The Alden Research Laboratory
Rotating Test Boom
THE IDEA OF CONSTRUCTING a rotating boom for
hydromechanical tests at the Alden Hydraulic Laboratory
originated with Professor Charles Metcalf Allen, head of
the lab from 1896 to 1950. The original boom was designed
in 1908 by Professor Allen, assisted by two Worcester
Polytechnic Institute students.
Professor Allen needed a moving test stand for hydraulic
experiments and for rating current meters. A circular test
apparatus was chosen over a towing tank because the
former: (a) was much less expensive to construct, (b) allowed
longer test runs, and (c) enabled larger objects to be
tested without experiencing boundary effects from channel
sides.
The original boom was constructed of wood on a submerged
rock foundation located about 45 feet from shore
in a pond adjacent to the Alden Hydraulic Laboratory in
Holden, Massachusetts. This boom had a 42-foot testing
arm balanced by a 21-foot arm loaded with counterweights.
Rotational power was supplied by a 24-inch Hercules water
turbine located onshore. The power from the turbine was
transmitted to the boom through a rope and pulley drive
system, producing tip speeds of up to ten feet per second.
In 1911, the original boom was replaced by an equal-arm,
84-foot steel boom. The turbine drive system was replaced
in 1936 by an electric motor located at the center of the
boom, which increased the maximum tip speed to 20 feet
per second. The boom has been used periodically since 1936
without any major changes.
USES OF THE ARL ROTATING TEST BOOM
DURING ITS 74-YEAR EXISTENCE, the rotating test
boom has been utilized in experiments and tests that reflect
the nation's needs and its developing technology.
Some examples are:
Current meter rating 1908 - Present
Aircraft propellers 1911 - 1918
Artillery shell ballistics 1915 - 1925
Ships' logs 1920 - 1950
Pitot tubes 1936 - 1950
Minesweeping paravanes 1940 - 1945
Darrieus water turbines 1981 - Present
The rating of current meters was one of the first functions
of the rotating test boom and has been one of its primary
uses. Due to the facility's ability to conduct long test runs,
accurate calibrations can be made. Through the years these
calibrations have been conducted for both the manufacturers
and the users of current meters.
THE BEGINNINGS OF WHIRLING ARMS
Rotating booms, earlier called "whirling arms, " had been around for more
than 160 years before the boom at the Alden Hydraulic Laboratory was
built. Probably the first one was devised during the 1740s by Benjamin
Robins in England for studying the air resistance of projectile forms. In the
early 1750s, John Smeaton, another Englishman, used one for windmill
tests. In addition, Jean Charles Borda of France tested various shapes in
water throughout the 1760s using a whirling arm.

A significant adaptation of the boom occurred in 1911. The
original boom was replaced by a stronger steel boom which
allowed Professor David Gallup of WPI to use it as a
moving platform for testing aircraft propellers. A 75-horsepower
electric motor, placed at the center of the boom,
transmitted power through a long drive shaft and angle
drive to a propeller mounted at the end of the boom. The
propeller's thrust caused the boom assembly to rotate while
a drag device in the water was used to calculate the power
dissipated. As one of the first non-stationary series of tests
to measure propeller efficiencies, this was an important application
of the boom. Several of the propellers from these
experiments are on permanent display at the Smithsonian
Institution's National Air and Space Museum in
Washington, D. C. as well as at the Alden Research
Laboratory.
During World War I, Major Victor E. Edwards, WPI 1883,
made another use of the rotating boom by conducting drag
tests for artillery shells. The tests proved to be valuable in
his subsequent studies of artillery shell ballistics at the
Aberdeen Proving Grounds in Maryland.
Ships' logs, distance measuring instruments for oceanic
travel, were also developed and calibrated using the boom.
Final production models of ships' logs—the result of prototype
testing on the boom—were used on many ships during
World War II. In addition, the designs for many of the
paravanes used by minesweepers in World War II were a
direct result of model tests which were conducted on the
boom.
In the 1930s, the boom was used by Clyde W. Hubbard during extensive investigations of errors in pitot tube measurements. His work greatly clarified the understanding of the behavior of pitot tubes. As a result of these and other investigations, the pitot tube became an accepted measurement device for fluid flow.
THE EQUIPMENT TESTED on the boom has been representative of the technology and the needs of the nation at different times in its history. The most recent use of the boom, the testing of Darrieus water-turbine designs, and the other examples demonstrate the variety and the importance of the Alden Research Laboratory's rotating test boom applications. After 74 years, the boom is still operational and is available for further imaginative uses to meet national interests and needs.
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Photographs are from the archives of Alden Research Laboratory and Worcester Polytechnic Institute.
Drawings by Mark W. Scott, WPI '83.