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ROBERTS 6X AEROPLANE ENGINE
THE ROBERTS Motor Company of Sandusky, Ohio, manufactured advanced aircraft engines in the early part of the last century. Indeed, according to the Smithsonian National Air and Space Museum, more Roberts engines were said to be built in that era than those of Curtiss and Hall-Scott combined.
One engine in particular, a Roberts 6X, earned a place in aviation history when, on January 1, 1914, it powered the first heavier-than-air regularly scheduled passenger flight. These qualifiers, heavier-than-air and regularly scheduled, narrow this event down to the St. Petersburg-to-Tampa flight of a Roberts-powered Benoist Type XIV.
The St. Petersberg Tampa Airboat Line inaugurated its scheduled service across Tampa Bay on January 1, 1914, with this Roberts-powered Benoist XIV; Tony Jannus, its pilot.
Edmund W. Roberts began producing boat engines in the early 1900s, and recognized an emerging business in aircraft. His designs differed from typical boat engines by being engineered as light as possible. This light weight and recognized durability attracted aircraft builders.
This and the following image from Aeroplane (or Flying machine) Scrap Book Number 3 1911-1941,
Artful advertising evidently helped. “Never Fails to Fly,” boasted an ad; “50 sold in 4 months.”
Another ad proclaimed “No More Difficult Feat has Been Accomplished in the History of Aviation.” On March 1, 1912, Tony Jannus (of St. Petersburg-to-Tampa fame) piloted Capt. Bert Berry to 1500 ft. above St. Louis, Missouri, County’s Jefferson Barracks.
There, Berry jumped off the aeroplane in an amazing feat of “parachuting.” Notes the ad, “The captain shot downward for 300 feet when the parachute opened with a jerk that nearly snapped his head off. The remainder of the descent was safely accomplished. Jannus nearly lost control while anxiously watching the parachute, but regaining his mastery of the machine reached the parade ground safely a few minutes after Capt. Berry.”
The Roberts Motor Company, headquartered in a St, Louis suburb, built both four- and six-cylinder versions of its water-cooled engines. Each cylinder was individually cast in ‘Aerolite,” a proprietary alloy claimed to be lighter than aluminum, yet twice as strong. An item in Aeronautics, November 1911, describes this alloy as “having a tensile strength of 38,000 lbs. and a specific gravity of 2.7. The metal is very dense and the bore shows less wear than cast iron and there is no tendency to cut.”
Among its technicalities, each cylinder was fitted with a “decompressor,” a gadget that reduced compression for easier hand starting. This was a common feature with early aeroplane engines.
A Roberts 6X, showing its aluminum jackets for water cooling of individually cast cylinders. Image from oldmachinepress.com.
Roberts engines were two-strokes, not the familiar Otto four-stroke variety. The choice of the two-stroke concept simplified intake and exhaust. What’s more, Roberts devised an intake scheme that minimized the two-stroke tendency to backfire when an incoming mixture ignited prematurely.
Dual exhaust ports for each cylinder led into a shared exhaust pipe for cylinder pairs—the three pipes were unmuffled and directly aft of the Benoist’s pilot and passenger.
Thomas W. Benoist (pronounced “ben-wah”) chose the Roberts 6X for his Type XIV flying boat for its 75 hp, light weight and durability.
In fact, though, the fates of Benoist and Roberts became intertwined tragically. Encountering financial difficulties in the mid-Teens, Benoist moved his company from its original St. Louis location to Chicago and then to Sandusky, where it affiliated with Roberts Motor Company.
On June 14, 1917, Thomas Benoist died after striking his head against a telephone pole while stepping off a streetcar in front of the Roberts works. Within several years, both companies were no more.
In celebrating the 100th anniversary of the St. Petersburg Tampa Airboat Line, aircraft enthusiasts fabricated replicas of the Benoist aeroplane and its Roberts 6X engine.
A test of the recreated Roberts 6X, December 2013.
Other videos accompanying the one listed here show development testing of the engine while fitted to the aircraft. My Internet research failed to turn up anything beyond a less than successful attempted liftoff from the water.
The Roberts 6X’s recreation certainly sounded potent. Maybe a reader can complete this tale of Mamma Never Worries; Papa Uses a Roberts. ds
© Dennis Simanaitis, SimanaitisSays.com, 2017
Simanaitis Says 
Kermit Weeks built the Benoist replica and had a Roberts engine built from scratch. The video of the engine run is: https://www.youtube.com/watch?v=eUN9TYAtVgQ and other videos of the airplane project are on the Fantasy of Flight YouTube site.