General Aircraft: Croydon

1937.

Note: This is a sub-section of General Aircraft.

1935 The S.T.18, designed and built by General Aircraft, Ltd., of Hanworth, incorporated all the latest aids to performance coupled with safety, such as retractable undercarriage, trailing-edge flaps and controllable-pitch airscrews.

Externally the machine was remarkable for the considerable sweep-back of its monoplane wing. From an aerodynamic point of view the S.T.18 follows in a general way the practice of cantilever wings and tail, retractable undercarriage, and generally clean design.

In the main, the structural principles followed in the construction of the S.T.18 were similar to those of previous Monospar machines. A single main wing spar was used, located approximately one-third of the chord from the leading edge. This main spar, designed to be strong enough to carry the bending loads imposed by the weight of the machine, would be too flexible to resist the torsion which arises owing to movements of the centre of pressure. It was therefore reinforced by two sets of tie-rod bracing, each forming a spiral around the spar and its drag struts and running in opposite direction to the other spiral. A considerable saving in wing weight was claimed for this method of construction, but possibly even more important is the fact that when a wing tip deflects, it does so without altering its angle of incidence, and wing flutter is less likely to arise.

For the fuselage construction there were four main longerons and diagonal strut bracing. The covering of both wing and fuselage was mainly with doped fabric.

The fuselage was composed of four distinct units : the front end, which contains the pilots' cockpit, the cabin, which is one unit, the rear fuselage portion, and a wedge-shaped structure carrying the tail wheel assembly. Seating accommodation for ten passengers was provided. The total capacity of the passengers' cabin was 406 cu. ft. One long window was built into each cabin wall, the only obstruction to the view being a few structural members which took up but a small part of the window space. A very substantial bulkhead separated the cockpit from the cabin. This bulkhead was a main structure member, and to it were secured the wing roots and the two wing-bracing struts, so that all the major loads were concentrated there.

The engines were Pratt and Whitney " Wasp Juniors."

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