No Hoper

Creampuff, that could be interesting; shock cooling versus engine mismanagement as cause of cylinder and head cracking.

Avgas172

Ummm isn't the continental 0300 a six cylinder engine ... It is on my 172 anyway ...
Continental O-300 - Wikipedia, the free encyclopedia

Creampuff

Errrrm, you might want to take a slightly closer look under the hood of your 172, 172

I thought bog standard 172s had a 320, which have 4 cylinders.

Maybe your 172 isn't bog standard, or you engine's been breeding cylinders in the dark.

Tankengine

Now you are showing your ignorance cream puff!
Early 172s are six cylinder, later ones four.

Creampuff

True, as anyone who can read wikipeadia knows.

But how many 172s with O300s are still flying? I realise Australia is a backwater, aviation-wise, but I thought that all surviving examples of the O300 were in the museum.

Avgas172

Creamy old mate the argument on my part was only about what or was not a Continental 0 300 engine as you no doubt learnt from Wiki I was right, and yes my machine is a H model which comes standard with only a motor as previously described. .... Now back to your corner

No Hoper

Out of the ether they come, or is that the Ethyl? We who know so little of our craft sit in AWE

cockney steve

Yr Right, Progressive....Thanks, Gents, but had the cranking-speed inhibited the Impulse-coupling, I'd have said so

There seems tobe some ignorance on that score.....So.....
The timing on an Aero-engine is, in technical terms, a compromise.
Retarding, via Impulse is , really a Kludge.....because of low cranking speed, the fixed-timing flame front would develop and cylinder -pressure would rise unacceptably, whilst the piston was still coming up to TDC...the delay introduced by the impulse,starts the burn later in the cycle, thus allowing the main "push " of the combustion to push the piston down the correct side of TDC. A secondary effect is the rapid "flick" to the Mag, giving a much stronger spark.

This particular correspondent had difficulty starting and due to the effect we've all seen....prop momentarily stopping as starter overcomes too-early ignition....(Don't believe me? crank with mags off...youll get it slowing, but no "kickback") So he changed the starter.
AFTER changing -out the faulty plugs, the engine now starts promptly.

The impulse coupling is a red-herring, you only need it because the cranking-speed is so slow that A- the mag doesn't generate a spark, due to the flux break being too slow.
B-cylinder combustion pressure rises too quickly, whilst piston is still BTDC.

To explain my remarks re-timing......
Fixed timing is a compromise, Fortunately, the average piston aero-engine spends most of it's duty-cycle at constant speed....therefore, ignition timing can be optimised for that speed.

Back in the day, cars had a manual advance-retard and a manual mixture control...some also had a hand-throttle. Agood driver used these controls to get the best out of the crude engines of the pre-war cars.

Anyone who has ridden a motorbike with Mag ignition and manual A-R ,knows how this affects Kick-starting, their shins and their ankles

The Panther 600 "sloper" single was capable of launching you over the handlebars, if you forgot to retard!

Plugs...I grew up believing the maker's tosh.....massive electrodes were needed 'cos they'd otherwise glow red-hot and cause "pinking" AKA pre-ignition or running-on The design of the ceramic insulator, was to ensure the plug got hot enough to burn off oil and lead deposits, whilst remaining cool enough to not pre-ignite.
Fine-wire plugs defy that logic and give a service-life far in excess of the usual massive-electrode alternatives.

Yes, I'm in agreement with LOP as well. Scientifically, it makes sense....ROP doesn't....It's supporters fail to explain what happens to the "extra" fuel....(hint...It carries on burning after the exhaust valve opens and the piston boots it out of the combustion chamber)
OTOH, the LOP charge has used most of it's energy, pushing the piston down

Gents, thanks for a very interesting and reasonably civilised debate.

Jabawocky

Sorry folks I have been unable to sit down to write a response for a few days. Will try to cover the major points as best I can.

From the 6th
The ATSB report was full of rubbish. There is no scientific data to prove deposits on the piston can cause preignition, this is an OWT. It comes from only a few sources, the vast majority are spark plugs with failed ceramics, the occasional heli-coil tang protruding into the cylinder, or from a cross firing mag/harness.

The topic of mixture causing detonation was from being a RICH mixture that was not rich enough. It was never a lean mixture. It had been leaned from full rich, that is true, but it is still a rich mixture. This is an important concept that many can't grasp.

I said fuel does not cool, because that is fact. Fuel changes the combustion event, refer to the colourful chart I posted previously. As you can see as you lean the CHT gets hotter, as you expected. However once you pass about 50dF the CHT cools off, as does the valve temperature, despite the EGT still having a little further climbing to do as you lean further, then once you reach peak EGT, CHT is falling already, and then as you lean further EGT drops also.

This is not how you understand things to work, and that is not your fault because you were never taught about anything past the point of 75dF ROP everyone disregarded, and it is a natural assumption that if things get hotter as you lean it is a fair assumption this continues. Wrong assumption, otherwise at ICO the thing would melt down.

Detonation;
Yes there is a very well defined set of criteria for detonation and it's intensity. The FAA have very sophisticated algorithms for determining what is Light, Medium and Heavy Detonation. As I stated previously, I am in the fortunate position of being involved in more detonation testing of aviation gasolines than probably anyone else in Australia. There is far more to this than just it explodes or it burns.

As for the Chieftain those engines live a fair part of their life with a little light detonation and if operated as per the POH, it certainly will at times be doing so.

The static timing on the Chieftain is as you state 20 degrees BTDC. What I said was the ACTUAL spark timing , when the plug actually fires is anywhere up to 13-16 degrees BTDC. I can show you this on the dyno runs during the APS class. It varies a lot. If you set the static timing at 15 degrees, this would result in an actual spark event at maybe 10-11 degrees and this would result in very high EGT(not harmful) and very high TIT (harmful for turbo's), and be very lethargic indeed.

Preignition;
This is an event that has a flame front initiated by some other source before the spark plug is fired. This could be maybe 40+ degrees BTDC, and the result is extremely high peak pressure, and occuring close to or at TDC. This is very destructive. We can show you some data files from real events and it is quite impressive to say the least.

Leaning;
As you lean the burn rate speeds up, once you get to about 30-50dF ROP it peaks and starts slowing down as you head towards peak and onto the lean side. The idea that you have a risk of combustion in the intake from an aggressively lean mixture is so far fetched for a 2700RPM or less engine that I think we should move past this, except to say as you have pointed out the difference to auto engines and those in drag cars ....they are clearly different in these areas and hence the risk.

Lead, or more correctly TEL.
Again a topic with which I have a lot of involvement with. TEL does not provide any soft cushioning material to anything. Think about the path of the fuel. In the inlet port, fuel and air is being sucked in, the valve guide is under negative pressure, no fuel is going to help the guide and if it does get there it is a highly effective solvent, not good for lubricating the guide or the seat.

Lets move to the exhaust gasses now after combustion event, the TEL has been converted to the a compound of lead and bromine, this is the deposits you see on the piston, and it is a salt. Salts make crummy lubricants, so they hardly help the valve seat and guide and these are the deposits you get giving some poor leak downs which you try to avoid.

TEL was the only thing to boost octane when the military needed more compression ratio and forced induction in the quest to deliver more bombs further. The 115/145 had higher doses. This was for the big engines with massive HP. It worked well, but those are the same engines that had 750hr TBO, until they were run LOP, and then up to 3600hrs. These were the CW R3350's and similar.

FAA did back to back twin flight testing on some close to avgas spec unleaded fuel Vs Avgas and there was no benefit to the lead.

Dexta, the reason some folk started to think avgas lead content helped was a new OWT called "lead memory". The FAA almost believed it, in fact they did for a while I believe, but the tests that showed correlation were flawed, there was later found to be no such thing. Just because Petersen have an STC does not mean things printed like that are true and correct.

Happy to take questions, and for those who attend in Perth on the 16-18th of May, most if not all your questions will be answered.

Cheers all


TW: time for a new thread title, perhaps something less silly?

yr right

.Steve
Yr Right, Progressive....Thanks, Gents, but had the cranking-speed inhibited the Impulse-coupling, I'd have said so


Do you know how the impulse coupling works.
1st it retards the ignition firing
2nd it introduce at better spark by spinning the mag faster than cranking speed.
Now this is done with smoke and mirrors.
Well actually springs and bob weights
With these geared starters they spin so fast that the impulse cannot do either of it functions. Hence extremely hard to start.
Now someone here going to tell me I don't know what im talking about so be fore you say anything ok I don't no sh^t.


Now someone ask me about data with dead cylinders well for F&*^ sake, I don't have any, but I do and have changed a **** load because of excessive leaning and when you have to change multiple cylinders on a engine gee may be im making that up as well and you can tell when it happen all you have to do is look at the exhaust valve. Its as clear as black and white. Now who here has actually changed a cly that has had that damage.


Next ive used a 10000hp race engine as and extreme example are you all to thick to see that. And by the way the idle speed on a nitro engine is approx. 2000rpm takes nearly 1500hp to drive the blower and produce zero vacuum as it manifold in in positive px up wards of 60psi so when it leans out and the intake valve is open the thing goes bang. extreme but the point im making is the flame front is still burning when it should be all gone.


Next no one has answered one simple question I have raised.
By going over peak how much saving in fuel are you making and hour difference LOP and say 50deg from peak .


Now where in the POH in a PA 31 dose it say you can lean out the engine in full power. to say its was rich enough is crap it failed if it was full rich are you saying it still would have failed and the point here im making is all this is great when it is all going right but when something goes wrong you have reduced your own safety margin. ie lost one engine increase power to full on the other didn't increase mixture to full rich and it also failed. Im not saying before anyone else has a go that he was using LOP as you cant on a positive px engine but on simple action and chances are he would have been alright. Fact remains the aircraft was lost. As for the other things you raised cracked ceramics miss firing harness once again im amused, umm what wasn't picked up in the engine run up. now ive have a lot of experience on this type of airframe and engine, what you have stated is im sorry but fiction. If there is one thing that has to be right its the ignition system other wise the engine will let you know be fore you even left the ground. So Jaba with out being rude you can PM if you wish but actually how much hands on in a shed have you actually had.


Now Aussie bob at no time did I ever mention that it was a 172 or any thing else for that matter. the reason I used a C-300 as it was close to a Holden 308. I could have use a o320 etc. the comparison is the size of the cly to a v8 of roughly the same size and the forces that happen if detonation happens.


Now someone said about cleaning nozzles and how it had a blockage, So whats the first thing in in trouble shooting that partial problem dose any one know ?
Cheers all and by the way im not pi&sed in any way just amused .

Progressive

I started formulating this post because the discussion had gotten civilized again but after yr rights last post i'm not so sure....

Cockney Steve,
1) Your friends aircraft had old massive electrode plugs and a low torque starter but presumably worked ok

2) He changed the starter and now it wont start

3) This is the plugs fault?

Anyone with a minimum common sense would see that with a high torque starter the engine will turn faster, the magneto will generate higher voltage and the resistance of the plugs will matter less than it dd before the starter change.

However I have been wrong before so please enlighten me on what difference the new starter made to operation of the plugs if the impulse worked fine.

Jabba,
You are correct is should have said many pilots should not TRY to run lean of peak - successfully running lean of peak is fine and regularly practiced by those who are educated.
It is the pilots have no desire to learn the correct method but who read "lean of peak can save me money" on the net and have a punt at it without any education who do damage. Mostly by being a little to timid with the red knob (due to misconceptions) and ending up just a little on the rich side of peak.

Also check ur PM's

gerry111

Goodness.. This is all becoming rather confusing for me.

Is 'yr right' perhaps one of the LAME's that maintained the Whyalla Chieftain?

On big oil company marketing: Who remembers the 1970's AMOCO adverts for their "Final Filter"? Or the supposed benefits of Shell's super grade petrol with Methyl Benzene?

LeadSled

Folks,
I think what is being referred to here as "Ethyl" was a brand of motor fuel which was a brand of Standard Oil of New Jersey, originally.
In Australia, a brand of petrol called Ethyl was sold by the old Vacuum Oil Company -- the trademark was a flying gargoyl, I have an old original baked enamel garage sign as proof.
Tootle pip!!

tail wheel

Goodness me Leadie, you are old!! Welcome to the Geriatrics Club!

Do you also remember Plume, Golden Fleece, Texaco, Ampol, Marfak lubricants and Red-X upper cylinder lube?

When a Chippie was £4/10/- per hour dual, I earned ten bob on Saturday morning and ten bob on Sunday morning, pumping petrol the old fashioned way.

Time to change the thread title I think???

Creampuff

But it’s only your wild *ssed guess as to what caused the damage.

Because you believe there is such a thing as “excessive leaning”, you attribute every problem to it.

There is no such thing as excessive leaning (except at the point where combustion stops but you need power …).

There are rich mixtures that aren’t rich enough, and there are lean mixtures that aren’t lean enough.

I know an aircraft that has a POH that says the ‘best power’ setting is 25 degrees C ROP. It has a CMI engine. The guys who fly it take off, set 25/25 and climb at best rate of climb speed to cruise altitude. That engine will almost certainly have valve and other failures way before TBO. (But it’s being operated ROP, so I suppose the 'cause' will have to be attributed to something else.)

About an engine’s worth, over the ‘book’ TBO of an engine.

At cruise power at altitude the difference between being rich enough ROP and LOP enough on the engine I usually fly is around 8 litres per hour (my fuel flow monitor is calibrated and validated to an accuracy of about 0.1 litre per 300). That’s about $20 per hour. That’s about $40,000 over 2,000 hours. (Of course it’s not quite that simple, because a substantial number of those hours are at climb power and much higher fuel flows. I’d expect to save at least $25,000.)

And BTW, the engine will likely last a lot longer, because it isn’t being run in cruise at the setting at which it will be getting the hardest flogging it can be given (ie around 50deg F ROP). Have a look at where ICP peaks on the graphs Jabba posted.

aldee

Or take a look at the FREE APS online seminar taster & then do as I did, pay the $395 for some data based education

Shame Perth is so far from Christchurch

No Hoper

It would appear that basic facts about what causes higher than normal operating temps are being massaged to suit particular view
The following are some causes
1. Ignition timing advanced
2. Lean mixture during sustained running
3. Cam timing dialed incorrectly
4. Hole in intake manifold - lean mixture
5. Engine baffling broken/US

your turn. Facts,just the facts

yr right

So ok I've got it all wrong and that's just not me. So recently we had to change 6 cly on 210 where the operator was experimenting with lop. Fuel flow px where check on cal gauges as per m/m. Mags check no further defect where found but we still has 6 dead cly. May be my imagination. Any way operator was ok about it. Yo see wasn't his areoane he just operated the owner had to put the bill for the cly and that with the aircraft out of service we'll mmmm $$$$$$. We used to do top o/h here and then get an extension on engine tbo but casa stop that. One place I worked had a system of maintenance that gave an enormous life extension to there tsio 540s with tops done same as hazeltons airlines. Now with all of this have a look what's in front of you. The weakest part is the exhaust valve. M/M states nil leakage past the valve on a leak rate test. Now if I'm wrong what causes 6 cly to all be u/s at the same time. Maybe I should give it all away and do some thing else.
Now still anyone tell me what the first indication is of a blocked injector is.

Creampuff

No Hoper

I think your ‘2’ should be: Mixture not rich enough, ROP, or not lean enough LOP. 4 should be amended accordingly.

Re your 3: How many standard piston aero engines have cams that you can ‘dial’?

5: Partially blocked injectors (resulting in a ROP mixture that’s not rich enough. Really a subset of 2.

6: Fuel enrichment function disabled during climb (throttle should be set to ‘full’ on engines with FCUs with this feature.

7: RPM reduced at high powers (moving PPP close to TDC).

Jabawocky

yr right

Depending on which Chieftain POH you read, the climb power is 38-40", 2400 RPM, TIT of 1500 and fuel flows between 27USG-30USG per hour.

Well it might surprise you but I have just run the live data recoding of exactly that scenario, just to recollect my facts. FACTS that is, not WAG's.

Now lets look at Full Rich, 42" 2600, about 40-41GPH and Internal Cylinder Pressure (ICP) = around 800-900 PSI.

40"/2400 and Full Rich = 36GPH and 750-800 PSI.

Climb power as per the Piper POH as noted above = a whopping 100-1100 PSI and that is with a nicely cooled (forced) engine. Imagine that in a sub-optimal installation.

ICP's that high are not good for the engine. No matter who makes it. By the way I noted the Detonation Index for cylinders 2,3,4&5 were all triggering the mild detonation level and at times were medium. This was at 28USGPH, imagine it getting worse at 27 GPH or mishandled and even worse again.

This is the effect of RICH mixtures that are not Rich enough.

To answer your question on diagnosing a partial injector blockage, assuming the engine was a "Conforming Engine" to begin with it is real easy, use the EMS, do a mixture sweep and it will show up. In fact do a BMP and you will know straight away. Did you read my post about who needs an EMS most? The answer lies within. Please read it.

If you are going to suggest the old coke bottle check, please explain how that is going help. If you did that with my injector set, and were accurate enough to get a good catch, the volumes would be all different, and by a noticeable amount. Now the question would be which is blocked? The one with the lowest amount? Or the one with the fullest amount?

It could easily be the fullest, because if it were partially blocked it would flow even more compared to the others when clean. So what does the old coke bottle test prove? Absolutely Nothing.

A coke bottle test is useful in testing the lines with the injectors removed. Not with them installed.

How about going back and answering some of the questions I asked. They were not hard.

Lastly, I have spent a fair amount of time in some pretty sophisticated sheds, but not doing the same tasks week after week. So my hours of hands on the tools will come nowhere near yours, I guarantee that. However this in no way discredits the validity of the data. Do not believe me, believe the data. I do not see the value in trying to discredit me. I am not doing that to you, however the presentation of scientific data is going to be rather challenging to those who have grown up on a diet of misinformation and OWT's. You are not alone there, I was also, we all were. In fact it is still being taught. You have to answer exams wrong in order to be marked correct.