Siezed low-time neglected turbocharger

[lutorm]

It was the exhaust valve rocker on cylinder #4.

Why did it break?

I don’t know for sure, but I believe that cheap VW aero engine kits are made up from cheap aftermarket parts that don’t hold up.

What I can tell you for sure is that it isn’t much fun when your engine stops running. Things get real serious in a hurry and the “advantages” of a “cheap” engine aren’t of much comfort.

Ok, so that's the right side? Not consistent with the oil supply to the left side then.

I don't doubt that you can get shitty parts, but I don't think you have to get shitty parts. People run these engines way harder in cars than we do in the airplanes. Maybe the Aerovee isn't there yet, maybe there are parts that need to be changed or there are things that need to be added to the instructions. But I agree that's not much comfort when it goes out on you.

[Gordon]

The Turbo fiasco.........

Brett.........I agree with your comments, this is the wrong turbo setup for this application.

With the right turbo and proper installation they will run a very long time. My back ground is a "long haul" truck driver for over 40 years. We could easily get 500,000 or more miles out of a turbo on a Cummins, Cat or Detroit Diesel. I only ever had ONE actually fail on the highway in all those years.

Maybe Sonex didn't do quite enough research and development.

Gordon......Onex......Hummel 2400

[Onex107]

What great conversations about the turbo problem. i think we all agree that it can be fixed. The question is how. I would suggest the first thing necessary is to get some good numbers. If I had one on my Onex the first thing I would do is move a cht probe to the turbo housing and record temps. We don't have to lower the housing temp to room temp, just below the critical temp of the oil which must be several hundred degrees. With the engine stopped and no egt input the small turbo casting would change pretty fast. Let's get some numbers and then continue on. For instance. No one suggested squirting water on it. Think outside the box.

[Brett]

If I’m not mistaken, the factory has done temp recordings inside the cowl and so on already in various locations during flight and after shutdown. One would assume they have carried out direct temp readings on the turbo also.

Is this part of the average homebuilders job btw? How many RV builders have to do this? It’s sadly very clear to me I’ve bought the wrong engine package for a second time. I wanted to build and fly not carry out a second apprenticeship as an aircraft engine mechanic.

In the interest of playing the game I’ll add a spark plug type CHT sensor I have lying around to the water jacket thread and give in flight, and post shut down readings, in the last few flights I get before it seizes up again.

[lutorm]

One thing worth noting is that the Rotax 914 uses a turbo cooled by oil only, even though it has an existing water cooling system, so it must be possible to avoid coking the oil even without water. Perhaps it's the installation, perhaps the turbo?

It's not trivial to find turbos that are small enough for a 100hp application. The turbo appears to run 5psi boost (10" Hg) which is a pressure ratio of 1.3, and 100hp gives an airflow of 10lb/min. If you look at even the smallest aftermarket turbos from Borg-Warner (S1BG) and Garrett (GT2052), that's below the efficiency range of the compressors. The smallest S1BG compressor might be reasonable, but they don't have an efficiency graph for it in their catalog.

I believe in the Aerovee Turbo webinar Jeremy Monnett said the turbo was from a diesel truck. I'm not aware of any trucks that make anywhere around 100hp, so that didn't give me a very good feeling for how well matched the turbo is to the application. Can anyone of you guys that have the turbo find a model number?

[Brett]

The factory grinds the numbers off the turbo for that exact reason before you receive them.
I’d like to rebuild mine in Australia this time as the price to rebuild it will be less than the postage to the US but without the numbers I’m afraid this may not be possible.

[NWade]

It's not trivial to find turbos that are small enough for a 100hp application. The turbo appears to run 5psi boost (10" Hg) which is a pressure ratio of 1.3, and 100hp gives an airflow of 10lb/min. If you look at even the smallest aftermarket turbos from Borg-Warner (S1BG) and Garrett (GT2052), that's below the efficiency range of the compressors. The smallest S1BG compressor might be reasonable, but they don't have an efficiency graph for it in their catalog.

Something to keep in mind (which you may or may not have accounted for): An automotive turbo is going to be put under very different loads and stresses than in an aircraft...
First, just like an automotive conversion engine, a turbo designed for a car is expecting some heavy acceleration followed by periods of cruising at low throttle (i.e. low boost); that's not how it will be operated in an airplane - our high throttle periods (i.e. takeoff and climb) last a lot longer than a normal 0-60mph acceleration in a car, and even at a mid-throttle cruise setting the turbo will be developing some boost pressure.
Second, the AeroVee turns pretty slowly compared to modern automobile engines; so the volume and pressure of the exhaust gasses through the turbo is probably quite a bit different in our airplanes than what was expected by the turbo's designers.

--Noel

[wlarson861]

This is the rebuild kit I put in: https://www.ebay.com/itm/Turbo-Rebuild- ... lg&vxp=mtr
it is a Garrett gt2554.

[Brett]

Thanks Bill. I've recorded that item on my watch list.

Btw how many have you put in?

I thought they were ball bearing turbos supplied? Journel bearings in the rebuild kit?

[marsolgp]

To those interested about temperatures: I got these numbers back in Sept '16 and shared them with a fellow Waiex'r at the time. Note the temps rise AFTER engine shutdown.


Thought you would be interested in this..... I went ahead and installed a k-type thermocouple to the turbo center section (using a steel plug into the water cooling inlet and tapped for a screw to hold the thermocouple), and went flying....

On T/O I saw ------------------------200°F
Start of cruise 35" MAP-------------235°F-------------CHT's 340-350
Cruise 34" MAP----------------------250°F
Cruise 30" MAP----------------------270°F

It slowly heats up regardless of MAP... more a function of Turbine Inlet Temp (TIT)

It stabilized at about 273° with 1260°F TIT

After landing and 3 minute cool down (Which I don't think helps anything) It was shutdown showing 258°F......

Then it started to RISE.

3 min later -------------------------305°F
5 min later--------------------------332°F
7 min later--------------------------343°F--- This also the temps for CHT matched, but they were on their way DOWN.
8 min later--------------------------347°F
12 min later-------------------------348°F
14 minutes and it stopped going up... by 18 minutes it finally started to go down.

I really can't believe the factory didn't do this during their testing, I think we all had an idea these things were getting hotter and heat soaking the inside of the cowling.

That's it for now,

Geary