The Arado W 2 was a two-seat twin-engine seaplane trainer developed for the DVS in 1928. It was a cantilever monoplane with a fabric-covered steel tube fuselage that accommodated the pilot and instructor in tandem open cockpits. The undercarriage consisted of two pontoons carried on steel struts.

• 
• 
• 

• 

The twin-engine sea trainer aircraft
Arado W II.
By G. Krupp.
Purpose of the aircraft.
The conversion of prospective commercial pilots to multi-engine seaplanes using existing commercial aircraft is too expensive due to the enormous maintenance and operating costs of these types. Therefore, a twin-engine sea trainer aircraft with relatively low-power engines was to be created, thus being inexpensive to purchase, maintain, and operate, but which, for training purposes, had to have good flight characteristics and seaworthiness up to sea state 3.
Design guidelines.
Two Sh 12 engines with a total output of approximately 210 hp were available as powerplants. A mixed construction method, i.e., steel tube, wood, and canvas, was to be used, as duralumin, as the main construction material, seemed too expensive to manufacture and maintain. Due to the relatively high engine weight and the material used for the floats, a high equipment weight had to be expected. Given the high power requirements, a low wing loading was chosen, which, however, further adversely affected the setup weight. The following aspects were crucial for the selected type in order to optimize takeoff and flight characteristics:
1. A surface with as little influence as possible, i.e., a cantilever monoplane.
2. Due to the large spar extension, this provides a large connection base for the floats, thus also low forces in the struts. The low-wing monoplane results in short struts and a low center of gravity above the waterline.
3. Favorable propeller action due to the wide forward projection of the engines in front of the wing and in front of the fuselage, the small cross-section of the engine nacelles, and the greatest possible clearance of the propeller jet from the struts.
4. A semicircular float shape, which provides the smallest cross-section with sufficient step area and sufficient volume (for the aircraft size). The type used (Figs. 1, 2, and 3) is a cantilever low-wing monoplane with a continuous wing and engines positioned far forward on both sides of the fuselage. Below the engines are semicircular floats supported only by a single vertical strut, which keep the propellers free from spray. The floats are secured laterally and to prevent twisting by four struts each against a simple center support.
Construction description.
1. Wing. The wing is constructed entirely of wood and has two continuous box spars. These consist of laminated chords and plywood struts and bulkheads. The struts have openings in each bulkhead section through which the interior of the box spar is completely preserved after the final gluing. These openings provide thorough ventilation. The spars are constructed in a lattice structure; the chords consist of continuous plywood strips with battens attached on both sides. Fig. 4 shows the assembly of the wing. A tubular steel cradle, which connects the front and rear spars, absorbs the cantilever moment of the engine nacelles. This cradle also serves as a fuel tank mount. Fig. 5 shows the fittings for connecting the engine nacelles, float struts, and fuselage. The spars are attached by tubular bolts, which are inserted into filler blocks, so that the spar trusses are not weakened. To ensure torsional rigidity, the wing is covered with plywood on both sides from the nose to the rear spar. Canvas is used from the rear spar to the trailing edge. The canvas is attached using a screwed-on wooden strip, with a cord inserted in the hemstitch transferring the tension of the canvas evenly to this wooden strip. The long, narrow ailerons are also made of wood and are made torsion-resistant by all-round sheeting. The control arms are hinged to the upper surface. All cavities in the wing have ventilation holes.
2. Powerplant. The Siemens engines are connected to welded-on steel tube extensions. A firewall separates the engine system from the oil tank and fuel switchgear located behind it. Since an electric starter system was not an option due to the high weight, a type of kickstarter was developed; with a lever and corresponding coupling rods, each engine can be individually cranked over intermittently and then started using the starter. Transmission is achieved by a ratchet wheel, which acts as a freewheel when the engine starts and is still coupled. This ratchet wheel is mounted on the drive shaft with a friction clutch as a backlash preventer. Fuel is supplied by A.M. pumps, which are directly coupled to the engine's crankshaft. Air chambers and pressure gauges complete the system. The A.M. pumps are automatically activated by the kickstarter when the engine is cranked, eliminating the need for a special hand pump. "Maximall" tire gauges are used as fuel gauges. Their housings are connected to the tank vent via a special vent line to prevent measurement errors caused by pressure differences between the interior of the fuselage and the upper surface of the wings.
3. Fuselage (Fig. 6). The fuselage is a steel tube and steel wire framework and is connected to the upper surface of the wings by means of fittings. The two seats, one behind the other, have dual controls: hanging pedals for the rudder and handwheel segments for the ailerons. The elevator is controlled by linkages. The front of the fuselage is exceptionally spacious to comfortably accommodate navigation instruments for instructional purposes. The forward-mounted nozzle of the pitot tube also serves as a sight for the aircraft's longitudinal position. The entire rear of the fuselage is removable for inspection of the interior. The tail unit is also constructed of steel tubing. The elevator and rudder are balanced.
4. Floating system. The floats are connected to the wings with four vertical attachment points each. The floats have three attachment points, the wing two. The rear connection is at the rear spar, but the front, to further increase the connection base, is at the forward engine nacelle. The lateral thrusts are transmitted directly to the wing spars via a central bracket. A horizontal cable cross-bracing between the floats relieves the wing of torsional forces (Figs. 7 and 8). The floats have a trussed central girder that utilizes the greatest height of the float. The frames are two-piece and are connected to the central girder by ash wedges. The advantages of this design lie not only in its strength, but also in its ease of manufacture, since the central girder eliminates the need for a complicated slipway (Fig. 9). The bottom of the float has a slight keel. To increase strength, it is slightly concave in front of the step. The floor behind the step is slightly raised, allowing the aircraft to take off with a relatively large angle of attack without the rear part of the float "scraping" the water. The tail, which is not very pointed, forms a second step, so to speak. Each float has six watertight compartments, each accessible through a closure. The back of the floats has several guide rails.
Flight performance.
The expected performance was achieved, and in some cases exceeded. In calm conditions, the takeoff time was approximately 12 seconds with a payload of 380 kg. In a 5.5 m wind, it took an average of seven seconds. The aircraft had a power load of approximately 9.5 kg/hp. The hydrodynamic lift of the float floor was so great that shortly after full throttle, the aircraft was already gliding on the step. Due to the long fuselage and the large vertical stabilizer, maneuverability on the water was excellent, even with one engine. The horizontal speed at full throttle was 150 km/h. During the climb, the aircraft reached 1000 m in approximately 11 minutes. The aircraft proved to be extremely maneuverable and agile in the air. Its takeoff and flight characteristics are therefore fully adequate for its intended use as a high-speed aircraft.