Stealth aircraft

Stealth aircraft are planes that use stealth or low observable technology to avoid detection by enemies during combat, thus giving the pilots of these planes the upper hand during war. Although it is impossible for any type of aircraft to be completely invisible to detection, especially by radar, these specially designed aircraft reduce radar cross-section by either absorbing or reflecting the radar signals and defusing the beam back to the transmitter to make the aircraft appear smaller and less noticeable. In some cases, the aircraft can be undisguisable on radar from a bird flying in the airspace. Reduced detection via infrared spectrum, electromagnetic energy, visible light, radio frequency, and acoustic sound waves is also important to be developed with stealth technology.

Stealth technology includes constructing aircraft with low observable features, such as designing the aircraft to be contoured to be less visible and able to maneuver in a way that differs from conventional military aircraft to avoid detection. Other low observable features used in stealth technology include the use of low-probability-of-intercept radar and advanced avionics navigational systems that reduce electromagnetic signatures, as well as reduced heat and sound emissions to prevent tracking. Because of improvements in design, stealth aircraft are capable of surprising enemy forces and not being tracked or targeted by radar-guided weapons, providing a decided military advantage in combat.

Background

The history of stealth technology in aircraft dates back to World War I (1914–1918) when the Germans covered planes with a transparent material called Cellon that was meant to reduce visibility. However, prototypes proved that not only did it not work effectively and was not durable, but sunlight also reflected off its surface, making the aircraft even more visible from the ground. As a result, the Germans abandoned the idea of using Cellon after initial testing.

In 1916, the British experimented with a design for a SS class airship that had a low-noise engine and a black gas bag to do night reconnaissance on the Western Front. They found that it was unable to be seen or heard at night. However, nighttime reconnaissance was not found to be valuable for information gathering, and the prototype was never put into general use.

During World War II (1939–1945), early radar technology was developed to detect enemy fighter aircraft. The Germans created an aircraft that had some features of stealth technology, although they did not initially intend the airplane to be a stealth aircraft. The Horten Ho 229 flying wing fighter-bomber was built with a lack of vertical surfaces and a shape that made it difficult for Britain’s radar systems to detect it flying at high speeds and low altitudes. This led to the Horten Ho 229 being noticeably less detectable than other aircraft. Following World War II, the United States developed the prototype Northrop YB-49 Flying Wing heavy bomber. It had no fuselage or tail and resembled a giant flying wing. Like the German aircraft, it was not initially intended to be a stealth aircraft, but during testing, was observed to be difficult for ground radar to detect.

In the 1970s, stealth technology was further developed by Lockheed Aircraft when mathematician Denys Overholser adapted a Soviet mathematical model from the 1960s to create a computer program called Echo 1 that could predict an aircraft’s radar signature, also called radar cross-section. Further research showed that faceted surfaces on an aircraft produced a low radar cross-section because of deflection. The use of newer high-strength lightweight materials also contributed to the feasibility of construction. Although the prototype was found to be aerodynamically unstable, it showed that the design of a stealth aircraft was possible. In 1980, the US secretary of defense announced at a Pentagon news conference the existence of a stealth program that was in the process of producing aircraft that could not be effectively detected by radar at normal combat ranges.

Other countries in addition to the United States, such as Russia and China, have developed stealth aircraft designs since the 1970s. However, only the United States and its allies have used stealth aircraft in active combat. In the 1990s the United States used stealth aircraft in the invasion of Panama, the Gulf War, and the Kosovo Conflict. In 1999, the United States used two stealth aircraft, an F-117 Nighthawk and a B-2 Spirit bomber, in the NATO bombing of Yugoslavia. Although one F-117 was shot down by Serbian forces, the mission was considered successful.

In the twenty-first century, aircraft from stealth fleets were used in the wars in Afghanistan and Iraq and the intervention in Libya. In 2011, a stealth helicopter was used to send in troops to kill Osama bin Laden. Although the aircraft crashed, the operation was successful. In 2018, it was reported that the Israeli army used stealth fighters to avoid detection in Iranian airspace and completed a successful strike in combat over Syria.

Overview

A key feature found in stealth aircraft is a flattened, less vertical surface that creates minimal radar cross-section. Stealth designs also avoid the use of right angles, sharp curves, concavities, and large flat surfaces because these can reflect radar signals back to the transmitter and increase the chance of detection. Instead, smooth convex or faceted surfaces are used to scatter radar waves and hide the aircraft on the radar screen. Fuel tanks and mounted artillery are set inside the aircraft without open bomb bays, and low-set or flush engine intakes and exhausts provide a smoother surface. However, because of this, ordnance loads, which refers to the weight of weapons that an aircraft can carry, are lower on stealth aircraft. These design features often affect flight ability, but to counteract this problem, modern computer flight systems provide constant flight corrections to enhance stability.

First-generation stealth aircraft were usually constructed with a lack of afterburners to reduce the infrared footprint from hot exhaust emissions. Because of this, they could not fly faster than the speed of sound. However, it also must be considered that supersonic flight creates a loud sonic boom, and heat is generated in the skin of the aircraft, which makes it more detectable by acoustic monitoring and infrared spectrum. Newer designs allow for better aerodynamic performance and faster speeds while taking advantage of enhanced technology for constructing quieter engines, radiation absorbent skins, and improved airframe materials.

Non-emitting navigational systems, such as inertial guidance, must be used to avoid interception of radar emissions in stealth aircraft. Laser radar, which uses an almost undetectable scanning laser beam ahead of the aircraft, is also a low-emission option in advanced avionics systems. On board, a low-probability-of-intercept radar is also used to avoid notice by passive radar detecting equipment while tracking a target.

F-117 Nighthawk

The F-117 Nighthawk ground-attack fighter is a retired stealth surface twin-engine, single-seat Airforce aircraft produced by Lockheed and its Skunk Works division. It was the first aircraft that the United States designed using stealth technology in 1977 and became operational in 1983. It had a flat, short pyramid shape with sharply swept-up wings and many faceted surfaces that were oriented to deflect radar signals. Despite being in use in test flights since the 1980s, the F-117 Nighthawk was not used in combat until the Panama invasion in 1989, and then it became public in 1990, thirteen years after its first test flight.

B-2 Spirit

The B-2 Spirit strategic bomber was the second operational stealth aircraft that was introduced in 1988, although work on it began shortly after the F-117. The B-2 was similar in shape to the F-117 but was of a flying-wing design that made it slightly longer. This convex shape gave it a lower radar cross-section. It was similar in appearance to the early YB-49 Flying Wing prototype of the 1940s. The fuselage shape had a series of large complex curved surfaces. Instead of vertical fin stabilizers to control flight, it had flaps on the edge of its wings that helped it to maneuver in flight. It has since been retired from combat use.

F-22 Raptor

First flown in 1997, the Lockheed F-22 Raptor became the first true stealth fighter with a combination of low observability and high performance. It is a second-generation stealth aircraft that is capable of super cruising, which is flying at supersonic speeds without an afterburner, and has excellent maneuverability. It boasts a minimal radar cross-section that is as undetectable as a small bird in flight. The fleet consists of 186 aircraft, of which 150 are considered capable of combat, and production has ceased because of the newer F-35 and other stealth aircraft still in developmental stages.

F-35 Lightning

This fifth-generation stealth aircraft is similar to the conventional but successful F-15 Eagle introduced in the 1970s, but stealth technology greatly reduced its radar cross-section and allows it to get within 21 miles of a target before it can be detected by radar. The United States and its allies in the Pacific and Europe have partnered in the F-35 Joint Strike Fighter program, and the aircraft is in use around the world. Although somewhat controversial due to its expensive production, the F-35 has a radar cross-section the size of a golf ball. The F-35 also has a powerful advanced onboard system, the AN/APG-81 Active Electronically Scanned Array (AESA) Fire Control Radar system, that makes it capable of being used in electronic warfare operations. It is thought to be one of the most tactically advanced aircraft in history. More than seven hundred aircraft are in the fleet and in operation in the United States and among its allies.

B-21 Raider

The United States expected its sixth-generation B-21 to replace the F-22 in 2030. The public has only seen a test B-21 during a ceremony at Air Force Plant 42 in Palmdale, California, in December 2022. The B-21 is part of a nuclear triad that can fly manned or unmanned. It was designed for long-missle strikes. The price for a B-21 aircraft was $300 million. The United States expected the B-21 to play an intergral role in its Next Generation Air Dominance Plan. The country planned to eventually purchase one hundred B-21 stealth aircraft from the manufacturer Northrop Grumman.

J-20 Mighty Dragon

The Chengdu J-20 Mighty Dragon was the first operational Chinese stealth aircraft introduced in 2017 and has comparable features to the F-22 and F-35. It is thought that the Chinese military gained access to classified information about the US Stealth program and used blueprints from these aircraft for their own development. The design also is similar to a prototype Russian stealth fighter, which was never put into production. The fleet has never been reported in active combat but has participated in a combat exercise. It has a larger radar cross-section than either the F-22 or the F-35 but is smaller than Russia’s stealth aircraft. In addition to the J-20, the Chinese military also has in production a J-31 that is designed to be flown from an aircraft carrier, and a stealthy bomber Xian H-20 with long-range bombing capability.

Su-57 Felon

Manufactured by Sukhoi, the Su-57 Felon is the first Russian stealth aircraft. It began as a collaboration called the PAK FA, which was being designed by Russia and India, but India eventually backed out after many years of failed prototypes. Sanctions placed on Russia following the invasion of Ukraine in 2014 also prevented further development and production. Three production fleet aircraft were eventually made, but one crashed shortly after its first takeoff. Researchers have found that the Su-57 has a reduced radar cross-section when compared with conventional aircraft but one that is much larger than the F-22. However, the aircraft is thought to be difficult to detect during a head-on approach that occurs during a fighter intercept and has very good maneuverability. Su-57s have been deployed to Syria, but none has been reported in combat.

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