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Monday, September 08 2014 00:00

From Hand Axes to Five-Axis: A Brief History of Hartzell Propeller

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September 2014- At the turn of the 20th century, George Hartzell and his son Robert were making rifle stocks from various hardwoods using a proprietary process they had developed that strengthened the wood and retarded the decay process inherent in hostile environments.


Robert Hartzell owned an airplane and dreamed of becoming a barnstormer—a rather dangerous pursuit back in the day—but at the behest of his mother, he opened an airplane repair business instead.
As his repair business grew, Hartzell noticed that airplane propellers had a rather high failure rate, and after discussing the problem with his friend Orville Wright, he decided to market propellers made from walnut hardwood using the parent company's unique steam processing approach to strengthen and preserve the product.


Hartzell constructed his first propellers from walnut logs using hand axes, and the Hartzell Walnut Propeller Co. was born. (In the 1920s, "Walnut" was dropped.) For prices ranging from $87 to $140, Hartzell supplied propellers for World War I airplanes and established his company as the premier source for durable, reliable propellers.


Hartzell's good reputation has spanned from the Dawn of Aviation through the Golden Age, and is well intact today. Through it all, the slogan "Built on Honor" has identified Hartzell propellers. The phrase is placed on each and every propeller and remains the company's three-word mission.
Hartzell may no longer manufacture wooden or metal fixed pitch propellers, but the factory is still located in the small Ohio town of Piqua—a long stone's throw north of Orville and Wilbur's hometown of Dayton. And although the processes used to manufacturer a propeller today would no doubt confound Robert Hartzell, he would be extremely proud of what his company has become.
Hartzell's vision


J.J. Frigge, Hartzell's executive vice president, says, "Technology is always dynamic and Hartzell is constantly improving the performance of its products." That explains the reason why Hartzell continues to be a prime mover in its business segment.
Led by Bruce Hanke, vice president of engineering; Dennis Zimpfer, director of engineering; and Bob Allenbaugh, vice president of manufacturing, the Hartzell technical team is constantly improving efficiency, updating manufacturing techniques and refining the choice of materials used to make these rather esoteric devices that pull or push an airplane through the air.
Composite propeller technology is a good example. "Carbon fiber props are the fastest growing segment of propeller technology because of the advantages they offer such as weight savings, very high strength and durability, plus performance benefits," Frigge explains.


But it didn't become the fastest growing segment overnight. Thirty-five years ago, Hartzell began development of composite technology and today leads the industry in both innovation and market share.
Over the years, Hartzell confronted and solved the many manufacturing and repair issues unique to composite technology, and combined the advantages of the material with airfoil innovations like the swept-tip Scimitar blade which yields more thrust, acceleration and climb performance.


Quality and safety are the heart of the Hartzell vision. The company's quality system is FAA approved and AS9100C certified, which means there is a Quality Management System used throughout the manufacturing and testing processes. All raw materials and OEM component parts are made in the United States with the utmost of oversight for individual parts.
Plus, there are 30 pilots scattered throughout the workforce in Piqua, so safety and quality are more than just vague company goals. By having active pilots involved in the engineering, manufacturing, testing and management structure, the integrity of Hartzell products becomes personal.


"Our people are passionate about aviation. Safety and quality are the most important components in a Hartzell propeller," said one employee. "I know that sounds like an advertising slogan, but it's true."
Hartzell's vision extends to its aftermarket service, too. With over 20 certified independent service centers worldwide, propellers in need of overhaul, repair or recertification are never far from knowledgeable technicians that can handle all levels of work, including field repair of composite propellers.


A service center audit program, coordinated from headquarters and administered in the field by Hartzell employees, makes certain that service centers are always staffed by trained, competent technical and management personnel. There's even a factory service center located at the plant in Piqua.
A true state-of-the-art manufacturing facility "State-of-the-art" has become such an overworked phrase, it's likely lost meaning for many people. But at its core, the phrase means "the best possible"—and that certainly describes the manufacturing approach used at Hartzell's factory.
Rather than a continuous assembly line (such as the Detroit approach to building cars), Hartzell instead uses a system of discrete manufacturing cells. Each cell has inspection and testing programs as well as procedures that are specific to that cell's function—and every cell is evaluated both individually and within the entire process with respect to efficiency and quality.
The first stop in the process is raw material intake. Blade blanks—forgings obtained from Alcoa Aluminum—are inspected and scheduled for the processes that follow in the other cells. Aluminum and steel forgings that serve as the basis of propeller hubs are also inspected and scheduled here.


Next comes two totally separate cells that handle the milling of the blade blanks. One cell mills the airfoil portion of the blank; the other mills the shank, which is the part of the blank that is captured and retained within the housing where the pitch adjustment hardware resides.
The airfoil milling procedure depends on the type of blade, and ultimately is controlled by the criteria developed by engineering to meet the mission for the propeller. The shank milling depends on whether the blade is intended to mate with aluminum or steel housing and the intended mission for the finished propeller.


Computer-controlled milling is supervised by machine operators. Dimensions are precisely monitored throughout the process and compared to specifications.
While these two cells are milling the blade stock, other cells are milling the hubs and other metal components that will house the blades. Five-axis robots are used to mill, turn in space, position and trim the hubs. And once programmed for the specific propeller hub, the robots could actually be left totally alone to fetch, process and stack the hubs on pallets. (In practice, this isn't done—but the automation is so precise that it could be.) Again, dimensions are precisely monitored throughout the process and compared to specifications.


All of the milling machines, whether computer-controlled machines or robots, have their cast-off scrap metal captured. This is melted and recycled by the suppliers into new forgings. Structural strength of the resultant new forgings is not compromised by recycling.
The next cells use robots to polish the blades and hubs. After polishing, the parts are visually inspected and sent to the nondestructive testing (NDT) cell where 100 percent inspection is accomplished to locate any forging voids or post-milling/polishing cracks to avoid catastrophic failure in the field.
In the NDT cell, fluorescent dye penetrant testing is done on the aluminum parts, and magnetic particle penetrant testing is done on the steel parts.


The dye is removed, and accepted components are moved to the paint unit—an automated facility where special coatings are applied to steel products to prevent corrosion. Protective coatings are applied to all components regardless of material type, and flat black paint is applied to blade face (which is not facing forward, but rather is the back side of the blade). As is the case throughout the process, there's an inspection protocol unique to this cell.
After painting, the next stop is inventory control. There each part that will eventually become part of a finished propeller is placed into inventory, ready to be used in the final assembly process.
The final cell is the assembly area. Here, the individual parts to make a propeller are requisitioned against orders generated by sales, and are either shipped directly to dealers, manufacturers or propeller shops throughout the world, or they are placed into finished goods inventory, ready to be used to fill quick-turnaround orders.


End to end, it takes about four to five hours to make an individual propeller blade, and approximately two days to assemble and test a complete propeller.
Composite propellers have similar completion times; however, due to the unique nature of composite blade manufacture, there are somewhat different cells involved.
For instance, carbon fiber blades have a nickel leading edge attached to control normal erosion. Foreign object damage (FOD) is also mitigated by the attachment of these high strength metal leading edges. Inspection procedures are also different for composite propeller blades, although the procedures used for hubs and internal component parts are very similar to metal propellers.
For composite propellers, about five business days are needed end to end to create and test a completed product.


Hartzell's OEM customers and racing support
Hartzell is the top propeller manufacturer for pilots that compete in the National Championship Air Races in Reno, and it supplies 100 percent of the propellers for the Red Bull racing series contestants.
Hartzell props are also used extensively on turboprop airliners and military trainers, and are standard equipment on the Piper Meridian, Mirage, Matrix and Seminole as well as Warriors and Archers. STCs are available for virtually all currently produced General Aviation aircraft.
Whether the whirling airfoil on a propeller-driven airplane is used for General Aviation, an airliner, or in the military, chances are it first saw the light of day at a plant in southern Ohio—a place that has held special status in the history of aviation for nearly 100 years.


John Loughmiller is a 4,700-hour commercial pilot and CFII MEI-A. He lives in Kentucky with Donna, his wife of 40 years, and often commits random acts of aviation. Send questions or comments to This email address is being protected from spambots. You need JavaScript enabled to view it..

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Last modified on Monday, December 01 2014 23:35

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