A.Brew Boulton Paul Aircraft since 1915 (Putnam)
John North became convinced that aircraft structures were better made of metal, both for lightness and strength, and also for durability. Despite the history of Boulton & Paul as woodworking manufacturers, the reason they had been brought into the aircraft business in the first place, he now turned to metal construction as the basis for the whole future of the company.
The logical first step in the move to all-metal construction, after a period of research and experimentation, was to rebuild the P.9 with a metal airframe, but though the P.10 was a two-seat light aircraft of the same layout as the P.9 it was a fundamentally different design.
It was slightly larger than the P.9, and did not resemble it in the slightest. Every part of the airframe structure was made of steel, the only wood used was for the four-blade propeller of 7 ft 6 1/4 in diameter. The engine was a Cosmos Lucifer three-cylinder radial. The Lucifer was a curious engine, being really one third of a nine-cylinder Jupiter, but with only a 6.25 in stroke. With only three cylinders producing 100 hp at 1,700 rpm, every firing stroke was noticeable! The most prominent feature of the Lucifer was the large doughnut-like exhaust collector ring.
Displaying the ingenuity which was to be a feature of most John North aircraft, the engine was fitted to a clever hinged mounting, so that the rear of the engine could be worked on without disturbing any of the control lines. The engine mounting consisted of two long hinge bolts, and by withdrawing one, the engine could be swung on the other to provide access to the magneto and carburettor at its rear. All the piping was arranged so that it did not need any disconnection. The Lucifer was enclosed in a close-fitting conical cowling from which the three cylinders protruded. A 26 gal fuel tank was fitted, which was thought would give the P.10 a duration of 5 hours at 90 mph at 3,000 ft.
The airframe was made entirely of steel treated and varnished to prevent corrosion. Rolled sections of high-tensile steel were formed into tubes, strips and angles for every part of the structure. Rolled steel sections had been extensively tested to destruction so that the full weight/strength advantages of steel over wood could be used. John North maintained that the P.10 was thus lighter and stronger than if it had been built of wood, and far more durable, especially for hot and humid climates. A further advantage of using steel was its consistency compared with wood, much of which had to be thrown away in the construction process because of irregularities of grain.
The unstaggered single-bay wings were of 30 ft span, rather more than the P.9 but with the same 5 ft 6 in chord and 5 ft 6 in gap. The spars were of I section built up of a box of four thin rolled sides. The flanges were corrugated for extra strength and rivetted to the webs, which had lightening holes at intervals, connected by horizontal lengths of tube, which were flanged over the webs to prevent them bending.
Ailerons were fitted to all four wings and connected by cables. The entire wing structure was covered with fabric. The interplane struts were of ordinary streamlined tube connected to the compression struts inside the spars. Further V struts supported the wing centre section on each side of the fuselage, with an additional strut angled forward to the engine bulkhead.
The forward fuselage consisted of four tubular longerons and the rear fuselage was a monocoque of oval formers of channel section placed back to back with double S-section longitudinal stringers. The fuselage covering was probably the most remarkable feature of the P .10, it featured the first ever use of plastic in an aircraft structure. Sheets of Bakelite-Dilecto, a cellulose-formaldehyde based plastic, were rivetted to the metal parts. This material, devised by Boulton & Paul, was claimed to be unaffected by heat and humidity, and both fire and insect proof.
Full dual controls were fitted to the two cockpits, and both had large windscreens. The front cockpit was beneath the leading edge of the upper wing, and the rear cockpit was just behind the trailing edge. With the close cowling of the engine, and its oval shape the fuselage was very streamlined and torpedo-like, the effect being slightly marred by the unstaggered wings. The P.10 was both 2 ft longer and taller than the P.9 at 26 ft and 12 ft respectively.
The fin and horn-balanced rudder were of tear-drop shape, and the tailplane was braced by two struts on each side, connected to the fin. The undercarriage was carried by V-struts of streamlined steel tube with rubber shock absorbers. It was stated that oleo struts would be fitted at a later date.
The P.10 was displayed at the Paris Salon d'Aeronautique of 1919 with the wings, tail and part of the fuselage left uncovered so that the structure could be examined. Representing, as it did, the first practical British aircraft with an all-steel structure, and the first use of plastics in aircraft construction, it caused a sensation. It was described as 'The only real advance in aeronautics on show'. Flight's technical editor reviewed it with the words 'The Boulton & Paul all-metal machine, the P.10, is the machine of the show, from a constructional point of view.'
Strangely the P.10 was not displayed at the Olympia Aero Show of 1920, making the Short Silver Streak the only British metal aircraft on show. It has been said that the P.10 was damaged when the engine failed, which does seem a likely reason for not exhibiting an aircraft which had caused such a sensation at Paris, but there is no record of it ever having flown or even being finished; so how it came to be damaged is not clear.
As the expected boom in civil flying had failed to materialise John North was by then of the opinion that the future for the company lay in seeking military contracts. He regarded the P.10 as an experiment in constructional techniques, and though sales brochures were produced for it, no price was quoted. With so few willing to pay ?700 for a P.9, it was clear that there would be little civil market for an aircraft with all the complications of steel construction.
With no market for it, and no real need to examine its qualities, given that it was an exercise in construction rather than aerodynamics, the P.10 quietly disappeared. I am also sure the AID and Air Ministry would have viewed the use of plastic covering with extreme skepticism - Shorts were making little headway in getting them to accept duralumin in aircraft structures.
The P.10 was not the first British aircraft with an all-metal structure, that honour goes to the Seddon Mayfly of 1910, though the Mayfly had no prospect of flying. It was however the first practical British aircraft with an all-steel structure, and set Boulton & Paul on the road to becoming the leading pioneers in steel aircraft structures. Amazingly the tail, and a wing of the P.10 still survive, in the Bridewell Museum in Norwich. They are the oldest pieces of British metal aircraft structure in existence.
100 hp Cosmos Lucifer.
Span 30 ft; length 26 ft; height 12 ft; wing area 309 sq ft.
Empty weight 1,l04 lb; loaded weight 1,700 lb.
Estimated performance: maximum speed 104 mph at 1,000 ft; climb to 5,000 ft 8 min; service ceiling 14,000 ft; endurance 3 1/2 hr at 100 mph at 3,000 ft, 5 hr at 90 mph at 3,000 ft.
Flight, December 18, 1919.
THE PARIS AERO SHOW 1919
PRELIMINARY REPORT ON BRITISH SECTION
Boulton and Paul, Ltd.
Probably the centre of attraction of v this stand will be formed by the new Boulton and Paul all-metal machine, the P 10, with 100 h.p. "Lucifer" Cosmos engine. This machine is of very original design as regards its construction. The body is built-up of formers and longerons of rolled steel sections, as shown in the accompanying photograph. Between the formers and longitudinals are interposed panels of special fibre sheet, which is riveted to the metal parts. Extensive experiments in the rolling of sheet steel strips into suitable sections have enabled Messrs. Boulton and Paul to provide forms of metal construction which have excellent strength/weight ratios and which approach very close to the ideal rolled metal section - i.e., a section in which the full strength of the material can be developed.
It is not only as regards the fuselage construction that P 10 is built of metal. The wings also are constructed entirely of steel, apart from the fabric covering, of course. The spars are of rolled-steel sections, the results of a number of experiments extending over a considerable period. Dr. Thurston, in his paper read before the Royal Aeronautical Society, mentioned and illustrated one of the Boulton and Paul spar sections, of which these new spars are a development.
The ribs also are made of steel, each part being specially designed to fulfil its own particular function. The mounting of the 100 h.p. Cosmos "Lucifer" engine on the P 10 is of special interest. It is so arranged that by removing the vertical hinge-pin on one side the whole engine and its mounting may be swung about the opposite vertical hinge, thus allowing easy access to the back of the engine for inspection and adjustments. The piping, controls, etc., are so arranged that they do not require disconnecting when the engine is swung out.
This feature of the design is one of the greatest importance from a practical point of view, and one to which other designers would do well to pay attention.