In 1943, Reichsmarschall Göring issued a request for design proposals to produce a bomber that was capable of carrying a 1,000 kg (2,200 lb) load over 1,000 km (620 mi) at 1,000 km/h (620 mph); the so called "3 X 1000 project". Conventional German bombers could reach Allied command centers in Great Britain, but were suffering devastating losses from Allied fighters. At the time, there was no way to meet these goals — the new Junkers Jumo 004B turbojets could provide the required speed, but had excessive fuel consumption.
The Hortens concluded that the low-drag flying 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 private project, the H.IX, as the basis for the bomber. The Government Air Ministry (Reichsluftfahrtministerium) approved the Horten proposal, but ordered the addition of two 30 mm cannons, as they felt the aircraft would also be useful as a fighter due to its estimated top speed being significantly higher than that of any Allied aircraft.
The H.IX was of mixed construction, with the center pod made from welded steel tubing and wing spars built from wood. The wings were made from two thin, carbon-impregnated plywood panels glued together with a charcoal and sawdust mixture. The wing had a single main spar, penetrated by the jet engine inlets, and a secondary spar used for attaching the elevons. It was designed with a 7g load factor and a 1.8x safety rating; therefore, the aircraft had a 12.6g ultimate load rating. The wing's chord/thickness ratio ranged from 15% at the root to 8% at the wingtips.[1]
Control was achieved with elevons and spoilers. The control system included both long span (inboard) and short span (outboard) spoilers, with the smaller outboard spoilers activated first. This system gave a smoother and more graceful control of yaw than would a single spoiler system.[1]
The aircraft utilized retractable tricycle landing gear, with the nosegear on the first two prototypes sourced from a He 177's tailwheel system. A drogue parachute slowed the aircraft upon landing. The pilot sat on a primitive ejection seat. It was originally designed for the BMW 003 jet engine, but that engine was not quite ready and the Junkers Jumo 004 engine was substituted.[1]
[edit] Operational history
[edit] Testing and evaluation
The first prototype H.IX V1, an unpowered glider, flew on 1 March 1944. Flight results were very favorable, but there was an accident when the pilot attempted to land without first retracting an instrument-carrying pole extending from the aircraft. The design was taken from the Horten brothers and given to Gothaer Waggonfabrik. The Gotha team made some changes: They added a simple ejection seat, dramatically changed the undercarriage to enable a higher gross weight, changed the jet engine inlets, and added a system to carry cold air to cool the jet engine's outer casing, as the wing was made of wood.[1]The H.IX V1 was followed in December 1944 by the Junkers Jumo 004-powered second prototype H.IX V2; the BMW 003 engine was preferred, but unavailable. Göring believed in the design and ordered a production series of 40 aircraft from Gothaer Waggonfabrik with the RLM designation Ho 229, even though it had not yet taken to the air under jet power. The first flight of the H.IX V2 was made in Oranienburg on 2 February 1945. All subsequent test flights and development were done by Gothaer Waggonfabrik. By this time, the Horten brothers were working on the Amerika Bomber and did not attend the first test flight. The test pilot was Leutnant Erwin Ziller. Two further test flights were made between 2 and 18 February 1945. Another test pilot used in the evaluation was Heinz Scheidhauer.
The H.IX V2 reportedly displayed very good handling qualities, with only moderate lateral instability (a typical deficiency of tailless aircraft). While the second flight was equally successful, the undercarriage was damaged by a heavy landing caused by Ziller deploying the brake parachute too early during his landing approach. There are reports that during one of these test flights, the H.IX V2 undertook a simulated "dog-fight" with a Messerschmitt Me 262, the first operational jet fighter and that the H.IX V2 outperformed the Me 262.
Two weeks later, on 18 February 1945, disaster struck during the third test flight. Ziller took off without any problems to perform a series of flight tests. After about 45 minutes, at an altitude of some 800 m, one of the Jumo 004 turbojet engines developed a problem, caught fire and stopped. Ziller was seen to put the aircraft into a dive and pull up several times in an attempt to re-start the engine and save the precious prototype. Ziller undertook a series of four 360 degree turns with the wings banked 20 degrees. Ziller did not use his radio or eject from the aircraft. He may already have been unconscious as a result of the fumes from the burning engine. The aircraft crashed just outside the boundary of the airfield. Ziller was thrown from the aircraft on impact and died from his injuries two weeks later. The prototype aircraft was completely destroyed.[4]
During the final stages of the war, the U.S. military initiated Operation Paperclip, an effort by the various intelligence agencies to capture advanced German weapons research, and keep it out of the hands of advancing Soviet troops. A Horten glider and the Ho 229 V3, which was undergoing final assembly, were secured and sent to Northrop Corporation in the United States for evaluation. Northrop was chosen because of their experience with flying wings, inspired by the Horten brothers' pre-war record-setting glider. Jack Northrop had been building flying wings since the N-1M in 1939.
[edit] Survivors
A Horten H.IV flying wing glider is in the Planes of Fame museum in Chino, California. The only surviving Ho 229 airframe, the V3, is at the Smithsonian National Air and Space Museum's Paul E. Garber Restoration Facility in Suitland, Maryland.[edit] Stealth technology
[edit] Northrop-built reproduction
After the war, Reimar Horten said he mixed charcoal dust in with the wood glue to absorb electromagnetic waves (radar), which he believed could shield the aircraft from detection by British early warning ground-based radar known as Chain Home.[5] A jet-powered flying wing design such as the Horten Ho 229 will have a smaller radar cross-section than conventional contemporary twin-engine aircraft. This is because, with wings blended into the fuselage, there would be no large propeller disks or vertical and horizontal tail surfaces to provide a typical identifiable radar signature. Horten's theories were tested by Northrop-Grumman in 2008 through the building of a replica that was found to give a radar cross section only 40% that of conventional aircraft.[2][4]Engineers of the Northrop-Grumman Corporation had long been interested in the Ho 229, and several of them visited the Smithsonian Museum's facility in Silver Hill, Maryland in the early 1980s to study the V3 airframe. A team of engineers from Northrop-Grumman ran electromagnetic tests on the V3's multilayer wooden center-section nose cones. The cones are three quarters of an inch (19 mm) thick and made up of thin sheets of veneer. The team concluded that there was indeed some form of conducting element in the glue, as the radar signal slowed down considerably as it passed through the cone.[2]
In early 2008, Northrop-Grumman paired up television documentary producer Michael Jorgensen, and the National Geographic Channel to produce a documentary to determine whether the Ho 229 was, in fact, the world's first true "stealth" fighter-bomber.[2] Northrop-Grumman built a full-size reproduction of the V3, incorporating a replica glue mixture in the nose section. After an expenditure of about US$250,000 and 2,500 man-hours, Northrop's Ho 229 reproduction was tested at the company's classified radar cross-section (RCS) test range at Tejon, California, where it was placed on a 15-meter (50 ft) articulating pole and exposed to electromagnetic energy sources from various angles, using the same three frequencies used by the Chain Home in the mid-1940s. RCS testing showed that a hypothetical Ho 229 approaching the English coast from France flying at 885 km/h (550 mph) at 15–30 metres (50–100 ft) above the water would have been visible at a distance of 80% that of a Bf 109. This implies an RCS of only 40% that of a Bf 109, from the front at the Chain Home frequencies. The most visible parts of the aircraft were the jet inlets and the cockpit, but caused no return through smaller dimensions than the CH wavelength.[2]
With testing complete, the reproduction was donated by Northrop-Grumman to the San Diego Air and Space Museum.[2][6] The television documentary, Hitler's Stealth Fighter (2009), produced by Myth Merchant Films featured the Northrop-Grumman full-scale Ho 229 model as well as CGI reconstructions depicting a fictional wartime scenario where Ho 229s were operational in both offensive and defensive roles.[7]
[edit] Variants
- H.IX V1
- First prototype, an unpowered glider, one built and flown (three-view drawing below).[1]
- H.IX V2
- First powered prototype, one built and flown with twin Junkers Jumo 004B engines.[1]
- Ho 229 V3
- Revised air intakes, engines moved forward to correct longitudinal imbalance. Its nearly completed airframe was captured in production, with two Junkers Jumo 004B jet engines installed in the airframe.
- Ho 229 V4
- planned two seat all weather fighter, in construction at Friedrichroda, but not much more than the tubular framework completed.[1]
- Ho 229 V5
- planned two seat all weather fighter, in construction at Friedrichroda, but not much more than the tubular framework completed.[1]
- Ho 229 V6
- Projected definitive single-seat fighter version with different cannon, mock-up in production at Ilmenau.
- H.IXb (also designated V6 and V7 by the Hortens)
- Projected two-seat trainer or night-fighter; not built.[1]
- Ho 229 A-0
- Projected expedited production version based on Ho 229 V6; not built.
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