Horten Ho IX / Ho 229
Jet-Powered Flying Wing / Fighter-Bomber
The Ho 229 brought about many firsts - advanced swept-back wings, a jet-powered flying wing design and radar absorbing stealth technology.
Authored By: Dan Alex | Last Edited:
The Horten Ho IX (or "Horten Ho 229" - sometimes incorrectly designated the "Gotha Go 229") maintains a certain level of celebrity status in the world of World War 2 military aviation, essentially becoming the first production-worthy form of any aircraft categorized as a true "flying wing" - that is an aircraft not relying on any sort of vertical tail surfaces to achieve flight and maneuverability. Additionally, the Ho IX/Ho 229 was the first to incorporate radar absorbing "stealth" technologies into its frame work - quite the accomplishment in forward thinking for 1944 - and made heavy use of swept-back wings before they became the norm of the jet age. In these ways alone, the Ho IX/Ho 229 was truly a marvel attempt in every way imaginable that a handful of prototypes were constructed to iron out the design. Though a production order was in the works by 1945 though the end of World War 2 saw to it that this machine never contributed to the German war effort in any respect, thus leaving the reader to his/her imagination as to the impact the system would have had in the skies over Europe.
Flying wing designs had been the focus of man-a-aircraft engineer for some time leading up to World War 2. American Jack Northrop himself was one of the big name pioneers in the realm, working on his own flying wing designs, while the Horten brothers - Reimar and Walter Horten - had been studying the capabilities and possibilities for some time now primarily in the field of unpowered glider flight (a third brother, Wolfram, would later die when his bomber was downed over Dunkirk).
Flying wings featuring a lack of vertical implements theoretically offered some inherent advantages by the deletion of such surfaces thus reducing drag to an extent. The Hortens strongly believed that such structures aboard a planform offered more drawbacks than additions. In a flying wing design, the fuselage was generally integrated into the wing roots for a very streamlined approach adding to effective aerodynamic principles. A larger wing surface area also promoted a better rate-of-climb, a larger fuel load (essentially increasing range) and a larger bomb load. However, the lack of vertical flying surfaces also brought about challenges in controlling such an aircraft - an issue that Northrop dealt with to a high degree in his XB-35 flying wing strategic bomber (finally realized in the modern Northrop B-2 Spirit stealth bomber). Northrop's attempt was in fact a commissioned effort to develop a wing-only design based on pictures received of the Horten early 1930's glider attempts. Such wing-only flight would not be realized until the advent of powerful computers in the modern age that could aid the pilot in flight, keeping the aircraft from entering irrecoverable actions.
With restrictions set forth by the Treaty of Versailles following World War 1, the German manufacturing capacity for waging war was severely restricted by the victors. As such, government funding that may have been intended for the production of tanks, guns, planes and the like were instead funneled to other "peacetime" ventures within the country. One such venture proved to be the various glider clubs forming across Germany. These clubs allowed Reimar and Walter the chance to forge some tail-less glider design concepts into practice. Essentially, the glider club was another German attempt to skirt the rules of the Versailles Treaty and train young pilots while testing out aircraft designs under a certain level of secrecy. Though never formally trained in aeronautics, the Hortens maintained a love affair with flight and grew into experienced pilots in their own right, this occurring in their critical early years and helping to pave a legacy now forthcoming. Even as teenagers, their first flyable glider was completed in 1933.
The brothers took to developing models in the beginning and then culminated this process with the production of the Ho I sailplane in 1934. The Ho I was a tail-less system with straight wings that, by all accounts, flew quite well. The pilot sat in a prone position within the apex of wing assembly while elevons were utilized for pitch and roll control while brake flaps were integrated to account for yaw. These brake flaps were affixed to the upper and lower sections of the wing leading edge.
Despite this early success, the Horten brothers were destined to get more out of their concept and put forth a newer design approach. They destroying their original Ho I and took to building a more efficient design. The second attempt was appropriately designated as Ho II and featured swept-back leading and trailing edge wings, a prone glazed-over cockpit and instantly set itself apart from the preceding design attempt. Four Ho II prototypes were produced to test out further flying wing concepts and while at least one of these was powered through a single Hirth-brand 80 horsepower engine mounted to the rear of the main body in a "pusher" arrangement. The Ho IIs were tested sometime in 1938, with one such flight occurring at Darmstadt in the capable hands of renowned female test pilot Hanna Reitsch.
Such developments in wartime Germany did not go unnoticed. Ernst Udet, the Director of the Technical Department of the German Air Ministry, found favor in the Horten's work and brought to them more funding for continued development of the perceived plans. The brothers moved into a more permanent environment operating out of Tempelhof Airport and quickly set to work on the Ho III. Like the Ho II before it, the Ho III featured swept-back wings with a retractable undercarriage. The system basically followed much of the same design lines of the Ho II, becoming an enlarged version of the second attempt. The Ho III was also produced in four working prototypes with one fitting an engine. Of note in the powered Ho III was the inclusion of folding propeller blades which could be collapsed in flight to help reduce drag. While being powered, the Ho III was still a glider through and through. The design made use of a wide span swept wing approach with the pilot seated at the center of the forward profile under a forward-opening glazed cockpit with the engine mounted to his rear.
The Ho IV followed the Ho III as two constructed prototype forms but were, from the outset, simply designed to test out theories and effects of high aspect ratio wings. One of these such aircraft was lost in a crash brought about through an irrecoverable spin.
The Ho V was also produced in two working prototypes, the second being of note for its use of plastic in the construction. The Ho Vs were destined to be powered research airframes and nothing more. These prototypes were originally fitted with a two man cockpit with construction running from 1936 into 1938. In 1942, however, the Ho V was modified to a single seat form. Once again turning to a swept-wing appearance, these gliders featured lesser sweepback along the leading edge and a straight trailing edge - effectively more of a "true" delta type shape. Construction of the internal main body frame was of welding steel tubing and space was made to accommodate 2 x Hirth engines of 80 horsepower in a "pusher" set up.
The Ho VI appeared as a "one-off" prototype example following in line with the Horten IV. This flying wing offered up a greater span than others before it but proved too delicate for the rigors of even basic ground operations. The similar Ho VII followed suit but fitted 2 x Argus As 10C engines of 240 horsepower each. A single prototype was constructed of this model and later relocated to Oranienburg in March of 1945. It is believed that the Ho VII was tested there to some extent.
The Ho VIII proved the most ambitious Horten flying wing attempt to date - a six engine, 60-passenger commercial endeavor. Power was to be supplied by no fewer than 6 x BMW 600 horsepower (each) engines fitted into a pusher arrangement. The wingspan of 262.5 feet alone made this flying wing design easily the largest Horten. Range estimations put the Ho VIII at 3,725 miles at speeds hitting over 200 miles per hour. The design would never reach a finished prototype form for the collapse of Nazi Germany by mid-1945 killed the project altogether. It was expected that the working prototype would have been completed by November of that year.
The "Amerika Bomber"
The Ho VIII was later considered for the "Amerika Bomber" project as the Ho XVIII - an attempt at designing and constructing a super-long range bomber capable of hitting industrial targets in America from possibly the Azores. The Hortens submitted their plan after Christmas of 1944 when other proposals from Messerschmitt, Junkers, Heinkel and Focke-Wulf could not meet the range requirement. The Amerika Bomber project, like many other of Hitler's ambitious visionary systems, came to naught by war's end. The Horten brothers were working on the Amerika Bomber while Gotha took to further developments of their flying wing fighter-bomber after model V2.
The Ho XVIII bomber would most likely have fitted an atomic bomb should both projects (the bomber and atom bomb) have advanced in Germany. The XVIII proved to be the Horten brother's final wartime contract, this awarded on March 12th, 1945. Construction of the XVIII began at Kahla near Weimar in April of 1945, under the concrete roof of bomb-proof shelters but was she never completed.
The XVIII A was, much to the dismay of the Horten brothers, accepted into a design-by-committee approach incorporating Messerschmitt and Junkers engineers. Reimar reworked the XVIII into the XVIII B flying wing instead, which was accepted for construction. Armament would have been 2 x MK 108 30mm cannons mounted under the cockpit floor, the cockpit itself seating three personnel. Power would have been supplied via 2 x Henschel He S 011 turbojet engines.
The German War Machine Comes Calling
Hermann Goring, the stout World War 1 ace (22 kills), Blue Max recipient and now Reichsmarshall of the German Luftwaffe, laid out his "3 x 1000 Projekt" requirement envisioning a fast, long-range bomber with a lethal payload capacity. The project name came about as the bomber would have to be capable of 1,000km speed with a range of 1,000km while ferrying a payload of up to 1,000kg (values translated respectively as 2,200lbs, 620 miles and 620 miles-per-hour). Ambitious to say the least, such a bomber would have been a pivotal war addition to the Luftwaffe toolbox. A long range bomber was always on Goring's scope, who saw the American war machine in the United States as a prime target for disrupting the air campaign ravaging Germany's industrial capacities. This particular bomber initiative, however, would be useful in striking at Allied targets throughout England. To get his prize plane, Goring announced no further contracts unless the proposed aircraft design could meet these requirements. Only one change was further added to the requirement, this by the Fighter Division. Their request was for the addition of 2 x 30mm MK 108 cannons for fighter-on-fighter engagements - a move that could take substantially from the aircraft's intended bomber role.
The Horten brothers jumped in with their flying wing concept believing that the only question mark left was in the selection of a capable engine to power their design and make their bomber reach the stated goals. The project was developed as a private venture and the brothers unveiled the Ho IX. The German Air Ministry accepted and required a first flight in a short six-month window.
The Ho IX
The Ho IX was reminiscent of previous Horten offerings though in many ways this could be considered the pinnacle of their previous attempts. The Ho IX served as the only military combat aircraft that the brothers would get close to full scale production. The design was again based on a large surface area wing an integrated fuselage containing armament, engines and cockpit. The center body's internal workings were again made of welded steel tubing. The wings featured single wooden spars and covered encased with carbon-covered plywood sections held together by a specialized mixture of charcoal and sawdust. The airframe was designed to withstand loads of up to 7g. The undercarriage was wholly retractable and of a tricycle arrangement with the nosewheel borrowed from a Heinkel He 177 Greif (Griffin) long-range heavy bomber. The nosewheel retracted rearwards under the cockpit floor whilst the two main landing gears recessed inwards towards the fuselage just under the wingroots. The single-seat cockpit (complete with a primitive ejection seat system) offered up exceptional views up, over and around the upper wing section but, as one can surmise, other views were generally restricted. The originally selected powerplant proved to be the BMW 003A-1 series turbojets straddling either side of the cockpit, though these were not yet available at the time and replaced with Junkers Jumo 004 series engines. With the lack of vertical tail surfaces, the Ho IX made use of elevons with two spoilers differing in lengths located along the wings. The dual-spoiler configuration allowed for an improved control action to replace the action brought about by a more conventional rudder arrangement or single wing-mounted spoiler.
Wood in the construction of the IX proved a natural choice as it was relatively available, readily accessible and required very little training to work with. Considering the manufacturing restrictions imposed against the German war machine at this time, it made perfect sense. Wood could in many ways take on battlefield punishment better than metal, all the while keeping the flying surfaces generally in check despite. With a wing full of wood, this could potentially make the Ho 229 a beast to bring down with machine gun fire unless leveling a critical hit against a component such as the cockpit or one of the engines. it was suspected that the wing could receive a blast as great as a 20mm projectile and still keep its integrity.
Though revolutionary at its core, the Ho IX further pushed the design curve by incorporating level wings integrated into an upward-angled fuselage. Internally, the wings themselves were already ahead of the current age of flight time so the general outward shape only served to further the Ho IXs "science fiction" type looks.
Stealth and the Ho IX
The charcoal and sawdust mixture is of special note here for has long been thought by some to be the first true attempt at making an aircraft take on "stealth" like qualities intended to absorb incoming radar signals and deflate the outgoing signature. It is stated by sources that the mixture balance was purposely engineered to absorb the electromagnetic waves put out by British early warning ground-based radar systems defending the British mainland - the system largely responsible for the British victory over Germany in the Battle of Britain. Britain utilized a series of inter-connected radar and radio stations to detect and react to incoming flights of German bombers and fighters in a network that would become collectively known as "Chain Home". Though this attempt at stealth technology was rather infant at the time and thusly never truly tested before, the mixture was found to be quite effective in 2008 under experimentation accomplished in a documentary by Northrop Grumman and the National Geographic Channel - an amazing fact considering the age that the Ho IX was developed in. The test proved the mixture to work as advertised and the result created a reduced radar signature for a new-build Ho 229. The signature was less than that of a standard (and rather smallish) Messerschmitt BF 109 fighter. The Ho 229 was further helped by the small forward and shallow side profiles made up only by the cockpit and engine bulges, the rest being nothing more than wing surface area. Additionally, the Ho 229 was constructed largely of wood as opposed to radar reflecting metals as in other German warplanes.
The Design Evolves
NOTE: German naming designations differed somewhat from conventional American systems used throughout the war. While American aircraft most often followed a simple "X" indicating a prototype or a "Y" to indicate a developmental model, the Luftwaffe utilized V1, V2, V3 and so on to indicate changing prototype and early developmental models. Similarly whereas the US Army Air Force utilized a simple A, B, C, etc.. protocol for production models, the Germans relied on A-0, A-1, A-2, etc... to signify changing production models (as in "Ho 229 A-2").
Work on the Ho IX began in 1942. The Ho IX V1 became the first prototype constructed and intedned to fit the BMW 109-003-1 series turbojets. However, the radius of said engine had changed by this point and were therefore unable to fit inside of the completed IX airframe. As such, the IX became a powerless glider for the duration of its life with additional flight testing carried out at Oranienburg through the summer of 1944. V1 was found near Leipzig around April 14th, 1945, by the US 3rd Army Corps, 9th Armored Division. First flight of the system was achieved on March 1st, 1944 and proved successful.
The Ho IX V2 became the series first "true" prototype and also became the first to fit turbojet engines when it was unveiled in December of 1944. The V2 was another "one-off" build (single example) and sported 2 x Junkers Jumo 109-004B-1 series engines. Goring ordered 40 into production under designation Ho 229 before the V2 had even flown. A successful flight was later achieved at Oranienburg though V2 was eventually lost to an accident on February 18th, 1945, resulting from an engine failure while undergoing a one-engine landing test. V2 would become the only aircraft in the series to achieve flight and log in any substantial hours (approximately 2) in the air. Despite the setback, a further 20 re-production aircraft were ordered and the entire project was greenlighted onto a fast path under Jager-Notprogramm on March 12th, 1945.
Horten Hears a Gotha
While the Horten brothers were responsible for the design and early construction efforts of the Ho IX flying wing, their creation was handed over to Gothaer Waggenfabrik (Gotha, GFW) by the Air Ministry for further development and intended production. Gotha was the air firm known best for its production of multi-engined wartime bombers in World War 1. As such, the designation of the Horten IX now incorporated the Gotha brand name into the new designation of "Gotha Ho 229". Horten brother involvement in the Ho 229 was all but over as Gotha took over the reins.
Now under the Gotha label, the Ho 229 advanced into a V3 prototype featuring 2 x Junkers Jumo 109-004C turbojet engines of 2,205 thrust in a revised engine intake. The engines were further moved forward in the fuselage and construction of the type was undertaken at Friedrichroda. An primitive-form ejection seat was added to allow for a pilot escape at speeds higher than conventional aircraft could cruise at. However, the end of the war would bring about an end to the V3 prototype and cancel any production dreams.
Further models of the Ho 229 were planned. The Ho 229 V4 was to be a two-seat all-weather fighter/nightfighter that was in the early stages of construction at Friedirchroda by the end of the war. The basic internal airframe was all that was completed of the type. The Ho 229 V5, of similar role to the V4, was also in the early stages of construction when overtaken. The V6 was a proposed single-seat fighter fitting alternate cannon armament but never proceeded past the mock-up stage. In essence this became an armament test prototype.
The Ho IXb was a planned two-seat trainer whose airframe was also considered for a nightfighter role. Neither form was ever constructed. The two-seat trainer was also known as the Ho IXb V6 and the nightfighter became the Ho IXb V7.
The Ho 229 A-0 was the official intended designation of a fast-production form of the Ho 229 flying wing. This model would have been based on the Ho 229 V6 prototype though none of the A-0's were ever produced (though 40 were on order by war's end). These differed somewhat from earlier Ho IXs in that they fitted 4 x MK 103 30mm cannons (in place of the original 2 x MK 108 systems) and held an external ordnance capacity of 2 x 2,205lb bombs. The A-0 would have been the definitive Ho 229 production model.
For whatever reason, the German Air Ministry required the production version of this bomber to also serve as a fighter - a special two-for-one initiative one can suppose. With a projected top speed of over 500 miles, this seemed feasible even against the top Allied fighters of the time. As such, the original Ho IX was fitted with 2 x 30mm MK 108 series cannons produced by Rheinmetall-Borsig. The MK 108 began life as a private venture in response to a German 1940 requirement for a weapon system capable of downing Allied bombers (the bane of the German war machine). Production of the system ran from 1943 through the remaining war months of 1945 and served on many German aircraft. The firing action was of a blowback design and a rate-of-fire of 650 rounds-per-minute was possible. Coupled with High Explosive (HE) ammunition, the MK 108 was a proven and reliable "bomber-killer".
Later revisions saw the production Ho 229 fitting 4 x MK 103 30mm cannons. The MK 103 was designed by Rheinmetall-Borsig as a further development of the MK 101 heavy autocannon. The MK 103 was equally adept at engaging land and air targets and fired from a belt-fed mechanism. The firing action was both gas an recoil actuated. Comparatively, the MK 108 fired the same projectiles of the MK 103 but through a smaller cartridge containing less propellant.
R4M "Hurricane" air-to-air/air-to-surface high-explosive rockets were also envisioned for the aircraft. The rocket was produced by the Heber AG company and put into action from 1944 and into 1945. As a bomber, the Ho IX could field 2 x 1,100lbs (envisioned as higher in the final production model), making for one complete fighter-bomber system.
Where Are They Now?
Not much is left of the legacy regarding the Ho 229 beyond a scant few airframes and a handful of black and white (and some color) pictures. The Ho IV and the Ho 229 V3 were captured by the Americans and shipped off to Northrop for further research. The Ho IV glider ended up at the Planes of Fame Museum in Chino, California. The Ho 229 V3 prototype airframe has been sitting in the Paul E. Garber Restoration Facility at Suitland, Maryland for some years now under the control of the National Air & Space Museum. Though at least five other Ho 229 airframes were recovered at the Gothaer Waggonfabrik plant, these were subsequently destroyed (under orders initiated through Operation Paperclip - the destruction of all advanced German materials and research for fear of them falling into Soviet hands) by General George S. Patton's 3rd Army troops in April of 1945.
Reimar Horten in Argentina
Despite the sudden end to the Ho 229 in Germany, brother Reimar Horten attempted to bring the HO VIII design back into the fold in the post-war years. Having relocated to Argentina by this time, the experimental tailless cargo transport derivative of the Ho VIII flew as the I.A.38 on December 9th, 1960. Though completed in 1959, mechanical issues with the engines forced the year-long delay. Performance was deemed sub-par no thanks to the under-performing engines and the entire project was therefore cancelled. Construction was of all-metal while the wings were shoulder-mounted and swept. Power was handled by 4 x IA 16 El Gaucho radial piston engines as pushers. The undercarriage was a tricycle arrangement and fully retractable. Seating was for two and the cargo bay took up a portion of the main body and wings, fitting some 13,448lbs of cargo and accessed via a rear door. Production was handled by DINFIA of Argentina. The single prototype became a permanent fixture at the Aeronautical School until destroyed by fire (suspected arson).
Performance estimates for the I.A.38 included a top speed of 155 miles per hour, a range of 777 miles and a service ceiling of 14,765 feet.
Raiders of the Lost Farce
The "flying wing" found in the motion picture "Raiders of the Lost Ark" is a fictional aircraft. The aircraft was specifically hand-picked by director Steven Spielberg and incorporated into the movie to showcase the technological advancements of German aircraft of the time. Designers used Northrop's B-36 flying wing bomber as the basis and construction of the aircraft was undertaken by Vickers Aircraft Company. It was shipped in pieces and assembled for filming in Tunisia.