The Curtiss 0X-5

In a class by itself


By 1915, and with war contracts as the incentive, Curtiss began building OX-5s by the hundreds, becoming the first massproduced aircraft engine designed by a U.S. company. At first, they used Schebler carburetors and Bosch magnetos (an option that cost a few dollars more than the standard battery-style ignition). When those became scarce due to wartime shortages, they switched to Zenith carburetors and Berling (later Dixie and Scintilla) magnetos. The OX-5’s 8 gph (at 75 percent power) fuel consumption rate was a plus, though the engine’s heavy weight (like other aircraft engines of the era) of almost 400 pounds resulted in a lack of performance, though the OX-5 could generate 105 hp for brief periods if the rpm was bumped up to 1,800.

But old-timers point out that the engine’s exceptional torque characteristics were more than adequate for turning the long, heavy wooden props of those early birds.

Concerns
Cooling leaks were a major concern. The engine vibrated so much that each cylinder gasket or water jacket connection was a potential source of loss of critically needed coolant, usually “Prestone,” but just as often plain water. The large capacity cooling system was not forgiving if much of it was lost. The long manifolds and large oil volume made the OX-5 difficult to start in cold weather. Many pilots living in cold weather regions drained the fluids from the engine after each flight and kept the oil and coolant warm inside, refilling them before the next flight. This made preflight preparations long, in addition to all the lubrication with the oil can.

Even filling the radiator could be tricky. As Curtiss described: “Be sure that the water from the radiator fills the cylinder jackets. Pockets of air may remain in the cylinder jackets even though the radiator may appear full. Turn the engine over a few times by hand after filling the radiator, and then add more water if the radiator will take it. The air pockets, if allowed to remain, may cause overheating and develop serious trouble when the engine is running.”

The OX-5 proved to be a perfect fit for the Standard J1 and JN-4 “Jenny” trainers that the Army needed and in which most American-trained pilots got their first taste of “real flight.” Veteran pilots and barnstormers often said, “If you could handle a Jenny [or Standard, or Canuck] you could handle anything else.” Plenty of civilian airframes used the OX-5 such as the Robin, Travel Air, American Eagle, several Waco models, Pitcairn Fleetwing, and many others. Amelia Earhart and Charles Lindbergh logged many of their early flying hours behind an OX-5 engine. As time went by, aftermarket improvements such as dual ignition, roller bearings, improved lubricants, and better carburetors were available to help in performance and reliability.

“Model T” of aircraft engines
After World War I, the U.S. government had a huge surplus of both training aircraft and spare OX-5 engines. Labeled “obsolete” by the military, they were offered to the public at very affordable prices. A “new-in-the-crate” OX-5 went for as low as $20. They were snatched up by barnstormers, air transport companies, flying schools, and individual enthusiasts, creating a whole generation of “golden age” pilots and mechanics learning their first lessons about aircraft on old Jennies, Standards, and OX-5 engines. Because of its availability, low cost and versatility, some people called it the “Model T of aircraft engines.”

The Curtiss team was never satisfied with any design, so it kept perfecting and modifying the OX-5. The 100-hp OXX models, which were basically OX-5s with a larger 4.25-inch bore, were developed as improvements on the original design. Licensing for construction was granted to companies like Liberty Iron Works, St. Louis Aircraft, Willys-Morrow Corp., Canadian Aero, Fowler, Howell & Lesser, Springfield, and U.S. Aircraft. Advertisements for “high performance aircraft assembled from war surplus stock” were published in many newspapers and virtually every aviation-related magazine.

One company, the Nicholas Beazley Airplane Company of Marshall, MO, had a typical mid-1920s ad boasting a “Standard J-1 Commercial” version with a maximum speed of 85 mph, cruising speed of 75 mph, landing speed of 30 mph, and 12,000-foot ceiling. The price (including complete assembly) with a “used OX-5” was $900. A government overhauled OX-5 was $1,000 and a brand new OX-5 was $1,200. (If the buyer wanted a new, used, or rebuilt OXX6 engine, the price increased by about $200 each.)

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