The classic definition of engineering is: “To utilize the available art and science to accomplish the desired end with a minimum expenditure of time, energy, and material.” That’s the dilemma Orville and Wilbur Wright faced around Christmastime in 1902. They were confident about having licked their airframe/airfoil/control-surface problems in the Wright Flyer, but now needed a lightweight engine to power it. They knew what they wanted — a four-stroke, in-line, four-cylinder, flat engine that could develop about 8 horsepower and weighed less than 180 pounds. Their goal was to keep their test aircraft as close to a “wet” 600 pounds as possible.
But where to find such an engine?
Orville Wright later recalled: “We wrote to a number of automobile and motor builders stating the purpose which we desired a motor and asking whether they could furnish one . . . Most of the companies answered that they were too busy with their regular business to undertake the building of such a motor for us.” So, the Wrights decided to take on the task themselves, with the help of the manager of their bicycle shop, Charles E. Taylor, who was a master “model maker” (as those who crafted “things” from drawings were called back then).
There were no formal blueprints. As Taylor later recalled: “We didn’t make any drawings. One of us would sketch out the part we were talking about on a piece of scrap paper.” Then the sketch was tacked to the wall or workbench as a guide for constructing the pieces in the Wrights’ Dayton, OH, bicycle shop. Changes were many and often, but Taylor’s skills prevailed. Orville Wright later said: “The ability to do this so quickly was largely due to the enthusiastic and efficient services of Mr. C.E. Taylor who did all the machine work in our shop for the first as well as succeeding experimental machines.”
The Wrights and Taylor had carefully calculated what they wanted that would fit their needs. Mounted to the right of the reclining “operator” on the lower wing, the engine’s weight would offset that of the operator. Also, in case of a nose-down crash, having the engine away from the operator lessened the risk of crushing him. They wanted four in-line cylinders, each with a 4-inch bore and pistons with a 4-inch stroke, creating a total displacement of just over 200 cubic inches, generating at least 8 horsepower (12 would be better) and weighing between 150 to 180 pounds. Maintaining a light weight was as important as completing a working engine before spring to allow for testing before the fall trip to Kitty Hawk, NC. Each part, no matter how small, was meticulously weighed and measured after final machining, with a cumulative total weight kept as reference.
Fortunately for the engine builders, Dayton had some of the best foundries in the country, so getting a cast aluminum crankcase was not a problem nor took very long. Cast into the case at the four corners, were “feet” for mounting the engine to the wing. Deciding on a one-piece, four-cylinder casting was rather bold for the day, but that created fewer machining operations and individual parts while also saving time. Taylor devised risers so he could machine the crankcase on the shop’s 14-inch lathe. Historians were skeptical of his ability to do this for many years until Howard DuFour, a retired staff member at Wright State University, not only found the risers in the restored Wright Bicycle Shop at Greenfield Village in Dearborn, MI, but also used them to demonstrate how the crankcase was mounted in the shop’s original lathe on display there.
The alloy was 8 percent copper and 92 percent aluminum, which was a lighter choice over cast iron or bronze as was being used in most automobile engines of the time. While an air-cooled design would have been lighter, many of the most reliable and highest performance automobile engines of the day were water-cooled, so the Wright 1903 engine crankcase was built with a small water jacket.
Crankshaft and cylinders
Main bearing surfaces were babbit plain sleeve type. The crankshaft itself was made from a solid 100-pound block of high carbon or “tool” steel and, even though the Wrights were concerned about engine vibration, the crankshaft contained no counterweights. A heavy cast-iron flywheel would be keyed and shrunk to the crankshaft later to absorb the vibration. “I traced the outline on the slab,” Taylor recalled. “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.”
Cylinders were kept short for ease of cooling and more effective sealing with the water jacket. The piston skirts extended far below the bottom edge of each cylinder during operation. The cylinder barrels were made of cast (also called “grey”) iron and machined as thinly as possible, again to save weight, but also to create more efficient heat transfer to the water jacket. They were threaded into the crankcase at the lower end.
The pistons, also of cast iron, used three rings between the wrist pin and top. They were essentially all compression rings since they wanted oil to move freely throughout the engine for adequate lubrication. The wrist pin was locked in place with a set screw. There is some controversy on whether the original 1903 engine used an oil pump or simply used a “slinger” lubrication system. The connecting rod ends had scuppers to fling the oil from the crankcase sump area throughout the engine. Later Wright engines used a small oil pump, but Charlie Taylor, in later years maintained that the first engine did not use a pump.
Pistons and cylinder walls were not honed to a fine finish because the Wrights figured the explosive charge and forces in each cylinder would “lap” the piston and cylinder surfaces adequately during operation.
The connecting rods were a unique five-piece design. A steel tube was fitted with threaded tool steel adapters at each end. Attached to one end was a bronze casting/bushing that attached to the piston pin while the other end held another bronze casting that attached to the crankshaft. Steel pins held the bronze ends in place to the steel threaded adapters. Each of the four connecting rods had to be carefully measured (with ruled height and surface gauges accurate to 1/64 of an inch by eye) to be precisely the same length to avoid engine vibration.
The valve system, though unique to us today, was not that unusual for automobile engines of the time. The valves were located, opposite each other, in a horizontal tubular chamber that was threaded “T”-style to each cylinder barrel top thus creating the combustion chamber. The intake and exhaust valve heads were identical — each 2 inches in diameter made of cast iron. The valve stems were made of carbon steel and threaded into the heads, then peened over to hold them. The intake valve was the “suction-operated” type which meant it opened upon the downward motion of the piston as suction was created in the cylinder during the intake stroke. A small coil spring helped close the valve upon the piston’s return on the compression stroke. This eliminated several parts that would have been needed in a more complex open/close mechanism such as the exhaust valve used.
For the exhaust valve mechanism, a camshaft, made of hollow mild carbon steel, was mounted in the opposite side of the crankcase from the crankshaft on three babbit-lined bearings, and turned by a sprocket and chain (standard bicycle hardware). Cams were machined separately and sweated onto the camshaft. No pushrods were necessary as the cams pushed directly on the rocker arms. The cams had sharp opening and long duration profiles which the Wrights felt would enhance both quick exhaust of gases and effective scavenging for the incoming air/fuel charge. Efficiency and power adjustments were made by increasing the size and tension of the valve springs. The 1903 engine had an average compression ratio of 4.4 to 1 and mean effective pressure of 36 psi at 870 rpm (31 psi at 1,000 rpm).
While there were spark plug and distributor ignition systems available during the Wrights’ era, they chose to use what was called a “make-and-break” system which basically meant a separate set of contact points located in each cylinder head. Their choice was mainly due to the amount of oil present in each cylinder which quickly fouled most spark plugs. Platinum faces were installed on the spring-loaded ignition points which were governed by a bar stock camshaft mounted half way between the exhaust valve camshaft and the valve “box.” It was run by a spur gear attached to the exhaust valve camshaft. A sleeve mechanism attached to a lever allowed the operator to advance and retard the spark as necessary for starting and different power settings. While the spark was supplied during flight by a magneto mounted next to the operator, dry cell batteries were used for start-up purposes, then removed before flight. Parts could be fashioned from materials available in the bicycle shop or easily procured nearby.
Carburetors available at the time were too heavy and too complex for the Wrights’ weight limits and timetable. So, once again, they made their own. The intake manifold was a sheet steel “box” mounted across the tops of the valve chambers. There was a flat induction chamber at each cylinder opening on the side toward the engine. A sheet steel “can” (some say Taylor used a soup can from his lunch) was attached to the manifold and a fuel line was attached to it, creating a crude carburetor that would introduce the fuel from the wing-mounted, 47-ounce tank, gravity fed through the line to the engine. Incoming fuel actually contacted the wall of the crankcase which also helped in vaporizing the incoming mixture. The system had two valves — one a simple on/off valve and the other providing a more gradual rate of supply in order to maintain a constant air/fuel ratio as fuel in the tank was used up.
Historians and engineers have marveled at the fact that the 1903, and subsequent Wright Flyer engines, not only had no real exhaust piping nor muffling system, but also that the engine was mounted in such a way that the noise and exhaust heat came out practically in the face of the operator lying on the lower wing. The reason for this was that the spark control mechanism and fuel valves were located on that side of the engine within reach of the operator. Changing the position would required more parts (and weight). The Wrights recognized the problem and Wilbur wrote of some work he was doing on a “muffling system” for later designs.
Completion and testing
The little engine was completed by late February 1903, in large part to Taylor’s master machining skills and input in the design features. Unlike the later engines, the 1903 engine was never tested on a prony brake, test-fan system to ascertain brake horsepower. Calculations were made related to engine speed and displacement. Horsepower ratings ranged from 8.25 hp at 670 rpm to 16 hp at 1,200 rpm. There were a few setbacks such as in April when the engine seized as a result of fuel leaking onto the exhaust valve camshaft from the manifold, requiring Taylor to do a complete engine rebuild. Testing went on until June when they determined the final engine design generated 13 hp and weighed 150 pounds. But their work was far from over.
Transferring the engine’s rotary power to the propellers required additional design challenges. Contrary to some speculation, they did not select a chain drive system from the engine to the propellers simply because they were in the bicycle business and had a lot of chain and sprockets available (though that certainly didn’t hurt). At the time many final drive mechanisms, including automobiles, used chain drives, so it wasn’t a stretch to decide on that design. It was a simple design, easy to maintain and service, even though the chain “whip” could create some instability, especially with engine misfires.
On to Kitty Hawk
As with any new design, there were many “bugs” that had to be worked out once the Wright brothers got to North Carolina. Taylor stayed behind in Dayton, as he was manager of the Wrights’ ongoing bicycle business. Thus, he was also available in the shop to rebuild or repair parts for the aircraft. They sent him plenty of work. For example, there was a 10-day delay after the propeller shafts were damaged when the sprockets sheered off. He eventually had to remanufacture the propeller shafts after one of the heavy gauge tubes cracked during testing. He replaced it with smaller solid tool steel material so the replacement shafts could better absorb the engine’s occasional misfiring or pre-ignition explosive forces. Taylor also had to repair the engine’s magneto when it failed to produce a spark, plus advise the brothers about a fuel feed problem.
Their goal was for the engine to run at 875 rpm which would drive the propellers at 305 rpm creating a static thrust of 100 pounds. Their “test equipment” comprised a 50-pound box of sand suspended from a pulley with a rope attached to one end of the machine whose center skids were supported on rollers. After switching the sprocket sizes several times they finally achieved a propeller rpm of 350 which created 135 pounds of static thrust. Testing of the fuel system resulted in an estimated engine running time of 18 minutes. By early December, they were ready for the “test track.”
Their first successful flight occurred on Dec. 14 with Wilbur flying just over 100 feet for 3.5 seconds, before stalling the wing and crashing to the ground. But the damage was minor and the brothers reported: “The machinery all worked in an entirely satisfactory manner, and seems reliable. The power is ample . . . There is now no question of final success.”
On the morning of Dec. 17, 1903, Orville Wright made their historic 12-second flight. They took turns that day with Wilbur piloting the final flight of 852 feet.
The engine was completely disassembled a year later to make detailed drawings which were incorporated into blueprints for the later 1904 and 1905 models and their engineering feats were documented.
DuFour, H. R. and Peter J. Unitt, Charles E. Taylor: The Wright Brothers Mechanician, Prime Digital Printing, Dayton, OH, 2002.
Hobbs, Leonard S., The Wright Brothers’ Engines and Their Design, Smithsonian Institution Press, Washington, D.C., 1971.