Flight, July 1921

THE SPAD "BERLINE" S.33 BIS
250 H.P. Salmson A-Z9 Engine

   GRADUALLY on the London-Paris air line the converted war machines are giving place to machines specially designed for the class of work for which they are being used. The original service started with de H.4's and similar types, with a small conservatory roof added above the heads of the passengers. It was soon found, however, that it was not a very paying proposition to run passenger services with such machines, and gradually they have been replaced by others. From Captain de Havilland's drawing-board, the latest - and most economical - machine to be used regularly is the 18, which has given most excellent results. Yet there is every reason to believe that the machines now coming along at Stag Lane will surpass in efficiency the 18. The French services have long been run - as regards the smaller types - with converted or "semi-commercial" types, and it is not until quite recently that attempts have been made to introduce more suitable types. As a representative of French 1920 commercial design, the Spad "Berline," type S.33 bis six-seater, is of interest in showing M. Andre Herbemont's ideas of a commercial aeroplane. Several of these machines may now be seen at the Waddon aerodrome near Croydon.
   In general lay-out, the Spad 33 bis follows previous machines of Herbemont's design. That is to say, the fuselage is of the monocoque streamline type, the wings are characterised by a backswept top plane, and a single interplane strut on each side. The rudder is of that curious fin shape (piscatorial not aerodynamic) which has for several years been typical of the Spads. The fuselage is of fairly ample proportions, much more so than in the earlier types, where the passengers were very much cramped. Seating accommodation is provided for five passengers, in addition to the pilot. The arrangement of the seats is reminiscent in a general way of that of the Westlands. That is to say the pilot sits well aft, on the port side. Next to him, and on a slightly lower level, is a seat for a passenger, who, however, sits with his head projecting through the roof, instead of being inside, as in the Westland. In front of the pilot's cockpit, which is partly partitioned off, are two wickerwork seats, one behind the other, along the port wall of the cabin. On the starboard side are two more seats, placed back to back. On the whole the cabin is fairly comfortable, although of somewhat Spartan appearance. There is no upholstery and no padding, but the cabin, with its white walls and numerous windows and port-holes, is light and well ventilated. The door is near the front of the cabin, on the starboard side, and it must be admitted that it is in an uncomfortably close proximity to the propeller. In fact it would appear that, as there are no external fastenings for keeping the door open against the slip-stream from the propeller, it has been the object of the designer to prevent the engine being run until all the passengers are on board.
   In the roof of the cabin, and just clear of the leading edge of the top plane, is a hatchway covered with transparent material. This hatchway is evidently intended as an emergency exit in case, for some reason, the door is jammed; also the cockpit next to the pilot affords a means of getting out of the machine, so that, even in case of alighting on the sea, there should be a good chance for the passengers of getting out safely. The monocoque fuselage would probably keep the machine afloat for a considerable time.
   The engine, a Salmson A-Z9 nine-cylindered radial water-cooled, is known as one of the most reliable of French engines. It is variously known as a 250 and 275 h.p., but in reality it develops, we believe, about 300 h.p. at 1,500 r.p.m. The bore and stroke are 140 mm. and 170 mm. respectively, and the fuel and oil consumption amounts to approximately 0.56 lb./h.p./hour at full power. The weight of the engine, including magnetos and carburettors, but without water, is 660 lbs. As will be seen from the accompanying illustrations, the engine is neatly covered in, with a circular radiator in front of it. A small door in the front wall of the cabin gives access to the carburettors and magnetos from inside the cabin, thus doing away with the necessity of removing the cowling for the purpose of inspecting these two accessories. Furthermore, there is a circular opening in the lower part of the cowl itself.
   The petrol system is of the simplest possible. Two large petrol tanks are placed on top of the upper plane, and the supply to the engine is by gravity from these main tanks, thus doing away with petrol pumps, and at the same time getting all the petrol away from the cabin.
   As regards the performance of the Spad "Berline," the machine should be fairly economical to run, as the load carried per horse-power is fairly high. At the same time, the speed is not by any means bad, the top speed being in the neighbourhood of 110 m.p.h., with a cruising speed of about 97 m.p.h. We have no information relating to the landing speed, but in view of the fact that the wing loading is approximately 9.5 lbs./sq. ft., the landing speed must be somewhat high. The machine is now in use by the Messageries Aeriennes, alternating with the older types, and probably it is the intention of the management to substitute it, as requirements demand, for these.

Following are the main characteristics and performance data for the Spad 33 bis :-
   Span, 38 ft. 4 ins.
   Length overall, 29 ft. 9 ins.
   Height, 10 ft. 6 ins.
   Area, 463 sq. ft.
   Weight empty, 2,200 lbs.
   Useful load, 2,200 lbs.
   Weight loaded, 4,400 lbs.
   Load per sq. ft., 9.5 lbs.
   Load per h.p. (300), 14.66 lbs
   Speed near ground, 110 m.p.h.
   Speed at 3,300 ft., 110 m.p.h.
   Speed at 6,600 ft., 109 m.p.h.
   Speed at 10,000 ft., 105 m.p.h.
   Climb: 3,300 ft. in 10 mins. 5 secs.; 6,600 ft. in 22 mins. 54 secs.; 10,000 ft. in 45 mins. 32 secs.