P-51 MUSTANG aerodynamics/armament?

Question

Why was the P-51's belly intake set down a few inches below the fuselage? Seems as if they could have reduced the plane's frontal area to cut drag, if they would've mounted that intake right up against the belly of the plane. Why the gap?

Also, why were the two lower-cowling guns of the P-51A omitted from later versions?

Thanks.

Oops, re: the cowling guns, I meant the A-36 Invader/Apache, the P-51's direct ancestor.

Answer 1

The air intake on the A-36 was located because of the engine air intake position...and it is the same for the fuselage machine gun.

On the P-51B, the Allison engine was replaced by the Rolls Royce Merlin and the general arrangement of this engine was different from the Allison so the armament was relocated in the wings only.
About the position of the radiator, it was put on this place for two effects:
Reduce frontal drag because the total frontal area of the engine was reduced.
Jet Effect: a new theory in the early 40s : the air passing through the radiator is ejected at a higher speed of the fuselage, helping the aircraft to gain some (precious in air combat) mph.

Answer 2

Remember they have learned a lot about aerodynamics since that time. The technology of the time required they put the air intake out into the slipstream, since maybe they thought the air right along the fuselage may have been inadequate due to turbulence from the propeller and the uneven surfaces of the sheetmetal (causing spots of "dead" air along the airframe), or maybe it was just to move the intake forward of the flaps so that they wouldn't interfere with the intake airflow.

I too have never heard of lower cowling guns. The only ones it had were the 4 in the wings.

Answer 3

I think that the air intake hung down from the fuselage a little bit to get the intake into "clean" air. This air would flow into the air intake and through the oil coolers and radiators smoother. The P-51s that race at Reno had a modified that I think was smaller in size but still hung down that inch or two into the air stream.

Answer 4

The air intake has to stick down into the slipstream to get air to the radiator. The early models had four 50 caliber machine guns in the wings, later models had six. Never knew of one with guns in the lower cowling. They would have to fire through the propeller arc, and the necessary timing equipment would have affected performance.

Answer 5

Do remember that the supercharger is huge and required a cool air source as well, and really about the only place that there was room for it was just aft of the cockpit..

Answer 6

the later versions are out of date