The OX-5 era

Dennis Parks is Curator Emeritus of Seattle’s Museum of Flight.

After the end of World War I, surplus warplanes were dumped on the market at a fraction of their original cost, leaving manufacturers with little demand for new aircraft. Without a doubt this availability of cheap aircraft hindered the development of new aircraft in the U.S., as surplus aircraft, many still in shipping crates, were sold for as little as a couple of hundred dollars.

In fact, the post-war market looked so good that Curtiss bought back more than 1,600 JN-4 Jennies and 4,608 OX-5 engines. The vast popularity of the war-surplus Jenny led to its being the second most registered aircraft design in the United States before 1940.

However, the corollary to the story is that the stocks of war surplus Curtiss OX-5 engines powered the growth in general aviation for a decade. The V-8, 90-hp OX-5 was the first mass-produced aircraft engine in the United States.

When Jennies began to fall apart in the late 1920s, a new generation of aircraft were specifically designed to take advantage of the huge supply of nearly free, brand new engines. Dozens of designs, including Swallows, Travel Airs, Wacos, Curtiss Robins, and many others, would never have happened so easily if the engines hadn’t been so readily available at the beginning.

The OX-5 engine powered an amazing amount of aircraft into the U.S. market. Of all of the aircraft produced in 1927, 69% mounted OX-5s. U.S. aircraft registrations for 1929 showed 58% OX-5 powered. And of all the aircraft registered before 1940, 18% had OX-5s.


In 1927 the Swallow Airplane Manufacturing Co. of Wichita published an ad claiming to be the “oldest manufacturer of commercial airplanes in America.” This could be true, as from 1924 through 1929 the company was one of the country’s leading builders of general aviation airplanes. Swallow was, in fact, the pioneer builder of the post-World War I generation of private aircraft and introduced many new features that soon became industry standards.

Swallow had its beginning when E. M. “Matty” Laird was brought to Wichita from Chicago to produce his aircraft designs there. His post-war model was named the Laird Swallow. It was a good airplane — better than the contemporary Curtiss Jennies and the similar Standards, outperforming them with the same 90-hp Curtiss OX-5 engine.

In 1924 Laird moved back to Chicago and the company was taken over by Jake Mollendick, one of the financial backers, who reformed the business as the Swallow Airplane Manufacturing Co. with Lloyd Stearman as engineer.

The first Swallow airplane, designed by Stearman and advertised as the New Swallow, was introduced in the spring of 1924. Except for the use of the war-surplus OX-5 engine and a wood-and-wire fuselage, this was an entirely new airplane from nose to tail. The OX-5 engine was enclosed in a neat cowling that was to become virtually standard for all subsequent designs using this powerplant. The use of only one bay of wing struts in place of two, as on the Jenny and the Laird Swallow, coupled with the neat nose design, gave the New Swallow a very new look.

Most important, however, was the fact that the timing of the new model was right — the war surplus models were beginning to wear out by 1924, and the greater cost of a new production model was not the sales handicap that it had been. The Swallow airplane became the first really successful commercial aircraft built in America, with nearly 600 produced.


Another successful manufacturer based in Wichita was the Travel Air Manufacturing Co., formed in the fall of 1924 by a number of former Swallow employees, including Lloyd Stearman, Walter Beech and Clyde Cessna.

The Travel Air design took a great step forward with the use of steel tubing instead of wire-braced wood for the fuselage and tail. The refusal of officials at the Swallow Co. to adapt has been given as the reason for the split of Stearman and others from that company.

Another significant advantage of the Travel Air was the provision for the mounting of various powerplants, from the cheap, surplus 90-hp Curtiss OX-5 to the new 200-hp Wright J-4 radial.

The first Travel Air was completed in March 1925. Walter Beech was soon entering the new plane in races and long-distance competitions, earning prize money and praise for the design. By the middle of 1925 Travel Air had 15 orders. Eventually, more than 800 of the OX-5-powered Model 2000s would be produced. This was a production number for OX-5-powered aircraft only surpassed by the Waco Aircraft Co.


The Waco name was extremely well represented in the U.S. between the wars, with more Wacos produced than any other aircraft.

The company’s roots go back to 1919 when Charles “Buck” Weaver formed the Weaver Aircraft Co. with the company’s aircraft known as Wacos. In 1923 the company was reorganized as the Advanced Aircraft Co. Among the new principals in the company were Clayton Burckner and Sam Junkin, former Curtiss employees.

Initial products were rebuilt and modified Curtiss Jennies. Their first successful design was the Waco 9 OX-5-powered three-seat biplane. It became popular very quickly with 47 produced in 1925. More than 300 of the Model 9s were produced before it was supplanted by the improved Model 10, which was advertised as quicker to takeoff and faster to climb than its predecessor. The Waco 10 would be the most popular of the OX-5 biplanes produced in the United States, with more than 1,000 registered. In fact, Waco was the most successful of the civil aircraft manufacturers prior to 1940. The company’s success was very dependent on the OX-5 engine, with more than one-third of its production powered by them.


Introduced in early 1928, the three-place Curtiss Robin cabin monoplane was an important aircraft in that it bridged the gap between the biplane and monoplane eras in the development of general aviation. It was also the only successful OX-5-powered cabin monoplane.

The Robin was also the first effort by one of the major aircraft manufacturers to bring out a low-cost modern cabin monoplane for private owners. It was, as well, Curtiss’ first significant private aircraft design since the Oriole of 1919.

Most of the private-owner types in production in the Robin’s class at the time of its introduction were open-cockpit biplanes. High-wing, strut-braced monoplanes pointed the way to the future of aviation, but most of the alternatives to the Robin were light transports with higher power radial engines, such as the six-passenger Wright-powered Stinson Detroiter.

In 1928 Curtiss advertised the Robin as “Today’s Biggest Value in Cabin Planes.” Production of the OX-5 Robin continued into 1930 when the supply of engines finally run out, with 41 built. The basic design would continue on with other engines, with more than 700 built.

The new Wright and Pratt-Whitney radial engines were the harbingers of a new era and the end of the OX-5. The last new aircraft to offer the OX-5 was the Parks P-1 in July, 1929.

The OX-5 would hold on a little longer with new Brunner-Winkel Birds still being offered with the engine in 1930.

For a decade, the Curtiss OX-5, last made in 1918, powered a new generation of aircraft.

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