The F-35B is the short takeoff and vertical landing (STOVL) variant of the aircraft. Similar in size to the A variant, the B sacrifices about a third of the other version’s fuel volume to make room for the vertical flight system. Takeoffs and landing with vertical flight systems are by far the riskiest, and in the end, a decisive factor in design. Like the AV-8B Harrier II, the B\u2019s guns will be carried in a ventral pod. Whereas the F-35A is stressed to 9 g, the F-35B is stressed to 7 g. The F-35B was unveiled at Lockheed Martin’s Fort Worth plant on 18 December 2007, and the first test flight was on 11 June 2008.
The three-bearing swivel nozzle that directs the full thrust of the afterburning jet engine is moved by a “fueldraulic” actuator, using pressurized jet fuel.
Unlike the other variants, because it can land vertically the F-35B has no landing hook. The “STOVL/HOOK” button in the cockpit initiates conversion instead of dropping the hook. The F-35B sends jet thrust directly downwards during vertical takeoffs and landing and the nozzle is being redesigned to spread the output out in an oval rather than a small circle so as to limit damage to asphalt and ship decks.
The United States Marine Corps plans to purchase 340 F-35Bs, to replace all current inventories of the F/A-18 Hornet (A, B, C and D-models), and AV-8B Harrier II in the fighter, and attack roles.
The Royal Air Force and Royal Navy had planned to use the F-35B to replace their Harrier GR9s. One of the Royal Navy requirements was that the F-35B design should have a Shipborne Rolling and Vertical Landing (SRVL) mode so that wing lift could be added to powered lift to increase the maximum landing weight of carried weapons. This method of landing is slower than wire arrested landing and could disrupt regular carrier operations, as the landing method uses the same pattern of approach as wire arrested. With SRVL, the aircraft is able to “bring back” 2 x 1K JDAM, 2 x AIM-120 and reserve fuel. However, in October 2010, Prime Minister David Cameron announced that the UK would change their F-35 order to the CATOBAR F-35C variant.
Italian Navy is preparing Grottaglie air station for future operations with the F-35B. The Italian Navy should receive 22 aircraft between 2014 and 2021, with its Cavour aircraft carrier set to be modified to operate them by 2016.
Commandant of the Marine Corps, General James Amos has said that, in spite of its increasing costs and schedule delays, there is no plan B to substitute for the F-35B. The F-35B is larger than the aircraft it replaces, which required the USS America (LHA-6) to be designed without needed well deck capabilities. In 2011, the USMC and USN signed an agreement that the USMC will purchase 340 F-35B and 80 F-35C while the USN will purchase 260 F-35C. The five squadrons of Marine Corps F-35Cs will be assigned to the Navy carriers while the Marine Corps F-35Bs will be used on Amphibious ships and ashore.
On 6 January 2011, Gates said that the 2012 budget would call for a two year pause in F-35B production during which the aircraft may be redesigned, or canceled if unsuccessful. Gates stated, “If we cannot fix this variant during this time frame, and get it back on track in terms of performance, cost and schedule, then I believe it should be canceled.”
Lockheed Martin executive vice president Tom Burbage and former Pentagon director of operational testing Tom Christie have said that most of the delays in the total program have been due to issues with the F-35B, which forced massive redesigns on the other versions.
The USMC intends to declare Initial Operational Capability with about 50 F-35s running interim Block 2B software in the 2014 to 2015 timeframe.
Lockheed Martin vice president Steve O'Bryan has said that most F-35B landings will be purely conventional in order to reduce stress on the vertical lift components.