McDonnell Douglas F/A-18 Hornet

McDonnell Douglas F/A-18 Hornet

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The McDonnell Douglas F/A-18 Hornet is a twin-engine, supersonic, all-weather, carrier-capable, multirole combat jet, designed as both a fighter and attack aircraft (hence the F/A designation). Designed by McDonnell Douglas (now Boeing) and Northrop, the F/A-18 was derived from the latter’s YF-17 in the 1970s for use by the United States Navy and Marine Corps. The Hornet is also used by the air forces of several other nations, and since 1986, by the U.S. Navy’s Flight Demonstration Squadron, the Blue Angels.

The F/A-18 has a top speed of Mach 1.8 (1,034 knots, 1,190 mph or 1,915 km/h at 40,000 ft or 12,200 m). It can carry a wide variety of bombs and missiles, including air-to-air and air-to-ground, supplemented by the 20-mm M61 Vulcan cannon. It is powered by two General Electric F404 turbofan engines, which give the aircraft a high thrust-to-weight ratio. The F/A-18 has excellent aerodynamic characteristics, primarily attributed to its leading-edge extensions. The fighter’s primary missions are fighter escort, fleet air defense, suppression of enemy air defenses, air interdiction, close air support, and aerial reconnaissance. Its versatility and reliability have proven it to be a valuable carrier asset, though it has been criticized for its lack of range and payload compared to its earlier contemporaries, such as the Grumman F-14 Tomcat in the fighter and strike fighter role, and the Grumman A-6 Intruder and LTV A-7 Corsair II in the attack role.

The Hornet first saw combat action during the 1986 United States bombing of Libya and subsequently participated in the 1991 Gulf War and 2003 Iraq War. The F/A-18 Hornet served as the baseline for the Boeing F/A-18E/F Super Hornet, its larger, evolutionary redesign.

Development

Origins

The U.S. Navy started the Naval Fighter-Attack, Experimental (VFAX) program to procure a multirole aircraft to replace the Douglas A-4 Skyhawk, the A-7 Corsair II, and the remaining McDonnell Douglas F-4 Phantom IIs, and to complement the F-14 Tomcat. Vice Admiral Kent Lee, then head of Naval Air Systems Command, was the lead advocate for the VFAX against strong opposition from many Navy officers, including Vice Admiral William D. Houser, deputy chief of naval operations for air warfare – the highest-ranking naval aviator.[3]

In August 1973, Congress mandated that the Navy pursue a lower-cost alternative to the F-14. Grumman proposed a stripped F-14 designated the F-14X, while McDonnell Douglas proposed a naval variant of the F-15, but both were nearly as expensive as the F-14.[4] That summer, Secretary of Defense James R. Schlesinger ordered the Navy to evaluate the competitors in the Air Force’s Lightweight Fighter (LWF) program, the General Dynamics YF-16 and Northrop YF-17.[5] The Air Force competition specified a day fighter with no strike capability. In May 1974, the House Armed Services Committee redirected $34 million from the VFAX to a new program, the Navy Air Combat Fighter (NACF),[5] intended to make maximum use of the technology developed for the LWF program.[4]

Redesigning the YF-17

Though the YF-16 won the LWF competition, the Navy was skeptical that an aircraft with one engine and narrow landing gear could be easily or economically adapted to carrier service, and refused to adopt an F-16 derivative. On 2 May 1975, the Navy announced its selection of the YF-17.[6] Since the LWF did not share the design requirements of the VFAX, the Navy asked McDonnell Douglas and Northrop to develop a new aircraft from the design and principles of the YF-17. On 1 March 1977, Secretary of the Navy W. Graham Claytor announced that the F-18 would be named “Hornet”.[4]

Northrop had partnered with McDonnell Douglas as a secondary contractor on NACF to capitalize on the latter’s experience in building carrier aircraft, including the widely used F-4 Phantom II. On the F-18, the two companies agreed to evenly split component manufacturing, with McDonnell Douglas conducting final assembly. McDonnell Douglas would build the wings, stabilators, and forward fuselage; while Northrop would build the center and aft fuselage and vertical stabilizers. McDonnell Douglas was the prime contractor for the naval versions, and Northrop would be the prime contractor for the F-18L land-based version which Northrop hoped to sell on the export market.[4][5]

The F-18, initially known as McDonnell Douglas Model 267, was drastically modified from the YF-17. For carrier operations, the airframe, undercarriage, and tailhook were strengthened, folding wings and catapult attachments were added, and the landing gear was widened.[7] To meet Navy range and reserves requirements, McDonnell increased fuel capacity by 4,460 pounds (2,020 kg), by enlarging the dorsal spine and adding a 96-gallon fuel tank to each wing. A “snag” was added to the wing’s leading edge and stabilators to prevent an aeroelastic flutter discovered in the F-15 stabilator. The wings and stabilators were enlarged, the aft fuselage widened by 4 inches (102 mm), and the engines canted outward at the front. These changes added 10,000 lb (4,540 kg) to the gross weight, bringing it to 37,000 lb (16,800 kg). The YF-17’s control system was replaced with a fully digital fly-by-wire system with quadruple redundancy, the first to be installed in a production fighter.[7]

Originally, plans were to acquire a total of 780 aircraft of three variants: the single-seat F-18A fighter and A-18A attack aircraft, differing only in avionics, and the dual-seat TF-18A, which retained full mission capability of the F-18 with a reduced fuel load.[8] Following improvements in avionics and multifunction displays, and a redesign of external stores stations, the A-18A and F-18A were able to be combined into one aircraft.[4] Starting in 1980, the aircraft began to be referred to as the F/A-18A, and the designation was officially announced on 1 April 1984. The TF-18A was redesignated F/A-18B.[4]

Northrop’s F-18L

Northrop developed the F-18L as a potential export aircraft. Since it was not strengthened for carrier service, it was expected to be lighter and better performing, and a strong competitor to the F-16 Fighting Falcon then being offered to American allies. The F-18L’s normal gross weight was lighter than the F/A-18A by 7,700 pounds (3,490 kg), via lighter landing gear, lack of wing folding mechanism, reduced part thickness in areas, and lower fuel-carrying capacity. Though the aircraft retained a lightened tailhook, the most obvious external difference was removed “snags” on the leading edge of the wings and stabilators. It still retained 71% commonality with the F/A-18 by parts weight, and 90% of the high-value systems, including the avionics, radar, and electronic countermeasure suite, though alternatives were offered. Unlike the F/A-18, the F-18L carried no fuel in its wings and lacked weapons stations on the intakes. It had three underwing pylons on each side, instead.[9]

The F/A-18L version followed to coincide with the US Navy’s F/A-18A as a land-based export alternative. This was essentially an F/A-18A lightened by about 2,500 to 3,000 pounds (1,130 to 1,360 kg); weight was reduced by removing the folding wing and associated actuators, implementing a simpler landing gear (single wheel nose gear and cantilever oleo main gear), and changing to a land-based tail hook. The revised F/A-18L included wing fuel tanks and fuselage stations of the F/A-18A. Its weapons capacity would increase from 13,700 to 20,000 pounds (6,210 to 9,070 kg), largely due to the addition of a third underwing pylon and strengthened wingtips (11 stations in total vs 9 stations of the F/A-18A). Compared to the F-18L, the outboard weapons pylons are moved closer to the wingtip missile rails. Because of the strengthened nonfolding wing, the wingtip missile rails were designed to carry either the AIM-7 Sparrow or Skyflash medium-range air-to-air missiles, in addition to the AIM-9 Sidewinder as found on the F/A-18A. The F/A-18L was strengthened for a 9 g design load factor compared to the F/A-18A’s 7.5 g factor.[10]

The partnership between McDonnell Douglas and Northrop soured over competition for foreign sales for the two models. Northrop felt that McDonnell Douglas would put the F/A-18 in direct competition with the F-18L. In October 1979, Northrop filed a series of lawsuits charging that McDonnell was using Northrop technology developed for the F-18L for foreign sales of the F/A-18 in violation of their agreement, and asked for a moratorium on foreign sales of the Hornet. McDonnell Douglas countersued, alleging Northrop illegally used F/A-18 technology in its F-20 Tigershark. A settlement was announced 8 April 1985 for all of the lawsuits.[11][12][13][14] McDonnell Douglas paid Northrop $50 million for “rights to sell the F/A-18 wherever it could”.[14] Additionally, the companies agreed on McDonnell Douglas as the prime contractor with Northrop as the principal subcontractor.[11][12][13][14] As principal subcontractor, Northrop will produce the rear section for the F/A-18 (A/B/C/D/E/F), while McDonnell Douglas will produce the rest with final assembly to be performed by McDonnell Douglas.[15] At the time of the settlement, Northrop had ceased work on the F-18L. Most export orders for the F18-L were captured by the F-16 or the F/A-18.[9] The F-20 Tigershark did not enter production, and although the program was not officially terminated until 17 November 1986, it was dead by mid-1985.[16]

Into production

During flight testing, the snag on the leading edge of the stabilators was filled in, and the gap between the leading-edge extensions (LEX) and the fuselage was mostly filled in. The gaps, called the boundary layer air discharge slots, controlled the vortices generated by the LEX and presented clean air to the vertical stabilizers at high angles of attack, but they also generated a great deal of parasitic drag, worsening the problem of the F/A-18’s inadequate range. McDonnell filled in 80% of the gap, leaving a small slot to bleed air from the engine intake. This may have contributed to early problems with fatigue cracks appearing on the vertical stabilizers due to extreme structural loads, resulting in a short grounding in 1984 until the stabilizers were strengthened. Starting in May 1988, a small vertical fence was added to the top of each LEX to broaden the vortices and direct them away from the vertical stabilizers. This also provided a minor increase in controllability as a side effect.[17] F/A-18s of early versions had a problem with insufficient rate of roll, exacerbated by the insufficient wing stiffness, especially with heavy underwing ordnance loads.

The first production F/A-18A flew on 12 April 1980. After a production run of 380 F/A-18As[18] (including the nine assigned to flight systems development), manufacture shifted to the F/A-18C in September 1987.[8]

Improvements and design changes

In the 1990s, the U.S. Navy faced the need to replace its aging A-6 Intruders and A-7 Corsair IIs with no replacement in development.[19] To answer this deficiency, the Navy commissioned development of the F/A-18E/F Super Hornet. Despite its designation, it is not just an upgrade of the F/A-18 Hornet, but rather, a new, larger airframe using the design concepts of the Hornet.

Hornets and Super Hornets will serve complementary roles in the U.S. Navy carrier fleet until the Hornet A-D models are completely replaced by the F-35C Lightning II. The Marines have chosen to extend the use of certain F/A-18s up to 10,000 flight hours, due to delays in the F-35B variant.[20]

Design

The F/A-18 is a twin engine, midwing, multimission tactical aircraft. It is highly maneuverable, owing to its good thrust-to-weight ratio, digital fly-by-wire control system, and leading-edge extensions, which allow the Hornet to remain controllable at high angles of attack. The trapezoidal wing has a 20-degree sweepback on the leading edge and a straight trailing edge. The wing has full-span, leading-edge flaps and the trailing edge has single-slotted flaps and ailerons over the entire span.[21]

Canted vertical stabilizers are another distinguishing design element, one among several other such elements that enable the Hornet’s excellent high angle of attack ability, including oversized horizontal stabilators, oversized trailing-edge flaps that operate as flaperons, large full-length leading-edge slats, and flight control computer programming that multiplies the movement of each control surface at low speeds and moves the vertical rudders inboard instead of simply left and right. The Hornet’s normally high angle of attack performance envelope was put to rigorous testing and enhanced in the NASA F-18 High Alpha Research Vehicle (HARV). NASA used the F-18 HARV to demonstrate flight handling characteristics at high angle-of-attack (alpha) of 65–70 degrees using thrust vectoring vanes.[22] F/A-18 stabilators were also used as canards on NASA’s F-15S/MTD.

The Hornet was among the first aircraft to heavily use multifunction displays, which at the switch of a button allow a pilot to perform either fighter or attack roles or both. This “force multiplier” ability gives the operational commander more flexibility to employ tactical aircraft in a fast-changing battle scenario. It was the first Navy aircraft to incorporate a digital multiplexing avionics bus, enabling easy upgrades.[8]

The Hornet is also notable for having been designed to reduce maintenance, and as a result, has required far less downtime than its heavier counterparts, the F-14 Tomcat and the A-6 Intruder. Its mean time between failures is three times greater than any other Navy strike aircraft, and requires half the maintenance time.[8] Its General Electric F404 engines were also innovative in that they were designed with operability, reliability, and maintainability first. The engine, while unexceptional in rated performance, demonstrates exceptional robustness under various conditions and is resistant to stall and flameout.[23] The F404 engine connects to the airframe at only 10 points and can be replaced without special equipment; a four-person team can remove the engine within 20 minutes.[24]

The engine air inlets of the Hornet, like that of the F-16, are of a simpler “fixed” design, while those of the F-4, F-14, and F-15 have variable geometry or variable intake ramp air inlets. This is a speed-limiting factor in the Hornet design. Instead, the Hornet uses bleed-air vents on the inboard surface of the engine air intake ducts to slow and reduce the amount of air reaching the engine. While not as effective as variable geometry, the bleed-air technique functions well enough to achieve near Mach 2 speeds, which is within the designed mission requirements.[25]

A 1989 USMC study found that single-seat fighters were well suited to air-to-air combat missions, while dual-seat fighters were favored for complex strike missions against heavy air and ground defenses in adverse weather—the question being not so much as to whether a second pair of eyes would be useful, but as to having the second crewman sit in the same fighter or in a second fighter. Single-seat fighters that lacked wingmen were shown to be especially vulnerable.[26]

The F/A-18 provides automatic alerts via audio messages to the pilot.[27]

Specifications (F/A-18C/D)

General characteristics

  • Crew: 1 (C)/2 (D – pilot and weapon systems officer)
  • Length: 56 ft 1 in (17.1 m)
  • Wingspan: 40 ft 4 in (12.3 m) with AIM-9 Sidewinders on wingtip LAU-7 launchers
  • Width: 32 ft 7 in (9.94 m) wing folded
  • Height: 15 ft 5 in (4.7 m)
  • Wing area: 410 sq ft (38 m2)
  • Aspect ratio: 4
  • Airfoil: root:NACA 65A005 mod.; tip:NACA 65A003.5 mod.
  • Empty weight: 23,000 lb (10,433 kg)
  • Gross weight: 36,970 lb (16,769 kg)
  • Max takeoff weight: 51,900 lb (23,541 kg)
  • Fuel capacity: 10,860 pounds (4,930 kg) internally
  • Powerplant: 2 × General Electric F404-GE-402 afterburning turbofan engines, 11,000 lbf (49 kN) thrust each dry, 17,750 lbf (79.0 kN) with afterburner

Performance

  • Maximum speed: 1,034 kn (1,190 mph; 1,915 km/h) at 40,000 ft (12,000 m)
  • Maximum speed: Mach 1.8
  • Cruise speed: 574 kn; 1,062 km/h (660 mph)
  • Range: 1,089 nmi (1,253 mi; 2,017 km)
  • Ferry range: 1,800 nmi (2,071 mi; 3,334 km)
  • Service ceiling: 50,000 ft (15,000 m)
  • Rate of climb: 50,000 ft/min (250 m/s)
  • Wing loading: 93 lb/sq ft (450 kg/m2)
  • Thrust/weight: 0.96 (1.13 with loaded weight at 50% internal fuel)

Armament

  • Guns:20 mm (0.787 in) M61A1 Vulcan nose mounted 6-barrel rotary cannon, 578 rounds
  • Hardpoints: 9 total: 2× wingtips missile launch rail, 4× under-wing, and 3× under-fuselage with a capacity of 13,700 lb (6,200 kg) external fuel and ordnance,with provisions to carry combinations of:

o    Rockets:

  • 2.75 in (70 mm) Hydra 70 rockets
  • 5 in (127.0 mm) Zuni rockets

o    Missiles:

o    Bombs:

o    Other:

Avionics

  • Hughes APG-73 radar
  • ROVER (Remotely Operated Video Enhanced Receiver) antenna for use by U.S. Navy‘s F/A-18C strike fighter squadrons

 

 

 

 

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