To: heedm
1) Centripetal force (plural centripetal forces) noun
force pulling towards centre: a force that pulls a rotating or spinning object towards a centre or axis
2) Centrifugal force (plural centrifugal forces) noun
force pulling away from centre: an apparent force that seems to pull a rotating or spinning object away from a centre. (Seems?)
3) Centrifugal, from the Latin Centrum (center) and fugere which means "fleeing" literally means moving away from the center and is considered by SCIENTISTS to be a fictional force. It causes no acceleration.
When traveling in a circle, it seems as if we are slung out away from the center. This is not the case. There is no force directed away from the center of the circle and therefore there is acceleration (change speed or direction) in that way.
Hopefully I don’t offend anybody but if you believe items 1 and 3 you have swallowed a lot of pap put out by SCIENTISTS. They can generate all types of formulae to prove their point but if you look at all of the illustrations provided to include the definitions above.
Centripetal force is not a force at all. It would not exist if there were no centrifugal force. Regarding the movement of the ball when it the string breaks all we have to do is look at David when he slew Goliath. His slingshot was rotated in a circle and his hand restrained any outward movement of the rock in the slingshot. It was the mass of the rock that created the centrifugal force and when the slingshot was let go the rock went out in a straight line and not at a tangent. They say that centrifugal force is a fictitious force and should not be considered because it does no work. In those devices that are constructed to employ centrifugal force the release of the spinning object projects it outward and that is the work.
On a rotor system the designers calculate the strength requirements for the rotorhead by calculating the centrifugal loading caused by the spinning blade. They incorporate a safety factor and build the rotorhead and then they test it to see if it meets the requirements. It is the resistance to the centrifugal force that is considered to be centripetal force and the only work it is doing is to keep the blade from flying off. In fact it is not a force at all. It is resisting the real force
1) Centripetal force (plural centripetal forces) noun
force pulling towards centre: a force that pulls a rotating or spinning object towards a centre or axis
In the example above the rotorhead is restraining the blade but it is not pulling the blade towards the center of rotation. The centripetal loading on the head if that is the correct term is the result of the centrifugal loading caused by the mass of the blade.
Once again I must caution that anybody that resorts to college texts to prove a point will have a hard time in any industry having learned about centrifugal and centripetal forces by swinging a ball in a circle. If you get in to the helicopter industry you will have to change your way of thinking. When you get into an engineering slot you will use that companies design handbook as your bible and you can throw your textbooks away.
Here are two examples:
Sikorsky Bluebook says “It can be seen that because centrifugal loading is the predominant force acting upon the blade, it will assume a position closer to horizontal than to vertical. The vertical force (lift) is considerably less than the horizontal force (centrifugal)”. It goes on to provide an example of the lift and centrifugal forces balancing forming the cone angle. It also addresses the centrifugal loading of one blade as being 50,000 pounds.
FAA Rotorcraft Flying Handbook says, “ As vertical takeoff is made, two major forces are acting at the same time. Centrifugal force acting outward and perpendicular to the rotor mast, and lift acting upward and parallel to the mast. The result of these two forces is that the blades assume a conical path instead of remaining in the plane perpendicular to the mast.
Every helicopter company I ever worked for always addressed centrifugal forces and the engineers calculated how strong the rotorhead had to be to react those loads. Maybe some wienie in the dynamics department dealt with centripital forces but he most likely was isolated from the real engineers.
[ 29 November 2001: Message edited by: Lu Zuckerman ]