On cars, old, new and future; science & technology; vintage airplanes, computer flight simulation of them; Sherlockiana; our English language; travel; and other stuff
THIS PARTICULAR aircraft engine earns being my all-time favorite not because of its power, but through its engineering evolution, its eventual ubiquity—and its wonderfully bizarre valve gear. The engine is Glenn Curtiss’ OX-5.
The OX-5 evolved in logical progression from Glenn’s initial manufacture of motorbikes. His first such effort, in 1902, was powered by a single-cylinder air-cooled powerplant of his own design. V-twins soon followed, including one in 1904 powering Tom Baldwin’s California Arrow, America’s first dirigible.
By 1907, the design had evolved into a V-8, albeit still air-cooled. Glenn earned the world speed record—land, water or air!—in taking his V-8 motorcycle across the sands of Ormond Beach, Florida, at 136.36 mph. This record wasn’t bettered in the air until 1911; no motorcycle went faster until 1930.
The same basic V-8 design got water cooling in 1908. A crossflow head and overhead valves came in 1909. Further development gave the engine its OX-5 nomenclature and a naval aviation contract in 1912.
The OX-5 powered the Curtiss JN biplane trainers, quickly nicknamed “Jennys,” thousands of which were built during and immediately after World War I.
Then came a post-war flying craze largely powered by surplus OX-5s. For example, 38 percent of all aircraft licensed in 1929 had these engines, some of which had sold new in the crate for $20 (figure around $260 in today’s money).
The OX-5 is a 90-degree V-8 displacing 8.2 liters and producing a modest 90 hp. Like many of its era, the engine has individual cylinders of cast iron residing in an aluminum block.
What sets the OX-5 apart, though, is the oddity of its valve actuation. A single camshaft nestling in the vee actuates each exhaust valve conventionally through a pushrod and rocker arm. The pushrod, though, resides concentrically within a pull tube operated by the same camshaft. Each pull tube actuates its intake valve through an A-shaped rocker the base of which shares a pivot point with the lengthy exhaust-valve rocker.
The engine shown above is in a car, not an aircraft. The popularity of OX-5 powerplants encouraged many vintage race car enthusiasts to swap standard power for something rather more exciting.
To get a hint at what sort of excitement an OX-5 can provide, check out the video at www.youtube.com/watch?v=eDd94xowWfs. ds
© Dennis Simanaitis, SimanaitisSays.com, 2012