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General
Dynamics F-111
The General Dynamics F-111 is a
long range strategic bomber, reconnaissance and tactical
strike aircraft.
The F111 began in the early 1960s as the TFX, an
ambitious project to combine the USAF requirement for a
fighter-bomber with the United States Navy's need for a
long-range air defence fighter to replace the F-4 Phantom II
and the F-8 Crusader. The prevailing fighter design
philosophy of the day was to concentrate on very high
speed, raw power, and air-to-air guided missiles. (This
would change within a few years as experience with
then-modern fighter types like the Phantom showed that
close-in dogfighting remained a important part of air
combat, leading to the reintroduction of guns as well as
missiles and a new emphasis on manoeuvrability, but not
until well after the basic F-111 design was completed.)
For the US Navy, the trend to ever bigger, more powerful
fighters posed a problem: the current generation of naval
fighters were already barely capable of landing on an
aircraft carrier deck; and a still larger and faster
fighter would be more difficult again. An airframe
optimised for high speed (most obviously with a
high-angle wing sweep) is inefficient at cruising speeds,
which reduces range, payload and endurance, and leads to
very high landing speeds. On the other hand, an airframe
with a straight or modestly swept wing, while easier to
handle and able to carry heavy loads a long way on a
minimum of fuel, has lower ultimate performance for
combat. It was these considerations that led to the
famous F111 variable geometry, the 'swing-wing'.
The birth of the TFX was marked by controversy, with the
Air Force, the Navy and the US Government all pulling the
project in different directions. At one stage, it was
even planned to use it for the United States Army and the
United States Marine Corps as a close support aircraft!
Several manufacturers submitted bids; the final two
shortlisted were General Dynamics and Boeing. The USAF
and the USN, in one of the few matters they were able to
agree on, both wanted the Boeing design, but United
States Secretary of Defense Robert McNamara overruled
them and chose the General Dynamics aircraft instead,
citing cost issues—an extraordinary irony
considering the eventual price of F-111s!
The design eventually emerged as a 20 tonne aircraft
(empty) with a maximum takeoff weight of almost 50
tonnes, powered by two afterburning Pratt & Whitney
TF-30 turbofans in the 80 kN class, with side-by-side
accommodation for a crew of two. The high mounted wings
were attached to a pair of giant swivels, allowing it to
take off, land, and loiter with a modest 16 degree sweep
(for maximum lift and minimum landing speed), cruise at
high sub-sonic speeds with a 35 degree sweep, or rotate
the wings right aft to a 72.5 degree sweep for a very
fast maximum speed of Mach 2.4—particularly so for a
bomber, which the F-111 had become by this time, its
"F" (for "fighter") designation
notwithstanding.
Production versions of the F111 did not have ejection
seats. The pressurized crew compartment ejected as a
self-contained survival module and descended under a 70
foot parachute.
First flight was in December 1964 and entry into service
with the USAF began in 1967. It was the first variable
geometry aircraft. Despite its clear advantages, variable
geometry remains a relatively unusual feature in military
aircraft, due to higher cost, and the extra weight
imposed by the swing-wing mechanism. Nevertheless,
several other types have followed, including the Soviet
Sukhoi Su-17 (1966), MiG-23 (1967) and Tupolev Tu-160
bomber (1981), the US F-14 Tomcat naval fighter (1970) and B-1 bomber
(1974), and the European Panavia Tornado (1974).
As of 2003, the F-111 remains in service in Australia's
RAAF
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