December 15 / F-35 Lightning II first flight
Lockheed Martin F-35 Lightning II
US Air Force conventional takeoff and landing (CTOL) variant the F-35A
The Lockheed Martin F-35 Lightning II is an American family of single-seat, single-engine, all-weather stealth multirole combat aircraft that is intended to perform both air superiority and strike missions. It is also able to provide electronic warfare and intelligence, surveillance, and reconnaissance capabilities. Lockheed Martin is the prime F-35 contractor, with principal partners Northrop Grumman and BAE Systems. The aircraft has three main variants: the conventional takeoff and landing (CTOL) F-35A, the short take-off and vertical landing (STOVL) F-35B, and the carrier-based (CV/CATOBAR) F-35C.
The aircraft descends from the Lockheed Martin X-35, which in 2001 beat the Boeing X-32 to win the Joint Strike Fighter (JSF) program. Its development is principally funded by the United States, with additional funding from program partner countries from NATO and close U.S. allies, including the United Kingdom, Australia, Canada, Italy, Norway, Denmark, the Netherlands, and formerly Turkey. Several other countries have also ordered, or are considering ordering, the aircraft. The program has drawn much scrutiny and criticism for its unprecedented size, complexity, ballooning costs, and much-delayed deliveries. The acquisition strategy of concurrent production of the aircraft, while it was still in development and testing, led to expensive design changes and retrofits.
The F-35 first flew in 2006 and entered service with the U.S. Marine Corps F-35B in July 2015, followed by the U.S. Air Force F-35A in August 2016 and the U.S. Navy F-35C in February 2019. The aircraft was first used in combat in 2018 by the Israeli Air Force. The U.S. plans to buy 2,456 F-35s through 2044, which will represent the bulk of the crewed tactical aviation of the U.S. Air Force, Navy, and Marine Corps for several decades; the aircraft is planned to be a cornerstone of NATO and U.S.-allied air power and to operate until 2070.
Royal Air Force short takeoff and vertical landing (STOVL) variant the F-35B
Design
Overview
The F-35 is a family of single-engine, supersonic, stealth multirole fighters. The second fifth-generation fighter to enter US service and the first operational supersonic STOVL stealth fighter, the F-35 emphasizes low observables, advanced avionics and sensor fusion that enable a high level of situational awareness and long-range lethality; the USAF considers the aircraft its primary strike fighter for conducting suppression of enemy air defence (SEAD) missions, owing to the advanced sensors and mission systems.
The F-35 has a wing-tail configuration with two vertical stabilizers canted for stealth. Flight control surfaces include leading-edge flaps, flaperons, rudders, and all-moving horizontal tails (stabilators); leading-edge root extensions also run forwards to the inlets. The relatively short 35-foot wingspan of the F-35A and F-35B is set by the requirement to fit inside USN amphibious assault ship parking areas and elevators; the F-35C's larger wing is more fuel efficient. The fixed diverterless supersonic inlets (DSI) use a bumped compression surface and forward-swept cowl to shed the boundary layer of the forebody away from the inlets, which form a Y-duct for the engine. Structurally, the F-35 drew upon lessons from the F-22; composites comprise 35% of airframe weight, with the majority being bismaleimide and composite epoxy materials as well as some carbon nanotube-reinforced epoxy in later production lots. The F-35 is considerably heavier than the lightweight fighters it replaces, with the lightest variant having an empty weight of 29,300 lb (13,300 kg); much of the weight can be attributed to the internal weapons bays and the extensive avionics carried.
While lacking the raw performance of the larger twin-engine F-22, the F-35 has kinematics competitive with fourth-generation fighters such as the F-16 and F/A-18, especially with ordnance mounted because the F-35's internal weapons carriage eliminates parasitic drag from external stores. All variants have a top speed of Mach 1.6, attainable with a full internal payload. The powerful F135 engine gives good subsonic acceleration and energy, with a supersonic dash in the afterburner. The large stabilators, leading edge extensions and flaps, and canted rudders provide excellent high alpha (angle-of-attack) characteristics, with a trimmed alpha of 50°. Relaxed stability and fly-by-wire controls provide excellent handling qualities and departure resistance. Having over double the F-16's internal fuel, the F-35 has a considerably greater combat radius, while stealth also enables a more efficient mission flight profile.
US Marines carrier-based (CV/CATOBAR) variant the F-35C
F-35A with all weapon bay doors open
Avionics and sensor
The F-35's mission systems are among the most complex aspects of the aircraft. The avionics and sensor fusion are designed to enhance the pilot's situational awareness and command and control capabilities and facilitate network-centric warfare. Key sensors include the Northrop Grumman AN/APG-81 active electronically scanned array (AESA) radar, BAE Systems AN/ASQ-239 Barracuda electronic warfare system, Northrop Grumman/Raytheon AN/AAQ-37 Distributed Aperture System (DAS), Lockheed Martin AN/AAQ-40 Electro-Optical Targeting System (EOTS) and Northrop Grumman AN/ASQ-242 Communications, Navigation, and Identification (CNI) suite. The F-35 was designed with sensor intercommunication to provide a cohesive image of the local battlespace and availability for any possible use and combination with one another; for example, the APG-81 radar also acts as a part of the electronic warfare system.
Much of the F-35's software was developed in C and C++ programming languages, while Ada83 code from the F-22 was also used; the Block 3F software has 8.6 million lines of code. The Green Hills Software Integrity DO-178B real-time operating system (RTOS) runs on integrated core processors (ICPs); data networking includes the IEEE 1394b and Fibre Channel buses. To enable fleet software upgrades for the software-defined radio systems and greater upgrade flexibility and affordability, the avionics leverage commercial off-the-shelf (COTS) components when practical. The mission systems software, particularly for sensor fusion, was one of the program's most difficult parts and was responsible for substantial program delays.
The APG-81 radar uses electronic scanning for rapid beam agility and incorporates passive and active air-to-air modes, strike modes, and synthetic aperture radar (SAR) capability, with multiple target track-while-scan at ranges in excess of 80 nmi (150 km). The antenna is tilted backwards for stealth. Complementing the radar is the AAQ-37 DAS, which consists of six infrared sensors that provide all-aspect missile launch warning and target tracking; the DAS acts as a situational awareness infrared search-and-track (SAIRST) and gives the pilot spherical infrared and night-vision imagery on the helmet visor. The ASQ-239 Barracuda electronic warfare system has ten radio frequency antennas embedded into the edges of the wing and tail for an all-aspect radar warning receiver (RWR). It also provides sensor fusion of radio frequency and infrared tracking functions, geolocation threat targeting, and multispectral image countermeasures for self-defence against missiles. The electronic warfare system is capable of detecting and jamming hostile radars. The AAQ-40 EOTS is mounted internally behind a faceted low-observable window under the nose and performs laser targeting, forward-looking infrared (FLIR), and long-range IRST functions. The ASQ-242 CNI suite uses a half dozen different physical links, including the directional Multifunction Advanced Data Link (MADL), for covert CNI functions. Through sensor fusion, information from radio frequency receivers and infrared sensors are combined to form a single tactical picture for the pilot. The all-aspect target direction and identification can be shared via MADL to other platforms without compromising low observability, while Link 16 is present for communication with legacy systems.
The F-35 was designed from the outset to incorporate improved processors, sensors, and software enhancements over its lifespan. Technology Refresh 3, which includes a new core processor and a new cockpit display, is planned for Lot 15 aircraft. Lockheed Martin has offered the Advanced EOTS for the Block 4 configuration; the improved sensor fits into the same area as the baseline EOTS with minimal changes. In June 2018, Lockheed Martin picked Raytheon for improved DAS. The USAF has studied the potential for the F-35 to orchestrate attacks by unmanned combat aerial vehicles (UCAVs) via its sensors and communications equipment.
Royal Netherlands Air Force F-35A during Frisian Flag 2022
Royal Air Force F-35B in hover at RIAT 2016
Cockpit
The glass cockpit was designed to give the pilot good situational awareness. The main display is a 20- by 8-inch (50 by 20 cm) panoramic touchscreen, which shows flight instruments, stores management, CNI information, and integrated caution and warnings; the pilot can customize the arrangement of the information. Below the main display is a smaller stand-by display. The cockpit has a speech-recognition system developed by Adacel. The F-35 does not have a head-up display; instead, flight and combat information is displayed on the visor of the pilot's helmet in a helmet-mounted display system (HMDS). The one-piece tinted canopy is hinged at the front and has an internal frame for structural strength. The Martin-Baker US16E ejection seat is launched by a twin-catapult system housed on side rails. There is a right-hand side stick and throttle hands-on throttle-and-stick system. For life support, an onboard oxygen-generation system (OBOGS) is fitted and powered by the Integrated Power Package (IPP), with an auxiliary oxygen bottle and backup oxygen system for emergencies.
The Vision Systems International helmet display is a key piece of the F-35's human-machine interface. Instead of the head-up display mounted atop the dashboard of earlier fighters, the HMDS puts flight and combat information on the helmet visor, allowing the pilot to see it no matter which way they are facing. Infrared and night vision imagery from the Distributed Aperture System can be displayed directly on the HMDS and enables the pilot to "see through" the aircraft. The HMDS allows an F-35 pilot to fire missiles at targets even when the nose of the aircraft is pointing elsewhere by cuing missile seekers at high angles off-boresight. Each helmet costs $400,000. The HMDS weighs more than traditional helmets, and there is concern that it can endanger lightweight pilots during ejection.
Due to the HMDS's vibration, jitter, night-vision and sensor display problems during development, Lockheed Martin and Elbit issued a draft specification in 2011 for an alternative HMDS based on the AN/AVS-9 night vision goggles as backup, with BAE Systems chosen later that year. A cockpit redesign would be needed to adopt an alternative HMDS. Following progress on the baseline helmet, development on the alternative HMDS was halted in October 2013. In 2016, the Gen 3 helmet with improved night vision camera, new liquid crystal displays, automated alignment and software enhancements was introduced with LRIP lot 7.
US Air Force F-35A in flight
Italian Air Force F-35A and F-35B at the Jesolo Airshow 2022
Engine
The single-engine aircraft is powered by the Pratt & Whitney F135 low-bypass augmented turbofan with rated thrust of 43,000 lbf (191 kN). Derived from the Pratt & Whitney F119 used by the F-22, the F135 has a larger fan and higher bypass ratio to increase subsonic thrust and fuel efficiency, and unlike the F119, is not optimized for supercruise. The engine contributes to the F-35's stealth by having a low-observable augmenter, or afterburner, that incorporates fuel injectors into thick curved vanes; these vanes are covered by ceramic radar-absorbent materials and mask the turbine. The stealthy augmenter had problems with pressure pulsations, or "screech", at low altitudes and high speed early in its development. The low-observable axisymmetric nozzle consists of 15 partially overlapping flaps that create a sawtooth pattern at the trailing edge, which reduces the radar signature and creates shed vortices that reduce the infrared signature of the exhaust plume. Due to the engine's large dimensions, the USN had to modify its underway replenishment system to facilitate at-sea logistics support. The F-35's Integrated Power Package (IPP) performs power and thermal management and integrates environment control, auxiliary power unit, engine starting, and other functions into a single system.
The F135-PW-600 variant for the F-35B incorporates the Shaft-Driven Lift Fan (SDLF) to allow STOVL operations. Designed by Lockheed Martin and developed by Rolls-Royce, the SDLF, also known as the Rolls-Royce LiftSystem, consists of the lift fan, drive shaft, two roll posts, and a "three-bearing swivel module" (3BSM). The thrust vectoring 3BSM nozzle allows the main engine exhaust to be deflected downward at the tail of the aircraft and is moved by a "fueldraulic" actuator that uses pressurized fuel as the working fluid. Unlike the Harrier's Pegasus engine that entirely uses direct engine thrust for lift, the F-35B's system augments the swivel nozzle's thrust with the lift fan; the fan is powered by the low-pressure turbine through a drive shaft when engaged with a clutch and placed near the front of the aircraft to provide a counterbalancing thrust. Roll control during slow flight is achieved by diverting unheated engine bypass air through wing-mounted thrust nozzles called roll posts.
An alternative engine, the General Electric/Rolls-Royce F136, was being developed in the 2000s; originally, F-35 engines from Lot 6 onward were competitively tendered. Using technology from the General Electric YF120, the F136 was claimed to have a greater temperature margin than the F135 due to the higher mass flow design making full use of the inlet. The F136 was cancelled in December 2011 due to a lack of funding.
The F-35 is expected to receive propulsion upgrades over its lifecycle to adapt to emerging threats and enable additional capabilities. In 2016, the Adaptive Engine Transition Program (AETP) was launched to develop and test adaptive cycle engines, with one major potential application being the re-engining of the F-35; in 2018, both GE and P&W were awarded contracts to develop 45,000 lbf (200 kN) thrust class demonstrators, with the designations XA100 and XA101 respectively. In addition to potential re-engining, P&W also plans to improve the baseline F135; in 2017, P&W announced the F135 Growth Option 1.0 and 2.0; Growth Option 1.0 was a drop-in power module upgrade that offered 6–10% thrust improvement and 5–6% fuel burn reduction, while Growth Option 2.0 would be the adaptive cycle XA101. In 2020, P&W shifted its F135 upgrade plan from the Growth Options to a series of Engine Enhancement Packages along with some additional capabilities, while the XA101 became a separate clean-sheet design. The capability packages are planned to be incorporated in two-year increments starting in the mid-2020s.
In December of 2020, GE's XA100 (A100) completed its first successful run. GE's detailed design was completed in February 2019, and initial testing at GE's high-altitude test facility in Evendale, Ohio was concluded in May 2021. GE expects that the A100 can enter service with the F-35A and C in 2027 at the earliest.
Italian Air Force F-35A leading the pair of AMX’s
Swiss Air Force F/A-18 Hornets leading the Italian Air Force F-35A at Axalp22
Armament
To preserve its stealth shaping, the F-35 has two internal weapons bays with four weapons stations. The two outboard weapon stations each can carry ordnance up to 2,500 lb (1,100 kg), or 1,500 lb (680 kg) for the F-35B, while the two inboard stations carry air-to-air missiles. Air-to-surface weapons for the outboard station include the Joint Direct Attack Munition (JDAM), Paveway series of bombs, Joint Standoff Weapon (JSOW), and cluster munitions (Wind Corrected Munitions Dispenser). The station can also carry multiple smaller munitions such as the GBU-39 Small Diameter Bombs (SDB), GBU-53/B SDB II, and SPEAR 3 anti-tank missiles; up to four SDBs can be carried per station for the F-35A and F-35C, and three for the F-35B. The inboard station can carry the AIM-120 AMRAAM. Two compartments behind the weapons bays contain flares, chaff, and towed decoys.
The aircraft can use six external weapons stations for missions that do not require stealth. The wingtip pylons each can carry an AIM-9X or AIM-132 ASRAAM and are canted outwards to reduce their radar cross-section. Additionally, each wing has a 5,000 lb (2,300 kg) inboard station and a 2,500 lb (1,100 kg) middle station, or 1,500 lb (680 kg) for F-35B. The external wing stations can carry large air-to-surface weapons that would not fit inside the weapons bays such as the AGM-158 Joint Air to Surface Stand-off Missile (JASSM) cruise missile. An air-to-air missile load of eight AIM-120s and two AIM-9s is possible using internal and external weapons stations; a configuration of six 2,000 lb (910 kg) bombs, two AIM-120s and two AIM-9s can also be arranged. The F-35A is armed with a 25 mm GAU-22/A rotary cannon mounted internally near the left wing root with 182 rounds carried; the gun is more effective against ground targets than the 20 mm cannon carried by other USAF fighters. The F-35B and F-35C have no internal gun and instead can use a Terma A/S multi-mission pod (MMP) carrying the GAU-22/A and 220 rounds; the pod is mounted on the centerline of the aircraft and shaped to reduce its radar cross-section. In lieu of the gun, the pod can also be used for different equipment and purposes, such as electronic warfare, aerial reconnaissance, or rear-facing tactical radar.
Lockheed Martin is developing a weapon rack called Sidekick that would enable the internal outboard station to carry two AIM-120s, thus increasing the internal air-to-air payload to six missiles, currently offered for Block 4. Block 4 will also have a rearranged hydraulic line and bracket to allow the F-35B to carry four SDBs per internal outboard station; integration of the MBDA Meteor is also planned. The USAF and USN are planning to integrate the AGM-88G AARGM-ER internally in the F-35A and F-35C. Norway and Australia are funding an adaptation of the Naval Strike Missile (NSM) for the F-35; designated Joint Strike Missile (JSM), two missiles can be carried internally with an additional four externally. Nuclear weapons delivery via internal carriage of the B61 nuclear bomb is planned for Block 4B in 2024. Both hypersonic missiles and direct energy weapons such as solid-state laser are currently being considered as future upgrades. Lockheed Martin is studying integrating a fibre laser that uses a spectral beam combining multiple individual laser modules into a single high-power beam, which can be scaled to various levels.
The USAF plans for the F-35A to take up the close air support (CAS) mission in contested environments; amid criticism that it is not as well suited as a dedicated attack platform, USAF chief of staff Mark Welsh placed a focus on weapons for CAS sorties, including guided rockets, fragmentation rockets that shatter into individual projectiles before impact, and more compact ammunition for higher capacity gun pods. Fragmentary rocket warheads create greater effects than cannon shells as each rocket creates a "thousand-round burst", delivering more projectiles than a strafing run.
US Air Force F-35A at the Sanicole Sunset Airshow 2022
Italian Air Force F-35A arriving for the NATO and Czech Air Force Days 2021
Maintenance and logistics
The F-35 is designed to require less maintenance than prior stealth aircraft. Some 95% of all field-replaceable parts are "one deep"—that is, nothing else needs to be removed to reach the desired part; for instance, the ejection seat can be replaced without removing the canopy. The F-35 has a fibermat radar-absorbent material (RAM) baked into the skin, which is more durable, easier to work with, and faster to cure than older RAM coatings; similar coatings are being considered for application on older stealth aircraft such as the F-22. Skin corrosion on the F-22 led to the F-35 using a less galvanic corrosion-inducing skin gap filler, fewer gaps in the airframe skin needing filler, and better drainage. The flight control system uses electro-hydrostatic actuators rather than traditional hydraulic systems; these controls can be powered by lithium-ion batteries in case of emergency. The commonality between variants led to the USMC's first aircraft maintenance Field Training Detachment, which applied USAF lessons to their F-35 operations.
The F-35 was initially supported by a computerized maintenance management system named Autonomic Logistics Information System (ALIS). In concept, any F-35 can be serviced at any maintenance facility and all parts can be globally tracked and shared as needed. Due to numerous problems, such as unreliable diagnoses, excessive connectivity requirements, and security vulnerabilities, ALIS is being replaced by the cloud-based Operational Data Integrated Network (ODIN). From September 2020, ODIN base kits (OBKs) were running ALIS software, as well as ODIN software, first at Marine Corps Air Station (MCAS) Yuma, Arizona, then at Naval Air Station Lemoore, California, in support of Strike Fighter Squadron (VFA) 125 on 16 July 2021, and then Nellis Air Force Base, Nevada, in support of the 422nd Test and Evaluation Squadron (TES) on 6 August 2021. In 2022, over a dozen more OBK sites will replace the ALIS's Standard Operating Unit unclassified (SOU-U) servers. OBK performance is double that of ALIS.
WWII era P-51 Mustang leading the US Air Force F-35A at the Sanciole Airshow 2022
US Marines F-35C at Oshkosh 2022
Stealth and signatures
Stealth is a key aspect of the F-35's design, and radar cross-section (RCS) is minimized through careful shaping of the airframe and the use of radar-absorbent materials (RAM); visible measures to reduce RCS include alignment of edges, serration of skin panels, and the masking of the engine face and turbine. Additionally, the F-35's diverterless supersonic inlet (DSI) uses a compression bump and forward-swept cowl rather than a splitter gap or bleed system to divert the boundary layer away from the inlet duct, eliminating the diverter cavity and further reducing radar signature. The RCS of the F-35 has been characterized as lower than a metal golf ball at certain frequencies and angles; in some conditions, the F-35 compares favorably to the F-22 in stealth. For maintainability, the F-35's stealth design took lessons learned from prior stealth aircraft such as the F-22; the F-35's radar-absorbent fibermat skin is more durable and requires less maintenance than older topcoats. The aircraft also has reduced infrared and visual signatures as well as strict controls of radio frequency emitters to prevent their detection. The F-35's stealth design is primarily focused on high-frequency X-band wavelengths; low-frequency radars can spot stealthy aircraft due to Rayleigh scattering, but such radars are also conspicuous, susceptible to clutter, and lack precision. To disguise its RCS, the aircraft can mount four Luneburg lens reflectors.
Noise from the F-35 caused concerns in residential areas near potential bases for the aircraft, and residents near two such bases—Luke Air Force Base, Arizona, and Eglin Air Force Base (AFB), Florida—requested environmental impact studies in 2008 and 2009 respectively. Although the noise level in decibels was comparable to those of prior fighters such as the F-16, the sound power of the F-35 is stronger, particularly at lower frequencies. Subsequent surveys and studies have indicated that the noise of the F-35 was not perceptibly different from the F-16 and F/A-18E/F, though the greater low-frequency noise was noticeable for some observers.
F-35B and F-35A side by side at RIAT 2016