North American NA-16 - Design and Development

Design and Development

The NA-16 was a family of related single-engine, low-wing monoplanes with tandem seating.

When the North American NA-16 was first conceived, five different roles were intended for the design, designated NA-16-1 thru NA-16-5:

• NA-16-1 general purpose 2 seat aircraft - which became the Harvard I
• NA-16-2 2 seat fighter - produced under licence in Australia as the CAC Wirraway.
• NA-16-3 2 seat light attack bomber. The first aircraft in this category was the retractable undercarriage NA-26 which evolved into the NA-36 (BC-1). The fabric covered fuselage was replaced by an all metal monococque to create the NA-44, which provided the basis for a line of light attack bombers whose improvements would result in the AT-6.
• NA-16-4 advanced trainer - became the BT-9 for the USAAC and which provided the bulk of early production. The improvement of the BT-9 with a longer metal skinned fuselage as on the NA-44 would create the NA-64 (Yale) and improved wings would result in the BT-14.
• NA-16-5 single seat fighter - although this designation was never used, it became the NA-50 for Chile, and later the NA-68, which saw limited USAAF service as the P-64.

Variants could have an open cockpit (the prototype and the NA-22) or be under a glass greenhouse that covered both cockpits. On some variants, the rear of the canopy could be opened for a gunner to fire to the rear. A variety of air-cooled radial engines, including the Wright Whirlwind, Pratt & Whitney Wasp and Pratt & Whitney Wasp Junior of varying horsepowers, could be installed depending on customer preferences. The fuselage was built up from steel tubes and normally fabric covered; however later versions were provided with aluminium monococoque structures. During the development of the design, a 6 inch stretch was made by moving the rudder post aft. Many versions had a fixed landing gear, but later versions could have a retractable undercarriage, mounted in a widened wing center section (which could have either integral fuel tanks or not. Most had a straight trailing edge on the outer wing while again, some had the wing trailing edge swept forward slightly in an attempt to fix a problem with stalls and spins. Several different rudders were used, with early examples having a round outline, intermediate examples having a square bottom on the rudder (Harvard I) and late examples using the triangular rudder of the AT-6 series, due to a loss of control at high angles of attack with the early types. Horizontal and vertical tails were initially covered in corrugated aluminum, but later examples were smooth skinned, and the horizontal stabilizer was increased in chord near its tips on later versions.

The NA-16 flew for the first time on 1 April 1935, and was submitted to the United States Army Air Corps for evaluation as a basic trainer. The Army accepted the trainer for production but with some detail changes. The modified NA-16 was re-designated by North American as the NA-18, with production examples entering Air Corps service as the North American BT-9 (NA-19). Similar aircraft continued to be sold outside the US under the NA-16 designation.

In Australia, the Commonwealth Aircraft Corporation produced 755 units of a modified version of the NA-16-2K known there as the Wirraway between 1939 and 1946.

Argentine experience with the NA-16-4P and deteriorating political relations with the US led to the local development of the I.Ae. D.L. 21, which shared the NA-16 fuselage structure, however it proved too difficult to produce and an entirely new design (the I.Ae. D.L. 22) of similar configuration, but structurally different and optimized to available materials was built instead.

In Japan, the NA-16-4RW and NA-16-4R inspired the development of the Kyushu K10W when the Imperial Japanese Navy instructed Kyushu to develop something similar. The resulting aircraft owed little to the NA-16, however Allied intelligence saw so few examples that the error was not corrected and some drawings show a modified NA-16.