Flight, March 1932

The Avro 631 "Cadet"
Coming from a firm which holds a leading position in the production of training aircraft, the Avro "Cadet" will attract world-wide attention. It is a two-seater training biplane fitted with Armstrong-Siddeley 7-cylinder "Genet Major" engine of 135 b.h.p. It is designed for full training duties at low first cost and very modest maintenance cost

   AT first sight is might appear that the production of the "Cadet" by A. V. Roe & Co., Ltd., represents a negation of that firm's policy. Actually this is not so. Those responsible for Avro policy have not changed their views in the slightest degree. The "Cadet" represents an addition to rather than an amendment of the policy. Our readers may recollect that in FLIGHT of July 3, 1931, the Avro firm contributed some very clearly expressed views on Air Force Training, in articles by Major F. P. Scott and Mr. K. J. Parrott. For the benefit of readers it may be recalled that in those articles the argument was used that in training aircraft true economy does not necessarily lie in low first cost, but that on the contrary it depends chiefly on other features, such as suitability for rapid all-through training in time of war, when there will be no time for advanced training following upon ab initio training, nor will there be war type aircraft available for such training, the machines being urgently wanted elsewhere. The Avro view, as expressed in those articles, was also that all-metal construction is essential, because of the difficulty in this country of getting suitable timbers in time of war, not to mention the longer life and lower maintenance cost of an all-metal aircraft.
   In the Avro "Cadet" the question of first cost has been seriously studied, and all-metal construction has been abandoned. This is not because A. V. Roe & Co., Ltd., have changed their views, but because it is realised that while the above arguments hold good where large nations are concerned, there are countries in which cost is a very vital consideration, and in which local supplies of timber are plentiful, while facilities or experience in handling and repairing steel wings may be lacking. The Avro, like all other British firms, must study closely conditions abroad, and must rely to a great extent on a healthy export trade. It is with this in view that the "Cadet" has been produced.
   In spite of a close family resemblance to previous Avro machines, the "Cadet," or Avro 631, incorporates a number of features not found in other Avro types, and these are obtained without any sacrifice of simplicity, which is, if anything, greater than ever. The machine is a normal single-bay tractor biplane, characterised by a very pronounced stagger. The engine is a 7-cylinder Armstrong-Siddeley "Genet Major" radial air cooled, and although the machine is to be marketed at a very reasonable price, such refinements as a Townend drag-reducing ring are fitted. That this has been worth while from a performance point of view seems clear from the fact that the top speed is no less than 118 m.p.h., while the initial rate of climb is 750 ft. per min. The lines of the "Cadet" are very pleasing indeed, and the machine is extraordinarily deceptive in that, although it has the wing span of the latest "Avians," its cockpits are as large as those of the Avro "Trainer." In spite of this, however, the fuselage does not look at all large for the size of the wings, and the general proportions are good and pleasing to the eye.
   Designed specifically for complete flying training, from ab initio to advanced aerobatics, the "Cadet" has its two cockpits absolutely identical, so that when a pupil changes from front to rear cockpit his surroundings remain unchanged, and he knows instinctively where to put his hand on everything. The flying controls are of a very intriguing simplicity, obviously the result of much thought and scheming to get price and weight down, and the same may be said of nearly everything about the machine. The instruments are well placed, and the cockpits are of ample dimensions, so that there is plenty of leg, elbow and shoulder room everywhere.
   Apart from the duplication of flying controls, instruments, etc., all engine controls are duplicated, as is also the tail trimming gear control, the latter in a most ingenious fashion. The notched quadrant in the front cockpit is the main "cheese cutter," but a somewhat similar control in the rear cockpit is linked up to it by Bowden cable, so that the tail setting can be effected from either cockpit.
   By dropping the top longerons in the middle portion of the fuselage it has been possible to provide unusually deep cockpit doors, which make it very easy to get into and out of the cockpits. The great degree of wing stagger, and the attachment of the rear lift wire to the front lower spar root, result between them in a particularly unhindered exit from the front cockpit, so that the occupant of this should have no more difficulty in jumping out with his parachute in case of emergency than the man in the rear cockpit. In a machine capable of stunting, and indeed designed for aerobatics, this is a point of very great importance.
   Controllability and manoeuvrability are other very desirable features in a training machine, and these are present in full measure in the Avro "Cadet." The aileron control is particularly effective, even at very low speed, and with the Bristol-Frise balance the ailerons are comfortably light in operation. They are fitted to top and bottom planes, but the balance extends over a relatively small proportion only to avoid over balancing.
   In a machine designed for school work, and which therefore will be called upon to make a very large number of landings, the undercarriage is often the deciding factor in the durability of a machine. In the "Cadet" Mr. Chadwick has introduced a somewhat novel type of telescopic leg, in which coil springs are placed end to end, although actually working in parallel. The shock absorbing qualities are quite remarkable, and it would take a very bad landing indeed to cause serious damage to the structure.

The Structure

   With a view to cheapness, and also because in several foreign countries timber is available in good qualities, the Avro “Cadet" has been made of composite construction, i.e., it has wooden wings and a welded steel tube fuselage.
   The wings, which are of modified T.64 aerofoil section, are of normal wood construction, with I-section spindled spars and plywood ribs. The ailerons are of the Bristol-Frise type, and are fitted to upper and lower wings, but have been modified by extending the balance over a portion of them only, so that over balancing does not occur. A further advantage of this particular arrangement of the balance is that the leads from ailerons to control column become very straightforward indeed. The wing tips are rounded in plan form, and the overhanging portions are fined down to a thin edge.
   The fuselage is of the type of welded construction which Avros have employed for a considerable time, and is so well known that it will need no detailed description here. It will suffice if we recall briefly that the top and bottom longerons are connected by a series of diagonal struts, the joints being made by welding the strut ends to the longerons, and the few bracing wires used being looped over tubular quadrants welded into the corners. The welded construction has facilitated the dropping of the top longerons to give deeper cockpit doors without making these a part of the primary structure. The outside form of the fuselage is given by spruce stringers carried on light skeleton wooden formers attached to the primary structure by simple clips. The fuselage covering is fabric, and in order to facilitate inspection the fabric is secured in appropriate places by "Zipp" fasteners. Normally the tags of the fasteners are locked by a small length of thin wire, but when this is removed the fasteners can, of course, be undone in a few seconds, and the interior structure examined.
   The Armstrong-Siddeley 7-cylinder "Genet Major" engine is mounted on a circular plate, which is in turn supported on four steel tube vees, the apices of which are secured to the forward ends of the longerons. This type of mounting has been found to resist torque reaction very well, and has the further advantage of making the back of the engine very accessible.
   By placing the petrol tank (capacity 28 gallons) in the deck fairing forward, the top centre section is kept thin, a fact which adds to the clean appearance of the machine. The oil tank is slung on straps on the fireproof bulkhead behind the engine.
   A very neat Townend ring has been designed for the "Cadet." As it promises to be very successful, it may be assumed that a similar principle will be applied to other Avro types. The ring is built in two halves, held together by quick-release devices. The ring is supported on the engine by fitting brackets on top of the cylinders, these brackets corresponding with other brackets on the cowling ring. The brackets serve merely to locate the ring, which is not bolted or otherwise attached to the engine direct. By interposing a felt pad between the engine brackets and their corresponding cowl brackets, rattle is eliminated, and the amount of vibration transmitted from the engine to the ring is negligible. The arrangement has the very great advantage that the time taken in removing or replacing the cowl is a few minutes only, and the engine is for practical purposes as accessible as an uncowled engine.
   The main data of the Avro "Cadet" are given in the table on page 254. From this it emerges that the ratio of gross weight to tare weight is 1.62. At first this may appear to be a somewhat low value, but it should be realised that the ratio is based on the gross weight corresponding to "Aerobatics" Certificate of Airworthiness. A considerably greater load could be carried for "Normal” C. of A., when the ratio becomes rather higher than the average.
   Aerodynamically the "Cadet" appears to be very efficient, the Everling "High-speed Figure" being no less than 21.7, which points to a low minimum drag coefficient.
   The speed range is from 45 to 118 m.p.h., a ratio of 2.62 to 1, and the initial rate of climb is 750 ft./min., all of which point to efficient aerodynamic design in proportion to the wing loading and power loading.
   Altogether the Avro "Cadet" is to be regarded as a very attractive training aircraft, and in spite of its relatively low power (135 h.p.) and sturdy construction, it has a performance which should make it suitable for full flying training, without the need for further training on high-power types.

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.
   In its standard form the "Cadet" remains basically the same as before. It is definitely made for primary flying training or for those owners who may have some antiquated prejudice against folding wings. It differs from the previous model only in minor details like the seating arrangement. In the 643 the pilot's seat has been raised a little, thereby giving him a somewhat better view over the head of the front passenger. It will still have very full dual equipment, including the delightful Avro type, tail trimming gear, fuel control cocks, wheel brakes, adjustable rudder bars and complete instrument installation.
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Flight, February 1936

A NEW RECRUIT
The Latest Type of Avro Cadet: More Power and Strength

   THE Royal Australian Air Force and Air Service Training, Ltd. have lately adopted a new type of Avro Cadet for training purposes. Designated the Avro 643 Mk. II, the machine differs in comparison with its progenitor in that it has a more powerful engine, has been strengthened up, incorporates detail refinements and has an aerobatic C. of A. for a gross weight of 2,000 lb. This latter innovation (the all-up aerobatic weight of the elder Cadet is only 1,800 lb.) enables the machine to carry such equipment as permits it to be used for training with a fixed camera gun or camera in addition to its more normal function as a flying training type. So it is a very attractive proposition to an air service in which economies are being practised and should, in addition, suit the requirements of a certain section of private owners.
   Structurally it resembles the earlier staggered Cadet, which means that the main planes and tail unit are of wooden construction. The fuselage is of welded-steel-tube construction with wooden fairings and fabric covering. A large portion of the fabric is removable for inspection.
   Both spars have been made more robust, not having been spindled to the same extent as in the earlier type of wing, and as the result of a re-arrangement of the bracing wires the whole wing cellule is more rigid torsionally. Of these the lift wires new run from the bottom front fuselage joint to the top front interplane strut joint; from the latter point to the bottom front wing root fitting; and another travels thence to the top rear interplane strut joint. Anti-lift wires lead from the top wing roots to the lower front interplane strut joint. The tail plane is stronger than before.
   Exit with a parachute from the front seat is still a matter of ease owing to the arrangement of the wires and the provision of side doors.
   Frise ailerons are fitted to upper and lower planes and Handley Page slots with controlled locking may be embodied if required. Other items are: full dual instruments and blind flying hood; night-flying equipment (the navigation lights may be of the single type or of the Demec three-in-one variety); dual-operated Bendix brakes permitting instruction in braking; a fully castering tail wheel interchangeable with a tracking skid consisting of a laminated steel spring with a replaceable shoe; and tankage for 26 gallons of fuel. Greater use has been made of ball bearings in the control system. The rear seat is now adjustable.
   The engine is the Siddeley Genet Major IA seven-cylinder radial rated at 150 h.p. at 2,200 r.p.m. and delivering a maximum of 165 h.p. It is mounted six inches further forward than that in the older Cadet, but retains the Townend ring (this is in two halves and is easily removed) and exhaust ring behind the cylinders. Other features are an oil cooler, a petrol system arranged for inverted flying, and a metal airscrew.
   Provision is made for the installation of a Hythe Mk.III camera gun on the bottom plane. When this is fitted the machine is used only as a single-seater. There is also allowance for the mounting of a P-7 camera beneath the fuselage in a streamline fairing which, it is claimed, does not affect the tail trim. The tail trimming gear, incidentally, has larger operating wheels than before.
   The wide-track undercarriage has oleo shock absorbers with steel springs in compression to absorb rebound and taxying shocks.

Flight, April 1936

MODERN LIGHT AIRCRAFT REVIEWED

AVRO

   SINCE pre-war days the firm of A. V. Roe and Company has specialised very largely in the production of training types and the famous "504" was actually the standard Service trainer for some fifteen years, until the Tutor was adopted. Any Avro machine, therefore, can be reasonably expected to possess nicely harmonised and effective controls as well as generally easy - but not too easy! - flying qualities. Some years ago the company introduced a smaller version of the Tutor which, while retaining all the good qualities of the larger machine, would be less expensive to operate and more suited to the needs of civil clubs and schools.
   This year the Avro 643 has been produced as a single standardised machine to take the place of the staggered and Club Cadets previously manufactured. In this new model the whole airframe has been strengthened, a castering tail-wheel is fitted and the power unit is the latest Genet Major Mk. 1a , which gives about 15 more b.h.p. and so reduces the take-off run. Full blind-flying equipment is standard for both cockpits and a simple inverted-flying fuel system can be installed if required.
   Those pilots who have been lucky enough to fly one of the Cadet breed will agree that, as an aeroplane pure and simple, it has few competitors. Although it is possible to make it perform any aerobatic manoeuvre known to pilots, it is, at the same time, a most stable and docile creature in the course of normal flight. The Cadet or 643 can, for instance, be sunk on a level keel with the stick held right back so long as the rudder is not too severely interfered with, and it is safe to glide at extraordinarily low speeds. The act of landing is the easiest imaginable, and the undercarriage will take anything within reason.
   The specification of the Avro 643 is as follows: Span, 30ft.; length, 24ft. 9in.; tare weight, 1,286 lb.; all-up weight (with aerobatic C. of A.), 2,000 lb.; maximum speed, 116 m.p.h.; stalling speed, 43 m.p.h.; duration at cruising speed, 3.25 hr.; initial rate of climb, 700 ft./min.; service ceiling, 12,000ft. Makers: A. V. Roe and Co., Ltd., Newton Heath, Manchester.