Jane's Encyclopedia of Aviation

Curtiss HS-1L and HS-2L (USA)
   Three-seat 298 kW (400 hp) Liberty-powered antisubmarine and patrol flying-boats of basically similar design, the HS-2L version having increased wing span and carrying heavier bombs. They became the subject of very large orders for the US Navy and were the only aircraft of indigenous design to serve with the Navy in Europe during World War I.

Flight, December 1919

THE U.S. NAVY HS-1L AND HS-2L FLYING-BOATS

   A VERY successful type of flying-boat for coastal patrol work was put into quantity production by the United States Navy during the War, the Curtiss Aeroplane and Motor Corporation and the Standard Aero Corporation turning out most of the machines between them. There are two models of this flying-boat, the HS-1L and the HS-2L, but the only difference between them is that the latter model is 12 ft. greater in span than the 1L, and has a larger rudder. Apart from this and minor details, therefore, both models are identical, so that the following description and illustrations of the HS-2L apply equally to the other model. The additional wing surface of the HS-2L is obtained by inserting a 6-ft. panel between each outer extension and the centre section. All the other parts - except, of course, the rudder - required to convert the 1L to the 2L are duplicates of other parts already on the former model, and the following is a list of the parts and alterations required in converting the 1L to 2L:- (1) Four 6-ft. panels, complete with hinges, and standard HS-1L wing-post fittings. (2) Upper centre section panel, with unrouted spars. [These are routed in the 1L.] (3) Front centre section lift wires changed from two 3/16-in. to two 1/4-in. non-flexible cable, and rear lift wires from two 3/16-in. to two 7/32-in. non-flexible cable. (4) Two 7-ft. front interplane struts 2 5/8 by 6 5/8 ins., and two 7-ft. rear 2 3/16 by 5 1/2 ins. (5) Four 1/8-in. stagger wires, with turnbuckles and end connections. (6) Larger size rudder, having 26.5 sq. ft. area instead of 19.6 sq. ft. (7) Aileron control cables lengthened.
   The main planes, which have neither stagger nor sweepback, have the R.A.F. No. 6 wing section, and comprise a centre or engine section, the lower panels of which being divided by the hull and attached to small "sidewalk" panels built integral with the hull; 24 ft. outer extensions, which in the case of the L1 are mounted direct to the centre section; and, in the L2, 6 ft. intermediate sections. The centre section surfaces are "straight," but the outer sections are set at a dihedral angle of 2°. Balanced ailerons are fitted to both upper and lower planes, the upper ailerons having a maximum chord of 2 ft. 2 ins., and span of 17 ft. 8 1/2 ins., whilst the lower ones have a maximum chord of 1 ft. 10 ins. and a span of 12 ft. 9 ins. The main spars are spaced 4 ft. apart, the front spar being located 9 ins. from the leading edge. The fabric is sewn to the wings with the seams laid diagonally or normal to the leading edge. It is doped with two coats of cellulose acetate, two to four coats of cellulose nitrate, two coats of anti-actinic grey wing enamel on the top and vertical surfaces, and one coat of the latter on the under surfaces. All the strut fittings are of steel stampings and forgings, the main spars are of spruce, and the trailing edges of flattened steel tubing. The compression ribs are of solid pine, and the intermediate ribs of lightened pine. The tail is of the non-lifting type, mounted high up on the stern above the fin. The elevators are divided and unbalanced, whilst the rudder is balanced.
   The hull is similar in form and construction to the other flying boats of the H-12 and F-5L type. It has an overall length of 34 ft. 5 ins., a width of 4 ft. for the main body and 8 ft. across the planing fins. The planking is of pine or cedar, made up of 3/16 -in. outer layer and 5/32-in. inner layer, with fabric in between. The frames, keel and stern post are of ash, whilst the keelson, deck stringers and floors are of pine or cedar. The chine stringers are also of pine, or Port Orford cedar, and the seam strips are Spanish cedar. The bulkheads are of three-ply waterproof veneer. The hull itself is finished with low visibility grey wing enamel, and all metal parts are enamelled.
   The power plant consists of a single twelve-cylindered, low-compression Navy type Liberty, developing 330 h.p. at 1,700 r.p.m., and driving a four-bladed pusher screw. The engine is carried on laminated ash-spruce-ash bearers mounted above the hull on streamlined steel tubing, braced with non-flexible tension cables. The main fuel tanks, having a capacity of from n o to 125 galls., are located in the hull at the centre of gravity, a gravity tank of about 30 galls, capacity being mounted on the top plane centre-section.
   Dual control is fitted, consisting of an inverted U ash frame equipped with two 16-in. hand-control (aileron) wheels. The rudder-bars are of ash, mounted on bronze blocks. The throttle and ignition levers are located in the cockpit, on a diagonal bridge between the two seats.
   All bracing cables are galvanised, non-flexible. The centre-section and intermediate cables in the 1L are 3/16- in., the outer cables being 5/32 in. All flying cables are doubled The following is a general specification of the HS-1L, and, in.brackets, HS-2L :-

Span, upper 62 ft. 0 ins. (74 ft 0 ins.)
Span, lower 52 ft. 1 5/8 in. (64 ft. 1 5/8 in.)
Chord 6 ft. 3 ins.
Gap 7 ft. 6 ins.
Overall length 38 ft. 6 ins.
Height 14 ft. 4 1/4 ins.
Angle of incidence, upper 5 1/2 #
Angle of incidence, lower 4#
Dihedral 2#
Area, main planes
   Upper 307 sq. ft. (380 sq. ft.)
   Lower 241 sq. ft. (315 sq. ft.)
Ailerons 105 sq. ft.
Total surface 653 sq. ft. (800 sq. ft.)
Area of tail plane 54.8 sq. ft.
Area of elevators 45.6 sq. ft.
Area of fin 19.6 sq. ft.
Area of rudder 19.6 sq. ft. (26.5 sq. ft.)
Area of non-skid 16 sq. ft.
Weights, 1L -
   Hull (including sockage) 1,265 lbs.
   Wings, tail, bracing, etc.1,400 lbs.
   Engine and equipment 1,336 lbs.
   Ordnance equipment 560 lbs.
   Electrical equipment 53 lbs.
   Navigation equipment 32 lbs.
   Crew and fuel 1,090 lbs.
   Accessories 52 lbs.
   Miscellaneous 112 lbs.
   Total weight 5,900 lbs.
Total weight, HS-2L 6,223 lbs.
Useful load, HS-2L 1,864 lbs.
Loading per sq. ft. 9.03 (7.77)
Loading per h.p. 17.9 (18.85)
Maximum speed 91 m.p.h.
Minimum speed 53 m.p.h. (55 m.p.h.)
Climb, 500 f t / 3 mins. (1,800 ft./10 mins.)