Walter Horten was a military man who had lost hundreds of Luftwaffe colleagues during the Battle of Britain in 1940.
Video: Designing Hitler's Stealth Fighter (Dramatic Re-creation)
"That loss never left him to the day he died," said Myhra, author of The Horten Brothers and Their All-Wing Aircraft.
"He was burning with revenge and felt the need for a plane that would be pretty much invisible to Britain's Chain Home radar system. That's what he wanted his brother to design."
The result of their collaboration was unique among Luftwaffe designs.
"It has no vertical surfaces for stability or control. Every exterior surface of that aircraft contributes lift," said Russell Lee, curator for the only remaining Horten 2-29 aircraft, at the National Air and Space Museum's Paul E. Garber Preservation, Restoration and Storage Facility outside Washington, D.C.
"That had been tried before and failed time and time again," Lee said. "Reimar Horten took the idea further and made it more practical than any other designer really up until the B-2."
Re-creating Hitler's Stealth Fighter
To determine once and for all whether the Ho 2-29 had stealth capabilities, experts first examined the surviving 2-29 and probed it with a portable radar unit based on World War II radar tech.
Then, in the fall and winter of 2008, they set about building the full-scale re-creation at a restricted-access Northrop Grumman testing facility in California's Mojave Desert.
The construction team embraced historic materials and techniques, and the Horten 2-29 replica, like the original, is made largely of wood and bonded with glue and nails.
Unlike the original, however, the replica wasn't built to fly, though it did soar, after a fashion.
The new craft's body was constructed around a rotor, which allowed the replica to be manipulated atop a five-story-tall column. There, in January 2009, the craft was subjected to World War II-style radar.
Initiated by Michael Jorgensen, writer and producer of the National Geographic Channel documentary Hitler's Stealth Fighter, the construction and testing of the replica was funded by Northrop Grumman. (The National Geographic Channel is part-owned by the National Geographic Society, which owns National Geographic News.)
Stealth by Accident?
Stealth aircraft rely on shapes that prevent radar waves from bouncing back to their sources and on materials that absorb radar energy (stealth-plane time line).
Some experts, like the Garber facility's Lee, question the Hortens' postwar claims that their plane had been intended as a stealth plane.
"My take on it is that their goal at the time was to meet requirements for speed and range," Lee said. "The all-wing concept was [Reimar Horten's] baby, and he designed the shape for aerodynamic reasons—he never started talking about radar until after the war.
"Reimar talked about a sawdust and carbon coating to absorb radar energy, but we found no evidence of that on the Horton that we have here," Lee added.
But Myhra argues that the plane was indeed intentionally designed for stealth.
"When I talked with Walter Horten in the 1980s and '90s he always referred to his aircraft as low-observable," said Myhra, a former aerospace scientist.
Horten also told Myhra about his time in a Berlin think tank, when he had learned about radar evasion from Nazi navy officers hoping to camouflage their submarines.
Walter claimed to have brought this information to his brother so that it could be part of the plane's design.
"These guys knew about this stuff," Myhra said. "They were probably the only people in the entire German aviation community that were pursuing this line of thought."
Proof of Stealth?
Radar tests on the replica show that the plane's radical, smooth design would indeed have given it a significant advantage against radar, according to Tom Dobrenz, a Northrop Grumman expert in stealth, or "low observable," technology, who led the Horten replica project.
In short: The Horten 2-29 looks to have been the world's first stealth fighter.
But was it meant to be?
"I believe they were [mainly] driven by the aerodynamic side of it," Dobrenz said.
Still, radar tests on the surviving Ho 2-29 revealed "that they put some kind of carbon-type material in between the layers of plywood on the plane's leading edges," he said.
"Personally, I cannot understand that being for anything other than doing something to [defeat] radar." Even so, Dobrez added, "I'm not so sure that they had any clue what it was going to do or whether it was going to work or not."
"Could Have Been a Game Changer"
At least one major mystery remains: How would Hitler's stealth fighter have affected the outcome of World War II, had the plane made it to mass production?
"This design gave them just about a 20 percent reduction in radar range detection over a conventional fighter of the day," Dobrenz said.
According to tests on the replica, World War II British radar would have picked up the Horten over the English Channel at about 80 miles (129 kilometers) out, versus 100 miles (160 kilometers) for a conventional World War II fighter.
But because of the Ho 2-29's tremendous speed, the time from detection to target—the British mainland—would have been lowered from the usual 19 minutes to just 8 minutes, making it difficult for Allied defenders to respond.
"Probably, for at least a short amount of time, it could have been a game changer, until a counter was developed for it," Dobrenz said.
But the Ho 2-29 design was far from perfect.
World War II-era jet engines were unreliable, for one thing. For another, the lack of stabilizing vertical surfaces—a bane of all-wing designs, past and present—resulted in frequent lurches, making sharp shooting and accurate bomb delivery that much harder.
In a different place and time, with further development, the promising Horten 2-29 might have made a difference.
But by early 1945, aviation historian George Cully said, "The Germans had run out of pilots, petroleum, and time."
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