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Last Updated: Mon Jan 27 11:18:09 UTC 2014

The Joint Strike Fighter Decision

Dr Carlo Kopp, MIEEE, MAIAA, PEng
First published in Defence Today Vol.1 No.3
September, 2002
© 2002,  2005 Carlo Kopp

On the 26th June this year the AIR 6000 contest changed in nature. In a joint media conference, the Minister for Defence Sen Robert Hill, the Industry Minister Ian Macfarlane and Chief of Air Force AM Angus Houston announced that Australia would participate in the Joint Strike Fighter development program. This was not unexpected, but what did come as a surprise to most observers was the concurrent announcement that the JSF would be the chosen AIR 6000 solution, providing it met the RAAF's needs and current costing estimates in 2006.

This in many respects pre-empted the planned A6K contest, and in effect knocked the European canard fighters and teen series offerings out of the game. The RAAF was in effect committed to a 4th/5th generation solution.

Whatever position one takes on the F-35 JSF, the DoD/RAAF/Cabinet decision to effectively shortlist the JSF as the preferred A6K solution raises a great many questions, answers to which may not become available for some time. This issue's report will explore some of these questions.

Comparing the F-35 Joint Strike Fighter

The Joint Strike Fighter is being developed as a replacement for the USAF's F-16CG/CJ fighter bombers, A-10A Warthog battlefield interdictors (JSF-CTOL), the USN's F/A-18A-D fighter bombers (JSF-CV), the USMC's F/A-18A-D fighter bombers and AV-8B Harrier close air support aircraft, and the RAF/RN's Harrier strike aircraft (JSF-STOVL).

The principal design optimisation of the JSF is battlefield strike, interdiction and close air support, with a respectable capability for self defence against opposing fighters. Despite the JSF's similarity to the F-22 in stealth shaping, the JSF is not an air superiority and deep strike fighter in the mold of the USAF's F-22A Raptor and is not intended to be such. Those observers in Australia who have publicly described the JSF as an air superiority fighter have evidently not studied the aircraft very closely.

The JSF program is ambitious - much more ambitious than the 1960's TFX (F-111) program which was aimed at producing a USAF strike fighter and USN interceptor, using then new variable geometry wing and turbofan engine technologies. The JSF program breaks ground in several new areas. It is to be the most software intensive fighter ever built, eclipsing the larger F-22 in complexity. The JSF will also be the first fighter to be built around Commercial Off The Shelf (COTS) standards based avionics, departing from the 4 decade old design practices based on Milspec standards. The JSF also pushes engine hot end temperatures beyond the limits in the F-22 which is the yardstick. Finally, the JSF amis to fulfill the needs of four primary users, the USAF, USN, USMC and RAF/RN.

The aggressive development schedule and ambitious aims in both capabilities and exploitation of immature technologies are a double edge sword for the JSF. While they offer the potential to produce a genuinely innovative and bleeding edge product they also introduce the highest level of basic program risk since the F-111 program during the sixties. Marketing literature aside, the builders of the JSF are pushing further ahead in technology than any recent aircraft other than the paradigm breaking F-22.

The first question an observer might ask when confronted initially with the JSF is that of where to fit this aircraft into the current and historical pantheon of combat aircraft.

Taking a deeper historical perspective the JSF is best compared to the famous Republic F-105D Thunderchief (Thud / Lead Sled) of Vietnam era fame. The JSF and Thud are nearly identical in empty weight, both with single engines and single seat cockpits, both optimised for trucking bombs and both in the 600 NMI combat radius class. The similarity ends here since the JSF is not built to use speed as a survival mechanism, it exploits very good stealth capability in the forward hemisphere. While the JSF is draggier than the F-105 at supersonic speed, it also has more installed thrust and will provide respectable maneouvre performance even if not the league of the F-22 or Eurofighter.

The JSF is much more difficult to compare against the smaller teen series (F-16C / F/A-18A-D) and Eurocanard (Typhoon/Rafale) fighters. These 1970s conceptual designs were all built for exceptional subsonic/transonic dogfighting agility and then burdened with ground attack duties, via enhanced avionics, external fuel and external bombs. This category of fighter delivers 300 - 600 NMI class combat radius with a generous load of fuel, and typically loses most of its agility at extended ranges and heavy fuel/weapon loads.

Unlike the 1970s generation of dogfighters which were progressively reshaped into bomb trucks, the JSF design aims to achieve exceptional bomb trucking combat radius for its size. The empty JSF weighs as much as an empty F-15A/C, yet carries a similar amount of internal fuel as the total fuel load of an F-15C with a centreline 610 USG drop tank. With a very clean profile, carrying all fuel and bombs internally, the F/A-18A sized JSF can achieve an unrefuelled radius close to 700 NMI - a remarkable performance for a fighter of similar dimensions to an F/A-18A-D.

The JSF is however not a one for one replacement for the F-111 or F-15E, both of which are in the 1,000 NMI radius class. The F-111 makes for a good comparison here, with about twice the internal fuel of the JSF and twice the nominal payload carried externally, the F-111 delivers about 45% better combat radius.

Bombers are typically judged by two metrics - payload/radius performance and survivability. Against the traditional yardstick of the former, the F-111, the JSF falls short. In survivability the current yardstick is the high flying F-22 with all aspect stealth capability. The JSF is claimed to have excellent stealth capability in the forward hemisphere, but is much weaker in the aft hemisphere due to the circular nozzle design, intended to minimise cost and weight rather than cleverly scatter microwaves.

The USAF would like to replace its fleet of F-117As and F-15Es with F-22s, since the all aspect stealth capability and supercruise allows the F-22 to penetrate deep with near impunity. The JSF, designed for battlefield strike and interdiction, will not match the F-22 in high threat density deep strike situations.

The JSF's exceptional combat radius for its compact size incurs a price. The wing design is optimised for subsonic cruise performance, and due to its leading edge sweep angle it will not be a hot supersonic performer like the F-22, F-15 or the Eurocanards. The other penalty the JSF pays is in its combat thrust/weight ratio. The large fuel load and voluminous internal bomb bays increase the empty weight and place the JSF in the 1:1 afterburning thrust weight ratio class. This will impact climb rates, acceleration and sustained turn performance - all criticial for good air to air performance.

The JSF is likely to be a respectable dogfighter, but will not have the eye watering close in agility of the F-22 or Eurocanards, nor will it have the supersonic cruise capabilities of the F-22. The JSF's F135 engine is a refanned derivative of the F-22's F119, designed for lower altitudes and subsonic cruise speeds.

How much agility is needed to be successful in post 2020 air combat remains open to some debate especially given the ever more potent capabilities of air air missiles. Top end supersonic threats may still present a genuine challenge for the JSF since the kinematic demands of supersonic high G intercept profiles required for a missile firing solution may well exceed the JSF's basic performance limits. Potential top tier opponents like the Sukhoi Su-30MK series will have kinematic performance advantages over the JSF, but will lack the stealth capability of the JSF.

How well the JSF stacks up in the air superiority game remains to be seen. A key issue will be the empty weight of the production JSF which is marginal even now for air air roles. Another key issue will be its radar performance - while stealth provides an important advantage, its radar is not a top tier performer like the F-22's APG-77 array. With cited optimisations for air to ground rather than air to air, and smaller power-aperture performance than the F-22's AN/APG-77, the JSF will be competitive against many off-the-shelf fighters but out of its league against the F-22.

To summarise the JSF the best contemporary comparison is that it is a strike optimised fighter of similar size and performance to an F/A-18A-C, with much better combat radius due to more internal fuel and zero drag internal weapon carriage, which exploits forward hemisphere stealth to yield a major survivability gain against the teen series and Eurocanard fighters. The JSF was not designed with a primary air superiority role and this is reflected in the very modest wing sweep angle and combat thrust weight ratio.

Issues for the RAAF

If the sole intent of the RAAF is to operate the JSF as a component of a USAF Air Expeditionary Force, relying upon the USAF to provide aerial refuelling and fighter escort by F-22s, then few force structure issues arise with the JSF. However, current defence policy is firmly centred in the defence of Australia, and regional landmasses and ocean areas via which an opponent might wish to strike at Australian territory or offshore assets.

With China and India likely to be operating in excess of 500 Sukhoi Su-27/30 Flankers by 2015, and capabilities such as the A-50 AWACS, the Il-78 tanker, the Tu-22M-3 Backfire and a wide range of late generation cruise missiles, all of Russian/Soviet origin, proliferating across the region, the argument for a coalition force optimised RAAF is unlikely to hold up to scrutiny.

As the would be replacement for the F/A-18A and F-111, the JSF will need to fulfill the very broad range of roles these two types currently perform.

In replacing the F-111, the immediate issue is aerial refuelling capacity. The existing AIR 5402 tanker replacement buy, mandated in the Defence 2000 White Paper, was largely intended to provide the F/A-18As with viable on station CAP endurance, especially over over water at useful ranges. The shorter combat radius of the JSF and its smaller nominal payload would require an increase in the number of tankers to be acquired by the RAAF. The metric of providing enough tanking capacity to offset the shorter combat radius of the JSF against the RAAF's existing fleet of cca 30 operational F-111s yields an immediate requirement for around four additional Boeing 767 sized tankers - or equivalent fuel offload capacity in a larger tanker type.

The next issue is how to address the demanding cruise missile defence role with a fighter which has a mid range bombing optimised radar design. It may prove necessary to enhance the Wedgetail radar package, or indeed to acquire additional Wedgetails to account for the smaller radar footprint of the JSF against air defence fighters with larger radars.

The JSF is a single engine fighter, and long range overwater sorties will see a need for increased Combat Search and Rescue capabilities. Since the loss of the engine could put a JSF pilot into the water at any point between its home base and the target, the ADF's Combat SAR assets will have to be capable of penetrating hostile airspace to extract downed pilots. This is a much lesser issue for twin engine fighters which can straggle into safe airspace for a pilot ejection.

Perhaps the biggest issue the RAAF will have to grapple with in the JSF is risk.

There are several key areas of risk which could bite the Commonwealth badly either in timelines, costs or both:

  1. Avionic hardware: the JSF's intended use of COTS technology rather than established Milspec is intended to cut costs, but could impair reliability and yield similar troubles to the 1968 digital F-111D, the all time reliability lemon of the USAF F-111 fleet. This could force costly redesigns and delays to achieve required reliability performance.
  2. Avionic software: the JSF will be more software intensive than the F-22, and large software projects have an established history of running over time and budget, and often having intractable bugs. Software may prove to be major issue later in the JSF program.
  3. Weight and Thrust: the JSF's ability to perform in air to air roles depends critically upon its thrust to weight ratio. Increases in empty weight could impair this key parameter, while durability problems in the very hot running F135 engine could yield similar results as the standard fix of derating would most likely be used. The JSF is not an F-15A or F-22A in thrust/weight ratio, and any significant degradation below current specs would be very damaging.
  4. Availability of Stealth, EW and Software Source Codes: the US State Dept has traditionally been reluctant to provide full access in these key areas, and this may also prove to be an issue for the JSF. Acquiring USAF spec stealth materials and components will be critical for JSF, since it lacks the performance to be credible without the stealth capability.
  5. Unit Flyaway Costs: historical experience, in the form of Augustine's Law, suggests that engineering changes between prototyping and full production can see the cost of a fighter double. Even assuming only a 50% increase over the existing US$ ~40-50M for the JSF yields numbers close to 70% to 80% of the cost of the far more capable F-22 (at US$ 84M for 339 aircraft). This risk factor is exacerbated by the potential for other large customers to cut buys or bail out of the JSF program - the USN/USMC are already debating a reduction of 400 in their JSF buys. Large multinational programs do not have a stellar track records in this respect.

The risk factors in the JSF program suggest that it would be wise for the RAAF, DoD and Cabinet not to invest too much politically in the JSF - it may yet return a unacceptable bang for the taxpayer's dollar. Wise commercial investors always hedge their risky investments with low risk investments, and a fallback position for the RAAF in an F-22 based solution is something which should be carefully explored. Otherwise the RAAF might find itself in an unhealthy political and strategic position, come 2006.

Editor's Note 2005: The reality which has materialised since 2002 reflects the predictions in this analysis.

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