CX-4 and Heavy Logistics System In 1961, several aircraft companies began studying heavy jet transport designs that would replace the
Douglas C-133 Cargomaster and the complement
Lockheed C-141 Starlifters. In addition to higher overall performance, the
United States Army wanted a transport aircraft with a larger cargo bay than the C-141, whose interior was too small to carry a variety of their
outsized equipment. This led to the CX-4 requirement of July 1962, for which Lockheed, Boeing, Convair, and
Douglas proposed six-engined designs. But when the US Army judged the CX-4 specification inadequate for its requirements in 1963, the proposed six-engined design was rejected because it was not viewed as a significant advance over the C-141. By late 1963, the next conceptual design was named CX-X for the specification that gave the way to the CX-HLC requirement specified and featured four engines. It was equipped with a gross weight of , a maximum payload of , and a speed of Mach 0.75 (). The cargo compartment was wide by high and long with front and rear access doors. USAF studies showed that high-bypass
turbofan engines were needed for thrust and
fuel efficiency requirements. The criteria were finalized and an official
request for proposal was issued in April 1964 for the "Heavy Logistics System" (CX-HLS) (previously CX-HLC, "Heavy Logistics Capability"). In May 1964, proposals for aircraft were received from
Boeing,
Douglas,
General Dynamics,
Lockheed, and
Martin Marietta.
General Electric,
Curtiss-Wright, and
Pratt & Whitney submitted proposals for the engines. After a downselect, Boeing, Douglas, and Lockheed were given one-year study contracts for the airframe, along with General Electric and Pratt & Whitney for the engines. All three of the designs shared a number of features. The cockpit was placed well above the cargo area to allow for cargo loading through a nose door. The Boeing and Douglas designs used a pod on the top of the fuselage containing the cockpit, while the Lockheed design extended the cockpit profile down the length of the fuselage, giving it an egg-shaped cross section. All of the designs had
swept wings, as well as front and rear cargo doors, allowing simultaneous loading and unloading. Lockheed's design featured a
T-tail, while the designs by Boeing and Douglas had conventional tails. The United States Air Force considered Boeing's design to be better than that of Lockheed, but Lockheed's proposal was the lowest total-cost bid. Lockheed was selected as the winner in September 1965, then awarded a contract in December 1965. General Electric's
TF39 engine was selected in August 1965 to power the new transport plane. Boeing lost the military contract, but went on to develop the CX-HLS concepts like the nose door and raised pod cockpit its proposal into the successful civilian
Boeing 747, the world's first
wide-body airliner, with 1,574 aircraft built when manufacturing ended in 2022 after 54 years of production.
Into production The first C-5A Galaxy (
serial number 66-8303) was rolled out of the manufacturing plant in
Marietta, Georgia, on 2 March 1968. On 30 June 1968, flight testing of the C-5A began with the first flight, flown by Leo Sullivan, with the
call sign "eight-three-oh-three
heavy". Flight tests revealed that the aircraft exhibited a higher
drag divergence Mach number than predicted by wind tunnel data. The maximum lift coefficient measured in flight with the flaps deflected 40° was higher than predicted (2.60 vs. 2.38), but was lower than predicted with the flaps deflected 25° (2.31 vs. 2.38) and with the flaps retracted (1.45 vs. 1.52). The aircraft weight was closely controlled during design and development. At the time of the first flight, the weight was below the guaranteed weight, but by the time of the delivery of the 9th aircraft, had exceeded guarantees. The C-5 program was the first development program with a $1billion (equivalent to $ billion today) overrun. Due to the C-5's troubled development, the
Department of Defense abandoned
Total Package Procurement. In 1969, Henry Durham raised concerns about the C-5 production process with Lockheed, his employer. Subsequently, Durham was transferred and subjected to abuse until he resigned. The
Government Accountability Office substantiated some of his charges against Lockheed. Later, the
American Ethical Union honored Durham with the Elliott-Black Award. The Deputy Assistant Secretary of the Air Force for Management Systems, Ernest Fitzgerald, was another person whose fostering of public accountability was unwelcome. Upon completion of testing in December 1969, the first C-5A was transferred to the Transitional Training Unit at
Altus Air Force Base, Oklahoma. Lockheed delivered the first operational Galaxy to the
437th Airlift Wing,
Charleston Air Force Base, South Carolina, in June 1970. Due to higher than expected development costs, in 1970, public calls were made for the government to split the substantial losses that Lockheed was experiencing. Production was nearly brought to a halt in 1971 as Lockheed went through financial difficulties, due in part to the C-5 Galaxy's development, as well as a civilian jet liner, the
Lockheed L-1011. The U.S. government gave loans to Lockheed to keep the company operational. In the early 1970s,
NASA considered the C-5 for the
Shuttle Carrier Aircraft role, to transport the
Space Shuttle to
Kennedy Space Center. However, the C-5 was rejected in favor of the
Boeing 747, in part due to the 747's low-wing design. In contrast, the
Soviet Union chose to transport its shuttles using the high-winged
An-225, which derived from the
An-124, which is similar in design and function to the C-5. During static and
fatigue testing, cracks were noticed in the wings of several aircraft, By 1980, payloads were restricted to as low as for general cargo during peacetime operations. A $1.5 billion program (equivalent to $ billion today), known as H-Mod, to re-wing the 76 completed C-5As to restore full payload capability and service life began in 1976. After design and testing of the new wing design, the C-5As received their new wings from 1980 to 1987.
Air-launched Minuteman ICBM feasibility test File:USAF MMIII C5 airdrop(Oct 1974).jpg|thumb|left|C-5A Minuteman Air Mobile ICBM Feasibility Demonstration – 24 October 1974 (video) On 24 October 1974, the
Space and Missile Systems Organization successfully conducted an
air-launched ballistic missile test, where an
LGM-30B Minuteman I ICBM was extracted by parachute from a C-5A Galaxy at over the Pacific Ocean. The missile descended to before its rocket engine fired. The 10-second engine burn carried the missile to again before it dropped into the ocean. The test proved the feasibility of launching an intercontinental ballistic missile from the air (see video). Operational deployment was discarded due to engineering and security difficulties, though the capability was used as a negotiating point in the
Strategic Arms Limitation Talks. 39 years later, aircraft 69–0014, "Zero-One-Four" used in the test was retired to the
Air Mobility Command Museum at
Dover Air Force Base, becoming the first C-5 Galaxy retired to a museum.
Restarted production and development In 1974,
Imperial Iran, having good relations with the United States, offered $160 million (equivalent to $ million today) to restart C-5 production to enable Iran to purchase aircraft for their own air force, in a similar climate as to their acquisition of
F-14 Tomcat fighters. However, no C-5s were ordered by Iran, and the prospect was firmly halted by the
Iranian Revolution in 1979 when the Imperial State of Iran was replaced by the
Islamic State of Iran. As part of President
Ronald Reagan's military policy, funding was made available for expansion of the USAF's airlift capability. With the C-17 program still some years from completion, Congress approved funding for a new version of the C-5, the C-5B, in July 1982, to expand airlift capacity. The first C-5B was delivered to Altus Air Force Base in January 1986. In April 1989, the last of 50 C-5B aircraft was added to the 77 C-5As in the Air Force's airlift force structure. The C-5B includes all C-5A improvements and numerous additional system modifications to improve reliability and maintainability. In 1998, the Avionics Modernization Program (AMP) began upgrading the C-5's avionics to include a
glass cockpit, navigation equipment, and a new autopilot system. Another part of the C-5 modernization effort is the Reliability Enhancement and Re-engining Program (RERP). The program replaced the engines with newer, more powerful ones. A total of 52 C-5s were contracted to be modernized, consisting of 49 B-, two C- and one A-model aircraft through the RERP. The program featured over 70 changes and upgrades, including the newer General Electric engines. Three C-5s underwent RERP for testing purposes.
Low-rate initial production started in August 2009 with Lockheed reaching full production in May 2011; 22 C-5M Super Galaxies have been completed as of August 2014. RERP upgrades were completed on 25 July 2018. The Air Force received the last modified aircraft on 1 August 2018. In 2014, Lockheed investigated drag reduction by plasma-heating of turbulent
transonic airflow in critical points, saving overall weight by reducing fuel consumption. The
Air Force Research Laboratory looked into
shape-memory alloy for speed-dependent
vortex generators. ==Design==