Overboost

[Chris Strube]

1965 M20E with Rajay turbo

I screwed up, as follows.  It's getting harder to get into and out of our Mooney.   As my hips don't bend as they should, I push all the controls in to give myself more room.  I forgot to pull out the turbocharger control, and departed with an overboost.  What are my options now?

[65eTurbo]

37 minutes ago, Chris Strube said:

1965 M20E with Rajay turbo

I screwed up, as follows.  It's getting harder to get into and out of our Mooney.   As my hips don't bend as they should, I push all the controls in to give myself more room.  I forgot to pull out the turbocharger control, and departed with an overboost.  What are my options now?

Yipes!

I believe you just asked, hypothetically, what would happen if you departed with an over boost.  Might want to check if you mis edited that.

If I had an overboost, I'd want to download a log to see what happened.  

If an overboost doesn't cause detonation that damages the piston or rings, I'd have a hard time imagining the marginal incremental mechanical stress would cause a failure at any point in the future.  

In the event of an over boost, I'd say a review of the data of the event, a careful borescope of all cylinders, careful test and inspection of all plugs, an oil change and filter examination, and a flight with careful examination of the pre and post overboost engine monitor logs would be the order of the day.

Thanks for the warning about scary potential hypotheticals.  I'll be careful with my pre takeoff checklist.  Maybe that pop off valve I was thinking of is still in order.

Edited August 26, 2019 by 65eTurbo

[Yetti]

How much seems to be the thing.  The plugs tell the story.  Pop off valves are a good thing.

https://www.lycoming.com/sites/default/files/Engine Inspection after Overboost.pdf

[orionflt]

how much overboost ,IE how many inches did it overboost. could be a log entry, could be a teardown with all rotating parts replaced.

Brian

 

[N201MKTurbo]

If you didn’t hear any detonation and you didn’t over temp the cylinders, you are probably fine.

[N201MKTurbo]

I knew a guy once with a Twinkie with RayJays. He called that “Emergency Power”

[N201MKTurbo]

The document referenced above is for factory turbocharged engines. It doesn’t necessarily correlate to the RaJay turbonormalized engine.

[65eTurbo]

2 hours ago, N201MKTurbo said:

If you didn’t hear any detonation and you didn’t over temp the cylinders, you are probably fine.

 I can't give you a source on this, but I recall hearing somewhere that detonation isn't really audible in our engines at high power here in that said, if there is no evidence of detonation on the plugs or the pistons or ring or valves and the compression or engine performance, and no Regulatory requirement, I wouldn't sweat it. I agree it depends on the magnitude of the over boost.   The detonation margin on these engines run as rich as they are for take off is likely pretty substantial to account for a worst case scenario. I'm curious how high  A manifold  Pressure our Turbo normalized engines are capable of on take off. I bet the acceleration was compelling.

[ArtVandelay]

Engine monitor would tell you if you had a combustion event, no? No high cylinder temperatures, no detonation.

 

Tom

 

[N201MKTurbo]

2 minutes ago, 65eTurbo said:

 I can't give you a source on this, but I recall hearing somewhere that detonation isn't really audible in our engines at high power here in that said, if there is no evidence of detonation on the plugs or the pistons or ring or valves and the compression or engine performance, and no Regulatory requirement, I wouldn't sweat it. I agree it depends on the magnitude of the over boost.   The detonation margin on these engines run as rich as they are for take off is likely pretty substantial to account for a worst case scenario. I'm curious how high  A manifold  Pressure our Turbo normalized engines are capable of on take off. I bet the acceleration was compelling.

I was playing with power settings one day to see where I got the best economy. At about 2100 RPM and 30 inches, I heard "Ting.....Ting...." It was very noticeable. I immediately pulled the throttle and went to a normal power setting.

I went home and pulled all the plugs, bore scoped all the cylinders and did a compression check. All looked normal. 

[orionflt]

2 hours ago, N201MKTurbo said:

The document referenced above is for factory turbocharged engines. It doesn’t necessarily correlate to the RaJay turbonormalized engine.

that document is based on the design pressure the  engine can handle and the turbo normalized engines were designed for normal atmospheric pressure, not turbo charged pressures. the margins that are applied to the turbo'd engines still apply.  there is the natural concern for damage to the cylinders and valves, but if the pressure was high enough the concern is more the stress being put on the rotating parts of the engine.

your friend who used it as "emergency power" was not doing himself or anyone else any favors, doing that over a period of time will lead to an engine failure. hopefully not during a critical phase of flight with passengers.

I recently did a prebuy on a twin Comanche where I had to tell the owner both his engines were potentially scrap for the same thing. he over boosted both engines to over 40" as recorded on the engine monitor.  

Brian

[MIm20c]

Mine will hold 27 inches easily at 15k.  My guess is the MP could have really spiked. No advice to give other than a year or so ago someone put a picture of a parked rayjay that had the knob all the way in, it made me sick to my stomach. 

[Chris Strube]

Acceleration was spectacular, and the climb rate was about 2400 fpm.  Manifold pressure gauge was topped at 35 inches for about 10 seconds, until I realised what was happening.  After talking with a Mooney expert, I'm going to check the intake tube o-rings, and the cylinder base gaskets, as well as bore-scope the valves.  It won't run smoothly LOP now, so I'm sure that I now have an intake leak.  Prior to this, it ran smoothly at 100 LOP.

[MIm20c]

The gauge limit was 35 or the system went to 35?

[N201MKTurbo]

2 hours ago, orionflt said:

that document is based on the design pressure the  engine can handle and the turbo normalized engines were designed for normal atmospheric pressure, not turbo charged pressures. the margins that are applied to the turbo'd engines still apply.  there is the natural concern for damage to the cylinders and valves, but if the pressure was high enough the concern is more the stress being put on the rotating parts of the engine.

your friend who used it as "emergency power" was not doing himself or anyone else any favors, doing that over a period of time will lead to an engine failure. hopefully not during a critical phase of flight with passengers.

I recently did a prebuy on a twin Comanche where I had to tell the owner both his engines were potentially scrap for the same thing. he over boosted both engines to over 40" as recorded on the engine monitor.  

Brian

Its OK, He is in prison for pushing his wife out of the plane over the ocean. He wasn't my friend, he was a friend of my ex airplane partner. He calls him the murder'n doctor.

That being said, The correlation is probably upside down. An engine that is rated for 40 inches, that goes 10 inches over is probably like a TN airplane going 7.5 inches over. 

I would think cracked cases would be the first failure.

https://murderpedia.org/male.B/b/bierenbaum-robert.htm

 

Edited August 27, 2019 by N201MKTurbo

[N201MKTurbo]

Does the RaJay system have a popoff valve? It should...

Mine has a pressure controller (fancy popoff valve) that limits the MP to 32. 

If you don't have a popoff valve, be very careful about rapidly closing the throttle. The turbo has inertia and will seriously overstress the compressor if the throttle is closed rapidly.

[Bolter]

7 minutes ago, N201MKTurbo said:

If you don't have a popoff valve, be very careful about rapidly closing the throttle. The turbo has inertia and will seriously overstress the compressor if the throttle is closed rapidly.

Do you mean surging the compressor?  Or is there another effect from rapid throttle closure?

[65eTurbo]

3 hours ago, N201MKTurbo said:

I was playing with power settings one day to see where I got the best economy. At about 2100 RPM and 30 inches, I heard "Ting.....Ting...." It was very noticeable. I immediately pulled the throttle and went to a normal power setting.

I went home and pulled all the plugs, bore scoped all the cylinders and did a compression check. All looked normal. 

Interesting.  If you've ever heard detonation on a super/turbocharged liquid cooled auto engine at full power it sounds like a machine gun. A distinct rat-tat-tat.  A light load overadvanced engine will make the ping ping sound.  Always was worried when fiddling with my engine power settings, even within limits, that I wouldn't hear anything.  I used to like 2400 RPM 27 inches 8 to 9ish gph (well lean of 30 lop, but hard to tell because of the linkage between fuel flow and boost pressure and EGT) at 17,500 as my econ cruise.

 

[N201MKTurbo]

4 minutes ago, Dan at S43 said:

Do you mean surging the compressor?  Or is there another effect from rapid throttle closure?

When you close the throttle, it blocks the airflow from the compressor side of the turbo. The engine doesn't instantly stop making power, so there is still exhaust to drive the turbine plus the turbine and compressor wheels have inertia. This situation can build up a very high pressure between the compressor and the throttle. This is very hard on the turbo. That's why the popoff valve is put there, to relieve that pressure spike when the throttle is closed. It also serves as a safety valve for over boost, but that's not their primary function.

https://en.wikipedia.org/wiki/Blowoff_valve

 

[65eTurbo]

31 minutes ago, N201MKTurbo said:

Does the RaJay system have a popoff valve? It should...

Mine has a pressure controller (fancy popoff valve) that limits the MP to 32. 

If you don't have a popoff valve, be very careful about rapidly closing the throttle. The turbo has inertia and will seriously overstress the compressor if the throttle is closed rapidly.

No, but I've seen them retrofitted to the turbo to flapper-box tube as an emergency relief.  I really liked the M20 Turbos setup with the 30 inch popoff after the intercooler.  Simple and elegant, and no wastegate manual valve needed.

 

[65eTurbo]

2 hours ago, Chris Strube said:

Acceleration was spectacular, and the climb rate was about 2400 fpm.  Manifold pressure gauge was topped at 35 inches for about 10 seconds, until I realised what was happening.  After talking with a Mooney expert, I'm going to check the intake tube o-rings, and the cylinder base gaskets, as well as bore-scope the valves.  It won't run smoothly LOP now, so I'm sure that I now have an intake leak.  Prior to this, it ran smoothly at 100 LOP.

Sounds good.  I'd look at the edges of the piston crowns and the cylinder walls for scoring from a broken ring.  

[N201MKTurbo]

Just now, 65eTurbo said:

No, but I've seen them retrofitted to the turbo to flapper-box tube as an emergency relief.  I really liked the M20 Turbos setup with the 30 inch popoff after the intercooler.  Simple and elegant, and no wastegate manual valve needed.

 

If you installed that valve, and pushed your knob most of the way in you would pretty much have my setup. It only takes a couple of hoses and hose clamps. You could probably get a field approval easily, using the approved data from the M20Turbos STC.

[MIm20c]

1 hour ago, N201MKTurbo said:

Does the RaJay system have a popoff valve? It should...

Mine has a pressure controller (fancy popoff valve) that limits the MP to 32. 

If you don't have a popoff valve, be very careful about rapidly closing the throttle. The turbo has inertia and will seriously overstress the compressor if the throttle is closed rapidly.

Not sure about the OP’s setup but mine does not have a pop off valve.  Turbo engagement and usage is limited to full throttle operation. 

[N201MKTurbo]

27 minutes ago, MIm20c said:

Not sure about the OP’s setup but mine does not have a pop off valve.  Turbo engagement and usage is limited to full throttle operation. 

In a perfect world.....

[65eTurbo]

1 hour ago, N201MKTurbo said:

If you installed that valve, and pushed your knob most of the way in you would pretty much have my setup. It only takes a couple of hoses and hose clamps. You could probably get a field approval easily, using the approved data from the M20Turbos STC.

I've got copies of a field approval doc that could work. The M20Turbos wouldn't, since it has an intercooler, or at least I wouldn't sign it off if I were an IA or DER.  However, as a safety backup, it really doesn't have a downside.  Used for boost control, you could wind up with higher than expected intake temperatures or something if the wastegate was closed but the extra air was blowing off to maintain 30 inches.