Messerschmitt Me 262
From Wikipedia, the free encyclopedia
....continued from Andrew Liu's Messerschmitt Me 262 a
.... the Me 262 was already under development as Projekt 1065 (P.1065) before the start of World War II.
Plans were first drawn up in April 1939, and the original design was very similar to the aircraft that eventually entered service. The progression of the original design was delayed greatly by technical issues involving the new jet engine. Funding for the jet engine program was also initially lacking as many high-ranking officials thought the war could easily be won with conventional aircraft. Among those were Hermann Göring, head of the Luftwaffe, who cut the engine development program to just 35 engineers in February 1940; Willy Messerschmitt, who desired to maintain mass production of the piston-powered Bf 109 and the projected Me 209; and Major General Adolf Galland, who supported Messerschmitt through the early development years, flying the Me 262 himself on 22 April 1943. By that time, problems with engine development had slowed production of the aircraft considerably. One particularly acute problem arose with the lack of an alloy with a melting point high enough to endure the high temperatures involved, a problem that by the end of the war had not been adequately resolved.
The project aerodynamicist on the design of the Me 262 was Ludwig Bölkow. 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 3 mm (0.12 in) thick at the root to 1 mm (0.039 in) at the tip. As a conservation measure, late in the war, wing interiors would not be painted. The wings were fastened to the fuselage at four points, using a pair of 20 mm (0.79 in) and 42 8 mm (0.31 in) bolts.
In mid-1943, Adolf Hitler envisioned the Me 262 as an offensive ground-attack/bomber rather than a defensive interceptor. The configuration of a high-speed, light-payload Schnellbomber ("fast bomber") was intended to penetrate enemy airspace during the expected Allied invasion of France. His edict resulted in the development of (and concentration on) the Sturmvogel variant. It is debatable to what extent Hitler's interference extended the delay in bringing the Schwalbe into operation. Albert Speer, then Minister of Armaments and War Production, claimed in his memoirs that Hitler originally had blocked mass production of the Me 262 before agreeing in early 1944. He rejected arguments that the aircraft would be more effective as a fighter against the Allied bombers that were 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.
Although the Me 262 is often referred to as a "swept wing" design, the production Me 262 had a leading edge sweep of only 18.5°, too slight to achieve any significant advantage in increasing the critical Mach number. Sweep was added after the initial design of the aircraft, when the engines proved to be heavier than originally expected, primarily to position the center of lift properly relative to the center of mass. On 1 March 1940, instead of moving the wing backward on its mount, the outer wing was repositioned slightly aft; the trailing edge of the midsection of the wing remained unswept. Based on data from the AVA Göttingen and wind tunnel results, the middle section's leading edge was later swept to the same angle as the outer panels, from the "V6" sixth prototype onwards throughout volume production.
The first 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.
This airframe, Wrknr. 111711
, was the first Me 262 to come into Allied hands when its test pilot defected in March 1945. It was subsequently lost in August 1946, the US test pilot parachuting to safety.
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 Fritz Wendel. This was almost nine months ahead of the British Gloster Meteor's first flight on 5 March 1943. The conventional gear — producing a pronounced tail-down attitude on the ground — of the Me 262 V3 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 (V1-V4) were built with this configuration. Changing to a tricycle arrangement (initially a fixed undercarriage on the fifth prototype (V5), with fully retractable on V6 (with Stammkennzeichen code VI+AA) and subsequent aircraft) corrected this problem.[Notes 2]
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 BMW 003. 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. This delay in engine availability was in part due to the shortage of strategic materials, especially metals and alloys able to handle the extreme temperatures produced by the jet engine.
Even when the engines were completed, they had an expected operational lifetime of approximately 50 continuous flight hours; most 004s lasted just 12 hours, even with adequate maintenance. A pilot familiar with the Me 262 and its engines could expect approximately 20–25 hours of life from the 004s. Changing a 004 engine was intended to require three hours, but this typically took eight to nine due to poorly made parts and inadequate training of ground crews. With one engine out, the Me 262 still flew well, with speeds of 450–500 km/h (280–310 mph; 240–270 kn), but pilots were warned never to fly slower than 300 km/h (190 mph; 160 kn) on one engine, as the asymmetrical thrust would cause serious handling problems.
Due to the high speed jet stream, turbojet engines develop much less thrust at low speed than propeller powered aircraft, resulting in poor low-speed acceleration. This was particularly noticeable in the Me 262, since early jet engines had relatively low power and responded slowly to throttle changes. The introduction of a primitive autothrottle late in the war helped only slightly. Conversely, the superior power of jet engines at higher speeds meant the Me 262 enjoyed a much greater rate of climb. Used tactically, this gave the jet fighter an even larger speed advantage in climb than in level flight at top speed.
Operationally, carrying 2,000 l (440 imp gal; 530 US gal) of fuel in two 900 l (200 imp gal; 240 US gal) tanks, one each fore and aft the cockpit, and a 200 l (44 imp gal; 53 US gal) tank beneath,[Notes 3] the Me 262 would have a total flight endurance of 60 to 90 minutes. Fuel was usually brown coal-derived J2, with the option of diesel oil or a mixture of oil and high octane B4 aviation petrol. 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 to notify pilots when the remaining fuel fell below 250 l (55 imp gal; 66 US gal).
Unit cost for an Me 262 airframe, less engines, armament, and electronics, was RM87,400.[Notes 4] To build one airframe took around 6,400 man-hours.
On 19 April 1944, Erprobungskommando 262 was formed at Lechfeld just south of Augsburg, as a test unit (Jäger Erprobungskommando Thierfelder, commanded by Hauptmann Werner Thierfelder) to introduce the 262 into service and train a core of pilots to fly it. On 26 July 1944, Leutnant Alfred Schreiber with the 262 A-1a W.Nr. 130 017 damaged a Mosquito reconnaissance aircraft of No. 540 Squadron RAF PR Squadron, which was allegedly lost in a crash upon landing at an air base in Italy. Other sources state the aircraft was damaged during evasive manoeuvres and escaped.