Engine Cooling Before Shutdown

Given that Rotax 9's ignition/combustion is optimised for flight rpms I sagest that ground operating rpms should always be kept to a minimum. Your taxi run "at least 1-2 minutes "plus shut down procedures conducted by all careful pilots, probably another 2 minutes and parking, engine inlets into prevailing wind, should be sufficient.

Sean said,

"I sagest that ground operating rpms should always be kept to a minimum. Your taxi run "at least 1-2 minutes "plus shut down procedures conducted by all careful pilots, probably another 2 minutes and parking, engine inlets into prevailing wind, should be sufficient."

I agree with Sean.

Ground taxi and engine shutdown procedures should be plenty.

I agree with Sean and Roger - the taxi to hanger time is plenty of "cool down"...  

I saw a study done by the folks at Tornado Alley Turbos with heavily instrumented engines.  It showed that ground running did NOT cool the engine down at all.  In fact, every engine they tested saw increased heat after ground runs.  Even the turbocharged and turbo-normalized engines saw their turbo oil temps RISE du ring the 1-minute "cool down" stated in the manuals.  I believe Cirrus actually changed their manuals after studying the TAT data.

James N Parker wrote:

I agree with Sean and Roger - the taxi to hanger time is plenty of "cool down"...  

I saw a study done by the folks at Tornado Alley Turbos with heavily instrumented engines.  It showed that ground running did NOT cool the engine down at all.  In fact, every engine they tested saw increased heat after ground runs.  Even the turbocharged and turbo-normalized engines saw their turbo oil temps RISE du ring the 1-minute "cool down" stated in the manuals.  I believe Cirrus actually changed their manuals after studying the TAT data.

For turbo'd engines, the main point isn't a cool down, but a spin down of the turbo before its oil supply gets shut off. Modern turbo cars fix this problem but aviation doesn't get "modern" anything.

In fact, just the opposite.  A turbocharger's rotational speed falls immediately when exhaust gas flow is reduced, due to aerodynamic drag on the compressor; there is no practical need for a spin-down period.  However, there is benefit to maintaining oil flow for some time while at a low power setting (and low exhaust gas flow) to pull heat out of the turbo's bearing assembly.  This prevents oil coking that can occur if oil flow stops while the turbo is still extremely hot.

See the first two pages of this report for an explanation.