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C-141A Starlifter

On 01 July 1960, Congress appropriated an extra $200 million for the Air Force to buy or modify existing airlift aircraft, earmarking $50 million of the additional funds to begin the development of a planes proposed by the Air Force less than a year before. On 15 November 1960, following several minor revisions, a final version of Specific Operational Requirement (SOR) 182 emerged, calling for a long-range jet designed principally to haul cargo. On December 21, requests for proposal were sent to Boeing, Douglas, Convair, and Lockheed, judged to be the most qualified competitors. For all practical purposes, the new strategic cargo aircraft that was to become one of the Air Force's favorite workhorses came into being during the last days of the Eisenhower administration. Of the four competitors, Lockheed had a clear advantage because of its experience in producing the C-130 tactical transport. On 13 March 1961, President Kennedy announced that the Lockheed Aircraft Corporation had won the competition.

The C-141 was designed for easy maintenance, efficient loading, and relatively short landing and takeoff. Powered by four Pratt and Whitney TF33-P-7 turbofan engines, the C-141, with an empty weight of 134,200 pounds, could to carry 70,000 pounds of cargo or 154 troops at more than 500 miles per hour. The transport could haul 63,000 pounds of cargo nearly 4,000 miles without refueling and exceed a range of 5,200 miles at reduced speed and payload.

The T-tail empennage configuration offers significant aerodynamic advantages over conventional designs. The relatively high location of the horizontal tail places the tail in a relatively undisturbed airflow at normal cruise conditions, thereby maximizing the contribution of the tail to stability and control. Many military and civil design teams have adopted this tail configuration very successfully. However, the application of the T-tail requires consideration of critical aerodynamic factors -- especially an analysis in wind-tunnel tests to ensure satisfactory handling characteristics at extreme pitch atti-tudes. At high angles of attack associated with wing stall, the low-energy wake of the stalled wing can impinge on the horizontal tail and result in a loss of longitudinal stabil-ity (pitch up) and markedly reduced longitudinal control effectiveness. As a result of these flow phenomena, the angle of attack can increase to a deep-stall condition, in which the aircraft enters a stable but uncontrollable trim point with a very high rate of descent.

In the 1950's, several high-performance aircraft configurations were developed that incorporated T-tail empennage configurations. Unfortunately, operational experiences with some of these aircraft indicated that tail flutter could be a critical problem for this configuration at high subsonic speeds. In July 1954, a British Handley Page Victor bomber experienced severe T-tail flutter and crashed during a low-altitude, high-speed flight test when the tail began wobbling and then tore off the aircraft, which dove into the ground. The accident raised doubts on the high placed T-tail configuration. In addition, jet-powered T-tail flying boats had been developed for the Navy that also expe-rienced flutter problems. In the early 1960's, a British BAC 111 T-tail transport experienced a fatal accident in which the aircraft entered a deep stall and descended in an uncontrollable condition at a very high rate of descent with an almost horizontal fuselage attitude until impact. Worldwide interest in the causes of this accident resulted in a research program at the NASA Langley Research Center on the behavior of T-tail configurations at high angles of attack.

The C-141 tail had been designed with a streamlined bullet-shaped fairing to improve airflow at the juncture of the vertical and horizontal tails. However, at transonic speeds the bullet shape caused adverse pressure gradients and shock-induced flow separation over the aft portion of the fin-stabilizer juncture. The flow separation acted as a forcing function to encourage certain flutter modes of the entire tail surface. A redesign of the bullet, included a nonstreamlined shape and a blunt "boat tail". Vortex generators on the fin and the bullet modifications entirely eliminated the vertical-tail flow separation and any tendency for flutter was pushed significantly beyond the flight envelope.

After the C-141 entered service, an unexpected unstable oscillation of the horizontal tail was experienced during high-altitude flight tests. The flutter was precipitated by a deflection of about 8 deg of the elevator relative to the stabilizer; no fix was found in flight tests. Analysis by Lockheed indicated that the flutter speed could be raised signif-icantly by increasing the elevator mass balance, and this approach was used to eliminate the problem.

Evaluations of the C-141 indicated that for certain flight conditions the aircraft experienced the phenomenon known as aileron reversal. This phenomenon occurs when a deflection for roll control of the aileron at the wing trailing edge results in aeroelastic twisting of the wing to the extent that the control effectiveness is nullified or actually reversed. That is, a pilot's input to intentionally roll the aircraft results in little or no response. In some cases, the effects of aileron reversal can actually roll the aircraft in the direction opposite to that intended by the pilot.

Lockheed's C-141 StarLifter has proven itself many times since the first flight of the C-141A on Dec. 17, 1963. The C-141A, built between 1963 and 1967, was the first jet aircraft designed to meet military standards as a troop and cargo carrier. It had a changeable cargo compartment that could transition from rollers on the floor for palletized cargo to a smooth floor for wheeled vehicles to aft facing seats or sidewall canvas seats for passengers, quickly and easily, to handle more than 30 different missions.

The first C-141A, delivered to Tinker AFB, Okla., in October 1964, began squadron operations in April 1965. Soon, Starlifters made flights almost daily to Southeast Asia, carrying troops, equipment and supplies, and returning patients to U.S. hospitals. The arrival of this aircraft, which would become the workhorse of MAC, the Military Airlift Command, was the start of the transition from the venerable C-124 Globemaster II, better known as "Old Shakey". Airdrop procedures were completely changed because 'Old Shakey' (C-124) relied upon reciprocating engines while the C-141s was the first jet transport.

Several C-141s have been modified to carry the Minuteman intercontinental ballistic missile in its special container, up to a total weight of 92,000 pounds (41,400 kilograms). Some C-141s have been equipped with intraformation positioning sets that enable a flight of two to 36 aircraft to maintain formation regardless of visibility. The C-141 was the first jet transport from which U.S. Army paratroopers jumped, and the first to land in the Antarctic. A C-141 established a world record for heavy cargo drops of 70,195 pounds (31,587.7 kilograms).

Testing of the C-141 Electric Starlifter Program ended in July 1998. This program represented the first time in aviation history that a large military cargo aircraft has both been fitted with electrically operated flight controls and flown in excess of 1,000 hours operationally. The aircraft used for the testing was a C-141A assigned to the 418th Flight Test Squadron here. Other aircraft have flown with electrically powered flight controls in the past, but only to demonstrate that such systems were feasible. While other programs typically flew 20 or 30 test hours before completion, the Electric Starlifter was targeted for a long-duration test. The modified C-141 was used in the Air Mobility Command's air cargo transportation system to acquire at least 1,000 flying hours in an operational environment. Flying hours were gathered on cargo missions to Kwajalein Atoll, Guam, Alaska, the Amazon Jungle in Brazil and even Europe. It was the second C-141 aircraft built by Lockheed more than 35 years ago, and the last C-141A in operational service. With testing completed, this aircraft was flown to Davis-Monthan Air Force Base, Ariz., where it was deactivated. The AMC Museum at Dover AFB houses an ever growing collection of vintage aircraft and artifacts that reflect the evolution of tanker/airlift operations, including the first C- 141A ever built.

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Page last modified: 07-07-2011 02:28:12 ZULU