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Aviation History
1931
1931 - 0097.PDF
JANUARY 30, 1931 THE AIRCRAFT ENGINEER SUPPLEMENT TO FLIGHT In considering curved bodies, the choice of a body having •is nearly a developable surface as possible is an obvious and fundamental advantage. There appeared to be very little panel beating on the bodies shown. The large monocoques were nearly all slab-sided ; the probable loss in body drag, due to this, must be considerable. Amends were made, in most cases, by fairings of wheels, tail skid, &c. Internal observations from the cockpits enabled one to obtain a good idea of the details of construction in many instances, but details of the internal construction of the wings were not so readily obtained. Only the Junkers firm had a stripped all-metal wing, and the details of construction of this, which were of special interest, are dealt with later. Generally, the wings appeared to be of two-spar construc- tion, although the existence of two external lift members is not necessarily conclusive evidence that there are only two spars in the wing. The principal difference in the wings exhibited was the use and disuse of external corrugations or other means of reinforcement. Why has Wibault turned all the seams inside the wing, leaving a fiat outer surface ? Certainly not for the sake of appearance, because that is definitely worse than on previous exhibits. Not that the existence of small local buckles can affect the aerodynamic efficiency of a wing to any very great extent. The statement has definitely been made that external ridges do affect the airflow adversely and appreciably; on the other hand, experiments made in America with vertical fins placed on the wings near the tips have indicated an aerodynamic advantage, although not sufficient to make the use of such fins worth while. Of the metal-covered wings shown, about half were plain and half corrugated or ridged. The use of very shallow corrugations can only be for appearance in the matter of removing or concealing local buckles in the sheets. The romigations in the Amiot wing covering, which might liave been •& in. deep and -j in. pitch did not, however, affect this purpose, as numerous shallow depressions were to be seen on the surface. Obviously, metal covering for wings has its advantages and disadvantages, compared with fabric covering, and unless the former outweigh the latter, its use cannot endure. We have often pointed out in these pages that unless rigid covering can be used structurally in addition to its function as a covering, it must compare most unfavourably with fabric. The cost of the material, labour charges, etc., certainly enter into the arguments, and Continental prices for the necessary materials, etc., may have an important bearing on the final choice of material used there. Apart from such considerations, it is essential, from the point of view of weight economy, that rigid covering should contri- bute something towards the structural strength of the aircraft. There are two ways of doing this : one way is to utilize the sheet coverings chiefly as a main load carrying member, as is done in some types of Rohrbach wing. That is, the coverings carry compressive and tensile forces directly, in addition to supplying the main torsional resistance of the wing. This method usually results in a heavy structure. The other method is to utilise the covering as a stabiliser and stiffener for the internal girder system ; economical use of rigid covering can be made in this way. This latter system usually leads to a multi-spar structure. In concluding these remarks on rigid covering, we would say that it does appear a desirable thing to explore fully the relative merits of fuselages consisting of an inner, load- carrying structure, attached to which is an outer fairing, compared with bodies in which the two separate parts are combined in one shell. Excellent shapes can be obtained by the first method, the manufacturing difficulties in the attainment of equally good shapes by the latter method are considerable. The former method lends itself to accurate strength computations ; the latter method does not. Once a suitable monocoque body has been developed, manufacturing costs should not be greater than for the manufacture of faired structures. The monveoque body gives more room for equipment, such as wireless, armament, etc., and the facilities for fitting this should not present any difficulties. Greater damage, without undue danger of collapse, may be permissible in a " shell " body than in a " frame " type of body, and repairs may be more readily effected. As to weight, it would be a difficult task to make the monocoque body lighter than the faired rectangular frame. The shell type of body gives the impression of great rigidity compared with the frame type, and incidentally one wonders whether this has anything to do with the change over to moiwcoques in France, for in previous Shows the strut-and- wire type did not appear to be too strong torsionally. In one respect, the Show was very disappointing, and that was in the number of details of construction on view. The Junkers Junior had the upper covering removed from the starboard wing, together with one-half of the body covering. A Breguet was shown in the stripped state, and that was the lot, with the exception of the English exhibits. The Bristol Aeroplane Co., Ltd., Messrs. Armstrong Siddeley, and Messrs. Boulton and Paul definitely exposed to view all details of construction, and in the former cases, where complete aircraft were exhibited, the utility of the aircraft could be readily estimated bv reason of the fact that the
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