Flight, May 1931

I.L.I.S. The Stockholm International Aero Show
May 15-31, 1931

The Heinkel Amphibian

   Dr. Ernst Heinkel is one of Germany's pioneers, and his name has, almost from the very earliest days, been associated mainly with the twin-float seaplane type of aircraft. In this connection it is perhaps worth while recalling that before he formed his own company Dr. Heinkel was associated with the Hansa-Brandenburg firm, whose machines were not unknown to British pilots during the war. In the main, Dr. Heinkel has remained faithful to his earlier ideals, but this has not prevented him from producing from time to time machines other than floatplanes. He has produced some very good landplanes, and at Stockholm he showed an even later type, the H.E.57, which is a boat-type amphibian, designed for passenger-carrying. A model of this machine was shown at the Paris Aero Show last December, and a photograph of this model was published in FLIGHT of December 12, 1930.
   At Stockholm the Heinkel H.E.57 Amphibian arrived from Warnemunde (where the Heinkel factories are situated) piloted by Herr von Gronau, the German pilot who flew from Germany to New York, via Iceland and Greenland, on a Dornier Wal last year. The advantages of the amphibian were demonstrated in a small way at once, in that Herr Gronau was able to alight on the water outside the exhibition and taxi on to the slipway, and then, with wheels lowered, bring the machine right up on the shore just outside the main exhibition hangar.
   The Heinkel H.E.57 is a strut-braced high-wing monoplane amphibian flying-boat of mixed construction. The hull is mainly built of Duralumin, while the monoplane wing is largely of wood construction.
   Although of the two-stepped type, the hull of the H.E.57 differs in its lines very materially from the majority of British flying-boat hulls, even from those of the well-known SARO boats with which the Heinkel may best be compared, because of its flat-sided hull. It is true that the Heinkel resembles other British boats in that it has two steps (the SARO boats having but one), but the general layout of the machine is more than that found in the boats of Mr. Knowler's design. The forward main step of the Heinkel is very like those found on all British flying-boat hulls, with a fairly pronounced vee, but the rear step is of totally different design, in that it resembles more the heel of a seaplane float, terminating in a vertical stern post which merges into the bottom of the rear, cocked-up portion of the main hull. This vertical stern post carries a water rudder by means of which the machine can be manoeuvred while taxying, and also forms a tail skid when the machine is used as a landplane.
   Constructionally, the boat hull is fairly orthodox, the flat sides simplifying the construction of the frames and planking. The bottom, from the bows to the rear step, has a pronounced vee, that ahead of the main step being a vee with curved planes, while aft of the main step the vee is of the straight-lined type. Two watertight bulkheads divide the boat into three compartments, of which the middle forms the cabin of the machine. In the forward compartment is stowed the marine gear, etc., and this part is reached either through a hatch in the forward deck or through a watertight door in the cabin bulkhead. The rear part of the hull, aft of the rearmost bulkhead, does not contain any load or equipment, but a watertight door in the bulkhead gives access to it for purposes of inspecting the controls and the interior of the boat hull.
   In the middle part of the interior of the hull is arranged the cabin and cockpit equipment, which consists of the usual chair seats, with a gangway down the centre. There are seats for four passengers, and the two seats for the crew are placed side by side, and not separated from the passenger cabin. In the roof there is a celluloid skylight, while in the sides of the cabin are rectangular glass windows. Around the sides and front of the forward part of the cabin are also glass windows of unsplinterable glass, the side windows being arranged to open and serving, in case of accident, as emergency exits for the crew and passengers. The cabin is reached through a hinged hatch in the deck, visible in one of our photographs.
   The land undercarriage consists of a tripod on each side, axle and radius rod being hinged to the sides of the hull, while the telescopic leg is attached near the top, at the point where the front wing spar fitting is mounted on the hull. The telescopic leg is of the oleo type, and raising the wheels is accomplished hydraulically by means of a hand-operated pump in the cockpit, next to the pilot's seat.
   The monoplane wing is of mixed construction, with wooden spars and duralumin ribs, covered with fabric. The wing is braced by a pair of vee struts on each side, the lower end of the vee being attached to the sides of the hull approximately at waterline height. This position might be expected to make the boat slightly "dirty" during take-off, but, as we did not see the machine take off during our stay in Stockholm, we are unable to state from personal observation whether this surmise is correct or not. Wing-tip floats are attached at the points on the wing spars where the lift strut fittings occur, and, owing to the fact that the machine is a high-wing monoplane, the struts supporting the wing-tip floats are unusually long. Laterally, the wing-tip float supports are braced by nearly horizontal struts to the main wing bracing struts, and thence by vertical struts back to the wing spars.
   A Pratt & Whitney "Wasp" engine is the standard power plant of the H.E.57, but, if desired, a "Hornet" can be substituted to give a better performance. The engine is mounted on struts above the wing, and drives a metal airscrew with blades adjustable for pitch. The airscrew blade tips pass very close in front of the wind-screen, and one would expect the beating of air on the screen to cause considerable buffeting and noise in the pilot's compartment. Another disadvantage of arranging the engine as a tractor instead of as a pusher is that, when on the water, and manoeuvring up to a buoy or anchorage, the member of the crew who is working from the forward hatch has the airscrew fairly close behind him. It is true that the hatch cover is so designed as to rest at a considerable angle with the deck, and thus to afford some protection, but one cannot help thinking that the Heinkel amphibian, like a good many other machines, would be improved in many ways if the engine were turned around and made to drive a pusher airscrew. The main petrol tanks are placed in the wings, one on each side of the hull, and supply to the engine is by engine-driven petrol pumps. In the fairing behind the engine is, in addition to the oil tank, a small reserve petrol tank, separated from the engine by a fireproof bulkhead.
   The Heinkel H.E.57 amphibian has a wing span of 16 m. (52 ft. 6 in.), and a wing area of 39.2 sq. m. (422 sq. ft.). The tare weight is 1,550 kg. (3,410 lb.), and the gross weight 2,450 kg. (5.380 lb.), so that the ratio of gross weight to tare weight is 1.58 to 1, a figure which is to be regarded as quite good for an amphibian type of aircraft. With a wing loading of 62.5 kg./m.2 (12.75 lb. / sq. ft.), and a power loading of 5.45 kg./h.p. (12 lb./h.p.) (based on 450 h.p.), the maximum speed is 195 km./h. (121 m.p.h.). The landing speed is given as 93 km./h. (58 m.p.h.), and the climb to 1,000 m. (3,280 ft.) in 5 min.
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