Flying the UK’s new fighter: Lockheed Martin F-35 Lightning II
- Credit: PIL SEPT16 SPECIAL FEATURE F35 S
The supremely capable fifth-generation jet fighter that outdoes everything that went before - and is the easiest yet to fly
Words: Dave Unwin
Photos: Lockheed Martin
Hovering slowly and precisely along the taxiway, I couldn’t help but be reminded of the time I flew a Harrier TMk10. I’d thought that was an incredible flying machine, but the F-35 is something else!
I’ve been lucky enough to fly around a dozen different fighters and fighter-trainers ? powered by piston, turboprop and jet-engines ? but as soon as I settled in the Martin-Baker Mk16 ejection seat, it was apparent the F-35’s cockpit is unlike any other fighter I’ve flown.
The UK has ordered 138 Lightning IIs while many other western nations are also intending to buy them. In fact, the F-35 will eventually be the only combat aircraft many countries operate, as it will certainly be flying well into the second half of the 21st century.
Some of the brilliant systems incorporated in the design will eventually filter down to airliners and business aircraft (think of how the B787 and many bizjets have now adopted military-style head-up displays).
What’s more, the F-35 may very well be the last ever manned fighter...
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So, what is the Lightning II? It is a ‘fifth-generation’ jet fighter produced in three distinct variants: the conventional takeoff and landing (CTOL) F-35A; the short takeoff/vertical landing (STOVL) F-35B and a carrier variant (CV), the F-35C. The UK is buying the B model to equip both the RAF and Royal Navy.
From the outset, the programme aim was to maximise commonality between the three versions, because the costs incurred in developing a jet fighter of this latest generation are colossal. The total life-cycle cost to the US Government alone may well exceed $1 trillion ? significantly more than any other military aircraft in history.
This advanced aircraft relies on a remarkable amount of software, with over eight million source lines of code (four times the amount used for the first of the fifth-generation fighters, the F-22 Raptor). The powerful F-35 systems and sensors include the Active Electronically Scanned Array radar (AESA), electro-optical Distributed Aperture System (DAS) and an Electro-Optical Targeting System (EOTS).
For me at least, the most amazing is the DAS as its six sensors give a pilot unlimited all-round day/night vision. Consequently, if the pilot looks down in the cockpit, they ‘see’ in their helmet display what is underneath the aircraft!
Before sampling the simulator, I took a leisurely walk round the full-scale mock-up. At 15.4m in length and a wingspan of 10.7m, it’s not as big as some fighters ? but is quite tall at 4.3m. One of the first things I notice is that although there are hardpoints on the wings, there are no pylons, as all the weapons are carried internally. This keeps the radar signature down, ensuring the aircraft is stealthy. The wings, tail and undercarriage all look conventional, although I know the propulsion system on the F-35B variant is far from being so.
Most powerful jet engine
The engine is the Pratt & Whitney F135, the most powerful jet engine ever made for a fighter. Additionally, the B model incorporates the Rolls-Royce ‘LiftSystem’, and this combination enables the aircraft to make a very short takeoff, fly supersonic and land vertically. The motor really is a mechanical marvel, as is the remarkable LiftSystem.
The F135 is a more powerful derivative of the Pratt & Whitney F119 engine, as used on the twin-engine F-22 Raptor. It can produce up to 28,000lb (124.55kN) of dry thrust and an incredible 43,000lb (191.27kN) ‘wet’ (with afterburner). To put this in context, the two Rolls-Royce Avon engines of Britain’s previous English Electric Lightning fighter each produced 16,000lb wet (32,000lb total thrust).
The F135’s two spools contra-rotate, which helps to shape the direction of core airflow as it transitions between the high-pressure turbine (HPT) and low-pressure turbine (LPT), improving engine efficiency and reducing the number of rows of static stators and vanes. The LPT also turns the driveshaft that powers the Rolls-Royce LiftFan, located behind the cockpit and ahead of the engine. This is a horizontally-mounted unit consisting of two contra-rotating fans, one directly above the other behind the cockpit and covered by a large door, which is only opened when the F-35B is hovering, performing a short takeoff or transitioning between horizontal and vertical flight.
Each fan is driven by a separate bevel gear system contained in a common gearbox to which power is transmitted by a driveshaft which runs along the aircraft’s longitudinal axis. In the hover, the driveshaft delivers 28,000shp to the LiftFan’s clutch-and-bevel-gear system so that the unit provides downward thrust as a column of cool air, along with a pillar of hot gas from the engine’s tailpipe, known as the Three-Bearing Swivel Module, or 3BSM.
This fantastic piece of equipment consists of three articulated sections of titanium nozzle casing, each section connected to the others and driven by its own ring bearing. It can direct air through a 95-degree range, from five degrees forward to horizontally aft. Interestingly the ring bearing actuators for the 3BSM are powered by ‘fueldraulics’, some of the jet fuel being bled off and pressurised to 3,500psi, functioning as hydraulic fluid to drive the servo-valve actuators.
The 3BSM can swivel fully from horizontal to vertical in 2.5 seconds, completely redirecting all the thrust downwards. The final component the vertical lift/control system is the pair of ‘Roll-Posts’, variable-area nozzles underneath each wing that provide roll control in hover mode by directing bypass air from the engine through a pair of flap-type titanium doors.
Together with the downward thrust produced by the LiftFan and the two wing-positioned ‘Roll-Posts’, the F-35B can turn 15,700lb of dry tailpipe thrust into 39,400lb of thrust directed vertically downward ? in less than three seconds.
As the hover demands very high power, behind the LiftFan’s big inlet door are a pair of Auxiliary Air Inlet Doors (AAIDs), providing additional air for the engine. Below the LiftFan, the variable area vane box (VAVB) directs the cool air driven downwards vertically by the LiftFan. The VAVB’s aluminium louvered doors can be angled all the way from 45 degrees back, through fully vertical to five degrees forward.
In good hands
I sit down in the cockpit under the watchful eyes of ? unlikely as it may sound ? Kenn and Barbie. Kenn Cooper and ex-F-18 driver Craig Dalle (callsign ‘Barbie’) know the systems inside out and back-to-front, so I’m in good hands.
The first thing that strikes me is just how clean the cockpit and panel are. There are few switches, knobs and levers, and even controls you’d think vital for a STOVL aircraft, such as nozzle and flap selectors are conspicuous by their absence. All you really have are the engine start switches, undercarriage lever, emergency jettison button, landing lights, park brake… and that’s pretty well it. Everything else is controlled either via the touchscreens or voice control.
Another item missing is the HUD. Nevertheless, F-35 pilots are presented with a truly phenomenal amount of information displayed in their helmet visors. This aircraft’s ancillaries (such as the ejection seat and pilot’s helmet) are just as sophisticated as the aeroplane itself.
The pilot of a Lightning II wears a very sophisticated helmet, which incorporates a Helmet Mounted Display system, or HMD. Made predominantly from Kevlar and weighing less than two kilogrammes (including the oxygen mask), the helmet features active noise reduction and a unit providing an ‘out of the canopy display’, which ensures the pilot is continually looking outside in a tactical situation.
Furthermore the onboard integrated system presents ‘fused’ data from all the sensors and data links onto the PCD in such a way that a pilot’s situational awareness is enhanced to unheard-of levels, while simultaneously filtering out unnecessary information and prioritising threats and targets. Situational awareness is further enhanced by a voice command system that issues warning messages from the direction of a threat, while the aircraft’s data fusion engine and the pilot-aircraft interface automatically display air and surface targets on the HMD.
The cockpit is dominated by an L-3 panoramic cockpit display (PCD) with touchscreen control and active matrix liquid crystal displays. The PCD features dual 250 x 200mm screens, mounted on either side of a centrally located 500 x 200mm display. The big screen has a 2560 x 1024 pixel display while the smaller two are 1280 x 1024. They’re extremely clear and easy to read.
The upper part of the large screen is primarily for sub-system information, such as engine gauges, fuel quantity and undercarriage status, caution and warning systems, autopilot/auto throttle and navigation information and lots more. Tactical information is displayed on the lower part of the screen and is split into four segments called ‘portals’. The pilot can place anything anywhere and even change the size of the portals. Symbology at the bottom left of the display on the F-35B’s PCD shows the status of the 3BSM and LiftFan. In the centre of the console is a battery-powered standby flight display. However, most of the information is displayed within the pilot’s visor, while situational awareness is enhanced by a voice command system that issues directional threat warning messages.
On the right side of the cockpit is the sidestick, which as well as operating the ailerons and elevator conventionally also enables the pilot of the STOVL variant to hover the aeroplane. The throttle is on the left and moves through a linear slide rather than a rotary arc. Both sidestick and throttle are liberally studded with switches and buttons and the HOTAS ‘switchology’ is pretty complex, although interestingly there isn’t a trim button.
Starting the engine is easy ? just turn on the IPP (a sort of APU) then set the engine switch to run and it, well, runs.
Taxying is equally straightforward: the nosewheel steers through the rudder and for tighter turns you can adjust the steering gain. The field out of view out of the forward hinged canopy is good, although as long as the synthetic vision Distributed Aperture System is functioning correctly the windscreen could be opaque.
Out on the runway of the simulated Nellis AFB, I run through the pre-takeoff checks and search in vain for the flap selector, until Barbie reminds me the flaps are purely automatic. Take off is simple ? line up, full ‘dry’ power then into afterburner.
The acceleration is phenomenal, rotate at 150kt after a very brief ground roll then retract the undercarriage as quickly as possible.
The speed just keeps building and in no time I’m flashing across the virtual desert at M0.9 and 100ft ? what a rush it would be to do this for real!
Clever symbology shows when your vector will coincide with the ground ? a useful safety factor. After a rapid climb to 25,000ft I try some slow flight, but the computer won’t let a full aerodynamic stall develop. Instead, the sink rate simply increases. I add power until the sink rate is arrested at 120kt, then Kenn says, “You can loop it from there ? just go to full afterburner and pitch up”. I can scarcely believe it is possible but do as I’m told, and it works as advertised.
The power and control available is incredible, yet the Lightning is so easy to fly.
The roll rate is pretty rapid, but the overwhelming characteristic is just how precise control feels around all three axes. As I’m more interested in flying than fighting in the sim, I don’t have time to examine the myriad weapons available, but can’t resist dropping a pair of 2,000 pounders on an ‘enemy building’. As with every other aspect of the F-35 (with the possible exception of the HOTAS, which clearly takes some learning) target cueing, aiming and bomb release are all perfectly straightforward. I don’t miss.
Heading back to the virtual Nellis at M0.9 takes no time at all, but as the field comes into view. I realise that although the throttle’s a long way back, the F-35 isn’t decelerating as much as I’d expected. Sensing my surprise Barbie explains “it really doesn’t like to slow down” so I thumb the airbrakes out to help get the speed below the 300kt VLO. Having selected the undercarriage down I look instinctively for the flap lever, then remember there isn’t one.
As Nellis has an elevation of about 1,900ft, I disregard the pressure altimeter and use the RadAlt instead. Having flown a reasonable circuit with the throttle in manual and a Vref of 150kt to a touch and go, I turn downwind at 250kt, re-select ‘gear down’, punch the ‘convert’ button and turn back towards the runway. (You can press the convert button at any speed, but the computer simply won’t engage the LiftFan above 250.) Symbols on the PCD show that the F-35 is ready to hover, so I simply press the speed command button on the throttle ‘in’.
Air speed controlled by a button
Air speed is now controlled by clicking the speed command button up and down to change the selected speed in the command box. You simply ignore the throttle and use only the stick: push forward for down, back for up, left to shift left and right to shift right ? it really is that simple.
Barbie recommends using sixty knots initially, and slowly reducing as the runway’s threshold is approached. He gently reminds me to stay off the rudder, unless I want to make a ‘pedal turn’ about the vertical axis. Once over the runway numbers I set ‘zero’ in the speed command box.
Although its been about fifteen years, I remember vividly that as the Harrier transitioned to purely jet-borne flight it all felt a little ‘knife-edge’. As it slowed to a stop in the sky ? somewhat improbably poised on four columns of screeching, scorching air ? I was aware the pioneering British VTOL jet could suffer divergent directional stability if an intake was blanked by yaw while in the hover, and could suffer the same thing in the low speed range when transitioning to and from wing-borne flight. This situation was so serious (it’s a sort of aerial ground loop that almost always ends with an accident) that Harriers were fitted with a device that senses if yaw is starting to develop and shakes the relevant rudder pedal as a cue for the pilot.
The Harrier was a product of a different technological time ? and only the best pilots were streamed to fly it. Well, the F-35 is nothing like that. There are no issues with divergent directional stability or a pedal-shaker. Of course, having never flown a real F-35 I can’t comment on the fidelity of the simulator, but even if a real one is two or even three times harder than the sim, it’s still pretty straightforward to fly.
Indeed, along with all the other tasks a 21st century fighter pilot must perform, simply flying the aircraft is probably the easiest bit!
The F-35 feels rock-solid and stable as I ease the stick forward and sink onto the runway. Emboldened by my success, I fly a STOL takeoff (full afterburner, stick back at sixty knots) then return for some more advanced hovering, including some brisk pedal turns, before descending to twenty feet and hover-taxying along the myriad taxiways at ten knots.
I doubt you’d do this in real life as it wouldn’t do the tarmac any favours at all (I saw a real F-35 hover at Farnborough the day after my sim flight, and the amount of energy being directed downwards was extraordinary), but it is good fun, while looking straight down through the floor at what is underneath the aircraft is simply surreal.
As an experiment I push the stick forward sharply to try and produce a heavy landing, but the computer simply won’t allow touchdowns with a sink rate above 750fpm.
As the fuel state is now low, I try a vertical takeoff and quickly pull the stick back. It goes up like a rocket powered lift. One more vertical landing and its irrefutable ? Lockheed Martin has done an amazing job in making an incredibly complex aircraft remarkably uncomplicated.
What a machine! STOVL, stealthy and supersonic, its ‘fused’ sensor system and stealth design mean the F-35B pilot sees everything, but no one sees the F-35.
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