"I'm a reformed shock cooling worrier"

Is shock cooling myth or reality? Can you run lean of peak with a carbureted engine? These questions and many more come at Mike, Paul, and Colleen in this month's episode. Send your questions to [email protected]

Full notes below:

Jerry has an RV-4 with a new battery but the original alternator. When he starts the engine and then turns on the alternator, he sees a big amperage spike. He tested turning on his alternator before starting, and sees the same spike. That piece of information is critical because according to the hosts it means it must be an instrument indication. Without the engine operating and the alternator not turning, it can’t possibly be producing current.

Ken has a Mooney M20 and thinks the inside of the tail section is messy and ugly. He’s looking for a way to clean it out. A vacuum won’t work because the flakes are sticky. Paul suggests that because it’s sticky someone has sprayed a corrosion inhibitor and only hand scrubbing will get it completely clean. Once it’s clean, he suggests spraying in a thin coating of Cor-Ban (https://zipchem.com) or Ardrox AV8.

Dave flies a 1946 Cessna 140 and a Hatz biplane with a carbureted engine. He wants to know how to fly lean of peak. Mike says that Lycoming engines are pretty symmetrical out of the factory, which means they are often ok to run lean of peak from the factory. Continentals are less so. The rear cylinders tend to run leaner and front cylinders tend to run richer. By reducing the droplet size you can better dial it in. Do this by using a little bit of carb heat to better atomize the fuel. The other method is to back the throttle off a little bit to make the airflow through the carb more turbulent. Without instruments to help, the technique is to lean aggressively until the engine stumbles and then enrichen only until the engine runs smoothly again.

Steve is wondering about unleaded fuels in development. He wants to know if the hosts would hesitate to use any of these new fuels in their airplanes. And also if their operating procedures will change as a result. Mike, Paul, and Colleen say they would have no hesitation running one of the fuels once it’s approved. They also don’t expect any operating changes.

Guest Mike wonders why the hosts don’t ever talk about leaning in a descent. Host Mike stresses that although power changes should happen somewhat slowly, it's not as slow as he used to think. Lycoming recommends limiting cooling to no more than 60 degrees per minute, and Mike has an alarm set on his engine monitor for 30 degrees per minute. The only time it ever goes off if he’s doing an “extreme slam dunk.” Colleen makes the point that aerobatic pilots often oscillate between full idle power.

Hannah flies a Super Decathlon and wants to make sure she takes care of it while doing aerobatics. Colleen says to keep it under 6Gs and a close eye on the engine mounts because they are the flexible attach point between the engine and the airframe. Although Hannah was originally asking about general tips, the hosts find out that she has experienced a governor failure that spewed out almost all her oil. Mike asks about rpm overspeed and Hannah said she noticed that used to happen before the governor failed. She’s also seen a drop in oil pressure in the dive. If her inverted system isn’t working well it would starve the governor of oil.