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Proposed engine with rolling maintenance (no TBO or life limit)

US AOPA article

I think this is what basically happens on big jet engines, but it needs a lot of monitoring of the condition.

They will also need to make the internal easier to inspect. For example you cannot inspect the camshaft on the Lyco engines without pulling a cylinder, which is ridiculous.

Administrator
Shoreham EGKA, United Kingdom

I think selling the engines for experimental airframes and letting them build a service record for use as a certification & TBO recommendation basis is a better approach, and its what experimental category is for. Certainly letting the market and users figure out a reasonable TBO by experience makes sense (especially since that’s how it works anyway). But I think the issue with using a mandatory instrumentation and inspections protocol as a new route to certification is that buyers are allergic to ‘mandatory’. In particular they are allergic to mandatory links to the original manufacturer – who may go broke.

My Lycoming O-320 is currently at 935 hours and 43 years since original manufacture. I’ll see how it goes and watch it carefully (using my own undocumented and non-mandatory inspection protocol) but it wouldn’t surprise me if it makes it 60 years before its first overhaul – either with me or a subsequent owner. It runs well – good power, good compression and no leaks.

Last Edited by Silvaire at 14 May 20:39

I think this is what basically happens on big jet engines, but it needs a lot of monitoring of the condition.

That’s what happens on newer car engines as well, but in combination with time based “overhaul”. One does not exclude the other. But in this case it sounds strange to me. The tolerances of a Lycoming or clone cannot even be compared with modern car engine, it’s like comparing an old steam engine to a Swiss watch. So any monitoring will be all over the place to start with. Also, the very reason monitoring is possible, is that modern engines already are operated by computers and sensors in closed loops. Monitoring is just an extension. On a Lycoming it is not even possible to install knock sensors, there is way too much noise in the readings.

If one is to improve a Lycoming, one should start with the production. Start using modern production methods, close tolerances and proper dynamic balancing. Then install FADEC. When all that is done, one can start monitoring the engine.

The elephant is the circulation
ENVA ENOP ENMO, Norway

If you want to improve a Lycoming the first move must be to get Lycoming to return to the quality of the product that was manufactured thirty years ago, I have no doubt Silvaire’s engine will fly for sixty years……………. But one that leaves the Lycoming factory now won’t.

The average life I get from new O-235 cylinders is around 500 hours with one set being scrap at 300 hours. The quality control is rubbish.

Last Edited by A_and_C at 15 May 06:11

When all that is done, one can start monitoring the engine.

I don’t think so, because no monitoring is going to detect say a rapidly wearing camshaft, when you have self adjusting hydraulic cam followers. The actual power loss is very small – one AAIB report (PA28 fatal accident on the Isle of Wight) found a 10% power loss for a 40% loss of valve lift, IIRC.

Piper_PA_28_140_Cherokee_G_AVRP_10_08_pdf

The average life I get from new O-235 cylinders is around 500 hours with one set being scrap at 300 hours

What actually happens to them?

Administrator
Shoreham EGKA, United Kingdom

I don’t think so, because no monitoring is going to detect say a rapidly wearing camshaft, when you have self adjusting hydraulic cam followers. The actual power loss is very small – one AAIB report (PA28 fatal accident on the Isle of Wight) found a 10% power loss for a 40% loss of valve lift, IIRC.

This is a mixed problem of design, poor operation and poor maintenance. Camshafts and tappets are known to be reground instead of replaced at overhaul for instance. Some things are to be replaced at specific times, hours run and/or actual time. Other things are easier to monitor.

The article is really weird. Condition based maintenance and time based maintenance are not contradicting terms. They want on condition because that is the only way they can compete with Lycoming, not because it is better or cheaper for customers.

The elephant is the circulation
ENVA ENOP ENMO, Norway

A and c. Have u tried millenium or titan cylinder heads?

no monitoring is going to detect say a rapidly wearing camshaft

You can check valve lift with a dial indicator, look for metal debris in the oil filter (apparently better than oil analysis for cam failure) and pull #1 cylinder and have a look. All a lot easier than an overhaul.

My concern for limited ability to monitor at 43 years is bearing corrosion but oil pressure is actually on the high end of the scale.

It will run for 60 years… but how many hours?

This “it’s good enough” mentality has driven US auto makers to their grave. Plane and piston aeroengine makers will follow sooner than later.

Remember – 5’000 (and increasing) US pilots disappear each year. That ain’t because they got a cheap, affordable and reliable product to fly.

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