Smithsonian.com

The Smithsonian Air and Space museum is in possession of the remains of an original Horten Ho 229.

At the close of World War II, Nazi scientists led by the pioneering Horten brothers, Walter and Reimar Horten, designed, built, and tested what was likely the most advanced aircraft to exist at the time: the Horten Ho 229, a jet-powered flying wing that historians believed to have been the first stealth fighter.

A few years ago, a team of engineers from Northrop Grumman, an aerospace and defense company, re-created a model of the craft. In Hitler’s Stealth Fighter, a documentary that tracked the effort, the team found that the Horten Ho 229 did indeed employ some basic stealth technology.

Nearly 70 years on from this first foray into stealth aircraft design, the basics of veiling a ship from detection remain unchanged, says David Axe for Wired‘s Danger Room. Innovations made over the years have remained the closely-guarded secrets of a few advanced militaries:

It’s no secret how America’s stealth warplanes primarily evade enemy radars. Their airframes are specifically sculpted to scatter radar waves rather than bouncing them back to the enemy. Somewhat less important is the application, to select areas, of Radar Absorbing Material (RAM) meant to trap sensor energy not scattered by the plane’s special shape.

In short, the four most important aspects of stealth are ”shape, shape, shape and materials,” to quote Lockheed Martin analyst Denys Overholser, whose pioneering work resulted in the F-117 Nighthawk, the world’s first operational stealth warplane.

In a descriptive list, Axe lays out some of the advanced tricks used by the American aircraft engineers to keep U.S. warplanes out of sight, everything from strict procedures on radio silence, to custom sensor packages, radar-absorbing paint jobs and intricate cooling systems.

Airplanes generate a lot of heat. And even if you completely mask a plane’s radar signature, it might still give off telltale infrared emissions, especially around the engine exhaust but also from electronics, moving parts and surface area exposed to high wind friction.

The B-2 and F-22′s flat engine nozzles spread out the exhaust to avoid infrared hot spots, but to save money all 2,400 planned U.S. F-35s will have a traditional, rounded nozzle that spews a lot of concentrated heat. The Spirit, Raptor and Joint Strike Fighter apparently all feature gear for cooling hot leading edges such as the fronts of wings. They also boast systems that sink much of the heat generated by the on-board electronics and actuators into the fuel.

But just like the Nazi-era Horten Ho 229, the most advanced technologies of the day are likely masked from view.

Perhaps the most remarkable quality of America’s stealth warplanes is their continuing ability to escape public notice during years or even decades of development, testing and initial operations.

…Today the Air Force is apparently designing or testing at least two new, radar-evading drones plus the new Long Range Strike Bomber, an even stealthier successor to the now-25-year-old Spirit. But the only evidence of these classified programs is oblique references in financial documents, vague comments by industry officials and the occasional revealing commercial satellite photograph. Who knows what new qualities the next generation of stealth planes might possess in addition to those of the current armada.

More from Smithsonian.com:

Horten H IX V3
Introducing the USS Zumwalt, the Stealth Destroyer
The Ultimate Spy Plane