Flight, February 1924
AN INTERESTING GERMAN LIGHT MONOPLANE
The Klemperer-Aachen with Siemens Engine
By Dipl.-Ing. ARTHUR MARTENS
[REFERENCE has been made in FLIGHT on several occasions to the small amount of development to which the light aeroplane has
been subject in Germany, and the opinion has been expressed that this is due, primarily, of course, to the financial conditions obtaining in present-day Germany, but also to a not inconsiderable extent to the fact that for some reason or other the Germans do not appear to possess engines really suitable for use in light 'planes. We in this country made an excellent start with motor-cycle engines at Lympne last year, and it is scarcely to be doubted that the forthcoming competitions for two-seater light 'planes will produce not only excellent machines but also engines better suited to the needs of low-power flying than were last year's models. Although Germany was, perhaps, the first country to realize the need for suitable low-power engines, little practical progress has, as already mentioned, actually been made. The subject has not, however, been overlooked by a certain section of German aviation circles, mainly those originally interested in gliders and gliding. Nor has there been a total absence of German light 'planes, and we have referred to at least one in these columns, the Budig, which was flown last year with a very small engine. We are very pleased to be able to publish this week a description of another German light 'plane, the Klemperer-Aachen monoplane, from the pen of Herr Arthur Martens, the well-known German glider pilot. Herr Martens is not only a pilot, but is also an engineer who has himself designed and built gliders and aeroplanes. He is, therefore, particularly qualified to speak on the subject of light 'planes. - ED.]
Shortly after the close of last year's Rhon glider meeting the Aachener Segelflugzeugbau-Gesellschaft commenced experiments with their first light aeroplane. The designers of the machine are the well-known glider pilot Dipl.-Ing. Klemperer, and Ing. Schulz. During the flying tests the machine was piloted by Herr Hoppe, one of the Darmstadt students. The light monoplane is a development of the glider "Rheinland," built by the same firm. The "Rheinland" is a cantilever monoplane with wings of peculiar design, resembling somewhat the wings of a seagull. The fuselage is of oval cross-section, and the control surfaces are balanced. During the actual Rhon competitions this machine was not very much in evidence, but later on it put up fairly good performances piloted by Klemperer. It appeared, however, to be close on the limits of stability.
The light monoplane, which is a sister type to the "Rheinland," has wings of similar form, but the fuselage is of entirely different shape from that of the glider, being built up on five longerons. The upper longeron, which runs forward as far as the engine mounting, carries the centre-section of the wing, which is braced from the fuselage by two short struts on each side. The undercarriage springs from the lower portion of the fuselage, or rather from a main bulkhead, and the members carrying the wheels are of streamline section. The wheels are mounted direct on these wing stumps, and there is no wheel axle. The only springing provided is that afforded by the pneumatic tyres. The undercarriage is reminiscent of that of the Dornier "Falke," except that in the latter the wing roots or stumps carrying the wheels are sprung. During the tests it has been found, however, that the arrangement adopted in the Klemperer-Aachen light monoplane is quite satisfactory. The pilot enters his cockpit through a door in the side of the fuselage. The petrol tank, which has a capacity sufficient for four hours' flight, is mounted in the centre-section of the wing. The oil tank, however, is carried immediately behind the engine.
Nearly all the metal fittings used are of Duralumin. This material is, for instance, used in the attachment of the centre-section to the top longeron. The wing is braced, in addition, by struts to the lower longerons. The leading edge of the wing is covered with 1 mm. three-ply. Celluloid is used for covering the slots occurring at the hinges of the control surfaces and at the point of attachment of the wings to the fuselage. All control cables are placed internally in order to reduce all avoidable air resistance. It is worthy of note that in the whole of the machine not a single nail is used, all wood joints being made by cold glueing.
The power plant consists of a normal two-cylinder vee motor-cycle engine manufactured by Siemens (Mabeco-Motorrad). This engine is air cooled, and its rated power is 5/11 h.p. In view of losses in the gearing, etc., it is doubtful, however, whether one can count of a maximum output of more than 9 h.p. The engine runs at 3,200 r.p.m., and the airscrew at 1,200 r.p.m. The static thrust on measurement was found to be 45 kg. (99 lbs.). The engine is started by means of a self-starter designed by Klemperer, which was found to work excellently.
The main characteristics of the Klemperer-Aachen light monoplane are as follows: Length overall, 4-5 m. (14 ft. 9 ins.); span, 13 m. (42 ft. 8 ins.); height, 1-8 m. (5 ft. 11 ins.). Wing area, 15 sq. m. (161-5 sq. ft.). Area of tail 'plane and elevator, 1-5 sq. m. (16-15 sq. ft.); area of fin and rudder, 1-5 sq. m. (16-15 sq. ft.); weight, empty, 160 kg. (352 lbs.); speed, 70 km./hour (43-6 m.p.h.).
During a flight the machine came into contact with the ground with one wing, with the result that a certain amount of damage was done which prevented the continuation of further experiments. When repairs have been effected the tests will be continued elsewhere, as weather conditions on the Wasserkuppe are not very favourable. In my opinion, it is likely that even better results will be obtained over lower-lying country, than in the Rhon, which is about 1,000 metres (3,300 ft.) above sea level, although it cannot be denied that the hilly country around the Wasserkuppe has certain advantages - for instance, when starting.