Horten Ho 229

Ho 229
Artist's concept of the aircraft in the air
Role	Fighter/bomber
Manufacturer	Gothaer Waggonfabrik
Designer	Horten brothers
First flight	1 March 1944 (glider)
Primary user	Luftwaffe
Number built	3

The Horten H.IX, RLM designation Ho 229 (or Gotha Go 229 for extensive re-design work done by Gotha to prepare the aircraft for mass production) was a German prototype fighter/bomber designed by Reimar and Walter Horten to be built by Gothaer Waggonfabrik. Developed at a late stage of the Second World War, it was one of the first flying wing aircraft to be powered by jet engines. ^[1]

The Ho 229 was designed in response to a call made in 1943 by Hermann Göring, the head of the Luftwaffe, for light bombers capable of meeting the "3×1000" requirement; namely, to carry 1,000 kilograms (2,200 lb) of bombs a distance of 1,000 kilometres (620 mi) with a speed of 1,000 kilometres per hour (620 mph).^{[ citation needed ]} Only jet propulsion could achieve the required speed, but such engines were very fuel-hungry, necessitating considerable effort across the rest of the design to meet the range requirement. The flying wing configuration was favoured by the Horten brothers due to its high aerodynamic efficiency, as demonstrated by their Horten H.IV glider. In order to minimise drag, the Ho 229 was not fitted with extraneous flight control surfaces. Its ceiling was 15,000 metres (49,000 ft). ^[2] The Ho 229 was the only design that came close to the requirements, and the Horten brothers quickly received an order for three prototypes after the project gained Göring's approval.

Due to the Horten brothers' lack of suitable production facilities, Ho 229 manufacturing was contracted out to Gothaer Waggonfabrik; however, the company allegedly undermined the project by seeking the favour of Luftwaffe officials for its own flying wing design, the Gotha Go P.60 ^{[ citation needed ]} On 1 March 1944 the first prototype H.IX V1, an unpowered glider, made its maiden flight, followed by the H.IX V2, powered by Junkers Jumo 004 turbojet engines in December 1944. However, on 18 February 1945 the V2 was destroyed in a crash, killing its test pilot. Despite as many as 100 production aircraft being on order, none were completed. The nearly complete H.IX V3 prototype was captured by the American military and shipped to the United States under Operation Paperclip. It was evaluated by both British and American researchers before entering long term storage. The H.IX V3 is on static display in the Smithsonian National Air and Space Museum.

Design and development

The Horten H.IX V2 before a test flight

During the early 1930s the Horten brothers had become interested in the flying wing configuration as a method of improving the performance of gliders. At that time the German government was actively funding glider clubs across the country as a response to the production of military and even motorized aircraft being forbidden by the Treaty of Versailles. The flying wing layout theoretically offered the lowest possible weight, and without the added drag of the fuselage. Their first aircraft of this configuration was the Horten H.IV. ^{[3] [4]}

In 1943 Hermann Göring issued a request for design proposals for a bomber that was capable of carrying a 1,000 kilograms (2,200 lb) load over 1,000 kilometres (620 mi) at 1,000 kilometres per hour (620 mph); the so-called "3×1000 project". Conventional German bombers were capable of reaching Allied targets across Great Britain, but were suffering devastating losses from Allied fighters in the process. ^[3] At the time, there was no conventional means for aircraft designers to meet these goals; the new Junkers Jumo 004B turbojets could provide the required speed, but had excessive fuel consumption. However, the Horten brothers concluded that the low-drag flying wing design could meet all of the goals: by reducing the drag, cruise power could be reduced 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.

While removing the vertical stabilizer reduced drag, it also led to issues with yaw control. In traditional aircraft, a vertical stabilizer works passively to ensure that sideslip is minimized by producing a force perpendicular to itself whenever any sideslip occurs. The lack of a vertical stabilizer on the Horten meant that attempting to fly without any yaw control could lead to uncontrolled sideslip, and potentially flat spins. This was rectified through the addition of split ailerons, which cause increased drag on one wing. While designs without vertical stabilizers require more active control by either the pilot or some flight control systems and lead to bank angle restrictions, they also lead to less aerodynamic drag, and a lower radar cross section. ^[5]

The Government Air Ministry ( Reichsluftfahrtministerium ) quickly 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. ^[4] German officials assigned the designation Ho 229 to the aircraft. Göring was reportedly impressed with the design and personally intervened to ensure that three prototypes were ordered at a cost of 500,000 Reichsmarks. ^[4] At one point, the Air Ministry issued an order for 100 production aircraft, although this was subsequently reduced to 20 aircraft. ^[6] Furthermore, as the Horten brothers lacked appropriate production facilities, it was decided that the manufacturing of the aircraft would be carried out by an established company, Gothaer Waggonfabrik. ^[7] This arrangement was somewhat complicated by Gothaer's alleged efforts to persuade German authorities to favour its own projects, which included flying wing designs, over the Ho 229. ^[8]

Observing the difficulties present in the Ho 229's design and development, Russell Lee, the chair of the Aeronautics Department at the National Air and Space Museum, speculated that an important motivating factor of the project for the Horten brothers was to prevent them and their workers from being assigned to more dangerous roles by the German military. ^[9] Looking beyond the Ho 229, the Horten brothers produced numerous flying wing designs, such as the Horten H.VII fighter-trainer and the Horten H.XVIII Amerikabomber. ^{[10] [4]} According to the aviation historian Jean-Denis G.G. LePage, various other wartime projects were inspired by the Horten brother's work. ^[11]

The H.IX was of mixed construction; while the center pod was made from welded steel tubing, the wing spars were composed of pine. ^[12] The wings were made up of a pair of thin plywood panels that were glued together with a charcoal and sawdust mixture. The exterior was covered by a fireproof paint. ^[12] 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 1.8× 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] There was relatively little available interior space, making the addition of new equipment or more crew members either difficult or impossible. ^[13]

The aircraft was fitted with retractable tricycle landing gear, with the nose gear on the first two prototypes sourced from a He 177's tailwheel system, with the third prototype using an He 177A main gear wheel rim and tire on its custom-designed nose gear strut work and wheel fork. A drogue parachute slowed the aircraft upon landing. The pilot sat on a primitive ejection seat. A special pressure suit was developed by Dräger. While the aircraft had originally been designed to be powered by the BMW 003 turbojet engine, this engine was not quite ready at the time, thus the Junkers Jumo 004 engine was substituted. ^[1] Flight control was achieved via a combination of elevons and spoilers. This control system included both long-span (inboard) and short-span (outboard) spoilers, with the smaller outboard spoilers activated first; it reportedly provided a smoother and more graceful control of yaw than would have been by a single-spoiler system. ^[1]

Operational history

Testing and evaluation

Horten IV glider (hanging, top)

On 1 March 1944, the first prototype H.IX V1, an unpowered glider with fixed tricycle landing gear, performed its maiden flight. 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. Following the transference of design responsibility from the Horten brothers to Gothaer Waggonfabrik, the company's design team implemented several changes: they added a simple ejection seat, substantially redesigned the undercarriage to enable a higher gross weight, changed the jet engine inlets, and added ducting to air-cool the jet engine's outer casing to prevent damage to the wooden wing. ^[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 had been preferred but was not available in sufficient quantity. 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. On 2 February 1945, the first flight of the H.IX V2 was conducted at Oranienburg. ^[3] The Horten brothers were unable to witness this flight as they were occupied with producing the design for a new turbojet-powered strategic bomber in response to the Amerikabomber competition. All of the subsequent test flights and development were conducted by Gothaer Waggonfabrik. The test pilot was Leutnant Erwin Ziller. Two further test flights were performed: on 2 February 1945 and on 18 February 1945.

Two weeks later, on 18 February 1945, disaster struck during the third test flight. After about 45 minutes in the air, at an altitude of around 800 m, one of the engines caught fire and stopped. Ziller was seen to put the aircraft into a dive and pull up several times in an attempt to restart the engine. ^[14] Ziller made a series of four complete turns at 20° angle of bank. He did not use his radio or eject from the aircraft, and may already have been unconscious as a result of the fumes from the burning engine. ^[4] 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 aircraft was completely destroyed. ^{[14] [15]}

Unloading of the captured Horten Ho 229 V3 in the United States.

Despite this setback, the project continued. On 12 March 1945, nearly a week after the U.S. Army had launched Operation Lumberjack to cross the Rhine River, the Ho 229 was included in the Jäger-Notprogramm (Emergency Fighter Program) for the accelerated production of inexpensive "wonder weapons". The prototype workshop was moved to the Gothaer Waggonfabrik (Gotha) in Friedrichroda, western Thuringia. The same month, work was started on the third prototype, the Ho 229 V3.

The V3 was larger than previous prototypes, the shape being modified in various areas,^{[ citation needed ]} 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. The V3 was meant to be powered by two Jumo 004C engines, each with 10% greater thrust than the earlier Jumo 004B production engine used for the Me 262A and Ar 234B, and could carry two MK 108 30 mm cannons 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.

In April 1945, George Patton’s Third Army found four Horten prototypes; a Horten glider and the Ho 229 V3, which was undergoing final assembly, were captured. Of three airframes, the V3 was nearest to completion, and was shipped to the United States for evaluation. ^[12] Along the way, the Ho 229 spent a brief time at RAE Farnborough in the UK; during this time the possibility of installing British jet engines was looked at, but the mountings were found to be incompatible with the early British turbojets, ^[16] which used larger-diameter centrifugal compressors as opposed to the slimmer axial-flow turbojets the Germans had developed. It is uncertain if the aircraft's original Junkers-supplied engines were ever run, although the American evaluation team at one point had the intention of flying it. ^[12]

Surviving aircraft

The only surviving Ho 229 airframe, the V3—and the only surviving Second World War-era German jet prototype still in existence—is on display in the main hall of the Steven F. Udvar-Hazy Center of the Smithsonian National Air and Space Museum (NASM) alongside other WWII-era German aircraft. ^[17] It is displayed partially restored, the wings of the aircraft displayed separately from the center section.

Prior to being placed on display in 2017, it was stored at the NASM's Paul E. Garber Restoration Facility in Suitland, Maryland, U.S. In December 2011, the National Air and Space Museum moved the Ho 229 into the active restoration area of the Garber Restoration Facility, where it was reviewed for full restoration and display. ^[18]

Horten 229 in 2016 while the center section (left) was under restoration. Wings stored separately (right).

The central section of the V3 prototype was moved to the NASM's Steven F. Udvar-Hazy Center in late 2012 to commence a detailed examination of it before starting any serious conservation/restoration efforts ^[19] and was cleared for the move to the Udvar-Hazy facility's restoration shops by summer 2014. ^[20] Following work performed within the Udvar-Hazy facility's Mary Baker Engen Restoration Hangar, it was put on display. ^[21]

Claimed stealth technology

Radar absorbent material

Cross-section of the Horten Ho 229 composite wood laminate

In 1983 Reimar Horten stated that he had intended to add charcoal dust to the wood glue to absorb electromagnetic waves (radar), which he believed could shield the aircraft from detection by the British early-warning ground-based radar known as Chain Home. ^{[lower-alpha 1] [12] [22]} This charcoal glue treatment was planned for the never-made production aircraft; however, it remained unclear if the V3 prototype would have benefited from an early use of this technology. ^[22]

During 2008 a team of engineers from Northrop Grumman made electromagnetic tests on the V3's multilayer wooden centre-section nose cones. They tested over a frequency range of 12 to 117 THz, with wavelengths of the order of 10 microns. The cones are 19 mm (0.75 in) thick and made from thin sheets of veneer. The team observed that the "Ho 229 leading edge has the same characteristics as the plywood [of the control sample] except that the frequency [do not exactly match] and have a shorter bandwidth." ^[23] The team, who had assumed the presence of carbon black from visual inspection, went on to conclude that the "similarity of the two tests indicates that the design using the carbon black type material produced a poor absorber." ^{[23] [24]} The Smithsonian Institution has since performed a study of the materials used on the prototype, and determined that there is "no evidence of carbon black or charcoal", thus invalidating the proposed presence of carbon black to explain the slightly different absorbent property of the prototype wood compared to the control sample of plywood used in the Northrop Grumman testing. ^[25]

Radar cross section and shape

Radar-testing H.IX V3 reproduction at the San Diego Air and Space Museum

A jet-powered flying wing design such as the Horten Ho 229 has a smaller radar cross-section (RCS) than conventional contemporary twin-engine aircraft because the wings blended into the fuselage and there are no large propeller disks or vertical and horizontal tail surfaces to provide a typical identifiable radar signature. ^{[24] [14]}

In early 2008, Northrop Grumman paired up television documentary producer Michael Jorgensen and the National Geographic Channel to make a documentary to determine whether the Ho 229 was the world's first true "stealth" fighter-bomber. ^[24] Northrop Grumman built a full-size non-flying reproduction of the V3, primarily made out of wood, unlike the original aircraft, which had an extensive steel space-frame to which the wooden skin was bolted. After an expenditure of about US$250,000 and 2,500 man-hours, Northrop's Ho 229 reproduction was tested at the company's RCS^{[ clarification needed ]} test range at Tejon, California, US where it was placed on a 15-metre (50 ft) articulating pole and exposed to electromagnetic energy sources from various angles at a distance of 100 m (330 ft), using the same three HF/VHF-boundary area frequencies in the 20–50 MHz range. ^[24]

Radar simulations showed a hypothetical Ho 229, with the radar characteristics of the mockup, which had neither metal frame nor engines, approaching the English coast from France flying at 885 km/h (550 mph) at 15–30 m (49–98 ft) above the water would have been visible to CH radar at a distance of 80% that of a Bf 109. ^[26]

Variants

Horten Ho 229 V3 prototype at the Smithsonian's Garber restoration facility (National Air and Space Museum)

Rear view of Horten Ho 229 prototype

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]

Gotha developments:

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 center-section's tubular framework completed. ^[1]

Ho 229 V5

Planned two-seat all-weather fighter, in construction at Friedrichroda, but not much more than the center-section's tubular framework completed. ^[1]

Ho 229 V6

Projected definitive single-seat fighter version with different cannon, one captured in production at Ilmenau by US troops. ^[27]

Horten developments:

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.

Specifications (Horten H.IX V2)

Data fromNurflügel, ^[28] (Ho 229A)The Complete Book of Fighters ^[29]

General characteristics

• Crew: 1
• Length: 7.4 m (24 ft 3 in) chord at centre-line
  

  

  Orthographically diagram

Ho 229A: 7.47 m (24.5 ft)

• Wingspan: 16.8 m (55 ft 1 in)
  

Ho 229A: 16.76 m (55.0 ft)

• Height: 1.1 m (3 ft 7 in) cockpit height
  

Ho 229A: 2.81 m (9 ft 3 in) overall height

• Wing area: 52.8 m² (568 sq ft)
  

Ho 229A: 50.2 m² (540 sq ft)

• Aspect ratio: 7.8
• Empty weight: 4,844 kg (10,679 lb)
  

Ho 229A: 4,600 kg (10,100 lb)

• Max takeoff weight: 6,876 kg (15,159 lb)
  

Ho 229A: 8,100 kg (17,900 lb)

• Fuel capacity: 1,700 kg (3,700 lb)
• Powerplant: 2 × Junkers Jumo 004B turbojet engine, 8.83 kN (1,990 lbf) thrust each

Performance

• Maximum speed: 960 km/h (600 mph, 520 kn)
  

Ho 229A: 950 km/h (590 mph; 510 kn) / M0.77 at sea level; 977 km/h (607 mph; 528 kn) / M0.92 at 12,000 m (39,000 ft)

• Cruise speed: 900 km/h (560 mph, 490 kn)
• Never exceed speed: 1,000 km/h (620 mph, 540 kn)
  
• Take-off speed: 150 km/h (93 mph; 81 kn)
• Landing speed: 130 km/h (81 mph; 70 kn)
• Range: 1,900 km (1,200 mi, 1,000 nmi) maximum
• Rate of climb: 22 m/s (4,300 ft/min)
• Wing loading: 130 kg/m² (27 lb/sq ft)
• Thrust/weight: 0.382

Armament

• Guns:Ho 229A: 2x 30 mm (1.181 in) MK 108 cannon

See also

Related development

• Horten H.XVIII
• Gotha Go P.60

Aircraft of comparable role, configuration, and era

• Armstrong Whitworth A.W.52
• Northrop N-9M
• Northrop XP-79

Related lists

• List of aircraft of World War II
• List of jet aircraft of World War II
• List of flying wing aircraft

Notes

1. During the war the British also introduced 200MHz radars for early warning of low flying aircraft (Chain Home Low) and target tracking for ground-controlled interception (AMES Type 7)

References

Citations

1. Green 1970, p. 247.
2. Boyne 1994, p. 325.
3. Dowling, Stephen (2 February 2016). "The Flying Wing Decades Ahead of its Time". BBC News.
4. Kindy, David (21 October 2020). "Truth Is Stranger Than Fiction With Horten's All-Wing Aircraft Design". Smithsonian.
5. "Horten Ho 229 V3 | National Air and Space Museum". airandspace.si.edu. Retrieved 2024-02-21.
6. Metzmacher 2021, p. 199.
7. LePage 2009, pp. 24-26.
8. Metzmacher 2021, p. 191, 196.
9. "Desperate for victory, the Nazis built an aircraft that was all wing. It didn't work". Smithsonian Insider. 5 April 2018. Retrieved 4 May 2018.
10. LePage 2009, pp. 199, 303-305.
11. LePage 2009, p. 201.
12. Maksel, Rebecca (August 2016). "Restoring Germany's Captured 'Bat Wing'". Air & Space Smithsonian.
13. LePage 2009, p. 305.
14. Handwerk, Brian (25 June 2009). "Hitler's Stealth Fighter Re-created". News.nationalgeographic.com. Archived from the original on June 27, 2009. Retrieved 29 July 2012.
15. "Horten Ho 229 V-2 (Ho IX V 2) der Absturz". DeutscheLuftwaffe.de. Archived from the original on 1 January 2016. Retrieved 21 February 2016.
16. Brown 2006, p. 119.
17. "Horten Ho 229 V3 - National Air and Space Museum". airandspace.si.edu. Retrieved 12 April 2023. This object is on display in the World War II Aviation (UHC) at the Steven F. Udvar-Hazy Center in Chantilly, VA
18. "Horten Ho 229 V3 Technical Study and Conservation". hortenconservation.squarespace.com. Archived from the original on 12 September 2014. Retrieved 11 September 2014.
19. "National Air and Space Museum Image Detail – Horten H IX V3 Plan – Condition of the Major Metal Components". Smithsonian National Air and Space Museum. Smithsonian Institution. Archived from the original on 1 May 2013. Retrieved 26 May 2013.
20. "Horten Flying Wing Heading to NASM's Udvar-Hazy Center". warbirdsnews.com. 24 June 2014. Retrieved 28 December 2014.
21. "Horten Ho 229 V3 | National Air and Space Museum". airandspace.si.edu. Retrieved 12 April 2023. They moved both the wings and the center section into the Boeing Aviation Hangar in September 2017.
22. "Flying under the Radar: A History of Stealth Planes". National Geographic. 2009. Archived from the original on 27 June 2009. Retrieved 6 November 2010.
23. Dobrenz, Thomas; Spadoni, Aldo; Jorgensen, Michael (September 2010). "Aviation Archeology of the Horten 229 V3 Aircraft, AIAA 2010-9214" . American Institute of Aeronautics and Astronautics. doi:10.2514/6.2010-9214.{{cite journal}}: Cite journal requires |journal= (help)
24. Myhra 2009, p. 11.
25. "Is It Stealth?". National Air and Space Museum. Archived from the original on 11 April 2021. Retrieved 24 March 2021.
26. National Geographic HD : Stealth Fighter - Hitler's Secret Weapons Recreated| Around 40 minutes in
27. Dabrowski 1997, ^{[ page needed ]}.
28. Horten 1985, pp. 135–151.
29. Green 1994, pp. 301–302.

Bibliography

• Boyne, Walter J (1994). Clash of Wings. New York, US: Simon & Schuster. ISBN   0-684-83915-6.
• Brown, Eric (2006). Wings On My Sleeve: The World's Greatest Test Pilot tells his Story. London, UK: Orion Books. ISBN   978-0-297-84565-2.
• Dabrowski, H.P. (1997). The Horten Flying Wing in World War II: The History and Development of the HO 229. Schiffer Publishing. ISBN   0-887-40357-3.
• Green, William; Swanborough, Gordon (1994). The Complete Book of Fighters. London, UK: Salamander. ISBN   1-85833-777-1.
• Green, William (1970). Warplanes of the Third Reich. London, UK: Macdonald and Jane's Publishers Ltd. ISBN   0-356-02382-6.
• Horten, Reimar; Selinger, Peter F. (1985). Nurflügel (in German) (1st ed.). Graz, Germany: H. Wieshaupt Verlag. ISBN   978-3-900310-09-7.
• Lepage, Jean-Denis G.G. (2009). Aircraft of the Luftwaffe, 1935-1945: An Illustrated Guide. McFarland. ISBN   978-0-7864-5280-4.
• Metzmacher, Andreas (2021). Gotha Aircraft: From the London Bomber to the Flying Wing Jet Fighter. Fonthill Media. ISBN   978-1-78155-706-8.
• Myhra, David (1997). The Horten Brothers and Their All-wing Aircraft. London, UK: Bushwood Books. ISBN   0-7643-0441-0.
• Myhra, David (July 2009). "Northrop Tests Hitler's 'Stealth' Fighter". 19 (6). Aviation History.{{cite journal}}: Cite journal requires |journal= (help)
• Shepelev, Andrei; Ottens, Huib (2007). Ho 229, The Spirit of Thuringia: The Horten All-wing jet Fighter. London, UK: Classic Publications. ISBN   978-1-903223-66-6.

Further reading

• Dobrenz, Thomas; Spadoni, Aldo; Jorgensen, Michael (2010). "Aviation Archeology of the Horten 229 v3 Aircraft". 10th AIAA Aviation Technology, Integration, and Operations (ATIO) Conference. 10th AIAA Aviation Technology, Integration, and Operations (ATIO) Conference. doi:10.2514/6.2010-9214. ISBN   978-1-62410-159-5.

External links

• National Air & Space Museum's Ho 229 V3 Restoration Project Homepage Archived 2015-11-14 at the Wayback Machine
• Horten Nurflügels
• Arthur Bentley's scale drawings of the Ho-229
• Construction of a model of the Horten IX including CAD files (in German)
• "Horten: Two brothers, one wing"
• The German Army Horten Ho-229 Archived 2015-02-18 at the Wayback Machine
• WarHistoryOnline's June 2020-dated Ho 229 V3 restoration photos article
• The Horten flying wing on YouTube