The Bleriot XI

If you wanted to study aerodynamics, all you had to do was look at the very early aircraft designs like the Bleriot XI. There are no high bypass ratio turbofans, upper deck lounges, or 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 of these “studies” can be done at Cole Palen’s Old Rhinebeck Aerodrome in Rhinebeck, New York.

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

The Bleriot VII, which formed its initial basis, had appeared with a partially enclosed fuselage to accommodate its single pilot; Wings braced to a tubular Cabane frame above the cockpit; a four-bladed, 50 hp Antoinette engine; a large horizontal stabilizer with two elevators; a small oar; and swiveling, independently sprung wheels. Although it crashed on December 18, 1907, it had nevertheless provided the basis for a later final design.

The fast-following Bleriot VIII had retained the low-wing configuration but was fitted with pivoting wingtip ailerons and tricycle landing gear, each composed of single wheels.

Although the Bleriot IX had been a larger variant of the VIII and the Bleriot X had introduced a triple canard rudder push-prop arrangement, these intermediate steps had done little to the final design and were therefore quickly discarded. This ultimate design had taken the form of the Bleriot XI.

Its long, gradually tapering fuselage, formed of ash longerons, spruce uprights and crossbeams held together by wire ties, had been light yet strong and provided the common attachment point for its aerodynamic surfaces and engine. Covered only half by cloth, it looked primitive and unfinished, but functional.

Cloth-covered, ribbed wings with rounded tips had a span of 28.2 feet and an area of ​​151 square feet, and connected to the fuselage at an angle, offering a substantial V-shape. Their upper surface camber and heavily drooping leading edge were themselves expressions of aerodynamics. Guided closely by their upper surfaces, the airflow sloped down and past their trailing edges, reducing pressure on the upper surface, increasing the speed of the airflow and causing the airfoil to “react” on the principle of lift. Neither high-lift devices such as slats and flaps nor ailerons were included. Instead, lateral control was provided by the wing-deforming method designed by the Wright Brothers, an inverted pylon mounted under the fuselage that provided a wire attachment for warp actuators. By twisting the entire wing differently, they turned it into a giant aileron, increasing its angle of incidence and creating bank during flight.

A 16-square-foot rectangular stabilizer end-mounted under the tapered structure provided deflection for pitch axis control, while a 4.5-square-foot, fully moving rudder, which seemed tiny for the aircraft, provided deflection yaw control provided at the very end of the fuselage.

Replacing the design’s original 30 hp REP powerplant, an air-cooled, 35 hp, three-cylinder, inverted-Y Anzani engine, mounted to an ash front frame, powered a mahogany-colored, Scitmar-shaped, 6th .87 foot long propeller diameter at 1,350 rpm. Due to the inadequate capability of existing engines at the time, the Bleriot XI, like all early designs, had struggled with power-to-weight ratio and its designers were forced to use strong but light wood for structures and fabric for use aerodynamic surfaces.

The smooth, finely ground, intricately shaped propeller itself had been a combination of carving artistry and aerodynamic expression. Essentially a tiny wing rotating perpendicular to the trajectory, it developed thrust in the same way a wing generated lift as the relative wind struck it at its plane of rotation. Because it was set at an angle of attack and had a cambered airfoil, it developed forward lift, redefined here as “thrust”, with the “twist” of the propeller allowing it to maintain the same angle of – attack along of its radius with a high helix angle near the hub but a low one near the rim.

The front ash frame had also provided the attachment point for two of the plane’s three fine-spoked, pivoting, rubber-tired wheels, the regular wraps of which provided adhesion between the tire and rim. The landing gear’s unique pivoting ability, dating back to the Bleriot VII, allowed the aircraft to better operate in crosswind conditions, as the tiny rudder did not provide enough area to counteract these to any significant extent and the assembly otherwise had been too weak to structurally withstand side loads . As a result, it had been able to track the ground at an angle.

The cockpit, which consisted of a wooden frame and rubber fabric on the sides, featured the control system designed by Bleriot, in which a small, circular, non-rotating wheel was mounted on a vertical post resting on a round metal pedestal. Semi-dome “cloche” or “bell” in French to which the two front and rear elevon operating and two side wing twist cables were attached. The surfaces were moved by tilting the stick forward, backward, or to both sides. The “sophistication” of the cockpit was completed with an engine throttle on the right side and two instruments: a compass and a fuel gauge.

A small, barrel-like fuel tank was installed horizontally between the engine and the cockpit.

The Bleriot XI, powered by the 35 hp Anzani engine, had a gross weight of 661 pounds and could reach a speed of 47 miles per hour.

It had only flown a distance of 8,200 feet on its first flight on March 15, 1909 with the earlier REP engine, but this unfavorable start was little indicative of the performance and success of the design as only four months later, on March 25, July, it had made the record-breaking 25-mile first cross-channel flight from Calais, France to Dover, England, and won the Daily Mail’s £1,000 prize for the achievement. The historical event, which attracted worldwide attention, triggered an influx of orders for this type.

The Bleriot XI’s design, low power and minimally effective surfaces determine its operation. The brakeless airplane, for example, can only be steered by its tiny rudder on the ground. Due to the high angle of incidence of the wing, take-off is optimally achieved with a full cloche or throttle advance movement, which lifts the tail into a position parallel to the ground and shifts the entire weight of the aircraft to the main wheels. Depending on the degree, wind-related toe angles can be fully or partially compensated for by rudder deflections , which is reinforced by the swiveling undercarriage. Thus profiled, the aircraft is placed in a flat climb. The camber and area of ​​the wing combined with the ground effect help this temporarily, but it still has abrupt stalling characteristics.

The stair climbing profile, dictated not by air traffic control restrictions but by speed requirements, creates lift at each “plateau”.

Although the full-throttle setting must maintain maximum flow through the engine to meet its “air-cooled” requirements, the slow-moving, frail design is susceptible to gusts of wind, and banks should be flat and gentle. There is not enough power available to counter the 30 degree and greater turns that exponentially increase wing loading and inevitably lead to stalls. Lateral, wing-twisting control is minimal and sluggish.

Full-throttle, nose-down descents are ideally halted by cutting back on the throttle just before the wheels touch the ground. Previous power reductions are unstoppable due to insufficient engine power and a pre-landing flare forces the airframe onto its tailskid.

The Old Rhinebeck Aerodrome Bleriot XI, Hull 56, is the oldest airframe still in service in the United States, surpassed only by the Shuttleworth Collection Bleriot, which is Hull 14.

After crashing during a 1910 dogfight at Sauguss, Massachusetts, Rhinebeck’s specimen was later acquired by Professor HH Caburn, who rode past it daily as he cycled to work, and who kept it until it was presented to Bill Champlin by Laconia, New Hampshire. Donated to Cole Palen in 1952, the engine and aerodynamic surfaces were bare, but its front and rear thirds were otherwise complete. Two years later, in October, newly designed wings, an elevator and a rudder had been installed at Stormville Airport.

Due to the plane’s fragility, it is restricted to “short hops” from Old Rhinebeck’s rolling grass surface during Saturday’s “History of Flight” air shows, as it has only reached a maximum altitude of 60 feet. Nonetheless, this brief leap of an elegantly simple expression of aerodynamics harkens back to the then “long haul” across the English Channel that the original Bleriot XI made a century ago as the world’s first practical monoplane and predecessor thereof, and therefore represents every modern aircraft that routinely connects the globe today.

Thanks to Robert Waldvogel | #Bleriot

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