In the 1930's and 1940's in Germany, the Horten Brothers, Walter and Reimar, built a succession of flying wing designs which were quite advanced, and on the cutting edge for their day. Their "Ho" series is as follows:
Ho I - 1931 - a flying-wing sailplane.
Ho II - 1934 - initially a glider, it fitted with a pusher propeller in 1935. Looked very like Northrop's flying wings.
Ho III - 1938 - a metal-frame glider, later fitted with a folding-blade (folded while gliding) propeller for powered flight.
Ho IV - 1941 - a high-aspect-ratio glider (looking very like a modern sailplane, but without a long tail or nose).
Ho V - 1937-42 - first Horten plane designed to be powered, built partially from plastics, and powered by two pusher propellers.
Ho VI "flying parabola" - an extremely-high-aspect-ratio test- only glider. (After the war, the Ho VI was shipped to Northrop for analysis.)
Ho VII - 1945 - considered the most flyable of the powered Ho series by the Horten Brothers, it was built as a flying-wing trainer. (Only one was built and tested, and 18 more were ordered, but the war ended before more than one additional Ho VII could be even partially completed. Ho VIII - 1945 - a 158-food wingspan, 6-engine plane built as a transport. Never built. However, this design was "reborn" in the 1950's when Reimar Horten built a flying-wing plane for Argentina's Institute Aerotecnico, which flew on December 9, 1960 -- the project was shelved thereafter due to technical problems.
Ho IX - 1944 - the first combat-intended Horten design, it was jet powered (Junkers Jumo 004B's), with metal frame and plywood exterior (due to wartime shortages). First flew in January 1945, but never in combat. When the Allies overran the factory, the almost-completed Ho IX V3 (third in the series - this plane was also known as the "Gotha Go 229") was shipped back to the Air and Space Museum.
Designers pursued the all-wing dream from the first decade of powered flight, notably Jack Northrop in the U.S. and the Horten brothers in Germany. Reimar and Walter Horten were a step ahead, testing an all-wing sailplane in 1933, a twin-engined pusher in 1937, and a turbojet fighter-bomber in 1944. When the war ended, Reimar was working on a six-engine Amerika bomber to carry a hypothetical atomic bomb to New York City.
If its fuselage, tail, and engine nacelles contribute nothing to an aircraft's lift, why not get rid of them?
Postwar, the western Allies dismissed their work, though the British toyed with a transport version of the Amerika Bomber. Walter stayed in Germany and eventually rejoined the Luftwaffe; Reimar went to Argentina and worked for the Peron government. Meanwhile, Jack Northrop was still trying to build a successful all-wing turbojet bomber in the 1950s. That he never hired the Hortens, as German engineers were recruited for the U.S. space program, may been one of history's great missed opportunities.I
In the end, all that came from their work was a dozen aircraft whose beauty still astonishes. This is especially true of the Ho 229 fighter-bomber, a batlike warplane that wouldn't look out of place at a 21st-century air show--or combat airfield.
The Horten Ho 229 (often erroneously called Gotha Go 229 due to the identity of the chosen manufacturer of the aircraft) was a late-World War II flying wing fighter aircraft, designed by the Horten brothers and built by the Gothaer Waggonfabrik. It was a personal favourite of Reichsmarschall Hermann Göring, and was the only plane to be able to meet his performance requirements.
In the 1930s the Horten brothers had become interested in the all-wing design as a method of improving the performance of gliders. The all-wing layout removes any "unneeded" surfaces and –in theory at least– leads to the lowest possible drag. For a glider low drag is very important, with a more conventional layout you have to go to extremes to reduce drag and you will end up with long and more fragile wings. If you can get the same performance with a wing-only configuration, you end up with a similarly performing glider with wings that are shorter and thus sturdier.
Years later, in 1943 Reichsmarschall Göring issued a request for design proposals to produce a bomber that was capable of carrying a 1000 kg load over 1000 km at 1000 km/h; the so called 1000/1000/1000 rule. Conventional German bombers could reach Allied command centers in England, but were suffering devastating losses, as allied fighter planes were faster than the German bombers. At the time there was simply no way to meet these goals; the new Jumo 004B jet engines could give the speed that was required, but swallowed fuel at such a rate that they would never be able to match the range requirement.
The Hortens felt that the low-drag all-wing design could meet all of the goals – by reducing the drag, cruise power could be lowered to the point where the range requirement could be met. They put forward their current private (and jealously guarded) project, the Ho IX, as the basis for the bomber. The Government Air Ministry (Reichsluftfahrtministerium) approved the Horten proposal, but ordered the addition of two 30MM cannon, as they felt the aircraft would also be useful as a fighter due to its estimated top speed being significantly higher than any allied aircraft.
Reichsmarschall Göring believed in the design and ordered the aircraft into production at Gotha as the RLM designation of Ho 229 before it had taken to the air under jet power. Flight testing of the Ho IX/Ho 229 prototypes began in December 1944, and the aircraft proved to be even better than expected. There were a number of minor handling problems but otherwise the performance was outstanding.
Gotha appeared to be somewhat upset about being ordered to build a design from two "unknowns" and made a number of changes to the design, as well as offering up a number of versions for different roles. Several more prototypes, including those for a two-seat "Nacht-Jäger" night fighter, were under construction when the Gotha plant was overrun by the American troops in April of 1945.
The Ho 229 A-0 pre-production aircraft were to be powered by two Junkers Jumo 004B turbojets with 1,962 lbf (8.7 kN) thrust each. The maximum speed was estimated at an excellent 590 mph (950 km/h) at sea level and 607 mph (977 km/h) at 39,370 ft (12,000 m). Maximum ceiling was to be 52,500 ft (16,000 m), although it is unlikely this could be met. Maximum range was estimated at 1180 miles (1,900 km), and the initial climb rate was to be 4330 ft/min (22 m/s). It was to be armed with two 30 mm MK 108 cannon, and could also carry either two 500 kg bombs, or twenty-four R4M rockets.
It was the only design to come close to meeting the 1000/1000/1000 rule, and that would have remained true even for a number of years after the war. But like many of the late war German designs, the production was started far too late for the plane to have any effect. In this case none saw combat.
The majority of the Ho-229's skin was a carbon-impregnated plywood, which would absorb radar waves. This, along with its shape, would've made the Ho-229 invisible to the crude radar of the day. So it should be given credit for being the first true "Stealth Fighter". The US military initiated "Operation Paperclip" which was an effort by the U.S. Army in the last weeks of the war to capture as much advanced German weapons research as possible, and also to deny that research to advancing Russian troops. A Horton glider and the Ho-229 number V2 were secured and sent to Northrop Aviation in the United States for evaluation, who much later used a flying wing design for the B-2 "Spirit" stealth bomber. During WWII Northrop had been commissioned to develop a large wing-only long-range bomber (XB-35) based on photographs of the Horton's record-setting glider from the 1930's, but their initial designs suffered controllability issues that were not resolved until after the war. Northrops small one-man prototype (N9M-B) and a Horton wing-only glider are located in the Chino Air Museum in Southern California.
The Ho-229's design employed a thoroughly modern wing shape far ahead of its time. The wing had a twist so that in level flight the wingtips (and thus, the ailerons) were parallel with the ground. The center section was twisted upwards, which deflected air in flight, and provided the majority of its lift. Because of this twist in its shape, If the pilot pulled up too suddenly, the nose would stall (or, lose lift) before the wingtips. This meant that the craft's nose would inherently dip in the beginnings of a stall causing the plane to accelerate downwards, and thus it would naturally avoid a flat spin. A flat spin is difficult to recover from, and many rookie pilots have crashed from this condition. Horten also noticed in wind-tunnel testing that in the beginnings of a stall, most airfoil cross-sections began losing lift on their front and rear edges first. Horten designed an airfoil cross-section that developed most of its lift along the centerline of the wing. Since the center line had high lift and the front and rear edges had low lift, it was called a "Bell-Shaped lift curve". The wings were also swept back at a very modern and optimum angle (his gliders from the 1930's used this sweep long before it became popular) which enhanced its stall-resistance, and also lowered its wind-resistance which helped its top speed. This made the Ho-229 easy to fly and very stall-resistant in all phases of its operation.
The only existing Ho-229 airframe to be preserved was V2, and it is located at the National Air and Space Museum (NASM) in Washington D.C. The airframe V1 crashed during testing, and several partial airframes found on the assembly line were destroyed by U.S. troops to prevent them from being captured by advancing Russian troops.
Nothing New Under the Sun.....
The Gotha factory was building the radar-equipped Horten Ho IX, a for that time futuristic jet-engine flying wing. Using the knowledge they gathered from the construction of these now named Gotha Go 229 (the other name used for the Horten Ho IX), they made a proposal for a fighter, the Gotha P60. The P60 used nearly the same wing layout as the Go 229. The first proposal, the P60A, used a cockpit with the crew (2) in a prone position laying side-to-side. The engines of the P60 were placed outside the wing. One on top of the central part, one under the central part. Maybe this was done for better maintenance of the engines. The second proposal, the Gotha P60B, no longer has the prone pilots. It seems to be that Gotha needed to make a simplified cockpit. Maybe they wanted to speed up development or production. Gotha got approval to start building the P60B-prototype, but work was stopped in favor of the final proposal, the P60C
The Gotha factory was building the radar-equipped Horten Ho IX, a for that time futuristic jet-engine flying wing. Using the knowledge they gathered from the construction of these now named Gotha Go 229 (the other name used for the Horten Ho IX), they made a proposal for a fighter, the Gotha P60. The P60 used nearly the same wing layout as the Go 229. The first proposal, the P60A, used a cockpit with the crew (2) in a prone position laying side-to-side.
The engines of the P60 were placed outside the wing. One on top of the central part, one under the central part. Maybe this was done for better maintenance of the engines.
The second proposal, the Gotha P60B, no longer has the prone pilots. It seems to be that Gotha needed to make a simplified cockpit. Maybe they wanted to speed up development or production. Gotha got approval to start building the P60B-prototype, but work was stopped in favor of the final proposal, the P60C
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 (8818lbs). 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.
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/
Artwork by Kyle Scott
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 cnnon 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.