Grumman A-6 Intruder - Design and Development

Design and Development

Following the good showing of the propeller-driven AD-6/7 Skyraider in the Korean War, the United States Navy issued preliminary requirements in 1955 for an all-weather carrier-based attack aircraft. The U.S. Navy published an operational requirement document for it in October 1956. It released a request for proposals (RFP) in February 1957. Proposals were submitted by Bell, Boeing, Douglas, Grumman, Lockheed, Martin, North American, and Vought. Following evaluation of the bids, the U.S. Navy announced the selection of Grumman on 2 January 1958. The company was awarded a contract for the development of the A2F-1 in February 1958.

The prototype YA2F-1 made the Intruder's first flight on 19 April 1960.

The A-6's design team was led by Lawrence Mead, Jr. He later played a lead role in the design of the Grumman F-14 Tomcat and the Lunar Excursion Module.

The jet nozzles were originally designed to swivel downwards for shorter takeoffs and landings. This feature was initially included on prototype aircraft, but was removed from the design during flight testing. The cockpit uses an unusual double pane windscreen and side-by-side seating arrangement in which the pilot sits in the left seat, while the bombardier/navigator sits to the right and slightly below. The incorporation of an additional crew member with separate responsibilities, along with a unique cathode ray tube (CRT) display that provided a synthetic display of terrain ahead, enabled low-level attack in all weather conditions.

The A-6's wing was very efficient at subsonic speeds compared to supersonic fighters such as the McDonnell Douglas F-4 Phantom II, which are also limited to subsonic speeds when carrying a payload of bombs. The wing was also designed to provide good maneuverability with a sizable bomb load. A very similar wing would be put on pivots on Grumman's later supersonic swing-wing Grumman F-14 Tomcat, as well as similar landing gear. The Intruder was also equipped with the "Deceleron", a type of airbrake on the wings with two panels that open in opposite directions; in this case, one panel goes up, while another goes down.

For its day, the Intruder had surprisingly sophisticated avionics (electronics systems), with a high degree of integration. It was felt that this could lead to extraordinary maintenance requirements, to identify and isolate equipment malfunctions. Hence, the aircraft was provided with automatic diagnostic systems, some of the earliest computer-based analytic equipment developed for aircraft. These were known as Basic Automated Checkout Equipment, or BACE (pronounced "base"). There were two levels, known as "Line BACE" to identify specific malfunctioning systems in the aircraft, while in the hanger or on the flight line; and "Shop BACE", to exercise and analyze individual malfunctioning systems in the maintenance shop. This equipment was manufactured by Litton Industries. Together, the BACE systems greatly reduced the Maintenance Man-Hours per Flight Hour, a key index of the cost and effort needed to keep military aircraft operating.

The Intruder was equipped to carry and launch a nuclear bomb, although that capability was never utilized. Because the A-6 was a low-flying attack aircraft, an unusual method was developed for launching an atomic bomb, should that ever be required. Known as LABS-IP (Launch Atomic Bomb System - Inverted Position) it called for a high-speed low-level approach. Nearing the target point, the pilot would put the aircraft into a steep climb. At a computer calculated point in the climb, the weapon would be released, with momentum carrying it upward and forward. The pilot would continue the climb, ever more steeply, until near a vertical position the aircraft would be rolled and turned, heading back in the direction from which it came. It would then depart from the area at maximum acceleration. During this time, the bomb would rise to an apogee, still heading in its original direction, then begin to fall toward the target while traveling further forward. At a pre-programed height, it would detonate. By that time, the Intruder would be several miles away, traveling at top speed, and thus able to stay ahead of the shock wave from the explosion. This unusual maneuver was known as an "over the shoulder" bomb launch.