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116-627: The Northrop/McDonnell Douglas YF-23 is an American single-seat, twin-engine , stealth fighter technology demonstrator prototype designed for the United States Air Force (USAF). The design team, with Northrop as the prime contractor, was a finalist in the USAF's Advanced Tactical Fighter (ATF) demonstration/validation competition, battling the YF-22 team for full-scale development and production. Two YF-23 prototypes were built. In

232-649: A great circle route. Hence, in case of an engine failure in a twinjet (like Boeing 777 ), the twin-jet could make emergency landings in fields in Canada , Alaska , eastern Russia , Greenland , Iceland , or the British Isles . The Boeing 777 has also been approved by the Federal Aviation Administration for flights between North America and Hawaii , which is the world's longest regular airline route with no diversion airports along

348-518: A podded engine usually mounted beneath, or occasionally above or within, each wing. Most notable examples of such a configuration are the Boeing 737 and Airbus A320 . The second has one engine mounted on each side of the rear fuselage, close to its empennage , used by many business jets , although some airliners like the Fokker 70 , Douglas DC-9 and COMAC ARJ21 utilise such a design as well. In

464-600: A USAF solicitation for an interim regional bomber , for which the Lockheed Martin FB-22 and Boeing B-1R were also competing. The FB-23 would have a two-seat cockpit and a similar planform shape as the F-23, but considerably larger in all dimensions to fulfill the bomber role with a combat radius of over 1,600 nautical miles (1,840 mi; 2,960 km). Northrop Grumman modified the YF-23 PAV-2 to serve as

580-473: A broad-span biconical delta, with each side bulging upwards towards the rear in a manner characteristic of the modern Rogallo wing . During the following year, in America U. G. Lee and W. A. Darrah patented a similar biconical delta winged aeroplane with an explicitly rigid wing. It also incorporated a proposal for a flight control system and covered both gliding and powered flight. None of these early designs

696-435: A deeper structure for a given aerofoil section. This both enhances its weight-saving characteristic and provides greater internal volume for fuel and other items, without a significant increase in drag. However, on supersonic designs the opportunity is often taken to use a thinner aerofoil instead, in order to actually reduce drag. Like any wing, at low speeds a delta wing requires a high angle of attack to maintain lift. At

812-405: A delta foreplane just in front of and above the main delta wing. Patented in 1963, this configuration was flown for the first time on the company's Viggen combat aircraft in 1967. The close coupling modifies the airflow over the wing, most significantly when flying at high angles of attack. In contrast to the classic tail-mounted elevators, the canards add to the total lift as well as stabilising

928-513: A display model for its proposed interim bomber. The possibility of an FB-23 interim bomber ended with the 2006 Quadrennial Defense Review , which favored a long-range strategic bomber with much greater range. The USAF has since moved on to the Next-Generation Bomber and Long Range Strike Bomber program. The Japan Air Self-Defense Force (JASDF) launched a program to develop a domestic 5th / 6th generation (F-3) fighter after

1044-515: A display model for the proposed FB-23 regional bomber in 2004. Data from Pace, Sweetman, Winchester, Metz & Sandberg, Aronstein & Hirschberg (note, some specifications are estimated) General characteristics Performance Armament None as tested but provisions made for: Aircraft of comparable role, configuration, and era Related lists Twinjet There are three common configurations of twinjet aircraft. The first, common on large aircraft such as airliners, has

1160-656: A fairing in the right wing. The NATF-23 had an increased 48 ft (14.63 m) wingspan, while length was reduced to 62 ft 8.5 in (19.11 m), the same as the F-14. Folded wingspan would be 23 ft 4 in (7.11 m). Like the Air Force version, the NATF-23 had both single-seat and two-seat variants. In 2004, Northrop Grumman proposed an F-23-based bomber called the FB-23 "Rapid Theater Attack" (RTA) to meet

1276-715: A fast-paced combat demonstration with six flights over a 10-hour period on 30 November 1990. Flight testing continued into December. The two YF-23s flew 50 times for a total of 65.2 hours. The tests demonstrated Northrop's predicted performance values for the YF-23. Both designs met or exceeded all performance requirements; the YF-23 was stealthier and faster, but the YF-22 was more agile. The two contractor teams submitted evaluation results and their PSC proposals for full-scale development in December 1990, and on 23 April 1991, Donald Rice ,

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1392-443: A shock body beneath the wing creates an attached shockwave and the high pressure associated with the wave provides significant lift without increasing drag. Variants of the delta wing plan offer improvements to the basic configuration. Cropped delta  – tip is cut off. This helps maintain lift outboard and reduce wingtip flow separation (stalling) at high angles of attack. Most deltas are cropped to at least some degree. In

1508-408: A specified distance from an available diversion airport. Overwater flights near diversion airports need not be ETOPS/LROPS-compliant. Since the 1990s, airlines have increasingly turned from four-engine or three-engine airliners to twin-engine airliners to operate transatlantic and transpacific flight routes. On a nonstop flight from America to Asia or Europe, the long-range aircraft usually follows

1624-406: A sufficiently high angle the wing exhibits flow separation , together with an associated high drag. Ordinarily, this flow separation leads to a loss of lift known as the stall . However, for a sharply-swept delta wing, as air spills up round the leading edge it flows inwards to generate a characteristic vortex pattern over the upper surface. The lower extremity of this vortex remains attached to

1740-433: A team to develop whichever of their proposed designs was selected, if any. Lockheed, Boeing, and General Dynamics formed a team with a similar agreement. Lockheed and Northrop, the two industry leaders in stealth aircraft, were selected as finalists on 31 October 1986 for Dem/Val as first and second place, although the approaches to their proposals were markedly different. Northrop's refined and well-understood design proposal

1856-541: A trijet aircraft) and Boeing worked on new widebody twinjet designs that would become the Airbus A330 and Boeing 777 , respectively. The MD-11's long range advantage was brief as it was soon nullified by the Airbus A330-300 and the extended-range Boeing 767-300ER and Boeing 777-200ER. The Airbus A320 twinjet stands out as the most produced jet airliner. The Boeing 777X is the world's largest twinjet, and

1972-728: Is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ). Although long studied, it did not find significant applications until the Jet Age , when it proved suitable for high-speed subsonic and  supersonic flight. At the other end of the speed scale, the Rogallo flexible wing proved a practical design for the hang glider and other ultralight aircraft . The delta wing form has unique aerodynamic characteristics and structural advantages. Many design variations have evolved over

2088-434: Is known to have successfully flown although, in 1904, Lavezzani's hang glider featuring independent left and right triangular wings had left the ground, and Dunne's other tailless swept designs based on the same principle would fly. The practical delta wing was pioneered by German aeronautical designer Alexander Lippisch in the 1930s, using a thick cantilever wing without any tail. His first such designs, for which he coined

2204-474: Is not an issue, as one of the engines is more than powerful enough to keep the aircraft aloft (see below). Mostly, ETOPS certification involves maintenance and design requirements ensuring that a failure of one engine cannot make the other one fail also. The engines and related systems need to be independent and (in essence) independently maintained. ETOPS/LROPS is often incorrectly thought to apply only to long overwater flights, but it applies to any flight more than

2320-527: The compound delta , double delta or cranked arrow , the leading edge is not straight. Typically the inboard section has increased sweepback, creating a controlled high-lift vortex without the need for a foreplane. Examples include the Saab Draken fighter, the experimental General Dynamics F-16XL , and the Hawker Siddeley HS. 138 VTOL concept. The ogee delta (or ogival delta ) used on

2436-518: The 777X in November 2013, while then-CEO Fabrice Brégier preferred to focus on product improvement rather than all-new concepts for 10 years. It would have a 10-abreast economy like the 777; its 565 m (6,081 sq ft) wing, slightly more than the 747-8, would have an 80 m (262 ft) span, as wide as the A380 , for a 892,900 lb (405 t) MTOW compared to 775,000 lb (352 t) for

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2552-633: The Bellefontaine Neighbors Klein Park Veterans Memorial in St. Louis, Missouri. The YF-23A (internally designated DP117K) was a prototype air vehicle intended to demonstrate the viability of Northrop's ATF proposal, which was designed to meet USAF requirements for survivability , supercruise, stealth, and ease of maintenance. Owing to its continual maturation from the HSF concept which it still greatly resembled,

2668-399: The Boeing 777 , Boeing 787 and Airbus A350 have matched or surpassed older quad-jet designs such as the Boeing 747 and Airbus A340 in these aspects, and twinjets have been more successful in terms of sales than quad-jets. In 2012, Airbus studied a 470-seat twinjet competitor for the Boeing 747-8 with lower operating costs expected between 2023 and 2030, revived after Boeing launched

2784-483: The Dassault Rafale use a combination of canard foreplanes and a delta wing. Like other tailless aircraft , the tailless delta wing is not suited to high wing loadings and requires a large wing area for a given aircraft weight. The most efficient aerofoils are unstable in pitch and the tailless type must use a less efficient design and therefore a bigger wing. Techniques used include: The main advantages of

2900-584: The F-106 Delta Dart and B-58 Hustler . At high supersonic speeds, the shock cone from the leading edge root angles further back to lie along the wing surface behind the leading edge. It is no longer possible for the sideways flow to occur and the aerodynamic characteristics change considerably. It is in this flight regime that the waverider design, as used on the North American XB-70 Valkyrie , becomes practicable. Here,

3016-611: The Secretary of the Air Force announced that the YF-22 team was the winner. The Air Force also selected the Pratt & Whitney F119 engine to power the F-22 production version. The Lockheed and Pratt & Whitney designs were rated higher on technical aspects, considered lower risk (the YF-23 flew considerably fewer sorties and hours than its counterpart), and were considered to have more effective program management. It has been speculated in

3132-407: The flight control surfaces controlled by a central management computer system. Raising the wing flaps and ailerons on one side and lowering them on the other provided roll . The V-tail fins were angled 50 degrees from the vertical. Pitch was mainly provided by rotating these V-tail fins in opposite directions so their front edges moved together or apart. Yaw was primarily supplied by rotating

3248-523: The 1980s, the USAF began looking for a replacement for its F-15 fighter aircraft to more effectively counter emerging threats such as the Soviet Union 's advanced Sukhoi Su-27 and Mikoyan MiG-29 . Several companies submitted design proposals; the USAF selected proposals from Northrop and Lockheed for demonstration/validation. Northrop teamed up with McDonnell Douglas to develop the YF-23, while Lockheed, Boeing , and General Dynamics developed

3364-753: The 777-200LR variant has the world's second longest aircraft range (behind Airbus A350-900 ULR). Other Boeing twinjets include the 767 , 757 (With the latter having stopped production, but still in commercial service) and 787 . Competitor Airbus produces the A320 family , the A330 , and the A350 . Some modern commercial airplanes still use four engines ( quad-jets ) like the Airbus A380 and Boeing 747-8 , which are classified as very large aircraft (over 400 seats in mixed-class configurations). Four engines are still used on

3480-432: The 777X, with a composite structure for an operating empty weight of 467,400 lb (212 t), and a 8,150 nmi (15,090 km) range at Mach 0.85. When flying far from diversionary airports (so called ETOPS/LROPS flights), the aircraft must be able to reach an alternate on the remaining engine within a specified time in case of one engine failure. When aircraft are certified according to ETOPS standards, thrust

3596-628: The ATB/B-2, gave their designers an early advantage, especially since Lockheed, the only other company with extensive stealth experience, had previously relied on faceting as on the F-117 and lost the ATB to Northrop as a result. That loss, along with the poor aerodynamic performance of their early faceted ATF concept, forced Lockheed to also develop designs and analysis methods with curved stealthy surfaces. Northrop's HSF design would be refined into DP110, which

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3712-589: The ATF request for information (RFI) in May 1981 to several aerospace companies on possible features for the new fighter. Eventually code-named "Senior Sky" , the ATF at this time was still in the midst of requirements definition, which meant that there was considerable variety in the industry responses. Northrop submitted three designs for the RFI, ranging from ultra low-cost, to highly agile, to low-observable missileer; all were on

3828-612: The Advanced Technology Bomber (ATB) program (which would result in the B-2 , or " Senior Ice "). Northrop was able to quickly adapt to the ATF's increasing emphasis on stealth. Since October 1981, a small team of engineers under Rob Sandusky within its ATB/B-2 division had been working on stealth fighter designs. Sandusky would later be the Northrop ATF's Chief Engineer, while fellow B-2 stealth engineer Yu Ping Liu

3944-692: The Anglo-French Concorde supersonic airliner is similar, but with the two sections and cropped wingtip merged into a smooth ogee curve. Tailed delta  – adds a conventional tailplane (with horizontal tail surfaces), to improve handling. Common on Soviet types such as the Mikoyan-Gurevich MiG-21 . Canard delta  – Many modern fighter aircraft, such as the JAS 39 Gripen , the Eurofighter Typhoon and

4060-468: The B-2 to reduce its susceptibility to radar and infrared detection, and Liu's understanding of both radar signatures and aerodynamics would lend itself to key design features, such as the shaping of the nose (nicknamed the "platypus" for the initial shape and pronounced chine edges) and canopy with their Gaussian surfaces . By 1985, HSF had evolved to be recognizably similar to the eventual YF-23 and emerged as

4176-481: The F-23 full system design, or Preferred System Concept (PSC). As DP117K had been frozen by then, the nacelles — nicknamed "bread loafs" for their flat upper surface — were not downsized on the prototypes. The number of internal missiles (with the AIM-120A as the reference baseline) was reduced from eight to six. Despite these adjustments, both teams struggled to achieve the 50,000-lb takeoff gross weight goal, and this

4292-503: The HSF would pay off for the Dem/Val RFP. By January 1986, the HSF would evolve into Design Proposal 86E (DP86E) as a refined and well-understood concept through extensive computational fluid dynamics simulations, wind tunnel testing, and RCS pole testing and became Northrop's preference for its ATF submission. Furthermore, Northrop's ability to design and analyze stealthy curved surfaces, stemming back to its work on Tacit Blue and

4408-463: The Javelin following the early loss of an aircraft to such conditions. Gloster's design team had reportedly opted to use a tailed delta configuration out of necessity, seeking to achieve effective manoeuvrability at relatively high speeds for the era while also requiring suitable controllability when being flown at the slower landing speeds desired. A lifting-canard delta can offer a smaller shift in

4524-577: The SPO's discussions with Lockheed and Northrop regarding their experiences with the F-117 and B-2, all-aspect stealth requirements were drastically increased in late 1985. The requirement to include the evaluation of prototype air vehicles from the two finalists was added in May 1986 due to recommendations from the Packard Commission , a federal commission by President Ronald Reagan to study Department of Defense procurement practices. At this time,

4640-587: The Second World War brought a halt to flight testing of the Pa-22 , although work continued for a time after the project garnered German attention. During the postwar era, Payen flew an experimental tailless delta jet, the Pa.49 , in 1954, as well as the tailless pusher-configuration Arbalète series from 1965. Further derivatives based on Payen's work were proposed but ultimately went undeveloped. Following

4756-544: The Second World War, developed the theory of the thin delta wing for supersonic flight. First published in January 1945, his approach contrasted with that of Lippisch on thick delta wings. The thin delta wing first flew on the Convair XF-92 in 1948, making it the first delta-winged jet plane to fly. It provided a successful basis for all practical supersonic deltas and the configuration became widely adopted. During

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4872-585: The Soviet Tupolev Tu-144 , the Tupolev first flying in 1968. While both Concorde and the Tu-144 prototype featured an ogival delta configuration, production models of the Tu-144 differed by changing to a double delta wing. The delta wings required these airliners to adopt a higher angle of attack at low speeds than conventional aircraft; in the case of Concorde, lift was maintained by allowed

4988-484: The U.S. Both Soviet models were expected to reduce the combat and maneuverability advantages of contemporary U.S. fighter aircraft, including the newly introduced F-15 Eagle and F-16 Fighting Falcon . Additionally, U.S. tactical airpower would be further threatened by new Soviet systems such as the A-50 airborne warning and control system (AWACS) revealed in 1978 and more advanced surface-to-air missile systems. In 1981,

5104-543: The U.S. Congress refused in 1998 to export the F-22 . After a great deal of study and the building of static models, the Mitsubishi X-2 Shinshin testbed aircraft flew as a technology demonstrator from 2016. By July 2018, Japan had gleaned sufficient information and decided it would need to involve international partners to complete this project. Northrop Grumman was one of the companies that responded and there

5220-528: The US, typically to lower its drag, resulting in the replacement of its large vertical stabilizer with a smaller and more conventional counterpart, along with a normal cockpit canopy taken from a Lockheed P-80 Shooting Star . The work of French designer Nicolas Roland Payen somewhat paralleled that of Lippisch. During the 1930s, he had developed a tandem delta configuration with a straight fore wing and steep delta aft wing, similar to that of Causarás. The outbreak of

5336-424: The USAF began developing requirements and discussing with the aerospace industry on concepts for an Advanced Tactical Fighter (ATF) with both air-to-air and air-to-ground missions in consideration. The ATF was to take advantage of emerging technologies, including composite materials , lightweight alloys , advanced flight-control systems, more powerful propulsion systems, and stealth technology . The USAF released

5452-484: The USAF envisioned procuring 750 ATFs at a unit flyaway cost of $ 35 million in fiscal year (FY) 1985 dollars (~$ 84.2 million in 2023). Furthermore, the U.S. Navy under the Navy Advanced Tactical Fighter (NATF) program eventually announced that it would use a derivative of the ATF winner to replace its F-14 Tomcat and called for the procurement of 546 aircraft. Northrop's early work on

5568-501: The USAF issued the request for proposal (RFP) for demonstration and validation (Dem/Val) to several aircraft manufacturers with the top four proposals, later cut down to two to reduce program costs, proceeding to the next phase; in addition to the ATF's demanding technical requirements, the RFP also emphasized systems engineering , technology development plans, and risk mitigation. The RFP would see some changes after initial release; following

5684-538: The YF-22 achieved Mach 1.58 in supercruise. The YF-23 was tested to a top speed of Mach 1.8 with afterburners and achieved a maximum angle-of-attack of 25°. The maximum speed is classified, though sources state a speed greater than Mach 2 at altitude in full afterburner. The aircraft's weapons bay was configured for weapons launch, and used for testing weapons bay acoustics, but no missiles were fired; Lockheed fired AIM-9 Sidewinder and AIM-120 AMRAAM missiles successfully from its YF-22 demonstration aircraft. PAV-1 performed

5800-716: The YF-22. The YF-23 was stealthier and faster, but less agile than its competitor. After a four-year development and evaluation process, the YF-22 team was announced as the winner in 1991 and developed the F-22 Raptor , which first flew in 1997 and entered service in 2005. The U.S. Navy considered using a naval version of the ATF as a replacement for the F-14 , but these plans were later canceled due to costs. After flight testing, both YF-23s were placed in storage while various agencies considered plans to use them for further research, although none proceeded. In 2004, Northrop Grumman used

5916-399: The YF-23's shaping was highly refined. It was an unconventional-looking aircraft, with diamond-shaped wings tapered symmetrically at 40° in both the leading edge back sweep and trailing edge forward sweep, a profile with substantial area-ruling to reduce aerodynamic drag at transonic and supersonic speeds, and all-moving V-tails , or "ruddervators". The cockpit was placed high, near

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6032-428: The aft deck to shield the engines from infrared homing (IR) missile detection from below. The troughs were lined with tiles built by GM Allison that were " transpiration cooled " from engine bleed air to dissipate heat. The YF-23's propulsion and aerodynamics enabled it to cruise at over Mach 1.5 without afterburners. The YF-23 was statically unstable — having relaxed stability — and flown through fly-by-wire with

6148-671: The airflow over the main wing. This enables more extreme manoeuvres, improves low-speed handling and reduces the takeoff run and landing speed. During the 1960s, this configuration was considered to be radical, but Saab's design team judged that it was the optimal approach available for satisfying the conflicting performance demands for the Viggen, which including favourable STOL performance, supersonic speed, low turbulence sensitivity during low level flight, and efficient lift for subsonic flight. The close-coupled canard has since become common on supersonic fighter aircraft. Notable examples include

6264-695: The aviation press that the Lockheed design was also seen as more adaptable as the basis for the Navy's NATF, but by FY 1992 the U.S. Navy had abandoned NATF. Following the competition, both YF-23s were transferred to NASA's Dryden Flight Research Center at Edwards AFB , California, without their engines. NASA planned to use one of the aircraft to study techniques for the calibration of predicted loads to measured flight results, but this did not happen. Both YF-23 airframes remained in storage until mid-1996 when they were transferred to museums, with PAV-2 briefly serving as

6380-530: The best solution. The NATF-23 design was submitted along with the F-23 proposal for full-scale development, or engineering and manufacturing development (EMD), in December 1990, although by late 1990 the Navy was already beginning to back out of the NATF program and fully abandoned it by FY 1992 due to escalating costs. A wind tunnel test model of DP527, tested for 14,000 hours, was donated (with canards removed) by Boeing St. Louis (formerly McDonnell Douglas) in 2001 to

6496-400: The center of lift with increasing Mach number compared to a conventional tail configuration. An unloaded or free-floating canard can allow a safe recovery from a high angle of attack. Depending on its design, a canard surface may increase or decrease longitudinal stability of the aircraft. A canard delta foreplane creates its own trailing vortex. If this vortex interferes with the vortex of

6612-426: The centre of the area covered by the vortex. In the subsonic regime, the behaviour of a delta wing is generally similar to that of a swept wing. A characteristic sideways element to the airflow develops. In this condition, lift is maximised along the leading edge of the wing, where the air is turned most sharply to follow its contours. Especially for a slender delta, the centre of lift approximates to halfway back along

6728-403: The controls. The second YF-23 (serial number 87-0801 , PAV-2) made its first flight on 26 October, piloted by Jim Sandberg. The first YF-23 was painted charcoal gray and was nicknamed "Gray Ghost". The second prototype was painted in two shades of gray and nicknamed "Spider". PAV-1 briefly had a red hourglass painted on its ram air scoop to prevent injury to ground crew. The red hourglass resembled

6844-423: The engines, designated YF119 and YF120 respectively, for the ATF engine competition. Because of the late addition of the prototyping requirement due to political pressure, the prototype air vehicles were to be "best-effort" machines not meant to perform a competitive flyoff or represent a production aircraft that meets every requirement, but to demonstrate the viability of its concept and mitigate risk. As one of

6960-531: The exhaust trough lining in the aft deck would be aligned with the planform. The inlet design changed from the trapezoidal profile with suction panels to a serrated semicircular with a compression bump and the boundary layer control vents were simplified. The fuselage and empennage trailing edge pattern would also have fewer serrations and the engine thrust lines were toed in at 1.5° off center. The EMD proposal had both single-seat F-23A and two-seat F-23B variants. The naval NATF-23 variant (internally designated DP527),

7076-530: The first operational jet fighters to feature a tailless delta wing when they entered service in 1956. Dassault's interest in the delta wing produced the Dassault Mirage family of combat aircraft, especially the highly successful Mirage III . Amongst other attributes, the Mirage III was the first Western European combat aircraft to exceed Mach 2 in horizontal flight. The tailed delta configuration

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7192-500: The flight control laws using both a large-scale simulator as well as a modified C-131 named the Total In Flight Simulator (TIFS). Throughout Dem/Val, the SPO conducted System Requirements Reviews (SRR) where it reviewed results of performance and cost trade studies with both teams and, if necessary, adjusted requirements and deleted ones that added substantial weight or cost while having marginal value. The ATF

7308-524: The foreplane can increase drag at supersonic speeds and hence reduce the aircraft's maximum speed. Triangular stabilizing fins for rockets were described as early as 1529-1556 by the Austrian military engineer Conrad Haas and in the 17th century by the Polish-Lithuanian military engineer Kazimierz Siemienowicz . However, a true lifting wing in delta form did not appear until 1867, when it

7424-665: The formation of large low pressure vortices over the entire upper wing surface. Its typical landing speed was 170 miles per hour (274 km/h), considerably higher than subsonic airliners. Multiple proposed successors, such as the Zero Emission Hyper Sonic Transport ZEHST), have reportedly adopted a similar configuration to that Concorde's basic design, thus the Delta wing remains a likely candidate for future supersonic civil endeavours. During and after WWII, Francis and Gertrude Rogallo developed

7540-425: The forward bay designed for short range AIM-9 missiles and the aft main bay for AIM-120 missiles and bombs. An M61 rotary cannon would be installed on the left side of the forward fuselage. The F-23's overall length was slightly increased to 70 ft 5 in (21.46 m) while wingspan remained about the same at 43 ft 7 in (13.28 m). Fuselage volume was expanded for more fuel and avionics, with

7656-653: The forward cockpit components of the F-15E Strike Eagle . The proposed production F-23 configuration (DP231 for the F119 engine and DP232 for the F120 engine) for full-scale development, or Engineering and Manufacturing Development (EMD), would have differed from the YF-23 prototypes in several ways. Rather than a single weapons bay, the EMD design would instead have had two tandem bays in the lengthened forward fuselage, with

7772-569: The idea of a flexible wing which could be collapsed for storage. Francis saw an application in spacecraft recovery and NASA became interested. In 1961 Ryan flew the XV-8 , an experimental "flying Jeep" or "fleep". The flexible wing chosen for it was a delta and in use it billowed out into a double-cone profile which gave it aerodynamic stability. Although tested but ultimately never used for spacecraft recovery, this design soon became popular for hang gliders and ultra-light aircraft and has become known as

7888-530: The introduction of ETOPS rules that allowed twin-engine jets to fly long-distance routes that were previously off-limits to them, Airbus was able to further develop the A300 as a medium- to long-range airliner to increased sales; Boeing launched its widebody twinjet, the Boeing 767 , in response. In the 1980s the Boeing 727 was discontinued, as its central engine bay would require a prohibitively expensive redesign to accommodate quieter high-bypass turbofans, and it

8004-449: The largest cargo aircraft capable of transporting outsize cargo , including strategic airlifters . Twin-jets tend to be more fuel-efficient than trijet (three engine) and quad-jet (four engine) aircraft. As fuel efficiency in airliners is a high priority, many airlines have been increasingly retiring trijet and quad-jet designs in favor of twinjets in the twenty-first century. The trijet designs were phased out first, in particular due to

8120-515: The late 1940s, the British aircraft manufacturer Fairey Aviation became interested in the delta wing, its proposals led to the experimental Fairey Delta 1 being produced to Air Ministry Specification E.10/47 . A subsequent experimental aircraft, the Fairey Delta 2 set a new World air speed record on 10 March 1956, achieving 1,132 mph (1,811 km/h) or Mach 1.73. This raised

8236-487: The late 1940s. When used with a T-tail, as in the Gloster Javelin , like other wings a delta wing can give rise to a " deep stall " in which the high angle of attack at the stall causes the turbulent wake of the stalled wing to envelope the tail. This makes the elevator ineffective and the airplane cannot recover from the stall. In the case of the Javelin, a stall warning device was developed and implemented for

8352-461: The leading edge root. This allows air below the leading edge to flow out, up and around it, then back inwards creating a sideways flow pattern similar to subsonic flow. The lift distribution and other aerodynamic characteristics are strongly influenced by this sideways flow. The rearward sweep angle lowers the airspeed normal to the leading edge of the wing, thereby allowing the aircraft to fly at high subsonic , transonic, or supersonic speed, while

8468-428: The leading edge. The sideways effect also leads to an overall reduction in lift and in some circumstances can also lead to an increase in drag. It may be countered through the use of leading-edge slots, wing fences and related devices. With a large enough angle of rearward sweep, in the transonic to low supersonic speed range the wing's leading edge remains behind the shock wave boundary or shock cone created by

8584-402: The main delta wing, this can adversely affect the airflow over the wing and cause unwanted and even dangerous behaviour. In the close-coupled configuration, the canard vortex couples with the main vortex to enhance its benefits and maintain controlled airflow through a wide range of speeds and angles of attack. This allows both improved manoeuvrability and lower stalling speeds, but the presence of

8700-404: The marking on the underside of the black widow spider, further reinforcing the unofficial nickname "Black Widow II" given to the YF-23 because of its 8-lobe radar cross section plot shape that resembled a spider. When Northrop management found out about the marking, they had it removed. A proposed naval variant of the YF-23, sometimes known as the NATF-23 (the design was never formally designated),

8816-410: The more complicated design and maintenance issues of the middle engine mounted on the stabilizer. Early twinjets were not permitted by ETOPS restrictions to fly long-haul trans-oceanic routes, as it was thought that they were unsafe in the event of failure of one engine, so quad-jets were used. Quad-jets also had higher carrying capacity than comparable earlier twinjets. However, later twinjets such as

8932-454: The multinational Eurofighter Typhoon , France's Dassault Rafale , Saab's own Gripen (a successor to the Viggen) and Israel's IAI Kfir . One of the main reasons for its popularity has been the high level of agility in manoeuvring that it is capable of. When supersonic transport (SST) aircraft were developed, the tailless ogival delta wing was chosen for both the Anglo-French Concorde and

9048-444: The name "Delta", used a very gentle angle so that the wing appeared almost straight and the wing tips had to be cropped sharply (see below). His first such delta flew in 1931, followed by four successively improved examples. These prototypes were not easy to handle at low speed and none saw widespread use. During the latter years of World War II , Alexander Lippisch refined his ideas on the high-speed delta, substantially increasing

9164-503: The nose and radome enlarged to accept sensors and mission systems, including the AESA radar . The forward fuselage cross section was more squared off with the forebody chines less pronounced and raised to the same waterline height as the leading edge of the wing. The deletion of thrust reversers enabled the engine nacelles to have a smaller, more rounded cross-section and the trough between them filled in to preserve area-ruling. The edges of

9280-408: The nose of the aircraft, for good visibility for the pilot, and the chiseled shape of the nose generated vortices to improve high angle of attack (AoA) characteristics. The aircraft featured a tricycle landing gear configuration with a nose landing gear leg and two main landing gear legs. The aerial refueling receptacle was centered on the spine of the forward fuselage. A single large weapons bay

9396-473: The optimal balance of stealth and aerodynamic performance. By November 1984, concept exploration had allowed the SPO to narrow its requirements and release the Statement of Operational Need, which called for a 50,000 lb (22,700 kg) takeoff weight fighter with stealth and excellent kinematics, including prolonged supersonic flight without the use of afterburners , or supercruise . In September 1985,

9512-552: The record above 1,000 mph for the first time and broke the previous record by 310 mph, or 37 per cent; never before had the record been raised by such a large margin. In its original tailless form, the thin delta was used extensively by the American aviation company Convair and by the French aircraft manufacturer Dassault Aviation . The supersonic Convair F-102 Delta Dagger and transonic Douglas F4D Skyray were two of

9628-658: The requirement that an aircraft be able to continue a takeoff if an engine fails after the takeoff decision speed is reached. Thus, with all engines operating, trijets must be able to produce at least 150% of the minimum thrust required to climb and quad-jets 133%. Conversely, since a twinjet will lose half of its total thrust if an engine fails, they are required to produce 200% of the minimum thrust required to climb when both engines are operating. Because of this, twinjets typically have higher thrust-to-weight ratios than aircraft with more engines, and are thus able to accelerate and climb faster. Delta wing A delta wing

9744-637: The schematics of which surfaced in the 2010s, was different in many ways due to the requirements of aircraft carrier operations as well as a greater emphasis on long range sensors, weapons, and loiter time for fleet air defense. The diamond wings were located as far back as possible, and the aircraft had ruddervators with more serrations to reduce overall length, folding wing capability for flight deck storage, reinforced landing gear, tailhook and slightly canted canards for increased maneuverability at low speeds to land on aircraft carriers , and two-dimensional thrust vectoring nozzles instead of SERNs. The inlet design

9860-665: The second YF-23 as a display model for its proposed regional bomber aircraft, but this project was dropped because longer range bombers were required. The two YF-23 prototypes are currently exhibits at the National Museum of the United States Air Force and the Western Museum of Flight respectively. American reconnaissance satellites first spotted the advanced Soviet Su-27 and MiG-29 fighter prototypes between 1977 and 1979, which caused concern in

9976-648: The small and light end of the response spectrum. In 1983, the ATF System Program Office (SPO) was formed at Wright-Patterson Air Force Base from the initial Concept Development Team. After discussions with aerospace companies and Tactical Air Command (TAC), the CDT/SPO made air-to-air combat the primary role for the ATF, which would replace the F-15 and emphasize outstanding kinematic performance with supersonic cruise and maneuver. Northrop's response

10092-511: The subject of SPO SRRs with contractors and adjusted during Dem/Val. For example, the infrared search and track (IRST) sensor was dropped from a baseline requirement to provision for future addition in 1989. Formally designated as the YF-23A, the first aircraft ( serial number 87-0800 ), Prototype Air Vehicle 1 (PAV-1), was rolled out on 22 June 1990; PAV-1 took its 50-minute maiden flight on 27 August with chief test pilot Alfred "Paul" Metz at

10208-439: The subsonic lifting characteristics of the airflow over the wing are maintained. Within this flight regime, drooping the leading edge within the shock cone increases lift, but not drag to any significant extent. Such conical leading edge droop was introduced on the production Convair F-102A Delta Dagger at the same time that the prototype design was reworked to include area-ruling . It also appeared on Convair's next two deltas,

10324-416: The surface and also accelerates the airflow, maintaining lift. For intermediate sweep angles, a retractable "moustache" or fixed leading-edge root extension (LERX) may be added to encourage and stabilise vortex formation. The ogee or "wineglass" double-curve, seen for example on Concorde , incorporates this forward extension into the profile of the wing. In this condition, the centre of lift approximates to

10440-662: The sweepback of the wing's leading edge. An experimental glider, the DM-1 , was built to test the aerodynamics of the proposed P.13a high-speed interceptor . Following the end of hostilities, the DM-1 was completed on behalf of the United States and the shipped to Langley Field in Virginia for examination by NACA (National Advisory Committee for Aeronautics, forerunner of today's NASA ) It underwent significant alterations in

10556-463: The tail fins in the same direction. Test pilot Paul Metz stated that the YF-23 had superior high AoA performance compared to legacy aircraft, with trimmed AoA of up to 60°. Deflecting the wing flaps down and ailerons up on both sides simultaneously provided for aerodynamic braking . To keep prototyping costs low despite the novel design, some " commercial off-the-shelf " components were used, including an F-15 nose wheel, F/A-18 main landing gear parts, and

10672-505: The tailless delta are structural simplicity and light weight, combined with low aerodynamic drag. These properties helped to make the Dassault Mirage III one of the most widely manufactured supersonic fighters of all time. A conventional tail stabiliser allows the main wing to be optimised for lift and therefore to be smaller and more highly loaded. Development of aircraft equipped with this configuration can be traced back to

10788-635: The third configuration both engines are within the fuselage, side-by-side, used by most fighters since the 1960s. Later fighters using this configuration include the Su-27 'Flanker', the F-15 Eagle , and the F-22 Raptor . The first twinjet to fly was the German fighter prototype Heinkel He 280 , flying in April 1941 with a pair of nacelled Heinkel HeS 8 axial-flow turbojets. The twinjet configuration

10904-408: The turbulent boundary layer and vent it over the wings. Of the two aircraft built, the first YF-23 (PAV-1) had Pratt & Whitney YF119 engines, while the second (PAV-2) was powered by General Electric YF120 engines. The aircraft had single-expansion ramp nozzles (SERN) and, unlike the YF-22, did not employ thrust vectoring. As on the B-2, the exhaust from the YF-23's engines flowed through troughs in

11020-569: The war, the British developed a number of subsonic jet aircraft that harnessed data gathered from Lippisch's work. One such aircraft, the Avro 707 research aircraft, made its first flight in 1949. British military aircraft such as the Avro Vulcan (a strategic bomber ) and Gloster Javelin (an all-weather fighter) were among the first delta-equipped aircraft to enter production. Whereas the Vulcan

11136-450: The way. On large passenger jets, the cost of the engines makes up a significant proportion of the plane's final cost. Each engine also requires separate service, paperwork, and certificates. Having two larger engines as opposed to three or four smaller engines will typically significantly reduce both the purchase and maintenance costs of a plane. Regulations governing the required thrust levels for transport aircraft are typically based upon

11252-603: The winning companies for the Dem/Val proposals, Northrop was the program lead of the YF-23 team with McDonnell Douglas; the two had previously collaborated on the F/A-18 Hornet . In addition to the government contract awards, the team would eventually invest $ 650 million (~$ 1.45 billion in 2023) combined into their ATF effort; General Electric and Pratt & Whitney, the two engine companies, also invested $ 100 million (~$ 222 million in 2023) each. Airframe fabrication

11368-526: The years, with and without additional stabilising surfaces. The long root chord of the delta wing and minimal area outboard make it structurally efficient. It can be built stronger, stiffer and at the same time lighter than a swept wing of equivalent aspect ratio and lifting capability. Because of this it is easy and relatively inexpensive to build—a substantial factor in the success of the MiG-21 and Mirage aircraft series. Its long root chord also allows

11484-681: Was patented by J.W. Butler and E. Edwards in a design for a low-aspect-ratio, dart-shaped rocket-propelled aeroplane. This was followed by various similarly dart-shaped proposals, such as a biplane version by Butler and Edwards, and a jet-propelled version by the Russian Nicholas de Telescheff . In 1909 a variant with a canard foreplane was experimented with by the Spanish sculptor Ricardo Causarás. Also in 1909, British aeronautical pioneer J. W. Dunne patented his tailless stable aircraft with conical wing development. The patent included

11600-514: Was a Mach 2+ fighter design designated N-360 with delta wings , a single vertical tail, and twin engines with thrust vectoring nozzles and thrust reversers . Around this time, however, the SPO would begin to increasingly emphasize stealth for survivability and combat effectiveness due to very low radar cross section (RCS) results from the Air Force's " black world " innovations such as the Have Blue / F-117 (" Senior Trend "), Tacit Blue , and

11716-439: Was a classic tailless design, the Javelin incorporated a tailplane in order to improve low-speed handling and high-speed manoeuvrability, as well as to allow a greater centre of gravity range. Gloster proposed a refinement of the Javelin that would have, amongst other changes, decreased wing thickness in order to achieve supersonic speeds of up to Mach 1.6. The American aerodynamicist Robert T. Jones , who worked at NACA during

11832-470: Was a significant advantage, especially in contrast to Lockheed's immature design, but the Lockheed proposal's focus on systems engineering rather than a point aircraft design actually pulled it ahead. Both teams were awarded $ 691 million in FY 1985 dollars (~$ 1.66 billion in 2023) and given 50 months to build and flight-test their prototypes. Pratt & Whitney and General Electric were contracted to develop

11948-531: Was adopted by the TsAGI (Central Aero and Hydrodynamic Institute, Moscow ), to improve high angle-of-attack handling, manoeuvrability and centre of gravity range over a pure delta planform. The Mikoyan-Gurevich MiG-21 ("Fishbed") became the most widely built combat aircraft of the 1970s. Through the 1960s, the Swedish aircraft manufacturer Saab AB developed a close-coupled canard delta configuration, placing

12064-545: Was also different, being a quarter circle with serrations and a bumped compression surface. The internal weapons bay was split into two compartments by a bulkhead along the centerline in the forward fuselage to strengthen the aircraft's keel and would have accommodated the Navy's planned AIM-152 advanced air-to-air missiles (AAAM) as well as potentially the AGM-88 HARM and AGM-84 Harpoon . The bay doors would carry AIM-9 missiles and an M61 rotary cannon would be installed in

12180-405: Was considered as an F-14 Tomcat replacement. The original YF-23 design was first considered but would have had issues with flight deck space, handling, storage, landing, and catapult launching, thus necessitating a different design. By 1989, the design was narrowed down to two possible configurations, DP533 with four tails and DP527 with two tails and canards . DP527 was eventually determined to be

12296-765: Was divided roughly evenly, with Northrop building the aft fuselage and empennage in Hawthorne, California and performing final assembly at Edwards Air Force Base while McDonnell Douglas built the wings and forward fuselage in St. Louis, Missouri . Manufacturing was greatly assisted by the use of computer-aided design software. However, the YF-23 design would largely be a continual refinement from Northrop's DP110 with little influence from McDonnell Douglas's design, which had swept trapezoidal wings, four empennage surfaces, and chin-mounted split wedge inlets and did not perform well for stealth. The YF-23's design evolved into DP117K when it

12412-465: Was frozen as the prototype configuration in January 1988, with changes including a sharper and more voluminous nose from the earlier "platypus" shape for better radar performance and a strengthened aft deck with lower drag shaping. Due to the complex surface curvature, the aircraft was built outside-in, with the large composite skin structures fabricated first before the internal members. To ensure precise and responsive handling, Northrop developed and tested

12528-448: Was initially required to land and stop within 2,000 feet (610 m), which meant the use of thrust reversers on their engines. In 1987, the USAF changed the runway length requirement to 3,000 feet (910 m) and by 1988 the requirement for thrust reversers was no longer needed. This allowed Northrop to have smaller engine nacelle housings with the space between them filled in to preserve area ruling in subsequent design refinements for

12644-477: Was its submission for the Dem/Val RFP. In July 1986, proposals for Dem/Val were submitted by Lockheed, Boeing, General Dynamics, McDonnell Douglas, Northrop, Grumman and North American Rockwell ; the latter two dropped out of the competition shortly thereafter. As contractors were expected to make significant investments for technology development, companies forming teams was encouraged by the SPO. Following proposal submissions, Northrop and McDonnell Douglas formed

12760-604: Was meant as a demonstrator for the airframe and propulsion system design and thus did not mount any mission systems avionics of the PSC. Instead, Northrop and McDonnell Douglas tested these systems on ground and airborne laboratories with Northrop using a modified BAC One-Eleven as a flying avionics laboratory and McDonnell Douglas building the Avionics Ground Prototype (AGP) to evaluate software and hardware performance and reliability. Avionics requirements were also

12876-445: Was placed on the underside of the fuselage between the nose and main landing gear. The cockpit had a center stick and side throttle. It was powered by two turbofan engines, with each in a separate engine nacelle with S-ducts to shield engine axial compressors from radar waves, on either side of the aircraft's spine. The fixed-geometry inlets were trapezoidal in frontal profile, with special porous suction panels in front to absorb

12992-723: Was recruited in 1985 as the chief scientist. Three design concepts were studied: the Agile Maneuverable Fighter (AMF) similar to N-360 with two canted vertical tails and the best aerodynamic performance of the three while having minimal stealth, Ultra Stealth Fighter (USF) that emphasized maximum stealth through edge alignment with only four RCS lobes and nicknamed "Christmas Tree" for its planform shape, and High Stealth Fighter (HSF) that balanced stealth and maneuverability with diamond wings , all-moving V-tail " ruddervators " (or butterfly tails), engine exhaust troughs, and aligned edges. HSF would take many design cues from

13108-656: Was soon supplanted by twinjets for the narrow-body market; Airbus with the A320 , and Boeing with the 757 and updated "classic" variants of the 737 . During that decade only McDonnell Douglas continued development of the trijet design with an update to the DC-10 , the MD-11 , which initially had a range advantage over its closest medium wide-body competitors which were twinjets, the in-production Boeing 767 and Airbus A300/A310. In contrast to McDonnell Douglas sticking with their existing trijet configuration, Airbus (which never produced

13224-512: Was speculation that it could offer a modernized version of the F-23 to the JASDF, while Lockheed Martin offered an airframe derived from the F-22; Japan ultimately did not select these proposals due to costs and industrial work-share concerns. The first YF-23, with Pratt & Whitney engines, supercruised at Mach 1.43 on 18 September 1990, while the second, with General Electric engines, reached Mach 1.72 on 29 November 1990. By comparison,

13340-410: Was subsequently increased to 60,000 lb (27,200 kg) while engine thrust was increased from 30,000 lbf (133 kN) class to 35,000 lbf (156 kN) class. Aside from advances in air vehicle and engine design, the ATF also required innovations in avionics and sensor systems with the goal of achieving sensor fusion to enhance situational awareness and reduce pilot workload. The YF-23

13456-484: Was used for short-range narrow-bodied aircraft such as the McDonnell Douglas DC-9 and Boeing 737 . The Airbus A300 was initially not successful when first produced as a short-range widebody, as airlines operating the A300 on short-haul routes had to reduce frequencies to try and fill the high-capacity aircraft, and lost passengers to airlines operating more frequent narrow-body flights. However, after

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