1942-45 USAAF/RAF western front high altitude interceptors.

[BarnOwlLover]

So I was wrong about the Mosquito, though the majority used in World War II were still unpressurized. As far as fighters went, the RAF did have the Spitfire VI and VII, which ended up being a handful as far as total production went, and other projects went no where (Welkin, Miles M23A, Mosquito NF XV, Vickers 432). But even the Welkin such did prove critical late in the war and afterwards, as lessons learned from the pressure cabin designs of the Welkin, Spitfire VI and VII, and pressurized Mosquitoes were used on aircraft like the Meteor and Vampire.

Also IMO odd that North American didn't design a pressurized fighter until they worked with jets, given that in testing that the XP-51F/G were reaching 46,000+ feet. Oddly, the G was doing this with the Merlin RM 14SM (Merlin 100/130), which was supposedly a GP/medium altitude rated engine, not the RM 16SM high alt engine (Merlin 110 series used on later Mosquito NF/B/PR aircraft). I don't think they ever got an accurate service or absolute ceiling from those test (they did get estimates), because while the plane continued to want to climb, the pilots were running out of oxygen due to the oxygen systems of the time petering out above 40,000 ft without pressure cabins.

For the record, the estimated performance as far as service vs absolute ceiling was 43,500+ ft/nearly 45,000 ft for the XP-51F (V-1650-3 Merlin), and 44,000+ft/46,000+ft for the XP-51G (RM 14SM Merlin). Source was World War II Aircraft Performance.

 

[wuzak]

About any German piston engine bomber that was used in numbers could be intercepted by any RAF or USAAF fighter that had like a 30,000+ foot service ceiling. But the RAF (also based on BoB experiences, as well as worries that the Ju-86 caused) wanted high altitude fighters. The resulted in stuff like the Welkin and the Spitfire VI/VIII and such.

The Welkin was never used operationally, though 70-odd were built.

The RAF/AM had figured that the high altitude threat had been dealt with.

The VI was a high altitude pressurised Spitfire, of which only 100 were made.

The VII was high altitude 2-stage Merlin Spitfire with pressurised cockpit, also initially fitted with extended wing tips. 140 built.

The VIII was the standard 2 stage fighter with standard wing tips and canopy. 1658 built.

The initial VIII (later the F.VIII) was fitted with the Merlin 63. The initial VII was fitted with the Merlin 64 (same as 63 but with cabin blower). The V-1650-3, fitted to many (most?) P-51Bs and -Cs, was based on the Merlin 63.

The Spitfire IX was also fitted with the Merlin 63.

Later there would be LF (Merlin 66) and HF (Merlin 70) versions of the VIII and IX, and an HF.VII (Merlin 71).

But there was the Ta-152, which could fly at over 47,000 feet. And remember that in testing the XP-51F/G topped out at just above 46,000 ft. Not because of lack of engine power, but lack of pilot oxygen. And as also suggested above, it seems that you do need a pressure cabin much above 40,000.

The Ta 152H was a response to a threat that was not really existent.

Maybe somehow the Allies convinced the Germans that high altitude bombers were coming, but even the B-29 flew at altitudes that the Bf 109 could intercept it.

 

[BarnOwlLover]

B-29s were capable of a service ceiling of over 32,000 feet, but usually few much lower than that after problems of flying at such altitudes (jet stream messing up navigation and accuracy problems, already bad with B-17s and B-24s over Germany flying at 20,000-25,000 ft were that much worse at 30,000+, and I'm sure other issues).

I do suggest reading this post in a thread talking about what the Luftwaffe could've/should've done post Battle of Britain:

Post-BoB: workable options for Luftwaffe

Do-17 production stopped in 1940 (?) Good. You need as many He 111s as you can get until you get your He-177 - 4 flown, tooled up and in production. I disagree, get the ju88 instead. They were getting into production. Problem is that it needs engines. The BMW 801 was a minimum I wonder...

ww2aircraft.net

The Ta-152 was ultimately developed for a threat that didn't materialize. But so was the Welkin (never operationally used and had problems of its own, namely the thick wing), and the various HF Spitfires, including the VI and the VII. The switch to the V-1650-7 in the P-51B/C/D/K after starting out with the -3 was because most Luftwaffe fighters didn't perform well above 20-25,000 ft. The -3 Packard Merlin ended up being a bit "too" high altitude rated (though at most alts from what I've seen there was little difference between a P-51B or D fitted with either engine until you got up to 25,000 ft, though the -7 did benefit from higher boost numbers later in the war that I don't think the -3 was usually operated at. at least by the USAAF).

And the Germans did give up pretty quickly on Ju-86 overflights after one partially successful interception over England (a modified Spitfire IX caught and chased one, but the Ju-86 escaped with only minor damage) and one totally successful one over Egypt (shot down by a modified Spitfire V at 49,000 ft). Maybe that convinced them that the RAF and probably the USAAF had high altitude fighters capable of shooting down high alt bombers, recon planes and other fighters.

And that did coincide with the RAF and USAAF scaling back development of high altitude interceptors, based on the fact that the overwhelming majority of German aircraft encountered could be easily dealt with by existing planes as far as altitude performance, and the USAAF ultimately killed their interceptor programs (XP-72, XP-67) or focused on multi-role long range fighters that could be converted into interceptors (P-51H, XP-82/P-82B, P-47M/N) after the Germans aborted the Amerikabomber program. For that, the USAAF feared that such a plane was possibly workable for the Luftwaffe, but didn't know until post-mortem how many problems that the Germans were having that crippled the program almost from the beginning.

 

[wuzak]

B-29s were capable of a service ceiling of over 32,000 feet, but usually few much lower than that after problems of flying at such altitudes (jet stream messing up navigation and accuracy problems, already bad with B-17s and B-24s over Germany flying at 20,000-25,000 ft were that much worse at 30,000+, and I'm sure other issues).

Well within the capabilities of a Bf 109G or K, Fw 190D.

The Ta-152 was ultimately developed for a threat that didn't materialize. But so was the Welkin (never operationally used and had problems of its own, namely the thick wing), and the various HF Spitfires, including the VI and the VII.

The Welkin was developed for an actual threat that had disappeared by the time it made it into production.

The Ta 152H (and Me 155/Bv 155) was developed for a threat that didn't exist, though the B-29 was part of the consideration.

But the B-29 didn't fly as high as the Germans maybe expected.

There were other variants of the Ta 152 under development, including the Ta 152C, which was a general fighter.

The switch to the V-1650-7 in the P-51B/C/D/K after starting out with the -3 was because most Luftwaffe fighters didn't perform well above 20-25,000 ft. The -3 Packard Merlin ended up being a bit "too" high altitude rated (though at most alts from what I've seen there was little difference between a P-51B or D fitted with either engine until you got up to 25,000 ft, though the -7 did benefit from higher boost numbers later in the war that I don't think the -3 was usually operated at. at least by the USAAF).

The V-1650-7 was fitted to P-51s because it improved the P-51's performance at the altitudes where combat was taking place, especially in terms of climb performance.

When you say "most Luftwaffe fighters didn't perform well above 20-25,000 ft", you are basically talking about the Fw 190A.

The Bf 109G and K performed quite well above 25,000ft.

And the Germans did give up pretty quickly on Ju-86 overflights after one partially successful interception over England (a modified Spitfire IX caught and chased one, but the Ju-86 escaped with only minor damage) and one totally successful one over Egypt (shot down by a modified Spitfire V at 49,000 ft). Maybe that convinced them that the RAF and probably the USAAF had high altitude fighters capable of shooting down high alt bombers, recon planes and other fighters.

It may be that the Luftwaffe could not afford too many losses of Ju 86s.

I can't quickly find the numbers of Ju 86P and Ju 86R models were produced.

 

[BarnOwlLover]

I don't know how many got made, but they operated over the Western Front theaters from as early as 1940 until 1943, though they largely disappeared after the Egypt fiasco.

The high alt flights sort of resumed with the Ar-234 jet and the Ju-388L high alt recon planes. And there were at one time plans for there to be heavy fighter/night fighter versions of them, apparently to counter the possible B-29 threat. Even though the USAAF never seriously thought about using the B-29 against Germany (unless the Allies decided to use nukes against Berlin, which weren't ready before VE day), it did seem to scare the Germans into looking into various high altitude interceptors.

As bad as Germany had it in 1944-45, they should be thankful that B-29s didn't enter the fray. Just their better performance and larger payload than the B-17 and B-24 would've been an issue.

Also, maybe the Nazis should've been thankful that the Hawker Tempest or the Fury (the latter missing the war) never got a good high alt. rated engine (such as the Griffon or a two-stage Sabre or Centaurus), though it could be said that the RAF had Merlin and Griffon Spitfires and P-51 for the high altitude stuff depending on mission.

But either way, it seems that the Germans and even the British overestimated the high altitude raider threat. It def. seemed that the German high altitude projects had issues that when resolved it was too little, too late, and the Allies pressed ahead with what they had and made it work.

Of course, we can say all of this with hindsight, something no one had in 1942-45. Hence, for example, the Western Allies believing in the rumors of the Alpine Redoubt (contributing to the RAF/USAAF bombing and strafing of the Berghof and other areas near Obersalzberg) and USAAF publicity about the B-29 spurring the Germans into trying to counter an ultimately essentially non-existent threat.

 

[Reluctant Poster]

The initial VIII (later the F.VIII) was fitted with the Merlin 63. The initial VII was fitted with the Merlin 64 (same as 63 but with cabin blower). The V-1650-3, fitted to many (most?) P-51Bs and -Cs, was based on the Merlin 63.

Later there would be LF (Merlin 66) and HF (Merlin 70) versions of the VIII and IX, and an HF.VII (Merlin 71).

The V-1650-3 was not based on the Merlin 63 it had the same much improved and larger supercharger as the Merlin 66 and 70. I have posted on this previously.