North American General Purpose Attack Weapon (NAGPAW)

In 1954 North American Aviation (NAA) submitted an unsolicited proposal to the U.S. Navy's Bureau of Aeronautics (BuAer) for a single-seat, carrier-based, twin-J46-powered attack airplane for nuclear-weapon delivery in all-weather conditions. It incorporated two unique design features, subsequently patented, one of the first inertial navigation systems and a so-called linear bomb bay, with the store being propelled out of the end of the fuselage along with two empty fuel tanks.

There were several illustrations in the patent (see https://patents.google.com/patent/US2977853). This is the perspective view included:

No NAA-produced three-view drawing or picture of a display model of NAGPAW have been found to my knowledge.  Jens Baganz created a three-view drawing based on the patent illustrations but without the benefit of knowing the basic dimensions of the airplane or the type of engines installed. However, several years ago while doing research at the Washington Navy Yard, I came across a handwritten note that appeared to have been part of a draft summary history of the A3J-1 program created by a historian at BuAer:

It was on the same page as similar data for "NAGPAW II", which matched the numbers for the A3J-1. Note that the thrust of the J46 engine was with afterburning. The length dimension is consistent with the 48-foot long Essex-class carrier elevator albeit a bit short on clearance. I used those dimensions, the patent illustrations, and a J46 three-view drawing along with some assumptions and standard requirements to create a notional three-view drawing.

For the wing planform, I assumed a 35-degree, quarter-chord sweep angle and eyeballed the basic shape. The result had an aspect ratio of 3.18 (seems a little low but acceptable for a tactical jet) and a wing area of 385.5 square feet, which provided a reasonable wing loading. The wing was placed relatively far aft on the fuselage because of the location of the center of gravity on takeoff resulting from the amount of fuel carried in the aft 3/4s of the bomb bay tunnel.

The horizontal tail planform was scaled down from the wing's. It had to be big like the A3J's because of 1) the short moment arm relative to the cg resulting from the aft location of the wing and the shortness of the fuselage necessitated by minimizing the "spot" on a carrier, and 2) the movement of the cg forward when the tunnel fuel tanks were emptied. There was a hint of horizontal tail anhedral in two of the patent illustrations; however, the A3J had none and I'd be in danger of making things up if I tried to justify it from a stability and control standpoint.

The vertical fin seems small given the one-engine-inoperative yaw control power required but its shape was the only element that was consistent among the patent illustrations, plus the NAA proposal for the Navy's 1953 day-fighter competition (won by Vought with what became the F8U Crusader) had a very similar vertical fin.

The width of the mid fuselage was established by the J46 engines separated by a tunnel 36 inches in diameter, which assumed that the bomb was 30.5 inches in diameter consistent with a Mk 8 device (the A3J bomb-train fuel tanks were 30 inches in diameter) repackaged in a downsized Mk 4 configuration. As a check against the length required for the bomb train, I created one with two fuel tanks each sized to hold 275 gallons, the quantity mentioned in the patent. The cross section of the fuselage had to be squared off to accommodate the accessory section located on the lower front end of the J46 as well as provide a well for the main landing gear.

The main landing gear wheel was placed by the required tip-back angle (the takeoff cg having been located with 10% margin relative to the aerodynamic center of the wing) and to provide ground clearance for the aft fuselage at a fairly high angle of attack on landing. The nose wheels (two were assumed to minimize internal volume of the wheel well) were located by having the strut mounted just aft of the ejection seat bulkhead and providing a static nose-up angle consistent with general practice and lining up the tip of the vertical fin and the end of the fuselage, again to minimize overall length for deck parking.

The chord and span of the leading and trailing-edge flaps were just eyeballed. The ailerons look big but my guess was that there was a lot of roll inertia that had to be overcome. The wing-fold line was based on the maximum 27.5-foot width when folded that was standard at the time.

As always, comments, corrections, and additions are welcome.