The diverterless supersonic inlet was installed on a F-16 Block 30 fighter, replacing aircraft’s original intake diverter.
Considered the backbone of the US Air Force’s (USAF) fighter fleet for more than three decades, the F-16 Fighting Falcon has, and continues to play, an important role in air superiority. Evolving from a 1972 competition that called for a lightweight, highly maneuverable fighter jet, the F-16 won the contest and entered production in 1972. Part of its initial production included an agreement creating a consortium between the United States and four NATO countries: Belgium, Denmark, Netherlands and Norway. From then on, the F-16 evolved from an air superiority day fighter to an all-weather, multirole aircraft—still in use today around the globe.
An F-16 was even modified with a diverterless supersonic inlet, or DSI, developed for the Joint Strike Fighter (JSF) – now the F-35 Lightning II – program. According to Code One Magazine, at high aircraft speeds through supersonic, the bump in the inlet works with the forward-swept inlet cowl to redirect unwanted boundary layer airflow away from the inlet, essentially doing the job of heavier, more complex, and more costly diverters used by several current fighters. The flight test program consisted of twelve flights flown in nine days in December 1996.
Initial research into the DSI was done by Lockheed Martin in the early 1990s. The first Lockheed DSI was flown on Dec. 11, 1996 as part of a Technology Demonstration project. It was installed on a F-16 Block 30 fighter, replacing aircraft’s original intake diverter. The modified F-16 demonstrated a maximum speed of Mach 2.0 (Mach 2.0 is the F-16’s clean certified maximum speed) and handling characteristics similar to a normal F-16. It was also shown that subsonic specific excess power was slightly improved.
The DSI concept was introduced into the Joint Advanced Strike Technology (JAST, which later became JSF) program as a trade study item in mid-1994. It was compared with a traditional “caret” style inlet. Than a DSI was incorporated into the design of the Lockheed Martin F-35 Lightning II after proving to be 30% lighter and showing lower production and maintenance costs over traditional inlets while still meeting all performance requirements.
Traditional aircraft inlets contain many heavy moving parts. In comparison, DSI completely eliminates all moving parts, which makes it far less complex and more reliable than earlier diverter-plate inlets. The removal of moving parts also reduces the overall weight of the aircraft.
DSIs also crucially improve the aircraft’s very-low-observable characteristics (by eliminating radar reflections between the diverter and the aircraft’s skin). Additionally, the “bump” surface reduces the engine’s exposure to radar, significantly reducing a strong source of radar reflection because they provide an additional shielding of engine fans against radar waves.
Analysts have noted that the DSI reduces the need for application of radar-absorbent materials (RAMs).
Photo credit: Lockheed Martin