Flight, July 1933

THE NEW “AVRO-CADET" SERIES
A. V. Roe's have answered the demand for a modified form of their "Cadet" by producing a series which will satisfy a wide range of users, at the same time retaining the flying characteristics of the original "Cadet" engine.

   OUR readers will remember that we have often commented upon the delightful flying characteristics of the Avro "Cadet." We have had the pleasure of flying this aircraft on several occasions, and the more we do so the more we like it. No one could help liking it, and we have not heard a single serious criticism levelled against it, even by certain well-known pilots, who are notoriously hard to please.
   In its original form the "Cadet" was an admirable aircraft for training, particularly where first cost was of considerable importance. It had, however, fixed wings, and was really more suitable for military training - the Irish Air Force have used it with conspicuous success - where hangar space is ample. Almost as soon as it came out there was a demand for it by private owners, and it is this demand, along with others, which has given birth to the present series.
   The new aircraft consist of: -
   The standard "Cadet" with fixed wings type Avro 643.
   A Club "Cadet" with folding wings type Avro 638.
   A three-seater "Cadet" type Avro 640.
   A cabin "Cadet" type Avro 639.
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   The 638 is mainly intended for club use or for private owners. It has folding wings, and therefore the pronounced stagger of the standard machine is greatly decreased. The fuselage remains the same, as does the equipment.
   The 640 is a new departure altogether. In this type there is no question of training or dual control, and it is intended mainly for joyriding. The front cockpit has been enlarged so that it now accommodates two passengers seated side by side in comfort. The wings and tail units are the same as the 638.
   The 639 is also something very new. Once again the wings and tail units are standard, but the fuselage has both been widened and extended upwards to fill the space between the top and bottom planes. The cabin so formed will accommodate three persons with the pilot in front, where he will have an excellent view.
   As we have already intimated, these machines are all in a series based on the original "Cadet," and it is therefore possible, from a structural point of view to treat them together.
   In keeping with Avro present-day practice, the fuselage is of welded-steel tube construction. Tubing of specification D.T.D.89a is used, and by this means the welding is able to be a straightforward job, not necessitating the use of pinned or strapped joints.
   In FLIGHT for April 27 we gave our readers an insight into the constructional methods in use in this factory, and these methods, although in that particular case were as applied to the Avro "Tutor," are the same for the fuselages of the "Cadet." The front half of the structure, forward from the bulkhead behind the rear seat, is strut braced, and is built up as one unit. The rear half has strut braced sides, but the top and bottom has piano-wire bracing anchored to small loops of tube which are welded into the corners. The wire itself is a continuous loop led around these small pieces of tube and has an Avro strainer in it for tensioning purposes. In the three-seater, 640, the depth of the sides, particularly around the cockpits, is decreased, while the width is very much greater in order to accommodate the two passengers side by side, while there are naturally several minor differences inasmuch as there is no necessity to provide mountings for the flying controls in the front cockpit. Apart from that, however, the structure is of the same type. The cabin machine is also basically the same, although here the greatly increased depth of the sides has enabled tube of smaller section to be used while retaining the same strength. The sides are led right up to the top centre section and form frames for the doors which hang either side and are built of steel tube themselves.
   In all cases the tail skids are of the leaf-spring type, full swivelling and restrained by a check spring. The shoe is a massive casting which has a coating of a specially hard metal welded over the bottom of it, preventing the wear which would otherwise take place.
   The tail plane is adjustable in flight, from either cockpit in the case of the standard and club models, by the neat screw gear raising or lowering the trailing edge which Avro's have used on their machines for some time now. The gear is operated by handwheels of ample size placed just on the left-hand side of the seats in each case, and a very fine adjustment is obtainable. This is one of the important points which makes the "Cadet" so nice to fly, it being possible to trim it exactly, whatever the conditions of load. The vertically-placed screw is worked by cables led through fairleads from the handwheels and works directly on to the trailing edge. A tell-tale is used in both cockpits showing the position of the tail plane, so that for training it is an easy matter to give a pupil marks to work to for landing, taking off or climbing, etc. The fabric covering of the rear part of the fuselage is secured over spruce stringers which are attached to the outside of the tubular structure in order to give it an efficient form. "Zip" fasteners are fitted where inspection holes are required. The three-seater, club and standard machines have a fabric-covered plywood top decking over the cockpits with large doors fitted on each side which make getting in and out of cockpits an easy matter. In the three-seater the front cockpit is also plywood lined, and over the flooring and footrest embossed aluminium is used. This gives a very clean, attractive appearance to the cockpit and has the added advantage not only of making the cockpit easy to clean - an important point for a joyriding machine - but also of keeping the passengers from sticking their fingers or feet through the sides. The footrest, a sloping board across the full width of the cockpit, is most comfortable, and should give confidence to those nervous passengers who like to "brake" hard when diving or coming into land - it is quite strong enough for the purpose too! In order to help them control their physical reactions still more, a polished rail has been mounted across the front of the dashboard which they can grip to their hearts' content, just as one sees them doing on switchback railways when they give vent to yells of terrified delight during a downward swoop. In the machine we tried, one of those which had been ordered by Scottish Motor Traction, the dashboard was bare except for an air-speed indicator, but there is ample room on it for anything, and no doubt if a luxuriously minded private owner wished to have anything else he could do so.
   The engine mountings vary according to the engine fitted. The S.M.T. three-seater had a "Hermes IV" and was mounted on a cantilever steel-tube welded structure of the normal type for this kind of engine. The engine feet themselves were fitted in the flexible rubber shoes as is general practice. The cabin machine and most of the standard "Cadets" have the 7-cyl. "Genet Major" engine, so that a ring mounting has to be used. Either of these engines, or others of similar type may be fitted to any of the series.
   The flying controls are all cable operated with dual cables and are particularly light and easy. As we have already said, both cockpits of the standard and Club machines have adjustable rudder bars, as well as brake-operating gear. This is similar to that used in the Avro "Tutor," the Bendix brakes being brought into action by a hand lever on a ratchet on the left-hand side of each seat, after which operation either rudder bar releases the brake on the wheel outside of the turn. In the joyriding machine the fuel is in the top centre section, but in the standard and Club machines this is accommodated in front of the front passenger below the top decking. In the cabin machine, as in the other machines, this is contained in a welded aluminium tank, but in this instance situated below the cabin floor in a position where it can easily be removed if required. Twenty-eight gallons is the normal capacity in most cases.
   The wings and other covered units are, in the interests of economy, of wooden construction carried out on normal lines with spruce spars spindled to the requisite section, in the case of the main planes, and boxed for the tail plane, fin and rudder. Spruce ribs form the aerofoil section for the main planes and steel tubes with swaged wires make up the drag bracing. Following usual Avro practice, the aileron hinges are of ample size so that no wear need be expected under ordinary conditions of use. The undercarriage is practically the same in each case, the compression leg being led to the top longeron, and being of very small cross section. The land shocks are taken by a series of three springs working in parallel, the rebound being catered for by an Oleo restriction arrangement. Dunlop medium-pressure tyres are lifted on the wheels and Bendix brakes. The three machines whose wings fold, that is, the three-seater, Club "Cadet" and cabin machine, have the top centre section farther aft than in the case of the standard machine, and the wings fold about the rear spar root joints.
   In the cabin machine the top centre section is clear as the fuel is below the floor and the cabin roof is therefore covered with cellastoid, giving the cabin a particularly light and roomy appearance, which entirely negates any boxed-up feeling and also gives the pilot a reasonable measure of backward view. In this machine the seating arrangement will be such that the pilot sits by himself in the front, behind a safety glass windscreen of large size. He sits higher than is usual in machines of this type and gets a particularly good view in consequence. Immediately behind him one passenger is catered for on a seat, the base of which is an elektron casting. This seat is on runners and slides to the right-hand side of the machine when three passengers are carried or to the centre of the machine when it is desired to use dual control. Behind this seat a plywood bench, well upholstered, goes right across the machine. This is fully large enough for two children or one adult.
   Luggage can be carried beside this passenger behind the middle seat and also beside this middle seat.