FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1932
1932 - 1318.PDF
bUPPLEMENT TO FLIGHT DECEMBER 29, 1932 THE AIRCRAFT ENGINEER machine, fixed slots, apparently about 30 in. long, were seen secured near the wing tips. The reason why ex tended and proper use of this wing device is not made in France does not concern us here. Whilst the use of slots appears generally to be neglected, the use of trailing edge flaps has greatly increased, and the use of servo strips on control sur faces was more in evidence at this Exhibition than before. The " follow-up " aileron strips of the Polish cabin machine appeared to have been designed during the original lay-out of the machine, and not added as an afterthought. A good deal of thought has evidently been given to the design of the P.Z.L. machines and from this point of view they deserve a high place in the order of merit of the aircraft shown. Two years ago adverse comment was made regarding the probable weight of the wings due to the shape and method of supporting the spars. On this occasion a spar was exhibited by itself, and on handling it one had no hesitation in saying that judged by English standards of spar weight, taking both upper and lower wing spars together, for similarly sized aircraft, the member was decidedly heavy. For reasons of strength it could not well be otherwise. The weight of the complete machine is, however, the thing that matters, and from the following figures, taken from the P.Z.L. catalogue, it will be gathered that the structure weight of the P9 was not undulv large. The figures refer to the Gnome- Rhone " K9 ""or " Mercury IVa." Dry weight ... 2,2701b. (including engine, prop, etc.) Fuel 539 lb. Military equip ment 440 ,, Total ... 3,249 lb. Top speed Csea level), 187 m.p.h. Speed at 13,000 ft., 218 m.p.h. Endurance at cruising speed, 2^ hours. Wing loading, 16-8 lb./ft.2 The sea level top speed of the Skoda " Jupiter " is 175 m.p.h. and speed at 13,000 ft. 197 m.p.h., the all- up weight in the later case being slightly less than the above. Thus the weight of a monoplane structure is once again shown to be not much in excess of simi larly-sized machines having biplane wings. The reason material in cantilever wings more economically than in biplane wings. A strict comparison of these Polish aircraft with similar English aircraft is not possible, since they are not built to the same strength requirements. They may be equally strong in the air, but it is inconceivable that the Polish undercarriage could withstand the side load condition imperative for Air Ministry stressing. The elimination of such cases in stressing must have a beneficial effect on the structure weight. The stress ing case in question is, in my opinion, however, not one to be ignored, even if, after two or three years' flying, no accident through sideways collapse of an under carriage has occurred. As to the details of the machine, the wings are built from duralumin strip and sheet, the section of the spar being as indicated in Fig. 1. This calls for no special comment. The web was of plain sheet, about 16G., and reinforced at intervals with vertical stiffeners. These stiffeners were also attached to the flanges as shown in the sketch, while light angle strips (a) were secured to the spar flanges between the vertical stiffeners. These strips are probably used for the attachment of the skin. Graduations in spar area were made through the use of different lengths of flange plates and angles (b) and (c) as indicated. The external support was attached to the spars via a fitting of the type shown, this being bolted to the web. The exact form and method of fixing ribs to the Polish spars cannot be described, but use was doubtless made of the above-mentioned web stiffeners. There is never any difficulty in the assembly of such parts, the task being to make the best choice from the many ways of assembly that are obviously possible. As to the wing covering of these two machines, in one case a plain duralumin covering was used and in the other the sheeting was ridged, in the manner introduced by Wibault a few years ago. The covering of the " ridged " wings was also very slightly corrugated, and this observation may conveniently introduce a note on metal covering which it is appropriate to include at this point. The utility of the covering material as a means of giving maximum torsional rigidity to a structure is beyond dispute. Sufficient stiffness may possibly be obtained by other means, but never for the same weight of material as by rigid covering. is that in the monoplane it is easier, due to the larger and more regular changes in the stresses in the spar6, to develop a system of laminar construction giving a structure of fairly uniform stress, at any rate much more uniform than is possible in the spars of small biplane wings, in which the load variation is erratic. In other words, whilst the advantage of distance be tween wings in resisting bending is lost as against biplane construction, it is always possible to utilise the It is most probably true to say that a metal-covered frame has never been considered as more economical from a strength-weight viewpoint than a fabric-covered girder construction, at any rate for small- and medium- sized aircraft. It has been shown mathematically that a " rigid " braced panel is lighter than an otherwise similar panel, wire-braced, but the thinness of panel required in the case of a lightly-loaded frame is alto gether smaller than can be considered commercially, 1232 6
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
