Heinkel He 162 Volksjäger

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 - possessing dihedral of some 14º apiece - 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 - a window in the lower forward cockpit area, between the rudder pedals, allowed for visual checking of the nosegear's retraction operation. Partly due to the late-war period it was designed within, some of the He 162's landing gear components were "recycled" existing landing gear components from a contemporary German military aircraft to save development time: the main landing gear's oleo struts and wheel/brake units came from the Messerschmitt Bf 109K, as well as the double-acting hydraulic cylinders, one per side, used to raise and lower each maingear leg. 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 successful Heinkel 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 panels' marked three degree 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's complexity required more experienced pilots. 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, and did not begin any training; it is doubtful that more than one or two He 162S gliders ever took to the air. The Hinterbrühl underground production line for the He 162A was captured in April 1945.

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) at 6,000 m (20,000 ft) using short burst extra thrust. The short flight duration of barely 30 minutes 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 original Baubeschreibung document submittal for the He 162 dated mid-October 1944 showed a pair of fuel tanks for the original version of the Spatz's airframe as-designed: a single, smaller capacity 640 litre (169 US gal) fuselage main tank in approximately the same location as the later 695 litre tank was placed, with an additional wing centre-section tank just above and behind it, never produced for the production run, of some 325 litres (86 US gal) feeding by gravity into the main fuselage tank. The production He 162A-2 was armed with a pair of 20mm MG 151/20 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.