572 FLIGHT. JUNE g 1938. WESTLAND LYSANDER MARK (890 b.p. Bristol Mercury XII DIMENSIONS AREAS Length o.a. ... — Wing span ... ... .... _ «• •• • Height o.a ... ... ... ... 1* Wheel track Chord at root .. ,.. ... Tailpiane span ... ... ... -• • • „ chord at roo t ,;- . . ... Airscrew diameter /_.../- ... Wing (incl. ailerons) „ elear o f fuselage Ailerons Fi n '. Rudder Tailplane Elevators Flaps sq.H. 260.0 250.0 18.5 17.5 8 35.0 3 S 29.0 When these considerations ax e taken into account, the adoption o thin type of undercarriage, which would other- wise be rather puzzling, becomes quite logical. From the aerodynamic point o f view, the Westland de- signers deserve the very greatest credit for having pro- duced a fully slotted and flapped wing in which all opera- tion is entirely automatic. The Handley Page leading-edge slots extend over the entire span of the wings, the inner portion being a lift slot, while the outer portion is a normal tip slot. The inner slot is connected by levers and linkages to the trailing-edge flaps. By very careful design the arrangement has been so adjusted that by a suitable choice o f take-off attitude the pilot can cause the lift flaps to come down the desired number o f degrees. If he lifts the tail more during the take-off, the machine will run along without the slots opening or the flaps coming down, whereas if the tail is kept lower than desired the slots and flaps will open fully, and the drag will be greater than desirable, so that probably the take-off run will be increased. Similarly, on landing: by dropping the tail sufficiently the leading-edge slot automatically brings the flap down to its full extent, which results in the steepest approach and shortest landing run. N o Snag It might have been thought that as the leading-edge slot is, so to speak, incidence-operated, it might be pos-, sible, in pulling the machine out of a steep dive, for example, to cause t he slot and flap t o open a t high speed. This, however, has not been found to be the case, pre- sumably because in a pull-out from a dive, the machine does not reach an angle o f incidence sufficiently great to cause the slot to open. Older readers o f light will doubtless recollect the little Widgeon monoplane built for one o f t he Lympne light plane competitions and afterwards bought by Dr. Reid. That little machine was also a strut-braced monoplane, and its plan form wa s very much like that of the modern Lysander monoplane. This is not, of course, any mere coincidence, b u t is due to the fact that on the one hand it is not desired to have a wide chord at the fuselage, and o n the other that the maximum wing strength is desired at the point where the lift struts are attached. Consequently, in plan form the chord is greatest along the line joining the lift strut attachments to the wing, and the wing tapers outward and inward from this line. The fuselage o f the Lysander has the usual girder type of construction, but the external shape is made rounded by the addition o f a light fairing of wood construction clipped to the me tal fuselage primary structure. Gener- ally speaking, the fuselage is o f good shape from a drag point of view, although the fact that it was desired to place the pilot high above the fuselage in order to give h im a good view ha s somewhat interfered with what would otherwise be a very nearly perfect streamline shape. That the drag cannot be excessive is proved by the fact that the Lysander Mk. I, when fitted with a Mercury XI I engine of 890 h. p., ha s a top speed o f about 23 0 m.p.h. The landing speed is 5 2 m.p.h., the wide speed range being attained very largely by a combination o f high-wing load- in g and the use of slots and flaps. From a structural point o f view, also, the Lysander is rather unorthodox. To sum it up quite briefly it might perhaps be said that the outstanding feature in its con - struction is the very extensive use of extruded sections o f light alloy. There has been very close co-operation be - tween the Lysander's designers and two specialist firms, High Duty Alloys, o f Slough, and the Reynolds Tube Co., Ltd. Accessibility and ease of maintenance and servicing were the guiding principles in deciding upon the general type of construction. That solved the problem, girder o r monocoque? There still remained the details. Ulti- mately it was decided to use in the front portion o f the fuselage the type o f construction of which the Westland firm had such long and successful experience in the Wapiti and Wallace biplanes: duralumin tubes o f square section joined by bolts and flat plates. For the rear portion, Straight an d sloping forked lugs are cut from special channel- section extrusions.