Graham opened by giving some basic information. The STOVL F-35B is for the USMC only (now that the UK has changed to the US Navy’s ‘C’ version). The total vertical thrust is 40,000 lb; 20,000lb from the forward mounted engine driven lift fan, 16,000 lb from the core engine via the aft vectoring main nozzle and 4,000 lb from the ‘roll posts’, downward pointing under-wing roll control nozzles .

The primary engine is the Pratt & Whitney F135 with the General Electric F136 as the alternative. There is no VIFF capability, thrust vectoring being for take-off and landing only. The maximum vertical landing weight is approximately 37,000 lb with good control margins, and the aircraft is stealthy.

The STOVL mode control system is derived from ‘Unified’ developed by the ‘RAE’ on the VAAC Harrier. The throttle commands acceleration and deceleration (or thrust on the ground and in the STO mode, and in all conventional modes); in the hover the stick moved backwards/forwards commands upwards/downwards vertical velocity (or pitch rate elsewhere); in the hover the stick moved from side to side commands bank angle (or roll rate elsewhere) and if released returns the aircraft to wings level; in the hover the pedals command yaw rate (or sideslip elsewhere).

Future development will clear full envelope autopilot/auto throttle, automatic deceleration to a spot, and TRC (translational rate command) which in the hover allows the pilot to make small positional corrections easily, and will then bring the aircraft to a standstill if the pilot releases the controls. A pilot’s helmet mounted display (HMD) is fitted instead of a HUD.

In the Harrier the pilot must obey the rules. The F-35B fly-by-wire system gives angle-of-attack and sideslip control, and departure protection. Further pilot workload reduction is given by performance deficit protection, conversion speed window protection and FOD protection warning; and flight test has a watching brief on the requirement for possible tail strike protection during slow landings (currently not considered necessary). Pilot cognitive errors (of trying to control thrust with the throttle) have been mitigated in the design. In the unlikely event of the lift fan failing catastrophically the aircraft would pitch inverted in 0.6 seconds, and the pilot is protected by auto-ejection signalled by pitch rate and attitude (derived from the YAK 38 & 141 systems).

The flying controls are powered by electro-hydraulic actuators (electric power to hydraulic pumps at the control surfaces). The IPP (integrated power pack) is a combined gas turbine and electric starter/generator. After starting the main engine, bleed air keeps the IPP spinning all the time to provide ECS and cooling air and standby power generation. Should the bleed air fail the IPP reverts to a gas turbine mode. To convert from the CTOL to STOVL mode a button push opens the necessary intake doors etc (13 in all), prepares the engine and engages the lift fan clutch which transmits 28,000 shaft hp.

Pit testing over a grid, based on the old Dunsfold design, measured thrust and pitch control power achieved through forward lift fan inlet guide vane adjustment and aft vectored nozzle area, both affected by engine RPM. The effects of opening the 13 doors in conventional flight showed buffet and more drag than expected.

For STOVL testing the F-35B was flown to the NATC at Pax River on Chesapeake Bay where there were 25 BAES flight test people (in addition to the peak number of 160 BAES staff at Fort Worth). Facilities included VTOL pads, a ski-jump, austere strips, hot pits (for refuelling without shutting down), telemetry, chase aircraft and a simulator for mission practice. Testing started with in-flight conversions, decelerating and accelerating at 5,000 ft and 210 kn, fixed throttle. There was no pitching but some mild heave. Testing then progressively approached the hover flying at 200 - 100 kn at 3-5,000 ft followed by slow landings (SL) at 130 - 110 kn ; then decelerations at less than 100 kn blending to the hover followed by SLs at 90 - 70 kn.

Apart from some intake door chatter causing a linkage distortion, and the failure of a flight test antenna, all went well. The Short take-off (STO) mode was checked at altitude followed by 100kn STO and  then 80 kn STO, circuit and VL from 150 ft on 18 March 2010. Post touchdown the procedure was all automatic. There were no problems in STO.

Problems in the early development testing, which are addressed in the production aircraft, included: clutch drag in conventional flight, driveshaft length issues due to expansion/contraction, intake door structure, roll post heating (it is a continuous bleed system), sideslip in wind-up turns, nose high attitude in land-aheads from hovers, and HMD vibration and latency issues.

In the following areas where problems might have been expected there were none; hot gas ingestion, ground effects, weight-on-wheels operation (gives signals to aircraft control systems), conversion dynamics, performance, deficit protection and help from mission control.

During questions the lack of VIFF was commented on. Graham replied that nowadays FBW allows 50 deg angle of attack as in, say, an F-18. This lets the pilot generate both high lift and high drag and compensates for the lack of VIFF.
On weapons carriage the primary method is in stealthy internal bays with external carriage an option when battle conditions allow. On battle damage vulnerability Graham said that the US Congress has mandated battle damage survival so survivability is a design parameter.

Barry Pegram gave the vote of thanks for this outstanding talk which had been of particular interest to the old ‘Harrier’ men present.