"Keep torturing those airplanes...and students"

John is a maintenance officer in a club, and he is wondering about tire ply ratings. The manual calls for 4 ply, but they often install 6 ply and he’s wondering if that’s ok. The hosts all agree that they have subbed in higher ply ratings when supply dictates. Paul’s rule of thumb is that he always allows a higher ply, but not lower. That’s because the ply rating relates to the weight of the aircraft. Heavier aircraft need higher ply ratings. They get into a discussion on retreads, which can cause issues. They like retreads, but caution that you must ensure they will fit in the wheel well on a retract. Paul worked on a 210 once that caught the skins when retracted.   Doug instructs in Aerostars, and he has worked with a number of clients lately who want him to omit the engine-out portion of the training in order to avoid stress on the engines. There’s talk in the Aerostar community about heavy and light cases. Mike said not to worry about the case. Rather, cylinders that rapidly cool are the concern and that’s because the piston and cylinder are different metal densities and cool at different rates, which can lead to scuffing. They all agree the training is important, but pulling the power back slowly, rather than cutting the fuel, will help reduce the risk of engine damage. Paul makes the point that flight schools do this in Seminoles all day, and that he doesn’t hear of widespread issues. Failure isn’t a concern, Mike said. Scuffing is a wear issue. If it’s an issue, Paul said his pistons probably look terrible, but he’s not going to worry about it. He already borescopes regularly. And Mike said he will run an aux tank dry on a long flight.   Jason has a Comanche 250 with some electrical issues. Throughout the flight the bus voltage will come down. After landing and taxiing in the voltage climbs back up, and rests around 13.8. Recently after takeoff, the low voltage alarm flashed and went to 10.8 while raising the gear. The hosts think it’s a voltage regulator issue, where it works when cold but not warm. Paul said he thinks of voltage as an indicator of whether the system is working and the amps as an indicator of how hard it’s working. It should be around 13.8 or 14 when working properly. Colleen said she had an electrical issue where her JPI would go offline when she would cycle the gear. Under the panel she found that there was a loose connection on the shunt, causing high resistance. Jason’s issue could be at the circuit breakers, voltage bus, voltage regulator, or any number of places. One way to easily troubleshoot is to see if he can find anything hot by running his hands along the wires. Or look for discoloration, Paul said.   Steve writes in asking about oil coolers. During his recent engine overhaul the shop asked if he wanted a congealing or non-congealing oil cooler. Congealing is bad, he thought, so he elected to go with non-congealing. But he lives in Arizona and he’s found the engine runs a bit hotter with a higher oil temperature in long climbs. He’s wondering if he made a mistake. Non-congealing oil coolers have a solid line running through the middle that passes warm oil through the cooler at all times. Mike thinks it’s possible the non-congealing has less cooling capacity because it has less surface area.