109 prop pitch (rpm) and the supercharger

[NZtyphoon]

Originally Posted by Crumpp

At high altitudes, the airplane is essentially in slow flight for most of the envelope. That makes cooling harder and overboost conditions will heat the motor up faster.

If they wanted to use a limited overboost condition, they would be constantly changing rpm between maximum continious and higher limited overboost to cool the motor.

Interesting how this only now becomes a measure to cool the hydraulic supercharger, according to our resident aviation expert; still it is correct that the hydraulic coupling of the DB supercharger led to problems with overheating that the pilots needed to control by constantly altering rpm - not maintaining it.

Originally Posted by Crumpp

A complete sidetrack as to how they are using the propeller and rpm to gain speed.

Wrong; the pilots were needing to adjust rpm and pitch constantly to periodically rest the supercharger - any gain in speed was a by-product, not a tactic.