FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1929
1929 - 0398.PDF
FEBRUARY 28. 1929 lines of the nose of the fuselage merge into the wind-screen, cabin, and wing without very abrupt changes of direction. The outboard engines are neatly cowled, the inverted pyramid mountings lending themselves to the production of cowls of smooth outline and without sharp corners, and which trail off to a point at the rear. The wing section used is that known as R.A.F. 34, which has an almost stationary centre of pressure. The minimum profile drag coefficient is 0-0051 and occurs at a lift coefficient of about 0-1, both in British "absolute" units. The maximum lift coefficient is not high, about 0-51, at least according to model tests. There may, however, be a con- siderable scale effect, which may increase kh max. to -6. Based on model figures, and with a wing loading of 10 lbs./sq. ft., which represents full load, the stalling speed of the Westland IV should be 62 m.p.h. It is likely, however, that the full-scale lift will-reduce this somewhat, and the actual stalling speed is probably in the neighbourhood of 55 m.p.h. ment, especially in view of the experience which the Westland Aircraft Works have gained with metal construction. The fuselage consists of the usual four longerons, but metal construction practice is followed in so far as wire bracing is not used. Vertical and diagonal struts are arranged in the form of an " N " girder, the joint between them and the longerons being by fishplates. In the forward or cabin portion three-ply wood is used as an internal lining, and also provides the diagonal bracing. The covering is of fabric throughout. The wing structure is of orthodox design, with two main spars of wood, and wooden ribs. The ailerons, which are of fairly large span, are hinged to a false spar some distance behind the rear main spar. The covering is fabric, but the leading edge of the wing is covered, under the fabric, with three-ply so as to maintain the aerofoil form. It is noticeable that the wing covering fabric is exceptionally smooth and without sag between the ribs. Possibly the use THE WESTLAND IV [" FLIGHT " Photograph This photograph shows the engines, undercarriage and cockpit windscreen. Note the streamline engine housing and wide wheel track. The total loaded weight of the machine is 4,900 lbs., and W as the wing span is 57 ft. 6 in., the span loading, or 'r span2 is 1 -485. Thus, at a take-off speed of 65 m.p.h., for instance, the horse-power required to overcome induced drag is only S7 T.HP. It would, therefore, seem that the wing arrangement chosen is a very efficient one. R.A.F. 34 section has a very good depth for spars, and its minimum profile drag is not much, if any, greater than that of R.A.F. 15. At a fa of 0-46 the profile drag coefficient is 0-008, so that the profile drag at 65 m.p.h. would be about 85 lbs., corresponding to a T.HP. of 15 or so, giving a total T.HP. required for wing drag of about 52. This figure does not include the drag of the wing-bracing struts, as it is a little difficult to decide how many feet of struts are properly wing struts and how many support the wing engines. At any rate, the wing drag at speeds slightly above stalling speed is very low, and the wing design must be regarded as an efficient one, apart from any practical advantages which the high-wing mono- plane machine may have. Structural Features The first machine is of composite construction, with wooden wing spars and ribs, and wooden fuselage construction, but it may be assumed that if the type should prove popular, which appears likely, an all-metal version is a logical develop- of R.A.F. 34 section is partly responsible for this, as it has no concave curves. The wing bracing is somewhat unusual, as has already been hinted at, Strictly speaking, the wing is braced on each side by but two relatively short struts springing from the points at the bottom of the engine mountings. But the engines themselves are not, as is more generally done, sus- pended directly from the wing. Rather must they be re- garded as being carried from the apices of two prone triangles, the bases of which are in line with the fuselage sides. The. inner ends of these two outriggers, as they may well be termed, are attached to lower longerons and wing centre- section respectively, so that the weight of the outboard engines is carried mainly from the fuselage, and only secon- darily by the outer wing struts. The arrangement is unusual, and one which we do not remember having come across else- where. Structurally everything is triangulated, and each engine mounting is balanced, so to speak, upon a knife's edge, being steadied against torque-reaction by a single strut running to the lower longeron, and crossing the upper main supporting strut on its way. With the cowling removed, the outboard engines are extremely accessible, and a small hinged platform is provided on each engine mounting, on which the engineer can stand when making adjustments, and which are also useful for filling the wing tanks by hand. 160
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
