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-   -   A Little Gem from CASA Experts (https://www.pprune.org/pacific-general-aviation-questions/607343-little-gem-casa-experts.html)

LeadSled 3rd Apr 2018 09:50

A Little Gem from CASA Experts
 
Folks,
From a new AWB:

AIRWORTHINESS BULLETIN
AWB 85-023 Issue 1 – 3 April 2018
Piston Engine Spark Plug Insulator Cracking

Fuel Management - Lean-of-peak operation where precise control over the engine's performance cannot be assured is to be avoided to negate the possibility of detonation. For appropriate fuel leaning practices refer to the aircraft POH (pilot's operating handbook) or AFM (aircraft flight manual), as applicable, for specific instructions.

And we are supposed to take CASA seriously???

Tootle pip!!

lo_lyf 3rd Apr 2018 09:52

That is pure gold. I thought we got passed this and the enlightenment was starting to spread... guess I was wrong.

gerry111 3rd Apr 2018 10:00

Yep. 50F ROP cruise is still their idea of perfection. :ugh:

Where's Jaba and the APS guys?

Lead Balloon 3rd Apr 2018 10:01

To quote the Spodman once again: May Jesus pee in a bucket. What are these wombats on?

A complete misunderstanding of what causes detonation.

A complete misunderstanding of what caused the cracked spark-plug insulators.

Apparently the spark-plugs on engines fitted to aircraft with POHs that deal with LOP operations ‘know’ they’re fitted to those engines and aircraft, and therefore ‘know’ not to crack. Not so when the spark-plugs are fitted to the same engine fitted to an aircraft without a POH that deals with LOP.

Complete muppets. :ugh:

Checklist Charlie 3rd Apr 2018 10:19

I do wish CAsA would stick to doing what they know best, whatever that maybe.

CC

Eddie Dean 3rd Apr 2018 10:23

Fuel Management - Lean-of-peak operation(missing comma) where precise control over the engine's performance cannot be assured (missing comma) is to be avoided to negate the possibility of detonation.

Perhaps that is what was meant to be said?????

kaz3g 3rd Apr 2018 10:41

It was released on 1 April!

Lead Balloon 3rd Apr 2018 10:59

It’s dated 3 April: https://www.casa.gov.au/file/197511/...token=7BkVew_q

If it’s an attempted late April Fool’s joke, it ain’t funny.

Muppets.

andrewr 3rd Apr 2018 11:17


For appropriate fuel leaning practices refer to the aircraft POH (pilot's operating handbook) or AFM (aircraft flight manual), as applicable, for specific instructions.
Perish the thought! What a ridiculous suggestion.

Lead Balloon 3rd Apr 2018 11:47

Sadly, it is an objectively risky suggestion in the case of POHs and AFMs that enshrine the sort of hogwash repeated in the AWB.

The primary causes of spark plug insulator cracking?

(1) LAMEs dropping plugs then surreptitiously refitting rather than replacing them.

(2) Manufacturing defects.

To the extent that the way in which an engine is run may cause insulator cracking, (3) would be running the engine RICH OF PEAK, but not far enough rich of peak.

But an evidence-based regulatory system should be run on the basis of folklore. It must be the fault of pilots running engines LOP. FFS. :ugh:

andrewr 3rd Apr 2018 12:41

You are obviously an APS convert.

What I have learnt since I first read the Deakin articles about 15 year ago:
1) APS don't know as much as they think they know.
2) Engine manufacturers know a lot more than APS give them credit for.

In a disagreement between the engine manufacturers and APS I give the benefit of the doubt to engine manufacturers.

What causes detonation? How about:
1) Heat
2) Time

Detonation is definitely associated with insulator cracking, but APS do have a tendency to put anything that doesn't fit their narrative down to LAMEs dropping plugs or manufacturing defects.

Lead Balloon 3rd Apr 2018 12:47

The laws of physics and the causes of problems aren’t about being a “convert” or the “benefit of the doubt” (and more fool you and your wallet in giving the benefit of the doubt to engine manufacturers).

You’ve identified “heat” as a (or is it “the”?) cause of detonation. OK then, on your superior knowledge:

1. At what mixture setting is cylinder head temperature at its highest?

2. At what mixture setting is exhaust gas temperature highest? Is it lean of peak, or rich of peak?

andrewr 3rd Apr 2018 12:59

APS have a few problems here and there with the laws of physics (and chemistry).

I said heat and TIME. If you understand a little of how tetra ethyl lead suppresses knock you will see where time comes into it.


At what mixture setting is cylinder head temperature at its highest?
That is the wrong question. The right question is "Under what conditions are unburnt gases exposed to the most heat for the longest time?"

The answer is: when combustion is slow, because you have heat from the already burnt gases acting on unburnt gases. Very lean mixture makes it worse because uneven mixing can give you very lean spots that are very slow to burn.

Cylinder head and valve temperature can contribute, but they are far from the only factor.

Lead Balloon 3rd Apr 2018 13:08


Under what conditions are unburnt gases exposed to the most heat for the longest time?
Well that’s a relief.

You’re completely bonkers.

andrewr 3rd Apr 2018 13:23

Whatever you say.

If you're interested in information from people other than APS, here is a good article:
Engine Basics: Detonation and Pre-Ignition by Allen W. Cline

I would wager that Allen Cline has done a lot more detonation testing with more instrumentation and under a greater variety of conditions than George Braly and co.

Lead Balloon 3rd Apr 2018 13:33

Again, if the article at the link is what you’re citing as authority for the proposition that running an engine LOP is the (or even a) cause of spark-plug insulator cracking, you’re completely bonkers.

gerry111 3rd Apr 2018 16:15

At risk of calling out the popcorn, I suggest a truce between andrewr and Lead Balloon.

For those that don't have an engine monitor and prefer to run 50F ROP, I say good on you. For those that appropriately run LOP, I say good on you too.

But personally, I'm a fan of the science that tells me that running LOP in the cruise can be a very good idea.

outnabout 3rd Apr 2018 17:46

Dammit, Gerry, I was just organising the deck chair and the esky, getting ready for the show.

Connedrod 3rd Apr 2018 21:21

Never let the turth get in the way. Even when they proven wrong they never give up. They just delete the thread. When they dont even know or understand the combustion temperatures very between rich and lean and which way the thoose changes go. Prove them wrong and hey presto thread deleted.

But the greatest one was when 70% lop is the same as 70%rop..
Wtf anyone knows that a reduction of airspeed running lop is greater than running rop. Therefore it cant be the same not even close.

Any way run it i dont care keeps me in employment. 😁

Eddie Dean 3rd Apr 2018 21:38


(1) LAMEs dropping plugs then surreptitiously refitting rather than replacing them.
You just made this up, admit it now.


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