В 1930 году были введены трехбуквенные обозначения самолетов, в которых первая буква указывала на тип двигателя, вторая - на тип планера, а третья - на серию. В некоторых случаях добавлялись дополнительные буквы или цифры для более точного
обозначения модели самолета.
В течение 1934-1937 годов «Waco» разработала целую серию самолетов военного назначения с закрытыми кабинами, которые получили общее название Model D и поставлялись ВВС ряда небольших стран мира, таких как Куба.
В 1937 году была разработана модификация Model JHD, представлявшая собой двухместный биплан с закрытой кабиной, на котором могло устанавливаться различное вооружение. Самолет оснащался двигателем Wright R-975 мощностью 365 л. с. Поступил всего один заказ на шесть самолетов для правительства Уругвая (поставлены в январе 1938 года).
Flight, February 1936
TWO of a KIND
The Waco Model D and the North American NA-16 Light Military General-purpose Types: A High Performing Biplane and Monoplane with Moderate Power
EFFORTS are continually being made by certain American manufacturers to develop versatile and economical aeroplanes for the export market. There are, of course, numerous countries whose requirements do not warrant the acquisition of high powered and, consequently, expensive machines, and it is these which show interest in such types as the Model D Waco and the North American NA-16. Such machines, incidentally, should make admirable advanced trainers for air services who employ "pukka" high-powered military aircraft.
The Waco Model D
Military Wacos built previous to the Model D were conversions of existing commercial designs, but the new type was constructed expressly to suit military requirements. Essentially a single-bay staggered biplane with wings of unequal span, the Model D is of composite construction. Its wings have spruce spars, spruce and mahogany plywood ribs, compression members of duralumin tubing, leading edges of duralumin and trailing edges of cadmum-plated steel, the whole being fabric-covered. There is no centre section to the top wings, the two panels being joined over the centre line of the fuselage and supported by two tandem vertical struts. Metal-covered ailerons, hinged at an angle to the transverse axis of the aircraft, are fitted to all four planes.
The fuselage is a rectangular structure of chrome-molybdenum steel tubes with rigid bracing, faired to an elliptical cross section which merges gradually into a circular section as it approaches the N.A.C.A.-type cowling.
The split undercarriage is interesting because its wheels maintain a constant angle during the travel of the shock-absorbers; there is no axle in the accepted sense of the word; all attachments are rigid; and the widest tread is available at the moment of contact with the ground.
Pilot and gunner are seated close together in a transparent sliding enclosure which is arranged so that for normal use of the rear gun the gunner is almost completely enclosed.
The Model D is designed to take a wide variety of equipment for fighting, "attack," bombing, observation, mail-carrying, photographic and ambulance work, and can be supplied with a pair of Edo floats.
As a two-seater lighter, the machine mounts two Browning guns, controlled electrically from the pilot's cockpit and placed in the lower wings. The rear gun, likewise a Browning, is mounted on an arm which swings from side to side of the rear cockpit. Two bomb racks, mounted in tandem under the fuselage, will accommodate five 25 lb. bombs each, or two 125 lb. demolition bombs may be carried in the front rack only.
Either the Wright Whirlwind, or the Pratt and Whitney Wasp Junior radial engine, is normally specified, the powers available ranging from 250 h.p. at ground level to 400 h.p. at 5,000 ft., with a moderately supercharged model. As a fighter the Model D attains speeds of well over 170 m.p.h.