Horten Ho 229

Horten Ho 229

Role Fighter/Bomber
Manufacturer Gothaer Waggonfabrik
Designed by Horten brothers
First flight 1 March 1944
Status Cancelled at the end of World War II
Number built 3

The Horten Ho IX (often called Ho 229, or Gotha Go 229 due to the identity of the chosen manufacturer of the aircraft) was a late-World War II prototype flying wing fighter/bomber, designed by Reimar and Walter Horten and built by Gothaer Waggonfabrik. It was the first pure flying wing powered by a turbojet,[1] and was the first aircraft designed to incorporate what became known as stealth technology.[2] It was a personal favorite of German Luftwaffe chief Reichsmarschall Hermann Göring, and was the only aircraft to come close to meeting his "1000, 1000, 1000" performance requirements. Its speed was estimated at 1,024 km/h (636 mph) and its ceiling 15,000 meters (49,213 ft).

Design and development

In the early 1930s, the Horten brothers had become interested in the flying wing design as a method of improving the performance of gliders. The German government was funding glider clubs at the time because production of military aircraft was forbidden by the Treaty of Versailles after World War I. The flying wing layout removes any "unneeded" surfaces and, in theory at least, leads to the lowest possible drag. A wing-only configuration allows for a similarly performing glider with wings that are shorter and thus sturdier, and without the added drag of the fuselage. The result was the Horten H.IV.

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 simply no way to meet these goals — the new Junkers Jumo 004B turbojets could give the required speed, but had excessive fuel consumption.

The Hortens deduced 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 Ho 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 Ho 229 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 roll 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 brake 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 engines were substituted.

Stealth technology

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. In the modern era it became known that a flying wing design will reduce the aircraft's radar cross-section, though no wartime documents survive to confirm that the Hortens were working specifically on a radar-defeating aircraft. In a 1950 document[citation needed] Horten brought up the possibility that their design may have such benefits, and the document specifically mentions reduced detection by sight and radar. It is now known that a jet powered flying wing design such as the Horten will have a smaller radar cross-section than a conventional WWII-era twin engine aircraft: with wings blended into the fuselage, no large propeller disks, or vertical and horizontal tail surfaces. Horten's theories were tested by Northrop-Grumman in 2008 and found to have been successful, resulting in a radar cross section only 40% that of conventional planes (see below).

Testing and evaluation

The first Ho IX V1, an unpowered glider, flew on 1 March 1944. Flight results were very favorable, but there was a landing 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 Horten Ho IX V1 was followed in December 1944 by the Junkers Jumo 004-powered Ho IX V2; the BMW 003 engine was preferred but unavailable at the time. Göring believed in the design and ordered a production series of 40 aircraft from Gotha 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 Ho IX V2 was made in Oranienburg on 2 February 1945. All subsequent test flights and development were done by the Gotha Waggonfabrik. By this time, the Horten brothers were working on the Amerika Bomber and they 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 Ho 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 Ho IX V2 undertook a simulated "dog-fight" with an Messerschmitt Me 262. It is stated that the Ho IX V2 out performed 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 a flight time of around 45 minutes, at an altitude of some 800m, one of the Jumo 004 turbojet engines developed a problem, caught fire and stopped. Ziller was seen to dive the aircraft and pull up several times in an attempt to re-start the engine and save the precious prototype aircraft. Ziller undertook a series of four 360 degree turns with its wings banked 20 degrees. Ziller did not use his radio and did not 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 hit a large tree. He was killed instantly. The prototype aircraft was completely destroyed.

Despite this setback the project continued with sustained energy. On 12 March 1945, the Ho 229 was included in the Jäger-Notprogramm for accelerated production of inexpensive "wonder weapons." The prototype workshop was moved to the Gothaer Waggonfabrik (Gotha) in Friedrichroda. In the same month work commenced on the third prototype, the Ho 229 V3. The V3 was larger than previous prototypes, the shape was modified in various areas, and it was meant to be a template for the pre-production series Ho 229 A-0 day fighters, of which 20 machines had been ordered. V3 was powered by two Jumo 004C engines, and could carry armament of two MK108 30mm cannon in the wing roots. Work had also started on the two-seat Ho 229 V4 and Ho 229 V5 night-fighter prototypes, the Ho 229 V6 armament test prototype, and the Ho 229 V7 two-seat trainer.

During the final stages of the war, the U.S. military initiated Operation Paperclip, which was an effort by the various intelligence agencies to capture advanced German weapons research, and to deny that research to 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.

Surviving airframes

* A Horten flying wing glider (Ho IV) is located in the Planes of Fame museum in Chino, California, USA.

* The only surviving Ho 229 airframe, the V3, is located at the Smithsonian National Air and Space Museum's Paul E. Garber Restoration Facility in Suitland, Maryland, USA.

* Five partial airframes found at the Gothaer Waggonfabrik factory assembly line were destroyed by soldiers of U.S. VIII Corps of Gen. George S. Patton's Third Army in April 1945 to prevent capture by the advancing Soviet forces.

Northrop-built reproduction

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. In early 2008, Northrop-Grumman paired up television documentary producer Michael Jorgensen, another long-time fan of the aircraft, 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]

A team of engineers from Northrop-Grumman ran electromagnetic tests on the V3's multilayer wooden center-section nose cones. The cones are three-fourths of an inch (19mm) 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 an experiment to determine the stealth characteristics of the design, 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 radar network of the British in the early 1940s. RCS testing showed that an 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 plane 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, while the television special aired on 28 June 2009 on the National Geographic Channel.

Ho IX V1
Unpowered glider, one built and flown (three-view drawing below).[1]
Ho IX V2
First prototype, one built and flown with twin Junkers Jumo 004B engines.[1]

Gotha Developments:

Ho 229 V3
Revised air intakes, engines moved forward to correct longitudinal imbalance. One 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.

Horten Developments:

Ho 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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