P-51b vs. P-51d

[Brakechk]

In real life there are two tangible benefits to the D, one to the B.

The D has better firepower, with guns that didn't frequently jam, and the D has better visibility.

The slight negative for the D is that the weight of the guns and extra ammo is about 370 pounds more than the B. So, for same Hp and boost at each altitude (which if late model B/C vs D is the same since they both had the 1650-7) the 51B will turn and climb very slightly better.

IIRC this group uses the P-51B with 1650-3 high altitude version of the Merlin which later morphed into the 1650-9 for the P-51H with the Bendix carburation and WI.

So, in this scenario the P-51B is faster above the Critical Altitude of the 1650-7 meaning above 24K.

On another forum I got entangled in this debate and went to both analytical models like Lednicer and exchanged emails with the guys that flew both in combat to add to the 40 years of asking the same question.  Without exception the P-51D was the Mustang of choice for combat ops because of the visibility (including the Malcolm Hood) and extra firepower.  In other words nobody said they turned the D down in preference to the B.

Take what you want and leave the rest.

BTW Lednicer showed that the B dveloped a stagnation pressure pocket at the base of the P-51B (and Spit I through IX) windscreen and on the aft top of the canopy wheres the P-51D windscreen and bubble canopy had no stagnation pressure pocket or separation on the canopy, presumablt because the D had more slope angle aft than the B and the Spits.

Don't fly mustangs much but love getting good info on all the planes we have in AH.  I'm not a pilot so this may be a stupid question:  What is a stagnation pressure pocket and what effect does it cause?

[drgondog]

Its simply a place where the flow is brought to a rest which results in a flow disruption and consequently a dynamic pressure increase/drag.  It has positive uses such as in a pitot tube where the freestream flow is brought to rest causing a pressure rise to assist in recording dynamic pressure for airspeed calcs.

You could visualize stagnation pressure when the freestream hits a flat plate.  In the case of the P-51B stagnation point at the base of the windscreen, it is a 'small' flat plate equivalent - whereas the flow  over the P51D windscreen changes direction but doesn't 'stop'.

[Hazard69]

I imagine a ponyD with the four gun option would be outmaneuver a pony B and the 6 gun D due to better engine and lower weight?

[drgondog]

I imagine a ponyD with the four gun option would be outmaneuver a pony B and the 6 gun D due to better engine and lower weight?

Simple answer - yes, probably - if you meant that a P-51D should outmanuever a B given the suggested armament swap.  

By the time the P-51D-5 was assigned to ETO and MTO squadrons in late May/June 1944 all the new P-51B-15NA's and P-51C-10NT's were equipped with the same Packard-Merlin 1650-7 engine. The earlier B's were being retrofitted with the -7 to replace the 1650-3 as they wore out.

The only tangible weight difference between the two was the armament (2x 50 cal plus ~ 600 more rounds of .50cal)and according to Lednicer from his VSAERO studies, the 51D had slightly less windscreen/canopy drag with a greater sloped windshield and the bubble canopy vs birdcage.

[Krusty]

The B and D have different loadouts even when you load 4 guns on the D.

B: 2 guns with 280 rpg ea.
    2 guns with 350 rpg ea.

D: 2 guns with 500 rpg ea.
    2 guns with 400 rpg ea.

So the D has a significantly better firing time even with the light guns package. I take it often enough, when I want to be able to fire longer.

[drgondog]

The B and D have different loadouts even when you load 4 guns on the D.

B: 2 guns with 280 rpg ea.
    2 guns with 350 rpg ea.

D: 2 guns with 500 rpg ea.
    2 guns with 400 rpg ea.

So the D has a significantly better firing time even with the light guns package. I take it often enough, when I want to be able to fire longer.

Krusty - I don't fly the sims, with the stated loads you quoted, but the real D/K inboard ammo capacity is 400 to the B load of 350 and the D center/outbd is 270 while B is 280 (10 more than D).  The total capacity for the D with six .50 is 1880.

[Krusty]

Krusty - I don't fly the sims, with the stated loads you quoted, but the real D/K inboard ammo capacity is 400 to the B load of 350 and the D center/outbd is 270 while B is 280 (10 more than D).  The total capacity for the D with six .50 is 1880.

I wasn't referring to the 6-gun loadout option. That is well known. That has 400 rounds inboard, and 270 rpg for the outboard guns. I was simply saying that the previous comparisons of the B and D using the same 4-gun loadout were not quite the same. There was a difference, even though both had 4 guns (in that comparison).