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Aviation History
1923
1923 - 0709.PDF
NOVEMBER 22, 1923 (KSS THE NEW UDET COMMERCIAL MONOPLANE A German Three-Seater of Very Clean Design •i HITHERTO the Udet-Flugzeugbau of Munich have confinedtheir attention to small machines mainly intended for school •work or for sports flying. Now, however, they have definitelyentered the ranks of the firms producing commercial aero- planes, and their first machine, which was to have been shownat Gothenburg, has now been finished, and promises to be a very useful type. As the accompanying scale drawingsindicate, the machine is of very " clean " design, in which external bracing has been entirely eliminated. As distinct from previous Ud'et machines, the new com-mercial three-seater is a " high-wing " monoplane. In fact it might justifiably be termed a " parasol " monoplane, as thewing does not rest directly on the top of the fuselage, but is separated from it by a small gap, and is carried on fourvertical struts. This arrangement of the wing was chosen for various reasons. The designer of the machine, HerrIng. Hans Henry Herrmann, believes that by having a gap between the wing and the top of the fuselage the slipstreameffect on the former is reduced. Another reason is that it has been found difficult to provide, in a machine with a verysmall cabin, sufficient ventilation to prevent air sickness. Consequently, in the Udet three-seater the cabin is not entirelycovered in, an opening being left in the roof, underneath the wing. It is claimed that with this arrangement the ventila-tion of the cabin is all that could be desired, while at the same time it has been found that there is no draught. Another advantage of the high-wing position is that it hasbeen found possible to place the pilot's cockpit under the The accommodation provides seating for two passengers inaddition to the pilot. Entrance to the cabin and pilot's cockpit is gained through a door on the port side. The frontseat in the cabin is placed slightly to the right of the centre line, so as to enable the pilot to get past it to his cockpit,and the second passenger to pass to his seat behind the front one. The seats are comfortably upholstered, and both pas-sengers face forward. As the wing is above the cabin the view through the side windows is particularly unrestricted,and by standing up the passengers can look over the edge of the opening in the roof of the cabin. Aft of the cabin, and com-municating with it by a door, is a fairly large luggage com- partment. It would seem somewhat difficult to get bulkyluggage through the cabin on its way to this compartment, and a door in the side would appear to be advisable, especiallyas the journeys to be undertaken by a machine of this type will scarcely be of such long duration as to necessitate thepassengers being able to get at their luggage during the voyage. The monoplane wing of the Udet three-seatcr is of the purecantilever type, and is of thick section, tapering both in chord and depth towards the rounded tips. It is constructed entirelyin wood, the spars being of box section and ribs having three- ply webs and spruce flanges. The spars, it will be noticed,are parallel in plan view, so that at the centre section there is a considerable overhang both in front of and behind the spars,the distance between which is determined mainly by the chord of the tip section. As already stated, the wing tapers bothin chord and thickness, the latter taper being approximately i .'••;? leading edge, so that it has not been necessary to cut out thelatter. This is thought to have contributed to some extent towards the aerodynamic efficiency of the design, as generallyspeaking any openings or breaks in the centre-section wing curve have an adverse effect on the smoothness of the airflow.The fuselage of the Udet three-seater is of oval section, and is covered with ply-wood. The shape of the body should bevery good aerodynamically, although nowadays it does not always follow that a shape that is good by itself is necessarilyalso the best when brought close to another body. However in the Udet probably the gap between the fuselage and thewing tends to reduce the mutual interference effect. The 70 h.p. Siemens radial air-cooled engine is mounted on a swivelmount, so that the back of the engine is readily accessible for inspection or adjustments. By undoing two bolts the wholeengine unit swings out, much in the manner first used in this country—and we believe patented—by Boulton and Paul,Ltd. In the Udet this idea has, however, been carried a step farther, as all the engine instruments and controls are mountedon the engine unit and removed with it. A similar arrange- ment was found in the Morane-Saulnier cabin monoplaneexhibited at the last Paris Aero Show. As the pilot's cockpit is immediately aft of the engine mounting, and the instrument-board drops into its normal position when the engine plate is bolted up, there is no necessity to interfere with any throttleor ignition adjustments, and the only connection that has to be broken is the petrol pipe. It should be possible, by asuitable arrangement of the piping, to avoid even the dis- connecting of this. The Udet Three - Seater Commercial Monoplane : Three-quarter front view. The engine is a 70 h.p. Siemens, and the machine carries rw« passengers ia addition to the pilot. symmetrical in relation to the centre line of the spars, whiH1the taper in plan is unsymmetrical, the leading edge being swept back 5° while the trailing edge is swept forward 7°.The leading edge is stiffened by a ply-wood capping extending to the front spar, the edges of this capping being of the " sawtooth " type, in which the points meet the centre line of the spar while the recesses lie on the wing ribs a short distanceahead of the spar. This form of nose stiffener was, we believe, first introduced by Fokker. The wing is secured to the fuselage by four struts insertedin the latter, and having corner plates to provide stiffness without bracing in a vertical fore and aft plane. Laterallythese struts do not appear to have any bracing whatever, the rigidity of the struts being apparently relied upon to take theplace of the usual transverse bracing of a centre-section. The struts, it should be noted, remain in place on the fuselage,and the wing is dismantled by undoing four bolts securing the wing spars to the top of the struts. The ailerons are ofapproximately triangular plan form, with the maximum chord at the inner end. The wing section used is not, as might havebeen thought, one of the Gottingen or " tadpole " sections, but has a perfectly flat bottom camber. The horizontal tail plane is of the trimming type, so as toallow of flying with or without passengers. While the main plane is set at no angle of incidence to the propeller shaft, thetail plane is normally set at an angle of -f- 2 -3°, and is thus at a greater apparent angle than the main plane. The down-wash behind the high-lift centre section probably changes this into a slight negative actual angle. 709 c i
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