Zmaj AF.2 / Fizir-Vega
Страна: Югославия
Год: 1931
Летающая лодка

Flight, May 1931

Flight, May 1931

A New German "Pusher" Two-Seater

  THOSE who, like we, have an opportunity of studying the aviation press of the world, cannot fail to have been impressed by the modern tendency of reverting to the "pusher" type of aircraft in the light 'plane class. There is scarcely a country in which the pusher principle is not being revived, and the present summer should be of considerable interest in showing what troubles are met with in cooling pusher engine installations. The question of cooling is easily the most serious obstacle to the successful reintroduction of the pusher type of machine. The relative inefficiency of pre-war pushers need not necessarily apply to modern design, although the gap left in our practical knowledge of pushers from the days of the open tail girder type to the modern clean tractor machine, will doubtless require a good deal of research and experiment before we can design pushers which are as efficient aerodynamically as is the modern tractor machine. It is likely that the pusher will always remain slightly less efficient than the tractor, but if the difference is not too great the sacrifice is well worth making for the sake of getting the engine behind the occupants, where not only is less noise transmitted to the cabin, but also vibrations and buffeting, caused by the slipstream of the propeller in front, are entirely absent. To these advantages must be added the possibility of providing an exceptionally good view from the pilots cockpit, a view far and away better than could ever be obtained with any tractor arrangement.
  In this country, the pusher has not so far been seriously tackled. The Hinkler "Ibis" is a twin-engined machine with two Salmsons in tandem, and the propeller of the front engine is, in fact, ahead of the cockpit. For all that the machine does to a large extent, give the advantaged of the single-engined pusher. The "Falcon Four," which is now being built at Shoreham, is a twin-engined machine with pusher engines out on the wing, and promises to be a very fine type for the private owner.
  In the two-seater class we have not yet attempted to apply the pusher principle, but there is, we think, little doubt that sooner or later this attempt will be made.
  In the meantime, it is of interest to see what is being done in this direction abroad, and our esteemed German contemporary, Flugsport, of February 18, 1931, contains two photographs and a brief description of a new German machine of the pusher class which, we think, will be of interest to our readers.
  The Fizir "A.F.2" is, in fact, more than an ordinary pusher two-seater, in that it also incorporates the amphibian principle. The machine is a high-wing monoplane with a flying-boat hull of the single-step type. From the sides of this hull, spring short wing stumps, similar to those which Dr. Dornier has made familiar. These wing stumps serve three purposes: they provide lateral stability on the water when the machine is being operated on the sea, they support the wing struts which brace the main monoplane wing, and finally they support the wheels of the land undercarriage in a rather neat way.
  The boat hull is of very simple construction, consisting of a light skeleton covered with plywood. It is not easy to make plywood really watertight, and British experience has been that for seaplane floats and flying-boat hulls the material is none too satisfactory as a planking. Water has a habit of getting in, no matter what pains one takes to dope, varnish and paint the surface, and once water has got in under the edge of the ply, swelling and deterioration rapidly set in. However, in the "A.F.2" it is assumed that the machine is intended mainly as a landplane, and only occasionally to operate on water, on which presumably it will never be left for very long periods, the more so as its land carriage enables it to be taxied up on the beach immediately after alighting. Under such conditions of use the plywood planking should be satisfactory enough.
  The main wing is of all-wood construction with two box spars and plywood covering over the leading edge, the rest of the covering being fabric.
  The small wing stumps on the hull are planked with plywood, and have been thoroughly varnished and painted to ensure, as far as possible, watertightness for considerable periods. The method of mounting the undercarriage is neat. At first sight, it looks very similar to the system adopted by Short Brothers on the single-float "Mussel" seaplane, in which a circular section steel tube runs right through the float and carries two wheels on a tubular fork at each end. In the "A.F.2," however, the system actually differs considerably in principle from that used on the "Mussel." The cross tube does not run through, but extends only just inside the wall of the hull, and, moreover, it differs from that of the Short machine in that the tubes serve merely for swinging the wheels into the up or down position, the load from the landing shocks not being taken by the tubes, but by the wing stumps. The arrangement is ingenious, although it does not, of course, aim at burying the undercarriage and thus reducing head resistance in the manner of a retractable undercarriage.
  The engine, a 5-cylinder radial Walter in the prototype, is mounted on the rear spar of the centre section of the wing, and the petrol tank is placed just ahead of the engine. While this arrangement does give simple gravity feed, it is a little difficult to regard with equanimity a petrol tank just ahead of the engine. In the case of a leak anywhere in the tank or petrol system, it is almost inevitable that petrol will be blown on to the hot engine, and the risk of fire would seem to be very considerable. Presumably, there would be no very great difficulty in dividing the petrol among two tanks mounted some little distance out-board in the wing, when there should be considerably less danger of getting petrol blown on to the engine.
  Normally, the "A.F.2" is intended to be used as an open touring machine, but provision has been made for the addition of a cabin top, and the machine is shown in the photographs with this in place. Personally, we do not think that in a pusher type, where there is no slipstream to worry the occupant, the cabin top is necessary, or even desirable. Good wind screens will provide all the protection required, and the freedom and pleasure of flying in an open machine in which there is no draught is, we think, one of the greatest points in favour of the pusher type. For winter flying there might, of course, be a good deal to be said for the cabin top. Altogether, the "A.F.2" is rather an interesting little machine and, although its performance is not startling, it is certainly not unduly poor, in view of the fact that the machine is an amphibian.
  The main dimensions of the "A.F.2" are as follows :- Span 11-2 m. (36 ft. 8 in.); length, 7-10 m. (23 ft. 4 in.); height, 2-70 m. (8 ft. 10 in.); wing area, 16 sq. m. (172 sq. ft.); weight, empty, 460 kg. (1,013 lb.); disposable load, 230 kg. (507 lb.); gross weight, 690 kg. (1,520 lb.); wing loading, 43 kg./m.2 (8-84 lb./sq. ft.); power loading, 7-10 - 8-10 kg./h.p. (15-6 - 17-8 lb./h.p.); maximum speed, 140 km./h. (87 m.p.h.); landing speed 60-65 km./h. (37-41 m.p.h.); ceiling, 3,500 m. (11,500 ft.).
THE FIZIR "A.F.2": These two views show most of the main features of the machine. The cabin top is detachable.