CX-X and Heavy Logistics System
In 1961, several aircraft companies began studying heavy jet transport designs that would replace the Douglas C-133 Cargomaster and 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. These studies led to the "CX-4" design concept, but in 1962 the proposed six-engine 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. It was equipped with four engines, instead of six engines in the earlier CX-4 concept. The CX-X had a gross weight of 550,000 pounds (249,000 kg), a maximum payload of 180,000 lb (81,600 kg) and a speed of Mach 0.75 (500 mph or 805 km/h). The cargo compartment was 17.2 ft (5.24 m) wide by 13.5 feet (4.11 m) high and 100 ft (30.5 m) long with front and rear access doors. To meet the power and range specifications with only four engines required a new engine with dramatically improved fuel efficiency.
The criteria were finalized and an official request for proposal was issued in April 1964 for the "Heavy Logistics System" (CX-HLS) (previously CX-X). 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 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 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. At the time GE's engine concept was revolutionary, as all engines beforehand had a bypass ratio of 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.
The C-5 is a large high-wing cargo aircraft with a distinctive high T-tail fin (vertical) stabilizer, and with four TF39 turbofan engines mounted on pylons beneath wings that are swept 25 degrees. Similar in layout to its smaller predecessor, the C-141 Starlifter, the C-5 has 12 internal wing tanks and is equipped for aerial refueling. Above the plane-length cargo deck, it provides an upper deck for flight operations and for seating 75 passengers including the embarked loadmaster crew, all who face to the rear of the aircraft during flight. Full-open(able) bay doors at both nose and tail enable "drive-through" loading and unloading of cargo.
The cargo hold of the C-5 is one foot longer than the entire length of the first powered flight by the Wright Brothers at Kitty Hawk. For its voracious consumption of fuel and its maintenance and reliability issues the Galaxy's aircrews have nicknamed it FRED, for: fucking ridiculous, economic/environmental disaster.
Takeoff and landing distance requirements for the plane at maximum-load gross weight are 8,300 ft (2,500 m) and 4,900 ft (1,500 m), respectively. Its high flotation main landing gear provides 28 wheels to distribute gross weight on paved or earth surfaces. The rear main landing gear can be steered to make a smaller turning radius, and rotates 90 degrees after takeoff before being retracted. "Kneeling" landing gear permits lowering the aircraft when parked, thereby presenting the cargo deck at truck-bed height to facilitate loading and unloading operations.
The C-5 features a Malfunction Detection Analysis and Recording (MADAR) system to identify errors throughout the aircraft.
The cargo compartment is 121 ft (37 m) long, 13.5 ft (4.1 m) high, and 19 ft (5.8 m) wide, or just over 31,000 cu ft (880 m3). It can accommodate up to 36 463L master pallets or a mix of palletized cargo and vehicles. The nose and aft cargo-bay doors open the full width and height of the cargo bay to maximize efficient loading of oversized equipment. Full width ramps enable loading double rows of vehicles from either end of the cargo hold.
The Galaxy C-5 is capable of moving nearly every type of military combat equipment, including such bulky items as the Army armored vehicle launched bridge (AVLB), at 74 short tons (67 t) , from the United States to any location on the globe; and of accommodating up to six Boeing AH-64 Apache helicopters or five Bradley Fighting Vehicles at one time.
The C-5A is the original version of the C-5. From 1969 to 1973, 81 C-5As were delivered to U.S. Air Force bases. Due to cracks found in the wings in the mid-1970s, the cargo weight was restricted. To restore the C-5's full capability, the wing structure was redesigned. A program to install new strengthened wings on 77 C-5As was conducted from 1981 to 1987. The redesigned wing made use of a new aluminum alloy that did not exist during the original production.
The C-5B is an improved version of the C-5A. It incorporated all modifications and improvements made to the C-5A with improved wings, simplified landing gear, upgraded TF-39-GE-1C turbofan engines and updated avionics. 50 of the new variant were delivered to the U.S. Air Force from 1986 to 1989.
The C-5C is a specially modified variant for transporting large cargo. Two C-5s (68-0213 and 68-0216) were modified to have a larger internal cargo capacity to accommodate large payloads, such as satellites. The major modifications were the removal of the rear passenger compartment floor, splitting the rear cargo door in the middle, and installing a new movable aft bulkhead further to the rear.The official C-5 technical manual refers to the version as C-5A(SCM) Space Cargo Modified. Modifications also included adding a second inlet for ground power, which can feed any power-dependent equipment that may form part of the cargo. The two C-5Cs are operated by U.S. Air Force crews for NASA, and are stationed at Travis AFB, California. Both 68-0213 and 68-0216 completed the Avionics Modernization Program by January 2007. 68-0213 is being upgraded in RERP to the C-5M (SCM) standard.
C-5 AMP and C-5M Super Galaxy
Following a study showing 80% of the C-5 airframe service life remaining, AMC began an aggressive program to modernize all remaining C-5Bs and C-5Cs and many of the C-5As. The C-5 Avionics Modernization Program (AMP) began in 1998 and includes upgrading avionics to Global Air Traffic Management compliance, improving communications, new flat panel displays, improving navigation and safety equipment, and installing a new autopilot system. The first flight of a C-5 with AMP (85-0004) occurred on 21 December 2002.
The Reliability Enhancement and Re-engining Program (RERP) began in 2006. It includes new General Electric F138-GE-100 (CF6-80C2) engines, pylons and auxiliary power units, upgrades to aircraft skin and frame, landing gear, cockpit and pressurization systems. The CF6 engine produces 22% more thrust (for 50,000 lbf or 220 kN) from each engine, providing a 30% shorter takeoff, a 38% higher climb rate to initial altitude, an increased cargo loadand a longer range.Upgraded C-5s are designated C-5M Super Galaxy.The C-5M reached initial operating capability (IOC) on 24 February 2014 with 16 aircraft delivered.
Lockheed also planned a civilian version of the C-5 Galaxy, the L-500, the company designation also used for the C-5 itself. Both passenger and cargo versions of the L-500 were designed. The all-passenger version would have been able to carry up to 1,000 travelers, while the all-cargo version was predicted to be able to carry typical C-5 volume for as little as 2 cents per ton-mile (in 1967 dollars). Although some interest was expressed by carriers, no orders were placed for either L-500 version, due to operational costs caused by low fuel efficiency, a significant concern for a profit-making carrier, even before the oil crisis of the 1970s, keen competition from Boeing's 747, and high costs incurred by Lockheed in developing the C-5 and later, the L-1011 which led to the governmental rescue of the company.
C-5 Shuttle Carrier
Lockheed proposed a twin body C-5 as a Shuttle Carrier Aircraft to counter the Conroy Virtus, but the design was turned down.