Fighter
Aviation Topics, Page 5
Fighter
Aviation Topics, Page 5
"Flying the F/A-18F Super Hornet"
(First published in May and June 2001 Australian Aviation.)
by Dr Carlo Kopp, PEng
Carlo.Kopp@aus.net
© 2002, 2001, Carlo Kopp
February 2, 2002
1 Part 1 History and Analysis
The F/A-18E/F Super Hornet will become over the next decade the mainstay of the US Navy's carrier-borne fighter fleet. As one of the very fewfighter aircraft to remain in production around the end of the decade, it is also very likely to be carefully scrutinised as a potential replacement for the RAAF's F/A-18A/B Hornet fleet.Therefore this aircraft is of considerable interest to the Australian observer. In this two part feature the author will explore the F/A-18E/F in some detail, including a demonstration flight performed during the 2001 Avalon airshow.
The best starting point for any discussion of the F/A-18E/F is the historical background of this aircraft.
1.1 Evolution of the Hornet
The genesis of the F/A-18 family of fighters is the period of the early seventies. At this time USN Carrier Air Wings were equipped with a mix of the MDC F-4 Phantom, the Grumman A-6E Intruder, the LTV A-7B/E Corsair, with the then new F-14A beginning to enter service. The F-14A, born from the late 1960s VFX/VFAX studies, was to replace initially the F-4 Phantom family, while plugging the gap in fleet air defence capability resulting from the collapse of the Phoenix equipped F-111B program.US Navy planning at that time envisaged a future force structure centred upon the F-14 family. The TF30 equipped F-14A was to be a transitional model, soon to be replaced in production by the more agile F-14B, equipped with the F401 engine, a derivative of the F100-PW-100 used in the F-15A. A follow-on multirole variant of the F-14B, designated the F-14C, was to replace the A-6E and the bombing capability of the F-4 series. This was a force structure designed to project force up to 600 NMI from the carrier battle group, in heavily defended airspace.
In the funding collapse following the Vietnam conflict, the F-14B and F-14C died. This was in part due to a large cost growth in the F-14A, which almost bankrupted Grumman, but also in part to a massive reduction in available funding during this period. Only the F-14A remained in production, to be supplanted by the F110 powered F-14B and F-14D models during the final years of production.
The A-6E soldiered on, intended to be upgraded during the early nineties to the A-6G configuration, and eventually replaced by the A-12A Avenger II (Dorito) stealth bomber. With the collapse of the Evil Empire, the A-6G and A-12A both died in the following budgetary upheavals, with the A-6E leaving service during the 1990s.
The F-14 was a superb replacement for the F-4 in the fleet air defence role, but its high cost and resulting reductions in numbers meant that no replacement would available for the multirole F-4 series, which performed a significant portion of the fleet's strike operations. The USN was thus confronted with the problem of how to provide a fighter bomber cheaper than the F-14 series, to replace the F-4 and the increasingly less survivable A-4 Skyhawk and A-7 Corsair bomb trucks.
A range of studies were performed to define a fighter to fulfill this role, as a second generation `VFAX' program. These included analyses of a navalised F-15 strike fighter, which were rejected due to the air force centred design optimisations of the basic aircraft - the wing design of an F-15 is not well adapted to carrier recoveries. The reality of the role to be performed was, however, was that the fighter would end up inevitably in the size and weight class of the F-4 or F-15. The dictates of Breguet's equation in payload radius impose a given airframe size. (Photo Neville Dawson)
At this time the USAF was experimenting with the idea of lightweight fighters to supplement the relatively expensive F-15A air superiority fighter, and very expensive F-111D/F strike fighter. The LightWeight Fighter (LWF) program yielded the Northrop YF-17A and the GD YF-16A. The General Dynamics fighter became the `Lawn Dart/Viper/Falcon', or production F-16A-D multirole fighter.
The Office of the Secretary of Defence (OSD), frustrated at perceived USN intransigence over the F-14 program, subsequently directed the Navy to pursue a similar program, with the aim of replacing the F-4, A-4 and A-7 with a similar lightweight fighter to the F-16. Given the USN's long standing aim of a force structure capable of power projection to a 600 NMI radius, this was not a popular directive. However, might is right, and the USN eventually proceeded with a lightweight fighter, based upon the YF-17 demonstrator. The new F/A-18A was based upon the aerodynamic design of the YF-17, but enlarged as much as the DoD bureaucracy would permit - to an empty weight of 21,000 lb, or about 2/3 that of the F-15A.
The F/A-18A was optimised from the outset as a dual role fighter, with BVR missile capability, superb manoeuvrability for the period, and a fully digital weapon system and glass cockpit which allowed reconfiguration between air-air and air-ground software modes at the touch of a pushbutton. Reliability and low support costs were deemed a priority, and the engines and electronics were significantly derated against contemporary designs to achieve an unprecedented mean Time Between Failure for the period. Top end performance was sacrificed to achieve cost and reliability optimisation.
The production F/A-18A entered service in VMFA/VFA or fighter-attack squadrons, progressively replacing fleet A-4, A-7 and F-4 squadrons with a single type. When introduced, it offered close in combat capability which was difficult to contest by most of its contemporaries, as the hybrid wing design and digital fly by wire controls provided exceptional high AoA manoeuvre and low speed turning performance. The aircraft's principal limitation was in its combat radius - the combination of `leaky turbojet' engines, pylon drag and 11,000 lb of internal fuel resulted in an effective unrefuelled radius between 250-400 NMI, depending on load, profile, combat fuel reserves and external tank configuration.
The F/A-18A/B was exported to Australia, Canada and Spain. It was supplanted in production by the F/A-18C/D, which had slightly uprated engines to offset weight growth, and a range of various avionic and detail modifications. This aircraft was exported to Switzerland, Kuwait, Malaysia and Finland. As an export product, the F/A-18 faced a lightweight fighter market saturated with cheaper and non-BVR capable F-16As, and a heavyweight fighter market saturated with F-15A-D (Israel, Saudi Arabia and Japan). As a result, it never achieved the hoped for volume of export sales.
Operationally the F/A-18A-D series has proved to be a popular aircraft, with excellent operational reliability, handling and flexible weapons capabilities. Its principal limitation was in combat radius performance, which proved to be a major issue with the progressive retirement of the A-6 fleet, which provided the USN's primary KA-6D tanker aircraft. As the larger KA-3D tankers had already been retired, tanking capacity was becoming an ever scarcer commodity by the nineties.
The nineties also resulted in ongoing budgetary and force structure cuts, as the post Cold War drawdown continued. As noted earlier, the A-12A and A-6 upgrades died, and the F-14D production was terminated. The USN's primary role of Cold War `blue water' maritime control, aimed at defeating the USSR's massive SSN and Backfire strike forces, was supplanted by `littoral warfare', in effect modern `gunboat diplomacy' intended to provide a rapid reaction capability to deal with problem nations disturbing the peace. USN carriers played key roles in the 1991 Desert Storm campaign, the 1990's Balkans campaigns, the ongoing war of attrition against Saddam Hussein's regime, and the late nineties standoff between Taiwan and the PRC, during which the PRC threatened Taiwan with ballistic missiles.
This is an environment in which top end air superiority and deep penetration strike capabilities are considered ancillary to the capability to flexibly strike against well defended coastal targets, suppress integrated air defences and provide air support and top cover for amphibious forces. Indeed, with the retirement of the A-6E, the remaining F-14 force has been progressively adapted to deliver guided and unguided bombs, earning the new informal label of `Bombcat'.
By the early nineties it was clear that the aging F-14 fleet would have to be replaced over the coming decade or so, and a replacement concurrently provided to plug the gap left by the never replaced A-6E fleet. The core requirements for such a replacement aircraft were a combat radius competitive against the 600 NMI class F-14/A-6 combination, and CAP endurance in fleet defence operations competitive against the F-14 series.
During the early nineties considerable effort was expended in studies aimed at adapting the new USAF F-22A to carrier operations, as the `F-22N'. Problems soon arose, as the baseline land-based F-22 is not optimised for the unique carrier environment. The most difficult issue proved to be the wing - the unhappy experience of the USN with blown flaps on the F-4 series, the obvious solution to achieving the required recovery speeds for trapping such a large aircraft, led to the adoption of a swing wing configuration. This in turn pushed up the cost of the redesign, since the stealth characteristics (ie shaping) would have to be completely requalified, adding already to the considerable costs of a structural redesign and avionic system redesign. In effect the F-22N would be a new aircraft, resulting in little saving through commonality. Given the required number of aircraft, this proved to be unaffordable to a USN already under major budgetary pressures.
What the USN needed was a aircraft which could eventually replace the aging F-14 and F/A-18A-D fleet, plug the hole left by the A-6E and KA-6D, and do so within a restricted development budget and timeline.
The result of these pressures is the F/A-18E/F Super Hornet.
1.2 The F/A-18E/F Super Hornet
The Super Hornet is substantially a new aircraft, which shares only limited structural commonality with the F/A-18A-D family of fighters. While the F/A-18E/F forward fuselage is derived from the F/A-18C design, the wing, centre and aft fuselage, tail surfaces and powerplants are entirely new. The baseline avionic system is however largely derived from the F/A-18C, with planned growth through further evolved derivatives of the radar, EW and core avionic systems, and entirely new systems where appropriate.The designation F/A-18E/F reflects the fact that the aircraft is derived from the F/A-18A-D, even if it is a significantly larger airframe design - the program was implemented as an Engineering Change Proposal (ECP) to avoid a costly demonstration program and fly-off, as has occurred with the F-22/YF-23 and JSF. A side effect of this idiosyncrasy in nomenclature is that the F/A-18E/F is frequently dismissed as `just another Hornet', yet the aircraft is different in many respects.
From a design perspective, the most notable change in the Super Hornet is its size, designed around an internal fuel (JP5) capacity of 14,700 lb, or 36% more than the F/A-18C/E. This most closely compares to the F-15C, which has around 10% less internal fuel than the Super Hornet.
Sizing around a 36% greater internal fuel load, with the aim of retaining the established agility performance of the F/A-18C, resulted in a larger wing of 500 sqft area, against the 400 sqft area of the F/A-18C, a 20% increase. The consequent sizing changes result in a 30,885 lb empty weight (31,500 lb basic weight) aircraft, a 30% increase against the F/A-18C. Not surprisingly, the aircraft's empty weight is 8% greater than the F-15C, reflecting the structural realities of catapult launches and tailhook recoveries.
The larger F414 engine, a refanned and evolved F404 variant, delivers 20,700 lb static SL thrust in afterburner, which is around 8% less than the F100-PW-220 in the F-15C. (Photo Neville Dawson)
The simplest metric of the F/A-18E/F is that it is an F-15A-D sized F/A-18C derivative, optimised for the naval environment. The similarity in size between the F/A-18E/F and F-15A-D is no coincidence - as the original VFAX studies in the 1960s and 1970s showed, this is the optimal fighter size for the given combat radius. In effect, the F/A-18E/F is what the F/A-18A Hornet should have been from the outset, had it not been hobbled at birth by a budget driven bureaucracy.
Size is where the similarity between the Super Hornet and Eagle end, since the Super Hornet is optimised aerodynamically around the F/A-18A-D configuration, with a focus on transonic manoeuvre and load carrying performance, and carrier recovery characteristics. In terms of raw performance, the Super Hornet is very similar to the F/A-18C, but provides significantly better CAP endurance and operating radius by virtue of its larger wing and internal fuel load.
With three 480 USG drop tanks, full internal fuel, combat and reserve fuel allowances, 8 x AIM-120 AMRAAMs and 2 x AIM-9 Sidewinders, the aircraft has a point intercept radius in excess of 650 NMI, with some assumptions made about expended missiles. This is radius performance in the class of the F-15C.
Like the F/A-18A-D, the F/A-18E/F was designed from the outset for a dual role fighter bomber mission environment. The enlarged wings have three hardpoints each, typically loaded with a pair of 480 USG tanks inboard and weapons on the pair of outboard stations. The wingtip Sidewinder rail is retained.
A notable aerodynamic feature is a significantly enlarged strake design over the baseline Hornet, intended to improve vortex lifting characteristics in high AoA manoeuvre, and reduce the static stability margin to enhance pitching characteristics - Boeing cite pitch rates in excess of 40 degrees per second.
Structurally the Super Hornet is built largely from aluminium alloys, with extensive use of carbon fibre composite skins in the wings, and titanium in several critical areas. The design load factor limit of 7.5G is identical to the F/A-18A-D.
The most notable visual difference between the F/A-18A-D and F/A-18E/F, to the casual observer, are the engine inlets. These are are fixed in geometry, but using a rectangular geometry more akin to the F-15 design.
The inlets represent a key design optimisation intended to reduce the aircraft's forward sector radar cross section. The edge alignment of the inlet leading edges is designed to scatter radiation to the sides, and fixed `fanlike' reflecting structure in the inlet tunnel performs a role analogous to the mesh on the inlets of the F-117A, keeping microwave illumination off the rotating fan blades. (Photo Neville Dawson)
The F/A-18E aircraft makes considerable use of panel join serration and edge alignment. Close inspection of the aircraft shows considerable attention paid to the removal or filling of unnecessary surface join gaps and resonant cavities. Where the F/A-18A-D used grilles to cover various accessory exhaust and inlet ducts, the F/A-18E/F uses centimetric band opaque perforated panels. Careful attention has been paid to the alignment of many panel boundaries and edges, to scatter travelling waves away from the aircraft boresight.
It would be fair to say that the F/A-18E/F employs the most extensive radar cross section reduction measures of any contemporary fighter, other than the very low observable F-22 and planned JSF. While the F/A-18E/F is not a true stealth fighter like the F-22, it will have a forward sector RCS arguably an order of magnitude smaller than seventies designed fighters. Since every deciBel of RCS reduction counts until you get into the range of weapon payload RCS, the F/A-18E/F represents the reasonable limit of what is worth doing on a fighter carrying external stores. None of the RCS reduction features employed in the F/A-18E/F are visible on any of the three Eurocanards, which raises interesting questions about the relative forward sector RCS reduction performance of these types.
The Super Hornet employs a further evolved derivative of the F/A-18C avionic package. While the AN/APG-73 radar, common to the RAAF HUG, is retained, provisions will be made in production blocks for the AN/APG-79 (formerly AN/APG-73 RUG III phased array) Active Electronically Steered Array (AESA) retrofit. The new ATFLIR targeting pod will also be used, employing a new `midwave' 4-5 micron band Focal Plane Array high resolution imager.
The APG-73 provides very respectable air-ground modes, including synthetic aperture modes (depicted). With the capability to interleave MTI modes with surface mapping modes, the radar provides a potent capability against battlefield and maritime targets . The APG-79 active phased array radar (formerly APG-73 RUG III) is a planned growth feature for the F/A-18E/F family of fighters. It is derived from the baseline APG-73 by the replacement of the planar array antenna with a solid state Active Electronically Steered Antenna array. This will provide the radar with the ability to timeshare operating modes concurrently, as well as improving jam resistance and reducing detectibility through much reduced sidelobes .
The core avionic computing package is based upon militarised COTS VMEbus PowerPC processors (common to desktop Apple PowerMacs and recently built F-15Es), which are of the order of a hundred times more powerful than the 16-bit generation AN/AYK-14 processors in the F/A-18C. This is a significant advancement in long term supportability, and provides a very robust platform for evolution of the onboard software OFPs. The cockpit software is highly integrated by the standards of Mil-Std-1553B bussed architectures, and provides facilities for display fusion of MIDS datalink, RWR threat information and digital moving map displays.
While the preproduction aircraft employ a mix of cockpit CRT and AMLCD displays, the intent is to employ high resolution NVG compatible AMLCD panels in production block aircraft. A strike optimised `missionised' aft cockpit with a large 10 x 8 inch AMLCD display is in development. The JHMCS Helmet Mounted Display will be employed to cue the new thrust vectoring AIM-9X missile, with growth to cue air to surface weapons.
The EWSP package is build around a late model ALR-67 warning receiver, the now revived ALQ-165 ASPJ defensive jammer, supplemented by the ALE-50 towed decoy and ALE-47 dispenser. Current growth plans include the ALQ-214 RF countermeasures package and ALE-55 fibre optic towed decoy from the IDECM suite. The latter is particularly effective against newer monopulse threat systems, since it can provide for long baseline crosseye jamming.
The current configuration of the F/A-18E/F avionic package is the most advanced of any production aircraft based upon a Mil-Std-1553B bussed federated architecture, and is surpassed only by the much newer F-22A and JSF architectures. It is very likely that growth variants of the F/A-18E/F will see the progressive incorporation of avionics technology used in the JSF.
In terms of broad comparisons, the F/A-18E/F most closely compares to the late model F-15 variants. While it does not have the supersonic optimised wing and top end BVR combat and supersonic agility performance of APG-63(V)2 phased array fitted F-15C models, it has a more recent avionic package, radar cross section reduction measures absent on the F-15 and a very modern defensive EW package. In most key respects, the Super Hornet is a substantial improvement over the established F/A-18A-D models, especially in combat radius performance. While the aircraft is frequently criticised for not offering a dazzling supersonic agility and thrust/weight performance increase over the baseline F/A-18C, this was not a primary design objective. Rather, the aim was to provide a low risk near term growth aircraft exploiting the established technology investment in the F/A-18C, and utilising newer technologies such as RCS reduction, integrated MIDS datalink and advanced countermeasures to improve the aircraft's survivability and lethality without the cost penalties of a clean sheet new design.
At this time Boeing and the USN have planned growth paths for the basic aircraft in avionics and weapons, and a new engine derived from the F-22/JSF technology base is seen to be an attractive addition, but as yet is unfunded. Considerable development has also been committed to an electronic combat derivative of the F/A-18F, colloquially termed the `F/A-18G'. This aircraft would replace the EA-6B Prowler, which is often considered too slow to keep up with strike packages, with a fully combat capable escort jammer and HARM shooter. The `Airborne Electronic Attack Variant' F/A-18F derivative would employ wing tip pods with receiver equipment, a mission avionics package in the M-61 gun bay, and a mixed payload of AN/ALQ-99 derivative high power support jamming pods and AGM-88 HARM or derivative anti-radiation missiles. This aircraft would in concept most closely resemble a fusion of the F-4G Weasel and EF-111A/EA-6B models into a single type, which would retain most of the multirole capabilities of the basic F/A-18F aircraft.
The use of a buddy refuelling pod in conjunction with four 480 USG wing tanks is envisaged as a standard role for the F/A-18E/F, to provide a tactical tanking lost with the KA-6D. As the last KS-3 Viking tankers will soon be out of life, the F/A-18E/F is likely to become the sole tanker asset available to carrier airwings. Unlike the KA-6D and KS-3, it is not going to be an easy kill for an opposing fighter force, and since it is substantially faster it will be much more effective in reactive or emergency refuelling situations.
In terms of meeting the USN's aim for a low risk F-14/A-6 and F/A-18A-D replacement, in a timescale and budget compatible with current circumstances, and prior to the production of the high risk high payoff full stealth JSF, the F/A-18E/F clearly meets this objective.
A key role in USN service will be tactical tanking, using a buddy refuelling store. With the loss of the KA-6D fleet and impending retirement of the KS-3 Viking tankers, the F/A-18E/F will become the sole carrier based tactical tanking asset. Unlike the KA-6D and KS-3, an F/A-18E/F gas truck is not a tanker to be trifled with by hostile fighters (Photo Boeing)
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