Flight, August 1920
THE AUSTRIAN W.K.F. SPORTING BIPLANE
THAT the small sporting aeroplane, with low-powered engine, is entitled to a by no means small share of the attention given to future progress in aviation is borne out by the recent remarkable, but none
the less practical, performance of Mr. Hinkler and his Baby Avro-Green combination, and by the results obtained from trials with machines of this class in various countries. The possibility of a small machine capable of being easily stored - as Mr. Handley Page remarked, in the coal shed - easily and safely flown, having a moderate initial cost, and a running cost as low as (if not lower than) an ordinary motor-car, will not only have a great future before it, but is more certainly a feasible proposition. We still have much to learn on this subject - for one thing we must disassociate ourselves from war practice, when performance was more or less the only consideration.
Any efforts along these lines should, in our opinion, receive every encouragement and exhaustive investigation. It is our intention, therefore, to publish particulars of as many of these types of aircraft as possible, and thus record how various designers tackle this very interesting problem.
This week we give some particulars, together with scale drawings and photographs, of a small sporting biplane built by the Austrian firm of W.K.F. (Wiener Karroserie Fabrik), motor-body and aeroplane builders in Vienna. This firm had obtained some five years of valuable experience in aircraft construction during the War, and immediately after the Armistice set to work on the design and construction of commercial machines.
One result of their efforts is the small sporting biplane in question, which possesses several remarkable features. The most prominent of these is, perhaps, its range of action, which is stated to be about 800 miles, or a duration of 10 hours.
Some difficulty was experienced at first in obtaining a suitable engine for this machine, and during the preliminary trials, in the Spring of 1919, a 30-35 h.p. Haacke three-cylindered fan-type air-cooled engine was installed - the machine illustrated being so fitted. We understand, however, that it is the intention of the firm to construct their own engines, specially for the machine, in the future.
The fuselage, of rectangular section, is built up of three-ply in the simplest possible manner, and although of fairly large cross-section it is exceptionally strong and light - weighing only about 37 1/2 lbs. The first bulkhead of the fuselage consists of a wooden panel, 10 mm. thick, which separates the engine from the pilot. This member also carries the engine supports, and the rudder bar. The pilot's cockpit is large and roomy, and ample protection from the elements is provided. The range of vision in all directions is exceptionally good, owing to the low position and forward stagger of the top plane.
A metal cowel encloses the nose of the fuselage and the engine, the latter having its cylinder heads projecting outside. The main petrol-tank is situated immediately behind the engine, and a small auxiliary tank is mounted behind the main tank. The latter has a capacity of 19.8 gals., and that of the auxiliary tank just over 2 gals. The oil-tank is mounted above the engine, and is of fairly large capacity, to meet the requirements of a long flight.
The main planes are of equal span and chord, and the top plane, which is staggered forward nearly 1 ft. g ins., is straight, whilst the lower plane is set at a dihedral angle of about 2°. The top plane is in one piece, and is supported above the fuselage by two pairs of struts. The lower plane is in two sections, each being attached to the lower longerons of the fuselage. Upper and lower planes are separated by one pair of interplane struts each side. Ailerons of tubular steel construction are fitted to the top plane only. Both planes are of simple construction, the front main spar, of U section, forming the leading edge, and the trailing edge is formed of steel wire. The rear spar is, we believe, of box-section. The ribs, of which there are 13, are equally spaced.
The tail plane, which is semi-circular in plan form, has a cambered upper surface, and is mounted at 0° angle of incidence on the line of thrust. It is braced top and bottom by steel tubes. The elevators are divided, and the rudder is hinged to a vertical fin of moderate streamline section. These surfaces are, it appears, of steel tube construction.
The control is extremely simple, as may be seen from the accompanying diagram. The "stick" consists of a tube terminating at its lower end, where it is attached to the floor of the cockpit, in a universal joint, and having four lugs, mounted on it a short distance above the latter. From two of these lugs cables are led to the port and starboard ailerons respectively, whilst the other two lugs form attachments for the elevator cables - one of which is led forward over a pulley mounted on the floor in front of the control column, and thence rearward, the other cable passing direct to the elevator crank arms.
From a constructional point of view, the landing-gear forms, perhaps, one of the most interesting features of this machine. The chassis itself is of the orthodox V type, with wood struts. It is in the wheels that a somewhat novel - and, we rather fancy, unique as far as aircraft are concerned - arrangement is employed. By the use of extremely resilient springs for the shock-absorbers, it has been found possible to dispense with the usual pneumatic-tyred wheels, and use in their stead solid wooden wheels! These consist of wooden discs, with metal hubs, the felloes, made in the form of, pneumatic tyres, being of oak. In size the wheels are uniform with usual practice, being 760 x 100.
A tail skid of the orthodox pattern is mounted at the tail end of the fuselage.
During the first trials, which were carried out at the firm's aerodrome the machine exhibited very good flying qualities being stable, and easy to fly. We have no information as to its landing speed, but judging from its loading and maximum speed (81 m.p.h.),we should say that it would not be particularly low.
The following are the principal characteristics of this machine :-
Span 17 ft. 3 ins.
Chord 3 ft. 3 ins.
Gap 3 ft. 1 in. to 3 ft. 4 ins.
Stagger 1 ft. 9 ins.
Overall length 14 ft. 4 1/2 ins.
Overall height 7 ft. 0 ins.
Area of main plains (inc. ails.) 101 sq. ft.
Area of ailerons (2) 6 sq. ft.
Area of tail plane 8 1/4 sq. ft.
Area of elevators 4 1/4 sq. ft.
Area of fin 3 1/4 sq. ft.
Area of rudder 3 1/2 sq. ft.
Weight fully loaded (approx.) 740 lbs.
Fuel capacity (10 hrs.) 22 gals.
Loading per sq. ft. 7-4 lbs.
Loading per h.p. 21 lbs.
Speed (max.) 81 m.p.h.
Engine 3-cyl. 30-35 h.p. Haacke or Hiero.