PHILIP JARRETT / LONDON CUTAWAY DRAWING: FRANK MUNGER
The 1903 Flyer made only four flights before it was destroyed, but achieved its aims and demonstrated the soundness of its concept
The 1903 Flyer, the first powered aircraft built by Wilbur and Orville Wright, was the culmination of experimental work that began in 1899 and included tests of kites and manned gliders, extensive windtunnel research and much mathematical calculation.
The 1903 Flyer was not simply the 1902 glider fitted with an engine, as has been periodically and erroneously stated; nor was it powered by a modified automobile engine; and neither were its take-offs catapult-assisted. From its inception the 1903 Flyer was designed as a powered aircraft and, except for a few minor off-the-shelf items and subcontracted components, was entirely the work of the Wright brothers, including the powerplant and propellers. Its three-axis control system - the first practical aeroplane control system - had been developed and proven on the preceding gliders.
Similarly, structurally and aerodynamically, the Flyer was based on technology already proven on the gliders, the basic airframe simply being enlarged and strengthened to allow for the added weight of the powerplant. Before construction started, every element of its design was investigated, and the structural loadings of all components were estimated to ascertain their optimum size.
Calculated design
Having estimated the size and weight of the planned machine using data amassed designing their gliders, the Wright brothers were able to determine the Flyer's speed, drag, thrust and power, and design the aircraft to meet the calculated requirements.
The 1903 Flyer's core component was its propulsion system, which comprised a liquid-cooled four-cylinder in-line horizontal petrol engine, driving a pair of large-diameter propellers through chains and shafts. Weighing 64kg (141lb) dry and 81kg with oil, water and accessories, the engine developed 12kW (16hp) at 1,200RPM immediately after starting, then settled at 9kW at 1,020rpm, though it was meant to run for only a few minutes. With a compression ratio of 4.4:1, the Flyer's cast iron cylinders were of 100mm (4in) bore and stroke, had automatic inlet valves, and were contained in a one-piece cast aluminium crankcase that also formed a water jacket around the cylinder barrels. There was no water pump. The engine was cooled by using natural convection to circulate hot water from the jacket into a vertical radiator made from sheet steel, attached to the front interplane strut immediately to the left of the engine.
Cut to rough form from a slab of high-carbon steel, the crankshaft was turned on a lathe by the Wrights' mechanic, Charlie Taylor, who also machined every other engine component in the brothers' bicycle shop. There was no fuel pump or carburettor; petrol was fed by gravity from the 1.5 litre (0.4USgal)-capacity tank attached to a forward interplane strut, just beneath the upper wing. After entering a shallow chamber above the cylinders, where it was mixed with incoming air, fuel was vapourised by the heat from the crankcase and passed into the intake manifold and on to the cylinders. Rather than using spark plugs, the Wrights opted for a low-tension make-and-break ignition system, with the current being provided by a generator driven by a 12kg flywheel. Starting was accomplished using a coil and four dry-cell batteries that were not borne by the aircraft. In its 1903 form, the engine was splash lubricated internally and externally, using liberal applications from an oil can.
The Wright brothers perceived propellers as "simply wings travelling in a spiral course", and using the results of their windtunnel tests of wing sections came up with an according propeller design. This enabled them to make efficient propellers that performed as predicted, and with an unprecedented efficiency. Built up from three laminations of 27.9mm West Virginia white spruce, each 2.6m (8ft 6in)-diameter, 190mm maximum-chord propeller was carved to shape using a hatchet and drawknife.
Propeller positioning
The tips were covered with fabric and then varnished to prevent splitting. To ensure the largest possible volume of air was acted upon, the Wrights elected to have two propellers, which also gave the highest possible pitch angle. Positioning the propellers as pushers behind the wing trailing edges avoided any disturbance of the airflow over these surfaces, and gyroscopic effects were cancelled out by the port propeller's clockwise rotation and the starboard propeller's anticlockwise rotation.
The Wrights knew that large-diameter, slow-turning propellers were more efficient than smaller propellers attached directly to the crankshaft of a high-revving engine, and designed their transmission system accordingly. The engine was bolted on the lower wing, immediately to the right of the pilot. On the driving end of the crankshaft was an eight-sprocket double sprocket-wheel that engaged a pair of 25.4mm-pitch roller chains that were fed through mild steel guide tubes to pass round 23-sprocket wheels at the foremost ends of the long propeller shafts, turning the propellers at 356RPM. The chain to the port propeller shaft was crossed to produce the counter-rotation.
Although the propeller shafts were initially made from steel tubing, vibration caused them to fail, and shafts of solid spring steel were substituted. The propeller shafts were carried in steel tubes braced between the upper and lower mainplanes by diagonal bearer tubes of 19mm steel and two bracing wires.
Each of the wings, which spanned 12.3m and had a chord of 1.98m, giving a total wing area of 47.4m2 (510ft2), consisted of a centre section and port and starboard outer panels. Because the engine was heavier than the pilot and offset slightly to the right, the starboard outer panels were made 100mm longer to give extra lift on that side. The wing panels were built up on front and rear spars of spruce. The front spars, which also formed the wing leading edges, were 516mm2 (1.25in2) in section and rounded on their front faces. The rear spars, positioned about two-thirds of the chord aft, were of 43 x 32mm cross-section. A simple metal band was slipped over the joints.
Wing ribs
The Wright brothers' gliders had solid, steam-bent wing ribs, whereas those of the Flyer were built up from two thin capping strips of second-growth ash separated by small rectangular spruce spacer blocks to which the strips were tacked and glued, the joints being reinforced with glued paper. Pitched at about 300mm (except in the load-bearing region of the lower centre-section, where the somewhat thicker ribs were slightly further apart), the ribs gave the wings their 1 in 20 camber. The bent-wood wingtip bows were manufactured by S.N. Brown, a Dayton firm, for use in folding carriages.
While the gliders had fabric applied only to the top surfaces of their wings, the Flyer's wings were covered both top and bottom with unbleached, tightly woven Pride of the West muslin, left unsealed to save weight. This resulted in a smoother and more efficient lifting surface. The fabric was attached by pre-sewn pockets that slipped over each rib. As with the gliders, the fabric was applied with the direction of the weave on the bias, the strips of fabric being laid at 45° to the spars. The warp and fill of the individual threads, acting in unison, absorbed any tendency of the wings to bend forwards or backwards, imparting stiffness to the frame without hindering its ability to be warped when lateral control was operated. This also eliminated the need for internal bracing, which was another valuable weight saving. A thin wire passed through the mid-point of all but the outermost front vertical struts, secured on both sides of each strut and at the junction of the cross-bracing in the outer bays. By stabilising the struts against lateral deflections under flight loads, the wire effectively halved the length of the struts and thereby increased their buckling load significantly, avoiding the need for broader and heavier struts.
The 1.88m gap between the upper and lower wings, which were rigged with 255mm of anhedral, was maintained by solid spruce interplane struts of rectangular section, with the edges rounded off. The four bays of the centre-section cellule structure were rigidly cross-braced both laterally and fore and aft by steel wire. The spars of the two-bay outer cellules were attached to the spar extremities of the centre-section spars by horizontal hinges, allowing a small amount of vertical movement. While the front struts of these bays were cross-braced, cross-bracing was omitted from the rear struts to allow the structure to move when the warping cables were operated. For the same reason, there was no fore-and-aft cross-bracing in these bays, and the interplane struts were attached to the wings using a flexible eyelet attachment.
Cockpit controls
To reduce drag, the pilot lay prone on the lower centre section, operating the wing warping (and the interconnected rudder) by moving a padded hip cradle from side to side. This pulled on cables running through pulleys to attachment points on the rear spar, thereby imparting a helical twisting or "warping" action to the flexible structure. At the pilot's right hand was a wooden lever that, in a single movement, stopped a stopwatch and tripped the fuel cut-off valve to stop the engine at the end of a flight. This also halted the revolution counter at the base of the engine crankshaft, and the anemometer attached to the forward strut that drove a meter, calibrated in metres, to display the distance travelled.
The stopwatch was mounted below the anemometer. Using the combined distance and duration readings from these simple instruments, the Flyer's average airspeed could later be calculated.
The 3.6m-span biplane canard elevator was mounted on a substantial spruce framework projecting from the upper and lower wings. This framework continued below the wings, where it joined ash skids braced to the underside of the lower wing by vertical and diagonal struts. The complex canard surfaces had spruce leading and trailing edges, and their moment arm was about 2.2m ahead of the wing leading edges. The upper surfaces of the canards were covered in a similar fashion to the wings.
Canard control
The pilot controlled the canard by moving a left-hand lever that operated a set of pulleys linked by sections of wire, which were wrapped in short lengths of sash chain. A torque tube attached to a pulley positioned at mid-gap between the canard surfaces linked three lever arms that served as fulcrums connected to spruce link-struts. Because these lever arms were much shorter ahead of the torque tube, the front links formed a connecting vertex resembling the letter K at the forward end. This arrangement caused the elevator ribs to bend more ahead of the central spars.
The Wrights regarded the canard surfaces as part of the aircraft's total wing area, and they carried a significant proportion of the loads, particularly during the initial stage of flight, when they were operating at a higher than usual angle of attack. But because they were designed to fly at a higher angle of attack than the wings, the canards would stall when headway was lost, causing the nose to drop and decrease the wings' angle of attack.
The twin single-surfaced rectangular vertical rudders, 2.1m high and 460mm deep, were carried on V-shaped booms extending aft from the wings. Their moment arm was 3.5m from the wing leading edge. The rudder control wires were linked to the wing-warping control wires in the same manner as on the 1902 glider so that, when the pilot's hip cradle was shifted, control in the vertical and longitudinal axes was actuated simultaneously. This counteracted the tendency of warp drag to reverse the machine's response to lateral control inputs at the very low speeds at which these aircraft flew, and also prevented incipient tailspin.
It is hardly surprising that, from the handling point of view, the first Flyer left something to be desired. The centre of gravity (CG) was located at about 29% chord, or 580mm aft of the wing leading edge, and its relationship to the canard surfaces and wings gave the aircraft notorious pitch instability. Added to this, the hinge points of the canard elevator were very near its centre of pressure. This exacerbated its sensitivity, as the airflow forced the elevator to deflect sharply of its own accord after the pilot had moved it only slightly from the neutral position, making it easy to over-control and adding to the difficulties of flying an unstable machine. Lateral control was poor owing to the excessive anhedral of the wings and the interconnected wing warping and rudder controls.
Despite these shortcomings, which the Wrights subsequently remedied, the 1903 Flyer did all that was required of it. It was a simple, ingenious first prototype of a powered aeroplane, designed to be capable of brief, sustained powered flights at low speed and altitude to prove all the elements embodied in its construction and demonstrate the soundness of the concept. Although the Flyer made only four flights, and was then blown over and wrecked, the Wrights were not disappointed; it had fulfilled its purpose, and the practical powered aeroplane was less than two years away.
Source: Flight International
