8/28/2015 Bellcrank - Wikipedia, the free encyclopedia

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Illustration from 1908 Chambers's

Twentieth Century Dictionary. Bell-

crank, n. a rectangular lever in the

form of a crank, used for changing

the direction of bell-wires.

BellcrankFrom Wikipedia, the free encyclopedia

A bellcrank is a type of crank that changes motion through an angle.The angle can be any angle from 0 to 360 degrees, but 90 degrees and180 degrees are most common. The name comes from its first use,changing the vertical pull on a rope to a horizontal pull on the striker of abell, used for calling staff in large houses or commercial establishments.

Contents

1 Angles

2 Mechanical advantage

3 Applications3.1 Aircraft

3.2 Automotive

4 References

5 External links

Angles

A typical 90 degree bellcrank consists of an "L" shaped crank pivoted where the two arms of the L meet. Movingrods (or cables or ropes) are attached to the ends of the L arms. When one is pulled, the L rotates around the pivotpoint, pulling on the other arm. A typical 180 degree bellcrank consists of a straight bar pivoted in the center. Whenone arm is pulled or pushed, the bar rotates around the pivot point, pulling or pushing on the other arm.

Mechanical advantage

Changing the length of the arms changes the mechanical advantage of the system. Many applications do not changethe direction of motion, but instead to amplify a force "in line", which a bellcrank can do in a limited space. There isa tradeoff between range of motion, linearity of motion, and size. The greater the angle traversed by the crank, themore non-linear the motion becomes (the more the motion ratio changes).

Applications

Aircraft

Bellcranks are often used in aircraft control systems to connect the pilot's controls to the control surfaces. Forexample: on light aircraft, the rudder often has a bellcrank whose pivot point is the rudder hinge. A cable connectsthe pilot's rudder pedal to one side of the bellcrank. When the pilot pushes on the rudder pedal, the rudder rotateson its hinge. The opposite rudder pedal is connected to the other end of the bellcrank to rotate the rudder in theopposite direction.

8/28/2015 Bellcrank - Wikipedia, the free encyclopedia

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Automotive

Bellcranks are also seen in automotive applications, as part of the linkage connecting the throttle pedal to thecarburetor, and connecting the brake pedal to the master brake cylinder. In vehicle suspensions, bellcranks areused in pushrod-style suspensions in automobiles or in the Christie suspension in tanks. Vertically-mountedsuspensions may not be feasible in some vehicle designs due to space, aerodynamic, or other design constraints;bellcranks translate the vertical motion of the wheel in to horizontal motion, allowing the suspension to be mountedtransversely or longitudinally within the vehicle.

References

External links

daerospace.com (http://www.daerospace.com/MechanicalSystems/Bellcrank.php).

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This page was last modified on 3 April 2015, at 19:36.

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