[djschaut]

>>So let's talk about stage cooling a turbocharged engine coming down from up high. Improper stage cooling of a hot (1650 degree TIT) turbocharged engine can easily ruin it, or at least prevent it from going to TBO--or require a top end. What I didn't know was that an engine can be damaged by NOT pushing it to full power on take-off, too. The engine needs full-power on take off to take advantage of the cooling of the rich mixture--though you can easily take off at less than full-power. I used to mistakenly think I was extending my P-Baron's engine life by taking off at less than full power, but the contrary is true. The rule about descents is to decrease manifold pressure about 2mmHg every couple of minutes--or come down gradually (500ft/min) and start the descent earlier. Another way is to 'dirty' up the airplane (gear down, speed brakes), to keep full power as long as possible while enjoying a rapid descent. At high altitudes, I used to turn off the autopilot, pull the nose up to get the indicated airspeed down to gear extending speed (167kts), extend the gear, then push the nose down to the previous airspeed, allowing a nice descent without touching the power settings. You could increase the airspeed after the gear was down and locked. Of course the cardinal sin is to pull the power back and simultaneously push the nose down, open the cowl flaps, and increase the airspeed and supercool the heads. Pulling the power back decreases the generation of heat in the cylinders, while pushing the nose down (esp. with cowl flaps open) increases cooling by air--shock cooling the different metals in the heads and cylinders of the engine, causing unequal contraction and warping. I need an A/P mechanic here. Graphic engine monitors (GEM) are useful to watch for shock cooling. Turbine drivers don't have to worry about this phenomenon--only recip drivers. That's makes it fun, though, to fly a turbocharged recip. It's all about flows, temperatures, speeds, and pressures--all monitored in the cockpit. Shoot, the airplane will fly itself! Navigation these days is cake! The challenge is to preserve the life of the engines and minimize costs at annual. Any other thoughts on supercooling would be welcome. Any suggestions, too.

------------------
DJSchaut