Speculative thread: Early Mustang envisioned for Merlin power, GP fighter/interceptor

I'm actually surprised that the RPG per cannon was so low, given that I've read that the 4x.50s carried 400 or 440 rpg, or is that figure an error? Granted, the Hispano MkV (and the AN/M3, T31 and M24 cannons that were fairly light and compact weren't out in 1943 when this began, the Hispano Mk II/M2 being significantly larger and heavier, weighing nearly twice as much a the AN/M2 .50 Browning. Also, a 20mm round weighed roughly twice as much as a .50 BMG).

Also, any idea on ammo capacity for the aborted 2x20mm, 2x50 project (similar to the Spitfire E wing, or the CAC CA-15--125/140 rpg 20mm, both 250 rpg for the .50s)?

I'm also a bit surprised that the H was never seriously looked at as far as being cannon armed (or the F-82), but then again, the USAAF had problems with the Hispano cannon though out most of World War II, and US produced versions tended to be jam prone compared to the British versions (I've read that the biggest/most common issue was an excessively long chamber that caused weak primer strikes, while British HS404s had a shorter chamber. Also, later Hispano cannons may've also used electric primers).

I think a P-51 H armed with 4 20mm cannons with maybe 150 rpg that could do both interceptor and escort missions would've been a winner. I do believe that NAA did make charts and such of at least projected/expected performance at varying gross weights (with interceptor configuration topping out at a max of approx 8500 lbs) that at max and WEP/sprint that up to 6000+ FPM climb rates were possible.

I wonder how that compared to the F/G, as well as maneuverability/agility vs the B/C and the F/G.

We also have to look behind the scenes a bit. The US Army was expecting the 1200rpm .50 cal guns to show up in late 1944 or into 1945. A batch of guns with a T number did show up in 1945 (?) and were later standardized as the M3. Six of those guns would equal nine of the standard .50 cal at about the same weight.
I don't know if that is what they were planning but it is possible.
It is also a fact that they were working on new ammunition for the .50, a light weight, high velocity, high capacity incendiary round that later became the M23. It was combat trialed in late 1944/early 45. Trials didn't go well with some rounds igniting in the barrel or just in front of the muzzles. However the Army/Air force did not give up and while it was in wide spread service in Korea, it required not only going into and out of production for modifications it also required changing the manufacturing facilities ( factories) twice to help solve the problems.
This was in peace time but shows what they were trying to do or importance as they could have sat on it and used the war time guns and ammo in 1946-48.

There were 20mm guns that used electric priming and some of them were based on the Hispano, well post war. However changing an existing gun to electric priming isn't quite as easy as it sounds. and the gun is either electric primed or it is not. To 'change' ammo needs a new breech block and firing system, electric contacts on the face of the bolt/breech block replace the firing pin assembly. Obviously this requires a supply of the electric primed ammo. The US had greater logistics problems than the Germans faced. The US could make a lot more stuff, getting it where it was needed sometimes took months from factory to front lines.

Not saying it was impossible, just saying there were a number of considerations that US planners had to take into account when considering gun/ammo changes.

Also in 1943/44 what were the XP-51s going to intercept? The Germans didn't have much for large 4 engine bombers or even large numbers of bombers of any type. Japanese bombers weren't that hard to shoot down. All respect due to the men that faced the defensive guns but need for the US was not need faced by the Germans and Japanese.

Problem is the same as what happens with a lot of things--when proposed, there was a want/need for it. By the time it got made in the flesh, there wasn't a big need or want for it. The F/G were intended it seems to be interceptors first, escort fighters second. But by late 1943 when the P-51B entered service en masse, the desire was for a high performance escort fighter, or at least one that can do both long range escort and interception equally as well.

As mentioned, the F/G couldn't make it to Berlin or points east reliably on internal fuel and even drop tanks, not without provision for a fuselage tank, which the F/G couldn't carry without a redesign, which lead to the H model. But even then, the H approximated the G's performance for the most part, even with more guns/ammo, more fuel and an resultant increase in weight. Only thing it couldn't do in interceptor trim from what I can tell is climb at 7000+fpm. But 5200-6000 fpm (depending on conditions and source) was still very competent for a piston engine interceptor by 1945 standards, if not phenomenal, just not 7000+ fpm phenomenal.

Also, did the H have the AN/M2 or M3 for armament? The F-82s got the M3 as did apparently some late production P-51Ds, but what did the H's get?

BarnOwlLover said:

Also, did the H have the AN/M2 or M3 for armament? The F-82s got the M3 as did apparently some late production P-51Ds, but what did the H's get?

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All sources I've seen online say the P-51H had 6x AN/M2. Some P-51D's used in Korea used the M3, but I'd guess these were retrofits and not factory installations.

I've been digging though threads about the Merlin Mustang's development (both production and lightweights), and I wonder if the P-51B/C/D/K would've been a good interceptor when "flying light"? Namely, loaded with half fuel or enough fuel to handle a Spitfire type interception mission? I did read at a TO weight of 8600 lbs that the XP-51B did do over 450 mph and was capable of a 4800 fpm climb rate (better than the Hawker Tempest), but that was when loaded with enough fuel to go between London and either the German/Dutch boarder or extreme western Germany.

Could a Merlin Mustang flying in "interceptor" trim (equal to or slightly heavier than an Allison Mustang in weight) been a good interceptor by World War II standards? For reference, I've seen mentions of the P-51H in interceptor trim (TO weight of about 8500 lbs) have up to a 6000 fpm climb rate, maybe more. Only planes that I know of that could do better than that were the XP-51F/G LW Mustangs (that were even lighter), and rocket propelled planes like the Me-163. I can't think of any thing that was a fighter that had a prop or a turbojet that could've done better in that period, at least that made it into production.

BarnOwlLover said:

I've been digging though threads about the Merlin Mustang's development (both production and lightweights), and I wonder if the P-51B/C/D/K would've been a good interceptor when "flying light"? Namely, loaded with half fuel or enough fuel to handle a Spitfire type interception mission? I did read at a TO weight of 8600 lbs that the XP-51B did do over 450 mph and was capable of a 4800 fpm climb rate (better than the Hawker Tempest), but that was when loaded with enough fuel to go between London and either the German/Dutch boarder or extreme western Germany.

Could a Merlin Mustang flying in "interceptor" trim (equal to or slightly heavier than an Allison Mustang in weight) been a good interceptor by World War II standards? For reference, I've seen mentions of the P-51H in interceptor trim (TO weight of about 8500 lbs) have up to a 6000 fpm climb rate, maybe more. Only planes that I know of that could do better than that were the XP-51F/G LW Mustangs (that were even lighter), and rocket propelled planes like the Me-163. I can't think of any thing that was a fighter that had a prop or a turbojet that could've done better in that period, at least that made it into production.

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Yes - The P-51B-15 hogged out at Max GW Internal load out (269gal, full amor) WITH wing racks; At 75"MP top speed 444mph at and ROC = 4360fpm mac; Time to climb to 20000 ft ~ 5min.

http://www.wwiiaircraftperformance.org/mustang/p-51b-24771-climb-blue.jpg

Light Fighter/Interceptor role w/o racks at 75", GW = 8600 with 100 gal fuel would be approximately ROCmax >4900 fpm and ~450mph at 20K.

Pretty good given how fairly large the Mustang was, but the Merlin had to be a big help (and 8600 lbs gross weight wasn't that heavy by 1943, certainly after). Also shows that different set ups and different power levels can be apples and oranges. For instance, when in the escort role I'd expect especially climb to be sluggish by comparison with climb rate, but once in combat or as an interceptor (or not having to carry as much fuel as when set up for long range), performance should improve.

Again, the P-51H and the LW XP-51s leave the B/D in the dust, but even then, the B/D can climb with or outclimb a Hawker Tempest, wasn't insanely far behind the Spitfire 14, was faster than the Tempest and as fast as the Spitfire 14. And aside from the Me 109K (speed and climb, marginally) and the Ta-152 (speed at high alt), those were better figures than the majority of Luftwaffe and probably IJA/IJN fighters.

However, again apples to apples, fuel load/weight and configuration should be similar for a fair comparison for a given role.

pbehn said:

I would use my 20/20 hindsight and have all Muslang MkI Mk II/ P-51A that were taken by the USA after Pearl Harbour to be shipped to UK for fitting with two stage Merlins when avalable, cancel the A 36 and do the same until two stage Merlin production starts at Packard. Along with the Merlin, fit a Malcolm hood as was done to many P-51Bs. Job done.

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Was the A-36 Apache a failure?

Howard Gibson said:

Was the A-36 Apache a failure?

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No, The A-36 Mustang was successful as low level attack/dive bomber - but dive bombing as CAS support changed to glide bombing about the time the A-36 started production run , hence P-51A and B and C contract follow up.

Howard Gibson said:

Was the A-36 Apache a failure?

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o, I was just employing hindsight to come up with a completely impractical solution that may have had P-51s with Merlins earlier but certainly would have reduced the numbers of A 36 Spitfires etc.

As long as we`re just speculating here, I would propose that this alternative history was possible, and probably lacked political backing, but had no serious technical impediment.

Interesting fact 1: The USA were desperate to buy a Schneider Cup Winning V12 from RR, as they knew perfectly well it was ahead of their own V12 at the time in several
respects. After a lot of wrangling, eventually they were sent a standard Buzzard, much to their annoyance.

Alternative History: The British, recognising that the USA were likely to be an essential ally in future wars (which we`d been wargaming on paper since 1928), decide to
send them a REAL "R" engine, the USA being very pleased agree to set up a joint technical partnership and exchange a set of engineers from Derby to Allison and
visa versa in 1932. The results of this were a totally revised V-1710 engine, incorporating the best features of each firms experience, critically, Allison bearings
and combustion chamber, with RR supercharging and high pressure high temperature cooling. It is first produced in volume in 1936 with a two-stage system
of supercharging appearing in 1939 after guidance from the Royal Aircraft Establishment who had already been working on such a scheme before Hooker (factually true)

The new engine provides unparalleled performance and RR agree to a joint production programme, both firms begin mass production in 1940, the Merlin-1 is
mothballed and the Vulture never happens, and the mustang begins service with the RR/Allison V-1710 MkII, with 2-stage supercharger and a Bendix pressure carburettor.

The entire negative-g issue also then never happens.