Lockheed Martin F-35B Lightning II
The F135 engine with lift fan, roll posts, and rear vectoring nozzle, as designed for the F-35B, at the Paris Air Show, 2007
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 some 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's guns will be carried in a ventral pod. Whereas F-35A is stressed to 9 g, the F-35B is stressed to 7 g. Unlike the other variants, the F-35B has no landing hook; the "STOVL/HOOK" button in the cockpit initiates conversion instead of dropping the hook.
The British Royal Air Force and Royal Navy plan to use this variant to replace their Harrier GR7/GR9s. The United States Marine Corps intends 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 USMC is investigating an electronic warfare role for the F-35B to replace the service's EA-6B Prowlers.
One of the British requirements was that the F-35B design should have a Ship-borne 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.
The U.S. Marines are investigating the use of the SRVL method to operate F-35Bs from CVNs without disrupting carrier operations as the landing method uses the same pattern of approach as wire arrested landings. However the aircraft is able to "bring back" 2 x 1K JDAM, 2 x AIM-120 and reserve fuel to a vertical landing.
The F-35B was unveiled at Lockheed's Fort Worth plant on 18 December 2007, and the first test flight was on 11 June 2008. The B variant is expected to be available beginning in 2012.
Function strike fighter
Contractor two competing teams:
Service U.S. Air Force U.S. Marine Corps
U.K. Royal Navy U.S. Navy
Variants Conventional Takeoff and Landing (CTOL) Short Takeoff and Vertical Landing (STOVL) Carrier-based (CV)
Unit Cost FY94$ $28M $35M $38M
Inventory Objectives U.S. Air Force
2,036 aircraft U.S. Marine Corps
U.K. Royal Navy
60 aircraft U.S. Navy
Inventory Objectives 1,763 aircraft 609 aircraft 480 aircraft
Propulsion Baseline: P&W F119-PW-100 derivative from F-22r
Alternate Engine: General Electric F120 core
Empty Weight ~22,500 lbs ~24,000 lbs
Internal Fuel 15,000 lbs 16,000 lbs
Payload 13,000 lbs 17,000 lbs
Maximum Takeoff Weight ~50,000 lbs
Length 45 feet
Wingspan 36 feet 30 feet
Combat Radius over 600 nautical miles
First flight 1999
Date Deployed 2008