DC-3 cowlflaps
All the DC-3's I flew were modified C-47's
Cowl flaps had 3 positions Open/Trail/Close
Open position on the ground for maximum heat dissipation.
Close in cruise if I remember correctly (also if the engines were going to be covered by engine covers after parking).
Trail was set prior to take-off/landing where the airflow would regulate the position of the cowl flaps - at higher forward speed they tended to the closed position and at lower speeds they tended to the open position.
This prevents cylinder head temperatures from getting too high.