Karel,
>
> I can not imagine that the presence of an oilthermostat changes the
> flow of the cooling air trough the radiators.
Of course not.
> What do you really mean by taking in more air permanently?
>
Using a thermostat : change oil flow through the radiator, not air flow
- Take in enough air to cool on the "worst case conditions", say
ISA+23C and take-off power. This is a great amount of air.
- Continuously flow it through the radiator. And so incur highest
cooling drag permanently.
- When you need less cooling (cruise, descent, cold day, etc.), prevent
the oil from getting into the radiator. But still flow as much air
through the radiator.
- Add extra plumbing and obstruction in the oil circuit.
Using a cowl flap : change airflow through radiator, not oil flow
- Take in just enough air to cool the engine
- Take in much air when on take-off on a hot day (highest cooling drag)
- Take in less air during cruise (lower cooling drag)
- Take in still less on a cold day or on descent (lowest possible
cooling drag)
- No disturbance in the oil circuit
That's why the Mosquito and Mustang were so fast. Works great for us.
Hope this helps,
Best regards,
Gilles
http://contrails.free.fr
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