Diverterless supersonic inlet

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The Lockheed Martin F-35 Lightning II is a major jet fighter design featuring DSI. 230315-F-WM701-1003 - F-35I Adir at Red Flag.jpg
The Lockheed Martin F-35 Lightning II is a major jet fighter design featuring DSI.

A diverterless supersonic inlet (DSI) is a type of jet engine air intake used by some modern combat aircraft to control air flow into their engines. It consists of a "bump" and a forward-swept inlet cowl, which work together to divert boundary layer airflow away from the aircraft's engine. This eliminates the need for a splitter plate, while compressing the air to slow it down from supersonic to subsonic speeds. The DSI can be used to replace conventional methods of controlling supersonic and boundary-layer airflow.

Contents

DSIs can be used to replace variable-geometry intake ramps and inlet cones, which are more complex, heavy and expensive. They have become the predominant inlet designs for modern combat aircraft due to their low weight and cost while having relatively decent performance up to Mach 2. [1]

Technical background

Testing of the F-35 diverterless supersonic inlet on a modified F-16. The original intake with its splitter plate is shown in the top image. F-35 Divertless Supersonic Inlet F-16.jpg
Testing of the F-35 diverterless supersonic inlet on a modified F-16. The original intake with its splitter plate is shown in the top image.

The fundamental design of a gas turbine engine is such that the air flow-rate entering its compressor is regulated by the amount of fuel burned in its combustor. For supersonic flight the air entering the inlet also has to be regulated to a similar amount by the design of the entrance of the inlet duct. The optimum design of the duct will minimize drag on the one hand and unstable shock position (manifested by "buzz") on the other, while presenting clean and uniform airflow to the fan and compressor. [2]

Inlets

The goal of an engine inlet is to present clean and uniform airflow with minimal distortion to the engine. When a body, such as a wing or a fuselage, passes through a fluid such as the air, a boundary layer of fluid attaches to the body and moves along with it. This boundary layer is turbulent and thickens with increasing airspeed and forebody distance. When it enters the inlet, it can cause airflow distortion and affect engine operation and performance. To prevent the boundary layer from entering the engine, inlets typically incorporate a splitter plate/gap to separate and bypass the layer, or a bleed system to remove it by suction, or a combination of both. [2]

Additionally, on supersonic jets, the high kinetic energy in the approaching air, or dynamic pressure, has to be transformed into static pressure while losing a minimum amount of energy (also known as pressure recovery). To do this the inlets are more complicated than subsonic ones as they have to set up two or three shock waves to compress the air. A cone (such as on the SR-71 or MiG-21) or inclined ramp (such as on the F-15 or Su-27) protrudes ahead of the inlet and is adjusted based on flight conditions, thus having variable geometry, to properly position the shocks with the cowl, ensuring stable operation and efficient pressure recovery. The complexity of these variable-geometry inlets increases with increase in design speed. Simpler fixed-geometry "pitot"-type inlets (such as those found on the F-16 and F/A-18) avoid these complexities, thus reducing weight and cost, but have poorer pressure recovery particularly at higher Mach numbers. More modern fixed-geometry "caret" inlet designs (such as on the F-22) achieve the efficient pressure recovery of variable intake ramps, but still require a splitter gap and bleed system for the boundary layer. [2]

Diverterless inlets

J-10B with a diverterless air intake displayed at Airshow China 2018 PLAAF J-10B with PL-12 and PL-8B at ZhuHai Air Show 2018.jpg
J-10B with a diverterless air intake displayed at Airshow China 2018

The DSI bump functions as a compression surface and creates a pressure distribution that prevents the majority of the boundary layer air from entering the inlet at speeds up to Mach 2. It does this by creating a spanwise static pressure gradient that deflects the forebody's boundary layer to the bump's sides; this bumped surface also performs flow compression at supersonic speeds by producing a conical shock system, serving a similar purpose as an inlet cone. The forward-swept cowl, which closes against the forebody at its aft-most points, then allows the diverted boundary layer to spill out of the sides of the inlet as mass flow ratio decreases, preventing much of it from entering the inlet duct. [3]

In essence, the DSI does away with complex and heavy mechanical systems for boundary layer control and pressure recovery with no moving parts. Because the DSI is highly integrated with the forebody shaping, all geometries must be carefully calculated in three dimensions (3-D) to ensure high pressure recovery, good supersonic stability, and acceptable distortion levels. [4] [3]

History

Initial research into the concept was done by Antonio Ferri in the 1950s and was then known as the "Ferri scoop"; it was incorporated in some supersonic designs such as the XF8U-3 Crusader III and the SSM-N-9 Regulus II. [5] The concept was further developed & optimized by Lockheed Martin in the early 1990s using 3-D computational fluid dynamics (CFD) as part of an independent research and development (IRAD) project for an efficient and affordable (reduced cost and weight) Mach 2-class inlet design, and was subsequently termed "diverterless supersonic inlet" (DSI). [6] The first Lockheed DSI was flown on 11 December 1996 as part of a Technology Demonstration project. It was installed on an F-16 Block 30 fighter, replacing the aircraft's original pitot-type intake that included a diverter. The modified F-16 demonstrated a maximum speed of Mach 2.0 (the F-16's clean certified maximum speed) and handling characteristics similar to a normal F-16 with no engine stalls or anomalies, validating CFD predictions. It was also shown that pressure recovery was comparable at transonic and superior at supersonic speeds; subsonic specific excess power was also slightly improved. [4] [1]

The DSI concept was introduced into the JAST/JSF program as a trade study item in mid-1994. It was compared with a traditional "caret" style inlet. The trade studies involved additional CFD, testing, and weight and cost analyses. [2] A DSI was incorporated into the Lockheed Martin JSF design after proving to be 30% lighter and showing lower production and maintenance costs over traditional inlets while still meeting all performance requirements; the weight savings were primarily due to the elimination of the bleed and bypass systems. It was flown on the X-35 in 2000 and further refined for the production F-35. [1] [4]

This concept, also called "bump inlet", has also been employed by Chinese aircraft designers, with the first production iteration from Chengdu Aircraft Design Institute on the JF-17. This first design still had a bleed system with suction holes on the bump for additional boundary layer control. [7] Chengdu further refined its DSI designs with the full elimination of bleed and bypass systems with efficient pressure recovery up to Mach 2, and incorporated it into the J-10B/C and J-20. Research indicated that the DSI's pressure recovery is considerably better than a pitot-type inlet and only slightly lower than a caret inlet while being lighter and less costly; the DSI thus replaced the caret inlet during the J-20's design process. [8] [9] Shenyang Aircraft Corporation has also incorporated the DSI into the FC-31/J-35.

Sukhoi incorporated a bump intake for its T-75 LTS (Russian : Лёгкий Тактический Самолёт - ЛТС, Light Tactical Aircraft), later designated as Su-75. The incorporation of the intake shape (called "U-shape") is meant to reduce the aircraft's RCS compared to the company's preceding Su-57 design. [10]

Benefits

Weight and complexity reduction

Traditional aircraft inlets contain many heavy moving parts for bypassing/diverting the boundary layer and/or ensuring efficient pressure recovery during supersonic flight. In comparison, DSI eliminates all moving parts, which makes it far less complex and more reliable than earlier diverter-plate inlets or variable-geometry ramps or cones. The removal of moving parts also reduces the weight of the aircraft. [11]

Stealth

DSIs improve the aircraft's very-low-observable characteristics by eliminating radar reflections between the diverter and the aircraft's skin. [1] Additionally, the "bump" surface reduces the engine's exposure to radar, significantly reducing a strong source of radar reflection [12] 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 in reducing frontal radar cross section of the aircraft. [1] [13]

List of aircraft with DSI

Active

Future

See also

References

  1. 1 2 3 4 5 Hehs, Eric (15 July 2000). "JSF Diverterless Supersonic Inlet". Code One magazine. Lockheed Martin. Retrieved 11 February 2011.
  2. 1 2 3 4 Hamstra, Jeffrey W.; McCallum, Brent N. (15 September 2010). Tactical Aircraft Aerodynamic Integration. doi:10.1002/9780470686652.eae490. ISBN   9780470754405. Archived from the original on 19 October 2021. Retrieved 19 October 2021.
  3. 1 2 Scharnhorst, Dr. Richard K. (12 January 2012). An Overview of Military Aircraft Supersonic Inlet Aerodynamics (Report). American Institute of Aeronautics and Astronautics. doi:10.2514/6.2012-13.
  4. 1 2 3 Chris Wiegand; Bruce A. Bullick; Jeffrey A. Catt; Jeffrey W. Hamstra; Greg P. Walker; Steve Wurth (13 August 2019). F-35 Air Vehicle Technology Overview . Progress in Astronautics and Aeronautics. Vol. 257. pp. 121–160. doi:10.2514/5.9781624105678.0121.0160. ISBN   978-1-62410-566-1.
  5. USExpired US2990142A, Antonio Ferri,"Scoop-type supersonic inlet with precompression surface",published 27 June 1961,issued 27 June 1961
  6. Saheby, Eiman B; Shen, Xing (2019). "Design and performance study of a parametric diverterless supersonic inlet". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering. 234 (2). Institution of Mechanical Engineers: 470–489. doi:10.1177/0954410019875384 . Retrieved 15 August 2025.
  7. Yang, Yingkai (August 2007). "Design of Bump Inlet of Thunder/JF-17 Aircraft". Journal of Nanjing University of Aeronautics & Astronautics. 39 (4). Nanjing, Jiangsu: Nanjing University of Aeronautics and Astronautics. Retrieved 22 August 2025.
  8. Zhong, Yicheng; Yu, Shaozi; Wu, Qing. "Research of bump inlet (DSI) model design and its aerodynamic properties". Journal of Aeronautical Power. 20 (5). Nanjing, Jiangsu: Nanjing University of Aeronautics and Astronautics. Retrieved 22 August 2025.
  9. Song, Wencong; Xie, Pin; Zheng, Sui; Li, Yupu (January 2001). A Research on the Aerodynamic Characteristics of a Small Aspect Ratio, High Lift Fighter Configuration. Strategic Study of CAE (Report). Vol. 3. Chengdu Aircraft Design & Research Institute, Engineering Science.
  10. RUpatent RU2770885C1,Mikhail Strelets, Alexei Bulutov, Mikhail Nikitushkin, et. al.,"Multifunctional supersonic single-engine aircraft",published 25 April 2022,issued 25 April 2022
  11. "F-35 JSF Technology". Archived from the original on 2012-05-06. Retrieved 2015-06-04.
  12. ""Fast History: Lockheed's Diverterless Supersonic Inlet Testbed F-16"". Archived from the original on 2013-09-07. Retrieved 2023-08-07.
  13. "J-20's Stealth Signature Poses Interesting Unknowns" Archived 2013-05-15 at the Wayback Machine . Aviation Week. Retrieved 13 January 2013
  14. "歼-10B改进型". AirForceWorld.com. Archived from the original on 2013-08-05. Retrieved 2013-08-01.
  15. "JL-9 Trainer Jet gets DSI inlet, Guizhou China". AirForceWorld.com. Archived from the original on 5 August 2013. Retrieved 29 Aug 2011.
  16. "Paris Air Show 2011 - Naval air trainer unveiled by Chinese media". home.janes.com, 15 February 2012.
  17. "AMCA could fly undetected during dangerous missions". Onmanorama . February 5, 2020. Retrieved 2020-02-06.