Douglas XA4D-1 Skyhawk

Last revised October 28, 2018


The A4D/A-4 Skyhawk is one of the more successful military aircraft of the postwar era. It entered service with the US Navy in late 1956 and served with distinction for many years. It bore much of the early action in carrier-based strikes against North Vietnam during the 1960s. Although the Skyhawk is no longer serving in its primary attack role with the US Navy/US Marine Corps, a few Skyhawks are still serving in 2001 in auxiliary roles such as target towing and adversary training. However, the Skyhawk is still going strong with several foreign military services. It may well be that the Skyhawk exceeds the DC-3/C-47/Dakota in worldwide military service.

The Skyhawk was in continuous production for over 27 years, mainly for the US Navy and US Marine Corps. Two-seat versions accounted for 555 of these. Four foreign nations purchased new Skyhawks from the Douglas production line, whereas four other nations purchased refurbished aircraft from US surplus stocks.

Long after the Skyhawk had been replaced by later types as the Navy's primary carrier-based attack aircraft, two-seat versions of the Skyhawk played a primary role in the training of the Navy's new pilots. The two-seat training Skyhawk remained in service until 1999.

An additional role undertaken by the Skyhawk was that of aggressor aircraft. During the Vietnam War, it was found that the air-to-air kill ratio against North Vietnamese fighter aircraft was too low. In an attempt to improve this, the Navy Fighter Weapons School (better known as "Top Gun") which was designed to train pilots to win air-to-air battles against Soviet-block aircraft. The Skyhawk, when stripped of its avionics and weapons systems, proved to be an extremely agile aircraft, one which could simulate the performance characteristics of the MiG-17.

The Skyhawk is perhaps best remembered today as being the plane used by the Blue Angels Navy flight demonstration team from 1974 to 1987, thrilling millions of air show attendees (including me) all throughout the world.

Alarmed at the trend towards ever-increasing weight in contemporary fighters such as the USAF F-86 Sabre and the Navy F9F Panther, Douglas Chief Engineer Edward Heinemann charted a team of engineers to work on a private venture to see if this trend could be reversed. They came up with a rather daring proposal for a jet fighter weighing only 7000 pounds. The team submitted the results of this preliminary design study to the Bureau of Aeronautics in early January of 1952.

The Navy showed some interest, but since they were already involved in the consideration of several other fighter designs, they suggested that the Douglas team should apply the same sort of philosophy to the design of a carrier-based attack aircraft. This plane would be intended for the nuclear strike role, with a top speed of 500 mph, a combat radius of 345 miles, a 2000-lb weapons load, and a maximum gross weight of less than 30,000 pounds.

Heinemann's team responded a couple of weeks later with a proposal that exceeded these requirements by a substantial margin. The normal loaded weight of the aircraft would be only 12,000 pounds, less than half the limit specified by the Navy, and the top speed was 100 mph greater and the combat radius 115 miles greater. Douglas was authorized to proceed with further design studies. During the evaluation, the range requirements were increased, raising the gross weight to 14,000 pounds

The design team came up with a low-winged jet-powered aircraft with a modified delta planform. The wing had a quarter chord sweep of 33 degrees. The span was only 27 feet 6 inches, which eliminated any need for wing folding and saving a lot of weight and complexity. The wing had three one-piece spars with spanwise stiffened skin. The delta shaped wing formed a single box with integral fuel tankage, and the upper and lower skins were single pieces. The spars and stringers were continuous from tip to tip. The wing leading edge was equipped with automatic leading edge slats and split flaps were provided on the trailing edge. Most of the wing between the spars contained an integral fuel tank with 560 gallon capacity.

The aircraft had a normal tail, with a rudder and a set of elevators. The dorsal fin had a delta shape, and had a rudder set at its rear. The horizontal tailplane was set at at the lower part of the vertical tail, just above the tailpipe. The horizontal stabilizer was electrically adjustable in incidence, and could be adjusted for trim throughout the entire flight range. A large speed brake was provided on each side of the rear fuselage.

The engine was to be a licence-built version of the British Armstrong Siddeley Sapphire turbojet, rated at 8000 lb.s.t. It would be built by Wright under the designation J65. The engine was mounted in the fuselage center with air intakes mounted high on both sides of the fuselage aft of the cockpit. The engine had a single exhaust in the tail.

The internal fuel capacity was 770 US gallons, carried in integral wing tanks and in a self-sealing cell aft of the cockpit and between the engine air ducts. All of the offensive weapons were to be carried externally on three stations--one underneath the fuselage centerline and one underneath each wing. The internal armament was to be a pair of 20-mm cannon, one in each wing root. Design gross weight with a single Mk 12 nuclear weapon was 14,250 pounds, and the combat radius with this weapon with internal fuel only was 400 miles.

The tall main undercarriage members were attached to the inner wing trailing edge, and retracted forward and rotated through 90 degrees to fit into wells in the leading edge of the wing. The wing was sufficiently thin so that long fairings had to be fitted underneath the wing to cover the landing gear legs when retracted. The nose landing gear retracted forward into a well in the nose. The forward-retracting landing gear had the avantage in that emergency extension systems were not required, since the airstream flow will lock the gear down after free fall. The landing gear appears at first sight to be rather long and stalky, but it facilitiates adequate ground clearance during rotation on takeoff

The cockpit canopy was of the "clamshell" variety, opening via a hinge located immediately to the rear. An upward- firing ejector seat was to be provided for the pilot.

A preliminary mockup inspection took place in February of 1952 Douglas was given a contract for one aircraft On June 12, 1952. The designation was XA4D-1, and the BuNo was 137812. The project was financed by diverting funds from the cancelled A2D Skyshark program. Final mockup inspection took place in October of 1952. By this time, the Navy had ordered 9 production aircraft, which was soon increased to 19.

The XA4D-1 was assembled at the Douglas El Segundo plant and was rolled out of the factory in February of 1954, the aircraft being given the popular name Skyhawk. In press releases, the plane was often referred to as "Heinmann's Hot Rod". The windscreen of the cockpit was frameless, and the nose was provided with a long instrumentation probe. The pilot was provided with a NAMC Type II ejection seat. Only the centerline weapons pylon was fitted, and there was no carrier arrester hook. No armament was fitted.

The XA4D-1 was trucked out to Edwards AFB, 100 miles away. The first flight was delayed by the late delivery of its 7200 lb.s.t Wright J65-W-2 turbojet. First flight took place at Edwards AFB on June 22, 1954, test pilot Robert Rahn being at the controls.

Late in the career of the XA4D-1, it was fitted with most of the features of the production A4D-1, including a tailhook, a jetpipe fairing, vortex generators, and all three weapons pylons.

Sources:


  1. McDonnell Douglas Aircraft Since 1920, Vol 1, Rene J. Francillon, Naval Institute Press, 1988

  2. American Combat Planes, 3rd Edition, Ray Wagner, Doubleday, 1982.

  3. United States Navy Aircraft Since 1911, GordonSwanborough and Peter M. Bowers, Naval Institute Press, 1990.

  4. Douglas A-4 Skyhawk Variant Briefing: Part 1, Harry S. Gann, Wings of Fame, Vol 4, 1996.

  5. The Douglas A-4 Skyhawk, Harry Gann, Aircraft in Profile, Doubleday.