M.Goodall, A.Tagg British Aircraft before the Great War (Schiffer)

Jane's All The World Aircraft 1913

PIGGOTT. Piggott Bros. & Co., Ltd., 220, 222 & 224, Bishopsgate, London, E.C. This well-known firm of shed makers built a novel biplane in May, 1910 (details Flight, May 21st, 1910), and in 1911 a monoplane with enclosed body (Flight, April 1st, 1911). In 1912, both were disposed of, and the firm is not proceeding with its experiments. It has, however, a staff of skilled mechanics and a great deal of floor space for the construction of aeroplanes to specifications.

Журнал Flight

Flight, May 21, 1910

THE PIGGOTT BROS. BIPLANE.

   A NEW British-built biplane, the trials of which are about to take place and should be watched with extreme interest, has been constructed by the well-known constructors, Messrs. Piggott Bros, and Co., Ltd., of Bishopsgate Street, to the designs of their engineer, Mr. S. C. Parr. The machine is in every way uncommon, but to the lay mind its outstanding feature of interest is its great size, for it has a span of no less than 60 ft. and is essentially designed for carrying one or more passengers in addition to the pilot. From the point of view of design, the machine is also exceptionally interesting, because Mr. Parr has embodied a very great deal of what may be described as Lanchester's theory. Those who have studied F. W. Lanchester's works on Aerial Flight will recognise certain characteristics in the general form of the aeroplane surfaces; and in other details, too, it is possible to discuss the design from Lanchester's standpoint. This fact is in itself one that we regard as being very important, and the designer is to be congratulated in having taken the trouble at the commencement to master another man's line of thought and to build up his own experience on that as a basis. We do not wish to imply that the design itself is in any way due to Lanchester, who possibly would disagree with much that is represented.
   From a constructional point of view the machine is full of interesting details, and possibly the outstanding feature is the extensive use of aluminium. As a system the leading features that are likely to attract most attention are the use of two propellers in tandem and the somewhat peculiar method of suspension.
   The accompanying illustrations are somewhat incomplete, having been taken under difficulties while the machine was being dismantled at the factory, but they serve to indicate the more important points. The uncommon character of the design more than justifies the publication of these particulars in advance of any practical performance on the part of the machine itself.
   The machine is, as we have mentioned, a biplane, the decks having a 60 ft. span and a maximum chord of 6 ft. measured on the minor axis of their elliptical plan form. The aspect ratio is thus nominally 10, but the equivalent value of this ratio for an ellipse as compared with a rectangle is unknown. The decks are double surfaced with a special cotton fabric that has been waterproofed and fireproofed by Piggott Bros. The fabric is stretched over built-up ribs shaped to the desired camber, which on the under surface has a maximum value of 3 1/2 ins. situated 2 ft. 3 in. from the leading edge.
   About 6 ft. in front of the main decks is a monoplane elevator, and about 15 ft. behind the decks is a fixed monoplane tail. Both members have an approximate elliptic plan form, their leading and trailing edges being elliptical curves, being drawn to different minor axes. Between the tail and the planes is a monoplane rudder, also similarly shaped. At the extremities of the main planes, between the last pair of vertical struts and midway in the gap, are situated balancing planes for controlling lateral equilibrium.
   The main planes and supplementary surfaces are all supported upon a central framework that is for the most part constructed of aluminium. This framework carries the engine and the pilot's seat. It is supported upon the ground by a pair of pneumatic-shod triple-spoked wire wheels that are carried by a peculiar pivoted arrangement of cantilevers. The resiliency of the suspension is obtained from a set of helical springs introduced between the inner ends of the cantilevers and the frame.
   One of the most uncommon features of the whole design is the propelling mechanism. There are as our illustrations show, two pro pellers in tandem; both are very large but differ in diameter and in pitch. The larger of the two has a diameter of 13 ft 6 ins.; the smaller has a diameter of 8 ft. 4 ins.
   The propellers are driven by chain transmission from the engine through a differential-gear that ensures each propeller taking up its full load. The arrangement of this differential-gear is illustrated by a sectional drawing. The chain wheel, which is driven by the engine, is rigidly bolted to the casing of the mechanism, which carries a toothed annulus. This latter member engages with a set of planet pinions carried by a three-armed spider that is coupled up to the tubular shaft on which the larger of the two propellers is mounted.
   The planet pinions also engage with a central sun wheel mounted direct upon the solid shaft that drives the smaller of the two propellers. It will be observed that neither propeller is directly driven by the chain wheel, and it will further be observed that the tendency of the planet pinions is to rotate the small propeller-shaft in the reverse direction to that in which the three-armed spider would "walk" round the sun if that member were held stationary. That is to say, that the propellers revolve in opposite directions.
   In order that the large propeller may rotate at all, it is necessary that the three-armed spider should "walk" round the sun, which in turn implies that the sun wheel itself is experiencing resistance to movement. Very two propellers. If there is less load on the smaller propeller than on the larger, the smaller propeller will revolve faster than the other, because the three-armed spider will tend to stand still and thereby cause the mechanism to become analogous to a simple reverse gear. If, on the other hand, it is the smaller propeller that experiences the greater resistance, then the sun wheel will tend to stand still so that the three-armed spider will thereupon walk round it at a relatively greater rate. Whatever happens, therefore, the two propellers must essentially balance one another, and consequently a simple observation of their relative speeds in practice, is sufficient to indicate whether they are operating in accordance with the conditions for which they were designed.
   The blades of the propellers have pointed extremities, and are constructed of sheet aluminium; they have a hollow section. Each blade is attached to the boss by a flange, and provision has been made for resetting this flange in order to give a slight variation to the pitch of the blade. The boss proper is enclosed in an ovoid casing so as to improve the stream line form.
   In order to compensate for any springing of the frame a flexible coupling is introduced into the solid propellershaft. This coupling, a sectional sketch of which is shown herewith, consists of a leather annulus riveted to the flanges on adjacent ends of the shaft. The thrust is communicated from one shaft to another through a steel ball abutment. It is also important to observe in connection with the very large propellers that are employed on this machine, that a clutch is necessary for setting them in motion and for this purpose a leather friction clutch similar to that used on motor cars has been introduced between the crank-shaft and chain sprockets.
   In addition to the figures incorporated on the outline drawing, the following data are of interest: power of engine, 70-h.p. at 1,400 r.p.m., 80-h.p. at 1,600 r.p.m.; weight of clutch, 56 lbs.; diameter of clutch over the driving face, 18 ins.; weight of differential gear, 55 lbs.
   The fabric weighs about 2 3/4 oz. per sq. yd. in its natural state and about 3 1/4 oz. per sq. yd. when dressed. The tail plane weighs 16 lbs. and the elevator weighs 12 lbs. The larger propeller is designed to give a flight speed of 48 miles an hour when the slip is 33 per cent, of the pitch velocity. The smaller propeller is designed to receive the slip stream from the large propeller under these conditions, that is to say it is advancing through air at 104 ft. per second when the larger propeller is working under the conditions above mentioned. The coefficient of longitudinal stability of the machine, calculated in accordance with Lanchester's equation, is 2.85.