Nazi Germany (1942)
Experimental Fighter Program: Six Prototypes Built
As the Second World War progressed, the development of high altitude aircraft became of critical importance. At the beginning of the war, extreme altitude flights were conducted only by highly specialized reconnaissance aircraft, prompting many nations to scramble for a means of shooting them down. With little investment before the war into high altitude interceptors, 1941 and 1942 would be critical years in the development of planes capable of fighting at once unthinkable heights. At Focke Wulf, the new Fw 190A would go through a number of modifications, eventually resulting in six turbo supercharged test aircraft under the program title Höhenjäger 2. The program would be fraught with technical challenges at every turn, was undermined by the disastrous politics within the Luftwaffe’s developmental offices, and would fail to deliver a badly needed high altitude fighter to the Luftwaffe.
Threats from on High
In early 1941, the Luftwaffe deployed the Ju 86R reconnaissance plane over Britain. With its specialized high aspect ratio wings, and GM-1 nitrous oxide injection for its engines, it could operate at extreme altitudes. Flying at nearly 14km, it was almost untouchable at the time, and only when specially modified Spitfires were fitted out could it be intercepted. The first of these Spitfires could only reach the Junkers by shedding all excess, its armor plates, much of its armament, and even its radios, with the fighter needing another aircraft to guide it towards the target before the final climb. There would soon be specialized marks built for this exact mission, the Spitfire Mark VI would incorporate a pressurized canopy to spare the pilot the worst effects of flying at extreme altitudes, and the Mark VII would be further modified with a addition of a better wing for maneuvering in thin air, and they would receive an oxygen boost system, to increase the available engine power in the thin air where its targets would be found. The Mk VI was delivered to the RAF only about a year after the first Ju 86R had flown over Britain, such was the rate of fighter evolution.
In Germany, the Luftwaffe had to contend with the Mosquito, which first flew over Germany in the summer of 1941. It did not reach the heights of the specialized Junkers bomber, but flying over 560 km/h at an altitude of 7km, it was enough to outrun anything the Luftwaffe could dispatch to bring it down. Improvements to this aircraft would only boost its already impressive performance, and new, specialized designs were posing even greater threats. As was the case, when German intelligence services revealed the development of the Vickers Wellington V, which possessed high altitude Merlin engines and a pressurized cabin, allowing the aircraft to operate at altitudes beyond 12km. Technical difficulties prevented its employment, but it nonetheless presented a threat which the Luftwaffe had no answer to. Likewise, the declaration of war against the United States would entail fighting their advanced bomber fleet, which had made major investments in the technologies that would enable them to conduct raids from high altitudes.
In the spring of 1942, the Messerschmitt Bf 109F had a full throttle height of roughly 6.2 km, and the Focke Wulf 190A’s was roughly the same. There were versions of the Bf 109 which utilized a nitrous oxide injection system to allow them to regain engine power lost at high altitudes, but as a system, the GM-1 boost was inconvenient as it could not be stored in aircraft for long, due to leakage, and it was a logistical burden beyond its deployment in Western Europe, where the infrastructure for supplying and handling the nitrous oxide existed. It was very useful aboard high altitude recon aircraft, and in interceptors that pursued high flying reconnaissance aircraft, but it was unusable as a means of giving high altitude performance to a large force of fighters which were on call around the clock. Thus came a top down push for a new high altitude fighter.
In May of 1941, the Reichsluftministerium, or Reich air ministry, convened a conference at the Messerchmitt plant at Augsburg to discuss the requirements for a new high altitude fighter, or Höhenjäger. The requirements were sent out to Messerchmitt, Focke Wulf, and a number of other firms. Their goals were ambitious, and pursued at a very inopportune time.
Working Conditions
At the start of 1942, there were few practical engines available for high altitude use in Germany. To make matters even more complicated, most firms were struggling to modify their engines to work with the new economy alloys and synthetic fuels available to them. Nickel was in short supply, leaving engines more vulnerable to corrosion, and chrome was soon to become scarce, so heat resistant alloys were less effective. Their stocks of aviation gasoline had transitioned to synthetic derivatives, whose differing properties from the original petroleum derived stock were causing great difficulty in the DB 601 engine, which powered the Bf 109, among other aircraft. In addition to the many technical challenges facing engine designers, the political situation was equally disastrous. In short, there were too many competing engine manufacturers vying for production, and the Luftwaffe’s technical offices badly managed what resources it had. The Luftwaffe’s chief of the relevant offices, Ernst Udet was a very capable pilot, but an incompetent administrator.
At this stage, neither of the primary fighter power plants in Luftwaffe service would permit acceptable high altitude performance, without significant modification. While both were advanced, they were geared to low and medium altitude use, and the supercharger impeller design on the Fw 190’s BMW 801 engine, was already quite dated. New models of these engines were forthcoming, but were being developed in parallel with a number of new high performance engines. Resources were accordingly spread very thin. The most important of these new engines were the Daimler Benz DB 603 and Junkers Jumo 213 V-12s. The DB 603 was similar to the preceding DB 601, and was a considerably larger design with its output eventually reaching the 2000hp class. The Jumo 213 was a further development of the Jumo 211, but with a pressurized cooling system for high altitude use, and it was designed to operate at significantly higher RPMs. The Junkers engine was the more advanced model, but was experiencing harsher developmental difficulties. In spite of their problems, they would represent an important second generation of fighter engines during the latter half of the war.
The Contenders
At Messerschmitt, the Bf 109 was not chosen to pursue the Höhenjäger program, but rather the Me 155. High altitude versions of the Bf 109E and F were already in service, but as specialized GM-1 boosted interceptors, and not air superiority fighters. Originally a project to develop a carrier based fighter, the Me 155 was repurposed for use as a Höhenjäger. Dubbed Me 155B, it was soon transferred to the a S.N.C.A.N. in Paris, as Messerschmitt was totally committed to existing projects. The project would eventually be brought to Blohm und Voss for assistance, before finally fully transferred to the firm, with a handful of aircraft being created in 1944. More modest attempts to build high altitude versions of the Bf 109 failed when the necessary high altitude engines failed to materialize. With Messerschmitt unable to produce a new high altitude fighter, what prospects remained lied with Focke Wulf’s efforts.
Focke Wulf would instead choose to try and modify their existing Fw 190 fighter, rather than take on the high developmental burdens of a new design. This took the form of three proposals which were proposed to the RLM. The Fw 190B, which would be powered by the BMW 801, featuring air frame modifications to improve high altitude performance, and a pressurized cockpit; the Fw 190C, the same but with a new DB 603 V-12 power plant; and the Fw 190D, which would utilize the Jumo 213. These projects would not only pursue the high altitude goal, but also produce new high performance standard fighter models of the Fw 190. All three programs would be developed in parallel, and were supplied with a series of pre-production Fw 190A-0’s for testing.
From an early date, the engineers at Focke Wulf were convinced that they needed to transition to one of the new V-12’s for the high altitude project. Fw 190 lead designer, Kurt Tank, favored the DB 603 as it was likely to be available sooner, though the RLM did not. The engine was not originally ordered at the behest of the military and it had its opponents within Luftwaffe R&D circles. Tank was however, able to convince the Technisches Amt, the Luftwaffe technical office, to continue Fw 190 development with the engine, but only as a back up design to the BMW 801, and Jumo 213, powered models. In any case, these would be available in greater supply, and there was a considerable risk that the Fw 190C could have been reliant on an engine the firm might be denied a supply of.
The Fw 190C
Kurt Tank’s highest hopes were placed on the DB 603 engine, the initial output of which was some 1500hp, with later developments hoping to push the engine into the 2000hp class. This engine would be selected to power both standard, and high altitude fighter projects. The engine was lighter than the BMW 801 and had good developmental potential. They were not however, without issue, as they were still running roughly at the start of 1942, with six out of ten engines in flight testing only surviving some 60 to 100 hours. There had been interest in equipping the Fw 190 with this engine at an earlier date, with the first proposals being drawn up in March of 1941, well before the high altitude fighter conference. This early proposal did little to advance the development time tables, as the engines themselves were not forthcoming, and the program awaited delivery for testing for quite some time. The new Fw 190C had been designed with the new engine in a new modular power unit, but it was not available for testing until March 1942.
The first three prototypes were Fw 190V13, V15, and V16, all built on old air frames and equipped with pressurized cockpits. To follow were over a dozen prototypes to test various configurations. V-17 through 33 were to test the performance of the aircraft with the DB 603 and Jumo 213 engines, along with pressurized canopies, a new tail section, and GM-1, all in various arrangements.
V13 was originally a Fw 190B prototype, and was tested at the Luftwaffe experimental unit at Rechlin between the 18th and 22nd, achieving a top speed of 650 km/h at 5.9km. V15 was modified by moving the air intake to the port side of the engine, rather than at the nose of the aircraft, to test cooling capacity. Performance was markedly improved despite continued issues with overheating, with the prototype making for 696km/h at 6.9 km, in June of 1942. This last figure represents good performance, but still not a significant enough improvement from the BMW 801D engine on the Fw 190A. The Daimler Benz engine had its advantages, but the DB 603 variant that was available was not a high altitude engine, even if its supercharger design was by far superior.
Regardless, development continued. The prototypes V15, and V16 were sent to the Luftwaffe research center at Rechlin, leaving Focke Wulf with only the V13 for DB 603 testing, but V17 and V18 were taken off Jumo 213 testing to be fitted with the Daimler Benz engine. This was until an engine failure caused the loss of V13 in July, as attested to by the test pilot. Focke Wulf continued testing and designed two standard fighter production variants, Fw 190C-1, with an armament of two cowl mounted MG 131 13mm machine guns, two inner wing mounted MG 151/20’s; and the Fw 190C-2, which included a pressurized cockpit, and provisions for a centerline cannon, being either a 30mm Mk 103 or Mk 108, or a MG 151, in either a 20mm or 15mm caliber. Both variants were equipped with a DB 603A engine. The Luftwaffe ordered the production of 727 Fw 190C’s in December 1942, but this order was quickly canceled, as the performance increase over the BMW 801D equipped Fw 190A was not significant enough to warrant its replacement, and the engine was still running very roughly. The new twin engine He 219 nightfighter, the Do 217 bomber, and Me 410 Zerstorer were less threatened by an engine failure, and it was against them that the new fighter would have to compete with for a supply of engines.
The project was shelved, but two of the prototypes, V15 and V16, were retained to test experimental, high altitude models of the DB 603 engine. In 1943 they utilized the experimental 1900hp, DB 603G, which replaced the single stage, variable speed supercharger, with a two stage supercharger. It showed a significant performance increase, with V-16 achieving 722km/h at 9km during testing in mid 1943. It later mounted the DB 603E in 1944, which used an improved model of the single stage, variable speed supercharger, which brought the engine’s critical altitude from 5.7km to 7.4km, and its maximum output rose to 1800hp, with water injection. Its overall performance was inferior to the DB 603G, but nevertheless allowed the aircraft to reach 12km during tests in the summer of 1944. However, neither engine saw mass production as they were unable to reach the minimum threshold for 100 hours between overhauls.
Höhenjäger 1
Despite the promise of a new V-12 engine, the BMW 801 radial was the standard power plant of the Fw 190A, and the new high altitude project, christened Höhenjäger 1, was to use it. The designation for this new high altitude model was Fw 190B, and the aircraft was proposed to the Luftwaffe in August of 1942.
The Fw 190B would be an extremely modest attempt at a high altitude design, comprising a new 12.4m wing, up from 10.5m, and incorporating a pressurized canopy. The new fighter would also include the GM-1 nitrous system, more or less as an expedient measure, as the BMW 801 had poor high altitude performance. It was quickly modified, with ground testing beginning in December of 1942, and flight tests were conducted in January the following next year. The capabilities of the Fw 190B were only modestly improved over the nitrous boosted Fw 190A, with the new model having its service ceiling raised to 12.5 km, an increase of only .7km. The four pre-production aircraft would later have their wings reverted to the standard Fw 190A span, and along with the only production model B-1, would be used to test the troublesome pressurized cockpit design in the following years.
The BMW 801C&D would not prove an acceptable power plant in a high altitude fighter, and the turbo supercharger arrangement proposed for the aircraft was in a pod directly under the engine, which was utterly unacceptable. BMW was developing a specialized turbo supercharged engine in the form of the BMW 801TJ, however, it was designed for bombers and the exhaust gate for the integrated turbine would have been in front of the cockpit. Any high altitudes variants of the BMW 801 for the Fw 190 would prove even less forthcoming than those of the DB 603. The failure of the Fw 190B thus made the DB 603 and Jumo 213 projects essential. Progress, however, remained slow and difficult, and through 1943, neither engine was running very well.
Where are the Engines?
The engineering and political chaos which dominated engine development in 1941 would hold true for the following year, and the rest of the war to come. The Jumo 213 was, on paper, still the planned premier high performance power plant for fighter use. However, the project was pursued alongside the need to improve the existing Jumo 211, in use with a number of Luftwaffe bombers, and the completion of the Jumo 222, an experimental 6-bank 24 cylinder inline engine which boasted extremely high performance. Likewise, at Daimler Benz, the further development, and re-engineering, of the existing DB 601/605 series of engines, along with delivering a workable DB 603, and completing the new DB 628, had pushed their developmental capacity to the limit. To further complicate matters, the DB 603 had begun as a private venture before the war by Daimler Benz, with the RLM initially being frustrated with them, that they had started work on an engine they had not requested. Daimler Benz was initially on the line for all resources spent on the project, and it was shelved, only to be restarted in 1940 with military approval and funding. To add insult to injury, neither the Jumo 222 nor the DB 628, would materialize in any useful capacity, in spite of the considerable efforts and resources spent on their development. The situation was abysmal, and, three years into the war, neither the new DB 603 or Jumo 213 engines were in reliable state for single engine fighter use.
In Britain and America, new technological breakthroughs led to the production of much improved radiators, and the use of new two-stage superchargers. Turbo superchargers had also been incorporated into new fighter designs with good high altitude performance, namely the P-38 and the P-47, the latter being judged a very dangerous opponent above 9 km. Across the board, the new British and American fighters were becoming leaner, mounting lighter, better cooling gear, and were faster at high altitudes, making use of the next generation, two stage Merlin, and a number of turbo supercharged engines. The RAF and USAAF would be receiving superlatively improved designs in 1943, perhaps best exemplified with the new Spitfire Mk IX, which shifted the balance of forces across the English Channel, and the European low countries.
In comparison, German manufacturers were still largely occupied with modifying existing engines on lower quality materials. The DB 605A would only be fully released to run at its full power settings in 1943, and the BMW 801D, in early 1942. The DB 603A would enter mass production, in a very rough state, at the end of 1942, with the Jumo 213 not being available until well into 1944.
How had this happened? Much of the blame can be placed on Generaloberst Ernst Udet, and the man who placed him in the role of the Air Master General, Reichsmarshall Herman Göring. The Aircraft Master General’s Office was enormous, once consisting of twenty six departmental heads and some four thousand officials. This sprawling office, which oversaw Luftwaffe procurement, and its research and development efforts, was utterly unmanageable in the early years of the war. It was dominated by confusion, unable to maintain the necessary supervision, and resource management, for its many new projects, and with its many heads, it had extremely poor communication with the Luftwaffe’s General Staff. Perhaps the greatest example of Udet’s shortsightedness are in his celebratory remarks in June of 1940, when he exclaimed to his staff, “The war is over! All our plans can be tossed into the waste-basket. We don’t need them any longer!” Such delusions were quickly dispelled following the RAF’s victory over the Luftwaffe later that year, and Udet himself was sent into a deep, personal crisis when Reichsmarshall Göring placed much of the fault of the Luftwaffe’s shortcomings during the invasion of the Soviet Union, on him.
Generaloberst Udet dithered in trying to reorganize his office, and only with the intervention of Luftwaffe State secretary, Erhard Milch, in October of 1941, were the department’s many heads reduced to four. In no uncertain terms, Milch dismissed the Luftwaffe’s Engineer-General, “Your plans are inaccurate. Your attitude is one of constant negativism. I have been ordered to inform you of these facts and let you know of his (Göring’s) displeasure. You are herewith relieved of your assignment, and you are expected to tender your resignation.” Milsch would be later be given Udet’s post, following his suicide, and curb the worst of the office’s dysfunction. Along with the efforts of Albert Speer, Reichsminister of Armaments and War Production, there would be considerable improvements in the development, and procurement, of Luftwaffe projects.
The confusion lessened, but many Luftwaffe projects, like the Me 210 and He 177, failed to deliver on time, if at all. Very promising power plants suffered the same fate, with the Jumo 213 and DB 603, competing for resources with projects that had little hope of delivering an engine in any relevant time frame. Two years following its reduction in staff, Reichsmarshall Göring would state “There’s still many a scoundrel there…You’ll find people there who have been thrown out on their ears three times already, and they come to light in some other department again, only bigger and stronger than ever”. As the chief of the Luftwaffe, it was, of course, his responsibility to ensure the office was well staffed, and it was his appointment of Udet, and continued administrative neglect, that effectively doomed it.
Höhenjäger 2
In August of 1942, a much more ambitious project was initiated to produce a high altitude fighter, under the title Höhenjäger 2. It was developed concurrently with the extremely modest Höhenjäger 1 project as a more technically ambitious alternative. The new fighter was to incorporate a number of features, notably the longer span wing of the Fw 190B, the pressurized cockpit, and with the addition of a new 2000hp turbo supercharged DB 603S engine.
Turbochargers, like superchargers, compress air before feeding it into the engine’s intake manifold, allowing for an increase in overall power, and can provide truly excellent high altitude performance. A supercharger is typically still required if one is using a turbocharger on an aircraft, and this arrangement of a supercharger, supplied charge air by a turbo charger, is referred to as a turbo supercharger. This type of system can be very challenging to incorporate in an aircraft. The turbocharger requires ducting to supply the exhaust to the turbine, then back to the engine, and it presents new cooling requirements, as the temperature of charge air from the turbine will be high, and some form of cooling will be needed before the charge air is sent to the supercharger.
On the Fw 190, this would prove challenging. There was simply not enough space available within the air frame to accommodate the ducting, cooler, and turbine. The turbine and exhaust ducting would also require high temperature alloys to build, which were in short supply. Despite these challenges, the project engineers would study ways of incorporating the Hirsch TK 11 turbocharger in the Fw 190, while receiving assistance from the Deutsche Luftfahrtforschungsanstalt, or German Aeronautical Research Institute.
While studies were underway, one of the first practical tests involved the development of the exhaust tubes which would lead from the engine to the turbine. These were first added to one of the earlier prototypes Fw 190V15 sometime during the latter half of 1942. The first of the true Höhenjäger 2 prototypes would be constructed from Fw 190V18, one of the aircraft transferred from Jumo 213 testing to the DB 603. It did not feature the long span wing, or the pressurized cockpit. The TK-11 turbocharger was mounted behind the cockpit, below the fuselage within a fairing. It would prove impossible to mount the turbine fully within the aircraft itself, and its cooling requirements demanded a large intercooler be installed in a ventral scoop. In addition to the large radiator, the ducting for the turbine was almost entirely outside the fuselage, giving the aircraft a very unique appearance, and adding considerable drag generating surfaces.
Fw 190V18/U-1 was completed by December, 1942, and took to the air on the 20th. After the first test flights numerous issues began to arise, mostly related to cooling, but also general reliability issues. A larger oil cooler was also subsequently fitted to the aircraft, along with a four bladed VDM propeller and a pressurized cockpit, as continuous testing was conducted to refine the turbo supercharger arrangement. Months later, after some 42 flying hours, V18/U-1 was able to achieve a top speed of 670 km/h at 11km, and had a ceiling of 14 km with the use of the turbocharger. The setup still proved troublesome, with continued issues with overheating. The exhaust piping was also prone to rapid wear, being consistently subjected to very high temperatures, and being made of an inadequately heat resistant alloy. It would be a fatal weak point of the program, in addition to the overheating, and the teething issues of the temperamental DB 603 engine. The turbine itself, however, seemed to be operating well enough.
The program was expanded in the hopes of finding a means of improving the design, and delivering a high altitude fighter to the Luftwaffe. To this end, several new prototypes were constructed from pre-production Fw 190A’s, V-29 through 33. These aircraft were all fitted with the pressurized cockpit, and enlarged vertical stabilizer. Fw 190V29 was delivered in March of 1943, with more to come in the following months. Of note, was Fw 190V32, which was the only example of these aircraft that had a provisional armament, featuring a pair of MG 151/20’s in the inner wing roots. This particular aircraft was completed in November, 1943. Despite the construction of several more test aircraft, the engineers failed to find a means of solving the issues which plagued the design. The inadequate supplies of heat resistant alloys, and the already rough running DB 603, would prove an insurmountable combination of challenges for the engineering team. Testing continued into January of 1944 before the program was canceled and the prototypes were converted to test the new Ta 152 fighter series.
The new series of fighters would be derived from the Fw 190, with a number of new features, namely more powerful engines. Among them was the Ta 152H, a high altitude design, and the only aircraft in the series to enter production. The Ta 152H would entirely dispense with the turbo supercharger arrangement, and utilize a Jumo 213E high altitude engine, with a two stage, three speed supercharger. Its development was rushed and it entered pre-production after a very short prototyping phase that saw few modifications to the design. It did however see service in the last weeks of the war. Very little of the Höhenjäger 2 project would make its way into the Ta 152H, save for the enlarged wooden vertical stabilizer, and the pressurized cockpit, which was modified considerably between the two programs.
Comparisons
The Fw 190 Höhenjäger compared poorly with aircraft already in Luftwaffe service. Despite the considerable effort expended, the aircraft did not present much of an improvement over the Bf 109G carrying a GM-1 nitrous boost system. The Höhenjäger 2 was faster at extreme altitudes, and had a theoretical ceiling of nearly 14km, but in practice the limitations of the turbo supercharger made sustaining this difficult. Simply put, it wasn’t capable of reliably achieving its most impressive test results given the inability to run the engine at high settings for extended periods. Beyond this was the fact that the test aircraft did not carry a full combat load. The 670 km/h record at 11km was achieved by Fw 190V18/U-1, which did not carry a FuG 16 fighter radio set, a FuG 25 IFF, armor plates, or any weapons. All of which rendered the aircraft several hundred kilograms lighter than any fighter aircraft that might have been based on its design.
On a practical level, the Bf 109G with GM-1 was able to largely match the combat capabilities of the Fw 190 Höhenjäger 2. The Fw 190 would have likely held some advantage in speed, but it had a projected service ceiling some 800 meters below the 13.2 km ceiling of the Bf 109G. The turbo supercharger also failed to create a fighter that could match the performance of a nitrous boosted aircraft, and eliminate its weaknesses. Namely, the added weight of a boost system, its ineffectiveness in providing any advantage at low altitude, and the inability to store the nitrous in the aircraft without it leaking out via evaporation. Only in the last factor could it really boast of an advantage. The turbo supercharger system also added considerable drag, which GM-1 did not impose on any aircraft. The scoop for the intercooler, and the turbine’s associated piping, were aerodynamically unsound features, creating enormous amounts of drag, and created a serious handicap at lower altitudes, where the turbo supercharger also offered very little advantage. Even without comparisons to specialized aircraft in foreign service, the Fw 190 Höhenjäger 2 had failed to exceed the performance of the expedient high altitude fighter model already in use with the Luftwaffe.
Construction
The Fw 190 took shape under the direction of Dipl.-Ing Kurt Tank, of Focke Wulf Flugzeugbau. In designing the aircraft, Kurt Tank sought to make a rugged fighter, a “work horse” rather than the “race horses” that were the Bf 109 and Spitfire. In his mind, these aircraft were too focused on pursuing performance over more practical concerns, like how well they could operate out of ill-prepared forward airfields, or being designed with ease of production in mind. Kurt’s Fw 190 would also feature considerable attention given to making the aircraft as convenient to fly as possible.
The core of the Fw 190 is a conventional, and rugged fuselage composed of two sections. The main fuselage is composed of a pair of sub assemblies. The forward section is of a semimonocoque construction and contains the engine firewall, cockpit, and fuel tanks, with the forward tank containing 232 liters, and the rear, 292 liters. Behind the front fuselage section is a monocoque rear section which connects to the tail unit. The tail unit is bolted to the fuselage and contains the horizontal and vertical stabilizers. On the Höhenjäger 2, the tail section included a fuselage extension to balance the added length of the longer DB 603, and a new enlarged vertical stabilizer. The new stabilizer was made of wood, with the rest of the aircraft being composed of duralumin, save for the fabric-covered control surfaces. The use of a wooden tail unit was carried over into the Ta 152 program.
The wing was of a single spar, monolithic construction. The tips were removable, but the wings were a single unit which was a single sub assembly. Doing so made them easier to produce, and in the event of damage, were replaced entirely, rather than have repair crews go through the time consuming process of repairing, and realigning the wings. The wide set landing gear made landings in rough, ad-hoc fields easier. The undercarriage lowered under its own weight, and was retracted by means of steel cables driven by electrically actuated drums. The Höhenjäger 2 project made use of an original wing with a 10.5 meter span with an area of 18.3 m2, and it was hoped to test a later set with a 12.4 meter span with an area of 20.3 m2.
The use of these sub assemblies made the aircraft much easier to produce. The sub assembly components could be produced with unskilled labor as the production steps kept the work as easy and simple as possible until wiring and final assembly, and the assembly process itself kept fitment and alignment to an absolute minimum. The wings were attached to the forward fuselage via flanges, requiring no fitting work, which was a time consuming and expensive step. Much of this was achieved by forgoing any complex or sensitive systems that were woven through the air frame, for example the wing mounted radiators on the Bf 109, or unfortunately, the ducting on for the turbo supercharger on these test aircraft.
The Hirth TK-11 turbocharger unit was half embedded in the lower fuselage, it was supplied by exhaust gas delivered from the engine through a set of pipes made of Sicromal 8, which was contained by an outer sheet metal tube at a separation of 5mm, to keep it from being in contact with the fuselage and the air flow across the skin of the aircraft. The alloy was totally inadequate for enduring exhaust temperatures of around 800 degrees Celsius, at some two atmospheres of pressure. In tests they could fail in as low as ten hours of use, and last as long as 20, after improvements were made to the design. The exhaust pipes extended across the fuselage, and were semi faired over to reduce drag, they went over over the wings, and into the turbocharger unit aft of the cockpit. The turbine itself proved adequate in its use, though the inability to mount it in the fuselage itself proved problematic. Hollow turbine blades served to adequately give the device adequate heat resistance when the materials alone would not have. The turbine waste gate was at the rear of the scoop. The charged air was sent through the intercooler in the air scoop, and directed in a pipe along the underside of the aircraft, before it entered the fuselage ahead of the cockpit. The charge air was then directed into the integral supercharger on the DB 603S engine.
The pressurized cockpit took a number of forms, never working quite right. The original layout consisted of reinforcement brackets along the canopy hood, a rubber canopy seal, stoppers around the electrical cables entering the cockpit, and a DVL air compressor. The windows could blow out and needed reinforcement, the cockpit frame could cut the rubber seal, and the various plugs around the cockpit had a tendency to fail. It wasn’t until December of 1943 that the pressurized cockpit was satisfactory, though the program’s cancellation followed soon after. The later Ta 152H included a much improved, and modified, pressurized cockpit.
The otherwise clean and workman-like cockpit of the Fw 190 was complicated considerably with the inclusion of the liquid cooled engine and turbocharger. The new powerplant required the installation of more instruments to allow for the display of the liquid coolant temperature of the DB 603, and the output of the turbine blower.
The Fw 190 typically made use of a unitary power unit which contained the motor and all its associated accessories and cooling systems. It was designed for ease of installation and removal through brackets attached to the fuselage. The Fw 190 Höhenjäger 2 represented a significant break from the design with the incorporation of the turbo supercharger. The Fw 190 prototypes it was based on used a DB 603A in a Kraftei unitary power unit, which was connected via a bracket to the firewall on the fuselage. The engine’s liquid cooling was facilitated by an annular radiator at the nose of the aircraft, a remarkably efficient layout in regards to drag, if somewhat inadequate in cooling capacity. Beneath the cowling was the scoop for the oil cooler.
The DB 603A is an inverted V-12, it was relatively straight forward for a German fighter engine, and its supercharger was its only true novelty. The single stage supercharger was mechanically driven by the engine and used a hydraulic coupling for variable transmission, effectively making it infinitely variable. Compared to the fixed gears on most fighter engines, this eliminated the performance gaps when an aircraft was flying at an altitude that was between the critical altitude for its otherwise fixed supercharger speeds. Like the DB 601/605 series, it featured a high degree of automation which adjusted the propeller RPM, mixture, and radiator flaps through a series of pre-set linkages, which were reactive on inputs from the throttle. The engine was otherwise only an interest to the Luftwaffe for its 44.5L displacement and relatively compact form. Unlike the more cutting edge Jumo 213, it was somewhat dated, though still powerful and possessed similar dimensions.
The DB 603A had a length of 2680mm, a width of 77.5 mm, and a height of 1067 mm It had a bore and stroke of 162 mm x 180 mm. It had a dry weight of 910 kg. It also used a Bosch direct fuel injection system. The DB 603S was the turbo supercharged model on the Höhenjäger 2 Fw 190.
While it was claimed the engine had a rating of some 2000 PS, its extreme unreliability and propensity for overheating meant that there was likely no stable upper level output. Overheating remained a chronic issue with the aircraft, and both the intercooler, and the engine liquid coolant temperatures were too high. A test pilot noted the engine temperatures were consistently elevated above what were typical on the Fw 190C prototypes, which already ran hot.
Pilot’s Notes and Handling
The Fw 190 has a well established pedigree of being a pilot’s plane. Everything that could be done to lessen the pilot’s workload, and generally make the aircraft as convenient to fly as possible, had been done. It was very stable, provided excellent visibility for a fighter of its day, had a cleanly laid out cockpit and instrument panel, and used a push-rod control system in place of more conventional cables, as they were more responsive and didn’t have any tension or play to them. In the case of the Höhenjäger 2, many of these conveniences were lost.
The cockpit was considerably more complicated as new instrumentation and controls for the turbo supercharger were installed. The BMW 801 and Jumo 213 engines were almost entirely automated, and required the pilot to do little more than adjust the throttle lever to bring the aircraft to the desired power setting. The DB 603S engine, in comparison, required constant supervision. Not only did the turbine management add to the otherwise light pilot workload, but the unreliability of the base engine, and the overtaxed cooling systems, required the pilot to remain highly attentive to the engine at all times.
With test pilots having flown the aircraft for roughly a year, from early 1943 to early 1944, there must have been considerable frustration among them. Its critical failings were never fully addressed, and the plane was still ill functioning through nearly all its test flights, the last of which was only two minutes long. For the considerable effort expended, it seems the only saving grace of the aircraft is that it remained stable. Only one major accident resulted in an air frame loss, being V-31, which overturned on landing on April 29, 1943.
Prototypes
The Fw 190 Höhenjäger 2 never entered mass production, nor did it possess a standard design under a military designation, as the Fw 190C had. The program delivered six prototypes in various configurations. They were built from Fw 190A-0’s, before being modified at Focke Wulf Workshops, and sent off to the Hirth motor works in Stuttgart to be fitted with the turbo supercharger equipment. It does not appear these aircraft were referred to as either Fw 190B or Fw 190C, with no defined model of either type having a DB 603S engine. Given the enormous troubles involved in this program, it does not seem to have reached a stage where a potential fighter design was proposed.
Fw 190V18/U-1: This was the first of the prototypes constructed, and transferred from Jumo 213 testing, first flown in December of 1942. It had the standard Fw 190A span wing, the enlarged vertical stabilizer, and was only later fitted with a pressurized cockpit, an enlarged radiator for the intercooler, and a metal four bladed VDM propeller. By May of 1943, it had flown 44 test flights, and was later passed on to the Hirth, and Daimler Benz test centers in Stuttgart in June of 1944.
Fw 190V29: Same as V18/U-1 and all the later additions it received. This aircraft carried fighter communication and identification gear, the FuG 16P and FuG 25A, respectively. The first of the freshly converted prototypes, and first flown in March of 1943. The turbo supercharger failed to function after being installed at the Hirth facilities in Stuttgart, and the prototype had to be rebuilt to begin testing.
Fw 190V30: The same as the V29, save for it testing a wooden four bladed VDM propeller manufactured by Schwarz. This prototype had considerably worse overheating problems. Completed in April, 1943.
Fw 190V31: Same as V29, this prototype was soon lost after engine failure during one of its early test flights. It overturned during a forced landing, and was written off on May 29, 1943.
Fw 190V32: Same as V29 and V31, with the addition of a pair of Mg 151/20 cannons in the wing roots. Completed in November 1943.
Fw 190V33: Same as V29. Completed in time to be turned over to the Ta 152 program.
Conclusion
The Höhenjäger 2 project can categorically be stated to be a failure. It was unable to produce a design which could have been offered for service, given the completely unworkable state of its turbo supercharger system. Both the victim of resource shortages, and the chaotic and dysfunctional Luftwaffe offices which oversaw new technical developments, the task set before the engineers was impossible. In the end, the program’s test aircraft were turned over to the more successful, if very short lived, Ta 152 project. Its only contribution seems to have been the enlarged, wooden tail section and pressurized cockpit.
Specification
| Höhenjäger 2 (Proposed) | Specification (Projected) |
|---|---|
| Engine | DB 603S |
| Engine Output | 2000 PS |
| Gross Weight | 3585 kg |
| Maximum speed | 685 km/h at 11,800 m |
| Height | 3.95 m |
| Length | 9.50 m |
| Wingspan | 12.30 m |
| Wing Area | 20.3 m2 |
Note: These figures do not depict any aircraft constructed by Focke Wulf, the prototypes have roughly the same dimensions and have a 10.5 m wing with an area of 18.3 m2
Illustration
Credits
Written By Henry H.
Edited By Henry H.
Illustration by Oussama Mohamed “Godzilla”
Sources:
Primary:
Pilot Training Manual for the P-47 Thunderbolt. AAF Office of Flying Safety. March 1945.
Motorhandbuch zum Mercedes-Benz-Flugmotor DB 603A Baureihe 0,1 und 2. Daimer-Benz A.-G. 1942.
Fw 190A-5/A-6 Flugzeug-Hanbuch Tiel 1: Rumpfwerk. Der Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe. 1943.
Fw 190A-5/A-6 Flugzeug-Hanbuch Tiel 3: Leitwerk. Der Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe. 1943.
Fw 190 A-2 bis A-6 Flugzeug-Handbuch Tiel 1 Rumpfwerk. Der Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe. 1943.
Fw 190 A-2 bis A-6 Flugzeug-Handbuch Tiel 2 Fahrwerk. Der Reichsminister der Luftfahrt und Oberbefehlshaber der Luftwaffe. 1943.
Horizontalgeschwindigkeit über der Flughöhe, Normaljäger Fw 190 A-5. 20.10.1943
Flugzeug Flugleistungen Me 109G-Baureihen. Messerschmitt AG Augsburg. August 1943.
Secondary
Cooper, M. The German Air Force, 1933-1945: An Anatomy of Failure. Jane’s Pub, 1981.
Douglas, Calum E. Secret Horsepower Race: Second World War Fighter Aircraft Engine Development on the Western Front. TEMPEST, 2020.
Smith, J. & Creek, Eddie. Focke-Wulf Fw 190, Vol. 2: 1938-1943. Specialty Pr Pub & Wholesalers. 2015.
Smith, J. & Creek, Eddie. Focke-Wulf Fw 190, Vol. 1: 1944-1945. Specialty Pr Pub & Wholesalers. 2015.
Brown, Eric Melrose. Wings of the Luftwaffe. Hikoki, 2010.
The Focke Wulf 190 A Famous German Fighter. Heinz J Nowarra. Harleyford Publications. 1973.
Nazi Germany (1939)
