Flight, December 1923

LIGHT AEROPLANES AS FLYING SCALE MODELS OF LARGE MACHINES
Good Beginning Made in France

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A Case in Point

   A very good example of the manner in which the small flying model of a large machine can be used for collecting certain data is provided by the de Monge twin-engined light monoplane, illustrated in the accompanying drawings and sketches. For the latter we are indebted to our excellent French contemporary L’Aeronautique. This machine represents a large three-engined commercial monoplane now under construction at the works of the French Buscaylet-de Monge firm. At the last Paris Aero Show, it may be remembered, a wind-tunnel scale model was exhibited on the stand of this firm. This model is shown in the accompanying photograph. The machine, known as the de Monge type 72, is to incorporate several unorthodox features, chief of which is, perhaps, the absence of a fuselage. The centre-section of the monoplane wing is very deep and will contain the passenger cabin. The tail is carried on narrow outriggers or tail booms, as the centre-section does not extend aft as far as the tail. Now it will be seen that such a machine represents fairly radical departures from usual practice, and questions of stability, controllability, etc., naturally arise. The distribution of fin areas would appear to be quite different from the more usual, and altogether it would be difficult to say with any degree of certainty whether or not the type might be expected to be successful. The three-engined arrangement is unusual, and the question at once arises whether the machine could fly on any two engines. On a basis of load per h.p. it would be easy enough to estimate the possibility or otherwise of flying on two engines, but the problem is complicated by considerations of the turning moment set up with one engine stopped. A fair amount of information could be obtained by elaborate wind-tunnel experiments, but even so there are certain problems which can be settled much more conveniently by actual flying tests. Consequently, M. de Monge decided to build what is termed a light 'plane, although, in point of fact, it could scarcely be so described, as its total engine power is 70 h.p. Nevertheless, the machine is a fairly low-power type, and shows what could be done with even smaller engines.
   The de Monge 72 will have the following characteristics: Length, o.a., 15-2 metres (49 ft. 10 ins.); span, 32 m. (105 ft.); height, 4 45 m. (13 ft, 7 ins.); wing area, 210 sq. m. (2,260 sq. ft.); engines, three Lorraine-Dietrich of 375 h.p. each; total engine power, 1,125 h.p.; useful load, 3,000 kgs. (6,600 lbs.), equivalent to 30 passengers; total loaded weight 9,000 kgs. (19,800 lbs.); power loading, 17 -6 lbs./h.p.; wing loading, 9-63 lbs./sq. ft. The estimated performance is: Maximum speed, 220 kms. (136-5 m.p.h.); minimum speed, 85 kms. (52-6 m.p.h.); ceiling, 5,000 m. (16,400 ft).

The de Monge Light Monoplane

   The light monoplane built to represent the larger machine is a one-third scale model of the type 72. From the general arrangement drawings it will be seen that it is not quite an exact reproduction, and that certain minor features have been changed. The general proportions, however, are reasonably closely to scale, and the main difference to be observed is in the substitution, in the smaller machine, of two engines for the three with which the large monoplane will be fitted. No doubt this change was dictated by considerations of simplicity. Otherwise there does not appear to be any reason why this feature of the design could not also have been represented in the light monoplane. As already mentioned, the light monoplane is to one-third the scale of the larger machine. Its wing area is, therefore, one-ninth of that of the type 72. As the total loaded weight of the smaller machine is 650 kgs. (1,430 lbs.), the wing loading is only 5-7 lbs./sq. ft. as compared with the 9-63 lbs./sq. ft. of the larger machine. The power loading, assuming the Anzani engines to develop 35 h.p. each, is 20-5 lbs./h.p. instead of 17 -6 lbs./h.p. Thus, to estimate the performance of the type 72 from that attained by the light monoplane certain corrections will have to be applied, but these should not introduce any great uncertainty. At any rate, nowadays it is not usually very difficult to predict with fair accuracy the performance of a machine, and it is in the determination of other features, such as stability and controllability, that the main difficulty lies.
   The accompanying scale drawings show the de Monge light monoplane in general arrangement, while the sketches illustrate some of the constructional features. The machine, like the larger type which it represents, is chiefly remarkable for the absence of a fuselage, the function of this member being performed partly by the deep centre-section of the wing, and partly by two tail booms projecting aft from the outer ends of the centre section. This centre section is of very nearly symmetrical section and fairly deep. Like the two end pieces of the wing, it is built up of two box spars, with spruce flanges and three-ply webs, and of spruce and three-ply ribs. The two end ribs of the centre section are of box section, and extend aft to form the enclosed tail outriggers. The end sections of the wing are bolted to the centre section at this point. While the centre section, or fuselage, is of uniform chord, the end sections show a pronounced taper, both in chord and thickness, and the extreme wing tips are somewhat raked. Ailerons run the whole length of the wing, right \ip to the tail booms, and as their chord is narrow the aspect ratio is high.
   The tail consists of a fixed monoplane tail plane, to which is hinged a divided elevator, and of twin rudders. The latter are placed over the ends of the tail booms, and are thus well separated. A small fixed fin is mounted above the tail plane, midway between the two rudders.
   The arrangement of the two 35 h.p. Y-type Anzani engines is unusual. In order to get the engines as close together as practicable, so as to reproduce as near as possible the conditions obtaining in the larger machine, the airscrews partly overlap one another. This has been done, not, as might be expected, by placing one engine slightly farther forward than the other, but by tilting the axes of the engines laterally. The plan view of the machine will make this point clear. How the fact that the propeller shafts are thus tilted laterally affects their running, if at all, we cannot say. As the angle is not very great, probably no ill effect results. The overlapping of the propeller discs, however, might be expected to cause a certain amount of flutter, or, at any rate, to reduce the efficiency somewhat. We understand, however, that no trouble has been experienced in this respect.
   The pilot and passenger are placed in the middle of the centre section, between the wing spars, and it would seem probable that the view, especially for getting off, cannot be particularly good. For coming in to land, when the tail is well up, probably the view is not bad, although just as the tail is dropped before the machine actually touches the ground it may be expected that but little of the ground in front of the machine can be seen.
   The undercarriage is of wide track, one wheel being placed under each end of the centre section or side of the fuselage. It is believed that an oleo gear is contemplated for the large machine, but in the small monoplane rubber shock-absorbers are employed. The sketch shows the undercarriage, as well as the engine plate.
   The end sections of the wings are not cantilevers, but are supported by two steel tube struts attached at their inner ends to the lower corners of the fuselage, at the points where are secured the legs of the undercarriage.
   The preliminary tests of the de Monge monoplane were carried out at the aerodrome at Orly by the late M. Maneyrol. It is understood that the machine proved very manoeuvrable, and that Maneyrol repeatedly throttled down one engine and was able to fly on the other, the rudder controls being ample to counteract the turning moment due to eccentric thrust.
   The main characteristics of the de Monge light monoplane are as follows: Length, o.a., 5-325 metres (17 ft. 6 ins.); span, 10-7 m. (35 ft. 1 in.); height, 1-65 m. (5 ft. 5 ins.); wing area, 23-33 sq. m. (251 sq. ft.); weight empty, 400 kgs. (880 lbs.); useful load, 250 kgs. (550 lbs.); total loaded weight, 650 kgs. (1,430 lbs.); wing loading, 28 kgs./sq. m. (5-7 lbs./sq. ft.); power loading, 9-2 kgs./h.p. (20-5 lbs./h.p.); power loading with one engine running, 41 lbs./h.p.; speed approximately 145 kms, (90 m.p.h.).