The Airplane - Jay Spenser [98]
This relative advantage increased in 1927 when Prestone, the trade name for ethylene glycol, was introduced. With boiling and freezing points respectively much higher and lower than those of water, Prestone allowed for smaller radiators and less coolant, reducing both drag and weight. This advancement allowed the Army’s P-1 Hawk pursuit plane of the mid-1920s, which had a deep-bellied front, to evolve by decade’s end into the svelte P-6E Hawk.
Just when it looked as if liquid-cooled engines would always have the edge, a young American in rural Virginia made a surprising discovery. A native Chicagoan with an engineering degree from the University of Illinois, Fred Weick worked briefly for the U.S. Navy’s Bureau of Aeronautics before accepting a position in 1925 with the National Advisory Committee for Aeronautics.
Established ten years earlier, NACA was fast evolving into the world’s premier aeronautical research entity. Because he had worked in propeller design for the Navy, NACA assigned Weick to its Langley Aeronautical Research Center in Hampton, Virginia (today the NASA Langley Research Center).
Now in his mid-twenties, Weick was asked to help design and build a full-scale wind tunnel for testing actual engines and propellers. When it was finished, he became its chief and conducted tests culminating in his writing a seminal book on propeller design.
In 1927, Weick looked at possible engine cowlings for the air-cooled radial engine, which held a lot of promise if their excessive aerodynamic drag could be mitigated. Since airplanes would soon be going faster and aerodynamic drag increases as the square of the airspeed, this was of great concern to the aeronautical engineering community.
For Weick’s planned tests, a Wright J-5 Whirlwind engine and propeller were mounted in the Propeller Research Tunnel on a support structure resembling the front of an airplane. NACA fabricators also built seven test cowlings requested by Weick for this study. Addressing the spectrum of possibilities, these ranged from a minimal cowling (a narrow-chord band around the cylinder heads akin to the British Townend ring) to a full cowling encasing the engine.
Before evaluating this spectrum, Weick and his team ran baseline tests of the uncowled engine. The wind tunnel’s scales registered 85 pounds (39 kilograms) of drag at an airspeed of 100 mph (160 km/h). This meant that a typical single-engine airplane with an exposed radial expended up to 30 percent of its fuel supply just to overcome engine drag, a patently unacceptable cost for any cooling system. Sobered, the team set to work.
In the late 1920s, Fred Weick tested his full NACA cowling in the full-scale propeller research wind tunnel at Hampton, Virginia.
National Air and Space Museum, Smithsonian Institution
Being methodical, Weick included a full engine cowling of airfoil cross section (it was in effect a circular wing) that would enclose the radial engine. Neither he nor anyone else expected this full cowling to provide acceptable cooling. The wind tunnel evaluation showed that while cylinder head temperatures were indeed somewhat higher, the cowling yielded a 60 percent reduction in drag.
If this full cowling could be made to work, it meant an instant reduction in fuel consumption and a concomitant increase in range and operating economy. It also heralded an end to the speed advantage that made liquid-cooled engines the only choice for fighter plane designers. With this new cowling, equivalent airframes with either a liquid-cooled engine