Flight, January 1924
THE STAHLWERK-MARK R.V/23 COMMERCIAL MONOPLANE
A New German Machine Carrying Four Occupants on a 100 h.p. Mercedes Engine
REFERENCE has been made on various occasions to the Inter-Allied restrictions on German aircraft design, which limit
the size of machine and engine that it is permissible to build and operate in Germany. The result has been, on the one hand, that German designers, impatient of the fetters, have gone abroad and there established factories, such as the Rohrback factory in Denmark, and the Heinkel works in Sweden, or else have perforce had to be content with producing machines of such size and power as come within the limits imposed. Quite a crop of low-power machines have consequently been built, most of which have been described and illustrated in FLIGHT from time to time. At the Gothenburg Aero Show were exhibited two single-seaters designed by Herr Rieseler and built by the Stahlwerk-Mark aircraft section. These were fitted with Haacke engines of 30 h.p., and bore the series numbers R.III. A two-seater of very similar design is known as the type R.IV. Now the same firm has produced a monoplane four-seater, the R.V., which, as it was built in 1923, is identified by the works numbers R.V/23. This machine forms the subject of our photographs and scale drawings this week.
As in the case of the R.III and R.IV Stahlwerk-Mark machines, the R.V/23 is a parasol monoplane, with the divided wing carried on a steel tube trestle rising from the top of the fuselage. The two wing-halves are supported by long steel tube struts running to the lower longerons. Thus, although a fairly deep wing section is used, the machine is not a cantilever monoplane. The lift struts, it will be seen, meet the wings a long way out towards the tips. In fact the overhang is of considerably smaller span than is the inner portion of the spars. The fuselage is of rectangular section, and a large flat nose radiator rather spoils the lines of the fuselage forward. Nevertheless, the machine appears to be very efficient, as it is carrying four occupants on 100 h.p. at a speed of 93 m.p.h. The design is a plain straightforward job, and the main objects aimed at by the designer were, apart from efficiency and economy, cheapness of production and ease of replacements and repairs.
The fuselage is a welded steel tube structure, cross-braced with wire, and fabric covered over the aft portion. Forward the covering is aluminium. The 100 h.p. 6-cylinder-in-line Mercedes engine is mounted on a steel tube structure. The sides of the engine compartment are covered with an aluminium bonnet which can be raised as in a motor-car, thus giving ready access to every part of the engine. A fireproof bulkhead forms the rear wall of the engine housing, and separates it from the passengers' compartment.
The cabin in the R.V/23 has accommodation for but two passengers, seated side by side and facing forward. The third passenger is placed next to the pilot in the open cockpit aft of the cabin. We understand, however, that in the production type the cabin will be extended to include the third passenger. The headroom in the cabin is not very great, being little more than just sufficient to allow the passengers to sit upright, and it is not possible for them to stretch themselves during the journey. Windows in the sides of the cabin and in the door provide sufficient light, and the cabin is heated in winter by hot air from the engine, ventilators in the roof allowing of regulating the temperature. The controls consist of a foot bar for the rudder and wheel mounted on a column for the ailerons and elevator. Behind the pilot's cockpit is a small compartment for luggage.
The wing of the R.V/23 is of normal construction, with two wooden spars and wooden ribs. It is built in two halves, attached at the centre to a steel tube cabane and braced by sloping struts to the bottom of the fuselage. By undoing eight quick-release bolts the wing can be dismantled, an operation requiring but a very short time. The ailerons are balanced, and are of high aspect ratio. The tail is of orthodox design, and rudder as well as elevator are balanced. The tail members are made of welded steel tubing and fabric covered. The undercarriage is a simple V-type of steel tubes, with the axle sprung by rubber cord.
The petrol system is of the simple gravity type, the petrol tanks being mounted in the wing, near the cabane. The tank capacity is sufficient for four hours at full speed, giving a range, in still air, of 370 miles.
The main characteristics of the Stahlwerk-Mark R.V/23 are as follows: Length o.a., 7-9 m. (25 ft. 11 ins.); Span, 14-25 m. (46 ft. 9 ins.); Chord, 2 m. (6 ft. 6f ins.); Wing area, 27 sq. m. (290? sq. ft.); the weight of the machine (empty) is 800 kgs. (1,760 lbs.); the useful load is 480 kgs. (1,055 lbs.) composed as follows: 1 pilot, 3 passengers, fuel for 4 hours, and 110 lbs. of luggage; the total loaded weight is 1,280 kgs. (2,815 lbs.) giving a wing loading of 9-7 lbs./sq. ft. The power loading is 28-15 lbs./h.p. It is stated that the maximum speed is 150 kms. (93 m.p.h.), and that the climb, with full load, to 1,000 m. (3,300 ft.) occupies eight minutes. We have no figures relating to the stalling speed, but in view of the high wing loading this must be somewhat high, although a high-lift wing section is used. When the experimental machine was tested at Breslau, it is stated to have exceeded the expectations of the designer, Herr Rieseler, and after a few minor modifications it will probably be put into production. As a taxiplane, the machine should be very economical to operate, and over relatively short distances the somewhat cramped passenger accommodation might not greatly matter.