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IT WAS fun celebrating Louis Blériot and his epic flight crossing the English Channel in his Type XI (www.wp.me/p2ETap-M7). Just as they extended the celebration back in 1909, let’s continue it today, only with a look at several of the aeroplane’s technicalities.
The Blériot Type XI was a monoplane, rare for its day, with a particularly interesting landing gear and powered by an engine of odd—yet logical—layout, one that was destined to show up in unexpected places.
Alessandro Anzani began building motorcycle engines around 1905. Originally, these were V-twins, but Anzani soon added another cylinder for increased displacement and power. Termed semi-radials or fan types, these had their cylinders all arranged in the upper half circle rather than spaced evenly.
One benefit of the fan configuration was to reduce the propensity of spark plugs fouled with a pooling of lubricating oil. Another was the fan layout’s fit into a motorcycle frame. A disadvantage was the necessary amount of piston counterbalancing.
The Anzani had individual cast iron cylinders and a crankcase of aluminum. The engine was air-cooled with side valves, each exhaust valve cam-actuated and the intake valves originally of spring-loaded atmospheric sort.
Blériot’s Anzani had its outer cylinders at a 55-degree angle. Milestones of the Air cites a 105-mm bore and 120-mm stroke, which works out to a displacement of 3.1 liters. (Another source suggests a 103-mm bore and 3.0-liter displacement.) The engine produced perhaps 25 hp running at 1400 rpm.
Anzani had factories in his native Italy, France (where he lived) and England. British Anzani, which still exists, supplied engines to the likes of AC Cars, Frazer-Nash and Morgan.
In a curious turnabout, in 1938 when the Dunstable Sailplane Company in England sought a powerplant for its Luton L.A.3 Buzzard, the perfect solution was a secondhand Anzani V-twin from a Morgan trike sports car.
The Blériot’s landing gear, called “starting and alighting gear” in original documentation, is a tail-dragger type. Setting it apart, though, each wheel is on a trailing arm, with both suspending as well as castering function. Main wheel suspension relied on a pair of sturdy elastic bands per side; a coil spring in each vertical column returned the castered wheel to straight ahead.
Castering had the benefit of giving crosswind capability, a helpful feature with this fragile craft weighing only 660 lb. fully loaded.
Blériot chose a single-wing layout for the Type XI based on earlier work with his Type VII, the true ancestor of the modern tractor monoplane. A single wing went against conventional wisdom for structural reasons: A biplane with struts forms a box section that resists twist. A monoplane does not, particularly one like the Type XI which depended upon wing warping for lateral control. (Curiously, the Type VIII had ailerons for this purpose.)
As noted in Blériot XI, modern engineers have identified torsional stress as a problem with several early monoplanes: Wings would simply twist off. What’s more, designs were found to have a torsional divergence that was airspeed-critical. Fortunately, the Type XI’s divergence speed was in excess of 100 mph, more than double the aeroplane’s capability.
It’s no wonder that the Blériot Type XI is considered one of the milestones of the air. ds
© Dennis Simanaitis, SimanaitisSays.com, 2013