Re: Good morning new member in Denver
After you land do long taxis so you allow the turbo charger to spin for about 4 mins and allow its rotor and its oil to cool at a reasonable rate rather than suddenly.
The oil could turn to carbon in the tubo if it doesn't keep circulating to cool slowly.
The rotor will not have as much of a problem but the oil will if you don't allow such cool down
Basically, I agree with everything else Sid wrote. But this statement caught my eye, and I wanted to share some recent learning...
I just returned from the Advanced Pilot Seminar "live" course in Ada, OK taught by George Braly, Walter Atkinson, and John Deakin. These guys have what is probably the most sophisticated aircraft engine test facility in the country, and have done many, many thousands of hours of testing with all kinds of engines. Their Advanced Pilot Seminar is kind of a "college-level course" in airplane engine management. It's not inexpensive, at nearly one AMU for the live course, but they offer a full refund if you're not satisfied. Continental (the engine manufacturer) sends 3-4 people through the course every year - they believe in it that strongly.
Specifically, on this "turbo cool-down" discussion, they installed temperature measuring probes in the turbocharger (one each in the oil inlet, oil outlet, and at the bearings for both the compressor and turbine sections) on three different airplanes (IIRC, a turbo-normalized Bonanza, a turbo-Baron, and a Piper twin that uses factory turbocharged engines).
They recorded the temperatures at each of those locations from the time the airplane was landed, all the way through engine shutdown. They measured the results when the followed the "4-minute cool-down" procedure, and when they just taxied in and shut down immediately.
What they found (consistently, across all three airplane types) was that the turbocharger temperatures were lowest during the idle / taxi procedure. During the "cool-down" operation (4 minutes at idle power), turbocharger temperatures actually
increased - by a minimum of 250 degrees F, and a maximum of 400 degrees F.
Without the 4-minute cool-down period, the turbo (and oil) temperatures started out lower (again, between 250-400 degrees F, compared to shutting down after a 4-minute idle period).
Both tests showed that after the engine was shut down, there was a slight rise (around 50 degrees or less) in the turbo bearing temperatures, which they attribute to heat transfer from the turbine itself. But again, the "4-minute idle" temps remained 250-400 degrees F HOTTER than the "shutdown immediately" tests.
The scientific evidence has led them to the conclusion that the recommendation to idle a turbocharged (or turbo-normalized) engine for 4 minutes actually
causes the exact problem it is purported to resolve - increased temperatures of the turbocharger, with the attendant possibility of "coking" of the oil. They currently recommend to all of their customers - they developed the Tornado Alley Turbo STCs for Bonanzas, Barons, and Cirruses (Cirri?) - specifically recommends against doing any sort of "cool-down" period for the turbo. The more recent "factory turbo" Cirrus models, which use a factory-turbo engine, also carry the same recommendation in the POH.
Food for thought...
