The Airplane - Jay Spenser [100]
In 1928 he filed patents for a hydraulically actuated propeller. He also left government service for a position with private industry because it alone had the resources and expertise needed to develop, perfect, and market the advanced propeller he envisioned. Caldwell selected the Standard Steel Propeller Company of Pittsburgh, Pennsylvania, which had built the propeller for the Spirit of St. Louis. However, he could just as easily have selected its U.S. competitor, Hamilton Aero Manufacturing of Milwaukee, Wisconsin, which was then the world’s leading propeller producer.
Ironically, the next year Fred Rentschler of Pratt & Whitney and Bill Boeing in Seattle collaborated to create the United Aircraft & Transport Corporation, America’s largest aviation holding company. During this industry consolidation, UA&TC (today United Technologies) acquired Standard Steel Propeller and merged it with Hamilton Aero Manufacturing, which it already owned, to create Hamilton Standard of East Hartford, Connecticut.
The ideas that Frank Caldwell brought to Hamilton Standard (today Hamilton Sundstrand) would make it famous around the world. Caldwell’s ultimate goal was to develop a constant-speed propeller that automatically adjusts its blades to any angle for maximum aerodynamic efficiency at any given engine power setting and regime of flight. With a critical need emerging for any workable system, however, Caldwell decided initially to bring out a simpler two-position propeller that could shift between low pitch for takeoffs or landings and high pitch for cruising flight.
Even as the stock market crashed and the Great Depression spread, Caldwell’s team at Hamilton Standard completed the world’s first variable-pitch propeller. This Hamilton Standard two-position propeller reached the market in 1932. Employing counterweights, it worked reliably in service.
United Air Lines had a problem. Proving trials with its new Boeing 247 in 1933 showed unacceptable field performance at Denver and other high-altitude airports on its young transcontinental route system.
The Boeing 247 was initially delivered with two-bladed, fixed-pitch propellers.
Boeing
Here was a golden opportunity for Hamilton Standard to show what its new propellers could do. Caldwell led a team to Cheyenne, a town on Wyoming’s high plains near the Colorado border. At the Cheyenne airport, some 6,000 feet (1,830 meters) above sea level, this team took the fixed-pitch propellers off the 550-hp Wasp engines of a Boeing 247 supplied by United and mounted variable-pitch propellers in their place.
Flight tests showed that the new propellers reduced the Boeing 247’s takeoff distance by 20 percent, increased its rate of climb by 22 percent, and allowed a more fuel-efficient cruise. Based on these dramatic results, United immediately placed a fleetwide order for the new propellers. So did Douglas for its new DC-2.
A key piece of propulsion technology had been added, but Caldwell was not through revolutionizing aviation. In 1935, Hamilton Standard brought out Caldwell’s constant-speed propeller. Compared to the variable-pitch units, which offered the equivalent of a single gear shift in the sky, these new Hydromatic propellers let pilots select whatever rpm yielded optimal aerodynamic performance. The automatic governors of these constant-speed units uniformly increased or decreased blade angle to maintain this selected rpm.
In 1938, Caldwell added feathering to the Hydromatic propeller’s features. If one of the plane’s engines failed, the extreme aerodynamic drag of its stilled propeller increased fuel consumption and impaired the airplane’s ability to maintain altitude on the remaining engine or engines. Feathering the blades, or turning them edge-on to the slipstream, greatly reduced this drag penalty, facilitating