Friday, May 6, 2016

Aircraft walkaround vol.64: Heinkel He162 Volksjäeger

Subject: Heinkel He162 Volksjaeger
Location: Musée de L'Air et de L"Espace, Le Bourget, Paris, France, 2015.
Comments:Heinkel had designed a relatively small, 'sporty'-looking aircraft, with a sleek, streamlined fuselage. Overall, the look of the plane was extremely modernistic for its time, appearing quite contemporary in terms of layout and angular arrangement even to today's eyes. The BMW 003 axial-flow turbojet was mounted in a pod nacelle uniquely situated atop the fuselage, just aft of the cockpit and centered directly over the wing's center section. Twin roughly rectangular vertical tailfins were perpendicularly mounted at the ends of highly dihedralled horizontal tailplanes to clear the jet exhaust, a high-mounted straight wing (attached to the fuselage with just four bolts) with a forward-swept trailing edge and a noticeably marked degree of dihedral, with an ejection seat provided for the pilot — which the Heinkel firm had pioneered in a front-line combat aircraft, with the earlier He 219 night fighter in 1942. The He 162 airframe design featured an uncomplicated tricycle landing gear, the first such landing gear system to be present from the very start in any operational Axis Powers single-engined fighter design, that retracted into the fuselage, performed simply with extension springs, mechanical locks, cables and counterweights, and a minimum of any hydraulics employed in its design. The Heinkel firm's previous experience with designing flightworthy, retractable tricycle undercarriage-equipped airframes extended as far back as late 1939 with the Heinkel He 280 jet fighter prototype, and further strengthened with the unexpectedly successfulHeinkel He 219A night fighter, which also used a tricycle undercarriage. The He 162 V1 first prototype flew within an astoundingly short period of time: the design was chosen on 25 September 1944 and first flew on 6 December, less than 90 days later. This was despite the fact that the factory in Wuppertal making Tego film plywood glue — used in a substantial number of late-war German aviation designs whose airframes and/or major airframe components were meant to be constructed mostly from wood — had been bombed by the Royal Air Force and a replacement had to be quickly substituted, without realizing that the replacement adhesive was highly acidic and would disintegrate the wooden parts it was intended to be fastening. The first flight of the He 162 V1, by Flugkapitän Gotthold Peter — the first German jet fighter aircraft design to be jet-powered from its maiden flight onward — was fairly successful, but during a high-speed run at 840 km/h (520 mph), the highly acidic replacement glue attaching the nose gear strut door failed and the pilot was forced to land. Other problems were noted as well, notably a pitch instability and problems with sideslip due to the rudder design. None were considered important enough to hold up the production schedule for even a day. On a second flight on 10 December, again with Peter at the controls, in front of various Nazi officials, the glue again caused a structural failure. This allowed the aileron to separate from the wing, causing the plane to roll over and crash, killing Peter. An investigation into the failure revealed that the wing structure had to be strengthened and some redesign was needed, as the glue bonding required for the wood parts was in many cases defective. However, the schedule was so tight that testing was forced to continue with the current design. Speeds were limited to 500 km/h (310 mph) when the second prototype flew on 22 December. This time, the stability problems proved to be more serious, and were found to be related to Dutch roll, which could be solved by reducing the dihedral. However, with the plane supposed to enter production within weeks, there was no time to change the design. A number of small changes were made instead, including adding lead ballast to the nose to move the centre of gravity more to the front of the plane, and slightly increasing the size of the tail surfaces. The third and fourth prototypes, which now used an "M" for "Muster" (model) number instead of "V" for "Versuchs" (experimental) number, as the He 162 M3 and M4, after being fitted with the strengthened wings, flew in mid-January 1945. These versions also included — as possibly the pioneering example of their use on a production-line, military jet aircraft — small, anhedraled aluminium "drooped" wingtips, reportedly designed by Alexander Lippisch and known in German as Lippisch-Ohren ("Lippisch Ears"), in an attempt to cure the stability problems via effectively "decreasing" the main wing panel's marked dihedral angle. Both prototypes were equipped with two 30 mm (1.18 in) MK 108 cannons in the He 162 A-1 anti-bomber variant; in testing, the recoil from these guns proved to be too much for the lightweight fuselage to handle, and plans for production turned to the A-2 fighter with two 20 mm MG 151/20 cannons instead while a redesign for added strength started as the A-3. The shift to 20 mm guns was also undertaken because the smaller-calibre weapons would allow a much greater amount of ammunition to be carried. The He 162 was originally built with the intention of being flown by the Hitler Youth, as the Luftwaffe was fast running out of pilots. However, the aircraft was far too complicated for any but a highly experienced pilot. Both a standard-fuselage length, unarmed BMW 003E-powered two-seat version (with the rear pilot's seat planned to have a ventral access hatch to access the cockpit) and an unpowered two-seat glider version, designated the He 162S (Schulen), were developed for training purposes. Only a small number were built, and even fewer delivered to the sole He 162 Hitler Youth training unit to be activated (in March 1945) at an airbase at Sagan. The unit was in the process of formation when the war ended, did not begin any training, and it is doubtful that more than one or two He 162S gliders ever took to the air. Various changes had raised the weight over the original 2,000 kg (4,410 lb) limit, but even at 2,800 kg (6,170 lb), the aircraft was still among the fastest aircraft in the air with a maximum airspeed of 790 km/h (427 kn; 491 mph) at sea level and 839 km/h (453 kn; 521 mph) at 6,000 m (20,000 ft), but could reach 890 km/h (481 kn; 553 mph) at sea level and 905 km/h (489 kn; 562 mph) /h (562 mph) at 6,000 m (20,000 ft) using short burst extra thrust. The short flight duration of barely 30 minutes - only somewhat better than the even shorter 7.5-minute flight duration of the faster-flying Me 163B rocket fighter - was due to only having a single 695-litre (183 US gallon) capacity flexible-bladder fuel tank in the fuselage directly under the engine's intake. The production He 162A-2 was armed with a pair of 20mm MG 151 cannon. He 162 construction facilities were at Salzburg, the Hinterbrühl, and the Mittelwerk. Output was expected to be 1,000 a month by April 1945, double that when the Mittlewerk plant began deliveries

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