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Aviation History
1936
1936 - 1155.PDF
478 FLIGHT. MAY 7, 1935, > • ,™:<:;,.:.;:...i... .....,;;,. •*:»,• -»•:." '.-"••; -•':'«-' • "• :,.-!- "• • "" ' - • ': •'"-«V* J* Ki. ,ii~''; 7-. '„%..«» J £ ijMJ..;- • „ ' • • | . *,:,, '•,.•: =, = .i i;,: ^l^ • - • ? , . ,, "' , . , ,•/., V,-.-'V ^':»>' :/' ; THE NEW MONOSPAR General Aircraft's S.T.18. Cruising at Nearly 200 ?n.p.h. : Comfortable Accommodation for Ten Passengers : Reasons for Unusual Design ONE'S reaction when seeing the new S.T.18 for the first time is to wonder at the somewhat unusual appearance of the machine. The very pro nounced sweep-back of the wings, the short nose of the fuselage, which is almost in line with the two air screws, the very low position of the tailplane over the ground, the straight bottom and somewhat hunch backed shape of the fuselage are all features not com monly met with in twin-engined aircraft, and have obviously been introduced not merely for the sake of "being different," but for some very good reasons. Flight had an opportunity the other day of discussing these reasons with the designer of the machine, Mr. D. L. Hollis Williams, and it may be of interest if some of them are set out here before describing the details of the construction and internal arrangement of the machine. It is a well-known fact that several modern high-speed twin-engined aeroplanes have a tendency to yaw slightly from side to side, a fact which points to a certain amount of directional instability. Another peculiarity of fhe twin engine arrangement is that, with one engine out of action, the rudder control necessary to hold the machine on its course is considerable, particularly if the engines are fairly widely spaced. Considerations such as these led to the adoption of the positioning of the fuselage rather unusually far back on the wing. Various effects result from this placing of the fuselage: the fuselage side area in front of the centre of gravity is reduced, that behind the centre of gravity is increased, and the lever arm, for a given fuselage length, on which the tail works, is increased. This rearward shift of the fuselage results, of course, in moving the centre of gravity back, and to restore the trim the sweep-back of the wings has been introduced. The low tail position represents an attempt to make- sure of getting the tail out of the area of disturbed air flow behind the wing at large angles of incidence ; tins disturbance, with certain relative tail positions, sometime3 sets up the phenomenon known as tail buffeting. Th- unusual shape of the fuselage results from the other con siderations on which the design is based. Apart from any saving in structure weight which may result from the use of the Monospar type of wing con struction, a very practical advantage arises in its par ticular application in the S.T.18. Owing to the fact that there is but a single spar, braced to. the top longerons 01 each side, there is only need for a single bulkhead in the cabin to be a primary structure member. The locatio of the spar so far forward in the wing section, and t e short nose of the fuselage to wrhich reference has alrea been made, bring the position of this single bulkhead • forward so that it can be" used to form a partition betwee the pilots' cockpit and the cabin. The passenger quarters, as a result, are therefore quite unobstrncte transverse structure members. . e The primarv structure of the fuselage is of normal >p-
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