Since World War Two, One of the Most Significant

Since World War Two, one of the most significant challenges Nazi Germany's head of the Luftwaffe, Hermann Goring, wanted the Ho-229 to for military aviation has been the task of defeating radar be able to penetrate enemy territory to a depth of 1,000km (621 miles). WORDS BY ROB COPPINGER The Ho-229 had a fatal test-flight crash before the end of the war, but a production order for 40 was still made. ADAR PROVED ITS could see the Bf 109's deficiencies, and However, it never actually went into effectiveness 80 years ago began to think about an aircraft that production and, when the United States' in the Battle of Britain, could defeat the RAF's Hawker Hurricane Third Army overran Friedrichsroda, when the new long-range and Supermarine Spitfire. Germany, in April 1945, its soldiers found detection technology The design that emerged from Horten's the Ho-229 prototypes, three through six. allowed the Royal Air subsequent contemplation, with the Above: The Convair The Horten brothers had built and Ki ngfish was Force to know where, when and how help of his brother, Rei mar, was the des igned with various flown delta-shaped flying wings since the to counter the waves of Nazi fighters Horten Ho-229, a single pilot, twin-jet, stea lth features. It 1930s, but they w ere not the only ones and bombers attacking the country. delta wing-shaped fighter bomber. With com peted for the US to have such an interest. Jack Northrop, govern ment's high One of the Messerschmitt Bf 109 pilots its two Junkers Jumo 004 8-2 turbojets, speed reconnaissance who would build the company that bore assaulting the UK was Walter Horten the Ho-229 was estimated to be able to aircraft contract, that his name, had also been working on them of the Luftwaffe's fighter squadron achieve a top speed of 527 knots (977kph). would eventually be during the same decade, and had first won by the Lockheed 26, stationed in occupied France. The According to the National Air and Space SR-71 Blackbird flown his flying wing Northrop Model 1 squadron's technical officer, Horten, Museum of the Smithsonian Institution, Alexander Fedosenko Mockup (N-1M ), on July 3, 1940. December 2020 // www.Key.Aero Seven years later, Northrop was ready to Northrop and the Horten brothers were test fly its own jet-powered flying wing, developing their flying-wing designs. but a far larger one than the N-1Mor the A number of nations were working on Ho-229. The Northrop YB-49 had a 52.4m radar at the time: the UK, Germany, (172ft) span, compared to the N-1 M's Netherlands, USA, France, Japan and 11 .6m or the Ho-229's 16.8m. However, Russia, then the Soviet Union. The US, UK like the Ho-229, the second prototype and Germany were advanced enough that crashed, coming down on June 5, 1948. by the mid-1930s they had functioning The flying wing bomber would not radar systems able to detect aircraft supersede the tried-and-tested tube more than 10 miles away. In 1936, the UK and-wing design and not until the 1980s achieved a 75-mile detection range. In would the US Air Force see its like again. 1938, an American radar on board a naval It was in the 1980s that Reimar Horten vessel detected an aircraft 100 miles away. made the claim that the Ho-229 had been Radar had arrived. designed with stealth in mind. Articles According to the Smithsonian, Rei mar by the Smithsonian explain that Rei mar first wrote about aircraft radar cross Horten made this assertion in 1983 - the section (RCS) in an article about flying same year the Lockheed Martin F-117 wings, which was published in the Nighthawk secretly entered service - in May 1950 issue of Argentina's National his book, Flying Wings: the History ofthe Magazine of Aeronautics. The RCS is a Horten Aircraft. According to Horten, he measurement of the strength of the had considered placing layers of charcoal returned signal from the aircraft painted within the wood construction of the by the radar beam. Ho-229, which he claimed would have According to Russell Lee, the absorbed the radar-signal energy. Smithsonian's aeronautics department Ideas about defeating radar are much supervisory curator for all-wing aircraft, older than the detection technology Reimar and Northrop had corresponded itself. Writing for the United States' after the war. Jack Northrop however Centennial of Flight Commission website, had no interest in collaborating with the historian Dwayne Day pointed out:"ln German engineer and former Nazi party the 19th century, Scottish physicist James member, who had migrated to Argentina Clerk Maxwell developed a series of after the war. If he had chosen to join mathematical formulas to predict how forces, Lee pointed out that Northrop electromagnetic radiation would scatter could have benefited, as the available data when reflected from a specific geometric shows that the Horten wing was stable. shape;' adding that Maxwell's equations The YB-49's stability was not as good, were later refined by the German scientist, hence the crash that was fatal for the pilot Arnold Johannes Sommerfeld. and for the type. Radar would arrive many decades after While history remembers the Horten Maxwell; in fact it became a reality while brothers for their engineering genius, www.Key.Aero II December 2020 December 2020 // www.Key.Aero not everything Rei mar claimed was true. Investigations into the Ho-229 by the Smithsonian staff and Northrop Grumman found that there was no clear evidence of stealth capabilities. There was also no confirmation of charcoal, and an investigation by a Northrop Grumman funded documentary production company discovered the Ho-229 could not have evaded the Allied forces' radars of that era. The radar signature test of a full-size Ho-229 model conducted by Northrop Grumman engineers did conclude that there was some reduction in the RCS compared to a normal fighter, but the notion that the Horten brothers had designed it w ith stealth in mind was found to be unconvincing. While Rei mar's boasts are apparently false, the flying w ing shape has since been closely associated with stealth. Despite Maxwell's 19th-century equations, deflecting or absorbing radar waves was not the immediate solution to counter the detection technology that defense scientists opted for. Jamming was their first idea, and, in May 1938, a British Saunders Roe A.27 London twin-engine Below: This rear view of the Horten Ho 229 biplane flying boat jammed radar. V3 shows its Nazi Knowing this was possible, the British then emblems of the installed anti-jamming technology across 1940s Luftwaffe Smithsonian Air and their radar network. Jamming is still a part Space Museum/Ben of the electronic-warfare portfolio, but Sullivan 2013 active sensors give away a transmitter's Right: The Teledyne location; being invisible to radar was Ryan AQM-91A ultimately the better option. Compass Arrow In the US, w hile the Ho-229 became a drone at the Nationa l Museum of the United World War Two curiosity, slow ly rotting States Air Force away in storage, Northrop's flying wing USAF test flights and the ideas of RCS signal w ith turbojet s, the Kingfish used ramjet reduct ion were not forgotten. engines to reach Mach 4 at 90,000ft and Towards the end of the 1950s and had stealth aspects to it. the beginning of the 1960s, the US The Kingfish's stealth feat ures included government was interested in high- a delta flying wing shape, exhaust speed reconnaissance aircraft. The shoot shielding and a more angular fuselage down by Russia of Francis Gary Powers for radar signal scattering, but its design and his Lockheed U-2 Dragon Lady in lost out to t he Blackbird, because ramjet 1960 made higher speed an imperative. engine technology was not developed Various designs competed, but they enough. While a t urbojet uses a series of would eventually lose out to the Lockheed rotating blades to increasingly compress SR-71 Blackbird. One of t hem was the the air before combustion, the ramjet Convair Ki ngfish. While t he Blackbird consists of a complex tube whose shape was designed for achieving Mach 3 does the same job compressing t hat www.Key.Aero II December 2020 , December 2020 // www.Key.Aero ...... ~--,... www.Key.Aero II December 2020 incoming air- but the rate of the airflow is significantly higher. Later in the 1960s, one attempt at stealthier aircraft was not even piloted - the Teledyne-Ryan AQM-91 A Arrow Compass drone. Air-launched, its vertical surfaces were canted inward to thwart radar reflections, and it used radar-absorbing materials. The Arrow Compass was ready to be deployed in 1971, but it was not deemed necessary. In the 1970s, the US Department of Defense's (DoD) Defense Advanced Research Projects Agency (DARPA) studied adversaries' new surface-to-air missile (SAM) systems, concluding that US aircraft were vulnerable to detection and attack by SAMs. The loss of Francis Gary Powers' U-2 a decade earlier had been clear evidence that Russian SAM systems were a threat. According to the United States Air Force Museum, by the 1970s new materials and techniques allowed engineers to design an aircraft with stealth qualities. DARPA embarked on a program to develop strategies and technologies for reducing radar detectability. These included reducing the radar cross section with a combination of aircraft shaping to minimize the number of radar return spikes and the use of radar absorbent materials.

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