The Bleriot XI

If you wanted to study aerodynamics, you would only have to look at early aircraft designs, such as the Bleriot XI. There are no high bypass ratio turbofans, no upper deck lounges, no global positioning systems. Instead, the aircraft is a pure expression of the design solutions required to overcome the four forces of flight: lift, weight, thrust, and drag. One such “study” may be conducted at Cole Palen’s Old Rhinebeck Airfield in Rhinebeck, New York.

The culmination of ten previous configurations built by Louis Bleriot, who reinvested 60,000 French francs accumulated during an automobile lamp manufacturing venture to develop a technologically successful aircraft in a career with names like the Wright brothers, Henri Farman, Santos Dumont and Glenn Curtiss. , the Bleriot XI itself had become the world’s first practical monoplane.

The Bleriot VII, which provided its initial basis, appeared with a partially enclosed fuselage to house its sole pilot; wings braced to a tubular cabin frame above the cabin; a 50-hp four-blade Antoinette engine; a wide horizontal tail with two sockets; a small rudder; and swivel wheels with independent suspension. Although it crashed on December 18, 1907, it laid the groundwork for a later definitive design.

The Bleriot VIII, which quickly followed, had retained the low-wing configuration, but featured pivoting ailerons on the wingtips and tricycle landing gear, each made up of individual wheels.

Although the Bleriot IX had been a larger variant of the VIII, and the Bleriot X had introduced a propeller-drive arrangement with triple canard rudders, these intermediate steps had offered little to the final design and were therefore quickly discarded. That latter design had taken the form of the Bleriot XI.

Its long, gradually tapering fuselage, made up of ash spars, spruce struts, and cross members joined by wire trusses, was light but strong, providing the common attachment point for its airfoils and engine. Only half covered by cloth, it looked primitive and unfinished, but functional.

The fabric-covered ribbed wings, with rounded tips, had a wingspan of 28.2 feet and an area of ​​151 square feet and were attached to the fuselage at an angle, offering considerable dihedral. The curvature of the upper surface and the steeply raked leading edge were themselves expressions of aerodynamics. Guided closely by its top surfaces, the airflow angled down and past its trailing edges, reducing top surface pressure, increasing airflow velocity and causing the airfoil to “react” accordingly. the principle of support. High-lift devices such as slats and flaps, not even ailerons, had been included. Instead, lateral control had been provided by the Wright brothers’ designed wing warp method, an inverted tower attached below the fuselage that provided a cable connection for the warp actuators. By differentially rotating the entire wing, they transformed it into a huge aileron, increasing its angle of incidence and inducing roll in flight.

A 16-square-foot rectangular-shaped stabilizer, mounted under the tapered structure toward the end, provided deflection for pitch axis control, while a 4.5-square-foot, seemingly miniscule, full-motion rudder for aircraft, provided yaw control. at the extreme end of the fuselage.

A 35 hp Anzani three-cylinder, air-cooled, inverted-Y engine, which replaced the design’s original 30 hp REP engine and mated to an ash front frame, drove a mahogany, scitmar-shaped, of 6.87 feet. diameter propeller at 1,350 rpm. Due to the then-inadequate power capacity of the existing engines, the Bleriot XI, like all early designs, had struggled with power-to-weight ratios, its designers being forced to use strong but lightweight wood for the frames and fabric for the wings. aerodynamic surfaces.

The smooth, finely sanded, intricately shaped propeller had been a combination of artwork carving and streamlined expression. Essentially, a tiny wing, rotating perpendicular to the flight path, developed thrust in the same way that a wing creates lift, the relative wind hitting it in its plane of rotation. Because it had been set at an angle of attack, and because it had a cambered airfoil, it developed lift in the forward direction, redefined here as “thrust”, the “twist” of the propeller allows it to retain thrust. same angle of inclination. -attacks along its radius with its pitch angle high near its center, but low near its edge.

The ash front frame had also provided the attachment point for two of the aircraft’s three thin-spoke rubber-tired swivel wheels, whose periodic wrappings of tape ensured adhesion between tire and rim. The unique rotating ability of the landing gear, which dates back to the Bleriot VII, allowed the aircraft to operate more adequately during crosswind field conditions, as the tiny rudder had not offered sufficient area to counteract this in a appreciable degree and the whole had been too fragile. to structurally support lateral loads. As a result, he had been able to track the ground at an angle.

The cockpit, made up of a wooden frame and rubberized fabric on its sides, featured the Bleriot-designed control system in which a small circular non-rotating wheel had been mounted on a vertical post that was based on a round metal. Half-dome “cloche”, or “bell” in French, to which the two elevon drive cables fore and aft and two wing warp cables had been attached. The surfaces had been moved by throwing the stick forward, backward, or to either side. The “sophistication” of the cabin had been completed with an engine throttle on the right side and two instruments: a compass and a fuel quantity indicator.

A small barrel-shaped fuel tank had been installed horizontally between the engine and the cabin.

The Bleriot XI, powered by the 35hp Anzani engine, featured a gross weight of 661lbs and could reach speeds of 47mph.

First flown on March 15, 1909, with the earlier REP engine, it had only jumped a distance of 8,200 feet, but this inauspicious start had hardly been indicative of the design’s performance and success, for only four months later, the By July 25, he had made the first record-breaking 25-mile cross-Channel flight from Calais, France, to Dover, England, winning the Daily Mail’s £1,000 prize for the feat. The historic event, which generated worldwide attention, caused an influx of orders for the type.

The design, low power, and minimally effective surfaces of the Bleriot XI dictate its performance. The brakeless plane, for example, can only be directionally controlled by its tiny rudder on the ground. Takeoff, due to the wing’s high angle of incidence, is best achieved with a full cloche advance, or acceleration, which raises the tail to a position parallel to the ground and places the full weight of the aircraft on its main wheels, while wind-induced tracking angles can be partially or fully offset by rudder deflections, depending on their degree, and its rotating landing gear further increases this. Thus profiled, the aircraft is induced into a shallow climb. The camber and area of ​​the wing, along with ground effect, temporarily aid in this, but it still has steep stall characteristics.

The stepped climb profile, dictated not by air traffic control restrictions but by speed requirements, generates lift at each “plateau.”

Although the full throttle setting must retain maximum flow over the motor to meet its “air cooling” requirements, the slow and brittle design is susceptible to wind gusts, and the banks must be shallow and soft. There is not enough power available to counteract turns of 30 degrees or more which exponentially increase wing loading and inevitably lead to stalls. Lateral wing roll control is minimal and slow.

Full power nose down descents are ideally stopped with throttle reductions just before the wheels touch the ground. The above power reductions are, due to insufficient engine power, unstoppable, and pre-landing flaring will force the airframe onto its tailskid.

The Old Rhinebeck Aerodrome Bleriot XI, Build No. 56, is the oldest aircraft fuselage still in flight in the US, dwarfed only by the Shuttleworth Collection Bleriot, Build No. 14 .

Having crashed during a 1910 air meeting in Sauguss, Massachusetts, the Rhinebeck example was subsequently acquired by Professor H.H. Caburn, who had passed it daily while cycling to work and stored it, until handed over to him. to Bill Champlin. of Laconia, New Hampshire. Subsequently donated to Cole Palen in 1952, it lacked an engine and aerodynamic surfaces, but its front and rear thirds were complete. Two years later, in October, newly built wings, a horizontal stabilizer and a rudder were installed at the Stormville airport.

Due to the aircraft’s fragility, it is restricted to “short hops” from Old Rhinebeck’s rolling grass field during Saturday’s “History of Flight” air shows, having only reached a maximum altitude of 60 feet. However, this short hop of an elegantly simple aerodynamic expression has its origins and thus represents the then “long distance” across the English Channel that the original Bleriot XI had made a century ago as the first practical monoplane. of the world and predecessor of all modern aircraft that now routinely connect the world.