WW2: Why was the 9th Air Force given P51 ins6tead of giving them to the 8th Air Force in 1943? (4 Viewers)

[Engineman]

I note that the V-1650-1, with a single stage two speed supercharger, apparently had no such plug problems, or at least none that I have read of. This, despite the P-40F being deployed to locations where maintenance and supply was something of a challenge, like Guadalcanal and North Africa.

View attachment 901133View attachment 901132
As for the difference between the V-1650-3 and the Merlin 61, Packard used removable heads, unlike RR, which had found them too leaky with their first attempts. Packard also redesigned the supercharger gears, presumably to make them easier to manufacture. The challenge of producing enough of the gears was cited as the main limiting factor for RR production. Packard also had Wright redesign the supercharger impellers, presumably for ease of production. And of course Packard used US made accessories, including most significantly the Bendix Pressure Carb, which eliminated the Merlin's notorious Lean Cut/Rich Cut power loss associated with negative G's.

Sparkplugs were a development issue at several stages of the Merlin developments. In the early Merlin's during the late 1930's the sparkplugs had just developed from versions that used worked natural Mica for the central insulator body of the sparkplugs. Cast and fired ceramic insulators were developed by companies in Germany during the late 1930's and the ceramic varieties of insulator were just establishing themselves at the start of WW2. These early war engines were working up to about 6lb Boost. As 100 Octane fuel was established
in use, Boost levels were raised to around 12lb and sparkplug issues came and went, with problems from internal gas leakage and Harder plugs that suffered more from fowled plugs at lower power settings. The particular sparkplug issues in the early days of the long-range escort Mustang were really just further problems with these issues, that happened to coincide with higher Boost levels, long cruise flights and more exotic fuels in the 2-stage engines. I believe that the rush for certain British sparkplugs for early 2-stage Packard engines was precipitated by the fact that Rolls-Royce had been pushing the sparkplug development with British manufacturers for these higher spec plugs for a while. As soon as the American companies got the details of the later plugs, they tooled-up and made them by the thousands.

Eng

 

[MIflyer]

Sparkplugs were a development issue at several stages of the Merlin developments.

Aircraft sparkplugs have special environments and one reason is that revving up an engine on the ground to full throttle is not the same as applying full power and actually flying, with the propeller loaded, even with relatively low power normally asperated engines. For that reason, the way to test an aircraft spark plug is to use a "bomb", a pressure vessel designed to simulate actual engine cylinder conditions when flying by pumping high pressure air into it.

 

[Engineman]

Aircraft sparkplugs have special environments and one reason is that revving up an engine on the ground to full throttle is not the same as applying full power and actually flying, with the propeller loaded, even with relatively low power normally asperated engines. For that reason, the way to test an aircraft spark plug is to use a "bomb", a pressure vessel designed to simulate actual engine cylinder conditions when flying by pumping high pressure air into it.

Sparkplugs are usually tested with a pressure testing rig. The sparkplug is screwed into a small pressure vessel with a window and pressurised to about 120psi. A repeating HT source then fires the plug and the appearance of the sparks at the electrodes is assessed. Particular engine overhaul manuals may specify other tests for plugs.
Most piston engine aircraft can be tested under load on the ground. Again, specific testing procedures are laid down for all certified types.

Eng

 

[Jugman]

M MIflyer The Merlin 61 had two piece blocks. In fact it was the first British built model to do so. Followed by the 22 and 55

 

[MIflyer]

The Merlin 61 had two piece blocks

But Packard introduced the first removable Merlin heads with the V-1650-1, for the P-40F.

 

[GregP]

The first Merlin model with removable heads was the Merlin C, 21 Dec 1935 in a Hawker Horsley ... unless I am mistaken?

My Excel file says it had separate ramp heads and crankcase as well as cylinder skirts.

 

[greatgonzo]

The 56th was scheduled for first conversion, 355th the next but 56th (Landry/Schilling turned Kepner down while Zemke was on leave doing a bond tour with LeMay).

It is usually said that 56th refused conversion to P-51. Would You know some details about that? I always wondered how it was even possible for lower level unit to stand against logistic plans of highest command.

 

[Engineman]

Hi all,

So, to try and help with the Merlin separate cylinder heads questions, here is a quite well thought-out illustration of Merlin structural development by Jerry Wells, copied from his excellent piece on Merlin development and available in the online AEHS site.

Here you can see that all development Merlins upto and including the Mk1 had detatchable heads, except the Merlin G that introduced the one-piece blocks and flat head which continued into the Merlin II onwards until the Mk 60.
Packard introduced their own design of detatchable heads on the Packard Merlin 28 / V-1650/1, changing to the Rolls-Royce redesign of detachable heads from the Merlin Mk 61 onwards for their V-1650/3 onwards.
Additionally, there were various upgraded rebuilds of engines, such as the Merlin Mk 22A, that were later fitted with 2-piece blocks after having been built with one-piece blocks.

Cheers

Eng

 

[drgondog]

It is usually said that 56th refused conversion to P-51. Would You know some details about that? I always wondered how it was even possible for lower level unit to stand against logistic plans of highest command.

Yes I do. Kepner offered the 56th FG first chance at converting from P-47. Zemke was in the US on a bond tour with LeMay and due back in March. Landy, Gp Exec and Schilling decided they preferred to stay with the P-47. Zemke was furious when he got back but decided not to appeal to Kepner to 'get back in line' as the new 370-gal internal tank P-47D-25 was scheduled for May deliveries.

He (Zemke) later wrote in his Wolfpack book that he wished that 56th had taken the Mustangs because their overall success would have been higher. He also stated that the Mustang was the best fighter due to the combination of maneuverability and range.

 

[greatgonzo]

Landy, Gp Exec and Schilling decided they preferred to stay with the P-47

That part makes me wonder. The 8th AF plans to convert to other type of aircraft, and a group CO says: 'No thank you, I'd rather prefer not to."
I always thought there had to be some turmoil behind it. Or was it that simple?

 

[drgondog]

That part makes me wonder. The 8th AF plans to convert to other type of aircraft, and a group CO says: 'No thank you, I'd rather prefer not to."
I always thought there had to be some turmoil behind it. Or was it that simple?

According to Zemke, it was that simple. After that all the other group COs agreed to conversion and 56th was placed at the end of the line after the 78th, 353rd and 356th P-47 conversions.

Notice that Zemke did not resist conversion from P-38 to P-51 when he commanded the 479th FG,

 

[greatgonzo]

According to Zemke, it was that simple

Did not expect that . I thought maybe the P-47M appearance and will to see it's performance in combat had something to do with it. But still, with the scale of production of everything at the time, I wouldn't think anybody really cared about one hundred aircraft with no future really.

 

[drgondog]

Did not expect that . I thought maybe the P-47M appearance and will to see it's performance in combat had something to do with it. But still, with the scale of production of everything at the time, I wouldn't think anybody really cared about one hundred aircraft with no future really.

The P-47M and N weren't on the horizon until after D-Day and the conversion decision to convert to Mustangs was made on or about Big Week, probably early February when the value of the 85-gal fuselage tank doubling the P-47D escort range with belly tank was a major factor. It was duly noted that the P-47D was still far short of P-51B even when wing pylons added 300 gallon more external fuel.

 

[greatgonzo]

drgondog, that's so cool! Thank You very much for Your attention.

 

[andy1967]

Did General Doolittle's change of tactics for Fighter escort from close bomber support to more aggressive seek and destroy and attacking of ground targets have anything to do with the reluctance to change to the P51.

 

[Frog]

Rather something to do with a bigger number of available fighters, not specifically P-51s.

 

[drgondog]

Did General Doolittle's change of tactics for Fighter escort from close bomber support to more aggressive seek and destroy and attacking of ground targets have anything to do with the reluctance to change to the P51.View attachment 901466

No. But complicated.

First, the doctrine of changing the role of escort to 'pursue and destroy' was encapsulated at AAF HQ with the release of FM-1-15 "Tactics and Techniques of Air Fighting" in late 1942. Led by MG Muir Fairchild, the foundation doctrinal change from convoy to pursuit was that the role of fighter aircraft was "Destroy Hostile Air Forces Freedom of the Air".

The priorities of the Combined Bomber Offensive changed in June 1943, raising 'destroy the luftwaffe' to number one, replacing 'destroy the Submarine industry'. Also in June, Arnold directed his CoS Barney Giles to field an escort fighter capable of escorting a B-17 to any target at limit of range. Giles personally drove NAA, Republic and Lockheed to increase internal fuel capacity, and all to conceptually place Range extension at top of new designs.

Lockheed and North American responded immediately with mods to increase fuselage fuel and leading edge fuel, respectively to compliment wing rack/drop tank capability, respectively. Republic added centerline (B-7) shackle in July, promised the deliver the wing pylon/fuel feed by December and begin designing for adding 65 gal to main fuel tank by Spring 1944.

Arnold prioritized delivery of P-38J and P-51B to ETO. That the P-51B was conceptually designated for CAS and delivered to 9th AF rests on General Saville - who believed that the P-51B was ideal to replace the P-39, and personally believed that the P-38 was the best fighter in AAF inventory. Long complicated story that I addressed in my Bastard Stepchild book, and well discussed in Ludwig's P-51 Mustang book.

Operationally, the 8th AF was handicapped by a.) too few Fighter Groups, b.) the limited range of the P-47C with no drop tank capability other than Republic designed Ferry tank, until September 1943. The original AWPD-1 Plan called for one FG per BG - which was Never achieved operationally. The disaster at Schweinfurt-Regensburg highlighted the urgency to deliver the P-51B and P-38J, already in production but not operational until December- and too few to execute on changing from defensive to offensive fighter strategy until shortly after Big Week. As an aside, only Zemke was developing offensive fighter tactics in fall 1943. Eaker knew that the LW had developed a 'ring strategy' in which major forces were not deployed until escorts turned back, but helpless to do anything but 'press on' beyond escort range.

The achievement of FM-1-15 doctrine was limited through the end of 1943, simply because no fighter capable of pursue and destroy anywhere over Germany existed in both strength and internal fuel to execute beyond mid-Germany. The P-47D equipped FG's had grown to seven, P-38 to two and the P-51 to one - but the latter two had not yet completed mods to increase internal fuel. So, the target selection post Black Thursday Schweinfurt (10-14-43) was limited to fighter escort range. The arrival of the 55th G with P-38H capable of two 150/165-gal drop tanks extended target escort range to Kiel, but only on a limited basis because they were too few in number. It took 20th FG nearly four months to become operational after their arrival in August 1943.

However, the Combined Chiefs had agreed Overlord and recognized that destruction of Luftwaffe capability to interfere with the invasion was a critical success factor - and Operation Argument was conceived leading to Big Week.

Now, to your question. Doolittle and Spaatz had zero reluctance to change from P-47 to P-51. Eaker had specifically appealed to Arnold to send both P-38 and P-51B to ETO in June, 1943. Doolittle, when asked for an opinion by Arnold (among others), which AAF fighter was best suited for long-range escort - replied "P-38 and then P-51", but he was citing the P-51A because of known range superiority although limited above 20,000 feet. Doolittle made it a point to stay up to speed with all aircraft of importance, so he also was aware of AAF Flight test results for the P-51B-1.

IMO, Doolittle's major contribution to FM-1-15 doctrine was to award equal victory credits for aircraft destroyed on the ground toward Ace status. Historically the first such awards were made by P-47D pilots of the 78th FG in February 1944, then to 355th FG on March 8, 1944 (the day before they were fully converted.

Even though the 'promise' of near equal range in the P-47D-25, it was operationally available only after D-Day. The first production article rolled off the Republic line on Feb 15, 1944.

By that time, nearly 600 P-51Bs had arrived in UK. Cheaper, more maneuverable, faster, better ROC, much better range = B-17. And, the P-38J was having serious reliability issues in comparison.

No brainer.
to P-51B0

 

[andy1967]

No. But complicated.

First, the doctrine of changing the role of escort to 'pursue and destroy' was encapsulated at AAF HQ with the release of FM-1-15 "Tactics and Techniques of Air Fighting" in late 1942. Led by MG Muir Fairchild, the foundation doctrinal change from convoy to pursuit was that the role of fighter aircraft was "Destroy Hostile Air Forces Freedom of the Air".

The priorities of the Combined Bomber Offensive changed in June 1943, raising 'destroy the luftwaffe' to number one, replacing 'destroy the Submarine industry'. Also in June, Arnold directed his CoS Barney Giles to field an escort fighter capable of escorting a B-17 to any target at limit of range. Giles personally drove NAA, Republic and Lockheed to increase internal fuel capacity, and all to conceptually place Range extension at top of new designs.

Lockheed and North American responded immediately with mods to increase fuselage fuel and leading edge fuel, respectively to compliment wing rack/drop tank capability, respectively. Republic added centerline (B-7) shackle in July, promised the deliver the wing pylon/fuel feed by December and begin designing for adding 65 gal to main fuel tank by Spring 1944.

Arnold prioritized delivery of P-38J and P-51B to ETO. That the P-51B was conceptually designated for CAS and delivered to 9th AF rests on General Saville - who believed that the P-51B was ideal to replace the P-39, and personally believed that the P-38 was the best fighter in AAF inventory. Long complicated story that I addressed in my Bastard Stepchild book, and well discussed in Ludwig's P-51 Mustang book.

Operationally, the 8th AF was handicapped by a.) too few Fighter Groups, b.) the limited range of the P-47C with no drop tank capability other than Republic designed Ferry tank, until September 1943. The original AWPD-1 Plan called for one FG per BG - which was Never achieved operationally. The disaster at Schweinfurt-Regensburg highlighted the urgency to deliver the P-51B and P-38J, already in production but not operational until December- and too few to execute on changing from defensive to offensive fighter strategy until shortly after Big Week. As an aside, only Zemke was developing offensive fighter tactics in fall 1943. Eaker knew that the LW had developed a 'ring strategy' in which major forces were not deployed until escorts turned back, but helpless to do anything but 'press on' beyond escort range.

The achievement of FM-1-15 doctrine was limited through the end of 1943, simply because no fighter capable of pursue and destroy anywhere over Germany existed in both strength and internal fuel to execute beyond mid-Germany. The P-47D equipped FG's had grown to seven, P-38 to two and the P-51 to one - but the latter two had not yet completed mods to increase internal fuel. So, the target selection post Black Thursday Schweinfurt (10-14-43) was limited to fighter escort range. The arrival of the 55th G with P-38H capable of two 150/165-gal drop tanks extended target escort range to Kiel, but only on a limited basis because they were too few in number. It took 20th FG nearly four months to become operational after their arrival in August 1943.

However, the Combined Chiefs had agreed Overlord and recognized that destruction of Luftwaffe capability to interfere with the invasion was a critical success factor - and Operation Argument was conceived leading to Big Week.

Now, to your question. Doolittle and Spaatz had zero reluctance to change from P-47 to P-51. Eaker had specifically appealed to Arnold to send both P-38 and P-51B to ETO in June, 1943. Doolittle, when asked for an opinion by Arnold (among others), which AAF fighter was best suited for long-range escort - replied "P-38 and then P-51", but he was citing the P-51A because of known range superiority although limited above 20,000 feet. Doolittle made it a point to stay up to speed with all aircraft of importance, so he also was aware of AAF Flight test results for the P-51B-1.

IMO, Doolittle's major contribution to FM-1-15 doctrine was to award equal victory credits for aircraft destroyed on the ground toward Ace status. Historically the first such awards were made by P-47D pilots of the 78th FG in February 1944, then to 355th FG on March 8, 1944 (the day before they were fully converted.

Even though the 'promise' of near equal range in the P-47D-25, it was operationally available only after D-Day. The first production article rolled off the Republic line on Feb 15, 1944.

By that time, nearly 600 P-51Bs had arrived in UK. Cheaper, more maneuverable, faster, better ROC, much better range = B-17. And, the P-38J was having serious reliability issues in comparison.

No brainer.
to P-51B0

Thanks for your comprehensive reply.