Why does my Rocket have a dent in its exhaust?

[FloridaMan]

[Cody Stallings]

7 minutes ago, Antares said:

I love that Feature on the Rockets.

Nothing is better than pulling up on a ramp an feathering the prop an getting out of the plane.

Then go inside the FBO, an watch all the head scratching.

1) The guys who know what just happened realize that it’s reserved for Twins.

2) The guys who don’t know, think it’s a Turbo-Prop thing, But they could hear the Pistons pounding during cooldown!!

Mysterious!!......lol 

[gsxrpilot]

That's a great picture, even without the cowl and sideways. 

On another note... you can safely eliminate that "cooldown" process. In reality you're just warming it back up.

[wpbarnar]

@R.May   Curious is to the function of the piece that has the three fire sleeved lines on it. Fuel pressure?  I assume it is hanging there due to the cylinder replacement and that is not the normal location.

Bill

[Guest]

11 hours ago, wpbarnar said:

@R.May   Curious is to the function of the piece that has the three fire sleeved lines on it. Fuel pressure?  I assume it is hanging there due to the cylinder replacement and that is not the normal location.

Bill

That’s the wastegate actuator. The small lower line is the vent/drain, the middle is oil supply, the upper one with the cap is the oil return to the controller.

Clarence

[R.May]

-So, there is a bit of aluminum tape around the engine mount to try to protect it a little.  Previous owner did that and I need to get it off for a look.  Don't want corrosion starting under that tape. 

On the "cool down", here is my take:

1. at idle, the exhaust gas is cooler; 2. the oil in the turbo bearing is taking heat away and the heat from inside that was built up is radiating out;  3. ALWAYS, every 100hrs, take the oil return line elbow off the underside of the turbo housing and make sure there are no carbon chips clogging it up.  It happened on mine.  This is the smallest orifice in this line.  I was doing 2-3min cool downs and got lots of chips.  It got clogged...you know what happens from there...  I returned to 5mins and less/no chips.  Flat out, I flew two years doing the 5mins, all was well, then went to the shorter interval for a year and got chips clogging.  Went back to 5mins and all is well.  FYI. (if you ever have turbo problems, Gary Main at Main Turbo is great.  He usually has one or two of these turbos on the shelf.  They are different than the Cessna turbo in that there is a gnats hair of the turbo housing shaved off to allow it to fit within the engine mount structure.)

[gsxrpilot]

15 hours ago, R.May said:

On the "cool down", here is my take:

1. at idle, the exhaust gas is cooler; 2. the oil in the turbo bearing is taking heat away and the heat from inside that was built up is radiating out;  3. ALWAYS, every 100hrs, take the oil return line elbow off the underside of the turbo housing and make sure there are no carbon chips clogging it up.  It happened on mine.  This is the smallest orifice in this line.  I was doing 2-3min cool downs and got lots of chips.  It got clogged...you know what happens from there...  I returned to 5mins and less/no chips.  Flat out, I flew two years doing the 5mins, all was well, then went to the shorter interval for a year and got chips clogging.  Went back to 5mins and all is well.  FYI. (if you ever have turbo problems, Gary Main at Main Turbo is great.  He usually has one or two of these turbos on the shelf.  They are different than the Cessna turbo in that there is a gnats hair of the turbo housing shaved off to allow it to fit within the engine mount structure.)

The guys at APS/GAMI tested the cool down theory with actual data. They drilled and installed temp probes in the housing at the bearings and in the oil. They discovered that the turbo was coolest on landing and rolling out on the runway. The taxi back to the ramp just slowly adds heat back to the turbo. And sitting and "cooling" it down, just actually adds heat as well. It's the oil and the hardware that is important, not the gasses.

I've been rolling up to parking and shutting down immediately for nearly 500 hours and have a whistle clean turbo and no "chips" anywhere to be found.

[R.May]

Nice, thanks for the update on the cooling off process.  I am glad someone properly looked into it.   I will pass this on.

[SpamPilot]

Thanks to everyone who replied on this thread.  I figured I'd provide an update.  Four years and ~400 hours later, there has been no change in the condition of this dent, and no evidence of cracking or leaking.  My A&P is unconcerned about it, so we'll just continue to monitor it.

I suppose one thing going for it is that this is after the turbocharger turbine, so you'd expect temperatures to be a few hundred degrees less than TIT at high power settings.  This would help with respect to both strength and creep resistance of the exhaust pipe material.

[Will.iam]

3 hours ago, SpamPilot said:

Thanks to everyone who replied on this thread.  I figured I'd provide an update.  Four years and ~400 hours later, there has been no change in the condition of this dent, and no evidence of cracking or leaking.  My A&P is unconcerned about it, so we'll just continue to monitor it.

I suppose one thing going for it is that this is after the turbocharger turbine, so you'd expect temperatures to be a few hundred degrees less than TIT at high power settings.  This would help with respect to both strength and creep resistance of the exhaust pipe material.

Thanks for the update. Still have that spaced out hard to read font though.