pe reivers

So there remains a large margin of uncertainty in failure mode cause analysis. Whether it be normal heat cycling cracking, or cracking due to "shock cooling"
Truely a tester's paradise, or asmall note in the user's maintenance manual

82blackbird

My Feedback: (3)

TOM, I'd be willing to bet that there are more jugs cracked from "shock heating" than "shock cooling". From my own experience the CHT's increase faster in a WOT climb than they decrease in a glide. I converted two 152's to a Sparrow Hawk Conversion and from that day on had little to no engine trouble, used less fuel too.

Kweasel

My Feedback: (29)

The term "shock cooling" came from Continental as the reason for cracks found in their large fuel injected engines. Many think the crack is caused by liquid fuel hitting the intake port (where it starts) when the mixture lever is pushed forward during decent. The term has propagated throughout aviation all the way down to us. Just pulling power and adding airspeed is not enough to lower temperature very rapidly, especially when compared to flying through rain.

pe reivers

Now, THAT is a different box of cookies.
Those cracks initially were due to a too large heat gradient inside the metal. Shock cooling is rapid cooling of a surface that was once hot, then cooled in an instant.. Any quicker than that and it becomes flash cooling, like in use for special aluminum alloys.

victorzamora

Kweasel, that's a good point. Flight that turns into soup would be MUCH quicker to cool your engine than any sort of airflow. Also, it's funny that you mention that about the Continentals. We had a Baron (B55) as well, and those were the quirkiest engines ever. Great power, great noise....but quirks that you had to learn to live with. I don't think we ever suffered from any signs of shock cooling, though.

Sport_Pilot

Also student pilot activity and shock cooling is blamed for the poor length of time of service for cylinders in C-150 and C-152 engines. However I used to belong to an full scale aero club with several older C 172's with the older O-300 engines and they were just as prone to cracking without much student pilot use. I would blame it on the engine design, and on some of the cylinder rebuilds. I am wondering why it takes $13,000 to do a top end overhaul on a C-152. It's been a while but back in the late 80's it cost about $1,000 to replace a cylinder on a C-152 and a lot less on a C-150. But I was doing much of the work myself. Have prices gone up that much?

Sport_Pilot

The technology and quality in aviation engines is dismal. Thanks to the FAA and liability issues. Some of the worst engines made are aircraft engines. Some of the best engines, but not the ones whose names begine with a C.

Super08

My Feedback: (2)

Yup still flying with the same basic engine as 50 or so years ago....