Extra 400

Update and more call for advice.
This could have become a major disaster:
The TSIOL 550 C engine is water cooled.
TCM went to great lengths to save weight but sadly this is sometimes at the expense of robustness of the water cooling setup.
A known weakness is the very thin-walled aluminum tubing that carries coolant around. It is vulnerable to chafing, tool impact cracks, etc.

If this gets dinged, it will fail when the pressure differential between inside and outside is maximal.
This would be the top of the climb, where high CHTs combine with low atmospheric pressure.

So we’ve just reached cruise altitude and all of a sudden a jet of coolant puts cooling out of service.
Whatever is not blown out boils away due to low air pressure.
Cylinders are hot and the cooling system is completely INOP in 2-3 minutes, with the mechanical pump running dry, etc…
In the absence of a coolant PRESSURE alert, the engine will likely overheat before the pilot notices anything.

Adding insult to injury, CHT alerts are primary indications, meaning that JPI and co will ONLY program them according to factory instructions – way too high.
So the CHT alert happens long after coolant is gone and damage possibly already done.
The only option is to go to idle, and there goes pressurization too – a double emergency .

I don’t know how many times this happened to others in the air, but fortunately my story is harmless and yet sobering:

When reinstalling the engine, I waited until the A&P team had finished re-assembling and went on a systematic hunt for chafing spots.
I covered all of the EXPOSED aluminum tubing with a thin layer of fiberglass-based chafing protection held in place by tie-wraps to allow inspection once a year.
There was this small segment of tube that was both inaccessible and seemed well protected enough. So I left it alone………

That very segment runs right above the oil pickup from engine to oil radiator.
This area is horribly inaccessible and the mechanics had a difficult time connecting the pair of large (AN10 I think) oil hoses in this cramped environment.
When they were done, the intercooler went in and I could no longer see the damage: three dings to the underside of the aluminum tube.
LOMA Air paint these tubes black, so any scratch is easily visible.

Fortunately, after installing the coolant PRESSURE alerting system ( A gauge and “low pressure” annunciator right in front of the pilot’s nose) I had developed a new preflight step whereby the coolant circuit is “pumped” by hand to 2 bar before startup. The idea is:
1) Check that it keeps pressure
2) Increase coolant boiling T before applying take-off. power. I won’t digress on this here.

So I switched electrical power on, pressurized the coolant circuit to 2 bar and… coolant started running on the hangar floor.
Half an hour of disassembly later, I found the crack. A minuscule scratch to the surface of the tube. You can see two more on this pic, but the leak is the leftmost one.

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It occurred on the ground and is only a nuisance.

Another lesson learned, another set of questions: aluminum tubing is subject to fatigue, cracks develop where the slightest ding happens. Dings just do happen …

Q: what do you think of replacing this tubing with braided AN-hoses? It will be heavier, but not so much (less than 500 grams, I reckon). We already have such hoses in the circuit (from coolant tank to pump and from pump to radiator) so this is not introducing a novelty, just making the existing setup more robust…

Thoughts?

Thanks for replies.

Peter: sadly the primary alert values are not user-editable in the EDM 930.
So I am stuck with a perfectly useless 375F limit for CHT which makes no sense – 300 is high enough to be caused by a major coolant issue…

My egoistic answer is that the combination of coolant pressure and coolant temperature probe (the latter connected to the EDM 930 with a suitable red line (240 F IIRC) give Galatea enough early warning.
I know of only one other E400 that has the coolant T probe connected to an active alerting system (engine monitor).
All others have a simple standalone coolant T display. Not enough in my opinion.
These are at the highest risk and I know of two such stories.

I know this will sound crazy… but I just acquired a second Extra 400. This is a beautiful G-reg sample, serial number 20.
It is difficult to explain WHY I did it, but the mere fact that I double down after 7+ years in this game is a statement.

I just realized that the Extra 400 owners group has over the years attracted a small pool of very competent people that has allowed us to largely take control of what was previously an endless source of technical challenges.

One subgroup is exploring a turboprop project, using a Walter turbine, under N-reg experimental rules.
I am a perfect turbine noob and someone else with lots of knowledge is driving this.
Either N121AG or G-CITW may end up with a long nose and jet-A labels all over.

I also want to start a new thread, with a special request for people with knowledge of turbocharged engines to help explore the fascinating topic of a liquid cooled 400 HP aircraft engine. After these 7 years, I genuinely feel that:

- There is a need for a powerplant of 400-450 HP take-off power with good altitude performance and reasonable weight
- the TSIOL 550 is the closest possible candidate in the “piston” category
- The RR 250 has become too expensive and lacks power at altitude anyway.

Join me there, and let’s have a good discussion. Thanks