EXPERIMENT-4OBJECTIVETo verify the Law of Moments by using a Bell Crank Lever. APPARATUSBell crank lever apparatus, slotted weights, spring balance and pointer. THEORY- A bell crank is a type of crank that changes motion through an angle. The name comes from its first use, changing the vertical pull on a rope to a horizontal pull on the striker of a bell, used for calling servants in upper class British households. The fixed point of the lever about which it moves is known as the fulcrum. The bell crank consists of an "L" shaped crank pivoted where the two arms of the L meet. Moving rods (or ropes) are attached to the ends of the L arms. When one is pulled, the L rotates around the pivot point, pulling on the other arm. When the pilot pushes on the rudder pedal. Applications Aircraft Bellcranks are often used in aircraft control systems to connect the pilot's controls to the control surfaces. but instead to amplify a force "in line". the more non-linear the motion becomes (the more the motion ratio changes). the rudder often has a bellcrank whose pivot point is the rudder hinge. and size. According to law of moments When an object is balanced (in equilibrium) the sum of the clockwise moments is equal to the sum of the anticlockwise moments. linearity of motion. For example: on light aircraft. There is a tradeoff between range of motion. the rudder rotates on its hinge. Automotive . which a bell crank can do in a limited space.Changing the length of the arms changes the mechanical advantage of the system. A cable connects the pilot's rudder pedal to one side of the bellcrank. Many applications do not change the direction of motion. The greater the angle traversed by the crank. The opposite rudder pedal is connected to the other end of the bellcrank to rotate the rudder in the opposite direction. and connecting the brake pedal to the master brake cylinder. allowing the suspension to be mounted transversely or longitudinally within the vehicle. or other design constraints. Here in this experiment we have to check the moment of a force about the various point on the lever and that moment must be equal to the spring force multiplied by the fixed distance d. Verticallymounted suspensions may not be feasible in some vehicle designs due to space.Bellcranks are also seen in automotive applications. The distance d in this experiment is fixed and equal to seven inch. So we have to verify Moment. bellcranks are used in pushrodstyle suspensions in automobiles or in the Christie suspension in tanks. M = W * D = s * d Where W = force applied on lever D = varying distance on lever S = spring force . bellcranks translate the vertical motion of the wheel in to horizontal motion. aerodynamic. In vehicle suspensions. as part of the linkage connecting the throttle pedal to the carburetor. 2 3 0.25 1 1.78 mm) PROCEDURE1) 2) 3) 4) 5) 6) Engage the chain of spring balance with the lever.8 2 2 4 8 1 1. adjust the weights to get the readings.5 6 9 1 1. Note down the spring readings. 7) Take at least six readings.75 11 8.28 21.And d = fixed distance (7*2. OBSERVATIONSS. Hang the weight on the end point marked on the lever.17 17.16 14.54=17. Check the pointer to match with the mark made on the lever.5 4 1 7 7 1 1 2 CALCULATIONSDistance from fulcrum (d) = 7 inch Using Moment M = W×D (Kg-inch) Calculated Spring Force (S’) = W D d (N) . Change the position of weight to be hanged on the lever & repeat the above steps.no Weight Distance Moment W kg D inches M=WxD Spring force S(kg) Calculat ed value of S %error (S1S)/S1 S1=WD/ d X 100 1 1. If the pointer does not match. 2. The apparatus should be kept on smooth and leveled surface. The pointer should exactly coincide with the mark on the bell crank lever. 5. . 8.%Error = S ' S 100 S' RESULTFrom the values obtained above. 3. 7. There should minimal disturbance as long as the pointer is concerned. Add weights in the hanger gently. Weights should not touch the table. because eye-judgement for matching the pointer with the mark on the lever will vary from individual to individual. 6. Proper lubrication of the joints of two arms of the lever should be done so as to reduce frictional force. Zero error of spring should be properly noted. it’s clear that the observed and calculated values obtained for the value of spring force are nearly equal and within the permissible experimental error limits. 9. 4. Hence the Law of Moments has been verified PRECAUTIONS1. The optimum starching of spring should be kept in mind. Only one person must take all the readings.