Deep Dive: The 1903 Wright Flyer "A" Engine
This is the engine that changed the world. It is deceiving in more ways than one. By all rights, its lack of technology should have dictated it would never make noise...but it did. This flat inline-four cylinder was built by hand by a man with little formal education, working out of the back of a bicycle shop in Dayton, Ohio in 1902. Barely out of the 19th century, the Wright brothers and their erstwhile employee Charlie Taylor designed a four-stroke, horizontal, four-cylinder engine with no carburetor or conventional throttle, no spark plugs, no valvetrain for the intake valve, and with no trace of a fuel or water pump. Despite its primordial start, this 4:1 compression engine made history.
The year is 1902. Henry Ford’s first automotive attempt this same year was powered by a single cylinder engine making 4 hp. He was more than ten years away from revolutionizing ground travel with the Model T. Automobiles were a rich man’s plaything and powered flight was generally considered beyond fantasy. The aeronautical basics of the Wright aircraft, the Flyer, was progressing but the brothers’ specs called for an engine that few automakers were willing to attempt, especially because the Wrights only wanted one engine. No one was interested in helping them.
This historic photograph of the first flight was taken by one of the Wrights’ helpers, John T. Daniels. The launching rail can be seen on the far left. The small shelf in the foreground is a rest for the right wing while the Flyer sat on the launching rail. Among the cluster of equipment on the far right is a shovel and the coil box housing the batteries used to charge the ignition at startup.
Most 8th graders and all aviation buffs know the Wright brothers built the first aircraft to achieve controlled powered flight at Kitty Hawk, North Carolina on December 17th, 1903. But to achieve this, they needed a powerplant that could produce a minimum of 8 and preferably 12 horsepower. It had to weigh around 180 pounds, and be reliable. They met this challenge like all others by building it themselves.
Charles Edward Taylor (May 24, 1868 - January 30, 1956)
Their lone employee at their bicycle shop was also a rather gifted mechanic and machinist by the name of Charlie Taylor. The term used for him was “mechanician” – a play on words combining mechanic and magician. He offered to build the engine. Their shop contained little more than a 14-inch lathe and a drill press in the back room of their bicycle business. These tools were powered by a cast iron, single cylinder, gasoline engine. Pulleys connected by a leather belt transmitted the power to the lathe and the drill press.
The most common metal used for engines during this time was either cast iron or bronze, but those materials proved to be way too heavy. Taylor contacted the Buckeye Iron and Brass Works in Dayton, Ohio to cast the engine’s crankcase from aluminum alloy sourced from the Aluminum Company of America in Pittsburgh, Pennsylvania that would later be renamed Alcoa. Most engines of the early 1900’s were designed with separate air-cooled cylinders attached to a common crankcase. The Wrights perceived that the engine would be more durable if water cooled with integral cylinders. The cooling system was not pressurized and did not circulate. As water around the cylinders turned to steam, it was replaced by water contained in a tank attached to a main wing strut.
The design sketched on a spare sheet of paper called for a four-cylinder engine where the cylinders would lay on their side to lower the engine’s center of gravity. The iron cylinders were kept short to aid with cooling. The actual cylinders were threaded into the crankcase and then the combustion chambers were threaded into the top of the cylinders in a “T” configuration. The engine’s dimensions included a four-inch bore and a four-inch stroke and the cylinder sleeves were kept thin to save weight and help with heat transfer. Displacement computed to 201 cubic inches, a displacement necessary to make sufficient power because operating speed would, as dictated by the technology of the day, be limited to less than 1,500 rpm.
The aluminum crankcase was a very complex casting for its time. Photos reveal five large flanges or bosses that straddle the base of each of the four cylinders that tie the cylinders to the five crankshaft main bearing bosses in the base of the casting. All bearings had to be poured using melted babbitt bearing material that was mainly lead mixed with tin and perhaps other soft metals like copper. Keep in mind this was a custom designed and built engine. There were no off-the-shelf bearing inserts during this time. Each main bearing boss contained a poured babbitt metal bearing with a similar treatment also used for the camshaft mounting bosses. This required the main bearing housing bores to be machined with grooves to retain the babbitt.
A major part of this design was the custom billet crankshaft. Taylor began the process by purchasing a 100-pound block of high-carbon steel. He then used the drill press to cut holes around the billet as excess that he chiseled away. The remainder was then placed in the lathe to whittle into a billet crank. To save weight, the crank did not employ counterweights, relying instead on a heavy flywheel to dampen vibration. The crankshaft looked like a piece of bent tubing, but it was strong. In 2002-‘03, the Hay Manufacturing company in Lake Geneva, Wisconsin built two recreations of the Wright “A” engine to celebrate the 100th anniversary of the brothers’ achievement. Hay claimed it required an entire week on their lathe to whittle the steel crankshaft out of such a large chunk of billet steel.
The connecting rods were another homemade affair starting with a tubular steel center section with the small end consisting of a bronze casting that was threaded onto the tubular center and connected to the piston wrist pin. The big end of the rod was another bronze casting, also threaded onto the tubular center using steel pins with threaded adapters to complete the connection.
Each of these connecting rod assemblies were carefully assembled for length so that each was within 1/64-inch (0.333-inch) to ensure the engine would run smoothly! The rods had to be light because the 4-inch bore cast iron pistons were incredibly heavy with long piston skirts. Later Wright engines retained the use of these iron pistons and very wide rings. The Wright brothers also did not finish hone the cylinder wall, choosing instead to allow cylinder pressure to seat the rings over time thus lapping the bores! This seems horribly crude by today’s standards, but this was typical internal combustion standards in 1902.
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The original Wright "A" engine, with the underneath view on the right. Note how the valves are oriented at right angles to the cylinder centerline. This was a common technique at the turn of the century. Note that the intake valve and spring assembly has no valvetrain connection. High cylinder vacuum during the intake stroke would pull the intake valve open against a light spring pressure. You can also see the “throttle” inlet on top of the engine that looks like a soup can with a copper fuel line entering at the bottom. The wide metal strap across each cylinder is the electrical power connection for the "make-and-break" ignition system. The exhaust camshaft and valvetrain are completely exposed. Also apparent is the small spur gear that turns the shaft above the camshaft that operates the “make-and-break” ignition system.
The connecting rods were another homemade affair starting with a tubular steel center section with the small end consisting of a bronze casting that was threaded onto the tubular center and connected to the piston wrist pin. The big end of the rod was another bronze casting, also threaded onto the tubular center using steel pins with threaded adapters to complete the connection.
Each of these connecting rod assemblies were carefully assembled for length so that each was within 1/64-inch (0.333-inch) to ensure the engine would run smoothly! The rods had to be light because the 4-inch bore cast iron pistons were incredibly heavy with long piston skirts. Later Wright engines retained the use of these iron pistons and very wide rings. The Wright brothers also did not finish hone the cylinder wall, choosing instead to allow cylinder pressure to seat the rings over time thus lapping the bores! This seems horribly crude by today’s standards, but this was typical internal combustion standards in 1902.
There is some confusion among historical accounts regarding whether the original “A” engine used an oil pump for pressurized lubrication. A NASA website description of the “A” describes the use of an oil pump driven off the camshaft that sprayed oil on the piston cylinder walls. This oil then dripped down onto the main webbing to lubricate the main bearings. However, the men who have recreated the “A” engine at the San Diego Museum of Flight in Balboa Park and Taylor’s own description contends it was splash oiled and not fitted with an oil pump.
