Some Impressions by the Technical Editor, Flight
German Aircraft Construction
Reference has already been made to the fact that the great majority of the machines taking part in the Round-Germany flight were of well-known types, from which it was to be expected that from a constructional point of view there would not be a very great deal to be seen in Berlin. An examination of the machines at the Tempelhofer Aerodrome during the days preceding the start, confirmed this impression, and it may be said at once that this country does not appear to have much to learn from Germany as regards quality of workmanship. When one comes to the question of cost, it might be a somewhat different matter, although in this respect also, there is a good deal of similarity between British and German methods. Generally speaking, it can we think, be said that if the German machines do not show outstanding merit in their construction they certainly cannot be said to show scamped workmanship, and the general average is about what one would expect from a painstaking race like the Germans.
On the whole, it seems that wood construction still leads in popularity, but this was to be expected from the fact that all the competing machines were necessarily of fairly small type. In her commercial aircraft, Germany shows a decided preference for all-metal construction, particularly as exemplified by the Junkers and Dornier machines. In the actual competition the only all-metal machines to turn up were the Junkers, and these all followed standard Junkers' practice in their construction, with structural members mainly in the form of Duralumin tubes and with fuselage and wing covering of corrugated Duralumin sheet. Another form of metal construction used fairly extensively, more particularly on the Dietrich machines, applies to the fuselage only,and is not used in the wing construction. This is in the form of welded steel tube members with piano wire bracing, of the type used so extensively by Fokker throughout and after the war. The Dietrich machines being small, this
form of construction is interesting because it seems to point a way towards reducing the cost of building light 'planes. It seems probable that no cheaper form of construction has ever been evolved than the Fokker welded-steel tube method, and if it is, as the Dietrich machines appear to show, applicable to light 'planes, it might be worth while adopting it for the construction of light 'plane fuselages. One outstanding advantage which this form of construction possesses is its elasticity. With most types of metal construction early standardisation is almost essential, if reasonable cost is to be attained, but with the Fokker method this applies to a much smaller degree, and changes in design are almost ridiculously easily made.
As regards the wood construction, ply-wood has long been, and still appears to remain, the favourite material among German designers. In the Rundflue machines it is used for the fuselage covering in a very great number of machines, and in not a small percentage it is used for the wing covering also. Although most of the machines built in this manner have flat-sided fuselages there were a number of machines in which the body was of circular or elliptical cross-section, and in cases where the plywood is used for covering fuselages of this type, the work of applying it evenly becomes, of course,considerably more difficult, since sheet material cannot be bent over a barrel-shape, although it is easily bent over a cylindrical former. In these cases, of course, the three-ply was applied in fairly small sheets, and was usually tacked on in preference to being screwed on. There is, in certain quarters, a tendency to regard wood screws as being preferable to nails for fastening ply-wood on a framework, but to the writer it has always seemed that there is a good deal to be said for using nails. A wood screw, if properly driven home and if not over-tightened, does doubtless hold better than a nail, but one can never be quite certain of whether or not a wood screw has been over-tightened. If it has, it is, of course, practically useless, while a nail driven in, provided it does not miss the material altogether, will hold pretty firmly.
Undercarriages appeared in the main to be of the standard type, with long axle and " V-struts," but there seemed to be a tendency towards the divided type, in which each wheel is mounted on a short bent axle and the undercarriage is formed by two separate pyramids. In some cases the shockabsorbing legs of the undercarriage were taken to the wing, a practice which is open to the objection that in a hard landing a wing may be badly stressed without actually breaking, with consequent risk of the wing collapsing the next time the machine takes the air.