Lockheed C-5 Galaxy





Date in service

C-5A . . . . . . December 1969

C-5B . . . . . . . .January 1986






General Electric TF39-GE-1C


U.S. Air Force (Active, Air National Guard, and Reserve)


Wingspan . . . . . . . . . . .222.8 ft

Length . . . . . . . . . . . . . 247.8 ft

Height . . . . . . . . . . . . . . 65.1 ft

Wing area . . . . . . . . .6,200 sq ft


Empty . . . . . . . . . . .370,000 lb

Gross . . . . . . . . . . . .837,000 lb


Cruise speed . . . . . . . .563 mph
Range . . . . . . . . . . . .3,000 n mi


Highlights of Research by Langley for the C-5

  1. The aerodynamic performance of three competing industry configurations for the C-5 contract was determined by model tests in the Langley 8-Foot Transonic Tunnel.
  2. Aerodynamic interference between the wing and the large engine nacelles and pylons were measured during tests in the 8-Foot Transonic Tunnel.
  3. Parametric tests in the Langley 16-Foot Transonic Dynamics Tunnel of a clipped-span C-5 model identified an abrupt drop in tail flutter speed at transonic Mach numbers that required increased stiffening of the fin spar.
  4. An active load alleviation system was developed in the Langley 16-Foot Transonic Dynamics Tunnel.
  5. Powered-model tests in the Langley 30- by 60-Foot (Full-Scale) Tunnel provided information on C-5 airdrop (wake) characteristics and power effects for the landing configuration.
  6. Tests of a C-5 model were conducted to determine an optimum ditching configuration.

The Lockheed (now Lockheed Martin) C-5 Galaxy heavy-cargo transport provides strategic airlift for the worldwide deployment and supply of combat and support forces. The C-5 can carry unusually large and heavy cargo for intercontinental ranges at high subsonic speeds. The aircraft can take off and land in relatively short distances and taxi on substandard surfaces during emergency operations. The C-5 is one of the largest aircraft in the world. It is almost as long as a football field and is as tall as a 6-story building with a cargo compartment about the size of an 8-lane bowling alley. The C-5 and the smaller C-141B Starlifter are strategic airlift partners. Together they can carry fully equipped, combat ready troops to any area in the world on short notice and provide the full field support necessary to maintain a fighting force. The C-5 can carry a payload that is more than twice as heavy as the C-141 payload. The lower deck of the C-5 has an unobstructed length of 121 ft and width of 19 ft that enables it to carry any piece of Army equipment, including self-propelled howitzers, personnel carriers, and tanks—none of which can enter the payload bay of the C-141.

Langley’s contributions to the C-5 program included wind-tunnel tests and performance analysis of the competing industry designs during the Cargo Experimental–Heavy Logistics System (CX–HLS) Program that resulted in the C-5. Langley conducted wind-tunnel assessments of engine and wing aerodynamic interactions; flutter studies of the T-tail configuration; flutter clearance tests for the complete configuration; wind-tunnel studies of an active load alleviation concept; flow surveys behind the configuration for analysis of airdrop characteristics; assessments of power-induced effects in the landing configuration, including studies of potential applications of the externally blown flap concept (subsequently incorporated in the C-17 transport); and model tests to determine the optimum ditching configuration. Langley facilities involved in C-5 tests included the 8-Foot Transonic Tunnel, the 16-Foot Transonic Dynamics Tunnel (TDT), the 16-Foot Transonic Tunnel, the 30- by 60-Foot (Full-Scale) Tunnel, and the Langley Impacting Structures Facility (Tow Tank).


Langley Contributions to the C-5


C-5 Evaluations


In 1964, the Air Force awarded study contracts to Boeing, Douglas, and Lockheed for the design of a heavy-lift transport for the Cargo Experimental–Heavy Logistics System (CX–HLS). In December 1964, the three manufacturers were invited to submit proposals for the new transport, which was intended to carry bulky and heavy military equipment that could not be accommodated in the C-141. All three industry designs incorporated high-wing configurations with four large turbofan engines in underwing nacelles and front and rear doors with ramps for flow-through loading and unloading. The Boeing and Douglas designs had conventional tail configurations, whereas the Lockheed design incorporated a T-tail configuration.

At the request of the Department of Defense (DOD), Langley conducted aerodynamic assessments of all three designs in the Langley 8-Foot Transonic Pressure Tunnel in 1965 under the leadership of Langley researcher Dr. Richard T. Whitcomb. The results of these tests were provided to a committee to select the winning C-5 design. In an extremely controversial decision based on proposal cost estimates, industry workloads, and geopolitical considerations, the Air Force announced in October 1965 that Lockheed had been selected to proceed with development of their C-5 design.

The C-5 design submitted by Boeing was found to have superior aerodynamic cruise performance in the transonic wind-tunnel tests performed at Langley. Boeing’s experience with the C-5 competition coupled with Boeing management’s vision of the marketability of jumbo civil transports (and interest from Pan American Airlines) led to the development of the Boeing 747, which enabled Boeing to dominate the world market with a new product line. Although the 747 was a completely new aircraft design (low wing, passenger-carrying civil aircraft), the general configuration influence of the earlier C-5 candidate is in evidence.

Research on Sting Interference Effects


Analysis of the data from the Langley 8-Foot Transonic Pressure Tunnel tests of the three C-5 configurations indicated that the high degree of aft-fuselage bottom upsweep of all the configurations increased cruise drag (especially the Douglas design, which had 19 deg of upsweep). Because of the critical nature of the aft-end drag, concern arose over potential interference effects caused by the model support sting on drag measurements.

Donald L. Loving and Arvo A. Luoma conducted tests in 1965 of all three configurations with conventional stings, dummy stings, and dorsal strut-support systems over a limited range of test variables from just below to just above the design cruise condition of each configuration. The results of their investigation indicated that the sting interference effects were of very small magnitude.

Research on Effects of Test Section Size


Also in 1965, a study was conducted by Langley researchers Arvo Luoma, Richard J. Re, and Donald Loving to address concerns over the effect of model size during transonic tests of large models in the 8-Foot Transonic Pressure Tunnel. In wind-tunnel tests, the largest model possible is generally desirable so that higher model Reynolds numbers are obtained, but if the model is too large potential tunnel wall effects and data corrections become concerns, especially at high subsonic and transonic speeds. Comparative aerodynamic data were obtained for the same 5-ft-span model of the C-5 in the Langley 8-Foot Transonic Pressure Tunnel and the Langley 16-Foot Transonic Tunnel for Mach numbers from 0.75 to 0.83. The 5-ft-span model was two to three times larger than usual models tested in the Langley 8-Foot Transonic Pressure Tunnel.

Competing C-5 configurations during tests in the Langley 8-Foot Transonic
Pressure Tunnel. Top to bottom: Douglas, Lockheed, and Boeing designs.

C-5 model mounted for tunnel test section study in the Langley 16-Foot Transonic Tunnel.

Langley 8-Foot Transonic Pressure Tunnel and the Langley 16-Foot Transonic Tunnel for Mach numbers from 0.75 to 0.83. The 5-ft-span model was two to three times larger than usual models tested in the Langley 8-Foot Transonic Pressure Tunnel.

The results of the study indicated that the data obtained in the two tunnels were in good agreement and that large models could be tested in a slotted tunnel such as the 8-Foot Transonic Pressure Tunnel at subsonic speeds with acceptable results.

Propulsion Integration Research


In 1966, Langley researchers James C. Patterson, Jr. and Stuart G. Flechner conducted parametric studies in the Langley 8-Foot Transonic Pressure Tunnel to determine the effects of large high-bypass engines on the interference drag of wing-nacelle configurations at cruise conditions. In the study, a large powered semispan model that incorporated tip-driven, nitrogen-powered engine simulators was used. The baseline model configuration represented the C-5; however, the horizontal and vertical positions of the engines relative to the wing were varied so the effects of the engine exhaust wakes could be studied in detail. The results of the study indicated that the interference drag effects could actually be beneficial for certain combinations of wing-nacelle geometric parameters.

Powered C-5 semispan model in the Langley 8-Foot Transonic Pressure Tunnel.

Low-Speed and Wake Characteristics


In late 1965, the Air Force requested that tests be conducted in the Langley 30- by 60-Foot (Full-Scale) Tunnel to investigate the application of the externally blown flap to the C-5 aircraft. Close examination of the C-5 configuration indicated that the engine exhaust would blow strongly on the trailing-edge flaps and that the aircraft would probably have considerable jet-flap lift effect in its basic configuration. The jet-flap lift effect might be sufficient to promote marked improvements in takeoff and landing performance that had not been anticipated. However, the jet-flap effect could induce pitch and roll trim problems that were also not anticipated. The Air Force request included tests of a semispan powered model, as well as a full-span powered model.

The examination by Langley of the C-5 configuration indicated that several features of the wing and flap did not lend themselves well to adaptation of a high efficiency jet-flap arrangement. For example, the flap configuration was not optimum for blown flap applications. As a result of concern expressed by Langley, a two phase program was conducted. The first phase of the program measured the effects of power on lift and drag characteristics and the effect of power (and engine-out conditions) on the longitudinal and lateral trim requirements, control, and stability of the basic C-5 configuration. The second phase of the research program consisted of modifying the wing and flap system to provide a more optimal configuration for an efficient jet flap.

In 1966, a powered semispan model of the C-5 underwent two test entries in the Full-Scale Tunnel to determine a limited amount of power effects, including the effects of thrust reversers. Unfortunately, Lockheed changed the trailing-edge flap system of the C-5 from a double-slotted configuration to a Fowler flap configuration, and the tests had to be conducted with an outdated flap system.

In 1967, a full-span 0.057-scale model of the C-5 was tested in the Full-Scale Tunnel to determine the effect of the externally blown flap concept on the aircraft. The initial work was done with the original, nonoptimized double-slotted flap design. Subsequent work was done with a new flap system that was designed specifically for the blown flap concept by the Langley staff under the leadership of Joseph L. Johnson, Jr.

Powered C-5 model mounted in the Langley Full-Scale Tunnel for externally
blown flap assessments with the double-slotted flap configuration.

Langley engineer Charles C. Smith, Jr. conducts flow visualization studies on the modified C-5 model.

Tail Flutter


The staff of the Langley 16-Foot Transonic Dynamics Tunnel (TDT) led research on flutter characteristics of the T-tail configuration as a design feature of large transport aircraft with transonic cruise capabilities in the late 1950’s. Although several aerodynamic theories had been developed for predicting subsonic and supersonic flutter of T-tails, the transonic regime posed special challenges because transonic flutter speeds tend to be lowest and are accompanied by complex shock patterns that make flutter analyses difficult. TDT staff members Charles L. Ruhlin and Maynard C. Sandford had been actively involved in the flutter issues that faced the C-141 and had contributed to the databases for the design of flutter-free T-tails for future aircraft. Their pioneering efforts in the C-141 program resulted in new test procedures, validation of computational methods, and fundamental research of the complex aerodynamic and structural coupling for the new tail designs. Two types of T-tail flutter had been identified by research: symmetric tail flutter, which was dominated by pitching-type relative motions of the surfaces, and antisymmetric flutter, which was characterized by yawing and rolling relative motions of the tail surfaces. Antisymmetric flutter is especially complex, and more data were needed to advance the understanding and design tools.
Clipped wing model of the C-5 in the Langley 16-Foot Transonic Tunnel for flutter tests.Full-span model of the C-5 in the Langley 16-Foot Transonic Dynamics Tunnel.

Clipped wing model of the C-5 in the Langley 16-Foot Transonic Tunnel for flutter tests.

Full-span model of the C-5 in the Langley 16-Foot Transonic Dynamics Tunnel.

Ruhlin and Sandford developed an innovative approach to testing large, isolated-tail and aft-fuselage models, which permitted more accurate simulation of structural and aerodynamic properties of full-scale aircraft. In late summer of 1966, they began studies of an isolated 1/13-scale model of the C-5 empennage, fuselage, and inner wings in the TDT. The T-tail, fuselage, and inboard wings were geometrically, dynamically, and elastically scaled. Two models of the T-tail were tested—one was built with the C-5 design stiffness, while the second had only half the design stiffness.

The tail flutter speeds for the designed C-5 empennage were beyond the required flutter demonstration speeds; however, a pronounced decrease in flutter speed was observed slightly above the maximum Mach number (between 0.92 and 0.98). As a result of these tests, the fin spar stiffness was increased, and flutter clearance for the full-span C-5 model in the TDT was subsequently obtained.

Load Alleviation


In the initial design of the C-5, Lockheed implemented an aggressive weight reduction program to meet performance requirements. The wing weight was reduced by using higher design stress levels and reducing primary component thickness. The higher stress levels proved to be a problem, and wing cracks were found early in full-scale ground fatigue tests in July 1969. After the aircraft had been in service several years, a wing tear-down inspection on one aircraft with a high number of flight hours revealed significant cracks. Lockheed proposed several approaches to restore C-5 wing fatigue life to a specified level of 30,000 flying hours. These approaches included (1) an active aileron system to alleviate gust loads on the wing, (2) local wing modifications to improve fatigue, and (3) redistribution of fuel within the wing to reduce bending moments.

Langley researchers Ruhlin and Sandford conducted tests of the C-5 active lift distribution control system (ALDCS) in the 16-Foot Transonic Dynamics Tunnel in 1973. The results of this study validated the use of active control technology for the minimization of aircraft aeroelastic response and showed that scaled aeroelastic wind tunnel models can be used in developing active control systems.

Active ailerons were retrofitted to 77 C-5’s in 1975 through1977. That approach, however, was superseded by a redesign of the wing that included a new center wing, two inner wing boxes, and two outer wing box sections, which were manufactured from advanced aluminum alloys that were unavailable when the original wings were produced in the late 1960’s and early 1970’s. As a result, all C-5 aircraft were modified with the new wings.

Active load alleviation test of the C-5 in the Langley 16-Foot Transonic Dynamics Tunnel.

Ditching Tests


Langley conducted ditching investigations for military and civil aircraft (including the Space Shuttle) for many years in a water tank facility known as the Langley Impacting Structures Facility. Following World War II, aircraft shapes and sizes did not vary significantly from the existing database that was generated by the Langley research. However, the introduction of the C-5 and other large wide-body civil transports required the prediction of ditching characteristics for heavier and larger configurations that were not included in the database. The design configuration and structural features of large cargo and transport aircraft also required that a dynamic model be investigated to determine overall motions, accelerations, and the approximate location and amount of damage that might be expected during a ditching at sea. In addition, the large number of main landing gear wheels (24) for the C-5 and the ability of the landing gear to be extended to various positions offered the possibility of an optimal ditching configuration, since previous wheels-down dynamic-model investigations had shown a wide variation of ditching performance with landing gear extended.

C-5 model in Langley Impacting Structures Facility for ditching tests.

C-5 ditching model with simulated structural skin on bottom of model.

At the request of the Air Force, Langley researcher William C. Thompson conducted ditching studies of a 1/30-scale model of the C-5 in the Impacting Structures Facility in 1969. The model was highly instrumented to measure accelerations, and a special scaled-structure lower fuselage was included to determine the structural damage incurred in ditching. The tests included various impact attitudes, flaps up and down, and landing gear retracted and down in simulated calm and rough (simulated sea state 4) water. Results of the study indicated that the most favorable condition for ditching was a 7-deg nose-high attitude with the flaps down 40 deg, the nose gear retracted, and the main gear fully extended. For these conditions, damage to the fuselage bottom would occur, and most of the main landing gear would probably be torn away.

Wind-Tunnel Test to Flight-Test Correlation


Analysis of flight data obtained with the C-5 indicated that significant differences existed between pressure measurements made in the wind tunnel and flight. Similar issues had previously arisen during the C-141 program. These issues involved difficulties with scaling effects in wind-tunnel tests. Extensive fundamental research was initiated in the Langley 8-Foot Transonic Pressure Tunnel under the direction of Richard Whitcomb. The research was initiated to develop an approach of simulating high Reynolds number flows by using specific placement of artificial boundary-layer trip strips on the wing upper and lower surfaces of the wind-tunnel model. The test program, which was conducted by Donald Loving, Arvo Luoma, and James A. Blackwell, Jr., successfully identified a methodology that more properly simulated the appropriate boundary-layer thickness in transonic wind-tunnel tests. This technique was used extensively in the development of the supercritical airfoil.



NASA Official
Gail S. Langevin

Gail S. Langevin


Page Curator
Peggy Overbey

Last Updated
October 17, 2003