Stuck Turbocharger, runs rich?

[Rynoth]

Aerovee Turbo with 1.1 flight hours on it. I have not installed the turbo cooling system yet. Was about to do my 4th flight in the plane today (plane sat 1 week since last flight, and I had idled it 3.5 minutes between touchdown and shutoff) and during the runup the engine only made 26 inches manifold pressure, turning the prop just under 2700RPM, then quit after about 3 seconds at WOT. Initial attempts at restart didn't work, however it did start after cutting the mixture, indicating to me that the engine was flooded. After restart, the engine continued to sputter at high throttle settings which improved when the mixture was leaned.

Basically this post has 2 parts. The first is that I've experienced my first post-first-flight stuck turbo, but I don't want to discuss that too much at this time as I didn't have time at the hangar to troubleshoot it since the engine was now too hot to work on. I'm moving the turbo cooling installation up my priority list.

The second and possibly more important point is that I believe I discovered a new emergency procedure to add to my checklist. That being if a stuck turbocharger were to occur in-flight (resulting in a normally aspirated-engine situation), the carb/Aeroinjector setup is probably running way too rich and a lot of mixture leaning will need to happen to keep the engine running smoothly under NA power. 2700 RPM on the ground with the aggressive pitch of the turbo climb prop is still pretty decent power and I think it would have kept the plane flying in the air, but I think it may be important for other Aerovee Turbo owners to be aware that in this situation the solution to keeping the engine running smoothly to a safe landing may be to lean the mixture.

I'm curious of others thoughts/opinions on this.

[WesRagle]

Hi Ryan,

I have one possibly relevant data point. Years ago, early in phase one of my Sonex I had my idle set too low and my AeroVee died on final. Now, with the AeroInjector, fuel will continue to flow as long as the mixture isn't pulled to the cutoff position. So, by the time I got my wits about me and tried a restart, it was too late. The engine was already flooded. I glided to an uneventful landing.

I guess what I'm trying to say is, turbo charged or not, if the engine dies, fuel continues to flow and the flooding begins immediately.

I had more burp/vapor lock type engine stops while taxiing (before insulating fuel lines and gascolator). I learned that the first thing to do when the engine dies is to pull mixture. Then hit the starter for either five seconds or until the engine fires. Then advance the mixture to full rich. That what worked for a standard AeroVee restart.

With the turbo, I guess it may be a little more complicated as far as how far to advance the mixture.

Best of Luck,

Wes

[Brett]

When the turbo is stuck on takeoff the Sonex with the cruise prop will still climb reasonably well. Stupidly I know this to be a fact.

The turbo won’t seize in flight, only when sitting for a period of time. My experience only.

Once it has seized on you once pull it off, get a kit put it in, costs next to nothing to have his done, add the water cooling before you run the engine again.

I had a Rotec tbi on when this happened to me and it still ran fine. At about 500 ft the turbo freed up and normal power restored...

I was stupid but I also had about 1.5 km of runway still left underneath me when this occurred.

I hope you find this useful.

[MichaelFarley56]

According to the AeroConversions power and torque graphs, a non-turbo AeroVee at 2700 RPM will be producing around 65 hp which should be plenty to keep an airplane in the air for a while, but climb performance isn't going to be stellar.

Personally, I had this happen to my turbo multiple times and each time it led to an aborted takeoff. I agree with Brett; it won't happen in the air, only during startup.

Ryan, I never had any mixture issues even with the stuck turbo. The only way I knew was lack of power; it never seemed to sputter or try to quit on me, but I was running a Rotec Mk. II TBI with the turbo. It's certainly possible that, if your AeroInjector is tuned for the fuel flow needed to run the turbo, you could have a rich situation if/when the turbo locks up.

Good luck getting it back in the air!

[Rynoth]

Thanks for the input guys. It does appear that my turbocharger bearings got fried, I'm able to turn it by finger but there's WAY more resistance then there should be and it still isn't making any boost on a short runup. I've now yanked it off the engine, loaded it up with WD-40 to see if it will loosen up but no joy so far. I went back and checked my flight video and had 3.5 minutes of idle between touchdown and shutdown so that shouldn't have been the problem. Plenty of clean oil drained from the turbo sump and lines when I disconnected them so I don't believe there were any oil delivery issues either.

Time to figure out if the Turbo can be repaired/overhauled (or replaced altogether) and get to work on the liquid cooling system. I had done everything else in the Service Bulletins (Brad Penn oil/filter, turbo oil sump cooler, vents at the top of cowling, new heat shroud, etc) but obviously shouldn't have waited on the radiator setup.

I was a little surprised to find that the turbo cooling system SB is still optional, it seems clear in my case that the turbo was never going to last without it but time will tell once I get everything up and running again.

[Outlaw6]

Ryan,
Kerry sent me this when my turbo stuck. The last paragraph has a link to a procedure to fill turbo bearing with B-12 chemtool and soak for 24 hours, this freed mine up:

Alternate Cause Theory and Optional Service Procedures:
Since the publication of Revision A of this service bulletin, no new turbocharger seizures have occurred in the factory or customer AeroVee Turbo fleet, and Sonex Aircraft has therefore not had an opportunity to analyze a seized turbine shaft “piston ring” type seal for possible rust deposits. Tornado Alley Turbo Inc. service bulletin TAT SI15-02 ( http://www.taturbo.com/TAT%20SI15-02%20 ... turbos.pdf ) and related Continental Motors service bulletin M71-21 ( http://www.tcmlink.com/pdf2/M71-21.pdf ) present a plausible theory regarding the cause of AeroVee Turbo turbine shaft ring seal seizures that is alternate to coked oil deposits as a cause of the seizures. These service bulletins state that rust deposits in low time (under 100 hours) turbochargers are the cause of turbine shaft ring seal seizures that have occurred in the applicable type-certified and STC turbocharger installations. Per the Tornado Alley service bulletin description:

"This condition occurs when the turbocharger is new or newly overhauled and heat and normal operation have not yet formed a protective layer on the internal parts that protects them against oxidation.

During periods of prolonged inactivity (typically several days to weeks, and more frequently in humid weather) these deposits from oxidation may cause a restriction so that on initial engine start up, the turbocharger does not spin up."

All AeroVee Turbo seizures to-date have occurred on turbochargers with less-than 100 hours, and prolonged periods of inactivity are common in VFR recreational aircraft such as the Sonex line of aircraft due to inclement weather and/or personal schedules. Therefore, Sonex Aircraft strongly suspects this alternate cause as a possible major factor in AeroVee Turbo seizures.

The above-referenced service bulletins prescribe troubleshooting remedies involving penetrating oil to free-up seized turbochargers that may be followed by AeroVee Turbo customers.

Note, however, that the Continental Motors service bulletin states:

"Units which are binding after long time service are coked internally and must be removed for cleaning or replacement."

Additionally, turbocharger STC vendor RAM Aircraft publishes an annual solvent flush procedure as preventative maintenance that may be utilized by AeroVee Turbo owners ( http://www.ramaircraft.com/Maintenance- ... -Turbo.htm ). Note that the turbo oil supply and oil drain lines must be disconnected to isolate the turbo from the engine’s oil system during this procedure, and that a thorough mineral spirits flush (may require several ounces of mineral spirits) must be made to remove any loose particles from the turbocharger before reconnection to the engine’s oil system. Sonex Aircraft has used the Berryman B12 Chemtool solvent prescribed in the RAM Aircraft flush procedure to free a seized turbo before return to the turbo manufacturer for overhaul, and found the solvent to be effective.

[Onex107]

I believe Sonex research showed the the Idle cool down time didn't help the problem. The hot side of the turbo is still hot at idle and after the engine is stopped, and the oil stops circulating, it heat soaks the bearing case to over 400 degrees. Even at idle speed the EGT is around 900 degrees. The cooling kit only needs to cool the bearing case after the engine is stopped, for 15 or 20 minutes.