Flight, May 1929

A.B.C. "ROBIN”
A New Cabin Single-Seater with "Scorpion" Engine

   SLOWLY but steadily the little "Scorpion" engine, designed and built by A.B.C. Motors, Ltd., of Walton-on-Thames, has been gaining popularity for use in low-power light 'planes, ДальшеMore>>> until at the present time it is to be found in most European countries, such as France, Germany, Austria, Italy, Poland, etc., not to mention places as far afield as Australia and New Zealand. At home, owing to the absence so far of machines specially designed for really low power, the market has been more restricted, but there is ample evidence that during the next few months quite a large number of machines will make their appearance, fitted with this popular power plant. Some of these will be exhibited at Olympia, while others may not be ready in time for the show but will come out later in the year. Already it is obvious that 1929 will in future be remembered as the year in which the cheap, low-power, single-seater, light 'plane was first seriously put on the market in England. The light 'plane of 30 h.p, or so is, of course, no novelty, and was produced in a variety of versions several years ago, but that was as a result of competitions intended to encourage the production of machines of this class. The light 'plane development in this country has followed lines very different from those originally contemplated, but we are now definitely returning to the real light 'plane via a somewhat roundabout road. This time, the revival of the type is not caused by competitions but as a result of the realisation of a demand which undoubtedly exists. That we in this country shall ever go to the same extreme as have the Germans, and design for a maximum of 20 h.p. or so is very unlikely. A spectacular performance is not required, but a useful turn of speed will without doubt be demanded, and the machine which is capable of making good over the ground a speed of 50 m.p.h. only against quite an average head wind will never, we feel sure, attain any degree of popularity in this country. Nor is there any very logical reason for such a machine. The difference in production cost between an engine developing a maximum of some 20 h.p. and one capable of close upon twice that power is relatively small. And as for running costs, the 40-h.p. machine win be very little more expensive to run than the 20 h.p. Yet the extra power is sufficient to enable a really useful performance to be attained.
   Mr. T. A. Dennis, managing director of A.B.C. Motors, has long realised the truth of what FLIGHT has been "preaching" concerning the need for a low-power single-seater machine, and becoming somewhat impatient with the slow progress made, he decided some time ago to enter the field of aircraft construction and to build machines to utilise the two types of engines which he was already producing: the 30-40-h.p. "Scorpion" and the 60-70 h.p. "Hornet." Looking around for a designer, Mr. Dennis secured the services of Mr. A. A. Fletcher, whose name will be familiar at least to the older readers of FLIGHT. "Tony" Fletcher was, back in the "dark ages," connected with the Martinsyde firm, and later with the L. & P. school at Hendon and the Central Aircraft Company at Kilburn and Northolt. Afterwards he joined the Whitehead company, and some years ago he went to Japan whence he was driven by the earthquake that wrought havoc with so much property. Mr. Fletcher has thus had a very long experience of aircraft design under varying conditions, and the first machine which he has designed for A.B.C. Motors is the little monoplane that forms the subject of the present notes and illustrations.
   The A.B.C. "Robin," as the first machine is to be named, is of more than ordinary interest in that it is the first low-power single-seater with conduite interieure to be produced in this country. The comfort of the pilot (who will in most instances be the owner) has been seriously studied, and in the "Robin" we have a machine which the owner can use all the year round without having to don special flying kit. The little cabin has its floor so low above the ground that the pilot (one feels he ought to be called the driver) can step in without the use of any built-on steps. Large windows on each side give a good view outwards and, as the windows can be opened, backwards during flight as well as forward while taking off and landing. In fact, as "Tony" Fletcher put it "if he is a sufficiently bad pilot he can watch his wheels until the actual moment of touching the ground." A V-shaped windscreen closes the cabin in front, and as the engine mounting is placed quite low, the view forward is also excellent. A hinged skylight forms the roof of the cabin, and can be raised to facilitate getting in and out, as well as forming an emergency exit through the roof in case of a crash. The cabin door itself is on the starboard side.
   Just behind the cabin, and with a hatch in the roof of the fuselage, is a luggage compartment large enough to take two large suitcases, so that the owner of a "Robin" will be able to go on a prolonged tour carrying with him changes of suits, linen, etc., in addition to the proverbial toothbrush.
   That the "Robin" will be a really useful and serviceable machine, and not merely a toy fit only for "tootling around an aerodrome," will be realised when we state that the estimated top speed is 105 m.p.h., while the machine should cruise very comfortably at 85 m.p.h., taking but 24 h.p. from the engine. The fuel consumption at cruising speed is but 2 gallons per hour or so, giving a mileage of more than 40 miles per gallon, which must be regarded as extremely economical. Taking the price of petrol as 1s. 7d. per gallon, the "Robin" would, in still air, do about 85 miles for a fuel cost of 3s. 2d., or, in other words, at the rate of less than 1/2 d. per mile! We believe that large operating companies reckon the fuel cost as being approximately one-third of the total running cost. Whether the same applies to a small machine like this is, perhaps, open to doubt, but assuming that it does, the total running cost of a "Robin" should be less than 1 1/2 d. per mile! Flying threatens to become cheaper than third-class railway travel. When small machines of this class become really popular, as they are bound to become very soon, the most serious item of expense is likely to be the insurance.

Structural Design

   Simplicity has been aimed at in planning the structural design of the "Robin," and wood is the material most extensively used, the employment of metal being confined to fittings and a few highly-stressed parts.
   The fuselage is a wooden "box" having four spruce longerons in the corners, and top, bottom and sides covered with a thin ply-wood veneer. Light formers are placed at intervals to retain the rectangular cross-sectional shape, these formers consisting of panels with very light spruce frames and thin ply-wood walls lightened by large cut-outs.
   Up to the cabin the fuselage is deep and the deck forms a roof except for the skylight already referred to. In front of the cabin, however, the deck drops considerably so as to provide the forward opening of the front window or windscreen. The lower longerons extend right up to the engine plate, but owing to the sudden drop in the deck in front of the cabin, the top longerons of the engine mounting are short separate lengths, stopping short at the front wall of the cabin. The engine plate itself is a multi-plywood former, and is attached to the longerons by rather neat steel fittings, which are simply short lengths of square-section steel tubes, split for a distance along the corners, and the free ends thus formed being turned out at right angles. In this way a flanged socket is formed without the use of welding. The diagonal bracing of the forward part of the fuselage, i.e., from cabin to engine plate, takes the form of steel tubes. The petrol tank, with a capacity of 8 gallons, is housed in the forward deck fairing, above the pilot's legs, a position which still gives sufficient "head" to enable direct gravity feed to the engine to be employed.
   The monoplane wing is built in two halves, hinged to the fuselage top corners, and braced each by a pair of struts arranged in the form of a Vee. The upper ends of the wing bracing struts are attached to the wing spars by steel straps, while at the fuselage end the two tubular struts have fork ends fitting over a sheet steel fitting bolted to the fuselage. As the lift is taken from this point, a steel strap bolted to the corner fitting runs right across the bottom of the fuselage to the corresponding fitting on the opposite side, while inside the fuselage a tie rod transmits the tension. This tie rod lies along a plane just above the top of the lower longerons, and as the external steel strap is just below the lower longerons, the whole structure is so stabilised that no twisting stresses are imposed upon the lower longerons.
   Across the top of the fuselage runs a Duralumin tube, which terminates at each end in a sheet steel fork, between the jaws of which a Duralumin block is swivelled. This block, which is vertical, has a horizontal hole drilled through it for the reception, in the case of the front spar fittings, of the locking pin used in connection with the wing-folding arrangement. This pin is rather in the form of a sort of key, as when the wing is erected and the pin pushed home and turned, it cannot accidentally come out of its socket, being held in by a coil spring and having a small projection or cam which fits into a corresponding recess in the block.
   The wing spars are of solid spruce, spindled out to an I-section. This form of spar is rather cheaper to make than a box-section spar, and as there is no difficulty in obtaining good spruce in such short lengths, the spindled I-section spar was chosen. The ribs are light girders, of square-section spruce, attached to the spars by corner strips. The rib flange strips are joined to the rib tie strips by thin three-ply wood gussets. The covering is doped fabric. The wing section used is a bi-convex one, R.A.F. 34, which has an almost stationary centre of pressure, and has been found to work excellently on full scale.
   The tail surfaces are also of wood construction, and perfectly normal, both in aerodynamic and structural design. The tail plane incidence can be adjusted while the machine is on the ground, the rear spar of the tail plane being supported from the fuselage by two threaded bolts, lock nuts on which locate the tail plane at the desired angle by being tightened up against a flat sheet steel fitting.
   The undercarriage is of the "split" type, the wheel on each side being supported on a tent axle, which is in turn located in a fore and aft direction by a radius tube, and in a vertical direction by the telescopic "leg," the upper end of which is bolted to the side of the fuselage. Endless rubber cord rings form the shock-absorbing medium, and the correct amount of springing is very simply determined by the number of rings employed. There is no damping device for checking bouncing. The wheel track obtained with this form of undercarriage is very wide, and there should be little danger of the machine turning over when taxying in a strong cross wind.
   The main dimensions, etc., are shown on the general, arrangement drawings. The estimated tare weight of the "Robin" is 415 lbs., but actually, the machine promises to come out quite a good deal lighter than that. The permissible gross weight for the certificate of airworthiness is 680 lbs., which will enable a fairly heavy pilot and a considerable load of luggage to be carried, in addition to fuel for 4 hrs. at cruising speed, or a range of about 340 miles.
   Assuming a maximum power of the "Scorpion" of 40 b.h.p., the power loading is 17 lbs./h.p., while on normal power (35) the power loading is 19-4 lbs./h.p. The wing loading is 7 lbs./sq. ft., which gives a landing speed of approximately 40 m.p.h.
   As the "Robin" is not yet finished, actual results of flying tests cannot be given, but the high placing of the wing, in conjunction with a wing section with stationary centre of pressure, should make for great stability. R.A.F. 34 shows no violent stall, and the machine should merely sink slowly when flying beyond the stall, and should show little tendency to go into a spin.

Flight, June 1929

BRITISH AIRCRAFT AT OLYMPIA

A.B.C. MOTORS, LTD.

   HITHERTO chiefly an aero engine firm, with two well-established engines in the 35 h.p. "Scorpion" and the 70-h.p. "Hornet," Mr. Dennis, managing director of A.B.C. Motors, Ltd., decided some months ago to enter the field of aircraft construction so as to utilise to the full the engines already produced by the firm of which he is head. He secured the services of Mr. "Tony" Fletcher as designer, and the little "Robin" to be exhibited on the stand of A.B.C. Motors is the first machine to be produced.
   The "Robin" is a single-seater light monoplane of all-wood construction, and is perhaps mainly remarkable on account of its enclosed drive, or conduite interieure, being the first light single-seater of this type to be produced in Great Britain. Cabin monoplanes have, of course, been constructed before, but in the "Robin" we have this arrangement incorporated in a very small and compact machine. Opinions will doubtless differ as to the necessity or otherwise of an enclosed cabin in such a small machine, and as this is almost entirely a matter of personal taste there is little need to discuss the question here. The advantage of the enclosed arrangement is that special flying clothes are unnecessary, and it is likely also that the engine noise reaches the ears of the pilot with less distressing effect, although as we have said pilots differ in their views on this subject. It should be recollected, however, that with a cabin machine having sliding windows (as does the "Robin"), the pilot does have the option of opening the windows and thus obtaining very largely the freedom of the open type of machine.
   In the "Robin" the cabin is entered through a door on the right-hand side, and although this may not always be needed, there is a hinged skylight in the roof so that with this raised it is rather easier to enter the cabin and get settled in the seat. Once the pilot has arranged everything to his satisfaction, the skylight is closed in such a manner that it cannot open accidentally while the machine is flying. The door on the starboard side, as well as the wall on the opposite side, are provided with windows, so that what with these and the skylight and the large windscreen in front, plenty of light finds its way into the cabin, which is more than one can say of some commercial passenger machines. In front of the windscreen the deck of the fuselage is dropped about a foot, and in addition the deck fairing slopes down towards the engine, thus giving a very good view forward. Aft of the cabin is a luggage compartment large enough to take two suitcases, so that the owner of a "Robin" can take with him (or her) plenty of clothes for a prolonged tour.
   The "Robin" fuselage is of the "box" type with light stringers and formers, and plywood covering. The wings also are of wood construction, with spindled I-section spars and light wooden ribs, the whole fabric covered. The two halves of the wing are braced to the lower longerons of the fuselage with a pair of Vee struts on each side, and hinges are provided on the rear spar attachments to enable the wings to be folded. When this is done, the overall width of the machine is reduced to 11 ft. 8 in.
   The undercarriage is of the "split" type, each wheel being supported on a tripod formed by the bent axle, the radius rod and the telescopic leg. The shock absorbers are in the form of endless rubber rings slipped over crutches, and enclosed in streamline fairings. The wheel track is wide (5 ft. 0 in.) in proportion to the span of the machine, so that there should be little tendency to "cartwheel"
   The engine of the "Robin" is an A.B.C. "Scorpion" two-cylinder, flat twin air-cooled, bolted to a multi-ply engine plate in the nose of the machine. The petrol tank is housed in the deck fairing in front of the windscreen, a position which is high enough to give direct gravity feed to the carburettor.
   The main dimensions and areas of the "Robin" are: Length, o.a., 17 ft. 7 in; wing span, 25 ft. 4 in.; total folded width, 11 ft. 8 in.; total wing area, 97 sq. ft.; area of ailerons, 13 sq. ft.; area of tail plane, 9 sq. ft.; area of elevators, 6 sq. ft.; area of fin, 2-5 sq. ft.; area of rudder, 4-5 sq. ft.
   The tare weight of the machine is about 400 lbs., and the certificate of airworthiness covers a gross weight of 680 lbs., which will cover a fairly heavy pilot and a good deal of luggage in addition to fuel for 4 hours at a cruising speed of about 85 m.p.h. At this speed the fuel consumption is remarkably low, and is estimated to correspond to approximately 40 miles per gallon. At the moment of going to press with this week's issue of FLIGHT, actual performance figures are not available, but the estimated top speed of the "Robin" is 105 m.p.h. and the landing speed approximately 40 m.p.h.

Flight, April 1930

AIRCRAFT FOR THE PRIVATE OWNER

ROBIN

   THE Robin is the only representative of its class on the market. As a single-seater cabin machine it has an appeal to those who wish for a small machine with a reasonably high performance, but who at the same time do not wish to give up the comfort of the cabin.
   Built by A.B.C. Motors, Ltd., of Walton-on-Thames, it is, as one would expect, fitted with the A.B.C. Scorpion engine.
   It is one of the neatest small cabin machines at present available, and though there will' always be a division of opinion as to the desirability of a single-seater cabin machine, there must at the same time be a small circle of pilots whose flying is mainly done for business, and who travel alone, and for such as these the Robin should make an admirable machine.
   It is one of the prettiest little machines we have seen, and will undoubtedly have an appeal to lady pilots; but in its present form it would seem as if it is just a little too light on the controls for anyone except an experienced pilot to handle with any degree of comfort. However, teething troubles are to be expected on any new machine, and by the time Robins are in production we may expect such things to have been modified.
   The cabin is entered through a door on the starboard side, and the skylight above the cabin is made to hinge upwards, so that when getting in the pilot will have more room for his head, and when he is settled he can fasten down this skylight, which incidentally allows a clear view upwards and backwards, making the cabin feel very light and airy, eliminating any feeling of being shut in. The side windows and those in front can be slid sideways so that the pilot can always look out without looking through glass should he desire to do so.
   Behind the cabin is a roomy luggage locker, which has an access door through the top of the fuselage. The fuselage is a boxed plywood structure with light internal stringers and formers so that its strength to weight ratio is high.
   The wing spars are spindled I-section spruce, and the ribs are built up in the form of N-girders, with spruce of square cross-section. The wing bracing is by a pair of vee-struts on each side, and the rear hinge of the wing allows them to be folded.
   The undercarriage looks somewhat diminutive, but is well designed, and has a wide track which should make the machine steady on the ground. The compression leg is made with rubber rings around steel crutches covered in a streamlined casing.