Flight, November 1923
A BRISTOL "JUPITER" MAKES HISTORY IN FRANCE
Over 223 m.p.h. in Gourdou-Leseurre Monoplane
THE radial air-cooled engine has had a hard fight to win recognition. To begin with, the critics said that it was very difficult to get air-cooled
cylinders of large capacity to work satisfactorily. Perhaps it was, but at any rate there is no gainsaying the fact that by now such capacities have been designed, built, and successfully run for long periods. Secondly, while admitting that the short radial air-cooled engine might score on the question of weight and low moment of inertia for fighters, there has been a widespread impression that what was gained in weight was lost in head resistance, owing to the large fuselage necessary for streamlining an engine of such large overall diameter. The performance recently put up in France by the Gourdou-Leseurre monoplane seems to indicate that this criticism also can be met.
As already recorded in FLIGHT, the speed race for the Coupe Beaumont, which was to have been held at Istres, near Marseilles, was abandoned this year, the reason being that one of the French entrants was not allowed to fly in the race, and the second, the Gourdou-Leseurre monoplane, very sportingly being withdrawn rather than letting it cover the course and thus win the race whatever the speed attained. No foreign entries had been received. With the machine already at Istres, the opportunity was, however, taken to try it out over the Beaumont circuit of 50 km. (31 miles). The astonishing speed of 360 km. (223-7 m.p.h.) was attained, which is probably a record for this distance and over a circular course. It will be remembered that the usual world's records are flown over a straight-line course, two laps in each direction, where consequently the speeds attained are considerably greater than over a circular course.
The Gourdou-Leseurre monoplane was designed as a single-seater fighter, and is built of metal throughout, mainly Duralumin, with fittings and highly-stressed parts of steel. The machine is of very clean design, as the accompanying photographs will show, and possesses several interesting features. The Bristol "Jupiter" engine with which it is fitted has been very carefully streamlined, not only with a crank-case cowling and a spinner over the propeller boss, but also as regards the cylinders themselves. These, it will be seen, have been provided with aluminium jackets of streamline section totally enclosing the cylinders. The jacket of each cylinder extends over the cylinder head, and the only openings are a narrow slot down the front, and a small outlet at the back, near the top of the jacket, and of course the holes for the short exhaust pipes. This arrangement has been chosen in preference to a very large fuselage, and the greater proportion of cylinder projecting has been more than made up for by streamlining each in the manner described. Thus the fuselage itself is not much larger than necessary to make it meet the circumference of the crank-case. The speeds attained seem to show that, contrary to general opinion, it is better, aerodynamically, to have a narrow body with nearly the whole of the streamlined cylinders projecting than to have a large body with the cylinder heads only, but un-streamlined, projecting. As far as can be ascertained no trouble with overheating was experienced.
Another unusual feature of the Gourdou-Leseurre monoplane is the retractable undercarriage. Each wheel is mounted on a fork enclosed in a streamline casing, and when the machine is in the air these forks are swung back in such a manner that they drop into a recess in the sides of the fuselage.
The principle upon which the retractable undercarriage gear works is very simple, and seems to have worked well in practice. Each of the wheel forks is carried on a pair of Vee struts, of which the front ones are hinged to the lower longeron of the fuselage. The rear struts are secured at their upper end to a guide in the recess in the side of the fuselage. A quadrant is mounted on and moves with the Vees of the undercarriage, and extends from the top of the rear strut, across the Vee, and projects slightly forward of the front strut, about two-thirds of its length down from the upper end. Engaging with the quadrant is a worm, operated from the pilot's seat. When this worm is rotated it raises the quadrant, and with it the wheel. The lower ends of the wheel forks work in slots in the Vee struts, and the upper end has a cross member resting against rubber cord shock absorbers carried on spools mounted on the front Vees and between fore and aft members across the Vee respectively. The travel obtained is not very great, but the tests carried out so far appear to have been entirely satisfactory. It might be argued that an undercarriage of this type will not be very strong under side loads. While that is probably true, it should be remembered that if a machine with such high landing speed lands with even a small amount of drift, it will probably turn over anyway, and no amount of undercarriage strength against lateral loads will prevent this. That the retractable chassis on the Gourdou-Leseurre does add materially to the speed is not to be doubted.
The original, or normal, machine has a wing area of 20 sq. m., and the speed attained with this wing was 300 km. (186-5 m.p.h.). It is estimated that the ceiling, with the service wing fitted, will be more than 9,000 m. (29,600 ft.), so that the Gourdou-Leseurre monoplane should, in addition to its role as a racer, be a very useful type for service purposes as a single-seater fighter. The view obtained is excellent, the machine guns can easily be installed, and, finally, the radial "Jupiter" engine gives a low longitudinal moment of inertia, so that the machine should be very manoeuvrable.
As rigged for the Coupe Beaumont the Gourdou-Leseurre monoplane had an overall length of 7 -2 m. (23 ft. 7 ins.) and a span of 7 -8 m. (25 ft. 7 ins.). The wing area of the racing machine was only 12 sq. m. (130 sq. ft.), and the maximum speed must be in the neighbourhood of 240 m.p.h.
The weight of the machine is given as 935 kgs. (2,060 lbs.), composed as follows: Engine installation, 345 kgs. (760 lbs.); pilot and instruments, 100 kgs. (220 lbs.); fuel, 160 kgs. (350 lbs.); machine, 330 kgs. (725 lbs.). The wing loading is 15 -86 lbs./sq. ft., and the power loading (on 450 h.p.) 4-58 lbs./h.p.
It might be mentioned that the engine speed was 1,650 r.p.m., which, on this particular engine, No. 855, was equal to a power of 450 b.h.p. This engine gave 490 h.p. at 1,875 r.p.m., so that when it has been thoroughly tuned and fitted with a suitable propeller to allow of its being run up to its full power a considerably improved performance should be obtained.