A review of the back ground history of the Pratt and Whitney round aircraft engine reveals some interesting aspects of the 985 used on many Stearmans.
The engine was not developed by Francis Pratt or Amos Whitney, who have become famous by name, but by Frederick Brant Rentschler who was employed in the engine engineering department at the Wright-Martin Company.
He presented his design to the Wright-Martin Company and they did not feel it would fit in with their product line at that. time. They were working with “in-line”, “V” and a liquid~ cooled engines, and they were really not interested in Rentschler’s engine.
Frederick Rentschler decided his design ideas were far superior to Wrights and that the engine was necessary for new aircraft designs on the drafting board. He resigned from Wright-Martin Co., along with another engineer, George Mead, who should get equal credit for the future production of these engines. They proudly displayed the emblem of a soaring eagle circular inscribed with the words “Dependable Engines.”
Rentschler had an aviation oriented friend, Chance Vought, who knew of the holding company controlling this Pratt & Whitney plant in Hartford, Connecticut. The Pratt and Whitney’s were gunsmiths with the Colt Firearms factory during the Civil War, and then started their own partnership as toolmakers in 1860. When they both passed away, their heirs were left with a some what idled shop and sophisticated equipment. These P & W employees were very highly skilled machinist’s, and an arrangement was made with the heirs to set up, with George Mead as design engineer in charge. This, to produce the parts and assemble an engine, on condition, it would carry the name of Pratt & Whitney, honoring their benefactors.
The production of the first engine was started in the summer of 1925 and it was final assembled on Christmas Eve, of the same year. The first Wasp was hung on the test stand and it developed 400 horse power on it’s initial run-up. They changed carburetor jetting, magneto timing and then the engine developed 410 horse’ power. With more refined adjustments, on the third test run to the unheard of brake HP. of 425. The Navy viewed the engine a few weeks later and placed a order for nine.
These engines were installed on biplanes, with the exception of the first. It was kept as a test bed and is now in the Navy’s Franklin museum. It never was flown, although it was used as the jigging for later biplane fighters. The first P & W engine was the R-1340 and it is also known as the Wasp. Even though the Wasp Jr. is smaller, it was not the first engine designed. The first Wasp’s appears very similar to the present R-985 externally. Both engines are of the square design meaning that the bore equals the stroke. This is a design that was then used in foreign countries and has worked well on low torque engines.
The R-985 has a bore and strike o~ 5.187 inches and the R-1340 is 5.750 inches. The weight of the original R-1340 engine was 645 pounds. When they decided to beef up the R-1340 Wasp engine, the crankshaft size was increased, basic case strength increased, heavier rods, and increasing the original weight to the present, approximately 865 pounds. This was quite a bit more weight, but with this addition in strength there was also a gain of about another 175 horse power, The engines were originally direct drive. Later, a 3:2 reduction drive was added, allowing for a larger propeller and slower prop speed.