P51's speed chart

[BrockS]

I love the 51B, my favorite to fly. When I do fly the D I like to hang around 11k to 14K because it has a sweet spot around 13k where it is one of the fastest birds in the game which allows you more options to dictate the fight. I think only the k4 and D9 are faster there. 51B hits it's sweet spot around 17k but there are a few other birds that can match and beat her at that alt. Now, off the top of my head the D peaks in speed again around 25K and the B at 29K...ish but not top of the class at those alts. What you gain in manueverability in the B is at the cost of a slightly longer firing time on target because of the 4 gun vs 6 gun arrangement. Here is a good link to compare perfomance with. While there are a lot of factors that go into a fight, these comaprisons will at least give a strt on determining your chosen rides advantages and disadvantages.

http://gonzoville.com/ahcharts/index.php

[colmbo]

R/L the wing on the B was a bit thinner than the wing on the D.  The wing was thickened to accomodate the guns sitting upright in the wing instead of at an angle.

[Charge]

"R/L the wing on the B was a bit thinner than the wing on the D.  The wing was thickened to accomodate the guns sitting upright in the wing instead of at an angle."

North American Aviation NA-102 P-51B Mustang               NAA/NACA 45-100                          NAA/NACA 45-100
North American Aviation NA-106 P-51D Mustang               NAA/NACA 45-100                          NAA/NACA 45-100

http://www.public.iastate.edu/~akmitra/aero361/design_web/airfoil_usage.htm

-C+

[MiloMorai]

The 51B/C used a PM1650-3 engine while the 51D/K used a PM1650-7 engine (some late production 51B/Cs had PM1650-7 engines)

Supercharger gearing

1650-3

low blower - 6.391:1
high blower - 8.095:1

1650-7

low blower - 5.802:1
high blower - 7.349:1

[Krusty]

North American Aviation NA-102 P-51B Mustang               NAA/NACA 45-100                          NAA/NACA 45-100
North American Aviation NA-106 P-51D Mustang               NAA/NACA 45-100                          NAA/NACA 45-100

http://www.public.iastate.edu/~akmitra/aero361/design_web/airfoil_usage.htm

Same numbers, perhaps... And yet quite different in actual layout and design.

Compare:
http://richard.ferriere.free.fr/3vues/p51b_3v.jpg
with:
http://richard.ferriere.free.fr/3vues/p51d_3v.jpg

They had thicker chord wing roots, cranked leading edges, redesigned gear doors in the wings, and the ever-so-slightly thicker wing did allow for the guns to sit upright. So maybe the airfoil description is the same, but the wing itself was not.

On the B they were canted outwards almost 45 degrees (which is just odd). The belt fed over the top of the gun but my guess is that was the thicker part of the wing (the peak of the wing thickness) and it was more forward or further aft where the body of the M2 .50cal bumps into the wing that required the angle in the first place.

[MiloMorai]

Same numbers, perhaps... And yet quite different in actual layout and design.

Compare:
http://richard.ferriere.free.fr/3vues/p51b_3v.jpg
with:
http://richard.ferriere.free.fr/3vues/p51d_3v.jpg

They had thicker chord wing roots, cranked leading edges, redesigned gear doors in the wings, and the ever-so-slightly thicker wing did allow for the guns to sit upright. So maybe the airfoil description is the same, but the wing itself was not.

On the B they were canted outwards almost 45 degrees (which is just odd). The belt fed over the top of the gun but my guess is that was the thicker part of the wing (the peak of the wing thickness) and it was more forward or further aft where the body of the M2 .50cal bumps into the wing that required the angle in the first place.

If the same airfoil was used, but the wing thickness was increased, then the chord would increase as well. Therefore the wing plan of the 'D/K' would be bigger than on the 'B/C'. That would increase the wing area. Did the wing area of the 'D/K' increase, from Station 61.5 outwards, over the 'B/C'?

[Krusty]

That wing angle was considerably noticable. It had to at least add a couple more square feet to the wing area, yes. It's a 3-foot-long angle change, roughly, and probably over a foot forward of the B's leading edge at the fuselage joint.

All just looking at the profiles. I've been aware of the difference for a while, just haven't had to describe it before.

Other than that I think wingspan was the same so generally wing area should be close.

[drgondog]

R/L the wing on the B was a bit thinner than the wing on the D.  The wing was thickened to accomodate the guns sitting upright in the wing instead of at an angle.

The NACA/NAA 45-100 was the same airfoil for ALL P-51 models except G/H/J. The only difference between the XP-51 through the P-51B/C was that the wing was 'dropped' to accomodate new cowl for Merlin.  The same amount of space was available for the 20mm and the .50 armament.  EXACTLY the same dimensions to provide space for weapons and ammo.

The D/K had the same airfoil but a longer root chord to accomodate the new wheel door design.

At ~ W/S 61.5 (the 'break point' of the leading edge strake), all the airfoils had the same lines, same max thickness (15.1%) and same chord. The location and planform of the wing was exactly the same for trailing and leading edges excpt at the break point for the strake into the CL of the airframe. I would have to research it but I believe the leading edge twist from CL to strake brake point was also the same.

[drgondog]

A couple of points for consideration on the 'thickness' question.

The prototype D's were two P-51B-15 (42-106539 and 42-106540) taken off the line to create the bubble canopy modification. No changes on either the wing airfoil or the wing at all! Strictly fuselage mods.

The P-51D leading edge was changed from the leading edge at the CL to STA 61.5 to accomodate the wheel door/uplock mods, the root chord was modified to make it longer and Thinner, a special airfoil line to ensure that no other tooling other than to accomodate the leading edge change would have to be made.. i.e. specifically zero changes to spars, ribs, lines, etc which would necessitate New Tools and Jigs to set up for production.

Can you imagine NAA going to USAAF and saying 'yes, great view, more .50 cal, less jams, fewer structural failures but it will set back delivery about 3-6 months..".. can you imagine the silence in the room?

[Masherbrum]

My mind is blown.  how is the b faster then the D, when the b. Doesn't have a supercharger at high ALT?

 

[drgondog]

The Bravo has the Merlin 61 engine and the Delta has the Merlin 66. Bravo is lighter, tighter turning, and more aerodynamic therefore faster at higher altitudes but the Delta still holds slightly better in the vertical and gunnery of course over the Bravo.

I'll fly the Bravo over the Delta anyday unless i get tired of it...

The first P-51B-1 and -5's had the PM 1650-3 which had a critical altitude ~ 29,200-29,800 for high blower and ~ 16,600-16,800 for low blower.

The P-51B-10 and P-51B-15 had the PM 1650-7 from factory and all existing -1/-5's were converted from 1650-3 to 1650-7.  The 1650-7 had high blower CA @~ 10,500-12,000 and CA high blower @~24,000ft

All the P-51D's had the PM 1650-7's. with high and low blower on the P-51D exactlythe same as the P-51B
The P-51D w 44-1 fuel and weighing about the same as the P-51B-15 (~300 pounds greater for same load out) was as fast as the B, at high altitude/high blower/ and faster than P-51B-15 at critical altitude low blower and sea level.

The Difference, given 44-1 fuel and 67"/3000rpm for both versions is that the P-51B-15 will climb, accelerate and turn just slightly better - all about the difference in WL due to the extra weight.

[MiloMorai]

That wing angle was considerably noticable. It had to at least add a couple more square feet to the wing area, yes. It's a 3-foot-long angle change, roughly, and probably over a foot forward of the B's leading edge at the fuselage joint.

All just looking at the profiles. I've been aware of the difference for a while, just haven't had to describe it before.

Other than that I think wingspan was the same so generally wing area should be close.

Let me help you with your reading comprehension Krusty by quoting Bill:

At ~ W/S 61.5 (the 'break point' of the leading edge strake), all the airfoils had the same lines, same max thickness (15.1%) and same chord. The location and planform of the wing was exactly the same for trailing and leading edges excpt at the break point for the strake into the CL of the airframe.

[Ack-Ack]

Didn't some of the B and C models receive the same modification to the wings to allow the fixing of the .50 cal gun layout?

ack-ack

[drgondog]

Didn't some of the B and C models receive the same modification to the wings to allow the fixing of the .50 cal gun layout?

ack-ack

No.   The same space existed for the Hispano as the Brownings.  I have not seen the Hispano 20mm mounts but it is possible they were mounted in an angle and the NAA engineers just followed the established principle  (or not).