Deep Dive: The 1903 Wright Flyer "A" Engine

05/10/2022

Deep Dive: The 1903 Wright Flyer "A" Engine

05/10/2022

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.


Wright Engine Flyer Launch

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.


Wright Engine Charlie Taylor

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.

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.


Wright Engine "A" Engine Cutaway

This cutaway illustration reveals many internal secrets of the original Wright engine.


The typical means of early connecting rod and crankshaft lubrication was the use of dippers on the ends of each connecting rod to scoop the oil in the crankcase to lubricate the rods and to splash oil the main bearings and pistons. The original “A” engine was damaged when a rogue gust of wind damaged the Flyer on the same historic flight day that also bent the crankshaft. When the engine returned to Dayton, the brothers used the original crankcase for an upgraded “B” engine and it is likely at that point that pressurized lubrication was added.


The Wrights did not extend lubrication to the valvetrain and it is assumed that the exhaust valve componentry received manual oiling from an oil can before each engine startup. Many aircraft and automotive engines of this era used what is called a total loss oiling system where the exposed valvetrain was splash oiled with excess allowed to leak off the engine. This is why most early pilots who sat directly behind the engine were always covered in a light sheen of engine oil. European aircraft engines used castor bean oil while domestic-built engines relied on a petroleum-based oils that were merely categorized as light, medium, or heavy viscosity oils.


While the cylinders were water cooled, the combustion chamber area was not. The chambers, positioned atop the cylinders were separate housings containing the 2.00-inch intake and exhaust valves and the spark mechanism. This configuration is referred to as a “T” design since the combustion chambers sat wide on the top of the cylinders, with the two valves on opposite sides resembling the letter “T”. Because these chambers were air-cooled, reports about early Wright engine operation mentioned how the tops of the cylinders glowed from the heat.


Wright Engine raw castings

This is a photo showing raw castings of both the aluminum crankcase as well as the combustion chambers which are the four, T-shaped components. The large cylinder to the left is one cast iron cylinder. The restriction at the top of the cylinder is where the T-shaped chamber would attach. The cylinder bore threaded into the crankcase and then the T-head was also threaded to the cylinder.


Among the many unique features of this engine is that there was no mechanical actuation of the intake valve. Its valve spring was very light and downward piston motion created a vacuum in the cylinder. This significant pressure differential with higher atmospheric pressure on top of the intake valve pushed the intake valve open during the intake stroke. The simple tubular steel camshaft employed only exhaust lobes that were sweated onto the shaft in the proper orientation. The camshaft was located on the opposite (bottom) side of the crankcase located by three babbitt-lined bearing housings. The shaft was driven by a simple bicycle chain and sprocket assembly that was likely sourced from the bicycle shop.


The exhaust lobes were shaped for quick opening and closure with long duration and it soon became apparent that, as engine speeds increased in search of more power, this valvetrain was the cause of many subsequent engine problems. Close inspection will reveal that the exhaust lobes acting directly on the exhaust rocker arms. Later engines enjoyed revisions to the original exhaust lobe shape along with the use of stiffer valve springs as rpm increased.


Wright Engine oiling

Most historians believe lubrication for the original engine was simply provided by scuppers that pulled and splashed oil up from the connecting rods to the bearings and also to the pistons and cylinders.


Robert Bosch had by 1902 already patented what would eventually evolve into the modern spark plug and the Wrights were probably aware of its existence. However, they chose instead a much more complex configuration that Charlie Taylor called a “make-and-break” ignition system. This consisted of spring-loaded contact points set with one located on a fixed pin and the other connected to a movable arm triggered by an eccentric driven by a spur gear on a shaft driven by the camshaft. When a timed spark was required, the cam would push on the linkage and move the arm away from the fixed-point arm, creating an arc fed by an on-board magneto bolted alongside the engine. A lever attached to a sleeve mechanism was used to advance or retard the ignition timing. Generally, timing was retarded during startup and then advanced for more power. This was the same kind of technique used in automobiles at the time with a linkage located on the steering column.


The magneto supplied the spark energy during engine operation and was spun through a friction drive off the flywheel. The magneto wasn’t all that powerful, putting out only 10 volts and 4 amps. To supply voltage for starting, a set of dry cell batteries in a box were used. This battery box was left on the ground after the engine started, again to save weight. The start procedure involved two helpers turning the two propellers. The Wrights realized that torque from two props turning the same direction would make it difficult to turn the aircraft in the opposite direction of the torque, so they merely twisted the chain driving the port side propeller (pilot’s left) to spin that prop in an opposite rotation and thus creating counter-rotating props.


As mentioned previously, the engine was a flat four or laydown orientation that placed the cam, valvetrain, ignition trigger, and the exhaust all in the upper location of the engine. The “A” engine did not employ any kind of exhaust pipe. The spent gases merely exited the head from a series of slots cut into the outer portion of the chamber. The exhaust was unfortunately aimed directly at the pilot, who lay to the left of the engine looking at the Flyer from behind. Because the pilot had to have easy access to the ignition controls, this orientation aimed the exhaust directly at the pilot. Subsequent Wright engine revisions changed this in deference to pilot and passenger comfort.


The fuel system is certainly the simplest of all. Carburetors of the day were large, complex, and unreliable and the Holley brothers had only in that same year begun to build what would eventually evolve into the traditional Holley four-barrel carburetor. But that was literally a half-century in the future.

The Wrights’ solution to creating a combustible fuel mixture was to construct a large tray placed horizontally on top of the four cylinders. The tray allowed gasoline from a small tank that was positioned above the engine to gravity feed fuel to the inlet from an adjustable petcock. The “intake manifold” tray was covered by a thin lid that mounted a short, small-diameter pipe perhaps two inches in diameter that served as the throttle but with no movable butterfly. Thus, engine speed was constant wide-open throttle and rpm was governed by the load of the twin propellers and tuned by ignition timing.


After calculating the combination of weight and aerodynamic drag, the Wrights knew how much power the craft would require to generate sufficient lift. Their calculations demanded a minimum of 8 horsepower with a preference for 10 or more. During this time, there were crude friction engine dynamometers called prony brakes that could measure engine torque and calculate horsepower from that number based on engine speed. The “A” engine was never tested on a dyno. Power calculations were made instead by conservatively estimating cylinder pressure with additional input of displacement and crankshaft rpm. Current data indicates each cylinder produced only around 36 psi indicated mean effective pressure (IMEP).


We performed our own math just to see if the claimed power numbers were accurate. With 36 psi as the IMEP and 675 rpm, horsepower equates to 6.17 hp. The formula also produced 9.1 horsepower at 1,000 rpm, and 11.4 horsepower at 1,250 rpm. These are incredibly low numbers when compared to modern 200ci engines but considering that the internal combustion engine was new technology, the team’s efforts were sufficient to push the aircraft through the air.


As mentioned, the original “A” engine in the Flyer was damaged in freak wind gust that irreparably damaged the Flyer and bent the crankshaft. The Wrights returned the Flyer and engine back to the shop and used parts of the original engine for later four-cylinder versions. Perhaps most impressive of all was the fact that Taylor and the Wright brothers constructed the original engine in only three months’ time.


Subsequent Wright engines quickly evolved into more sophisticated vertical four-cylinder variants and eventually an inline six and even one water-cooled V8 engine that combined a pair of vertical four-cylinder castings to a common crankcase. Eventually Curtiss-Wright engines would mutate into massive, air-cooled radial aircraft engines with twin rows of 9 cylinders displacing 3,350 cubic inches and making over 3,700 horsepower. These were the piston engines that powered fighters and bombers that won WWII for the Allies. These Curtis-Wright behemoths can easily trace their lineage right back to that simple, Charlie Taylor-built four-cylinder engine of 1903.

On machining the billet crankshaft:

I traced the outline on the slab...Then drilled through with the drill press until I could knock out the surplus pieces with a hammer and chisel. Then I put it in the lathe and turned it down to size and smoothness. It weighed 19 pounds and she balanced up perfectly, too.


Charlie Taylor

Early Wright Engines

19031904-051908-111911-15
EngineFlat-4Flat-4Vertical 4Vertical 6
Bore4.004.1254.3754.375
Stroke4.004.004.004.500
Displacement201214240406
Horsepower8.25-1615-2128-4250-75
RPM670-1,2001,070-1,3601,325-1,5001,400-1,560
Weight (Lb.)140-180160-170160-180265-300

Sources

If you would like to read more about the Wright brothers and the Charlie Taylor-built “A” engine, there are multiple resources available on the internet. We’ve listed a few below that we used to research this story.


author

Jeff Smith
37 Posts