The military term ‘stealth’ brings to mind the Hollywood movie Hollow Man (2020), in which Kevin Bacon becomes invisible during a scientific test, or the 2022 film Invisible Man, where Oliver Jackson-Cohen acquires the ability to go invisible. While such ideas are intriguing for fiction or entertainment purposes, the question remains: is ‘stealth’ a valid concept in reality? Specifically, can an aircraft truly be invisible to ground or airborne radar?
Major powers such as China, Russia, and the US have invested billions of dollars in research and development in this field to produce operational aircraft, with the US taking the lead by manufacturing the F-117, F-22, F-35, B-2, and the upcoming strategic bomber B-21. However, neither China nor Russia currently possess a truly stealthy flying machine, and all so-called stealth flying machines fall into the category of ‘Low Observables’. The J-20 of China and Su-57 of Russia may not even be considered low observable.
As we focus on designing a stealthy airframe, we must also keep in mind advancements in radar technology. For example, experimental Quantum Radar, if it becomes a reality, may change the stealth concept forever. The pace of development of radars and sensors already incorporated in Surface-to-Air Missiles (SAM) and Air-to-Air Missiles (AAM) is faster than the stealth design development of modern fighters.
The stealth capability or quality of a flying machine can be divided into physical attributes and technological requirements. Physical stealth is non-existent in the case of flying machines. Noise created by the aero-engine and friction caused by air resistance cannot be minimized or eliminated. Shock waves created when flying in trans-sonic/Supersonic range result in a sonic boom indicating the aircraft’s speed, and condensation or smoke trails produced by jet engines cannot be hidden from sight.
The heat signature of a jet airplane remains a significant threat despite efforts to keep exhaust gas temperature under control. Heat signature can be minimized but not eliminated, and measures adopted to reduce exhaust gas temperature result in reduced stealth characteristics.
All non-stealth aircraft with light-colored surfaces merge with blue sky and are difficult to spot despite engine noise, while current stealth aircraft are clearly visible due to their black color, increasing their vulnerability to shoulder launch human-sighted missiles.
Design stealth focuses on reducing the reflectivity coefficient by providing inclined surfaces, wing-fuselage blending, internal weapons bay, embedded air intakes and jet pipes, and composite control surfaces. However, technological stealth, such as the development of Radar Absorbent Material (RAM), has been developed to provide a higher degree of stealth. RAM paints are susceptible to damage and require considerable maintenance, while ceramics have better radar signal absorbent quality than polymers but are heavier.
Currently, the inventory of genuine stealth-design aircraft is with the USAF only, and ground-based sensors have been produced that can detect them. Nebo-M Radar, capable of detecting stealthy flying machines, entered operational service in Russia in 2017, and its faintest reflected signal received is amplified many times over to distinguish the aircraft from slow-flying drones, birds, etc.
In conclusion, while stealth design has created significant hype and interest, its efficacy in highly dense air defense environments is yet to be proven under operational conditions. The future of stealth technology must consider critical operational issues such as the presence of jammers with strike formation.