Pendulum-and-hydrostat control is a control mechanism developed originally for depth control of the

Whitehead torpedo The Whitehead torpedo was the first self-propelled or "locomotive" torpedo ever developed. It was perfected in 1866 by Robert Whitehead from a rough design conceived by Giovanni Luppis of the Austro-Hungarian Navy in Fiume. It was driven by a t ...

. It is an early example of what is now known as proportional and derivative control. The hydrostat is a mechanism that senses pressure; the torpedo's depth is proportional to pressure. However, with only a hydrostat controlling the depth fins in a negative feedback loop, the torpedo tends to oscillate around the desired depth rather than settling to the desired depth. The addition of a pendulum allows the torpedo to sense the pitch of the torpedo. The pitch information is combined with the depth information to set the torpedo's depth control fins. The pitch information provides a damping term to the depth control response and suppresses the depth oscillations.

Operation

In control theory the effect of the addition of the pendulum can be explained as turning the simple proportional controller into a proportional-derivative controller since the depth keeping is not controlled by the depth alone anymore but also by the

derivative In mathematics, the derivative of a function of a real variable measures the sensitivity to change of the function value (output value) with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. ...

(rate of change) of the depth which is roughly proportional to the angle of the machine.Bennett, "A History of control engineering: 1800-1930" The relative gain of the proportional and derivative functions could be altered by adjusting the linkages. It was mainly used to control the depth of

torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, s ...

es until the end of the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposi ...

, and it reduced depth errors from ±40 feet (12 meters) to as little as ±6 inches (0.15 m). The pendulum and hydrostat control was invented by

Robert Whitehead Robert Whitehead (3 January 1823 – 14 November 1905) was an English engineer who was most famous for developing the first effective self-propelled naval torpedo. Early life He was born in Bolton, England, the son of James Whitehead, ...

. It was an important advance in torpedo technology, and it was nicknamed "The Secret".

References

External links

* https://archive.today/20120530070555/http://www.btinternet.com/~philipr/torps.htm * {{cite journal , last=Milford , first=Frederick J. , title=U.S. Navy Torpedoes: Part One: Torpedoes through the thirties , date=April 1996 , location=Annandale, VA , journal=Submarine Review , publisher=Naval Submarine League , url=http://www.geocities.com/Pentagon/1592/ustorp1.htm , archiveurl=https://web.archive.org/web/20091023132602/http://geocities.com/Pentagon/1592/ustorp1.htm , url-status=dead , archivedate=2009-10-23 Control devices Mechanisms (engineering) Pendulums Torpedoes