The First Aerospace Aluminum Alloy
The Wright Flyer Crankcase
Frank W. Gayle
National Institute of Standards and Technology
President Lettieri called the 2078th meeting to order at 8:22 p.m. on September 12, 1997. The Recording Secretary read the minutes of the 2077th meeting and they were approved.
The speaker for the 2077th meeting was Frank W. Gayle of the National Institute of Standards and Technology. The title of his talk was, “The First Aerospace Aluminum Alloy: The Wright Flyer Crankcase.”
Mr. Gayle stated that aluminum played an essential role in aerospace history from its very inception. For example, the engine crankcase used in the historic first flight of the Wright Flyer in 1903 was an aluminum alloy with 8% copper. Significantly, today's shuttle booster uses essentially the same aluminum alloy with 6.3% copper - also known as Alloy No. 2219.
This use of aluminum did not come about from a well-founded basis of proven designs and materials. The Wrights needed eight horsepower to drive their airplane through the sky and could accommodate only 200 pounds for the engine. They looked in vain for such an engine since available designs using cast iron and bronze were much too heavy. Consequently, Orville and Wilber turned to aluminum as the material of choice for their very special engine. Now the plot thickens.
The engineering and scientific community all knew this crankcase material had some very special properties to withstand the temperatures and pressures of an internal engine and yet be light enough for use in the Wright Flyer. It was also common knowledge that the airplane and the crankcase were damaged when the airplane flipped over by a gust of wind during handling after the forth trial flight on that fateful 17th day of December in 1903. Although the airplane was repaired and flew again, the crankcase disappeared and was not found until 1985 – 80 years later. The National Park Service at Kitty Hawk, North Carolina had it squirreled away and was not aware that anyone was interested in it. Confirmation that this was the (W)right crankcase – no pun – intended came from Wrights' secretary, Ms. Mabel Beck who identified the 1903 crankcase by tool marks, residual thread sealant and fitup with the original cylinder liners.
With the original crankcase missing for so many years, attempts to assess the metallurgy of this wondrous thing were for naught for most of the 20th century. However, once the crankcase was recovered, laboratory tests showed amazing results and provided an early example of an engineering practice predating the scientific theory that explains it.
The recent laboratory examination of the Wright Flyer crankcase showed it was strengthened by nanometer scale copper “precipitates” which formed during the casting process. Remarkably, this precipitation hardening in the Wright Flyer occurred in 1903 — six years before the process was “discovered” in Germany during experiments by Alfred Wilm in 1909. Further, the metal alloy phase diagrams that we all know and love and which describe the alloy casting processes were not invented until 1919 by Paul Merica at our own National Bureau of Standards — opening the golden age of alloys. This makes the metallurgical work of our much maligned “bicycle mechanics” even more wondrous.
Without the Wright's precipitation hardening process for their crankcase, their airplane would never have flown and none of us would have heard of Kitty Hawk. However, because of their creative work, we still retain similar precipitation-hardened alloys as the bases of all high-strength aerospace aluminum alloys used today.
Mr. Gayle pointed out the Wright brothers derring-do with aluminum castings was not the only extraordinary thing they had to accomplish in their quest to build and fly the first real airplane. Prior to their famous 1903 flight, Orville and Wilber had to rework the existing lift and drag tables which were found to be all wrong. New and correct tables had to developed by working with gliders and control designs to get more lift. Similarly, they had to design and build the first wind tunnel to validate their designs without jeopardizing life and limb in full-scale tests. Finally, they had to design the airplane propellers from scratch. This was because it quickly became apparent that an airplane propeller design cannot be adapted from a ship propeller design. The Wrights were clearly some very unique “bicycle mechanics.”
Mr. Gayle then closed his presentation and kindly responded to questions from the audience. President Lettieri thanked Mr. Gayle for the society and announced the next meeting. He then made the usual parking announcement and adjourned the 2078th meeting to the Social Hour at 9:35 p.m.