What is a P-51M?

[drgondog]

The 1650-9A was essentially a stronger, more reliable 1650-3. I would have performed better at altitudes> 25000 fet than the D/K with 1650-7.

In production, could have been a candidate for the much more powerful 1650-9 had space for the ADI been made available.

The P-51M was a D-25-NT spare, modified with the 1650-9A.

 

[BarnOwlLover]

But was it to be a stop gap or a major variant? IE, if the war went on, would Dallas have eventually made the Mustangs built to lightweight standards (P-51H/L, P-82), or would they build the P-51M on existing D/K tooling to free up Inglewood for LW spec Mustang production? Granted, this hinged on NAA/USAAF plans, and if Dallas could've been converted to use LW Mustang tooling.

As far as the "quantity is it's own quality" aspect, building an uprated D model on existing tooling was an economical way to get a higher performance fighter without significant production shortfall worries. The H/L/P-82 were built on new or heavily modified tooling, and that's why the USAAF were slow to volume order them in the first place. I do remember reading that NAA at Inglewood could've been delivering P-51Hs by the fall of 1944, but the USAAF told them to hold off and do a slow phase in, since they didn't want any noteworthy slowdown in the delivery of P-51Ds, which were "good enough" (often more than "good enough") and could be purchased in quantity quickly.

Again, sometimes the best is the enemy of the good (or however it goes or how you want to interpret it). I'd have to say that the P-82 might have had a higher priority than the P-51H up until then. Also, though great press photos exist (at both Boeing and SDASM, and maybe 1-2 other places), there was relatively little fanfare at first for the P-51H, even at NAA. Probably because the war was almost over, and the P-82 had by then become a parallel program of maybe even higher importance.

 

[Sabrejet]

I've read through this thread with interest, frustration and annoyance. But mainly the last two. In case it helps, the transcription of s/n 45-11743's IARC is thus (I haven't seen it listed, so apologies if it has been - there's a lot of words in the last 8 pages):

P-51D [sic] s/n 45-11743 Contract AC-2400, AAF Pri[ority] 1-1; Project Del 3203.
Accepted at NAA Dallas 07Jun45 for Inglewood
Delivered 15Jun45
Available 18Jun45 (08Jun45 crossed out)
Arrived Inglewood 25Jun45
redesignated P-51D to P-51M 06Jul45 at Inglewood
ATC Ferry Command 03Oct45
ATC Ferry Command to RFC 21Oct45
Walnut Ridge 25Oct45

Hope this adds to the discussion. This would seem to support the assumption that the aircraft was ferried to NAA at Inglewood, converted to P-51M there for a brief test campaign and then disposed of to the RFC at Walnut Ridge in October 1945.

 

[Geoffrey Sinclair]

I've read through this thread with interest, frustration and annoyance. But mainly the last two.

Sounds right for a universe currently reported to be dominated by dark energy and dark matter. Remember physics says everything tries to achieve its lowest possible energy state and stay that way until something just right excites them. Meaning the universe is fundamentally lazy unless something specifically interesting comes along.

SC-AP-12 Report Monthly US Airplane Factory Deliveries and Allocations, June 1945 report dated 5 July, 1 P-51M delivered in June.

USAAF RC-301 cumulative aircraft acceptance reports
Dated 31 May 1945 Dallas contract AC-2400 for 530 P-51D of which 299 accepted plus 70 F-6D of which 33 accepted.

Dated 30 June 1945 Dallas contract AC-2400 for 528 P-51D, all accepted plus 70 F-6D, all accepted and 2 TP-51D, neither accepted, contract AC-2400 S.2 for 357 P-51D of which 33 accepted, plus 35 F-6D, none accepted plus 8 TP-51D none accepted also 695 P-51M of which 1 accepted, plus 230 F-6M, none accepted and 75 TP-51M, none accepted. Contract AC-8387 for 629 P-51M, none accepted.

 

[Sabrejet]

Not sure why this got gaslighted but here goes again. In case it helps, the transcription of s/n 45-11743's IARC is thus:

P-51D [sic] s/n 45-11743 Contract AC-2400, AAF Pri[ority] 1-1; Project Del 3203.
Accepted at NAA Dallas 07Jun45 for Inglewood
Delivered 15Jun45
Available 18Jun45 (08Jun45 crossed out)
Arrived Inglewood 25Jun45
redesignated P-51D to P-51M 06Jul45 at Inglewood
ATC Ferry Command 03Oct45
ATC Ferry Command to RFC 21Oct45
Walnut Ridge 25Oct45

Hope this adds to the discussion. This would seem to support the assumption that the aircraft was ferried to NAA at Inglewood, converted to P-51M there for a brief test campaign and then disposed of to the RFC at Walnut Ridge in October 1945.

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[BarnOwlLover]

I wouldn't say (at least for me) that I gaslighted the post, but considering how many years it took to even confirm that the P-51M even existed, let alone photos of it (only one photo is known, inflight even--can't say that to my knowledge of the XP-51 lightweights!), I think that some are wondering what Bill and Lowell may've turned up in their research of the P-51D and later variants for the sequel to P-51B: Bastard Stepchild. I'd love to hear how things have progressed on that book, as last I heard the P-51M might be the ending point unless they get some more info on the XP-82/P-82 to keep that from being little more than maybe and addendum or bonus material.

That said, it seems that they do have enough info on the M to write an entry about it in their next book. I also wonder if some performance info exists for it. After all, it's a P-51D airframe fitted with the P-51H engine (minus ADI), so it'd be safe to assume that maybe performance overall would be between the D and H levels. And I do guess for the P-51L (P-51H with uprated V-1650-11) would be estimates, since none were built or converted, and Packard only reportedly built a couple of -11s.

But it does seem that the H, L, M and P-82B (how it would've differed it any from the XP-82s and the 20 actual P-82Bs built) were all subject to significant orders that were scrapped (L/M) or cut back (H/P-82B) at VJ Day.

Oddly, I did read somewhere that we had pseudo-P-51Ms in USAAF/USAF/ANG use when -9 Merlins were put into P-51D airframes, and sometimes -7 or -3 engines also ended up in P-51Hs as well.

 

[drgondog]

I've read through this thread with interest, frustration and annoyance. But mainly the last two. In case it helps, the transcription of s/n 45-11743's IARC is thus (I haven't seen it listed, so apologies if it has been - there's a lot of words in the last 8 pages):

P-51D [sic] s/n 45-11743 Contract AC-2400, AAF Pri[ority] 1-1; Project Del 3203.
Accepted at NAA Dallas 07Jun45 for Inglewood
Delivered 15Jun45
Available 18Jun45 (08Jun45 crossed out)
Arrived Inglewood 25Jun45
redesignated P-51D to P-51M 06Jul45 at Inglewood
ATC Ferry Command 03Oct45
ATC Ferry Command to RFC 21Oct45
Walnut Ridge 25Oct45

Hope this adds to the discussion. This would seem to support the assumption that the aircraft was ferried to NAA at Inglewood, converted to P-51M there for a brief test campaign and then disposed of to the RFC at Walnut Ridge in October 1945.

To add to the discussion, although the IARC is NOT the last word on production sequence - only acceptance and movement
P-51D-25-NT #407 first block 44-84796 accepted 6-7
P-51D-35-NT redesignated P-51M-NT #1 45-11743 accepted 6-7, delivered 6-15 (Dallas), 6-25 (inglewood)
P-51D-25-NT #600 first block 44-84989 accepted 6-14
P-51D-25-NT #1 last block 45-11343 accepted 6-29 delivered 7-2
P-51D-30-NT #200 45-11542 delivered 7-20
P-51D-30-NT #1 45-11543 delivered 7-20 immediately after last P-51D-25-NT

P-51D-35/P-51M was fabricated from D-20 or -25 Spares. My notes/source point to V-1650-9A conversion at Dallas - not Inglewood

Both the M (wih 1650-9A) and the L (with 1650-9) were in play for Dallas before the cutback on P-51H occurred.

USAF did indeed replace -3 or -7 with 9A's but it wasn't a programmed replacement as there weren't many built. The 9A is still a stronger (not more powerful) -3 with same gears, stronger crankshaft for better high altitude performance.

 

[Sabrejet]

Well hopefully it helped. It seems that the "wave your arms about" approach is alive on this thread, so I understand the frustration.

 

[BarnOwlLover]

To add to the discussion, although the IARC is NOT the last word on production sequence - only acceptance and movement
P-51D-25-NT #407 first block 44-84796 accepted 6-7
P-51D-35-NT redesignated P-51M-NT #1 45-11743 accepted 6-7, delivered 6-15 (Dallas), 6-25 (inglewood)
P-51D-25-NT #600 first block 44-84989 accepted 6-14
P-51D-25-NT #1 last block 45-11343 accepted 6-29 delivered 7-2
P-51D-30-NT #200 45-11542 delivered 7-20
P-51D-30-NT #1 45-11543 delivered 7-20 immediately after last P-51D-25-NT

P-51D-35/P-51M was fabricated from D-20 or -25 Spares. My notes/source point to V-1650-9A conversion at Dallas - not Inglewood

Both the M (wih 1650-9A) and the L (with 1650-9) were in play for Dallas before the cutback on P-51H occurred.

USAF did indeed replace -3 or -7 with 9A's but it wasn't a programmed replacement as there weren't many built. The 9A is still a stronger (not more powerful) -3 with same gears, stronger crankshaft for better high altitude performance.

I thought that the L was slated for the -11 Merlin (different carb and uprated power), but was otherwise similar to the H? It seems that the -11 died when the P-51L got cancelled. And it does seem that the L was slated for Dallas, which does mean that at least a line for lightweight-based P-51s was intended for there (?).

 

[drgondog]

I thought that the L was slated for the -11 Merlin (different carb and uprated power), but was otherwise similar to the H? It seems that the -11 died when the P-51L got cancelled. And it does seem that the L was slated for Dallas, which does mean that at least a line for lightweight-based P-51s was intended for there (?).

The L was the same as the H, and the -11 was 'tentatively' designated for the H but the decision to change mid block to retrofit the existing H was never made before L cancelled entirely. Additionally the -11 was in very early stage of production testing at a time when the H/-9 was experiencing consistent issues delivering rated power at 80 and 90".

It was a 'wait and see' to determine a.) replace -9 for H with -11, b.) replace -11 with -9. The P-82 flight testing was delayed nearly 6 weeks due to issues encountered with the -11 density carb and you will note that it was discontinued after XP-82 in favor of the -21 & -23 with pressure carb

 

[Geoffrey Sinclair]

Interesting responses, I was more expecting ideas about how to reconcile the contradictions, or whether it was the reports catching up to the card or the card catching up to the reports. Since the engine defines the version the information from Drgondog indicates the card was catching up to the reports.

The factories were making daily production reports and if they were late could be told the official figures had been published, alter factory figures to match. The delivery report came out on 5 July, the day before the card changes the model designation, the RC-301 date is 30 June which is theoretically possible as acceptance flights were done in daylight.

Going to the USAAF Delivery Logs the first page heading has the P-51 version erased and replaced by a hand written M, as expected the acceptance and completion dates are the same as the 45-11743 card, the extra dates given are completed on 31 May, left pre modification 5 June, allocated to AAF, Assignment E+P. The logs add P-51M 45-11744 was completed on 25 July 1945, while P-51M 45-11745 to 11794, F-6M 45-11795 to 11823, P-51M 45-11838 to 11850 and TP-51M 45-11983 were completed 3 to 14 August 1945. Only P-51M 45-11743 was accepted and delivered.

On the D model front, either P-51 or F-6, 44-84390 to 84989 were D-25, accepted April to June 1945, 45-11343 to 11542 were D-25 accepted in June and July, 45-11543 to 11742 D-30 accepted July and August 1945. 45-11538 to 11542 were the last D-25 to be completed on 12 July, 45-11514 and 11539 the last accepted on 20 July. While 45-11543 was the first D-30 completed on 27 June, 45-11545 the first accepted and delivered on 17 July 1945. The final D-30 completions were on 3 August, final acceptances were three on 10 August then 45-11735 on 27 August 1945. All completed D models were accepted and delivered.

P-51M 45-11743 completion and acceptance dates make it contemporary with the D-25 model serials roughly from 44-84757 to 84802.

 

[BarnOwlLover]

The L was the same as the H, and the -11 was 'tentatively' designated for the H but the decision to change mid block to retrofit the existing H was never made before L cancelled entirely. Additionally the -11 was in very early stage of production testing at a time when the H/-9 was experiencing consistent issues delivering rated power at 80 and 90".

It was a 'wait and see' to determine a.) replace -9 for H with -11, b.) replace -11 with -9. The P-82 flight testing was delayed nearly 6 weeks due to issues encountered with the -11 density carb and you will note that it was discontinued after XP-82 in favor of the -21 & -23 with pressure carb

Sorry for getting back to this late, but I have to say (as with a lot of things concerning WWII aircraft development), I didn't know that about the XP-82. I knew of the delays caused by take off problems with the engines being set up to rotate the props the "wrong way" and stalling the center wing section. But then again, the -9 Merlin had issues with consistent power output (being able to reach rated power on a consistent basis) with the boost control at 80" dry, let alone 90" with ADI. So it probably shouldn't be surprising that the -11 had issues, and with war's end, the P-51H and P-82B with -9 based Merlins were seen as "good enough (as well as boosted P-51Ds/Ks) until P-80s, F-84s and F-86s supplemented and eventually replaced them in front line units.

 

[BarnOwlLover]

I know that this question probably won't have a good answer, but is it known what the performance of the P-51M might have been? Did any estimates exist, since it probably didn't get much testing (if any)?

 

[drgondog]

I know that this question probably won't have a good answer, but is it known what the performance of the P-51M might have been? Did any estimates exist, since it probably didn't get much testing (if any)?

No reason to believe any increase over 1650-3. Same gearing (IIRC), just a better engine reliability wise.

 

[BarnOwlLover]

Aside from that, then why go with the P-51M? Especially since the -7 was maxing out in USAAF service at 75" Hg. I also wonder the reasoning why the USAAF never went for 80-81" with the V-1650-7 or other Merlins (aside from the -9), though it seems that the British did for a combat rating for both the Rolls-Royce and Packard Merlins.

I can understand more durability, but at that stage of the war if they was no (at least worthwhile) performance increase, what's the point? Unless the -9 (with or even without in the case of the M, ADI) had a wider performance envelope, such as altitude or more evenly distributed performance across altitude. And in fairness, the P-51H and XP-82/P-82B were capable of between a 1500-2000 ft higher service ceiling than the P-51D.

 

[BarnOwlLover]

Having said the above and having read though the Grugenhagen book again last night, was it possible to get better high alt. performance without harming low and mid alt performance with the -9A engine, being essentially the Packard equivalent of the Merlin 110/RM.16SM engine (which was also tested in a P-51B)?

 

[BarnOwlLover]

I apologize for dredging this back up, but I was looking though Boeing's images of the P-51 on their image site, and it seems that there's a second image on there (other than the one that's been floating around for a few years) of a P-51D that has the same tail number as the other known P-51M photo. So could that be another photo of the elusive P-51M?

 

[drgondog]

I apologize for dredging this back up, but I was looking though Boeing's images of the P-51 on their image site, and it seems that there's a second image on there (other than the one that's been floating around for a few years) of a P-51D that has the same tail number as the other known P-51M photo. So could that be another photo of the elusive P-51M?

Boeing has Many errors in image citations. There was one and only one P-51M.

 

[BarnOwlLover]

The Image was titled "Last P-51D Mustang" or something along those lines. I thought that the "last" P-51D (at least built at Dallas) was converted into the M's prototype. The photo in question had the same tail number and such as the P-51M photo that's been floating around for a while. Then again, Boeing's site has a lot of P-51H's captioned as P-51Ds, etc.