Originally Posted by
Lead Balloon
So for the aircraft that don’t have EDMs, how do you know where on the lean curve each cylinder happens to be when leaning is by reference to a single probe? If we assume that LOP operations are not only “not approved” but “unsafe”, how do you know that each cylinder is peak or rich of peak far enough? Do the laws of physics and safety only apply to the cylinder with the probe?
You say that the mixture with the smallest detonation margins at any given power setting is peak EGT. Are you sure about that?
You don’t know precisely where each cylinder is. The assumption is that the leanest cylinder is within 25F of the indicated EGT when using the thermocouple on the collecter. The recommended best power setting for the engine is 50ROP so that is where our minimum 75ROP comes from.
Even the aircraft in our fleet with EDMs cannot be relied upon because the environment is too harsh, hot and high, dusty and corrosive. These aircraft are doing 100 hours a month, 10 or 12 starts a day and it isn’t long before one or other probe plays up. One day it is an aircraft with an EDM, the next it is an unreliable EDM, the next it’s no EDM. We cannot afford our aircraft to go in for a 50hour check and get stuck for a week waiting for a thermocouple or harness. We have to have them back online. There are enough other snags to sort out such as the brakes, starter motors, alternators and radios. However, the alcor type EGT installation is robust so our SOP is based on it. That is the real world for us.
Yes, I am sure that the minimum detonation margin for a given power is at peak EGT or at least very close. I am sure because the extensive research published on detonation says so.