eBay: North American P-51 Mustang

[drgondog]

"


One Mustang document that might be of interest here relates to the original P-51B and P-51C designations. The addition of the Merlin engine led to some aerodynamic concerns and minor repositioning of the wing. The P-51B was originally to be produced with the Merlin, but without the repositioned wing; the new wing was planned for the P-51C. Obviously, both models went into production with the repositioned wing, but I've never seen the original designations explained in any of the many Mustang books.

Then there's my all-time favorite Wright Field inter-office memo on the P-51, dated 28 August 1942. It doesn't relate directly to designations, but I'll drop it in here in its entirety:

Left by Alec Burton together with the dope on the Griffin 61, this date. "Dutch" Kindleberger says the Merlin 28 is out for installation in the P-51, but they are going full blast on the Merlin 61. About all the re-design necessary is to move the wing forward 3 inches and down 1 inch; also, the nose will be dropped a little to give better visibility than in the P-51.

If the aerodynamics isn't ruined, looks like they might have a pretty good airplane.

That 'package'was dropped to Colonels Chidlaw and Philips - Materiel Command on August 26, 1942 - approximately three months before first flight of XP-51B. It had the projected Performance @ GW 8350#, 2x20mm guns, no armor plate or radio with top speed of 445MPH @ 28K, service Ceiling 42K, ROC 3460fpm at 13K - all figure the P-51B-1 exceeded in AAF Flight tests May 1943 with production airplane at 8500#.

That one should be in the dictionary next to "understatement..

Quote from above -"Then there's my all-time favorite Wright Field inter-office memo on the P-51, dated 28 August 1942. It doesn't relate directly to designations, but I'll drop it in here in its entirety:

Left by Alec Burton together with the dope on the Griffin 61, this date. "Dutch" Kindleberger says the Merlin 28 is out for installation in the P-51, but they are going full blast on the Merlin 61. About all the re-design necessary is to move the wing forward 3 inches and down 1 inch; also, the nose will be dropped a little to give better visibility than in the P-51.

If the aerodynamics isn't ruined, looks like they might have a pretty good airplane."

That 'package' was dropped to Colonels Chidlaw and Philips - Materiel Command on August 26, 1942 - approximately three months before first flight of XP-51B. It had the projected Performance @ GW 8350#, 2x20mm guns, no armor plate or radio with top speed of 445MPH @ 28K, service Ceiling 42K, ROC 3460fpm at 13K - all figure the P-51B-1 exceeded in AAF Flight tests May 1943 with production airplane at 8500#.
Subject B/C - literally timing as XP-78 was renamed XP-51B - and subsequently when the Merlin Mustang contracts far exceeded Inglewood production capacity at a time when B-25s were still built at Inglewood.

The confusion (very brief) arose when the NA-102 P-51B-1 contract was executed in August 1942 before the XP-51B # 1 was complete and followed on 10-8 with AAF deciding to truncate the P-51A part of the AC-30479 to procure the NA-104 890 P-51B-5 (later extended to include more orders for the P-51B-10 and B-15 with the odd 90 from the P-51A contract added to the P-51B-15). The NA-104 contract was a revision of NA-99 AC-30479, executed on 10-20-42. While that contract change deviation was explored, the next order AC-3340 for NA-103 was executed for Dallas effectivity was executed 12 days earlier than N-104.

It was at that time that AAF and NAA would separate the nomenclature for the same airplane just as Republic did with the P-47G. With this delineation, the hinged canopy Merlin Mustang Made in Inglewood retained the P-51B designation as NA 102 and the NA-103 Mustang made in Dallas was now P-51C. When the six gun variant was proposed at the end of 1942 the contract negotiations for NA-106 (Inglewood) and NA-107 (Dallas) was executed in February 1943 for the P-51D and P-51E respectively. NAA at this time also negotiated the addition of a bubble canopy to replace the hinged canopy and the Top Drawing and Master lines were completed for the six gun wing and bubble canopy. The original 106-9000002 P-51D/E Top Assembly Breakdown drawing was completed 3-15-43 and about that same time the AAF issued Material Change Order C-258 to design and install new Cockpit Enclosure, Sliding on two P-51D to be crafted from NA-102 spares and a complete existing P-51B-1 airframe.

Contract negotiations were initiated to Produce NA-109 P-51D-5-NA in large scale production, cut NA-106 to two (P-51D-NA and D-1-NT), redistribute remaining (large) funding from the NA-106 to NA-103 and NA-104 and cancel NA-107/P-51E... and finally kill the name P-51E and rename all future P-51D Inglewood and Dallas ships of same designs and effectivities within blocks with "NA" and"NT".

And that, children is all there is for today.

 

[Navalwarrior]

Quote from above -"Then there's my all-time favorite Wright Field inter-office memo on the P-51, dated 28 August 1942. It doesn't relate directly to designations, but I'll drop it in here in its entirety:

Left by Alec Burton together with the dope on the Griffin 61, this date. "Dutch" Kindleberger says the Merlin 28 is out for installation in the P-51, but they are going full blast on the Merlin 61. About all the re-design necessary is to move the wing forward 3 inches and down 1 inch; also, the nose will be dropped a little to give better visibility than in the P-51.

If the aerodynamics isn't ruined, looks like they might have a pretty good airplane."

That 'package' was dropped to Colonels Chidlaw and Philips - Materiel Command on August 26, 1942 - approximately three months before first flight of XP-51B. It had the projected Performance @ GW 8350#, 2x20mm guns, no armor plate or radio with top speed of 445MPH @ 28K, service Ceiling 42K, ROC 3460fpm at 13K - all figure the P-51B-1 exceeded in AAF Flight tests May 1943 with production airplane at 8500#.
Subject B/C - literally timing as XP-78 was renamed XP-51B - and subsequently when the Merlin Mustang contracts far exceeded Inglewood production capacity at a time when B-25s were still built at Inglewood.

The confusion (very brief) arose when the NA-102 P-51B-1 contract was executed in August 1942 before the XP-51B # 1 was complete and followed on 10-8 with AAF deciding to truncate the P-51A part of the AC-30479 to procure the NA-104 890 P-51B-5 (later extended to include more orders for the P-51B-10 and B-15 with the odd 90 from the P-51A contract added to the P-51B-15). The NA-104 contract was a revision of NA-99 AC-30479, executed on 10-20-42. While that contract change deviation was explored, the next order AC-3340 for NA-103 was executed for Dallas effectivity was executed 12 days earlier than N-104.

It was at that time that AAF and NAA would separate the nomenclature for the same airplane just as Republic did with the P-47G. With this delineation, the hinged canopy Merlin Mustang Made in Inglewood retained the P-51B designation as NA 102 and the NA-102 Mustang made in Dallas was now P-51C. When the six gun variant was proposed at the end of 1942 the contract negotiations for NA-106 (Inglewood) and NA-107 (Dallas) was executed in February 1943 for the P-51D and P-51E respectively. NAA at this time also negotiated the addition of a bubble canopy to replace the hinged canopy and the Top Drawing and Master lines were completed for the six gun wing and bubble canopy. The original 106-900002 P-51D/E Top Assembly Breakdown drawing was completed 3-15-43 and about that same time the AAF issued Material Change Order C-258 to design and install new Cockpit Enclosure, Sliding on two P-51D to be crafted from NA-102 spares and a complete existing P-51B-1 airframe.

Contract negotiations were initiated to Produce NA-109 P-51D-5-NA in large scale production, cut NA-106 to two (P-51D-NA and D-1-NT), redistribute remaining (large) funding from the NA-106 to NA-103 and NA-104 and cancel NA-107/P-51E... and finally kill the name P-51E and rename all future P-51D Inglewood and Dallas ships of same designs and effectivities within blocks with "NA" and"NT".

And that, children is all there is for today.

 

[Navalwarrior]

Resp:
Well done, Professor!

 

[Spitlead]

Just wanted to post a P-51 photo I took a couple of years ago. Enjoy!

 

[MIflyer]

Ehhh, you can't fool me, that's the Hawk model.

 

[Spitlead]

Ehhh, you can't fool me, that's the Hawk model.View attachment 583366

Wow, cool model. Where on earth did you get the plans? Interesting that the camo pattern appears to be the same even though they are different airplanes. Both airplanes flew out of Bottisham.

 

[MIflyer]

Oh, I scanned the instruction sheet and can provide the rest of it if anyone is interested.

That was a very high quality model for its time and the only decent 1/48 P-51D for well over a decade. Only big flaw I know of is that the belly radiator is way too narrow, so I presume the rear fuselage is too narrow as well. I still have an unbuilt example in my collection that uses those same decals. Attached is the original box art it was first issued with. They also issued a chrome plated version.

 

[Navalwarrior]

Quote from above -"Then there's my all-time favorite Wright Field inter-office memo on the P-51, dated 28 August 1942. It doesn't relate directly to designations, but I'll drop it in here in its entirety:

Left by Alec Burton together with the dope on the Griffin 61, this date. "Dutch" Kindleberger says the Merlin 28 is out for installation in the P-51, but they are going full blast on the Merlin 61. About all the re-design necessary is to move the wing forward 3 inches and down 1 inch; also, the nose will be dropped a little to give better visibility than in the P-51.

If the aerodynamics isn't ruined, looks like they might have a pretty good airplane."

That 'package' was dropped to Colonels Chidlaw and Philips - Materiel Command on August 26, 1942 - approximately three months before first flight of XP-51B. It had the projected Performance @ GW 8350#, 2x20mm guns, no armor plate or radio with top speed of 445MPH @ 28K, service Ceiling 42K, ROC 3460fpm at 13K - all figure the P-51B-1 exceeded in AAF Flight tests May 1943 with production airplane at 8500#.
Subject B/C - literally timing as XP-78 was renamed XP-51B - and subsequently when the Merlin Mustang contracts far exceeded Inglewood production capacity at a time when B-25s were still built at Inglewood.

The confusion (very brief) arose when the NA-102 P-51B-1 contract was executed in August 1942 before the XP-51B # 1 was complete and followed on 10-8 with AAF deciding to truncate the P-51A part of the AC-30479 to procure the NA-104 890 P-51B-5 (later extended to include more orders for the P-51B-10 and B-15 with the odd 90 from the P-51A contract added to the P-51B-15). The NA-104 contract was a revision of NA-99 AC-30479, executed on 10-20-42. While that contract change deviation was explored, the next order AC-3340 for NA-103 was executed for Dallas effectivity was executed 12 days earlier than N-104.

It was at that time that AAF and NAA would separate the nomenclature for the same airplane just as Republic did with the P-47G. With this delineation, the hinged canopy Merlin Mustang Made in Inglewood retained the P-51B designation as NA 102 and the NA-102 Mustang made in Dallas was now P-51C. When the six gun variant was proposed at the end of 1942 the contract negotiations for NA-106 (Inglewood) and NA-107 (Dallas) was executed in February 1943 for the P-51D and P-51E respectively. NAA at this time also negotiated the addition of a bubble canopy to replace the hinged canopy and the Top Drawing and Master lines were completed for the six gun wing and bubble canopy. The original 106-900002 P-51D/E Top Assembly Breakdown drawing was completed 3-15-43 and about that same time the AAF issued Material Change Order C-258 to design and install new Cockpit Enclosure, Sliding on two P-51D to be crafted from NA-102 spares and a complete existing P-51B-1 airframe.

Contract negotiations were initiated to Produce NA-109 P-51D-5-NA in large scale production, cut NA-106 to two (P-51D-NA and D-1-NT), redistribute remaining (large) funding from the NA-106 to NA-103 and NA-104 and cancel NA-107/P-51E... and finally kill the name P-51E and rename all future P-51D Inglewood and Dallas ships of same designs and effectivities within blocks with "NA" and"NT".

And that, children is all there is for today.

Resp:
I recently came across this statement in print inre to P-51B/C Mustnags; "Several pilots complained that they could no longer obtain their usual evasive action because of the addition of the dorsal fin and change in the rudder boost tab." Thoughts?

 

[MIflyer]

I suppose those changes could have made it more difficult to do a slip at high speed. Crossing controls is a technique for making the nose of the airplane point in a different direction than its motion in order to throw off the enemy's attempt to lead the airplane - an approach mainly useful in avoiding ground fire, I think.

 

[Spitlead]

I suppose those changes could have made it more difficult to do a slip at high speed. Crossing controls is a technique for making the nose of the airplane point in a different direction than its motion in order to throw off the enemy's attempt to lead the airplane - an approach mainly useful in avoiding ground fire, I think.

Pilots would also "slip" the airplane to throw off an attackers aim from behind. Plus, "slipping" the airplane is also used on approach to land.

 

[MIflyer]

I have mainly heard of the slipping technique for evasive action used to avoid ground fire - it is still used for that with jets. It could be used to avoid fire from an attacker on your tail but would also slow the airplane a bit. I have done forward slips many times to kill off excess airspeed on short final, although that is not possible with the airplane I currently fly.

A slip points the nose of the airplane to one side of the flight path, making it appear to be heading off to one side when in fact it heading somewhere else and is attained by applying opposite rudder and aileron. I can see how that could throw off ground fire. A skid is where rudder is applied with not enough aileron, not opposite aileron, and I think would be less useful in evasive action. See attached figure.

The P-51D Training Manual says, "Because of the reverse-boost rudder tab and dorsal fin, the airplane has very good directional stability, with a directional change requiring definite pressure on the rudder pedal in proportion to the amount of yaw required." In other words you did not get yaw without pressure on the rudder pedals.

The Guenhagen book on the Mustang says that the dorsal fin and reverse boost tab were standardized on P-51D-10NA, and P-51D and P-51K Dallas production. So maybe P-51B/C pilots were complaining about the later D models being different from what they were used to?

 

[Navalwarrior]

I have mainly heard of the slipping technique for evasive action used to avoid ground fire - it is still used for that with jets. It could be used to avoid fire from an attacker on your tail but would also slow the airplane a bit. I have done forward slips many times to kill off excess airspeed on short final, although that is not possible with the airplane I currently fly.

A slip points the nose of the airplane to one side of the flight path, making it appear to be heading off to one side when in fact it heading somewhere else and is attained by applying opposite rudder and aileron. I can see how that could throw off ground fire. A skid is where rudder is applied with not enough aileron, not opposite aileron, and I think would be less useful in evasive action. See attached figure.

The P-51D Training Manual says, "Because of the reverse-boost rudder tab and dorsal fin, the airplane has very good directional stability, with a directional change requiring definite pressure on the rudder pedal in proportion to the amount of yaw required." In other words you did not get yaw without pressure on the rudder pedals.

The Guenhagen book on the Mustang says that the dorsal fin and reverse boost tab were standardized on P-51D-10NA, and P-51D and P-51K Dallas production. So maybe P-51B/C pilots were complaining about the later D models being different from what they were used to?
View attachment 583688

Resp:
No, it specifically states P-51B/C. The way it was stated made it sound like they had flown P-51B or C models before the 'field modification adding the dorsal fin.' So they knew the difference. This may help explain few theater photos of dorsal fin B/Cs as this info of loss of air manuvers may have stopped any further field installment of the dorsal fin. P-51D-5 NA are a different matter.

 

[MIflyer]

While I can't find it now, I had some info that said that the main reason for the dorsal fin installation on the B/C models was to reinforce the horizontal tail by tying it more strongly into the fuselage.

Do we know if any P-51B/C got the dorsal fin at the factory? At one time I was under the impression that the C model s, being later than the B's, all got the mod at the Dallas factory but subsequent photographic evidence refutes that.

 

[Navalwarrior]

While I can't find it now, I had some info that said that the main reason for the dorsal fin installation on the B/C models was to reinforce the horizontal tail by tying it more strongly into the fuselage.

Do we know if any P-51B/C got the dorsal fin at the factory? At one time I was under the impression that the C model s, being later than the B's, all got the mod at the Dallas factory but subsequent photographic evidence refutes that.View attachment 583689

Resp:
After seeing two stateside clean aluminum P-51Cs parked postwar with dorsal fins, I began to think that they were assembled at Dallas so configured. But you know what 'assume' means. I have only seen one b/w photo (ETO) with the dorsal fin (could have been a B or C), and it was posted on this blog. Also of note, two postwar models became F-51C that were retained with one Air National Guard Unit.

 

[drgondog]

I will try to comment on all the discussions above about the DFF and Reverse Rudder Boost Tab.

First, The installation/retrofit of the DFF kit for P-51B/C/D applied to all Merlin Mustangs in AAF that left the factory without them.
Second, the P-51D-5-NA 44-13903 was factory equipped with DFF. P-51C-10-NT, second block under NA-111 was factory equipped with DFF. The end of the P-51C-10-NT was the beginning of the P-51D-5-NT. It, and all P-51s built in Dallas had factory DFF.
Third, the P-51D DFF was different from P-51B/C DFF - for obvious reasons related to top fuselage line. See dwg 104-25001 and 109-25001 if you are a tech nerd for the differences in B/C vs D/K designs. Both emerged Engineering in late March 1944
Fourth, I'm not sure that the reverse rudder boost tab installation did not also occur as early as P-51D-5 44-13903 but I trust Bob G on that subject.
Fifth, there were structural improvements in the form of doublers applied to fin and elevator spars to reinforce the empennage that went out as kits along with the Tech Order of April 8, 1944 for DFF and Reverse Rudder Boost Tab. See TO 01-60J-18 for details on the structural mods.

The issues causing empennage failures were multifold. One issue was applied rudder pressure combined with a rolling pullout, but to a lesser degree caused by applying too much rudder in a high speed dive to maintain a 'straight' line while aero forces tended to cause increasing yaw forces - all resisted by both the fin/rudder but also on the horizontal stab. Visualize the asymmetric forces caused by the prop vortex putting the stabs (vert and horiz) into a torqueing moment on the fuselage at the bulkhead/spar carry through structure. Then visualize the addition of rudder input to offset the yaw inputs experienced in dives and rolls while increasing/decreasing throttle.

Over control of the rudder to damp yaw when high q loads present is the reason for the Reverse Rudder Boost Tab - to make the pilot have to apply more rudder Force than previously to decrease the yaw input.

The Dorsal Fin Fillet was to improve the flow characteristics passing the immersed empennage, including the prop vortex, It was an improvement but yaw issues associated with Merlin Mustangs weren't truly and effectively addressed until the P-51H increased fuselage length behind the cockpit and increased empennage area (including tall tail fuselage cap)

The reported 'loss of some maneuverability' in maneuvering combat was essentially true - it was a result of improving Yaw magnitude and damping for structural safety

 

[drgondog]

Resp:
After seeing two stateside clean aluminum P-51Cs parked postwar with dorsal fins, I began to think that they were assembled at Dallas so configured. But you know what 'assume' means. I have only seen one b/w photo (ETO) with the dorsal fin (could have been a B or C), and it was posted on this blog. Also of note, two postwar models became F-51C that were retained with one Air National Guard Unit.

The DFF is mandated by FAA for all Merlin Mustangs. The existing warbirds are 90% total reconstructed airframes, many recovered with basically data plates and a few usable parts from the original. The ONLY P-51B/C block that emerged from Dallas with factory DFF was NA-111 P-51C-10-NT 44-10753 thru 44-11152. IIRC nne of those exist today.

Essentially, if you see a warbird, it is attired in colors and codes that suit the owner and has nothing in common from the represented airframe that was built in WWII.

 

[drgondog]

Ehhh, you can't fool me, that's the Hawk model.View attachment 583366

P-51D-5-NA (not -20 as shown on instructions) and the DFF in real life was a field installed kit. This airplane had field installed brown/green camo applied to the arriving NMF P-51D. To this day I do not know if any OD paint to correct specification was available in UK. If so, it was a UK based production. Every ship I have seen with paint applied in ETO over NMF, especially for the 357th FG, was an RAF Green/Brown hue type.

The bazooka type rocket launcher was an artistic touch. AFAIK only used in CBI before the P-51D-20 emerged with rocket stubs for HVAR type rockets.

 

[Reluctant Poster]

I will try to comment on all the discussions above about the DFF and Reverse Rudder Boost Tab.

First, The installation/retrofit of the DFF kit for P-51B/C/D applied to all Merlin Mustangs in AAF that left the factory without them.
Second, the P-51D-5-NA 44-13903 was factory equipped with DFF. P-51C-10-NT, second block under NA-111 was factory equipped with DFF. The end of the P-51C-10-NT was the beginning of the P-51D-5-NT. It, and all P-51s built in Dallas had factory DFF.
Third, the P-51D DFF was different from P-51B/C DFF - for obvious reasons related to top fuselage line. See dwg 104-25001 and 109-25001 if you are a tech nerd for the differences in B/C vs D/K designs. Both emerged Engineering in late March 1944
Fourth, I'm not sure that the reverse rudder boost tab installation did not also occur as early as P-51D-5 44-13903 but I trust Bob G on that subject.
Fifth, there were structural improvements in the form of doublers applied to fin and elevator spars to reinforce the empennage that went out as kits along with the Tech Order of April 8, 1944 for DFF and Reverse Rudder Boost Tab. See TO 01-60J-18 for details on the structural mods.

The issues causing empennage failures were multifold. One issue was applied rudder pressure combined with a rolling pullout, but to a lesser degree caused by applying too much rudder in a high speed dive to maintain a 'straight' line while aero forces tended to cause increasing yaw forces - all resisted by both the fin/rudder but also on the horizontal stab. Visualize the asymmetric forces caused by the prop vortex putting the stabs (vert and horiz) into a torqueing moment on the fuselage at the bulkhead/spar carry through structure. Then visualize the addition of rudder input to offset the yaw inputs experienced in dives and rolls while increasing/decreasing throttle.

Over control of the rudder to damp yaw when high q loads present is the reason for the Reverse Rudder Boost Tab - to make the pilot have to apply more rudder Force than previously to decrease the yaw input.

The Dorsal Fin Fillet was to improve the flow characteristics passing the immersed empennage, including the prop vortex, It was an improvement but yaw issues associated with Merlin Mustangs weren't truly and effectively addressed until the P-51H increased fuselage length behind the cockpit and increased empennage area (including tall tail fuselage cap)

The reported 'loss of some maneuverability' in maneuvering combat was essentially true - it was a result of improving Yaw magnitude and damping for structural safety

Rolls Royce added dorsal fins to two of the Mustangs they converted. They also tried extending the chord of the fin itself which was their preferred solution.

 

[MIflyer]

Has anyone ever seen an F-6C that did not have the dorsal fin extension?

 

[drgondog]

Rolls Royce added dorsal fins to two of the Mustangs they converted. They also tried extending the chord of the fin itself which was their preferred solution.

True that AL963 (only one) was modified with both a DFF and simply adding extra chord/fin area. The extra area/increased chord was, however, deemed too stable and sluggish to enter a roll. NAA experimented with adding a fin cap as well as a DFF and settled on the DFF w/o the tall tail.