leaning/enriching on descent - M20J

[Shadrach]

3 hours ago, Mac80 said:

This fellow and his son were both pilots and his son still work on planes, not mine I trust the other FBO mechanics manager. The other one I trust likes 50 degree rich of peak. I have no idea what caused the deformed piston but it scared the heck out of me. 

I do not want to get into lean of peak vs rich of peak debate. If “I try to keep cylinder and oil temps up and descend slowly but always try to keep the mixture on rich side while descending.” is incorrect help me understand. If I let it go without enriching in the descent then the engine stumbles so I enrich the mixture till it stops.

I am not defending him like I said  I use the other guys. So are you explaining that the mechanic/pilot was incorrect and running to lean and resulting overheating was not probable cause of the loss of the cylinder as he was illustrating to group?

Can you explain how you monitor you exhaust temperature in descent if slightly enriching is incorrect?

Thanks

Steve

 

 

 

 

 

 

There was no deformed piston according to the report

Postaccident examination of the airframe and engine did not reveal any evidence of preimpact mechanical anomalies that would have precluded normal operation, and the engine achieved full and continuous power during a test run. 
I

I can’t speak to what his pilot was doing. Very little of it follows logic. He clearly was challenged by a number of factors. What an odd accident.

 

[PT20J]

1 hour ago, EricJ said:

all of these things about how to run reciprocating aircraft engines in various mixture regimes has been known for a long, long time.

For those that like to read technical history, and understand just how much was known about the effects of mixture on aircraft engine operation 80+ years ago, check out NACA Technical Note 772, August 1940. It's available on the NASA Technical Reports Server https://ntrs.nasa.gov/.

John Schwaner, former owner of the Sacramento Sky Ranch, told me he once got a wash tub, filled it with dry ice and acetone and dropped in a cylinder head from an IO 550 which he had heated with a torch to just below the melting point. He said it put on quite a show, but did not crack. I think the head cracking problem (which was often attributed -- without offering any proof as the news folks say -- to shock cooling) mostly went away when Lycoming and Continental started offering new cylinders to rebuilders for prices competitive with overhauled cylinders. Aluminum wears out, and after two or three (or more) TBO runs, fatigue cracks begin to show up.

 

[EricJ]

48 minutes ago, PT20J said:

For those that like to read technical history, and understand just how much was known about the effects of mixture on aircraft engine operation 80+ years ago, check out NACA Technical Note 772, August 1940. It's available on the NASA Technical Reports Server https://ntrs.nasa.gov/.

John Schwaner, former owner of the Sacramento Sky Ranch, told me he once got a wash tub, filled it with dry ice and acetone and dropped in a cylinder head from an IO 550 which he had heated with a torch to just below the melting point. He said it put on quite a show, but did not crack. I think the head cracking problem (which was often attributed -- without offering any proof as the news folks say -- to shock cooling) mostly went away when Lycoming and Continental started offering new cylinders to rebuilders for prices competitive with overhauled cylinders. Aluminum wears out, and after two or three (or more) TBO runs, fatigue cracks begin to show up.

When I was a lineboy in the 70s overseas we ran 115/145 fuel because that was all that was available to us from the Army, because the civilian stuff cost about 10x as much.   An Air Force flying club not too far away that we visited from time to time also ran the same fuel for the same reason, and they kept complaining because they were getting cracked heads a lot and were blaming it on the fuel.   I, an annoying teenager, pointed out that we ran the same fuel and had no cracking problems, nor did several of the other military flying clubs in the region that all burned the same fuel.   I received some stern glares.

Much later I realized that their mechanic was probably over-torqueing their spark plugs, which can also cause the commonly seen crack between the plug and exhaust  port.

Any hints on search terms for that document?   I can't seem to get the bot to find it.   Edit:  nm-found it.

Gerrish, Harold C Voss, Fred, Analysis of cylinder-pressure-indicator diagrams showing effects of mixture strength and spark timing, NACA TN-772, August 1940

 

 

[Pinecone]

14 hours ago, PT20J said:

For those that like to read technical history, and understand just how much was known about the effects of mixture on aircraft engine operation 80+ years ago, check out NACA Technical Note 772, August 1940. It's available on the NASA Technical Reports Server https://ntrs.nasa.gov/.

John Schwaner, former owner of the Sacramento Sky Ranch, told me he once got a wash tub, filled it with dry ice and acetone and dropped in a cylinder head from an IO 550 which he had heated with a torch to just below the melting point. He said it put on quite a show, but did not crack. I think the head cracking problem (which was often attributed -- without offering any proof as the news folks say -- to shock cooling) mostly went away when Lycoming and Continental started offering new cylinders to rebuilders for prices competitive with overhauled cylinders. Aluminum wears out, and after two or three (or more) TBO runs, fatigue cracks begin to show up.

 

Think of the cooling when you fly into rain.

[A64Pilot]

On 2/22/2024 at 8:21 AM, Pinecone said:

Think of the cooling when you fly into rain.

It’s not as much as you might think, I know it surprised me too, but watch Cyl head temp, if there is a lot of cooling the temps will drop drastically, one would suppose especially the front two, but they don’t, there is no drastic drop even with the front two.