Originally posted by funked:
Also note that the cooling of the engine is being done by that big open "hole". On inline engine planes there are radiators and oil coolers in various places on the fuselage. They usually aren't very big but if you add up all the drag from them it brings them closer to the drag of the radial "hole".
Actually the smaller fin surfaces of the radiator, such as the Mustang, create more drag (per area of surface) as compared to the very wide channels of the radial cooling heads (but of course radials have a much larger surface area). Depends on how far down the ramp is on the rear of the P-51's intake. In a near closed position, the engine gets less cooling, but the back pressure from the air already rammed into the intake prevents more air from entering rapidily.
It works basically like a cowling flap. P-47's have an exhaust ramp that lets the exhaust exit from the turbo charger, between the cockpit and tail. It's on the underside and adjusts with exhaust flow.
The FW, on the other hand, has a fan within the cowling that spins with the prop, and in effect creates a buffer zone that helps against drag over the cooling fins.
- Jig
