Silent skies: How stealth aircraft remain undetectable
By Ethan Mandel, Electrical Engineering, 2023
Control of the skies has been an important military objective since the invention of the aircraft in the early 20th century. Military aircraft were used primarily as a scouting tool during World War I but have grown to be a key tool in both combat and policy in the late 20th and early 21st centuries. Key advances in technology improving both the detection and concealment of aircraft have led to their rise in prominence over the past century. With technological advances in stealth, militaries can trade out their axes for scalpels in an effort to act with more precision and fewer unintentional casualties than ever before.
Aircraft can be detected through active and passive signatures. Active signatures are produced when radar is reflected from the surface of the aircraft back to a receiver. Passive signatures are a product of the aircraft’s flight. These signatures consist of audio signals and infrared radiation that are created as a byproduct of releasing exhaust and powering jet engines. Radar cross section (RCS) is a measure of how much of a radar signal reflected off of a target returns in the direction of the radar receiver. A combination of various factors including size, shape, and wavelength of a radar signal determine an aircraft’s RCS. Minimization of the aircraft’s RCS is the main goal of a stealth aircraft’s design.
As with all military technological improvement, stealth technology has had a profound impact on civilian life.
One approach to this goal is through the geometry of the aircraft itself. Surfaces and edges must be oriented to reflect signals in directions away from the source. Adding flat surfaces and removing external weapons minimizes perpendicular reflections. However, many design choices that lead to the reduction of the aircraft’s RCS make it less aerodynamic and efficient. Optimizing for a combination of aerodynamics and RCS reduction is key in the design of these aircraft.
Another approach to RCS reduction is through implementation of Radar Absorbent Material (RAM). RAMs reduce radar scattering through reflection of the signal so that it destructively interferes with itself and is negated. Carbon fibers are mainly used for this purpose as they have energy dissipating properties as well as being light and durable.
The invention and constant improvement of stealth technology has both improved the combat and reconnaissance capabilities of aircraft as well as the ability of radar to counter such technology. As with all military technological improvement, stealth technology has had a profound impact on civilian life as well. The improvement of carbon fibers and better detection radar has led to massive improvements in cellular transmission as well as commercial transport. Although stealth aircraft are important military and political assets unseen by civilians, the technology behind their inner workings has led to massive improvements in communication and materials used by millions.
The Aeronautical Journal (2002). DOI: 10.1017/S0001924000011702