Editing Stealth technology (section)

===Vehicle shape===

====Aircraft====
{{Main|Aircraft design process}}
[[File:JSF F35 P1230144.jpg|thumb|The [[F-35 Lightning II]] offers better stealthy features (such as this landing gear door) than prior American multi-role fighters, such as the [[F-16 Fighting Falcon]]]]
The possibility of designing aircraft in such a manner as to reduce their radar cross-section was recognized in the late 1930s, when the first radar tracking systems were employed, and it has been known since at least the 1960s that aircraft shape makes a significant difference in detectability. The [[Avro Vulcan]], a British [[bomber]] of the 1960s, had a remarkably small appearance on radar despite its large size, and occasionally disappeared from radar screens entirely. It is now known that it had a fortuitously stealthy shape apart from the vertical element of the tail. Despite being designed before a low RCS and other stealth factors were ever a consideration,<ref name="newscientist82">Sweetman, Bill. [https://books.google.com/books?id=HVJyHCXAOtsC&dq=Vulcan+Bomber&pg=PA566 "The Bomber that radar cannot see."] ''New Scientist'', 4 March 1982.</ref> a Royal Aircraft Establishment technical note of 1957 stated that of all the aircraft so far studied, the Vulcan appeared by far the simplest radar echoing object, due to its shape: only one or two components contributing significantly to the echo at any aspect (one of them being the [[vertical stabilizer]], which is especially relevant for side aspect RCS), compared with three or more on most other types.<ref>Dawson 1957, p. 3.</ref>{{#tag:ref|Writing for the American Institute of Aeronautics and Astronautics, J. Seddon and E. L. Goldsmith noted that "Due to its all-wing shape, small vertical fin, and buried engines, at some angles [The Avro Vulcan] was nearly invisible to radar".<ref>Seddon and Goldsmith 1999, p. 343.</ref>}} While writing about radar systems, authors Simon Kingsley and Shaun Quegan singled out the Vulcan's shape as acting to reduce the RCS.<ref>Kingsley and Quegan 1999, p. 293.</ref> In contrast, the [[Tupolev Tu-95]] Russian long-range bomber ([[NATO reporting name]] 'Bear') was conspicuous on radar. It is now known that [[Propeller (aircraft)|propellers]] and jet turbine blades produce a bright radar image;{{Citation needed|date=March 2011}} the Bear has four pairs of large {{convert|5.6|m|ft|order=flip|adj=on}} diameter [[contra-rotating propellers]].

Another important factor is internal construction. Some stealth aircraft have skin that is radar transparent or absorbing, behind which are structures termed [[Concave polygon|reentrant triangles]]. Radar waves penetrating the skin get trapped in these structures, reflecting off the internal faces and losing energy. This method was first used on the Blackbird series: A-12, [[Lockheed YF-12A|YF-12A]], [[Lockheed SR-71 Blackbird]].

The most efficient way to reflect radar waves back to the emitting radar is with orthogonal metal plates, forming a [[corner reflector]] consisting of either a dihedral (two plates) or a trihedral (three orthogonal plates). This configuration occurs in the tail of a conventional aircraft, where the vertical and horizontal components of the tail are set at right angles. Stealth aircraft such as the F-117 use a different arrangement, tilting the tail surfaces to reduce corner reflections formed between them. A more radical method is to omit the tail, as in the B-2 Spirit. The B-2's clean, low-drag [[flying wing]] configuration gives it exceptional range and reduces its radar profile.<ref name="croddy 341-2">Croddy and Wirtz 2005, pp. 341–342.</ref><ref>Siuru 1993, pp. 114–115.</ref> The flying wing design most closely resembles a so-called infinite flat plate (as vertical control surfaces dramatically increase RCS), the perfect stealth shape, as it would have no angles to reflect back radar waves.<ref>{{cite web |url=https://www.northropgrumman.com/wp-content/uploads/B-2-Spirit-of-Innovation.pdf |title=B-2: The Spirit of Innovation |website=Northrop Grumman Corporation |access-date=15 October 2023 }}</ref>
[[File:Northrop McDonnell Douglas YF-23A PAV-1 87-0800 Black Widow II LEngineIntake R&D NMUSAF 25Sep09 (14414042127).jpg|thumb|right|YF-23 [[S-duct]] engine air intake conceals engine from probing radar waves]]
In addition to altering the tail, stealth design must bury the engines within the [[wing]] or [[fuselage]], or in some cases where stealth is applied to an extant aircraft, install baffles in the air intakes, so that the compressor blades are not visible to radar. A stealthy shape must be devoid of complex bumps or protrusions of any kind, meaning that weapons, fuel tanks, and other stores must not be carried externally. Any stealthy vehicle becomes un-stealthy when a door or hatch opens.

Parallel alignment of edges or even surfaces is also often used in stealth designs. The technique involves using a small number of edge orientations in the shape of the structure. For example, on the [[Lockheed Martin F-22 Raptor|F-22A Raptor]], the leading edges of the wing and the tail planes are set at the same angle. Other smaller structures, such as the air intake bypass doors and the [[air refueling]] aperture, also use the same angles. The effect of this is to return a narrow radar signal in a very specific direction away from the radar emitter rather than returning a [[diffuse reflection|diffuse signal]] detectable at many angles. The effect is sometimes called "glitter" after the very brief signal seen when the reflected beam passes across a detector. It can be difficult for the radar operator to distinguish between a glitter event and a digital glitch in the processing system.

Stealth [[airframe]]s sometimes display distinctive [[serration]]s on some exposed edges, such as the engine ports. The [[YF-23 Black Widow II|YF-23]] has such serrations on the exhaust ports. This is another example in the parallel alignment of features, this time on the external airframe.

The shaping requirements detracted greatly from the F-117's [[Aerodynamics|aerodynamic]] properties. It is [[relaxed stability|inherently unstable]], and cannot be flown without a [[Aircraft flight control system#Fly-by-wire control systems|fly-by-wire control system]].

Similarly, coating the [[cockpit (aviation)|cockpit]] canopy with a [[thin film]] [[transparent conductor]] ([[physical vapor deposition|vapor-deposited]] gold or [[indium tin oxide]]) helps to reduce the aircraft's radar profile, because radar waves would normally enter the cockpit, reflect off objects (the inside of a cockpit has a complex shape, with a pilot helmet alone forming a sizeable return), and possibly return to the radar, but the conductive coating creates a controlled shape that deflects the incoming radar waves away from the radar. The coating is thin enough that it has no adverse effect on pilot vision.

[[File:K32 HMS Helsingborg Anchored-of-Gotska-Sandoen cropped.jpg|right|thumb|{{HSwMS|Helsingborg|K32|6}}, a stealth ship]]

====Ships====
{{main|Naval architecture}}
Ships have also adopted similar methods. Though the earlier American {{sclass|Arleigh Burke|destroyer|1}}s incorporated some signature-reduction features.<ref>{{Cite web |title=DDG-51 Arleigh Burke-class |work=FAS website |publisher=Federation of American Scientists |url=https://fas.org/programs/ssp/man/uswpns/navy/surfacewarfare/ddg51_arleighburke.html |access-date=2 February 2011 |archive-url=https://web.archive.org/web/20131224113129/https://fas.org/programs/ssp/man/uswpns/navy/surfacewarfare/ddg51_arleighburke.html |archive-date=24 December 2013}}</ref><ref>{{Cite web |last=Benson |first=Robert |title=The Arleigh Burke: Linchpin of the Navy |work=Asia-Pacific Defense Forum |publisher=Federation of American Scientists |date=November 1998 |url=https://fas.org/man/dod-101/sys/ship/docs/ArleighB.htm |access-date=2 February 2011}}</ref> the Norwegian {{sclass|Skjold|corvette|1}}s was the first coastal defence and the French {{sclass|La Fayette|frigate|1}}s the first ocean-going [[stealth ship]]s to enter service. Other examples are the Dutch {{sclass|De Zeven Provinciën|frigate|1}}s, the Taiwanese {{sclass|Tuo Chiang|corvette|1}}s, German {{sclass|Sachsen|frigate|1}}s, the Swedish {{sclass|Visby|corvette|1}}, the American {{sclass|San Antonio|amphibious transport dock|1}}s, and most modern [[warship]] designs.