Editing Lockheed F-117 Nighthawk (section)

== Design ==
[[File:F-117 Front View.jpg|thumb|Front view of an F-117|alt=Closeup view of the nose of a black jet, emphasizing the many angled-surfaces]]

When the USAF first approached Lockheed with the stealth concept, Skunk Works Director Kelly Johnson proposed a rounded design. He believed smoothly blended shapes offered the best combination of speed and stealth. However, his assistant, Ben Rich, showed that faceted-angle surfaces would provide a significant reduction in radar signature, and the necessary aerodynamic control could be provided with computer units. A May 1975 Skunk Works report, "Progress Report No. 2, High Stealth Conceptual Studies", showed the rounded concept that was rejected in favor of the flat-sided approach.<ref>{{cite web |url= http://www.airspacemag.com/military-aviation/secrets-skunk-works-180952122/?page=6 |title= Secrets of the Skunk Works – 'Little Harvey, Concept B' |first= Chad |last= Slattery |publisher= [[Air & Space/Smithsonian]]}}</ref><ref name="crickmore 1213">Crickmore and Crickmore 2003, pp. 12-13.</ref><ref name= "bomber 278">Gunston and Gilchrist 1993, p. 278.</ref> The resulting unusual design surprised and puzzled experienced pilots; a [[Royal Air Force]]<!-- (RAF) --> pilot who flew it as an [[exchange officer]] stated that when he first saw a photograph of the still-secret F-117, he "promptly giggled and thought [to himself] 'this clearly can't fly{{'"}}.<ref name="crickmore 856">Crickmore and Crickmore 2003, pp. 85-86.</ref>

The single-seat F-117 is powered by two nonafterburning [[General Electric F404]] turbofan engines. They were extensively modified to suit a stealth aircraft, such as to have a cooler operational temperature, and somewhat resembled a [[turbojet]], instead.<ref name= "bomber 2801">Gunston and Gilchrist 1993, pp. 280-281.</ref> The engine was redesigned to produce a minimum of mass thrust, which eased the task of designing a suitable inlet and nozzle. To obscure the engine from enemy radar, a conductive metal mesh grill was installed in the intake, while the exhaust gases were intentionally mixed with cool air to lower the thermal signature.<ref name= "bomber 281">Gunston and Gilchrist 1993, p. 281.</ref>

The aircraft is [[Aerial refueling|air refuelable]] and features a [[V-tail]]. The maximum speed is {{cvt|623|mph|km/h kn}} at high altitude, the maximum rate of climb is {{convert|2820|ft}} per minute, and the service ceiling is {{convert|43000|to|45000|ft}}.<ref>Dorr 2016, p. 315.</ref><ref name= "bomber 27980">Gunston and Gilchrist 1993, pp. 279-280.</ref> The cockpit was quite spacious, with ergonomic displays and controls, but the field of view was somewhat obstructed with a large blind spot to the rear.<ref>Nijboer 2016, p. 210.</ref>

=== Avionics ===
Early stealth aircraft were designed with a focus on minimal radar cross-section<!-- (RCS) --> rather than aerodynamic performance; because of this, the F-117 is aerodynamically unstable in all three [[aircraft principal axes]] and requires constant flight corrections from a fly-by-wire (FBW) flight system to maintain controlled flight.<ref name="janos 3046">Rich and Janos 1994, pp. 30–31, 46.</ref><ref name= "bomber 280">Gunston and Gilchrist 1993, p. 280.</ref> It is equipped with quadruple-redundant FBW flight controls. To lower development costs, the avionics, FBW systems, and other systems and parts were derived from the General Dynamics [[F-16 Fighting Falcon]], [[Boeing B-52 Stratofortress]], [[McDonnell Douglas F/A-18 Hornet]], and [[McDonnell Douglas F-15E Strike Eagle]].<ref name="crickmore 1415">Crickmore and Crickmore 2003, pp. 14-15.</ref> To maintain a high level of secrecy, components were often rerouted from other aircraft programs, ordered using falsified addresses and other details, while $3 million worth of equipment was removed from USAF storage without disclosing its purpose.<ref name="janos 46">Rich and Janos 1994, p. 46.</ref>

[[File:Lockheed F-117A cockpit at the National Museum of the United States Air Force, Dayton, Ohio, USA.jpg|thumb|YF-117A cockpit|alt=Lockheed YF-117A cockpit at the National Museum of the United States Air Force, Dayton, Ohio, USA]]
The aircraft is equipped with sophisticated navigation and attack systems integrated into a digital avionics suite. It navigates primarily by [[Global Positioning System|GPS]] and high-accuracy [[inertial navigation]].<ref name= "bomber 282">Gunston and Gilchrist 1993, p. 282.</ref> Missions are coordinated by an automated planning system that can automatically perform all aspects of an attack mission, including weapons release.<ref name="fas2" /> Targets are acquired by a [[thermal imaging]], [[infrared]] system, paired with a [[laser rangefinder]]/[[laser designator]] that finds the range and designates targets for [[laser-guided bomb]]s. The F-117's split internal bay can carry {{convert|5000|lb}} of ordnance. Typical weapons are a pair of [[GBU-10]], [[GBU-12]], or [[GBU-27]] laser-guided bombs, two [[BLU-109]] penetration bombs, or, after 2006, two [[Joint Direct Attack Munitions]] (JDAM) GPS/INS-guided stand-off bombs.<ref name="janos 26">Rich and Janos 1994, p. 26.</ref><ref>{{cite journal |last1=Enos |first1=James R. |title=Applying real system age to DoD systems |journal=Systems Engineering |date=May 2022 |volume=25 |issue=3 |pages=242–253 |doi=10.1002/sys.21614 |s2cid=246811908}}</ref>

=== Stealth ===
{{main|Stealth aircraft}}

The F-117 has an RCS around {{Convert|0.001|m2|sigfig=3|abbr=on}}.<ref name="richardson" /> Among the penalties for stealth are subsonic speeds to prevent frame heating, heat on the engine inlet and outlet prevent certain thrusting maneuvers, a very low [[Aspect ratio (wing)|wing aspect ratio]], and a high [[sweep angle]] (50°), needed to deflect incoming radar waves to the sides.<ref name=":0" /><ref name="richardson36"/><ref name="richardson51"/> With these design considerations and no [[afterburner]], the F-117 is limited to subsonic speeds. Additionally, to maintain its low observability, the F-117 was not equipped with radar; not only would an active radar be detectable through its emissions, but also an inactive radar antenna would also act as a reflector of radar energy.<ref>{{cite web |last= Holloway |first= Don |date= March 1996 |title=Stealth Secrets of the F-117 Nighthawk |url= https://www.historynet.com/stealth-secrets-of-the-f-117-nighthawk-mar-96-aviation-history-feature.htm |access-date= 19 January 2022 |website= Historynet.com |publisher= HistoryNet}}</ref> Whether it carries any radar detection equipment remained classified as of 2008.<ref name=":0" />

Its [[faceting|faceted]] shape (made from two-dimensional flat surfaces) resulted from the limitations of the 1970s-era computer technology used to calculate its RCS. Later [[supercomputer]]s made subsequent aircraft like the [[B-2 bomber]] made use curved surfaces while maintaining stealth possible, through the use of far more computational resources to perform the additional calculations.<ref name="rich4" /> The radio-wave absorbing materials<!-- (RAM) --> covering the F-117 weighed almost one ton and were held in place by glue.<ref>{{Cite web |date=August 17, 2021 |title=Stealth Aircraft Technology in the F-117 Nighthawk and Beyond |url=https://www.aerospaceutah.org/stealth-aircraft-technology-in-the-f-117-nighthawk-and-beyond/ |access-date=December 16, 2024 |website=Hill Aerospace Museum}}</ref> The gaps between the sheets are filled with a kind of [[putty]] material called "butter".<ref name=":0" /><ref name="crickmore 2728">Crickmore and Crickmore 2003, pp. 27-28.</ref>

An exhaust plume contributes a significant [[infrared signature|infrared (IR) signature]]. The F-117 reduces IR signature with a noncircular [[exhaust system|tail pipe]] (a slit shape) to minimize the exhaust cross-section and maximize the mixing of hot exhaust with cool, ambient air.<ref name="crickmore 1516">Crickmore and Crickmore 2003, pp. 15-16.</ref> The F-117 lacks afterburners, because the hot exhaust would increase the infrared signature, breaking the [[sound barrier]] would produce an obvious [[sonic boom]], and surface heating of the aircraft skin would also increase the IR footprint. As a result, its performance in [[air combat maneuvering]] required in a [[dogfight]] would never match that of a dedicated fighter aircraft; this was unimportant in the case of the F-117, since it was a dedicated attack aircraft.<ref name="history" />

[[Passive radar|Passive (multistatic) radar]], [[bistatic radar]], and especially [[multistatic radar]] systems detect some stealth aircraft better than conventional [[monostatic radar]]s, since first-generation stealth technology (such as the F-117) reflects energy away from the transmitter's [[Line-of-sight propagation|line of sight]], effectively increasing the RCS in other directions, which the passive radars monitor.<ref name="Bistatic Radar Sets">{{cite web |url=http://www.radartutorial.eu/05.bistatic/bs04.en.html |title=Bistatic Radar Sets |publisher=Radartutorial.eu |access-date=16 December 2010}}</ref>