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Republished by F-111.net with the express permission of Carlo Kopp.  More articles here.


F-111 Upgrade Options

Part 4 ASRAAM, HMDs, Integration and Supportability

by Carlo Kopp
Copyright Carlo Kopp & Aerospace Publications Pty Ltd

In the preceding part of this series, we explored a number of upgrade options which could enhance the long term survivability of the F-111. In this final part, we will discuss remaining upgrade options for the aircraft.

Defensive AAMs and Helmet Mounted Displays

There is an excellent case for equipping the F-111 with the ASRAAM and a suitable Helmet Mounted Display. If dealing with hostile fighters, the ASRAAM is a seriously deterrent to a forward quarter BVR attack since it has competitive range performance with many BVR missiles, and the seeker sensitivity to acquire such against a clear night sky background. Moreover, due to its combination of inertial and thermal imaging guidance, it can be cued by a rangefinding RWR receiver package to acquire a specific fighter in a forward quarter engagement geometry, through an overcast.

Under visual conditions, if a fighter bounces the F-111 in a beam or aft quarter attack, unless it can get a successful early shot, a tight turn by the F-111 will place the fighter within the visual acquisition envelope for an over the shoulder ASRAAM shot. Since the ASRAAM is compatible with the Sidewinder rail, the only integration issues are those to do with a Helmet Mounted Display, which are in many respects simpler than integrating systems into the airframe.

An F-111 with a loadout of six or more ASRAAMS, a HMD, a passive targeting RWR and a modern multimode radar becomes a useful long range air defence asset, and serious threat to reconnaissance aircraft, maritime patrol aircraft, transports, and bombers without fighter escorts.

The choices in HMD technology are growing rapidly, as many manufacturers are working on this technology. Alternatives range from simpler lightweight day-only HMDs for close-in fighter combat, to integrated HMD/NVG systems (ie NVGs embedded within the helmet) which project combined raster/stroke and NVG imagery on the pilot's visor. The latter are of particular interest, since with NVG compatible cockpit lighting they allow the F-111 pilot to see outside the aircraft at night, improving situational awareness in a manner not previously possible. Integrated NVG/HMDs thus combine the weapon cueing and flight information display capability of the HMD with the night vision capability of the NVG, without the cumbersome handing, limited peripheral vision and ejection hazards of clip-on NVG attachments. It is expected that PtSi or InSb Focal Plane Array FLIRs will later supplant NVGs in integrated night vision helmets, thus providing a true low cost head steered high resolution FLIR capability.

A genuine integrated HMD/NVG solution provides in effect the capabilities usually found in a head steered navigation FLIR, a Head Up Display and a helmet mounted cueing device for weapons. The technology allows for features such as "virtual" instruments, "virtual" HUDs, "virtual" moving map displays, and EW warning displays. Instead of looking for "bugs" on the RWR scope, you see cueing boxes or bars outside the aircraft. Typical HMDs will blank out the symbology which might occlude instruments when the user is looking down into the cockpit.

The absence of a HUD and navigation FLIR in the F-111 is often criticised, the emerging generation of HMD/NVG packages would allow an equivalent capability to added in at a very modest cost, with the additional ability to display sensor data without the costly and messy hardware penalties of a major cockpit rework.

This is another area where a modest upgrade can provide important dividends in capability and survivability. What is particularly attractive about this technology is that it opens up opportunities to improve critical data presentation in a flexible and evolvable manner, addressing a large part of the "sensor fusion" data presentation problem. Major upgrades in imagery and data presentation can be achieved by simply altering software, and replacing or upgrading the HMD in use. With a mixed inventory of HMDs with varying capabilities, the optimal balance between cost and capability can be achieved.

Integration is relatively painless, with software modules and a driver library added into the mission computer Operational Flight Program (OFP), very similar to that already used for the existing Programmable Display Generators (EXPDG), and a box of electronics (typically compact enough to fit into an F-5E) to drive the HMD tubes and support the head position sensing, attached directly to the Mil-Std-1553B databus. The existing AUP system can support this with no difficulty.

Should a HMD be adopted to provide a virtual HUD, then the existing and somewhat ancient ASG-23/25 series Lead Computing Optical Gunsight becomes redundant and may be removed. The space occupied by the gunsight control panel is a good fit for an off the shelf colour flat panel AMLCD display, these are typically only 2-3 inches thick. Such a display would be well positioned for use as a pilot's SAR/GMTI radar display, moving map navigational and situation display, threat warning display, JTIDS track display or an integrated tactical situation display merging moving map, waypoint, threat warning and JTIDS track data. This is another "tack on" addition which could be directly integrated into the existing AUP architecture via the Mil-Std-1553B bus, and would significantly reduce pilot workload.

Other technologies such as cockpit voice control of systems and spatial aural threat warning, the latter being developed by DSTO AMRL, are like the HMD basically "tack on" additions which can be readily grafted on to the existing Mil-Std-1553B bussed AUP architecture, with appropriate additions to the mission computer OFPs.

Integration and Ongoing Upgrade Issues

The last decade has seen an unprecedented growth in the capability of computer and digital signal processing hardware performance, and concurrently a significant drop in hardware costs per capability. Moore's Law, which states that computing performance doubles every eighteen months, is beginning to bite very hard. The rate of technology evolution has and continues to accelerate, with computer performance the primary technological "enabler" across the board.

This has some important implications. The first is that the supportability life cycle of any single piece of hardware is contracting. In commercial computing, Silicon goes obsolete in 2 years, and the total life-cycle of any component, from design through production to total obsolescence, has contracted from about a decade or more, down to several years. This is also reflecting in shortening life cycles for Milspec components, be they Silicon, board level assemblies, or complete Line Replaceable Units (LRU). In practical terms, this means that supporting any hardware requires that you start throwing out unsupportable hardware, such as computer boards, after 5-10 years of operation, since you won't be able to buy any more spares.

The other side of this effect is that capabilities are evolving now much faster, and to remain competitive, you must be able to adapt as quickly as other players do. This means that you have to upgrade more frequently.

One or two decades ago, it was feasible and reasonable to schedule major block level technology upgrades for platforms at 10-15 year intervals, with the comforting knowledge that over that 10-15 year interval your aircraft would remain competitive, and you could get any spare you needed. This is no longer true.

The current trend is to build weapon systems to be fully modular, using standard architectures and interfaces, such as Mil-Std-1750A, MIPS, i960 or COTS Alpha, PowerPC or SPARC for computers, Mil-Std-1553B/1773 for systems bussing, and Mil-Std-1760 for stores interfaces. The only part of the weapon system which retains some stability over the life of the system is the software running on the system's computers, which will be refined and improved over the life of the system, in an incremental fashion. Hardware is replaced on an ongoing basis, as components become obsoleted, and new weapons are deployed and integrated. This is a direct equivalent of the "Plug and Play" model which is central to commercial computing today, and a wide range of manufacturers provide chip, board and even LRU "drop in" upgrade hardware. Mil-Std-1750A computer chipsets currently available outperform those in the existing AUP installation many times over (to compare objectively, the AP102A computer in the AUP delivers about 1 DAIS MIPS performance, current technology can do 50 DAIS MIPS or better).

Arguably, the ADF's whole funding model, and committee centred and program structured funding approval process is geared to a model which is becoming increasingly an artifact of history. The idea that we spend a given amount on a platform in a single block upgrade, and not touch it for a decade or two, is simply no longer representative of the evolving game in technologically centred warfare.

Fortuitously, the F-111 AUP has given the aircraft a core avionic system which is well matched to this new model, and can continue to be incrementally upgraded throughout the remaining life of the system. The Echidna package will also fit this model nicely, if implemented properly as a modular, bussed, internal suite.

From a long term supportability perspective, and also the perspective of technological adaptability to maintain competitiveness in combat, the remaining artifacts of the F-111's analogue and early digital heritage will become a problem. From either perspective, an excellent case can be made for the replacement of the remaining first generation avionic hardware on the aircraft, with current digital technology. Much of what has been proposed in this paper achieves exactly these two longer term objectives, aside from their evident utility in improving the aircraft's combat capability and survivability.

Providing the F-111 with a current technology avionic suite in all areas produces a system which is fully supportable in the longer term, and provides the ability to adapt to any opposing technological developments very quickly, be it by upgrading internal systems or by integrating new weapons.

The argument may be raised as to why it isn't better to replace the aircraft early with a current build F-15E, Eurofighter or F/A-18E, all modern digital multirole fighters. This bears some closer examination to determine precisely where these types differ in penetration and weapons capability from the F-111. All share a Mil-Std-1553B bussed architecture weapon system, which the F-111 has. However, they are fitted with new technology engines, DBS/SAR/GMTI capable multimode radars, modern EW packages, and will have Helmet Mounted Displays. All are inferior to the F-111 in combat payload radius and airframe design for high speed low level penetration. The F-111 upgrade package discussed in this paper essentially equalises the avionic advantages of newer types against the current F-111 AUP, and provides the low ownership cost of new technology, particularly the engines. What is important however is that this proposed F-111 upgrade package achieves this at a fraction of the cost of buying 35 new USD 50M multirole fighters, and provides anything up to twice the combat radius of these new types, ie much more bang for many less bucks.

Another argument which may be raised is that "very smart weapons on dumb or not very smart aeroplanes" are more cost effective than "less smart weapons on very smart aeroplanes". The case of highly intelligent, relatively autonomous weapons, carried by aircraft with limited sensor packages is not supportable unless some very smart offboard sensors already exist, sensors which are both accurate enough to position a smart weapon for terminal homing, and sensors which are accessible by sufficiently fast and robust communications channels to allow a rapid response. It is argued that by keeping the complexity in the weapon, and taking it out of the aircraft, money can be saved. This model is in the simplest of terms, basically wrong.

Experience in the US with both the Rivet Joint and the JSTARS has shown that dumb aeroplanes can be successfully directed into the vicinity of the intended target, but at that point the model fails most often since they are unable to locate the target accurately enough to engage it successfully. The accuracy and coverage of long range sensor platforms such as the Rivet Joint and the JSTARS is simply not adequate for remote weapon targeting, and may not achieve the required capability for 1-2 decades.

The proof of this pudding lies in the actions of major overseas air forces. We see the proliferation of SAR/GMTI capable fighter attack radars. We also see the installation of the ASQ-213 HTS homing receivers on the F-16CJ HARM shooter, the US Navy effort on the TAS homing receiver, as well the UK's commitment to a passive targeting ESM on the Eurofighter instead of a conventional RWR. This is demonstrable proof of the fact that the "not very smart aeroplane" model is seriously wanting when it comes to getting the job done.

An expendable one shot sensor, such as a missile or bomb seeker, is by its nature inferior in coverage and performance to a robust onboard sensor package. It must have smaller apertures, and a lesser number of apertures than carried by an aircraft, since it must be packaged into a very much smaller airframe volume. The only party who gains from the "very smart weapon" model is the vendor community, who instead of building several dozen or hundred targeting sensors for airframe installation, will be building several thousand for weapon seekers. The ADF does not have the resources to field multiple platforms in the class of the Rivet Joint and the JSTARS, or to deploy the the amount of satellite capability to provide suitable targeting intelligence, therefore it cannot even approach the offboard targeting capability the US has, even with the inadequacies that are forcing the US to upgrade sensor packages on their combat aircraft.

Therefore it makes no sense for the ADF to place all of its eggs into the provenly inadequate model of "very smart weapons on not very smart aircraft, with smart offboard sensing", since it will never have the offboard sensor capability to support this model, and the model itself has yet to deliver the results claimed for it to date. For the F-111 this means a modern radar package, and passive targeting capabilities for the new EW package. Importantly, these additions in no way preclude the later addition of an offboard targeting capability.

Conclusions

It is evident that the best utilisation of the F-111 during the latter half of its operational life cycle, a twenty year period at this time, will require some further improvements to the aircraft's systems. These are not difficult to identify, the issue is not so much of whether they should be adopted, but rather one of how best to go about blending them into the existing and planned systems to provide the best tradeoff between cost and capability. In summary these are:
 

  • introduction of a modern SAR/GMTI capable attack radar in the 1 ft resolution class, with provisions for SAR strip mapping, imagery recording, pseudo-differential (GAM/GATS) weapon guidance and surface target tracking and identification. As the attack radar is a vital capability to support the standoff weapons being acquired under AIR 5398, and an enabling capability for later weapons, it would appear that the best approach would be to extend the scope of AIR 5398 to include the acquisition and integration of the new radar. Whether to equip all aircraft with a recce capability would be an issue to be considered. The most attractive approach would be to use a dual redundant LPI active array radar, to concurrently replace the TFR. IOC cca 2003-5, cost cca USD 100-200M.
  • Investigate the alternatives in reducing the detectability of the TFR, either through replacement, modification to an LPI waveform, or integration of the TF function into a dual redundant LPI active array attack radar.
  • Expedite the AIR 5391 EW upgrade, but schedule in a near term incremental upgrade (IOC 2005+) to incorporate a precision direction finding and rangefinding package, and the capability to detect basic spread spectrum LPI threats. The latter should preferably be integrated into the ALR-2002 design, IOC 2005+, cost TBD.
  • acquire and integrate the GBU-31 JDAM at the earliest date. Since the weapon is a defacto replacement for the Paveway, it may be argued that the JDAM should be funded separately from AIR 5398. IOC cca 2000, cost cca AUD 1M.
  • reactivate the internal weapon bay. Choices are the "Hi" option with additional station decoders for a total of 6 smart stations, or the "Lo" option with 4 smart stations, selectable 4/5 or RH/LH internal, with 3/6 retaining existing AUP wiring. Clearance testing to be performed for the GBU-31 (Mk.84/BLU-109) JDAM. Investigate feasibility of internal Harpoon carriage, and clear the weapon if feasible. IOC cca 2000, modification costs (Lo) cca AUD 1M or less, clearance costs TBD.
  • Acquire a suitable raster/stroke capable Helmet Mounted Display with the growth option of integrated NVG (IIT) or FPA FLIR. Integrate the HMD to provide flight information display ("virtual HUD"), ASRAAM/AIM-9M and other weapon cueing, and threat information display. IOC 2002, cost TBD.
  • Replace the TF30 with the GE F110-GE-129 EFE or similar engine variant, to increase sustained top speeds, and combat radius. To minimise risks, a good case can be made for refitting a single aircraft with F110s as a demonstrator, and trial testing the aircraft in tactical scenarios, against fighter aircraft. IOC 2003, cost USD 300-350M.
    Apply basic RCS reduction measures to the cockpit, radar bay and inlets, and explore the opportunities to apply radar absorbent appliques to other problem areas. IOC between 2005 and 2010.
     

These are a package of possible upgrade measures which would enable the F-111 to remain viable and effective in the post 2005-2010 period, given the availability of suitable fighter escorts (ie Hornet replacements) in the 2010-2015 period, and essentially equalise the F-111's running costs, avionic and weapons capability against new build conventional multirole fighters. With the exception of the attack radar and powerplant replacements, all of these measures are either minor upgrades, or extensions to existing programs, which can exploit existing program management and funding structures.

It is important to not lose sight of the fact that each of these measures contributes in several ways to enhancing the aircraft's survivability in a more competitive regional environment.
 

  • The SAR/GMTI radar allows highly precise targeting of standoff weapons, emerging glide weapons, and all weather GPS guided bombs, thus extending the aircraft's all weather reach without any penalty in accuracy, while also providing a credible supporting recce and BDA capability. Air-air modes in the most viable candidates enhance survivability by providing a credible self defence capability against fighters. GMTI / NCTR modes allow for engagement of non-emitting "pop-up" mobile SAM threats, and Army support all weather CAS/BAI. Employing a dual redundant active array radar combining the attack and TF functions would significantly improve system reliability, and the use of LPI modes would enhance survivability by a large margin in all environments.
  • The adjunct rangefinding receiver and channelised warning receiver provide detection of LPI threats, early detection of all threats, and facilitate early evasion of SAMs. Anti radiation missiles and the ASRAAM can be cued for the engagement of emitting SAM systems, be they land based or naval, and fighters from BVR ranges.
  • Internal weapon carriage increases penetration speeds, increases combat radius, and reduces signatures. This allows the full exploitation of the capabilities inherent in the latest generation of GPS guided bombs and glidebombs.
  • Modern powerplants increase sustained penetration speeds and high speed persistence, combat radius, and reduce high speed infrared signature. This will much improve survivability against fighters and SAMs, and improve achievable combat payload radius and thus aircraft reach. A side benefit is lower long term support cost and better long term supportability.
  • reduction of airframe radar signature, and attack radar and TFR emission detectability, will both reduce available warning times and engagement times for fighters and SAMs, reducing their ability to perform effectively. Integration of the TF function into a dual redundant LPI attack radar would solve two emission problems with a single modification.
  • a suitable Helmet Mounted Display can provide for the cueing of air-air and anti-radiation weapons, significant cockpit workload reduction, and an embedded night vision capability. Potentially it can provide the centralised display for a basic sensor fusion capability on the aircraft, concentrating critical threat, status and targeting information into a single, flexibly reprogrammable, digitally controlled display.

Importantly, this package reinforces the aircraft's strengths, and retains and enhances existing capabilities. The RAAF's existing Concept of Operations (CONOPS) combining fast low level penetration and standoff weapons is made to be more survivable, more accurate, more robust and more flexible.

A separate issue is the acquisition of an operational tanker force with the capability to refuel the F-111. This is a major strategic force structure decision, and is not specific to the F-111, but has been discussed here due to its pivotal importance. The installation of the JTIDS/Link-16 datalink on the F-111 falls much into the same category, and has therefore not been discussed, it will be a vital capability for interoperability with the US, as well as providing the means of passing target and threat data between the F-111 and other platforms, such as the Wedgetail and surface assets. The adoption of a Wide Area Differential GPS network and integration of this capability into the F-111 has also not been discussed, since it is another major strategic force structure decision, not specific to the F-111.

The issue of how much to spend on the F-111 to retain its capability in the latter half of its operational life is bound to produce some lively debate in Canberra. The aircraft is without doubt the ADF's most potent asset for maritime strike, counter-air strike, strategic strike and battlefield interdiction. Until a suitable replacement becomes available, which can match its diverse capabilities, replacement is simply not an option, cost factors aside. The earliest credible prospect is the planned F-15E replacement, an enhanced F-22 Raptor variant, which is unlikely to be available until 2015 or later. So the only option is to apply upgrades.

We can expect that many a question will be asked as to why should further money be spent on the F-111. In perspective the best answer to this is to pose another question: "should we be pouring taxpayers dollars into assets of marginal utility, or pouring them into assets of proven high utility ?" In less formal terms, it is a simple question of whether to throw good money after bad, or invest it into the best asset we have. There are a number of surface bound assets in the current ADF force structure which have doubtful combat capability, and much less than the phenomenal sums of money proposed to be spent on these would clearly provide a much better return if invested into the F-111 force.

Last year's strategic policy document stated that the "Knowledge Edge" is the ADF's top priority for the coming decade, and that defending the nation's air-sea gap is the primary focus in developing combat capabilities. Most of the upgrades proposed in this paper are specifically aimed at giving the F-111 a decisive "Knowledge Edge" over its opposition. As the most potent asset in the ADF's inventory of tools for defending the air-sea gap, be it by maritime strike or counter-air strike, investment of resources into the F-111 is wholly consistent with the government's stated strategic policy. There should be no argument in this matter. The resources can be made available, the technology is available, the risks are minimal and the purpose of the upgrades is in every respect consistent with stated policy. The time to act is now, so that the investment into the AUP production infrastructure can be exploited, and a good return in aircraft life cycle can be realised - there is nothing to be gained by procrastination.

The USAF plans at this time to retain the B-52 until 2030. Stretching the F-111 to 2020 is a much less demanding task.


Author's note:

This series was compiled from the best available open source material, and is as detailed and accurate as is possible without engaging in specific engineering proposal development. The draft was reviewed both in the US and locally by a number of experts, including both former USAF F-111 aircrew and design engineers with experience on the F-111 and the powerplants discussed. The author would like to extend his sincere thanks for the support provided and advice given.


Pic.1 Sextant Topsight (sextant-topsight.jpg)

The latest generation of Helmet Mounted Displays for fighter applications enable the cueing of heatseeking missiles, and provide HUD like display of aircraft and weapons status and parameters, all projected at infinity on to a curved visor. A more recent development are binocular raster capable HMDs, which can display FLIR imagery. A number of current types also include fully embedded NVG tubes, which project directly on the visor, avoiding the cumbersome clip-on installation of existing NVGs. Depicted is the day only Topsight E, slated for use on the Rafale (Sextant Avionique).

Pic.2 ASRAAM

The AIM-132 ASRAAM is to become the RAAF's primary WVR AAM, carried on the F/A-18 Hornet. This missile would be a potent addition to the F-111, particularly if integrated with a Helmet Mounted Display, since the latter would allow the crew to fire the missile "over the shoulder" at any fighter which strays into their field of view. With range performance competitive with many BVR missiles, and support for passive targeting, the ASRAAM would make a forward quarter fighter intercept a potentially very risky proposition for an attacker (Matra-BAe).

Pic.3 ... (APG-76 Imagery)

Without doubt the most urgent upgrade priority in the existing F-111C AUP/F-111G avionic suite is the fitting of a modern Synthetic Aperture Radar / Ground Moving Target Indicator mode capable attack radar. Weapons such as the AGM-142 SOW and follow-on AIR 5398 standoff munitions require such a radar for both supporting reconnaissance and effective inflight targeting of these weapons. This imagery was produced by the Norden APG-76 MMRS, which the Israeli Air Force use to support and target the AGM-142 from their upgraded F-4E Phantoms. The upper three images show Roswell AFB at 42.1 NMI (3 metre resolution), Langley AFB at 101.0 NMI (9 metre resolution), a road bridge at 37.8 NMI (18 metre resolution), the lower images show an LCAC hovercraft approaching a beach at 29.2 NMI (9 metre resolution), a convoy departing the beachhead, and helicopters departing a staging area, imaged at 27 NMI (9 metre resolution), and finally an image with 5 metre absolute registration accuracy, measured against a radar reflector. The rectangle is the Nav Box cursor, which surrounds the programmed coordinates. In the latter image, the radar was assisted by GPS (Norden).

Pic.4 (HMD Symbology)

Modern HMD technology allows the projection of critical flight, status, threat and engagement data directly on the pilot's visor. This example shows the pilot cueing an anti-radiation missile seeker against an offending threat emitter (Carlo Kopp).

Pic.5 (PaveTack.tiff)

While the Pave Tack is now dated technologically compared to newer electro-optical/laser pods, it is still regarded to be a highly accurate sensor with excellent jitter performance, suitable for bombing from all altitudes. It primary limitation is poor resolution and moisture penetration in the tropics (82 WG RAAF).

Pic.6 (FLIR Imagery)

Current state of the art 8-12 and 4-5 micron band FLIR technology offers considerably higher image resolution and reliability than the sixties/seventies rotating mirror technology AAQ-9 FLIR imaging module in the Pave Tack. A good case can be made for a technology upgrade of the Pave Tack, inserting a current technology thermal imaging module into the existing pod design. The cost of buying up retired USAF Pave Tack pods and cradles, and refitting them with a new computer and thermal imaging module is a fraction of the cost of acquiring and integrating a new production pod design (Lantirn, Litening, TIALD), thus enabling the provision of a standardised installation across both the C and G model aircraft.


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