Flight, December 1930
The PARIS AERO SHOW
A very imposing exhibit is that of Louis Bleriot, and a sentimental note is lent to this stand by the presence there of the old type XI, with fan-type Anzani engine of 28 h.p., on which M. Bleriot flew
across the Channel in 1909. The old veteran of a machine makes one smile a little pityingly nowadays, and causes one to look back on Bleriot's feat as rather heroic, but the type XI was regarded as quite a thoroughbred in those days. The flat steel tape wing bracing is a reminder that Bleriot was rather ahead of his time, and actually used then what must be regarded as the forerunner of the modern streamline wire.
In some ways, one of the most interesting machines in the exhibition, because of its unusual design, is the Bleriot 125. We are aware that very many visitors to the Grand Palais sneered quite openly at this machine, as, indeed, people are apt to do at anything new or anything which they do not understand, because they have not taken the trouble to understand it. Certainly a superficial inspection does not reveal the ideas which the designers had in mind when they conceived this machine. To appreciate the design (and to judge it without any attempt at appreciation would be unjust, apart from being idle): it is necessary to look deeper. One's first reaction when standing in front of the 125 is to do a rapid mental calculation: Two large fuselages and two engines in tandem, with a cabin for the pilot between them. The drag is likely to be great. And in any case, why two fuselages? The easiest way is to take the line of least resistance and merely to dismiss the whole subject with a shrug of the shoulders and an expression of the opinion that the machine was made unusual solely to attract attention. We, personally, would credit M. Bleriot's designers with more sincerity, and with a modicum of commonsense. After all, the machine must have cost quite a good deal to build, and as it was, presumably, paid for by the Bleriot firm and not by the French Government, it is only reasonable to accept it as a serious attempt to achieve something. That much granted, the next step is to try to discover what it was the designers aimed at. This is not altogether an easy matter. They may have had all manner of things in mind. But some, at least, seem obvious to anyone who attempts to get a little below the surface of things.
It may, perhaps, be recollected that some years ago we published in THE AIRCRAFT ENGINEER (monthly technical Supplement to FLIGHT) an article giving details of wind-tunnel tests made by Gottingen on a model of a twin-fuselage monoplane designed by the American designer, Mr. James V. Martin. According to Gottingen, that machine had a maximum L/D of about 19. This is a figure not approached, let alone achieved, by any modern "normal" aircraft. The Martin design had its two engines in the noses of the fuselages, and the two undercarriages retracted into the fuselages. There was no obstruction in the centre of the wing. It may also, perhaps, be recollected that in his very interesting and instructive paper describing the Fairey long-distance monoplane, Mr. Fairey stated that the undercarriage drag accounted for some 15 per cent, of the total drag. In a machine like the Fairey long-distance monoplane such an item would represent a greatly increased range, and in a normal commercial machine it might come very near making all the difference between commercial and uncommercial aviation. To us it seems that the raison d'etre of the Bleriot 125 may be found by bearing in mind these two machines, the Martin twin-fuselage monoplane, and the harmful effects of an exposed undercarriage. The Fairey was very efficient, but would have been even more without its exposed undercarriage. What further confirms this hypothesis is the fact that Bleriot is showing another commercial machine, a single-engined low-wing monoplane, which is fitted with a retractable undercarriage. Thus, one has definite evidence that the Bleriot designers are alive to the importance of reducing drag. With a twin-fuselage arrangement the undercarriage can either be of fairly normal arrangement, and so placed that but little of the wheels project. This is actually what has been done in the 125, in which the two pairs of tandem wheels are nearly buried inside the fuselage. Or the undercarriage can be designed to project by the usual amount, but capable of being drawn into the fuselage, as was done in the Martin monoplane design. To design a retractable undercarriage for a machine of orthodox lay-out is not easy except by adding a good deal of weight. By having two fuselages it becomes a relatively simple matter.
The Bleriot 125 is an all-wood, cantilever monoplane, with the two fuselages hung directly below the wing, and the two engines, placed in tandem, in the centre of the wing. It is open to argument that this placing of the engines is likely to have harmful effects on the air flow over the wing at a point where the flow is very sensitive to excrescences of any sort. We are in ignorance concerning the actual flow in this machine, and interference effects are so uncertain that it is dangerous to generalise. In the 125 they may have been small or they may have been large. We believe that wind-tunnel tests on a model have been made, but do not know whether or not they were made with the airscrews running. In the absence of data it is impossible to judge whether the drag of the two smaller fuselages and the central engine placing is likely to be greater or smaller than would have been the drag of a single large fuselage with the two engines placed outboard. But that is what the Bleriot designers have set out to determine, and one can only await results of actual flying trials.
As a practical machine one may find points to criticise in the 125. The clearance between the bottoms of the fuselages and the ground seems very small, and on rough ground the fuselages might be liable to suffer damage. Tail wheels projecting farther out of the stern would help matters in this respect. The view out of the cockpit or pilots' cab does not appear to be too good; and the radiator arrangement, in which the single nose radiator serves to cool both engines, might be improved.
The main data relative to the Bleriot 125 are as follows: length, 13-8 m. (45 ft. 3 in.); wing span, 29-4 m. (96 ft. 5 in.); wing area, 100 sq. m. (1,076 sq. ft. ); nominal power, 1,000 h.p.; tare weight, 3,930 kg. (8,640 lb.); gross weight, 6,300 kg. (13,860 lb.). The estimated maximum speed is 205 km./hr. (127 m.p.h.) The two cabins have seating accommodation for 12 passengers (six in each), and the view is good, while the fact that the engines are above and behind the cabins should help to decrease the noise a good deal.