Military aviation history: The final air campaign that mattered in Europe

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I spent much of the 90's as an aviation buff, soaking up ridiculous amounts of information about aviation (most of all historical military aviation). The internet finally offered me a horizon way past the few books on offer in local bookstores and libraries around 1997, but sometime around 2000 there still seemed little info of interest left to be learned in the field. Diminishing returns.

I still have this in the background and one topic is nagging me a bit; the dominance of attention on late-war hardware. The last campaign that really mattered was the air superiority campaign over Central Europe, which started for real with the introduction of P-51B as long-range escort fighters (first mission over Germany 11 December 1943, substantial involvement began in January 1944) and ended with the near-total destruction of the (aviation) fuel supply in the summer of 1944. The relentless bombing of oil industry and storage sites beginning in May largely devalued further production of German combat aircraft, tanks and motor vehicles in general. By September 1944 the German pilot training program had crashed and its output was reduced to low quality cannon fodder. New fighter pilots had much-reduced flying hours before they joined operational units, leaving much of the type familiarisation and tactical training to those supposedly operational units. Furthermore, all pilots had to become fighter pilots, whereas pre-1944 the less skilled pilots would get to fly transport or bomber aircraft.

We have thus very little reason to pay attention to what aircraft types and versions appeared  in service only by summer of '44 or later. The last militarily really relevant (NOT decisive) German hardware was the hardware of the winter 1943/44, at most spring 1944.

So, what was available as best German fighters at the time?

The Fw 190A-7 fighter with four good 20 mm guns (two of them synchronised electrically, which reduced rate of fire by about 10%) and two 13 mm guns (also synchronised electrically). Its engine was famously poor at high altitudes because of a single stage supercharger with a full pressure altitude* of less than 6,000 m (the U.S.A.A.F.'s 8th Air Force B-17 and B-24 bombers usually flew at about 7,600 m). It was outmatched by the two stage supercharger P-51B fighter (which also enjoyed superior aerodynamics) not only because of the supercharger issue, but also because the Fw 190A-7's BMW 801D-2 engine was essentially unchanged since 1942.** The Fw 190A-7 was generally marginally improved over the Fw 190A-4 version of July 1942 (biggest improvement was probably the thickening of armour to withstand .50BMG).

The Fw 190 offered great all-round view, great roll rate, very robust undercarriage, great firepower and great resistance to battle damage (air-cooled engine without vulnerable liquid cooling system except for the lubricating oil).

The Bf 109G-6 was the best available Bf 109 fighter version by New Year 1944. The G-6 version had been in production since February 1943 already and wasn't much better than the G-2 version of early 1942. The G-6 featured a single 20 mm or 30 mm gun (the latter had a slow muzzle velocity, but single hits often killed a fighter and 3...4 hits often killed a 4-engine bomber) and two 13 mm guns (synchronised electrically.
An "AS" designation was applied to the few and late G-6 with a DB 605AS engine (with DB 603's supercharger) likely beginning before February 1944, and there as also the /U2 modification with GM-1 injection (nitrous oxide, as substitute for the missing oxygen supply from the supercharger above approx. 5,800 m altitude). Only about 325 G-6AS and 324 G-6/U2 were produced in factories altogether (compared to almost 8,000 basic G-6).

The Bf 109 had no especially advantageous characteristics except that its power/weight ratio was fine (and it was a fairly small target), resulting in a high climb rate. It was plagued by an unsatisfactory undercarriage, which resulted in many accidents.

The basic Bf 109G-6 and G-6AS or G-6/U2 were rather unsuitable for the destruction of four-engine bombers, and probably even so with the 30 mm gun. Their firepower was quite poor; a problem that had plagued the Bf 109 since the F series in 1941.

Two additional underwing-mounted 20 mm or 30 mm guns could be installed, but this increased the weight, reduced the roll rate, reduced the climb rate and reduced the top speed. The E series' installation of older model 20 mm guns in slightly bulged wings was not reintroduced. There was a choice between a clean but still not really competitive fighter and a by comparison clumsy and in contact with hostile fighters even less competitive 'bomber destroyer'.

The obvious option would have been to go for a fighter group equipped with Bf 109G-6ASM (ASM = AS with MW-50 injection) as escorting force and a Fw 190A-7 fighter group as bomber destroyers by spring 1944, and something similar (more extreme) was attempted with the Sturmgruppen approach, to completely insufficient effect as the heavily armed (and armoured) bomber destroyers were not properly secured against the escort fighters.

Both Fw 190A-7 and Bf 109G-6 represented mid-1942 to mid-1943 technology and this didn't suffice even though the same could be said about the P-51B (the P-51's basic fuselage design was approx. two and six years younger than the German designs and this showed in the aerodynamics of the wing profile and the cooler design).

All the fancy technical advances made in summer 1944 to winter 1944/45 didn't matter any more. You wouldn't quite get that impression with the usual literature on the period and campaign, for there's an inappropriate level of attention on the irrelevant German aircraft variants and types that became available for service in relevant quantities only after the spring of 1944. There are 'too late, too few' remarks, but the authors don't resist paying excessive attention to fancy very late war designs while largely neglecting the types introduced in 1942/1943 relative to their actual importance.

A one-year lapse in competitiveness of in-service fighter designs rooted in raw material shortages (which caused a failure of turbocharger development programs) and a way too belated counter to the Rolls-Royce Merlin 61's two-stage supercharger revealed in the summer of 1942 doomed the Luftwaffe to not only fight in a severe quantitative inferiority, but also in a severe qualitative inferiority situation during its last air campaign that mattered.

The Luftwaffe's fighter designs were usually very competitive and at times clearly superior before and after, but not so during the half year when the 8th AF finally employed some good ideas for offensive strategic air warfare in combination.

Moreover, one could ask whether we should trust our modern fighter arsenals with their about 40 year design lifecycles.

S O

defence_and_freedom@gmx.de

*: I translated "Volldruckhöhe" literally, as "full pressure altitude". I don't know the correct translation, though "critical altitude" and "full throttle altitude" popped up as a candidates. The "Volldruckhöhe" is the altitude at which giving full throttle usually makes sense for the last time during a climb, but that depends on engine control mechanisms. Aircraft usually reached their top speed a little above their full pressure altitude.
**: The usual statement (in literature) that the Jumo 213A of the Fw 190D series was superior to the BMW 801 at high altitudes does not square with its actual performance curves at all. 
Fw 190A (BMW 801) reached top speed slightly higher than 650 kph at about 6,400 m, with externel air intake it's a bit faster at about 6,900 m. A Fw 190D reached top speed about 670 kph at about 6,600 m. The Jumo 213A installation allowed for a little extra performance in general (especially with MW-50 added and in use by very late 1944), but it was no high altitude engine.

The Jumo 213A's full pressure altitude was 5,900 m, almost indistinguishable from the basic versions of the competing German engines. The Jumo 213A was no real high altitude engine. The DB 605 engine versions with DB 603's supercharger (such as DB 605AS) were the closest thing to high altitude piston engine available for German fighters. The only real alternative were DB 605 with GM-1 (nitrous oxide) injections systems (AFAIK BMW 801 with GM-1 were not used in fighters).
  
Some data:

Bf 109G-5AS and Bf 109G-5 speeds at different altitudes (equivalents to G-6AS and G-6, equipped with pressurised cabin and thus a little heavier) 

Fw 190A-6 speeds at different altitudes (very similar to A-7, graph also shows speeds achieved with an alternative external air intake)

P-51 speeds at different altitudes (in antiquated dimensions)

DB605AS performance at different altitudes
 
DB 605AM performance at different altitudes (This powerplant appeared in 1944 with MW-50.)

MW-50 did almost nothing for high-altitude performance (it made sense up to full pressure altitude only - there was but a few per cent power gain from the cooling effect above it), so we can compare contemporary DB 605AM and AS versions' high altitude performance: The DB 605AM's full pressure altitude was 5,800 m and the AS version had a full pressure altitude of 7,800 m. Performance steeply dropped above full pressure altitude. AM delivered 1080 hp at 5,500 m while AS with bigger charger still delivered 1050 hp at 7,800 m altitude.)

BMW 801D-2 performance at different altitudes with improved C-3 fuel and increased pressures (not relevant in first half 1944, used in Fw 190A-8); this shows the sharp drop in power above the full pressure altitude of the ordinary 5,800 m. The full pressure altitude wasn't changed by the summer '44 modifications to the engine.

http://109lair.hobbyvista.com/techref/systems/engine/as_vs_d/as_vs_d.htm

Hat tip to http://www.wwiiaircraftperformance.org/ and kurfurst.org - having such easily accessible free resources is delightful compared to the many unsupported statements made most of the aviation literature!

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