Flight, July 1923
AN UNORTHODOX FRENCH COMMERCIAL AEROPLANE
The Bleriot 115, with Four Hispano Engines
As in this country so also in France, the question of single-engined or multi-engined machines has been occupying the minds of constructors, designers,
and users. Among those who believe that absolute engine reliability is an essential feature if public confidence is to be gained and retained is M. Louis Bleriot, who has backed up this opinion by financing the construction of several multi-engined machines. The latest of these to be shown was the Herbemont-designed four-engined commercial machine exhibited at the Paris Aero Show in 1921. That machine, it may be recalled, had but one single strut on each side, after the fashion of the well-known Spad-Herbemont machines. At the time we rather doubted the adequacy of single-strut wing bracing on a machine in which the engines were placed tandem fashion on the wings. As a matter of fact, we believe that the type was abandoned, partly because static tests indicated that it would be somewhat difficult to provide the necessary strength without undue weight, and partly because Bleriots found, as German and British designers have found, that engines in tandem is not a very good arrangement.
Early this year it was decided to proceed with the design of an entirely different type, still using four engines, but placing them on the wings, somewhat after the fashion of the "Mammoth" Bleriot of the years immediately after the War. The engine placing is, however, the only feature of resemblance between the two types, as the accompanying illustrations will show.
For the particulars and illustrations of the new Bleriot 115, as the machine is styled, we are indebted to M. G. Brun of Bleriot Aeronautique, Suresnes (Seine), and it is worthy of note that this machine, which represents M. Bleriot's latest ideas on multi-engined machines, has already established a world's record by carrying a useful load of 2,200 lbs. to an altitude of 5,600 metres (18,400 ft.), piloted by Jean Casale.
Apart from the employment of four engines placed on the wings, the main feature at which the designers of the Bleriot 115 have aimed is simplicity of construction. The fuselage, wings, and tail members are all straight-lined, and wherever joints occur they are almost without exception at right angles. This, of course, facilitates and cheapens the construction enormously. Another feature is that the engine installations have been designed as complete units, so that any engine of the group of four may be placed in any position.
The fuselage is of rectangular section, the front portion being ply-wood panels on spruce longitudinals and struts, while the rear portion has top and bottom covered with ply-wood, but the sides fabric covered over duralumin tubes and R.A.F. wire bracing. The whole fuselage is, finally, covered with fabric, both over the ply-wood portion and the braced girder rear section.
The wings are chiefly remarkable for the fact that they are placed at no angle of incidence to the fuselage, the bottom surface of the lower wing being flush with the bottom of the fuselage, and that the spars are so situated in the section that front and rear spars are alike. The result is that all the interplane struts are identical, and can be used for either front or rear, inner or outer bay. This, of course, not only facilitates construction, but reduces the number of spares. The wing ribs are all alike, as the wings are parallel, and are square-ended. The aspect ratio is high (9-6), which fact should materially assist in enabling the machine to fly at reduced speed with two engines running. In this connection it is of interest to note that the Bleriot 115 has been definitely proved to be capable of flying on any two engines - i.e., two top engines, two bottom engines, or two diagonal engines. How this is accomplished is a little of a puzzle, as the centre of thrust would be very high with the two top engines running and the lower ones adding resistance, but the fact remains that the machine does fly with any two, which is certainly a matter for congratulation. Not only will the machine fly level, it will even get off with but two engines running.
The four engines are Hispano-Suizas of 180 h.p., and the mounting of all four is identical, so that, as already stated, any engine will fit in any of the four positions. Thus again the question of spares becomes much simpler, while the mountings are so designed as to allow of changing an engine in a very short time (about 1 hour). All four engines run in the same direction.
From the illustrations it will be seen that the petrol tanks are placed behind the engines, and that the latter are not cowled-in at all. This arrangement has been chosen as tending to reduce fire risk, and from an aerodynamic point of view it is quite possible that the exposed engine with but a small radiator offers no more resistance than would the cowled-in engine with a larger radiator. We are not altogether in favour of running the exhaust pipes along the sides of the tanks, although it is possible that the blast of air past the pipes and tanks would effectively prevent the petrol from being ignited. It should be mentioned, in this connection, that the tanks are provided with jettison valves, so that they can be emptied in a few moments, should a fire occur. The Hispano-Suiza engines used are of the low-compression type, and probably do not develop much more than 150 h.p. each. Compressed-air starters are fitted, and it is possible for the pilot to start any engine at any time, whether on the ground or in the air.
The cabin has seating accommodation for eight passengers, in addition to a crew of three (pilot, navigator, and engineer). The passengers' seats are arranged along the sides of the cabin, and entrance is by a trap door in the floor, near the nose of the cabin. By this arrangement passengers can enter and leave the machine, while an emergency exit is provided in the wall of the lavatory aft of the cabin, and for the purpose of inspecting the bracing of the rear portion of the fuselage, the tail skid, control cables, etc., a gangway is provided, running from the after end of the cabin to the stern post. The floor of the cabin is oak ply-wood, waxed and polished, and the cabin walls are painted yellow and blue. A carpet runs along the middle of the floor.
The pilot's seat is placed on top of a large box containing control wires, starting sets, etc., and the pilot and engineer sit with their heads above the roof so as to have a clear view. Two of the passengers occupy seats ahead of the pilot's cockpit, and look out through "bay windows" in the nose of the fuselage. Steps are provided so that it is possible for the mechanic to climb out to any one of the engines even during flight, although this would require considerable acrobatic skill. A luggage compartment is placed aft of the toilet, and luggage is loaded and unloaded through a separate door, and it does not have to be passed through the cabin at all.
Following are the main characteristics of the Bleriot 115: Length, o.a., 13-8 m. (45 ft. 3 ins.); span, 25 m. (82 ft.); chord, 2-6 m. (8 ft. 6 1/2 ins.); wing area, 126 sq. m. (1,360 sq. ft.); weight empty, 2,750 kgs. (6,050 lbs.); weight of fuel (for 3 1/2 hours), 700 kgs. (1,540 lbs.); useful load, 1,000 kgs. (2,200 lbs.); total loaded weight, 4,450 kgs. (9,790 lbs.); wing loading, 7-2 lbs./sq. ft.; power loading (on 180 h.p/per engine), 13-6 lbs./h.p.; useful load per h.p. (on 180 h.p.), 3 1/4 lbs.; maximum speed near ground, 175 km. (108 m.p.h.); landing speed.