Messerschmitt Me 262
The Messerschmitt Me 262, nicknamed Schwalbe in fighter versions, or Sturmvogel in fighter-bomber versions, is a fighter aircraft and fighter-bomber that was designed and produced by the German aircraft manufacturer Messerschmitt. It was the world's first operational jet-powered fighter aircraft and one of two jet fighter aircraft types to see air-to-air combat in World War II, the other being the Heinkel He 162.
The design of what would become the Me 262 started in April 1939, before World War II. It made its maiden flight on 18 April 1941 with a piston engine, and its first jet-powered flight on 18 July 1942. Progress was delayed by problems with engines, metallurgy, and interference from Luftwaffe chief Hermann Göring and Adolf Hitler. The German leader demanded that the Me 262, conceived as a defensive interceptor, be redesigned as ground-attack/bomber aircraft. The aircraft became operational with the Luftwaffe in mid-1944. The Me 262 was faster and more heavily armed than any Allied fighter, including the British jet-powered Gloster Meteor. The Allies countered by attacking the aircraft on the ground and during takeoff and landing.
One of the most advanced World War II combat aircraft, the Me 262 operated as a light bomber, reconnaissance aircraft, and experimental night fighter. The Me 262 proved an effective dogfighter against Allied fighters; German pilots claimed 542 Allied aircraft were shot down, although higher claims have sometimes been made.
The aircraft had reliability problems because of strategic materials shortages and design compromises with its Junkers Jumo 004 axial-flow turbojet engines.
Late-war Allied attacks on fuel supplies also reduced the aircraft's readiness for combat and training sorties. Armament production within Germany was focused on more easily manufactured aircraft. Ultimately, the Me 262 had little effect on the war because of its late introduction and the small numbers that entered service.
Although German use of the Me 262 ended with World War II, the Czechoslovak Air Force operated a small number until 1951. Also, Israel may have used between two and eight Me 262s. These were supposedly built by Avia and supplied covertly, and there has been no official confirmation of their use.
The aircraft heavily influenced several prototype designs, such as the Sukhoi Su-9 and Nakajima Kikka. Many captured Me 262s were studied and flight-tested by the major powers, and influenced the designs of production aircraft such as the North American F-86 Sabre, MiG-15, and Boeing B-47 Stratojet. Several aircraft have survived on static display in museums. Some privately built flying reproductions have also been produced; these are usually powered by modern General Electric CJ610 engines.
Design and development
Origins
Before World War II, the Germans saw the potential for aircraft powered by the jet engine constructed by Hans von Ohain in 1936. After the successful test flights of the world's first jet aircraft—the Heinkel He 178—within a week of the invasion of Poland which started the conflict, they adopted the jet engine for an advanced fighter aircraft. As a result, the Me 262 was already under development as Projekt 1065 before the start of the war. The project had originated with a request by the Reichsluftfahrtministerium for a jet aircraft capable of one hour's endurance and a speed of at least. Woldemar Voigt headed the design team, with Messerschmitt's chief of development, Robert Lusser, overseeing.During April 1939, initial plans were drawn up and, following their submission in June 1939, the original design was very different from the aircraft that eventually entered service. Specifically, it featured wing-root-mounted engines, rather than podded ones. The progression of the original design was delayed greatly by technical problems with the new jet engine.
Originally designed with straight wings, problems arose when the long delayed engines proved heavier than originally promised. While waiting for the engines, Messerschmitt moved the engines from the wing roots to underwing pods, allowing them to be changed more readily if needed. That turned out to be important, both for availability and maintenance.
When it became apparent that the BMW 003 jets would be significantly heavier than anticipated, on 1 March 1940, it was decided that instead of moving the wing backward on its mount, the outer wing would be swept slightly rearwards to 18.5 degrees, to accommodate the change in the centre of gravity and to position the centre of lift properly relative to the centre of mass.
Initially the inboard leading edge retained the straight profile as did the trailing edge of the midsection of the wing.
Based on data from the AVA Göttingen and wind tunnel results, the inboard section's leading edge was later swept to the same angle as the outer panels, from the "V6" sixth prototype onward throughout volume production.
The shallow leading edge sweep of 18.5° may have inadvertently provided an advantage by slightly increasing the critical Mach number however, its Tactical Mach number remained a relatively modest at Mach 0.82 and both German and British test pilots found that it suffered severe controllability problems as it approached Mach 0.86.
The jet engine program was waylaid by a lack of funding, which was primarily due to a prevailing attitude amongst high-ranking officials that the conflict could be won easily with conventional aircraft. Among these was Hermann Göring, head of the Luftwaffe, who cut the engine development program to just 35 engineers in February 1940. The aeronautical engineer Willy Messerschmitt sought to maintain mass production of the piston-powered, 1935-origin Bf 109 and the projected Me 209. Major General Adolf Galland had supported Messerschmitt through the early development years, flying the Me 262 himself on 22 April 1943. By that time, the problems with engine development had slowed production of the aircraft considerably. One particularly acute problem was the lack of an alloy with a melting point high enough to endure the temperatures involved, a problem that had not been adequately resolved by the end of the war. After a November 1941 flight ended in a double flameout, the aircraft made its first successful flight entirely on jet power on 18 July 1942, propelled by a pair of Jumo 004 engines.
File:Messerschmitt Me 262.jpg|thumb|left|Hans Guido Mutke's Me 262 A-1a/R7 on display at the Deutsches Museum in Munich
Ludwig Bölkow was the principal aerodynamicist assigned to work on the design of the Me 262. He initially designed the wing using NACA airfoils modified with an elliptical nose section. Later in the design process, these were changed to AVL derivatives of NACA airfoils, the NACA 00011-0.825-35 being used at the root and the NACA 00009-1.1-40 at the tip. The elliptical nose derivatives of the NACA airfoils were used on the horizontal and vertical tail surfaces. Wings were of single-spar cantilever construction, with stressed skins, varying from skin thickness at the root to at the tip. To expedite construction, save weight, and use fewer strategic materials late in the war, the wing interiors were not painted. The wings were fastened to the fuselage at four points, using a pair of and forty-two bolts.
During mid-1943, Adolf Hitler envisioned the Me 262 as a ground-attack/bomber aircraft rather than a defensive interceptor. The configuration of a high-speed, light-payload Schnellbomber was intended to penetrate enemy airspace during the expected Allied invasion of France. His edict resulted in the development of the Sturmvogel variant. Hitler's interference helped to extend the delay in bringing the Schwalbe into operation;. In his memoirs, Albert Speer, then Minister of Armaments and War Production, claimed Hitler originally had blocked mass production of the Me 262, before agreeing in early 1944. Similar criticisms were voiced by Lieutenant General Adolf Galland. Hitler rejected arguments that the aircraft would be more effective as a fighter against the Allied bombers destroying large parts of Germany and wanted it as a bomber for revenge attacks. According to Speer, Hitler felt its superior speed compared to other fighters of the era meant it could not be attacked, and so preferred it for high altitude straight flying. Claims that Hitler’s edict delayed operational deployment of the aircraft for several months, are, however incorrect. In fact, his decree delayed the operational introduction of the Me 262 in the first fighter unit, Kommando Nowotny, by less than three weeks. The most significant factor was the short running life of the Jumo 004 turbojet; even in spring 1945 the Jumo 004 was still not fully reliable.
Test flights
Test flights began on 18 April 1941, with the Me 262 V1 example, bearing its Stammkennzeichen radio code letters of PC+UA, but since its intended BMW 003 turbojets were not ready for fitting, a conventional Junkers Jumo 210 engine was mounted in the V1 prototype's nose, driving a propeller, to test the Me 262 V1 airframe. When the BMW 003 engines were installed, the Jumo was retained for safety, which proved wise as both 003s failed during the first flight and the pilot had to land using the nose-mounted engine alone. The V1 through V4 prototype airframes all possessed what would become an uncharacteristic feature for most later jet aircraft designs, a fully retracting conventional gear setup with a retracting tailwheel—indeed, the very first prospective German "jet fighter" airframe design ever flown, the Heinkel He 280, used a retractable tricycle landing gear from its beginnings and flew on jet power alone as early as the end of March 1941.The V3 third prototype airframe, with the code PC+UC, became a true jet when it flew on 18 July 1942 in Leipheim near Günzburg, Germany, piloted by test pilot Fritz Wendel. This was almost nine months ahead of the British Gloster Meteor's first flight on 5 March 1943. Its retracting conventional tail wheel gear, a feature shared with the first four Me 262 V-series airframes, caused its jet exhaust to deflect off the runway, with the wing's turbulence negating the effects of the elevators, and the first takeoff attempt was cut short.
On the second attempt, Wendel solved the problem by tapping the aircraft's brakes at takeoff speed, lifting the horizontal tail out of the wing's turbulence. The first four prototypes were built with the conventional gear configuration. Changing to a tricycle arrangement—a permanently fixed undercarriage on the fifth prototype, with the definitive fully retractable nosewheel gear on the V6 and subsequent aircraft corrected this problem.
Test flights continued over the next year, but engine problems continued to plague the project, the Jumo 004 being only marginally more reliable than the lower-thrust BMW 003. Early engines were so short-lived that they frequently needed replacement after only a single flight. Airframe modifications were complete by 1942 but, hampered by the lack of engines, serial production did not begin until 1944, and deliveries were low, with 28 Me 262s in June, 59 in July, but only 20 in August.
By mid-1943, the Jumo 004A engine had passed several 100-hour tests, with a time between overhauls of 50 hours being achieved. However, the Jumo 004A engine proved unsuitable for full-scale production because of its considerable weight and its high utilization of strategic materials, which were in short supply. Consequently, the 004B engine was designed to use a minimum amount of strategic materials. All high heat-resistant metal parts, including the combustion chamber, were changed to mild steel and were protected only against oxidation by aluminum coating. The engine represented a design compromise to minimize the use of strategic materials and to simplify manufacture. With the lower-quality steels used in the 004B, the engine required overhaul after just 25 hours for a metallurgical test on the turbine. If it passed the test, the engine was refitted for a further 10 hours of usage, but 35 hours marked the absolute limit for the turbine wheel. Frank Whittle concludes in his final assessment over the two engines: "it was in the quality of high temperature materials that the difference between German and British engines was most marked"
Operationally, carrying of fuel in two tanks, one each fore and aft of the cockpit; and a ventral fuselage tank beneath, the Me 262 would have a total flight endurance of 60 to 90 minutes. Fuel was usually J2, with the option of diesel or a mixture of oil and high octane B4 aviation petrol. Fuel consumption was double the rate of typical twin-engine fighter aircraft of the era, which led to the installation of a low-fuel warning indicator in the cockpit that notified pilots when remaining fuel fell below.
Unit cost for an Me 262 airframe, less engines, armament, and electronics, was. To build one airframe took around 6,400-man-hours.