The events of World War 2 proved beyond any doubt that the strategic bombing campaign greatly contributed to the Allies’ ultimate victory over Nazi Germany.
British night bombing raids and daylight carpet bombing missions flown by the USAAF crews rained destruction on German cities killing thousands of civilians in the process. Amidst this massive loss of civilian life the destruction of German industrial targets seemed almost like a side note. The arms race that kicked off even before the war began produced military aircraft capable of reaching ever higher operational ceilings. At first thin air at high altitudes was the domain of reconnaissance machines, but before long fighter and bomber aircraft began to venture there as well. In those early days high-altitude flight was a challenging business: it required the use of pressurized cockpits and boosted powerplants capable of delivering adequate power at altitude.
The two most common piston-powered fighter types operated by the Luftwaffe during the war were Messerschmitt Bf 109 and Focke-Wulf Fw 190. The latter, thanks to its sturdy design, proved to be easier to adapt to a variety of roles. It was used as a pure fighter, bomber destroyer, ground attack platform, reconnaissance aircraft and a fighter-bomber. The Fw 190’s excellent flight characteristics and a huge development potential inherent to the aircraft’s design led to the development of a new high-altitude fighter capable of holding its own against the USAAF escort fighters and heavy bombers.
Powered by a fourteen-cylinder BMW 801 radial engine the standard Focke-Wulf Fw 190 A went into action in mid 1941 and quickly demonstrated its superiority over the RAF’s Supermarine Spitfire Mk. V. However, it became clear just as quickly that the BMW 801’s stellar performance was limited to altitudes of about 6 000 meters. Aware of his aircraft shortcomings, prof. Kurt Tank, the Fw 190’s chief designer, began to look for feasible ways of turning the machine into a true high-altitude fighter. His first step was to take a closer look at the liquid-cooled Daimler-Benz DB 603 A in-line engine. However, the use of the powerplant by Focke-Wulf had to be authorized by the RLM and than there was a daunting task of adapting the Fw 190 airframe to the new engine.
Until those issues could be resolved the Focke-Wulf design team focused on improving high-altitude characteristics of the existing Fw 190 design equipped with the original BMW 801 powerplant. The work had to be done quickly and efficiently since the competition was already busy at work developing their own high-altitude fighter design – the Messerschmitt Bf 109 H.
In mid 1942 the United States entered the war and soon the skies over Europe saw high-flying USAAF heavy bombers. While Bf 109s, equipped with their liquid-cooled Daimler-Benz DB 601 engines, had little trouble operating above 6 000 meters, the Fw 190 was unable to fight at such heights. An interim solution was to be the introduction of light-weight Fw 190 variants: A-4/U5, A-4/U6 and A-4/U7. The Fw 190 A-4/U5’s engine was supposed to be moved forward, while most of the aircraft’s armor was to be removed. Only the pilot’s seat and the area around frame 5 would retain their original armor plating. All armor protection around the oil cooler and fuel tanks was stripped. The A-4/U6 variant was even more radical: the only armor left was light protection behind the pilot’s seat. The position of the engine mount remained unchanged. The A-4/U7 version was do be identical to the U6 variant with the exception of armor plates protecting the aircraft’s oil cooler and fuel tanks. Initially three prototypes of each variant were to be built, but the project was abandoned just a month later in favor of a new design – the Fw 190 A-3/U7. The aircraft was essentially an Fw 190 A-3 airframe partially stripped of armor plating and fuel tank protection, which reduced the fighter’s empty weight from 3 850 kg to 3 660 kg. Cockpit armor (including the pilot’s seat side and back protection) was removed, but the 48 kg engine armor and the 16 kg bullet-proof windshield remained in place. To further reduce the fighter’s weight the design team opted to remove the pair of fuselage-mounted MG 17s, which reduced offensive armament to two wing-mounted MG 151 20 mm cannons. Two air scoops added on each side of the engine bay were designed to improve the BMW 801’s high-altitude performance. Further modifications included the replacement of the FuG VII radio with the FuG 16 unit. The FuG 25 set was also removed. The revamped fighter’s operational ceiling increased to 12 000 m (previously 11 800 m), while its turn radius at 10 000 m dropped from 1 450 m to 1 250 m.
Three prototypes of the Fw 190 A3/U7 were built in September 1942 (W.Nr. 528, 531 and 532). However, after a series of tests the plans for serial production were abandoned. The main issues proved to be the lack of pressurized cockpit and a rather modest gain in performance at a cost of drastic reduction of offensive armament and decreased pilot protection.
The Focke-Wulf engineers moved on to the next stage – the development of Höhenjäger 1 and Höhenjäger 2 (high-altitude fighter 1 and 2).
Höhenjäger 1 and 2
Höhenjäger 1 was another variant of the Fw 190 featuring a modified BMW 801 D powerplant and the GM-1 nitrous oxide boost system, which allowed the engine power output to increase by as much as 300 HP over a period of up to 15 minutes. The GM-1 installation weighed in at 150 kg. The aircraft was to be equipped with a pressurized cockpit and feature larger wing area (20.3 sq m compared to 18.3 sq m on the standard Fw 190).
The RLM showed considerable interest in the new design and authorized Focke-Wulf to continue work on the project, which was tentatively scheduled to enter serial production in June 1942 as the Fw 190 B-1. In company documents the project was referred to as the Fw 190 Ra-3. The production machines were assigned block numbers starting from W.Nr. 190.0210. The plans called for the production of 2 991 fighters, including 998 assembled at the Focke-Wulf plant, 608 delivered by Fiseler, 685 manufactured by Ago and 700 built by Arado. Production machines were to be armed with two fuselage-mounted 7.92 mm MG 17 guns and four wing-mounted 20 mm cannons (two pairs of 151/20 and MG FF weapons). The avionics suite was to consist of FuG 16 and FuG 25 sets. The aircraft could carry an additional 300 l drop tank on the centerline station.
In the meantime, for reasons unknown, the officials at the RLM had a change of heart and cancelled the original order. Now only six examples of the Fw 190 B-1 were to be built (W.Nr. 811-816). Eventually five of the aircraft (W.Nr. 812-816) were used as test beds in weapons trials of the Fw 190 A-5.
The prototype of the B model was Fw 190 V12, W.Nr. 0035, which was built using the airframe of the last pre-production Fw 190 A-0 variant equipped with pressurized cockpit and the GM-1 boost installation. The airframe was used only very briefly before being scrapped. It was followed by other experimental aircraft, first of which was the Fw 190 B-0, W.Nr. 0046, TI+IK. The machine first flew on January 20, 1943 with Werner Bartsch at the controls. Originally the fighter featured pressurized cockpit and the new, larger wing. However, the latter was quickly replaced with the standard 18.3 sq m unit. The fighter had undergone a series of tests at Focke-Wulf before being handed over to Erprobungsstelle Rechlin on June 1, 1943.
Another experimental vehicle was the Fw 190 B-0, W.Nr. 0047, TI+IL, which was first flown by Hans Sander on March 30, 1943. Initially the aircraft was equipped with a single-layer canopy, which proved to be a disappointment in high-altitude operations due to excessive icing. The canopy was soon replaced with a double-layer type, which took care of the icing problem. However, the canopy was still prone to internal fogging, which greatly reduced visibility from the cockpit. The designers experimented with the use of special hygroscopic foil to address the issue. Like its predecessor, the fighter was eventually handed over to E-Stelle Rechlin on January 4, 1944.
The Fw 190 B-0, W.Nr. 0048, TI+IM was the third experimental aircraft. On April 6, 1943 Hans Sander took the fighter for its maiden flight. The machine, similarly to W.Nr. 0047, carried two fuselage-mounted MG 17s and a pair of MG 151/20 cannons mounted in the wing roots. Just like its predecessor, the aircraft featured a standard Fw 190 wing, but was equipped with an upgraded version of the pressurized cockpit. On August 5, 1944 the fighter was slightly damaged (about 10%) during a heavy air raid on Langenhagen factory.
The other two experimental aircraft that followed received production designations Fw 190 B-1. Both machines were powered by the BMW 801 D engines featuring GM-1 boost systems. The first aircraft (Fw 190 B-1, W.Nr. 0049) made its maiden flight on January 11, 1944 when it was ferried from Adelheide to Langenhagen. On February 16, 1944 the fighter was damaged during a forced landing resulting from engine fire. It was quickly repaired and rejoined the test program. On March 23, 1944 the machine was handed over to BMW for further trials.
The second Fw 190 B-1 (W.Nr. 0811, BH+CA) first flew on August 25, 1943. On March 30, 1944 it was ferried to E-Stelle Rechlin, but by that time the GM-1 system had already been removed from the airframe. In its place an additional 115 l fuel tank had been installed.
The last experimental versions of the Fw 190 B were Fw 190 V45 and V 47. Both aircraft were powered by the BMW 801 D-2 engines and featured GM-1 boost systems with a supply of nitrous oxide sufficient for 20 minutes of continuous use. Neither machine had a pressurized cockpit. The Fw 190 V45, RP+IU made its first flight on July 9, 1943 under the designation of Fw 190 A-6/R4. It was then handed over to Rechlin on September 18, 1943 before being ferried to a flying school at Altenburg on October 27, 1944. The Fw 190 V47 was not assembled until February 1944 and it went on to become the experimental airframe for the GM-1 equipped Fw 190 A-8.
While trials of the radial-powered Fw 190 B continued, Tank’s team were looking at ways of mating the inline Daimler-Benz DB 603 engine to their design. The re-engined fighter received a temporary designation Höhenjäger 2.
Daimler-Benz engineers began their work on the DB 603 as early as September 1936. However, the RLM’s priorities where elsewhere at that time, so the development work was suspended and did not resume until late 1939 and early 1940. In the summer of 1942, during one of the many meetings held to discuss progress of the Fw 190 and Me 309 programs, a decision was made that both types should be ultimately powered by the DB 603. The first Focke-Wulf to receive the DB 603 A-0 powerplant was the Fw 190, W.Nr. 0036, SK+JS. The DB 603 A-0 had a capacity of 4 450 ccm and was capable of delivering dash power output of 1 750 HP at 2 700 rpm. In continuous operation at 5 700 m the engine was rated at 1 375 HP at 2 300 rpm. The powerplant was fully compatible with the GM 1 boost system. The test program using prototypes of the Focke-Wulf Fw 190 C powered by the DB 603 engine eventually led to the full-scale production of the Fw 190 D.