"What about high powered, high performance machines, like the humble Aerostar, which is completely devoid of cowl flaps?! They seem to get by in hot parts of Australia just fine without them!"
If they do then they are simply unnecessarily overcooled in the cruise and suffering from excessive cooling drag.
Bit oversimplified here. High performance machines generally do a few things differently like:
1. Climb faster (higher TAS - more cooling airflow)
2. Cruise higher (cooler air)
3. Climb quicker (less time to get hot)
My Aerostar, when it's hot, can't climb at anything near best angle or best rate without the CHTs creeping up. Fortunately, I can still climb at >500fpm at Vy + 30kts. Ted Smith has been accused of many things but 'unecessarily overcooled in the cruise' isn't one of them. Never have any problems with CHTs on the ground.
Your Pawnee example is true because they're designed to fly slow and low - and need to compensate for a lack of cold ram air.
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