Before there was the mound like intake bulges and racked intake cowlings seen on the American F-35 and Chinese J-20, JF-17, J-10 and J-31, there was Lockheed’s Diverterless Supersonic Intake F-16 testbed. During the mid-1990′s, Lockheed modified the forward structure of a block 30 Viper in an attempt to prove technologies that would be part of the looming Joint Strike Fighter tender. Diverterless inlet technology utilizes a hump on the inboard side of a jet intake along with a forward swept outer intake fairing to separate boundary layer air and to slow down airflow reaching the jet’s engine face during supersonic maneuvers. It does this without moving parts and allows for the deletion of heavy and complicated intake diverters, intake ramps and cones. Also, by allowing for smooth transitions between a combat jet’s fuselage and intake, such configurations can provide a drastic reduction in radar cross section, thus lowering an aircraft’s detectability on radar, especially those that function at higher bandwidths. Another useful byproduct of the interaction between the forward swept intake cowl and the smooth hump-like blended surface between the intake and the fuselage is that it provides for far less exposure to radar waves, especially from oblique angles, of an aircraft’s jet engine fan face. The engine face is traditionally one of a combat jet’s most radar reflective components. When the DSI concept is integrated into a clean sheet design and/or an aircraft utilizes curved intakes, baffle systems, and radar blocking devices in conjunction with it, a radar return caused by a combat jet’s motor face and traditional intake can be almost totally eliminated.
The DSI modified F-16 was one mean looking machine as its super-critical “under-bite,” blended hump and canted intake fairing gave the jet an aggressive and totally futuristic look. The prototype was said to have handled almost identically to a stock F-16 and it even saw boosts in available thrust during certain areas of its flight envelope. This makes me wonder as to why the DSI inlet was not integrated into modern versions of the F-16. With other “low observable” enhancements, such as inclusion of the Low Observable Nozzle (now flying in an operational form of the F-35) and the installation of radar absorbent coatings and skin, the F-16 may have been able to have been fielded with a reasonable reduction in overall radar cross-section. Although the jet’s single vertical tail is a problem when it comes to radar reflectivity, eliminating the tail all together, which is a far greater design change than adding a diverterless inlet and a new exhaust nozzle, would have been almost necessary. None the less, the F-16X concept proposed such a tailless design. The F-16X would have included almost double the internal fuel compared to a standard F-16 and conformal air to air missile weapons bays would have been integrated into the design. Sadly, the F-16X never made it to fruition as the Joint Strike Fighter program suppressed any funding for such developmental evolutions of existing platforms. Fast forward to today and the F-16X concept would offer a tremendously relevant, and most likely cost effective alternative, to the F-35A as we know it today. With the deletion of the jet’s tail, and the addition of a new stealthy skin, diverterless inlet, low observable nozzle, conformal weapons bays, and a radar blocking device over the jets motor, the F-16X would be one serious machine with an almost perfect mix of range, survivability, flexibility, and economy.
In the end two aircraft were used to prototype modern DSI technology by Lockheed Martin. Apparently, the flying example was returned to its original form and sent to AMARG after the tests were complete while another airframe for mockup tests sits rotting in the back-lot of Lockheed’s Skunk Works at Plant 42 in Palmdale, California.
Here are some pictures of the Chinese jets that also leverage DSI technology, they include the J-20, J-10B, JF-17 Block II and almost certainly the J-31. How exactly the Chinese gained this advanced aerospace know-how is still a mystery although the DSI F-16 was not highly classified. Then again maybe there were complete instructions on how to build a DSI inlet in the thousands of pages of classified documents related to US stealth designs that have been stolen via Chinese hacking campaigns over the last decade or so…