The F-117, the first operational stealth combat aircraft, was designed with a computer program which could only predict the reflection of radar waves off of flat surfaces, necessitating a strictly faceted surface. A flat bottom diamond was determined as the ideal shape for a radar-evading aircraft. The shape was dubbed the “Hopeless Diamond” in reference to its poor inherent aerodynamics. Engineers cut out the minimum necessary to allow the shape to fly.
Credit: U.S. Air Force
This front view of the F-117 shows the screens covering the engine intakes. The screen blocks most radar waves and trap the rest inside. Note also the hexagonal auxiliary intakes with edges aligned with the main intakes and side of the fuselage and the sawtooth pattern surrounding the canopy.
Credit: U.S. Air Force
Tacit Blue was a technology demonstrator built in the early 1980s that influenced later stealth aircraft such as the B-2. It proved stealthy aircraft could have curved surfaces and operate radars without being detected. Note the very narrow edges, to minimize edge diffraction, and the blended facets that compose the airframe.
Credit: Lockheed Martin
From above, the strict planform alignment of the Lockheed Martin F-22 becomes apparent. The angle of the forward fuselage is the same as the leading edges of the wings and horizontal tails as well as the inner trailing edge of the horizontal tail. The angle of the side fuselage is the same as the lateral edges of the wing and horizontal tails. The angle of the outer trailing edges of the horizontal tails match the trailing edges of the wings.
Credit: Lockheed Martin
This frontal view of the F-22 highlights an iridescent canopy—evidence of metallization—as well as the planform alignment of the fuselage sides and vertical tails.
Credit: Lockheed Martin
A Lockheed Martin F-22 from the side. Note the sheen of the skin, indicating the presence of RAM and the band of lighter gray around the wings, tails and engine inlets, indicating the presence of edge treatments.
Credit: Wikimedia/Allocer
The Irbis-E radar on Sukhoi’s Su-35 has an impressive range against conventional aircraft because of its large aperture and high peak power. But its X-band operating frequency restricts the range at which it can detect targets with a low radar cross section in X-band.
Credit: Bill Sweetman
The 55Zh6UME is one of the most advanced VHF-band radars in operation. Its AESA antenna and other advancements likely allow it to detect stealth fighters at far greater ranges than higher-band radars. It also has far better accuracy than earlier VHF-band radars but is still probably not accurate enough to target missiles.
Credit: Wikimedia/Allocer
Sukhoi’s new T-50 PAK FA fighter carries an N036 radar suite with five AESA antennas, including two of these N036L-1-01 L-band antennas in the leading edges of its wings. Their operation in L-band could provide them with early warning of approaching stealth aircraft. The N036L-1-01 might also be integrated on the Su-35.
Aviation Week’s State of Stealth series aims to deliver readers a comprehensive understanding of stealth and counterstealth technology. Much of that low-observable technology resides in shapes and materials that are evident in photographs of the F-117, B-2, F-22 and F-35. Here we illustrate the fundamentals of the technology and highlight some key features of these aircraft. We also present some of the threat systems these aircraft face, both state-of-the art conventional radars as well as sensors, big and small, which are claimed to have counterstealth properties.
