The Lockheed C-5 Galaxy is a large four-engine military transport aircraft designed and built by Lockheed Corporation, and now maintained and upgraded by its successor, Lockheed Martin. It provides the United States Air Force (USAF) with a heavy intercontinental-range strategic airlift capability, one that can carry outsized and oversized loads, including all air-certifiable cargo. The Galaxy has many similarities to the smaller Lockheed C-141 Starlifter and the later Boeing C-17 Globemaster III. The C-5 is among the largest military aircraft in the world. All 52 in-service aircraft have been upgraded to the C-5M Super Galaxy with new engines and modernized avionics designed to extend its service life to 2040 and beyond.
The C-5 Galaxy's development was complicated, including significant cost overruns, and Lockheed suffered significant financial difficulties. Shortly after entering service, cracks in the wings of many aircraft were discovered and the C-5 fleet's use was restricted until corrective work was completed.
The USAF has been operating the C-5 since 1969. In that time, the airlifter supported US military operations in all major conflicts including Vietnam, Iraq, Yugoslavia, and Afghanistan, as well as allied support, such as Israel during the Yom Kippur War and operations in the Gulf War. The Galaxy has also distributed humanitarian aid, provided disaster relief, and supported the US space program.
Development 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.Norton 2003, p. 7.
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.Norton 2003, pp. 8–9. 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.Norton 2003, pp. 12–13.
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.Norton 2003, p. 11. Lockheed was selected as the winner in September 1965, then awarded a contract in December 1965.Erving 1993, pp. 189–190. General Electric's TF39 engine was selected in August 1965 to power the new transport plane. At the time, GE's engine concept was revolutionary, as all engines before had a bypass ratio less than two-to-one, while the TF39 promised and would achieve a ratio of eight-to-one, which had the benefits of increased engine thrust and lower fuel consumption.Bakse 1995, pp. 39, 74.Phillips 2004, p. 127. 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.Veronico and Dunn 2004, p. 62. 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).Garrard, Wilfred C. "The Lockheed C-5 Case Study in Aircraft Design". AIAA Professional Study Series.
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. In July 1969, during a fuselage upbending test, the wing failed at 128% of limit load, which is below the requirement that it sustain 150% of limit load. Changes were made to the wing, but during a test in July 1970, it failed at 125% of limit load. A passive load-reduction system, involving uprigged ailerons, was incorporated, but the maximum allowable payload was reduced from . At the time it was predicted, with a 90% probability, that no more than 10% of the fleet of 79 airframes would reach their fatigue life of 19,000 hours without cracking of the wing.
Cost overruns and technical problems of the C-5A were the subject of a congressional investigation in 1968 and 1969."Plane costs suppressed, Colonel says". Milwaukee Journal, 30 April 1969."C-5A Foe says Pentagon stripped him of duties". The New York Times, 18 November 1969. The C-5 program was the first development program with a $1billion (equivalent to $ billion today) overrun.Garwood, Darrell. "Newest Air Force planes grounded". Times-News, 17 January 1970. Due to the C-5's troubled development, the Department of Defense abandoned Total Package Procurement.Nalty 2003, pp. 192–193. 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."A Whistle-blower on the C-5A Gets a New Life". People, 15 July 1974. 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."General asks U.S. to share Lockheed loss". Spokane Daily Chronicle, 29 June 1970. 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."New Life for TriStar". Time, 17 May 1971. Retrieved 6 January 2007. The U.S. government gave loans to Lockheed to keep the company operational.Aspin, Les. "The Lockheed Loan Revisited". The New York Times, 29 August 1972.
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.Miles, Marvin."Jumbo Jet will ferry Space Shuttle Piggyback across U.S". Los Angeles Times, 19 June 1974. In contrast, the Soviet Union chose to transport its shuttles using the high-winged An-225,Goebel, Greg. . The Antonov Giants: An-22, An-124, & An-225. vectorsite.net, 1 November 2009. Retrieved 18 June 2006. 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, and as a consequence, the C-5A fleet was restricted to 80% of maximum design loads. To reduce wing loading, load alleviation systems were added to the aircraft.Norton 2003, pp. 31–36. 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,National Research Council 1997, p. 90. to re-wing the 76 completed C-5As to restore full payload capability and service life began in 1976.Finney, John W. "C-5A jet repairs to cost 1.5 billion; Pentagon outs outlay to fix Wing Defects at 1.3 Billion as 'Overruns' continue". The New York Times, 15 December 1975.Coates, James."Disputed C-5 jet gets Pentagon nod". Chicago Tribune, 21 January 1982. After design and testing of the new wing design, the C-5As received their new wings from 1980 to 1987.Norton 2003, pp. 53–56.
Air-launched Minuteman ICBM feasibility test
On 24 October 1974, the Space and Missile Systems Organization successfully conducted an air-launched ballistic missile test, where an LGM-30B Minuteman I ICBMNote: The designation "LGM" indicates: L=silo Launched, G=surface attack (Ground), M=guided Missile. If this concept had gone further, it would be expected that the "G" designation would be changed to A=Air launched. 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."Thursday, 01 January 1970 – Sunday, 31 December 1989." U.S. Air Force, Inside the AF.MIL Heritage section.Marti and Sarigul-Klijn. "A Study of Air Launch Methods for RLVs. Doc No. AIAA 2001–4619." Mechanical and Aeronautical Engineering Dept, University of California, Davis, California. 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