
Ringed engines generally need to be run slightly rich, again leaning out occasionally to a ‘clean’ two stroke.
Still, the bottom line is “READ THE FLIPPING MANUAL” and follow their recommendations.
A balanced approach
Something that is regularly overlooked is that of propeller balance. Most of the time a moulded prop is OK, but you do get exceptions that are wildly out of balance, causing engine-killing vibration (airframe & radio killing too). Wooden props can be a little out, due to the varying density of the wood.
The best solution is to invest in a proprietary prop balancer (money well spent in my mind) but simply spinning the prop on a screwdriver is better than nothing.
Always sand the profile to remove sharp edges created by the moulding process. Props are ‘fettled’ to get the worst off, but there are always edges that are guaranteed to cut your finger as soon as you touch it. Once smooth, you can start to balance your prop. Always sand the back face of the heavy blade to help to obtain a sensible dynamic balance. Unfortunately you can only deal with the static balance, but you can’t have everything!
An option with a wooden prop is to apply a coat of varnish to the light blade – if the balance is a long way out I have used both methods to get the prop sorted.
Not too lean, not too rich
Assuming that you now have a run-in engine, securely fixed to your model, get the engine started and move out of the pits area. Run the engine up to full throttle and get your helper to hold the nose up vertically. Now lean the needle out so that revs increase, continue carefully leaning out until the revs start to die. This is the TOO LEAN setting, remember the position. Now richen the mixture so the revs increase again, then start to die, this is the TOO RICH setting. Turn the needle to a position mid-way between the two settings for the ideal, reliable position. Provided you don’t have air leaks, dirt in the fuel or a dying plug, this setting should stay put almost for ever. You may have to adjust the mixture a click or two to compensate for the weather conditions, but if you are having to adjust it each flight then you have a problem somewhere.
The same approach is used to set the low needle. Reduce throttle to a reliable tickover and then listen. If the engine fairly quickly speeds up and stops the setting is too lean. If the engine gradually slows down and stops it’s too rich. The motor should maintain the same tickover speed for as long as you leave it.
It is worthwhile spending a fair time getting these settings ‘just so’ for reliability, especially when you’ve got a fun fly model, you want the motor to be 100% reliable when you’re prop-hanging at three feet!
Putting them to bed
At the end of a flying session, either run the engine out of fuel, or inject an after run product into the carb.
With helicopters do the former as you can’t normally get at the carb to squirt anything down it. With a four-stroke, running the engine out of fuel doesn’t purge the crankcase fully so you need to squirt something up the breather nipple anyway.
Why do this? Two reasons.
- The residue of fuel containing Nitromethane has nitrides that attack your balls! Methanol, the principal constituent of glow fuel is also hygroscopic (it absorbs water like a sponge) so the ball races are stored in a damp, corrosive environment.
- The oil solidifies & gums up the works so that when you start the engine next session the needle setting is going to be out, the bearings are not going to rotate, and you’ll probably resort to a starter to turn the thing over. A move guaranteed to shorten the life of your motor! The modern, synthetic oils aren’t quite so bad as they tend to burn away, rather than leave a residue as Castor oil does.
The best after run oil I have found is Hales gun oil, as a gun barrel has to put up with similar corrosive residue. Redex petrol treatment is a good alternative, as is the proprietary brands of after run oil from the model shop. Really, any prevention is better than none at all!
The last motor that I had bearing trouble with was a nine-year old SC 53, in my Rapier delta, so you can see I get my money’s worth!
Tom Gaskin
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