Republished by F-111.net
with the express permission of Carlo Kopp. More articles here.
"The RAAF F-111G `G-Model
Pig' "
(Australian Aviation, June 1995.)
Carlo
Kopp, PEng
Carlo.Kopp@aus.net
© 2001, 1995, Carlo Kopp
Last
Updated 29 May 2001
The government's
decision to acquire 15 former USAF F-111G aircraftwas a major surprise for most observers
of the Australian defence scene.Fortuitously for the ADF, the government did the proper
thing and followedthrough on its promise, with the aircraft entering service over the last
twelvemonths.
The primary reason for acquiring these aircraft
was to reduce the number of hours flown on the F-111C airframes, which like all highly
stressed airframes have a finite number of flying hours in their structures. Spreading the
flying hours across the expanded fleet effectively extends the life of the F-111A/C
airframes. The F-111G airframes have substantially lower accumulated airframe fatigue than
their TAC and RAAF counterparts, as they spent most of their previous life in Strategic
Air Command.
The issue of the F-111A/C fleet size has always
been problematic, as the original purchase of 24 airframes to equip two essentially
operational squadrons really fell somewhat short of the number of airframes properly
required to provide full squadron strength, with an allowance for conversion training,
depo overhauls and attrition reserves. The RAAF has always needed the extra airframes, but
the US were loath to part with the aircraft during the Cold War and our government was
always lukewarm on the subject, as it involved spending a lot of money. The only
additional airframes acquired were the four attrition replacement F-111As which now equip
6 SQN. The acquisition of the G-model airframes has finally provided the airframe reserves
to allow for full squadron strengths in a sustained operational environment.
The RAAF's F-111Gs were built as General Dynamics
FB-111A strategic bombers, serving with USAF Strategic Air Command (SAC) and tasked with
suppressing Soviet strategic air defences and related C3 systems, using the AGM-69 SRAM
missile. SAC had originally acquired 75 aircraft, with IOC being declared in October,
1971. These aircraft equipped the 509th BW at Pease AFB, and the 380th BW at Plattsburgh
AFB. In SAC service the aircraft would have carried 170 kT W69 armed SRAMs or free fall 1
MT B43, 10 kT B57 or variable yield (10 -¿ 500 kT) B61 `special' devices. With a maximum
payload of six SRAMs or freefall weapons, the FB-111A was truly a doomsday machine. Had
the balloon gone up, the FB-111A force would have preceded the B-52G and H aircraft into
Soviet airspace, carving `glow in the dark' corridors through the PVO's air defence SAM
belts.
After a distinguished but thankfully uneventful
career in SAC, the FB-111A wings were deactivated and the aircraft reassigned to Tactical
Air Command, to bolster the 4 Wing TAC F-111 fleet. TAC redesignated the aircraft as
F-111Gs and formed the 427th TFTS at Mountain Home to operate the aircraft. The F-111G
aircraft assigned to TAC went through a factory refit which substantially modernised the
aircraft's offensive avionic suite and communications equipment, to a standard very close
to the RAAF's AUP.
From a technical viewpoint the FB-111A was a
distinct variant in USAF service, an optimised strategic penetrator built to defeat the
massive IADS of the Soviet V-PVO. The airframe shared the `big' wing of the USN F-111B and
RAAF F-111C, and the strengthened undercarriage of the latter subtype. The aircraft's
fuselage was closest to that of the F-111D, and employed the `stall proof' Triple Plow II
inlet geometry shared by later model airframes. The FB-111A was fitted with the TF-30P-7
engine which delivered nominally 16% higher thrust than the P-3 used in the earlier A/C
and E models.
SAC had specified a wide range of detail design
changes to the aircraft, including a stowable crew access ladder, jettisonable weapon
pylons, wiring and plumbing to the outer wing stations, various cockpit ergonomic changes
(primarily in switch locations), dual 285/300 USG internal weapon bay fuel tanks and a
distinct avionic and electronic warfare fit.
The original offensive avionic system was built
around an AJN-16 inertial nav-attack system and AYK-6 mission computer, both common to the
F-111D Mk.II and F-111F Mk.IIB systems. With the D-model, the FB-111A also shared the
AYN-3 cockpit display and the APN-167 radar altimeter. Unique to SAC were the newer
APQ-134 Terrain Following Radar, the APN-185 Doppler navigation equipment and the ASQ-119
Astrocompass. The latter two items were needed to improve the aircraft's navigational
accuracy on long polar sorties into Siberian airspace.
The recent USAF avionic refit of the F-111G fleet
replaced the antiquated seventies offensive avionic system with a contemporary digital
computer and dual ASN-41 (Honeywell H523 or Litton LN-39) Ring Laser Gyro Inertial Systems
(INS), integrated with new APN-218 Doppler nav equipment, which replaced the obsolete
APN-185. The integrated nav-attack system uses Kalman filtering techniques to yield the
best possible position estimate from the dual INS channels and the Doppler velocity
readings, providing very high accuracy. A newer TFR was fitted, replacing the seventies
APQ-134. The elderly ASQ-119 astrocompass was removed. The provisions to fire the SRAM
missile were deactivated, as this weapon was not used by TAC. Much of the new avionic
equipment is identical to the RAAF AUP systems, albeit slightly older production versions.
The FB-111A defensive avionic suite was enhanced
to provide for better survivability in the V-PVO's hunting grounds. While the aircraft
shared the ALR-62 Radar Homing And Warning System (RHAWS) with the other variants, the
improved ALQ-137 defensive ECM system was fitted, with additional aft facing antennas,
improved band coverage and more sophisticated jamming techniques generation, compared to
the TAC standard ALQ-94 (used by the A/C/D/E/F models). The only other type to carry this
sophisticated system is the high value EF-111A tacjammer. Unlike most aircraft defensive
ECM systems, the ALQ-137 combines both trackbreaking and noise jamming techniques. The
AAR-34 IR tail warning system (MAWS) is retained, as is the ALE-28 chaff/flare dispenser.
The RAAF F-111G aircraft retain the USAF (SAC) EW suite, and thus have the most capable
ECM fitted to any aircraft in the Southern hemisphere.
Compared to the basic F-111C airframe, the F-111G
carries an additional 585 USG of JP-4 fuel which is about 3,500 lb or 11% more than the
basic capacity. The fuselage and wing tank capacity is identical, at 4990 USG or about
32,400 lb. The engines deliver almost 20% higher thrust in service.
With the aircraft freshly out of the USAF avionic
refit, the Doppler enhanced dual RLG INS provides superb accuracy, in fact the F-111G is
the most accurate bomb delivery platform in RAAF service today, with blind radar dumb bomb
delivery errors a fraction of the analogue F-111C's sixties LN-14 system's errors. It will
be interesting to see whether the post AUP digital F-111C system matches the F-111G.
Australian Aviation had the opportunity to discuss
aircraft performance with the 6 SQN G-flight aircrew deployed to the Avalon airshow. The
RAAF crews are very happy with the aircraft, which are easier to fly than the standard
C-model aircraft due the more robust intake, accelerate and climb much better due higher
installed thrust, fly further due greater fuel capacity, and are so accurate with the
Doppler enhanced INS that the navigators have to be selective about terrain features used
for INS updates, so as not to fall foul of accuracy limitations in current maps.
Current RAAF intentions are to refit the aircraft
with the digital flight control system to be used on the AUP F-111A/C and the AWADI/DSTO
ALR-2002 Radar Warning Receiver also to be fitted to the F-111A/C. This would save
maintenance costs on two of the most critical aircraft subsystems. There is no intention
at this time to rework the remaining F-111G avionic system to the AUP standard. This is a
sensible decision, as the F-111G offensive avionics are only several years older than the
AUP systems, of the same generation of technology, and share many common components. An
issue will be integration with RAAF specific weapons such as the AGM-84 Harpoon ASM. Such
weapons, whilst not particularly technically difficult to integrate, do require some
software and hardware changes, and it remains to be seen whether the RAAF will do so.
Even if the RAAF does not integrate its full suite
of PGMs into the F-111G avionic system, the aircraft can still be most effectively
employed in defence suppression and blind radar (dumb) bombing sorties, and as laser
guided bomb or standoff weapon `carrier' aircraft, paired with an F-111C which would use
its Pave Tack or datalink to guide weapons for both aircraft. This approach was used very
effectively both by the USAF and the RAF in the Gulf, the latter having many more bombers
than laser designator pods.
It is worth noting, that the F-111G with its
better performance, endurance and defensive ECM capability would make an excellent
electronic combat platform to support the strike aircraft as anti-radiation missile (eg
HARM) firing platforms. The RAAF would be well advised to consider this in the course of
the upcoming ALR-2002 upgrade, and look at fitting the G-model 2002s with Emitter Locating
System (ELS) facilities for this purpose. This would be a very cheap way of enhancing the
RAAF's electronic combat capability, as the incremental cost of adding an ELS capability
to the 2002 is much lower than fitting out with additional equipment. To date electronic
combat has not received the attention it properly deserves in the ADF force structure, and
the 2002 upgrade is a golden opportunity to redress this deficiency at a minimal cost.
It is the author's view that the F-111G
acquisition was the single best value for money defence purchase in the last two decades,
and has finally brought 82 WG/SRG up to an operationally effective strength. We can hope
the government will fully capitalise on this wise investment.
Pic.1 F-111G
The F-111G provides better performance, endurance
and Electronic Counter Measures capability than the existing F-111A/C fleet. As such the
aircraft would be well suited to the electronic combat role, supporting the strike
aircraft with anti-radiation missile fire. Modifications to support this role could be
readily accommodated during the planned ALR-2002 RWR upgrade. This would be a very cheap
way of providing the electronic combat capability which the RAAF, uniquely among Western
air forces, at this time lacks.
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