This will most likely result in my being jumped on by everyone that has attended a helicopter POF course.
A common analogy often used in describing lead and lag is the speeding up and slowing down of an ice skater as he/she moves their arms in or out while spinning around. They say as the skater brings his/her arms inward the center of mass is more closely concentrated and the speed of rotation increases and, when the arms are moved outward the center of mass moves outward and the spinning becomes slower.
Once this point is made they include a diagram of a rotor system where the blades are flapping above and below the pure radial position. The point made with this diagram is that the upward flapping blade has its’ mass closer to the center of rotation and as a result increases speed (leads). It is further pointed out that the downward flapping blade has its’ center of mass further from the center of rotation and it slows down (lags). There are inconsistencies in this theory. If you look at the diagram in flapping up the blade mass moves closer to the center of rotation and according to the laws of physics it should speed up. The downward flapping blade moves its’ center of mass also but it is also moving closer to the center of rotation and it too should also speed up. If this is the case, there is only leading and no lagging.
There is another major inconsistency in using this diagram, as it is not the correct diagram to use. This diagram represents a sideward view of the rotor system and it should be not a sideward view but a head on view of the rotor system. In looking at this view it can be assumed that the blade on the left is the advancing blade and the blade on the right is the retreating blade. Since the advancing blade is diving and the retreating blade is climbing it can be seen that both blades are at the same point in relation to the pure radial position and as such the respective masses of the blades are equal. Granted, the advancing blade at one point is higher than the retreating blade but the blades move up and down and are always equally distributed above and below the radial position and therefore the mass distribution is equal. The only conclusion that can be reached assuming I am correct is that there are the laws of conservation of angular momentum but the ice skater should be left out of it.
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The Cat