Hello engine experts,
Ringed stunt engines have always had problems with ring fits. It turns a good engine into a heap of rubbish, if the fit isn't good. I have had problems down the years with the likes of the ST60 and big Mercos. You can hone the bores, get good rings from Frank and carefully fit them, some running in and hey presto a really good stunt engine.
However sooner or later (usually sooner from my observations of others) the ring seal goes and the engine is all over the place with power down and also in the wrong places.
Now I have been watching some helicopter drivers. They use ringed engines because of the "harsh environment" they have to operate in. Well that is the reason most heli pilots give. Now these engines seem to go on for a very long time without any apparent performance drop. It seems to me that they last far longer than our stunt engines do?
So is there any advances in ringed engines for helicopters over our old stalwart ringed stunt engines? It seems to be the case (that word "seems" because I can't be sure) or is it simply that the helis are vastly overpowered and the average pilot wouldn't notice the drop off? They simply open the throttle a bit wider.
I can't imagine much advance in ringed model engines, but you never know until you ask the question.

Regards,

Andrew.

The demands we put on stunt engines are unique, and the outcome that's most important to us -- that the engine self-regulate -- is going to be far down on a helicopter pilot's list of desirable engine characteristics, because if he's serious he's using an engine speed governor.

So it may be that a ringed engine can easily settle into a state where it pumps out reliable power but, on its own, will never go the same speed twice.  That's death to a stunt engine, but may never even be noticed in a heli engine.

Andrew,

Other than the difference between iron traditional square section and newer iron Dykes L-section rings, the difference may be in how we run engines, compared to helicopter fliers.

Dykes rings' L-section form applies combustion pressure inside the upright of the L-form to seal to the sleeve. Traditional square-section rings do the same, but not as well - they rely more on their own 'spring pressure' to retain working contact with the sleeve.

Running conditions differ too. Helos generally have plenty of throttle activity, so steady-state conditions are relatively rare. We want a smaller range of load conditions, unrelieved by occasional lightening of load and variation of RPM. From the exhaust trails I've seen in occasional glimpses, and videos, of helos, they generally run richer than we do - also good for ring life.

I have no idea of the duration of typical helo flights, but we know we need at least 6 solid minutes of consistency at a single "throttle" setting. That, too, may enter consideratiion.

I have used ringed stunt motors of one kind or another since got my first ST46 as a young teenager. I still run ringed stunt 4 strokes today.

My first ringed stunt engine was the Enya 45 model 6001 (early twin ringed version) and I had to put new rings in it after only about 200 hours because it wasn't starting first flick anymore. Next was an ST G51 which had about 40 hours on it (still one flick starter and dead reliable) before I went to my current Enya 61RE which so far only has a bit over 10 hours on it. I've never had a stuck ring (or any ring problem) using all castor fuels.