Flight, November 1924
THE DRIGGS-JOHNSON LIGHT MONOPLANE
Four-Cylinder Henderson Engine
WE have previously recorded in our Light 'Plane and Glider Notes the fact that at the Dayton meeting the Driggs-Johnson light monoplane secured first place in the Davton
Daily News race on October 3, and also, that the same machine was second in the “Speed and Efficiency" race, and in the cross-country race for the Rickenbacker trophy. We have now received from the manufacturers of this interesting little machine the accompanying photographs and particulars.
The designer of the Driggs-Johnson "D.J.-1" is Mr. Ivan H. Driggs, an engineer of considerable experience, as he was formerly assistant chief engineer to the Dayton-Wright Co., under Col. V. E. Clark. All the constructional work was carried out in the shops of the Johnson Airplane and Supply Company, of Davton, Ohio. The only part not constructed there is the Henderson engine.
The fuselage, which is of rectangular cross-section in front, merging into a triangular section aft of the cockpit, is built up of welded steel tube, braced by Roebling wire. It may be recalled that a week or two ago we referred to this form of construction in connection with bringing down the cost of light 'planes, and it is thus interesting to have a practical example of this form of fuselage construction, familiar from the Fokker machines, applied to an actual light 'plane with apparently satisfactory results.
An unusual feature of the Driggs-Johnson monoplane is the totally-enclosed "cabin" for the pilot. The wing, it will be seen, is mounted high above the fuselage, "parasol" fashion, and the space between the lower surface of the wing and the deck of the fuselage is covered with celluloid sheet passing all round the cabane struts supporting the wing. Access to the cockpit is by a door on the port side. The object of this unorthodox arrangement is obviously to give the pilot a good view, while at the same time avoiding the extra resistance that would be caused by leaving the pilot's head and shoulders exposed. Further to improve the view, and also the lighting of the "cabin," a celluloid window covers an opening in the wing and forms a sort of skylight through which the pilot can look upwards. It is, perhaps, a debatable point whether the majority of pilots would care to be so enclosed, but the arrangement does give a very good view, and is probably quite efficient aerodynamically.
The monoplane wing is of the pure cantilever type, with spars of laminated spruce. The spars are not spindled-out, but are decreased in width from root to tip by leaving off successive laminations. The ribs have webs of 1/16-inch Spanish cedar three-ply, and divided flanges 3/16 by 3/16 inch nailed and glued to each side of the rib. In order to stiffen the wing against torsion the covering is 1/16-inch birch up to the rear spar, the trailing edge being covered with fabric. The wing section used is U.S.A. 45, and the wing is tapered in chord and thickness. The aspect ratio is high (9-8). The ailerons are of welded steel tube construction and are fabric covered. The tail surfaces also are of welded steel tube construction, and are externally braced.
The undercarriage is of simple type, with a single stream-line strut on each side, wire-braced fore and aft and laterally. The wheels are Palmers, 450 by 60 mm.
The power plant, as already mentioned, is a four-cylinder Henderson air-cooled. It is a standard engine in all respects except for the removal of the regular flywheel and housing, which have been supplanted by thrust bearings and a propeller hub. The air enters the cowling through a scoop in front, under the propeller-shaft, and is forced up the left side of the engine to the exhaust and inlet valve cages. The air is then drawn across the engine from left to right by louvres in the starboard side. An air scoop is also provided at the front of cylinder No. 1 to aid in the circulation. In the same manner a small louvre throws air on to the top of each cylinder. The petrol tank is mounted in the leading edge of the wing, the filler cap being visible in the photographs. An excellent head of petrol for direct gravity feed is thus provided.
It might be mentioned that the Henderson engine is of 80 cub. in. (1,320 c.c.) capacity, or considerably more than that allowed for this year's Lympne two-seater competitions. No actual performance figures of the "D.J.1" are available, but the top speed is believed to be about 85 m.p.h. Following are the main data: Wing span, 27 ft.; mean chord, 33 ins.; wing area, 70 sq. ft. Weight of machine empty, 326 lbs.; total loaded weight, 511 lbs.; wing loading, 7-3 lbs./sq. ft. The wing weighs 82 lbs., the fuselage 50 lbs., the landing gear 26 lbs., and the power plant, including tanks and piping, 141 lbs. The total structure weight is 168 lbs.