Technology Explained – US Tactical Aviation Pt 111

The Grumman F-14D Super Tomcat

The F-14D is the Tomcat the F-14 was always supposed to have been. The D model represents a substantial advance over its fleet predecessor, the F-14A, with substantially better manoeuvring performance, combat radius and a vastly improved avionic suite.

The F-14D was preceded by the F-14A+, a small number of late production F-14As which trialed a key component of the D model upgrade, the propulsion installation. Both the F-14A+ and the F-14D are powered by a pair of GE F110-GE400 afterburning turbofans. The F110-GE400 is a two spool low bypass ratio (0. 85) fan derived from the F101 used on the B-1B and the F404 used in the F/A-18. By combining the core technology of the F101 and fan and nozzle technology of the F404, GE produced an engine with 27,000lb of afterburning thrust and almost 17,000lb of dry thrust, with very good fighter handling characteristics.

As the GE engine is shorter than the original TF-30 fan it replaces, the tailpipe has been stretched by 50in to fit into the F-14 airframe, while the only other design changes involve inlet ramp control and detail changes to accommodate different engine systems.

The effect of the additional thrust on F-14 performance has been dramatic, with a 34% increase in CAP (Combat Air Patrol) loiter time at 150nm and a 45% increase in radius for 1 hr CAP. Catapult launches no longer require reheat and dogfight manoeuvring performance has been substantially improved. The low thrust F-14A is still an excellent dogfighter largely due to its computer controlled swing wing and substantial body lift, which translate into good turning performance in spite of the poor thrust/weight ratio. The additional thrust further improves turn performance, while also improving acceleration and climb performance. (The more powerful GE F110 turbofans also do not have the stringent operating restrictions placed upon them that affect the earlier generation TF30s. ) This provides the F-14A+/D with more manoeuvring options in the vertical, in comparison with the A model which must play the engagement largely in the horizontal plane.

Where the D model improves upon the A+ is in its contemporary avionic suite, two areas having seen substantial changes, the radar and the mission computers.

The now obsolete AN/AWG-9 fire control radar was the most powerful air intercept radar in the Western world, with the capability to concurrently track 24 targets and illuminate for six long range AIM-54 Phoenix AAMs, prior to the missiles transitioning to active radar terminal homing. It also provides a range of dogfighting modes to support the internal gun, AIM-9 heatseekers and AIM-7 medium range missiles.

In the F-14D the AWG-9 is replaced with the APG-71radar, which uses much of the technology developed for the F-15’s APG-70 set. The APG-71 uses some modules from the original AWG-9, but has a new programmable digital signal processor and digital scan control system. The new radar provides monopulse angle tracking, non-cooperative target recognition modes, raid assessment and both high and low PRF modes to expand the range of target speeds which can be usefully tracked. Substantial ECCM improvements have been made, a new antenna with much lower sidelobes is used and a sidelobe blanking channel is employed, these in addition to frequency agility and the ECCM facilities provided by the new signal processor.

In addition to the APG-71, the D model retains the Northrop AXX-1 Television Camera System stabilised telescope and adds in a sensitive GE Aerospace passive Infra-red Search & Track subsystem. With detection range at altitude of the order of 60nm, the IRS&T is a potent addition to the sensor suite. The use of the IRS&T to passively detect targets, which can than then be identified by the TCS system allows the F-14D to silently stalk its prey, lighting up its radar only to guide its missiles.

The remainder of the A model’s largely analogue avionic suite has been replaced. The F-14D employs dual Mil-Std-1553B mux bus architecture built around a pair of CDC AYK-14 Mission Computers, a system identical to that used in the F/A-18. Mux bus No 1 carries the IRS&T control interface, the ALR-67 threat warning system, the ALQ-126B trackbreaker ECM set, the JTIDS datalink interface, the Tacan receivers, the ASN-130 Inertial Nav equipment, the AHRS and the engine monitor facilities. Mux bus No 2 carries the Radar Data Processing system, the mass storage subsystem and the Stores Management System processor, the latter interfacing to a Mil-Std-1776 Stores Control Bus which ties into weapon station decoder modules. As with the F/A-18, an interprocessor 1553B bus is used, while the radar has its own dedicated 1553B bus for control traffic.

The forward and aft crew stations employ 1553B bussed multifunction displays (MFD), the pilots panel has two MFDs, one centreline, one right hand side, and a HUD, while the Radar Intercept Officer’s station has two MFDs. All MFDs employ peripheral switches as in the F/A-18, to support menu driven software.

The production status of the F-14D is unclear at this time. Initial plans were to see Grumman new build several hundred airframes, while also refitting a large fraction of the operational F-14A fleet into D configuration, with the Navy itself refitting the remainder. New production of the D model has been cancelled, and it appears that Grumman’s manufacturing program may suffer the same fate, with remaining upgrades done by the Navy itself.

While the F-14D offers a much needed growth in air superiority mission capability,it is also significant that the aircraft can easily accommodate changes to support the strike mission. The USN had initiated air-ground weapons separation tests on the F-14A during the seventies, using BRU-10 ejector racks. The BRU-10 however did not provide adequate ejection force for clean separation of larger munitions, and this together with the spending on the F/A-18 program led the USN to stop the program. In1988the USN did rethink the issue, recognising the benefits gained from the multirole capability of the F/A-18. Adding strike capability to another 20 high performance aircraft in every CVW was seen to be a verycheap way of getting morebombs on target, and the Strike Tomcat program was initiated at the Navy test centre at Pax River.

The strike capable F-14As will employ the newer BRU-32 bomb rack, mounted via ADV-703 adaptors to the fuselage Phoenix stations. In addition, HUD display modes must be expanded to support air-ground delivery symbology and the ballistic computer must have its equations changed to reflect current ordnance and delivery profiles. The integration program was well underway at the time of writing, with F-14s delivering payloads of four Mk84 2,000lb bombs. Follow-on objectives include the integration of the AGM-88 HARM antiradiation missile and the Harpoon antishipping missile.

The strike capable F-14A will suffer the limitations associated with a weapon system optimised for the air superiority mission, and it lacks the sensor suite required for all weather precision delivery. Given the expense in integrating such devices into an obsolete weapon system, it is unlikely to happen. However the 15538 based digital avionics of the D model could accommodate additional sensors far more easily. Grumman had on this basis proposed the use of the F-14D as a gap filler until the tv< reaches the fleet. Strike capable F-14Ds would be designated F-14D Quickstrike and would include additional air-ground radar modes such as synthetic aperture high resolution ground mapping, Doppler beam sharpening, fixed target track and support for a range of PGMs. Navigation and attack Flir pods would be fitted. Cockpit upgrades would include a raster scan HUD for the Flir, colour displays and NVG compatible lighting. HARM and Harpoon capability is included.

Follow on derivatives of the F-14D would include the further upgraded Super Tomcat 21 and its derivative, the Attack Super Tomcat 21 (AST-21), the upgrade path culminating in the ATF technology ASF-14.

Grumman’s strategy has been to offer incremental upgrades which may be retrofitted into the existing F-14A fleet by block upgrades. The F-14D Quickstrike is a conservative upgrade involving primarily software enhancements to the existing design and the addition of navigation and attack Flir pods, while the Super Tomcat 21 and Attack Super Tomcat 21 include substantial structural and system upgrades. The Super Tomcat 21 would see the addition of a composite 3 segment single slotted Fowler flap, an extended chord 2 segment composite slat, enlarged wing gloves containing fuel tanks with 2,200Ib capacity and an enlarged horizontal stabiliser. These would provide 25% more lift with a 5% weight penalty. With two 425 USG nacelle drop tanks this configuration would offer in excess of 28,000lb total fuel capacity, yielding a 50 to 100% increase in combat radius for a range of mission profiles. Additional thrust would be provided by a pair of F110-GE-429 or navalised P&W F119 powerplants, and an APU would be fitted.

The new powerplants would allow for Mach 1. 3 supercruise, a capability absent in current naval aircraft. System upgrades would see new VHSIC based implementations of the Navy standard AYK-14 mission computers, helmet mounted cockpit displays and large colour head down displays, with forward visibility Improved by a single piece windshield. The aircraft would retain the existing ASW-27C datalink. The ALQ-165 ASPJ trackbreaker jammer would be enhanced to a two transmitter configuration, and over twice the volume of expendables would be carried.

The Super Tomcat 21 would have a further improved radar with an electronically scanned phased array antenna which would substantially improve detection range. In addition, inverse synthetic aperture and ground Moving Target Indicator modes would be added.

The Attack Super Tomcat 21 has additional equipment dedicated to the strike role, this including the phased array radar developed for the A-12 ATA, with terrain avoidance and terrain following modes, a wide field of view HUD, a digital moving map display and GPS satnav. The aircraft would be capable of carrying up to 24 Mk82, 14 Mk83 or 6 Mk84 free fall bombs, or up to six AGM-84 Harpoon rounds.

The final evolutionary upgrade proposed is the ASF-14, which would employ a new wing, ATF technology powerplants and a number of system upgrades derived from technology used in the ATF Whether all F-14As and Ds eventually become strike capable and what additional offensive avionics they will acquire is unclear at this time. The USN’s pursuit of the E/F model Hornet has further clouded the issue, as the F/A-18E/F has comparable strike payload radius to the F-14D for a range of profiles and is already fully integrated with the Navy’s air-ground weapon suite and a range of suitable sensors. At the time of writing a major debate on this subject was taking place in the US.

The MDC F/A-18E/F

The F/A-18E/F is the Hornet the USN would have liked to have had from the outset. A direct evolutionary development of the A/C model, the E/F model employs a fuselage stretch, bigger wing, more internal fuel and more powerful engines than its predecessor.

MDC had proposed a range of enhanced Hornet derivatives during the late 1980s, these involved a range of incremental changes such as higher thrust engines, a larger dorsal hump with more internal fuel, a larger wing and improved all weather air-ground sensors. The most radical proposal involved a major structural redesign with a new wing and canards.

The F/A-18E/F is a rather conservative airframe and propul- sion upgrade, involving the addition of a 34in centre fuselage plug, a wing 25% larger in area, 25% larger horizontal tail surfaces and new powerplants. The powerplants initially proposed are 22,000lb after burning thrust derivatives of the F404, using much of the technology applied to the F412 powerplant developed for the cancelled A-12.

The GE proposal would see a new F404 which employs the core developed for the F412, with a low pressure turbine derived from the 110 and full authority digital electronic control system, also derived from the F110, and a new afterburner stage derived from the new F120 used in the ATF program. However, Pratt & Whitney and GM Allison have also expressed interest in supplying the new powerplant, with P&W proposing a new engine design and GM Allison expected to propose a derivative of the GMA 800 technology demonstrator engine.

The structural modifications to the Homet design are substantial. The larger wing will require appropriate changes to fuselage structure and will differ from the existing wing in having an additional outboard weapon station. The larger wing together with the fuselage plug will increase empty weight to 30,000lb and increase internal fuel capacity to 13,900lb, both in the class of the early F-15s. The new powerplants will also require the resizing of the inlets and ducts for increased air flow.

The performance gains of the new configuration are not trivial. The combat thrust/weight ratio is improved by almost 10%, while the CAP loiter time at 400nm is almost doubled. The improvement in radius performance is so great, that the aircraft on some profiles betters the much larger F-14D, which it also easily out- classes in transonic manoeuvring performance. The cockpit of the E/F Hornet will also see changes, with the adoption of a large 8 x 8in colour multifunction display in the centre position, the two outboard 5 x 5in displays being retained. The HUD up-front control panel will be upgraded with a touch sensitive flat panel display device.

The avionic suitewill see the APG-65 radar eventually replaced with the much more capable APG-73, Global Positioning System satellite navigation added, an automatic target handoff system datalink incorporated and provisions for the AIWS standoff munition and the AAAM missile, the planned replacement for the AIM-54 Phoenix missile.

The USN at the time of writing envisaged the phasing in of E/F Hornet production in 1995/6, with development commencing in 1992. This has been interpreted by some US observers as the USN yielding to DoD pressure to finally kill off F-14O production, the USN acquiring an alternative fighter approaching the same payload/radius class. It is very likely that the E/F Hornet will also kill off any major plans for all weather strike equipped F-14O derivatives, as the concurrent expense of two such programs will not be affordable if the Iv<. is to enter development.

The performance issues involved in comparing two radically different airframes such as the F-14O and F/A-18E/F cannot however be easily trivialised into comparing a single mission profile. Grumman have argued strongly that the F/A-18E/F cannot achieve the payload/radius of the F-14O at the same high Mach number, as the drag of the large external tanks will rapidly eat into radius at supersonic speed, unlike the semi-conformal tanks carried by the F-14. Grumman figures suggest that a fleet defence mission involving 90 minute loiter, a Mach 1. 2 engagement, and a 4 x BVR/2 x AIM-9 missile loadout would see the F/A-18C/D achieve a 120nm radius, the F/A-18E/F a 260nm radius, while the F-14O and Super Tomcat 21 could achieve 350 and 430nm respectively. On strike missions with an 8,000Ib payload of 8 x Mk83, where the F/A-18 is penalised due to the loss of external tanks, Grumman argue that the F/A-18C/D will achieve only 190nm, the F/A-18E/F 265nm, while the F-14O and Super Tomcat 21 will achieve 400nm and 500nm respectively.

Grumman have also argued that the larger F-14 will have an inherent advantage in the area of air-air sensors, as the F-14O already carries aTV telescope, IRS&T set and its radar produces 6 times the average peak power of the APG-65 with twice the

antennaarea, resulting in twice the detection range and 14 times the search volume.

The battle to save the F-14 is vital to Grummanwho may cease to produce any airframes if the program is killed off. The DoD and the official Navy position has, however, been that the F-14 is a necessary sacrifice required in order to retain the 12 CVBGs projected for the early 21st century. The cost of the new F-14s would apparently threaten the funding required to keep the carriers, and the USN considers the need for the F-14 to have diminished with the decline of the Soviet empire, as the saturation Backfire/Kitchen/Kingfish attack scenario becomes increasingly unlikely. At the time of writingGrumman even proposed substantial cost reduction in the aircraft, in order to match MDC’s price. To complicate this debate, the USN was to have acquired a derivative of the USAF F-22A ATF or the Northrop YF-23A technology demonstrator as an eventual replacement for the F-14D in the long range air superiority role. Whether this occurs and whether deliveries take place before the end of the decade is very uncertain at this time. A navalised derivative of either the F-22A or the YF-23 is not a trivial proposition in terms of development costs and this will bear heavily upon any USN decisions to spend on tactical aircraft development. Without the Naval ATF (NATF) the USN faces a severe shortage of air superiority airframes by the middle of the first decade of the next century, when much of the F-14 and F/A-18 force will have been worn out, airframe life expended and maintenance costs soaring upward. The death of the A-12 has severely disrupted the USN’s schedules for deployment and spending, the resulting AX expenditure falling into the same time frame the NATF was to have occupied.

Without a major and unplanned for injection of funding, the USN will now face block obsolescence across the tactical aircraft fleet in the first decade of the next century. As additional funding is not likely, the probable effect this will have will be a stretching of deliveries and a protracted period of significantly reduced capability the nineteen thirties all over again.

The Australian Perspective

The problems which the USN has suffered in acquiring the force structure it requires to implement its strategic objectives are not surprising. The philosophy of defining strategic objectives and fitting technology to the role is appropriate as the technology can be optimised for the roles and thus yield better performance/price ratio. This contrasts with the idea of fitting a warfighting strategy to available assets, which has a tendency to hamper longer term force development by imposing artificial and often strategically irrelevant constraints.

A key issue in the USN’s battle for assets has been tactical radius performance, as it is this parameter which has fundamental implications in naval engagements. The ability to outrange an opponent severely constrains his offensive and defensive options, and this allows the CVBG commander to concentrate his resources more effectively. The USN’s initial resistance to the 300nm class F/A-18 is clearly understandable in this context, as a third of its offensive and defensive capability is unusable unless the CVBG closes to this distance. The 1,000nm radius class stealthy ATA would have provided the USN with an offensive capability against naval and coastal assets at radii where the CVBG is very difficult to engage even by the most sophisticated opponents.

The adoption of the F/A-18E/F and strike capable F-14 derivatives cannot be a substitute for the ATA, as even these aircraft are constrained to 500nm class radio. The use of tankers is an option, but the limited deck space of a carrier severely limits the numbers of such specialised aircraft which can be dedicated to a support mission. Land based tankers are not a serious option during blue water operations, as their operational flexibility is severely limited by long transit times to station, which will also severely impact fuel offload capacity. Arguably, land based tankers would be most useful and most usable in engaging the Soviet Northern and Far Eastern fleets, but the scenarios involved would most likely see the tankers’ land bases subjected to interdiction by Fencers and Backfires escorted by Flankers.

Much debate has centred on the usefulness of the CV in the modern environment, where hunter killer submarines and strike aircraft both fire potent anti-shipping cruise missiles. Many naval strategists have argued that the CV is at the end of its useful life, as it must dedicate more of its air assets to defensive operations than to offensive operations. This argument is however sensitive to the issue of tactical radius performance: where a CV is equipped with short legged aircraft the argument carries some weight; where the CV’s strike aircraft can outrange defending aircraft, the argument is meaningless.

If a CVBG is to wage a classical two phase air battle against a land based opponent, superior tactical radius will ultimately translate into defeat for the land based side, who cannot engage the CVBG directly and will be subjected to counter-air and interdiction operations against its fixed bases. An interesting case study is the Japanese advance into the Pacific in 1942, where the A6M2 Zeke consistently outranged all of its opponents with devastating consequences for the defending Allies. Were the deception at Midway to have failed, the Allies would have had to have waited until substantial numbers of F6F and F4Us became available, before they could take the initiative. Similarly the role of the P-51 Mustang in the European air battles of 1944 cannot be overlooked. The alternative is to suffer all or even more of the pain the Royal Navy did in the Falklands, its short legged Sea Harriers being unable to maintain air superiority in spite of a superb air-air kill ratio in those engagements which did take place The Australian observer must never lose sight of this reality. The RAAF’s commitment to the F-111 force is above all else due to the aircraft’s 1,000nm class tactical radius. Successive governments and generations of bureaucracy have proposed replacing the F-111s for a wide range of reasons; clearly all of these individuals display a fundamental and inexcusable ignorance of what matters in air warfare strategic terms. The US Navy is suffering the consequences of this mindset, with legislators repeatedly denying the resources required for the CV to perform its role effectively. As a result, the USN will have to engage upon less than optimal terms in many scenarios. A Third World opponent bristling with Fencers and Flankers (or similar) could very well be one of these.

Without appropriate aircraft, the expense in building and operating large vessels such as carriers may not yield the desired payoff, as the asset will be far more exposed to hostile action than it necessarily need be, or will have to commit much of its complement to fleet defence operations at the expense of offensive power projection. The assumption that all opponents will be of the calibre of Iraq is both naive and dangerous, and hardly the basis for rational force structure planning.

Australia is a maritime nation and therefore must consider the capabilities of both its opponents and allies when planning its force structure. The USN’s ongoing difficulties with the implementation of its desired CV complement force structure suggest that theUSN may have to play more cautiously in the latter phase of the decade. It would therefore be prudent for Australia to look very carefully at the constraints likely to be imposed by this situation, and ensure that our force structure allows for these. Acquisition of additional boom/probe tankers would be a step in the right direction.

As the Gulf conflict clearly demonstrated, the post Cold War world is likely to be more turbulent than the past three decades, as the existing power blocs relax their hold on Third World governments. Not to be prepared could prove to be more expensive in the long term than any current expenditure on assets.

References: N Friedman, The US Maritime Strategy, Jane’s Publishing Company, 1988.