Small engine tick-over

[Roger Dyke]

Hi All,

I have an old Enya 15 III glow engine which is in very good condition with decent compression. I have recently had it all apart, cleaned everything and reassembled. Fixing it to the test stand and running it I have made the following observations:-

Prop - 9x4 Fuel - 5% Nitro (9x4 prop is for intended use)

Max revs - 10400rpm Tick-over - 2900rpm

Question: What would be the lowest reliable tick-over speed you would expect? I have heard people claim 2000 - 2200rpm but if I reduce mine down to anywhere near those figures I cannot rely on that it won't quit.The tick-over I have is solid and even. If I reduce it more it is still stable and even, but occasionally it will quit. It may be after a few seconds or it may be a couple of minutes but it will definitely quit. I have very carefully tweaked the settings but cannot improve from the figures I have.

Am I missing something, or do smaller engines warrant slightly higher tick-overs?

[john stones 1 - Moderator]

Been a while since I had those size engines, 9x4 sounds a lot, I may be wrong, if tickovers stable and would give you landing speeds, do you care what tacho says ?

[J D 8]

I run a couple of old 15's and recon you are on the money with 2800/2900 rpm.

[Jon H]

There are loads of variables but in general about 3k is reasonable for an engine like that on 'normal' props. Fit a big heavy prop and you might get down below 2500 but why worry.

This is something that crops up often when discussing petrol vs glow. Some use 800 or 900rpm idle vs 1800 for a similar glow as a pro for petrol. My question is why? If the model wont trundle forward on its own at 1800 rpm then any lower than that is of no advantage at all. Its a similar story here. If the idle you have is well suited to your purposes then dont worry too much about it

[Denis Watkins]

The bench will show you some of the story Roger

In the air is more important, and for landing

2900rpm needs testing for too long a landing run as this may be still pulling at nearly 3K

And 8 x 4 is a more usual prop, until run on the chosen model in the air

[Roger Dyke]

John, JD8, Jon, and Denis,

Thank you all for your valued replies. It looks like I'm probably on the money then. That's good news.

Denis: I am using a 9x4 instead of an 8x4 to try to keep the revs and noise down. It also appears permissible on the manufacturers instructions. I remember years ago using the engine with an 8x4.

[PatMc]

Roger, you may find Peter Chinn's test report on the Enya 15 III of interest.

[Roger Dyke]

PatMc,

Many thanks for the link. I've had a look and the figures quoted are in general, a little lower than mine. But as the engine in the review is probably a newish one with tighter clearances and slightly better compression than mine I think that my figures are probably okay.

Edited By Roger Dyke on 03/09/2019 17:45:09

[Malcolm Fisher]

I use a 9 x 4 prop on an old 15 with no problems. The engine, a Chinese copy of an Enya by the look of the exhaust and silencer, was thought to be not much good by most modellers but it does what I need powering my Veron RF5 motor glider.

Malcolm

[Roger Dyke]

Hi Malcom,

Thank you very much for the info and benefit of your experience.

[Jon H]

i wouldnt want to see more than 10500. While i agree 8x4 is a typical prop for a 15 if you can get revs up over 10k with a bigger prop then you are doing just fine.

[Roger Dyke]

Hi Jon,

I am now reassured that the figures I'm getting for this little engine are fine. Thanks for the info.