Cylinder Cracking

[S-Works]

Our twin has just gone onto annual and the engineers have discovered all 8 cylinders are cracked and require replacing.

I am curious about the cause of this. Could it have been the last flight which was an hours "local" bimble or a longer term accumulation of abuse? This seems to have happened since the last 50hr check and there were a number of signs that the cylinders have run very hot during this time.

The aircraft is used a lot of training and so spends a lot of time being flown around on one engine.

Views please?

[Zlin526]

Causes can be many, but what you don't say is what type, what engine, who flies it etc etc....

Is it a group aeroplane? Are you aware of the engine leaning techniques used by the other members? Does the aircraft carry out glide approaches if a little high on finals?
:ugh:

[S-Works]

I dont know how everyone flies it which is why I am looking for as many possible reasons as possible. Apart from training it is a fairly small number of people who fly it.

SOP is fly it to the ground, lean carefully and dont fly it firewalled. Which is why I am trying to ascertain what sort of mistreatment could cause this sort thing and prevent it in te future.

[shortstripper]

Shock cooling?

SS

[Ludwig]

Would have to be some spectacular dive from a great and cold altitude to crack all eight cylinders wouldn’t it?

[Sensible]

My understanding is that the worse thing you can do to an aero engine is to fly high in the cruise with the engine over leaned to get the CHT to "red line" and then turn power to idle for a descent through near freezing air. There are problems with aircraft used for glider tugging when the engine goes from full chat with a glider in tow to idle for the descent. Special care is taken to gradually reduce the CHT to prevent such shock cooling and subsequent destruction of the heads.

[Zlin526]

Ludwig,

Would have to be some spectacular dive from a great and cold altitude to crack all eight cylinders wouldn’t it?

D'oh.... it would have to be a spectacular power off dive to do it on a single occasion, but an aircraft engine can fly for ages with a cracked cylinder, so if some bozo consistently does it, say at least eight times, then it might crack eight cylinders in total....:rolleyes:

[IO540]

We could have another "lean of peak" thread here :O

From the limited amount I know about aero engines in general (I've read up a lot on IO540-type engine management because I need to know, but engines do vary) I agree - it would have taken something spectacular to crack all eight by shock cooling.

ASSUMING they weren't cracked already, and got cracked one or two at a time over a long period of mismanagement.

Flying schools rarely crack cylinders, despite spectacular abuse, and this has been used as counter evidence for the existence of shock cooling. However they tend to do PFLs after some period in relatively slow cruise (EFATO aside and then the power obviously has to come back on pretty quickly :O )

It appears, from anecdotal data from tug operations, that they manage to eliminate cracked cylinders by ensuring that the engine has been running at somewhere well below max power, say < 75%, for long enough to thermally stabilise, before they descend, and then they can descend as quick as they like.

So, from what I know, and assuming all eight got cracked together, somebody had to run the engine on max power in slow flight (back of the curve), got it really hot, and then dived.

Is there evidence of detonation bose-x ?

The other possibility is straight overheating, combined with (also caused by) detonation. Detonation wouldn't be evident in the cockpit. It happens about 50F ROP (on the EGT) at high power settings, typ. over 75%, but one has to lean to do it. This isn't "overleaning"; it is actually UNDERleaning, because if one leaned further, to peak EGT, there would be no detonation and the CHT would be way lower. If one leaned LOP it would be lower still but people are afraid of that because they think it is over-leaning.

I reckon if you ran your engines with max power in cruise, and then leaned a little bit (right into the detonation window which is about 50F ROP) and left it there, you would get detonation. If you then climb, to push the CHTs past 500F through reduced cooling, they will crack. I know I could do this very very easily if I wanted to, exactly as described.

A lot of good stuff on

http://www.sacskyranch.com/

[Wunper]

Check out John Deakins column on Avweb, the best reasoned engine management articles available, period.

http://www.avweb.com/news/columns/182146-1.html

Also read this poop from Lasham Tug guru Phil Philips

http://www.faasquadron.org.uk/gascosafety1.html

W

[High Wing Drifter]

Bose,

This seems to have happened since the last 50hr check and there were a number of signs that the cylinders have run very hot during this time.
I flew in for a 50hr-while-u-wait a few months ago. Can't say I noticed the engineer paying much visual attention to the engine. I assumed this is properly examined during the annual.

Basically, are you certain that it would have been spotted then?

[Say again s l o w l y]

I hate to disagree with IO540, but flying schools do sometimes suffer from cracked cylinders, sometimes in the most spectacular fashion possible.

I have seen 5 such problems on a variety of different a/c, but all were approaching their TBO's. One a/c blew a cylinder almost completely off, amazing to see, but very sobering.

I think longterm abuse is more likely in this case, but to have all 8 go at once.... If it has been overheating recently, there maybe a magnitude of issues, all small but a combination may create this problem.

Poor leaning technique, high power settings followed by sudden shut downs. Has alot of EFATO training happened, especially on that side?

If an engine of that size is at full temp when shut down due to the practise of "flying it to the ground" this may exacerbate a problem. The rate of temp drop at shut down is pretty fast and since you have cracking on all cylinders rather than just the forward ones, this may point at a problem.

This is by no means authorative, but having a look at how it's operated usually can help point in the right direction.

[Final 3 Greens]

Bose

Let me ask the dumb question.

Could this be due to defective manufacturing/materials?

Can you trace the engine history and disprove this possibility?

[2Donkeys]

Two separate engines suffering from an extreme case of cylinder cracking. These engines were obviously caused to become extremely hot. This might be for a variety of reasons, but the fact that both sides were similarly affected points to pilot abuse rather than manufacturing or mechanical problems.

Overly aggressive leaning at low levels would be an obvious candidate, followed by a rapid cooldown.

2D

[Final 3 Greens]

2D

I tend to agree with your view, but as a consultant have often found it a good approach to eliminate the less likely causes in the first instance and then to focus attention on the remaining suspects.

Should be relatively easy to trace the engine history and disprove it as a cause.

[IO540]

I reckon somebody flew it at 100% power, in detonation. CHT well over 500F. An hour...

[A and C]

Please tell what type of engine we are talking about and maybe we can come up with some helpfull comment this thread is to general at the moment to be of any real help to you.

[dirkdj]

I would rather suspect faulty maintenance: could be improperly timed magnetos (too far advanced timing) or full rich fuel flow set too low for full power.

Another good case for an all-cylinder engine analyser with data memory.

[S-Works]

Lots if interesting responses thanks. It strikes me as being difficult to recognise an exact cause?

I could perhaps understand one engine but both leaves me wondering.

It is used a lot for multi ratings so plenty of EFATO and single engine work.

[Hairyplane]

Were you hiring it out 'dry'?

If ever there is an incentive to save some gas when flying somebody elses aeroplane......... I don't think we need to draw you a picture.

Change it to 'wet hire' and you control the fuel. The net result is zero incentive to lean the thing.

Consider also an engine monitoring system. The EDM 700 is STC'd. You can dowload the historic data onto your computer and presumably use the 'offending' traces to support your invoice for engine repairs.

Why not include a clause in the contract 'must operate the aircraft and engines in accordance with m'f's recommendations.'

This, plus the above evidence of abuse would probably stand up in court.

Failing that, do as I do and don't let anybody else fly your machines unless you know them well.

Lease an aircraft to a school and you will hear the following phrase on CofA - 'Take out your wallet and repeat after me, help yourself'.

HP
HP

[IO540]

I suspect that in this case, with all eight cylinders cracked, EDM700 evidence would be of no help at all with getting something out of the manufacturer. It will probably show all cylinders running at a very high CHT.

It would point a finger at the offending pilot, but what can one do? In an ah hoc self fly hire situation, the pilot is almost certain to argue that he was never given adequate training on engine management, and in general he would be right.

This happens all the time in self fly hire. Somebody does a heavy landing, bends a few things, keeps quiet about it.

I don't think wet hire is the answer, because flying with fully rich mixture is OK only at low levels (a few thousand feet or less). Above that one needs to lean, and leaning only a little is the most dangerous thing because it places the engine right into the detonation region. The only thing which prevents detonation actually occuring is a power setting (and CHT) that is low enough.

Wet hire encourages full power operation and if somebody tries to be a bit clever and plays with the mixture, they can damage the engine. Whereas if flying at say 65% power (or less) one cannot damage the engine through leaning; one would also have to get the CHTs high and for that they would need to do slow flight (i.e. a climb, or flying on the back of the curve).

[dirkdj]

IO540,

I still assume that most pilots have some respect for the engines. A magneto timing that's too far advanced will give very high CHT's even if the pilot is doing everything by the book.

A few years ago an Australian Navajo lost both engines at night over the sea. Fingers were pointed at the pilot's leaning practices. Luckily there were paper records of the engine parameters at every flight as required. Careful examination of these data pointed to improperly set magneto timing on a new engine. In order to fit the engine in the Navajo nacelle, the magnetos must be canted for installation, they were only retimed after about 100 hours of high CHT operation, by then the cylinders were heat damaged.

A proper monitoring system would have caught these errors on the first flight before any damage was done an lives lost.