As with so many military aircraft designs, the A-6 Intruder, known originally as the YA2F-1, had some pretty ambitious features that never really panned out. The jet's swiveling exhausts were one of them.
The mid to late 1950's were an incredible time for aerospace engineering as the world came to grips with the vast possibilities that jet power provided. The A-6 Intruder came out of a requirement for a deep penetrating all-weather precision attack platform. As part of this requirement, the Navy wanted the aircraft to be capable of short takeoffs and landings (STOL), even though it would mainly be hurtled from the decks of aircraft carriers via steam catapults and "trapped" back on deck via the use of a hook and arresting cable. Nonetheless, Grumman moved forward with the design requirements and came up with the Intruder's unique silhouette that some describe as "a flying tadpole."
The YA2F-1's centrally mounted engine nacelles housed a pair of non-afterburner J-52 turbojets that produced a combined 18,600 lbs of thrust. The jet already had a large and relatively thick ring, but the STOL requirement would require more innovation than just a wing design. With this in mind, Grumman engineers designed the aircraft with a motor placement that could accommodate exhaust nozzles that would swivel up to 23 degrees downward. The idea was for the YA2F-1 to vector its thrust dynamically during its takeoff roll by rerouting the aircraft's thrust downward, along the airframe's vertical axis, thus shortening the aircraft's takeoff distance. This same configuration, along with a unique trim setting, could also slow the stout aircraft's approach speed, thus shortening its required landing distance.
The concept was innovative, and was certainly a forerunner of things to come with the famous Harrier Jump Jet years later, an aircraft that used rotating nozzles with fantastic results. This includes the Harrier's "viffing" ability, where a pilot toggles its rotatable nozzles during air combat to decelerate quickly. One can only wonder what the Intruder could have been able to do when it comes to evading enemy fighters with its variable geometry nozzles.
In testing, the YA2F-1's swiveling nozzles only significantly helped the aircraft get off the ground faster when it was lightly loaded, and only reduced the aircraft's approach speed a few knots. Considering the added complexity, cost and training requirements that were involved with the unique exhausts, the idea was dropped on production models. Still, you can see this unique design element's lasting mark on A-6s in museums and EA-6B Prowlers, the A-6 Intruder's electronic attack sibling that is still flying, via the design's low mounted engine nacelles and serpentine exhaust that is still canted slightly down and outward to avoid the aircraft's long tailboom and tailplane.
In retrospect, the YA2F-1's swiveling exhausts made a lot of sense, just not for the Intruder, an aircraft that would spend its decades long career often loaded down with thousands upon thousands of pounds of gas and dozens of 500lb bombs and other munitions. A light attack aircraft, or light fighter would have benefited better from the swiveling exhaust technology than the beast of burden, bomb truck of a jet that was to become the Intruder. Although I am sure that there are some Marine Corps A-6 pilots who would swear to you that every foot less of runway needed to get their max-loaded A-6 off the ground on a hot day in South Vietnam was worth the complexity and the cost of the swiveling nozzles!
Fast forward to today, and STOL is still a very important requirement for some air arms, and the ultra complex and super-expensive F-35B, that also features a downward swiveling exhaust, is proof of this.
Regardless of Grumman's failed attempt at fitting this unique thrust vectoring concept to their prototype Intruders, the aircraft would go on to set the bar when it comes to range and payload capabilities for the US Navy. A bar which has never been raised since its retirement in 1997.
Some would say that the Intruder's long legs, massive weapons carrying ability, highly efficient side by side cockpit arrangement and incredible tanking ability (in the form of the KA-6D) would have proven to be more valuable in the wars of the last decade than the pointy nosed, fuel hungry fighters that remained in Marine Corps and Navy inventory long after its demise, but this is another story, one that I will save for next week...
Photo Credit: USN, USMC, NAVAIR, Grumman