Thursday, October 1, 2009

The Messerschmitt Me 163 Komet

The Messerschmitt Me 163 Komet, designed by Alexander Martin Lippisch, was a German rocket-powered fighter aircraft. It was the only operational rocket-powered fighter aircraft to date. It was a revolutionary design, capable of performance unrivaled at the time. Messerschmitt test pilot Rudy Opitz in 1944 reached 1,123 km/h (698 mph). Only about 300 were built   and it proved ineffective as a fighter responsible for the destruction of about nine Allied aircraft.

Messerschmitt Me 163 Komet


Me 163B-1a at the National Museum of Flight in Scotland
Role
Interceptor
Manufacturer
Messerschmitt
Designed by
Alexander Lippisch
First flight
Me 163 A V4 in 1 September 1941
Introduction
1944
Primary user
Luftwaffe
Number built
~500[citation needed]
Work on the design started under the aegis of the Deutsche Forschungsanstalt für Segelflug (DFS) - the German Institute for the Study of sailplane flight. Their first design was a conversion of the earlier Lippisch Delta IV known as the DFS 39 and used purely as a glider testbed of the airframe.

A larger follow-on version with a small propeller engine started as the DFS 194. This version used wingtip-mounted rudders, which Lippisch felt would cause problems at high speed, and he later redesigned them to be mounted on a conventional vertical stabilizer at the rear of the aircraft. The design included a number of features from its glider heritage, notably a skid used for landings, which could be retracted into the aircraft's keel in flight. For takeoff, a pair of wheels, each mounted onto the ends of a specially designed cross-axle, together comprising a takeoff "dolly" mounted under the landing skid, were needed due to the weight of the fuel, but these were released shortly after takeoff. It was planned to move to the Walter R-1-203 cold engine of 400 kgf (882 lbf) thrust when available.

Heinkel had also been working with Walter on his rocket engines, mounting them in the He 112 for testing, and later the first purpose-designed rocket aircraft, the He 176. Heinkel had also been selected to produce the fuselage for the DFS 194 when it entered production, as it was felt that the highly volatile fuel would be too dangerous in a wooden fuselage, with which it could react. Work continued under the code name Projekt X.

However the division of work between DFS and Heinkel led to problems, notably that DFS seemed incapable of building even a prototype fuselage. Lippisch eventually requested to leave DFS and join Messerschmitt instead. On 2 January 1939, he moved along with his team and the partially completed DFS 194 to the Messerschmitt works at Augsburg.

The delays caused by this move allowed the engine development to "catch up", and once at Messerschmitt the decision was made to skip over the propeller-powered version and move directly to rocket power. The airframe was completed in Augsburg and shipped to Peenemünde West in early 1940 to receive its engine. Although the engine proved to be extremely unreliable, the aircraft had excellent performance, reaching a speed of 342 mph (550 km/h) in one test.

Me 163 A

Production of a prototype series started in early 1941, known as the Me 163. Secrecy was such that the number, 163, was actually that of the earlier, pre-July 1938 Messerschmitt Bf 163 project to produce a small two-passenger light plane, which had competed against the Fieseler Fi 156 Storch for a production contract, as it was thought that intelligence services would conclude any reference to the number would be for that earlier design. Me 163 A V4 was shipped to Peenemünde to receive the HWK RII-203 engine on May 1941, and on 2 October 1941, the Me 163 A V4, bearing the radio call sign letters, or Stammkennzeichen, "KE+SW", set a new world speed record of 1,004.5 km/h (623.8 mph), piloted by Heini Dittmar. This would not be officially approached until the postwar period by the new jet fighters of the British and U.S., and was not surpassed until the American Douglas Skystreak turbojet-powered research aircraft did so on 20 August 1947. Five prototype Me 163 Anton A-series experimental V-aircraft were built, adding to the original DFS 194 (V1), followed by eight pre-production examples designated Me 163 A-0.

During testing the jettisonable main landing gear arrangement proved to be a serious problem and caused many aircraft to be damaged at takeoff when the wheels rebounded and crashed into the aircraft. Malfunctioning hydraulic dampers in the skid could lead to back injuries for the pilot on landing, as the aircraft lacked steering or braking control during the landing run, leaving the pilot unable to avoid obstacles. Once on the ground, it had to be retrieved by an adapted tractor-like vehicle, towing a special retrieval trailer that rolled along on a pair of short continuous track setups (one per side), with twin trailing lifting arms, that lifted the stationary aircraft off the ground, from under each wing panel. The tractor itself was originally meant for agricultural use on small farms, the three-wheeled Scheuch-Schlepper, as the Komet was unpowered and lacked wheels at this point.

During flight testing, the superior gliding capability of the swept-wing Komet proved detrimental to safe landing. The aircraft would rise back into the air with the slightest updraft. Since the approach was made unpowered, there was no opportunity to make another landing pass if the aircraft failed to stop at the proper airfield. For production models, a set of landing flaps allowed somewhat more controlled landings. This issue remained a problem throughout the program, however.

Nevertheless, the performance was tremendous and plans were made to put Me 163 squadrons all over Germany in 40 km (25 mi) rings. Development of an operational version was given the highest priority.

Meanwhile, Walter had started work on the newer HWK 109-509 hot engine, which added a true fuel of hydrazine hydrate and methanol, designated C-Stoff, that burned with the oxygen-rich exhaust from the T-Stoff, used as the oxidizer, for added thrust. (See List of Stoffs.) This resulted in the significantly modified Me 163 B of late 1941. Due to the Reichsluftfahrtministerium (RLM) requirement that it should be possible to throttle the engine, the originally simple power plant grew complicated and lost reliability. The new fuel proved an unfortunate choice as well, since hydrazine hydrate was also used in the launcher of the V-1 "Doodlebug" flying bomb and was in short supply throughout the 1943-45 period.

The fuel system was particularly troublesome, as leaks experienced during hard landings easily degenerated in fires and explosions. Metal fuel lines and fittings, which failed in unpredictable ways, were used as this was the best technology available. Both fuel and oxidizer were toxic and required extreme care when loading in the airframe - yet there were still occasions when Komets simply exploded on the tarmac. The corrosive nature of the liquids also mandated special protective gear for the pilots.

Two prototypes were followed by 30 Me 163B-0 aircraft armed with two 20 mm MG 151/20 cannon and some 400 Me 163B-1s armed with two 30 mm (1.18 in) MK 108 cannons, but which were otherwise similar to the B-0. Occasional references to B-1a or Ba-1 subtypes are found in the literature on the aircraft, but the meanings of these designations are somewhat unclear. Early in the war, when German aircraft firms created versions of their aircraft for export purposes, the a was added to export (ausland) variants (B-1a) or to foreign-built variants (Ba-1) but for the Me 163, there were neither export nor a foreign-built version. Later in the war the a, and successive letters, were used for aircraft using different engine types (Me 262A-1a with Jumo engines, A-1b with BMW engines). As the Me 163 was planned with an alternative BMW P3330A rocket engine it's quite safe to assume the a was used for this purpose on early examples. Only one Me 163, the V10, was tested with the BMW engine so this designation suffix was soon dropped. The Me 163 B-1a didn't have any wingtip "washout" built into it, and as a result had a much higher critical Mach number than the Me 163 B-1.

The Me 163B had very docile landing characteristics, mostly due to its integrated leading edge slots, located directly forward, along the wing's leading edge, of the elevon control surfaces. It was found to be impossible to stall, nor would it spin. One could fly the Komet with the stick full back and have it in a turn and then use the rudder to take it out of the turn and not fear it snapping into a spin. It would also slip beautifully. Because it was derived from a glider, it had excellent gliding qualities which meant it had the tendency to keep on flying above the ground. On the other hand, making a too close turn from base onto final, the sink rate would increase, and one could quickly lose altitude and come in short. Another main difference from a propeller-driven aircraft is that there was no slipstream over the rudder. On takeoff, one had to attain the speed at which the aerodynamic controls become effective - about 129 km/h (80 mph) - and that was always a critical thing. One had to be careful the control stick wasn't somewhere in the corner when the control surfaces began working. These, like many other specific Me 163 problems, would be resolved by specific training.

The performance of the Me 163 far exceeded that of contemporary piston engine fighters. At a speed of over 320 km/h (200 mph) the aircraft would take off, in a so-called "sharp start" from the ground, from its two-wheeled dolly. The aircraft would be kept at low altitude until the best climbing speed of around 676 km/h (420 mph) was reached, at which point it would jettison the dolly, pull up into a 70° angle of climb, and rapidly climb to the bombers' altitude. It could go even higher if need be, reaching 12,000 m (40,000 ft) in an unheard-of three minutes. Once there, it would level off and quickly accelerate to speeds around 880 km/h (550 mph) or faster, which no Allied fighter could hope to match. Because of its thin wings it didn't suffer from compressibility or other aerodynamic problems as much as other early jet aircraft. What's more, the aircraft was remarkably agile and docile to fly at high speed. According to Rudolf Opitz, chief test pilot of the Me 163, it could "fly circles around any other fighter of its time".

By this point, Messerschmitt was completely overloaded with production of the Bf 109 and attempts to bring the Me 210 into service. Production in a dispersed network was handed over to Klemm, but quality control problems were such that the work was later given to Junkers, who was at that time underworked. As with many German designs of World War II, parts of the airframe (esp. wings) were made of wood, which allowed furniture manufacturers to act as subcontractors.

For training purposes, the older Me 163A and first Me 163B prototypes were used. But it was planned to introduce the Me 163 S, which removed the rocket engine and tank capacity and placed a second seat for the instructor behind the pilot. The 163 S would be used for glider landing training, which as explained above, was essential to operate the Me 163. It appears the 163 Ss were converted from the earlier Me 163B series prototypes.

In service, the Me 163 turned out to be difficult to use against enemy aircraft. Its tremendous speed and climb rate meant a target was reached and passed in a matter of seconds. Although the Me 163 was a stable gun platform, it required excellent marksmanship to bring down an enemy bomber. The Komet was equipped with two 30 mm (1.18 in) MK 108 cannons which had a relatively low muzzle velocity, with the characteristic ballistic drop of such a weapon, which meant they were only accurate at short distance, and that it was almost impossible to hit a slow-moving bomber when the Komet was traveling very fast (four or five hits were typically needed to take down a B-17).

A number of innovative solutions were implemented to ensure kills by less experienced pilots; the most promising was a unique weapon called the Sondergerät 500 Jägerfaust. This consisted of a series of single-shot, short-barreled 50 mm (2 in) guns pointing upwards. Five were mounted in the wing roots on each side of the aircraft. The trigger was tied to a photocell in the upper surface of the aircraft, and when the Komet flew under the bomber, the resulting change in brightness caused by the underside of the aircraft could cause the rounds to be fired. As each shell shot upwards, the disposable gun barrel that fired it was ejected downwards, thus making the weapon recoilless. It appears that this weapon was used in combat only once, resulting in the destruction of a Halifax bomber, though other sources say it was a Boeing B-17

 

The biggest concern about the design was the short flight time, which never met the projections made by Walter. With only seven and a half minutes of powered flight, the fighter truly was a dedicated point defense interceptor. In order to improve on this, the Walter firm started on the development of a more advanced engine with two separate combustion chambers of differing sizes, oriented one above the other, as a more efficient powerplant. The upper chamber, intended as the motor's primary power output unit, was of a larger size, and supported by the "thrust tube" exactly as on the 509A motor's single chamber had been. It was tuned for "high power" for takeoff and climb, and the smaller volume, lower chamber with approximately 400 kg (880 lb) of thrust at its top performance level, was intended for use as a way of allowing more efficient, lower-power cruise flight. This HWK 109-509 C would improve endurance by as much as 50%. Two 163 Bs, V6 and V18, were experimentally fitted with the new engine and tested in 1944. On 6 July 1944, the Me 163 B V18 (VA+SP) set a new world speed record of 1,130 km/h (702 mph), piloted by Heini Dittmar, and landed with almost all of the vertical rudder surface broken away from flutter.   This record was not broken in terms of absolute speed until 6 November 1947 by Chuck Yeager in a flight that was part of the of the Bell X-1 test program, with a 1,434 km/h (891 mph), or Mach 1.35 supersonic speed, recorded at an altitude of nearly 14,820 m (49,000 ft) altitude. . But the X-1 never exceed this speed in a normal runway liftoff, Heini Dittmar reached this 1,130 km/h (700 mph) performance, after a normal "sharp start" ground takeoff, without an air drop from a mother ship. Neville Duke exceed Heini Dittmars record mark in 31 August 1953 with the Hawker Hunter F Mk3 with a speed of 1,171 km/h (728 mph), after a normal ground start.[11] Aircraft of the configuration the Me 163 used were eventually found to have serious stability problems when entering transonic flight, like the similarly configured, and turbojet powered, Northrop X-4 Bantam and de Havilland DH 108, which made the V18's record with the Walter 509C "cruiser" rocket more remarkable.

Woldemar Voigt of Messerschmitt's Oberammergau offices started a redesign of the 163 to incorporate the new engine, as well as fix other problems. The resulting Me 163 C design featured a larger wing through the addition of an insert at the wing root, an extended fuselage with extra tank capacity through the addition of a "plug" insert behind the wing, and a new pressurized cockpit topped with a bubble canopy giving dramatically improved visibility. The additional tank capacity and cockpit pressurization allowed the maximum altitude to increase to 15,850 m (52,000 ft), as well as improving powered time to about twelve minutes, almost doubling combat time (from about five minutes to nine). Three Me 163C-1a prototypes were planned, but it appears only one was flown, and that without its intended engine.

But by this time the project was moved to Junkers. Here a new design effort under the direction of Heinrich Hertel at Dessau attempted to improve the Komet. The Hertel team had to compete with the Lippisch team and their Me 163C. Hertel investigated the Me 163 and found it was not well suited for mass production and not optimized as a fighter aircraft, with the most glaring defeciency being the lack of a retractable landing gear of any sort. For this the Me 163V-18 was equipped with a non-retractable tricycle landing gear. (This prototype is often called the Me 163D but it is now clear that there never was a 163 D.) The resulting Junkers Ju 248 used a three-section fuselage to ease construction. The V1 prototype was completed for testing in August 1944, and was glider tested behind a Junkers Ju 188. Some sources state that the Walter 109-509 C engine was fitted in September, but it was probably never tested under this power. At this point the RLM re-assigned the project to Messerschmitt, where it became the Me 263. This appears to have been a formality only, with Junkers continuing the work and planning production

However, by the time the design was ready to go into production, after many delays, the plant it was to be made at was overrun by Soviet forces. While it did not reach operational status, the work was briefly continued by the Russian Mikoyan-Gurevich (MiG) design bureau as the Mikoyan-Gurevich I-270[14].

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