Horten Ho XVIII (Amerika Bomber)
In 1944 the RLM issued a requirement for an aircraft with a range of 11000 km (6835 miles) and a bomb load of 4000 kg (8818 lbs). This bomber was to be able to fly from Germany to New York City and back without refuelling. Five of Germany's top aircraft companies had submitted designs, but none of them met the range requirements for this Amerika Bomber. Their proposals were redesigned and resubmitted at the second competition, but nothing had changed. The Hortens were not invited to submit a proposal because it was thought that they were only interested in fighter aircraft..
After the Hortens learned of these design failures, they went about designing the XVIIIA Amerika Bomber. During the Christmas 1944 holidays, Reimar and Walter Horten worked on the design specifications for their all-wing bomber. They drew up a rough draft and worked on weight calculations, allowing for fuel, crew, armaments, landing gear and bomb load. Ten variations were eventually worked out, each using a different number of existing turbojets. Several of the designs were to be powered by four or six Heinkel-Hirth He S 011jet engines, and several of the others were designed around eight BMW 003A or eight Junker Jumo 004B turbojets.
The version that the Hortens thought would work best would utilize six Jumo 004B turbojets, which were buried in the fuselage and exausted over the rear of the aircraft. They were fed by air intakes located in the wing's leading edge. To save weight they thought of using a landing gear that could be jettisoned immediately after takeoff (with the additional help of rocket boosters) and landing on some kind of skid. The Ho XVIII A was to be built mainly of wood and held together with a special carbon based glue. As a result, the huge flying wing should go largely undetected by radar.
Reimar Horten says in his biography:
Our final contract; to develop a six jet long range bomber, was received on March 12, 1945.
To gain some experience with large flying wings, I had proposed to double the size of a Ho III, equip it with six 640 HP pusher engines, give it an endurance of 20 hours at 500 km/h, and the ability to carry a few bombs. Such an aircraft would be useful in the North Atlantic war. The official argument against it was that "our bombers already do 500 km/h!
The order to proceed with the building of the Ho XVIII came, despite my arguments that preliminary calculations were not completed. Construction was started in Kahla near Weimar in April 1945.
The Hortens were told to make a presentation for their Amerika Bomber design on Febuary 25, 1945 in Berlin. The meeting was attended by representatives of the five aircraft companies who originally submitted ideas for the competition. No one challenged their assertion that their flying wing bomber could get the job done. A few days later the Hortens were told to report to Reichsmarshall Göring, who wanted to talk to the brothers personally about their proposed Amerika Bomber. There they were told that they were to work with the Junkers company in building the aircraft.
Several days later Reimar and Walter Horten met with the Junkers engineers, who had also invited some Messerschmitt engineers. Suddenly it seemed that the Horten's design was to be worked on by committee. The Junkers and Messerschmitt engineers were unwilling to go with the design that the Hortens presented several days earlier. Instead, the committee wanted to place a huge vertical fin and rudder to the rear of the Ho XVIII A. Reimar Horten was angry, as this would add many more man-hours, plus it would create drag and thus reduce the range. The committee also wanted to place the engines beneath the wing, which would create additional drag and reduce the range even further. After two days of discussion, they chose a design that had huge vertical fins, with the cockpit built into the fin's leading edge. Six Jumo 004A jet engines were slung under the wing, three to a nacelle on each side. The bomb bay would be located between the two nacelles, and the tricycle landing gear would also be stored in the same area. The committee would present the final design to the RML and recommended that it be built in the former mining tunnels in the Harz Mountains.
Dissatisfied with the committee designed Ho XVIII A, Reimar Horten redesigned the flying wing Amerika Bomber. The proposed Ho XVIII B had a three man crew which sat upright in a bubble-type canopy near the apex of the wing. There were two fixed main landing gear assemblies with two He S 011 turbojets mounted to each side.
During flight, the tires would be covered by doors to help cut down on air resistance and drag, a nose wheel being considered not necessary. Overall, the aircraft would have weighed about 35 tons fully loaded. Fuel was to be stored in the wing so that no auxiliary fuel tanks would be required. It was estimated that the Ho XVIII B would have a range of 11000 km (6835 miles), a service ceiling of 16 km (52492 feet) and a round-trip endurance of 27 hours.
Although armament was considered unnecessary, Reimar Horten proposed that two MK 108 30mm cannon could be mounted directly below the cockpit. It was decided that construction was to be done in two bomb-proof hangers near Kala, which had concrete roofs 5.6 meters (18.4 feet) thick. In addition, extra long runways had been constructed so the aircraft could be test flown there too. Work was supposed to start immediately, and the RLM expected the Ho XVIII B to be built by the fall of 1945, which Reimar Horten reported to be impossible. At any rate, Germany surrendered two months later before construction could begin.
Artwork by Kyle Scott