Over the years, the General Dynamics F-111 has become one of the most iconic aircraft
designs of all time. Its long career
in both the US and Australian air forces proved that
it was a capable aircraft. In Australia, the aircraft is likely
the most iconic design remembered by the public. The F-111 was even selected
as the aircraft to be immortalized on Voyager's
gold record, to be sent into space with a recording of the aircraft
passing by. In 1968, the Royal Australian Air Force received its first F-111C. This arrived
after a period of consideration. General Dynamics
Design had been chosen for its good range terrain navigation
and ability to fulfill multiple roles. However, before
receiving the full 24 F-111s from America, a fatal incident
would cause the Australians to hold off on the aircraft
until a particular flaw was fixed. This particular flaw
was seen as so dangerous that the Australians would wait
until 1973 to accept the design. The F-111 had been designed in the early 1960s.
At the start of the decade in 1960, a Soviet surface to air
missile site had shot down a U-2 at over 60,000 feet. To the Americans, this was alarming. It meant that the Soviets had better anti-aircraft systems
than the Americans had thought. It also meant that the aging fleet
of V bombers, nuclear bombers designed in the early 1950s, like the Victor
and Vulcan, were basically obsolete. In fact, the F-105, which had just been introduced,
was already showing its weaknesses. Tactical Air Command wanted a design
that could fly fast and low below enemy radar and carry
anything from a large payload to a nuclear bomb hundreds of kilometers
into enemy territory and then get out,
all without being shot down. For General Dynamics,
the request came at the perfect time because the Navy was also looking
for a similar aircraft. They had been worried that the F-4 Phantom
would not be able to fulfill the role of Fleet Air Defense, or FAD,
and were looking for an aircraft with good speed, good range and longer
range missile systems. It would need to be an interceptor
like the F-4, but with a bomber characteristic
allowing it to carry large amounts of anti-air
and anti-ship munitions. The following year, in 1961,
everything would fall into place. Both the Navy
and Air Force had been reassured by NASA that variable sweep
wing designs were now safe, and both branches were asking for something
which could act as a bomber and interceptor and,
if need be, even a fighter. Not only that, but the aircraft would need two seats, twin engines and extreme speed. At the insistence of the newly appointed
Robert McNamara. A single aircraft should be developed
under the tactical fighter experimental or TFX program. However, things would become challenging. Disagreements between Navy and Air Force
heightened as requirements were listed and proposals
put forth. All aircraft proposals
were deemed unacceptable by the Navy. In fact, most of this stemmed
from the fact that the Air Force and Navy did not want their programs
to be intertwined. McNamara himself would step in choosing
the General Dynamics design, which shared the most commonalities
as a platform between the Air Force and Navy versions, and thus the F-111
would begin development. It would be part of what was nicknamed
the Century Series Aircraft, a series of combat aircraft
designed to fill various roles. Among them were the iconic combat tested
F-100 super saber and the F-105 Thunder Chief,
which would see massive use in Vietnam. Other designs in the series
included the F-101 Voodoo, the F-104 Star Fighter
and the lesser known F-102 Delta Dagger. A key feature of the aircraft
was the configuration of its wings. Variable geometry
wing designs had been avoided, but following intense testing by NASA,
aircraft manufacturers were encouraged in the late 1950s to begin
exploring swept wing designs. The F-111 would be the first production combat aircraft with proper variable
sweep wings. While the variable geometry system
offered many advantages. It also made the aircraft more complex. More moving parts
meant more issues could occur. In the case of the F-111
a fatal accident would prove this to be the case. In July 1968, the first
test flight of the Charlie Model F-111C in Fort Worth, Texas, highlighted
the flawed integrity of the wing box. Without proper integrity, the aircraft's
wings could detach completely. Other issues were noted in an August 1968
fatigue test, where the aircraft developed several
issues traced to poor manufacturing. Then on the 22nd of December 1969, during a pull up
from a simulated rocket attack run at Nellis Air Force Base,
an F-111A suffered catastrophic failure. When the left wing detached
from the aircraft, the experienced crew were unable to eject in the F-111
pod due to how quickly the aircraft began rolling. Both crew were killed in the accident.
With only 100 hours clocked on the aircraft, the aircraft should not have had such
a catastrophic failure. The issue was traced to the wing pivot
in which a crack had formed due to a sharp edged
forging defect. Some of these aircraft were bound
for Australia. Australian crews had been training
on earlier version of the aircraft since 1967. However, after this incident
the order was put on hold and Australia would be leased F-4E Phantoms
until the order could be completed. The Australians were rightly cautious. Since its first flight in 1964, the F-111 Alpha had suffered
from various issues both in the US and in testing in Vietnam,
resulting in the aircraft being sent home. This included an issue in which the tail
plane weld joins would fail under fatigue. This resulted in two failures in 1968, one in Vietnam
and one at Nellis Air Force Base. There was another fatal incident
in February 1969 in which the terrain following radar
failed after a signal was absorbed by snow resulting in the aircraft
flying into a mountain where it lay undiscovered
until June that year. The US Navy F-111 Bravo would also suffer
technical issues, with the Navy later scrapping the Bravo model
in favor of another aircraft. While the Charlie model
was an improvement to the aircraft, there were still major flaws
which would need correcting. This 1969 incident was widespread news. It directly resulted in the US Air Force
developing a new philosophy
for aircraft damage tolerance. What surprised everyone was just how
rapidly a small defect led to disaster. The incident occurred in the 7.26 millimeter lower plate of the wing pivot fitting a manufacturing flaw at 5.72 millimeters deep in the plate
began to grow during the flight. A crack grew to 23.6 millimeters
across the plate and 6.16 millimeters
deep enough to become a critical failure. The wing pivot fitting broke,
which led to a chain of events in which the entire left
wing flew off of the aircraft. Testing
was undertaken over the following year. Similar issues would occur a component
fatigue failure in an echo model in 1970 and a catastrophic failure
of an alpha model in 1971. The process of manufacturing was slowly
improved and ultra high strength D6AC Steel was heat
treated to improve tensile strength D6AC a medium carbon low alloy steel was chosen over aluminum alloys since aluminum at the time didn't
possess the same strength to weight ratio. However, since the majority of failures
traced back to the manufacture of steel components, it was believed that
the heat treatment process had been inconsistent, resulting in variations
of the fracture toughness of the steel. A low fracture toughness
meant that even the smallest inconsistency could result in a catastrophic crack
or failure. On the 15th of March 1973,
the first redesigned F-111C was accepted by the RAAF at Nellis
Air Force Base, after a long process
known as the recovery program. Following this, the first six aircraft
would arrive at Amberley on July 1st, 1973, with the fatal problem
now resolved. The F-111 would enter service and proved to be extremely valuable
in the Australian inventory. It had a longer range and a faster
top speed than any other aircraft being operated in South East Asia,
giving Australia an edge in defense. Not only that, but despite its early
teething problems, the F-111 would end up establishing the best safety record
of any of the Century Series fighters, with only 77 losses
after 1 million flying hours. the F-111C
would continue to serve until 2010, making the RAAF the last operators
of this iconic aircraft.
