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Stealth
The stealth of the F-22 is due to a combination of factors, including the overall shape of the aircraft, the use of radar absorbent material (RAM), and attention to detail such as hinges and pilot helmets that could provide a radar return.[154] However, reduced radar cross section is one of five facets of presence reduction addressed in the designing of the F-22. The F-22 was designed to disguise its infrared emissions, reducing the threat of infrared homing ("heat seeking") surface-to-air or air-to-air missiles, including its flat thrust vectoring nozzles.[155] The aircraft was designed to be less visible to the naked eye; radio, heat and noise emissions are equally controlled.[154]
The F-22 apparently relies less on maintenance-intensive radar absorbent material and coatings than previous stealth designs like the F-117. These materials caused deployment problems due to their susceptibility to adverse weather conditions.[156] Unlike the B-2, which requires climate-controlled hangars, the F-22 can undergo repairs on the flight line or in a normal hangar.[156] Furthermore, the F-22 has a "Signature Assessment System", which presents warning indicators when normal wear-and-tear degrades the aircraft's radar signature to the point of requiring substantial repair work.[156] The exact radar cross section (RCS) remains classified; however, in early 2009 Lockheed Martin released information on the F-22, indicating it to have a RCS (from certain angles) of −40 dBsm – the equivalent radar reflection of a "steel marble".[157] However, the stealth features of the F-22 require additional maintenance, decreasing their mission capable rate to approximately 62–70%.[N 2]
The effectiveness of the emphasis on stealth characteristics is difficult to measure. While its radar cross-section is almost nonexistent, this is merely a static measurement of the aircraft's frontal or side area and is valid only for a radar source in a stationary location relative to the aircraft. As soon as the F-22 maneuvers, it exposes a different set of angles and a greater surface area to any radar, increasing its visibility. Furthermore, the use of stealth contouring and radar absorbent material are chiefly effective against high-frequency radars, usually found on other aircraft. Low-frequency radars, employed by weather radars and ground warning stations, are alleged to be less affected by stealth characteristics and are more capable of detecting aircraft employing them.[159][160] The result of these low resolution and fleeting radar contacts will mean that while the defense may know that a stealth aircraft is in the area, they will be unable to vector defenses in to shoot down the aircraft, especially a high performance airframe like the F-22.[161]
