Friday, March 13, 2020

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.

Sunday, February 9, 2020

HUP Pylon Air Inlets

A second pair of air inlets was added to leading edge of the HUP's aft pylon at its intersection with the fuselage after it first entered service in order to increase cooling air to its hard working radial engine mounted in the fuselage. The opening looks like a rounded rectangle from the side but because of the airfoil shape of the pylon cross section and the pylon's interface with the fuselage, it looks very different when viewed from other angles.

For more on the HUP from a modeler's standpoint, see https://tailhooktopics.blogspot.com/2016/04/piasecki-hup-interior.html

Friday, January 24, 2020

1/72 Airmodel AM-1 Mauler



The AM-1's purchased under the original contract (BuNo's 22257-22355), used the Curtiss electric propeller that had cuffed blades and rounded tips.
The aircraft purchased under the subsequent contract (BuNo's 122388-122437) used the Hamilton Standard prop with squared off tips.

The "C" is for NAS Columbus VA-691/ VA-692. Yellow spinners.

Monday, January 6, 2020

Blue Production FJ-2s

The first 14 production FJ-2s (BuNos 131927-40) were completed in the then-standard overall-blue color scheme. Few if any were assigned to operational squadrons. The remainder were delivered as part of the "natural metal" experiment.

BuNo 131927, first production FJ-2




BuNo 131928

BuNo 131937 assigned to Service Test, NATC, Patuxent River


Friday, January 3, 2020

F6F Hellcat wf Torpedo and Frameless Canopy


Note that there was an earlier torpedo trial with an early F6F (note gun barrel fairings and no plywood appurtenances on the torpedo).



Tuesday, November 26, 2019

AD-4W Three Views

My drawings based on original Douglas Aircraft Company drawings.




Thursday, November 7, 2019

Douglas AD-4W/AEW.1 Antenna Configurations

Ed Barthelmes has done a great deal of research on the various AD-4W radio-antenna configurations, including preparing the following illustrations.

There were basically three different suites, which Ed summarizes as A, B, and C.

BuNos 124076 through 124127 were delivered with suite A: 
BuNos 124761 through 124777 were delivered with suite B:
BuNos 125765 and subsequent were delivered with suite C:
This table identifies the various antennas by number:
The following pictures are of the Details (A through P) listed in the table above:




Note that the smaller HF relay antenna is located a bit farther forward on the tip of the vertical fin as shown above. The lower portion is housed within a dielectric panel, which necessitated the relocation of the wire antenna farther down on the leading edge of the vertical fin.


Because the AEW.1s were transferred from different AD-4W production blocks, their antenna configurations varied.

Note that Configuration A aircraft had "naked" landing gear struts and flush windows in the crew compartment doors (see https://tailspintopics.blogspot.com/2019/08/sword-172-douglas-ad-4w-skyraider.html)