Focke-Wulf Fw 190
The Focke-Wulf Fw 190, nicknamed Würger is a German single-seat, single-engined, fighter aircraft designed by Kurt Tank at Focke-Wulf in the late 1930s and widely used during World War II. Along with its well-known counterpart, the Messerschmitt Bf 109, the Fw 190 became the backbone of the Jagdwaffe of the Luftwaffe. The twin-row BMW 801 radial engine that powered most operational versions enabled the Fw 190 to lift larger loads than the Bf 109, allowing its use as a day fighter, fighter-bomber, ground-attack aircraft, and to a lesser degree, night fighter.
The Fw 190A started flying operationally over France in August 1941 and quickly proved superior in all but turn radius to the Spitfire Mk. V, the main front-line fighter of the Royal Air Force, particularly at low and medium altitudes. The 190 maintained its superiority over Allied fighters until the late 1942 and early 1943 introduction of the improved Spitfire Mk. IX. In November/December 1942, the Fw 190 made its air combat debut on the Eastern Front, finding much success in fighter wings and specialised ground attack units from October 1943.
The Fw 190A series' performance decreased at high altitudes, which reduced its effectiveness as a high-altitude interceptor. From the Fw 190's inception, efforts had been going on to address this with a turbosupercharged BMW 801 in the B model, the much longer-nosed C model with efforts to also turbocharge its chosen Daimler-Benz DB 603 inverted V12 powerplant, and the similarly long-nosed D model with the Junkers Jumo 213. Problems with the turbocharger installations on the -B and -C subtypes meant only the D model entered service in September 1944. These high-altitude developments eventually led to the Focke-Wulf Ta 152, which was capable of extreme speeds at medium to high altitudes . While these "long nose" 190 variants and the Ta 152 derivative especially gave the Germans parity with Allied opponents, they arrived too late to affect the outcome of the war.
The Fw 190 was well-liked by its pilots. Some of the Luftwaffe's most successful fighter aces claimed many of their kills while flying it, including Otto Kittel, Walter Nowotny and Erich Rudorffer. The Fw 190 had greater firepower than the Bf 109 and, at low to medium altitude, superior manoeuvrability, in the opinion of German pilots who flew both fighters. It was regarded as one of the best fighter planes of World War II.
Early development
Genesis
Between 1934 and 1935, the German Ministry of Aviation ran a contest to produce a modern fighter for the rearming Luftwaffe. Kurt Tank entered the parasol-winged Fw 159 into the contest, against the Arado Ar 80, Heinkel He 112 and Messerschmitt Bf 109. The Fw 159 was hopelessly outclassed and was soon eliminated from the competition along with the Ar 80. The He 112 and Bf 109 were generally similar in design, but the 109's lightweight construction gave it a performance edge the 112 was never able to match. On March 12, 1936, the 109 was declared the winner.Even before the Bf 109 had entered squadron service, in autumn 1937, the RLM sent out a new tender asking various designers for a new fighter to fight alongside the Bf 109, as Walter Günther had done with Heinkel's follow-on to the unsuccessful He 100 and He 112. Although the Bf 109 was an extremely competitive fighter, the ministry was worried that future foreign designs might outclass it, and wanted to have new aircraft under development to meet these possible challenges. Tank responded with a number of designs, most powered by a liquid-cooled, inline engine.
The Ministry of Aviation's interest was not aroused, though, until a design was presented using the air-cooled, 14-cylinder BMW 139 radial engine. As this design used a radial engine, it did not compete with the inline-powered Bf 109 for engines, when already too few Daimler-Benz DB 601s were available. This was not the case for competing designs such as the Heinkel He 100 or twin-engined Focke-Wulf Fw 187, where production would compete with the 109 and Messerschmitt Bf 110 for engine supplies. After the war, Tank denied a rumour that he had to "fight a battle" with the ministry to convince them of the radial engine's merits.
Design concepts
At the time, the use of radial engines in land-based fighters was relatively rare in Europe, as their large frontal area were believed to cause too much drag on something as small as a fighter. Tank was not convinced of this, having witnessed the successful use of radial engines by the U.S. Navy, and felt a properly streamlined installation would eliminate this problem.As to the rest of the design philosophy, Tank wanted something more than an aircraft built only for speed. He outlined the reasoning:
Engine
The hottest points on any air-cooled engine are the cylinder heads, located around the circumference of a radial engine. To provide sufficient air to cool the engine, airflow had to be maximized at this outer edge. This was normally accomplished by leaving the majority of the front face of the engine open to the air, causing considerable drag. During the late 1920s, NACA led the development of a dramatic improvement by placing an airfoil-shaped ring around the outside of the cylinder heads. The shaping accelerated the air as it entered the front of the cowl, increasing the total airflow, and allowing the opening in front of the engine to be made smaller.Tank introduced a further refinement to this basic concept. He suggested placing most of the airflow components on the propeller, in the form of an oversized propeller spinner, whose outside diameter was the same as the engine. The cowl around the engine proper was greatly simplified, essentially a basic cylinder. Air entered through a small hole at the centre of the spinner and was directed through ductwork in the spinner, so it was blowing rearward along the cylinder heads. To provide enough airflow, an internal cone was placed in the centre of the hole, over the propeller hub, which was intended to compress the airflow and allow a smaller opening to be used. In theory, the tight-fitting cowling also provided some thrust due to the compression and heating of air as it flowed through the cowling.
The eventual choice of the BMW 801 14-cylinder radial over the more troublesome BMW 139 also brought with it a BMW-designed cowling "system" which integrated the radiator used to cool the motor oil. An annular, ring-shaped oil cooler core was built into the BMW-provided forward cowl, just behind the fan. The outer portion of the oil cooler's core was in contact with the main cowling's sheet metal. Comprising the BMW-designed forward cowl, in front of the oil cooler was a ring of metal with a C-shaped cross-section, with the outer lip lying just outside the rim of the cowl, and the inner side on the inside of the oil cooler core. Together, the metal ring and cowling formed an S-shaped duct with the oil cooler's core contained between them. Airflow past the gap between the cowl and outer lip of the metal ring produced a vacuum effect that pulled air from the front of the engine forward across the oil cooler core to provide cooling for the 801's motor oil. The rate of cooling airflow over the core could be controlled by moving the metal ring to open or close the gap. The reasons for this complex system were threefold. One was to reduce any extra aerodynamic drag of the oil radiator, in this case largely eliminating it by placing it within the same cowling as the engine. The second was to warm the air before it flowed to the radiator to aid in warming the oil during starting. Finally, by placing the radiator behind the fan, cooling was provided even while the aircraft was parked. The disadvantage to this design was that the radiator was in an extremely vulnerable location, and the metal ring was increasingly armoured as the war progressed.
Landing gear
In contrast to the complex, failure-prone, fuselage-mounted, main gear legs of the earlier Fw 159, one of the main features of the Fw 190 was its wide-tracked, inwards-retracting, landing gear. They were designed to withstand a sink rate of, double the strength factor usually required. Hydraulic wheel brakes were used. The wide-track undercarriage produced better ground handling characteristics, and the Fw 190 suffered fewer ground accidents than the Bf 109. The Fw 190's retractable tail gear used a cable, anchored to the "elbow" at the midpoint of the starboard maingear's transverse retraction arms, which ran aftwards within the fuselage to the vertical fin to operate the tailwheel retraction function. The tailwheel's retraction mechanical design possessed a set of pulleys to guide the aforementioned cable to the top of the tailwheel's oleo strut, pulling it upwards along a diagonal track within the fin, into the lower fuselage; this mechanism was accessible through a prominently visible triangular-shaped hinged panel, on the left side in the fin's side sheetmetal covering. On some versions of the Fw 190 an extended tailwheel oleo strut could be fitted for larger-sized loads beneath the fuselage.Control systems
Most aircraft of the era used cables and pulleys to operate their controls. The cables tended to stretch, resulting in the sensations of "give" and "play" that made the controls less crisp and responsive, and required constant maintenance to correct. For the new design, the team replaced the cables with rigid pushrods and bearings to eliminate this problem. Another innovation was making the controls as light as possible. The maximum resistance of the ailerons was limited to, as the average man's wrist could not exert a greater force. The empennage featured relatively small and well-balanced horizontal and vertical surfaces.The design team also attempted to minimize changes in the aircraft's trim at varying speeds, thus reducing the pilot's workload. They were so successful in this regard that they found in-flight-adjustable aileron and rudder trim tabs were not necessary. Small, fixed tabs were fitted to control surfaces and adjusted for proper balance during initial test flights. Only the elevator trim needed to be adjusted in flight. This was accomplished by tilting the entire horizontal tailplane with an electric motor, with an angle of incidence ranging from −3 to +5°.
Another aspect of the new design was the extensive use of electrically powered equipment instead of the hydraulic systems used by most aircraft manufacturers of the time. On the first two prototypes, the main landing gear was hydraulic. Starting with the third prototype, the undercarriage was operated by push buttons controlling electric motors in the wings, and was kept in position by electric up-and-down locks. The armament was also loaded and fired electrically. Tank believed that service use would prove that electrically powered systems were more reliable and more rugged than hydraulics, electric lines being much less prone to damage from enemy fire.