Closing the throttle in flight - nicely (shock cooling)

Diamond had loads of problems with the coolant system in the early days. I once spoke to a Thielert guy at some show and he blamed Diamond for a bad installation design on the DA40, with the DA42 having fewer issues.

Sure these things can be fixed over time but one can also understand why GA pilots are conservative. In the main market – the US – the ability to do field repairs/overhauls is rightly seen as very valuable, since it prevents Lyco/Conti adopting obvious anticompetitive practices and screwing everybody with e.g. what might be a $50k factory overhaul on an IO540. Here in Europe, we are already pretty well screwed with poor choice of shops, the need for an EASA-1 with almost everything, so people are more accepting of exploitative practices. But also I think the vast majority of diesels have gone to flying schools for whom reliability is not an issue provided (a) Diamond pay for it and (b) they don’t get excessive downtime. The early Thielert issues nearly killed some FTOs, with e.g. 75% of the fleet grounded. In the US market, that player would be history, for ever.

Diesels do come with their issues, and liquid cooling is one of them. Thielert/Continental’s main market is now for UAVs, maintained by the military which wants single fuel at any cost. In the civilian world, owned and maintained by me, my carbureted O-320 is simple, easy to work on and reliable. Cracked cylinders are not an issue. Two-thirds of my fairly capable motorcycle collection is also air cooled and while variety is the spice of life, in many ways I’d prefer it to be all of them.

It is nice to be able to have this discussion.
So 6 cylinders are sensitive to shock cooling, but not everyone agrees.
How should stalls and engine failures be trained then ? I doubt cutting power in 1 or 3 seconds makes much of a difference, but I could be wrong.

What you write is interesting Silvaire. I thought german companies could barely export anything which could be used for a slightly lethal application. Good to know.

How should stalls and engine failures be trained then ?

You just reduce power to get CHTs down to say 320F, or less, which takes a few mins at most, and then tell the examiner you are ready for the engine failure That’s what I always do.

I think the reason an IO540 will crack cylinders much more easily than say an O200 is because the CHTs are higher. It can’t be anything else, because the cylinders are basically the same. Certainly a Lyco 360 has the same cylinders as the 540. If you look at a typical O200 installation, you could hide a couple of refugees in there while in a typical IO540/550 installation you can barely get an arm in, especially with some like a Bonanza where you can barely get a spanner in between the parts.

Jujupilote wrote:

So 6 cylinders are sensitive to shock cooling, but not everyone agrees.

It’s more like “6 cylinders are NOT sensitive to shock cooling, but not everyone agrees” :-)

Diesels do come with their issues, and liquid cooling is one of them.

Indeed there has been a steep learning curve for Diamond using the Thielert design, but that seems to be history now. Conti’s (Thielert) second and third generation engines seems to have ironed out the issues, and the Austro engine seems bullit proof too. Maintenance costs have dropped quite a bit owing to increased intervals for exchange of components. The only nuisance that I had during the 10 years of operating two of them were ECU failure warnings which turned out to be spurious sensor signals that were momentarily out of limits (and just required an ECU-reset). Maybe Diesel flyers like @emir can chime in whether these problems still exist or not.

As to liquid cooling, not sure there is an issue. AFAIR, in the DA42 prototype stage the cooling inlets/outlets were too small and were sized up, causing an impressive decrease in the originally claimed cruise speed. But on production aircraft I can only think of one problem with liquid cooling: The temp gauges never move in flight, whatever the OAT or power setting, which makes it all a little boring

1. I am in sympathy with Pilot_DAR.

2. There does not seem to be anybody here who has flown an aircraft with a Lyc 320 or 360 with a 4×CHT engine monitor with downloadable temp data.
Hence the guessing going on.
These engines are suffering a lot of temp/cooling abuse in the training environment. Such engines will take a lot of abuse before experiencing cylinder cracks but an engine monitor will put an end to all that abuse when the facts are stirring one in the face as an owner pilot.

Stanley wrote:

There does not seem to be anybody here who has flown an aircraft with a Lyc 320 or 360 with a 4×CHT engine monitor with downloadable temp data. Hence the guessing going on.

Outside of developing cowlings (e.g. for new experimental aircraft development) nobody actually needs that data on those engines. That’s why they don’t have it. As far as I remember I have never changed any engine control setting on my carbureted O-320 in response to reaching any engine operating limit, nor experienced any engine reliability issue related to temperature of any engine part. The current cooling system design has zero moving parts and the only thing that might arguably be improved by changing the thermal management design is the elimination of 1 quart per 12 hrs oil consumption on an engine that hasn’t been apart since 1971. It could also be done more simply and better by developing air cooled, hard coated aluminum cylinders as per motorcycle practice.

Along those lines, it occurs to me that the IO-320 equipped Twin Comanche is a good performing 320 HP aircraft with both simple engines and no cylinder problems. Also the Wing Derringer

Malibuflyer wrote:

Therefore if shock-cooling is a proble, shock-heating is the same problem in the same temperature range.

If closing the throttle faster than 2‘‘-MAP/min is a problem, opening the throttle faster than that is the same problem.

Unfortunately at my field the runnway is not long enough, that I can do the takeoff-run by opening the throttle only 2‘‘/min ;-) Therefore if shock-cooling or heating was a problem, my engine is doomed to fail anyways.

You are wrong sir. :)

You have aluminium heads on the steel barrels.
Aluminium expands faster than steel (it’s lighter). During heating there will be no such stress as the head expands over the barrel but during cooling the head will shrink onto steel barrel and create some stress which could create cracks when too strong.
Lycoming recommends to stay below 50deg F per minute of cooldown.
Of course the hotter the engine is (more than 380-400F) – more sensitive to fast cooling it will be. Alloys are much weaker when very hot.
I personally think that shock cooling problem exists when engines are over 330-350F. Not so much when less than that.