Lu ~ Centrifugal Force is alive and well

[Dave_Jackson]

Lu ~ Centrifugal Force is alive and well and living in every rotor blade

` . ` . ~or~
Regurgitating the Centrifugal - Centripetal conflict


A definition in my web site;

Centripetal Force and Centrifugal Effect:
Action-reaction force pair associated with circular motion. Centripetal (center-seeking) force is the constant inward force necessary to maintain circular motion. The centripetal force is balanced by a reaction force, the centrifugal (center-fleeing) force, which acts not on the circling object but on the source of centripetal force, usually located at the circle's center. The two forces are equal in magnitude and opposite in direction.


A response to this definition;

You have the role of centripetal/centrifugal forces nearly perfect. You are way ahead of any physicist I have encountered. [How do I tell him that the definition was stolen?] The action force is the acceleration/Action centripetal force. The reaction force is the acceleration/Reaction centrifugal force. All that is left to think about is the supporting role of the centrifugal force.

First of all, as a reaction force, it is caused by the action force and serves only to support the action force. Thus it is better to say that the centripetal force is "supported" by the centrifugal force rather than "balanced" which implies "canceled". If it were "balanced" the centrifugal force would also have to be an action force and no acceleration would occur. Also the centrifugal reaction force is incapable of acting as the cause of anything. Thus it is not correct to say that the centrifugal force "acts" on the source of the centripetal force.

Further, it is also not right to say that the centrifugal force does not re"act" on the circling object.
It is not correct to think that the centrifugal acceleration/Reaction force just appears at the axis without being present in a real measurable sense all along the rotor blade. In truth as a reaction force, it is present in exactly equal amounts wherever the acceleration/Action force is present. Say you cut a foot off the blade to aid in the measurement of the action/reaction forces present at the one-foot-from-the-tip location. Place a short tension scale between the shortened blade and the 1 foot tip. Now spin up the rotor and read the scale. At this point along the blade, the tension scale will show equal and opposite forces present. The inward-directed force is the centripetal acceleration/Action force, yes? The outward-directed force present during inward-directed acceleration is the centrifugal acceleration/Reaction force, yes? Weld the tip back on securely for now you know the magnitude of the equal and opposite action/reaction forces present on each side of the weld. You also know now that I speak the truth about how the support force (a/R) is always present wherever the action force (a/A) is present.

[Joker's Wild]

Do we really have NOTHING better to do?????

AGAIN????????????????????????????????????????

[The Nr Fairy]

JW:

Try this link to ease your pain.

[Grainger]

Dave;

I think you need to get a basic physics book and revise your Newton's three laws of motion.

The problem with your use of Newton III is that the two forces of a third-law pair always operate on two different objects. This should not be confused with the condition for equilibrium.

Third law pairs are always equal and opposite. What's important is the total force acting on a single object.

If you isolate a short element of the rotor blade (say by making a second cut one centimetre further out from your first cut in the example above), it is obvious that the total force on that element cannot be zero - because it is not travelling in a straight line a la First Law.

If you measure the forces by placing a second tension scale in the outer cut you will find that they are slightly less than the reading on the scale inserted in the inner cut. The total force acting on our element is therefore inwards and this is what keeps it going around in a circle.

G

[Lu Zuckerman]

Dare I stick my nose into this argument? Is NickLappos reading this.

Sever the connection between the blade and the rotorhead. Don’t even think about if the blade will fly off in a straight line from its’ former connection point or on a tangent from the attachment point. It will however fly off. If there were only centripetal force the blade would stay in the same relative position until the following blade(s) hit it. What is the force or load on the blade that makes it fly off?

For those of us that have never been exposed to Newtonian Physics this is called centrifugal force. This force is well recognized in the training curriculum of helicopter manufacturers. It is fully referenced in Frank Robinson’s patent application for his rotorhead design. It is recognized in the FAA’s handbook on helicopter flight. Even propeller manufacturers recognize centrifugal force (centriugal twisting moment). The uneducated masses recognize centrifugal force but those of you that are élitists you are above recognizing this fact of life.

Dare I duck for cover? Hey Dave is that you cowering in the foxhole?

[Dave_Jackson]

Oops!

[Grainger]

Lu;

Once you sever the connection there is no force acting on the blade - so it continues moving in a straight line at constant speed (until air resistance and gravity takes over). Newton's first law again.

[heedm]

Lu, you're okay to use the term "centrifugal force". There is a technicality that labels it an apparent force, but you don't need to worry about that.

What you can't do is refer to the two forces at once. centripetal and centrifugal are not equal and opposite because they don't both exist in the same reference frame. If you're in a spinning (non-inertial) reference frame, you feel a pull away from the center. If you're in an inertial reference frame you realize that the spinning parts are not travelling in a straight line, therefore a force must be pulling them towards the center of rotation.

Final Answer: both terms good. only use one at a time. they are NOT equal and opposite. one does NOT cause the other.

Matthew.

[helmet fire]

I love this arguement with Lu.

I think we got to about 30 different examples of trying to describe this relationship to you last time Lu. Everytime you were in a corner and about to gain knowledge, you would choose yet another example for us to explain the same day 1 physics to you.

In that previous thread, I asked you (or a younger colleague) to spin slowly around with a tennis ball in the hand of arm extended out in front of you. Open your hand when your arm passes an observer. Does the ball

a. Fly outwards directly to the observer? (Centrifugal is real and observer gets hit by ball, sorry observer!)

OR

b. Now continue on a straight path (tangential) at the release point (Centripetal is real, Lu just dont get it)

OR

c. Your arm comes around on the next pass and hits the ball again as it has not moved from the point of release (Lu's radical new take on physics rocks the planet, and I resign from life in disgrace in order to pay homage to the Dalai Lu with RD Rickster)

I dare you to try it Lu (again!).



Amuse me baby..........

[Flight Safety]

I weighed in pretty heavily on the last major thread on this subject, I sometimes wish I had that kind of time again.

The answer to Helmet Fire's question is B.

I found a little time to think about this, and it's interesting to note that a rotating mass like a rotor blade experiences both linear and directional acceleration. Each of the 2 types of acceleration show 2 forces, the accelerating force, and the force (mass inertia) resisting the acceleration.

The fact that both types of acceleration exist is demontrated in the fact that when a rotor blade is released (meaning the centripetal force is released) the rotor blade travels in the tangential direction.

The tangential vector (or departure path) shows that LINEAR acceleration of the rotor blade mass must have previously occurred when the rotor assembly was spun up, and thus the accelerated mass (the rotor blades) continues in motion (with an established velocity) both when they remain attached to the rotorhead, and in the tangential direction once released. The resistance (mass resistance, or inertia) to the linear component of the rotor blade's acceleration is shown in the rotor's resistance to being spun up to an established RPM (discounting the air resistance for this discussion), prior to the rotor blade's release.

The tangential vector (or departure path) also shows that DIRECTIONAL acceleration is involved. The "heading" of the departure path is directly influenced by the exact timing of the release point of the rotor blade while the rotor assembly is spinning. The DIRECTION of the rotor blade's velocity vector is contantly being changed by the rotor assembly's rotation, thus DIRECTIONAL acceleration is contantly present while the rotor assembly is spinning. The force causing the directional acceleration is the centripetal force, because it's this force that is constantly changing the "direction" of the linear velocity of the rotor blade's mass. The resistance (again mass resistance, or inertia) to the directional acceleration is the centrifugal force. The success of the centrifugal force in resisting directional acceleration is demonstrated, when the rotor blade is released and the linear velocity of the rotor blade suddenly ceases to change its direction, and the rotor blade flies away on the tangential path in a straight line.

I hope this helps.

(edited to correct an sp)

[Lu Zuckerman]

Ipital=IN Ifugal=OUT

To: Flight safety

The success of the centrifugal force in resisting directional acceleration is demonstrated, when the rotor blade is released and the linear velocity of the rotor blade suddenly ceases to change its direction, and the rotor blade flies away on the tangential path in a straight line.

Thank you very much.

As for the rest of you I would suggest the following:

1) Check with Dave Jackson to determine the author of the first paragraph in his post.

2) Check with the FAA and their explanation of centrifugal force on page 3-2 of the Rotorcraft Flying Handbook.

3) Check with Sikorsky relative to their explanation of centrifugal force being one of the forces that establishes coning angle. The other force being lift. This is the same as the explanation provided in the Rotorcraft Flying Handbook. This is on page 14 of Sikorsky Helicopter Flight Theory For Pilots And Mechanics.

4) Those of you that have attended the Robinson safety course check your notes where they should have explained how the coning angle is established. Ref paras. 2 & 3 above

5) If any of you attend a factory school and try to correct the instructor when he mentions centrifugal force he / she will in most cases not understand you.

If you are successful in changing the thinking of the FAA, Sikorsky
and Frank Robinson then I might change my thinking in this matter.

Until then stop ragging on me showing how smart you are and thinking how dumb I am.


Here is a point to ponder. On a rotorhead that has say a three-foot offset (measured from one offset hinge to the other) the pulling force is 18" from the center. In this case it would seem that the centripetal force is not truly center seeking but instead it is dragging the rotorblade around in a circle 113' in circumfrence. Is there perchance vector mechanics involved?

I may be wrong and if I am please explain remembering that I am 73 years old.

[heedm]

Lu: You, the FAA, Sikorsky, etc. are not wrong in using centrifugal force to describe this stuff. I won't try to change their thinking, they explain things well. Please consider my post regarding not using both terms in the same reference frame. I think that FlightSafety has a good understanding of this stuff, but if you follow his definitions, you'd be leading yourself away from a complete understanding.

Dave Jackson's first paragraph was written by someone who doesn't understand this topic as well as he/she thinks.

Regarding your offset hinge example, centripetal force by definition is centrally seeking. The pull of the hinge to the blade may not be entirely centrally seeking. In that case, the centripetal force is defined as the radial component of that force, the remainder (tangential component) is used to change angular momentum and/or balance drag forces.

If you still feel you don't get what I'm saying, rather than starting a new example, why don't you explain as far as you follow then we can fill in the rest.

BTW, I don't think you're dumb. Perhaps the ragging from the others is more sport than criticism.

Matthew.

[Lu Zuckerman]

As the rotor turns so do the days of our lives.

To: heedm

In making reference to those sources that address centrifugal force and what it does it has to be assumed that they are not scientific treatises. They do not address the necessity to never mention centripetal and centrifugal forces in the same breath. In fact they do not even refer to centripetal force. These documents are for pilots and mechanics and it is easier to understand centrifugal force if you do not relate it to the forces that cause it. They just address a spinning rotor and the outward force that results from the spinning.

It is extremely difficult to understand the workings of nuclear fusion. But, it easy to understand that you don’t want to be near it when it is taking place. Having a detailed understanding of these two forces (centripetal and centrifugal) has its’ place. However I have never been in that place.

Quite some time ago I contacted the Service department of Sikorsky and I asked the service rep what is the most important force when designing a rotor system. He contacted the engineering department and asked the question. Several days later he contacted me telling me that they felt that centrifugal force was the most important in calculating the required strength of the rotor components and the blade structure. A similar argument was going on at that time and I was being ragged on by my reluctance to see the other guys’ point of view. I posted the engineers reply and no other than NickLappos told me both the engineer and I were full of beans or something like that.

Somewhere on these threads is a reference to the US Patent office site and the patent number for the Robinson R-22 rotor head. Frank Robinson references in several places centrifugal force and he never mentioned centripetal force. Maybe that’s the problem with his rotorhead.

[helmet fire]

Flight Safety:
I like your explanation and it shows yet again that you contirbute a lot to the forum whilst being still able to learn from it.

I do, however, have a slight issue with the last paragraph of your explanation.

Firstly, Your term "Directional Acceleration" is a new one and will only serve to confuse the issue. ALL acceleration is directional - for example, acceleration in a straight line (or Linear acceleration as you have termed it) still has direction - straight ahead. What you are in fact trying to label is centripetal acceleration, so why not call it that?


Secondly, I think that throughout our earlier discussions on this topic and again above, you have repeated your thought that centrifugal is a real force because it can be felt. I think that we agreed last time that a van accelerating in a straight line doesnt produce a force in the opposite direction, but has, as you say above, a resistance of mass/inertia. In the exact same way, a turning object does not, and cannot produce a force either. Acceleration is acceleration is acceleration the direction of which is immaterial - it does not, and cannot produce a force in the opposite direction.

Thus your example, and the one Lu so profoundly thanks you for, is flawed. The released blade now flies in a straight line because it no longer has an acceleration acting upon it to change its direction (remember that as velocity is speed AND direction, an object can only change direction if an acceleration is applied). In other words, the blade "suddenly ceases to change direction" because it is no longer being accelerated in a different direction, not because of the presence of centrifugal force. If centrifugal force DID exist, then the blade would adopt an outward trajectory when released, not a tangential one, which, as you agree with, is the reality of the situation.

Lu.

Your 5 points are the four of the same you have been applying to this discussion for years now. Your arguement is undergoing an increasingly rapid centripetal acceleration.

Go and try the experiment. Then explain the results in terms of centrifugal.



PS: I know you wont Lu. "The truth? You cant handle the truth"

[heedm]

Lu, forgive me. I thought you were asking what the difference was. Go ahead and just talk about centrifugal force if you like. You can get a better understanding of things if you look at problems from different points of view, but for basic understanding of helicopter stuff, centrifugal works okay.

Helmet fire, if you were in the rotating reference frame and let go of the blade, it would move away from center initially, would then appear to have an increasing centrifugal acceleration, then would bend it's path towards what used to be the trailing edge. We see this effect all the time, call it coriolis force, blame weather and flushing toilet effects on it. Those things aren't really bending paths, they're just trying to "...move in a straight line unless compelled to [move] by a force impressed upon them".

[helmet fire]

heedm,
understood, thanks. I am trying to stick to the single, stationary reference point to keep it simple as I believe the point that centrifugal is not a real force has yet to be accepted, let alone that although reference points change and paths appear different, reality, and the forces involved do not change, and are consistent. A different reference frame does not create or prove the existance of centrifugal, as you have pointed out in the past.

I note in a review of previous threads that your opening line about using the term centrifugal has been said by you on many occaisions, and completely disregarded each time. Good luck this time.

[Lu Zuckerman]

Which part of the glass are you looking at. Part II

To: helmet fire

Here is a description of centrifugal force that is contained on the web site of RW-1. I believe the words are from other sources but in any case the words reflect what is taught in factory schools for pilots and mechanics and not necessarily in college classrooms.

http://www.dynamicflight.com/aerodyn...rifugal_force/

Here is what is taught in universities and it totally supports what you are saying. Although it states that centrifugal force and centripetal force act in opposition to each other it is not the centrifugal force that causes the blade to fly out but it is the energy imparted by the centripetal force.

http://www.infoplease.com/ce6/sci/A0811114.html

I believe that we are in the same argument as the one about flapping to equality and aerodynamic precession as opposed to flapback and gyroscopic precession. All of the arguments are based on what and where the person was taught and the unwillingness to accept the other guys arguments. If you remember I accepted the two foreign terms but you did not. You and others from OZ and the UK

[Flight Safety]

It all depends on your point of view, academia or the engineering lab, the ivory tower or the back of the garage.

You can tie a piece of sewing thread to your car bumper and try to pull your car with it. But when it breaks, you can argue all day long whether it was your pulling force, or the mass resistance to change in velocity of the car, that broke the thread. And if you tied the thread to a spider instead of a car and tried to pull it, how would the outcome be different?

In the end, if you're an engineer, you MUST take into account the resistance of any mass to changes in its velocity or direction. That mass resistance (or inertia) can strain, bend, and break things.

Whether it's academically, holistically, or cosmologically correct to refer to mass resistance to change in velocity or direction as a "force", I don't know. I do know that in the real world, inertia can give engineers fits. It's handy to have a name for something you refer to often enough, and "centrifugal force" is as good a name as any, for mass resistance to directional acceleration for rotating objects.

[helmet fire]

LU:
Have you carried out the experiment?

Yet again you assert that the "blade will fly out". NO NO NO. Re read the uni text. NOTHING "flys out", it merely stops changing direction and departs tangentially. And this has nothing to do with semantics.

It appears that you have reached an acceptance of aerodynamic precession and flapping to equality, and I am glad you have been able to gain that knowledge. The reason some of us (and I dont think Nick or heedm are from Oz/UK) dont accept your alternate is because they are not the primary forces responsible for the rotor behaviour we observe. It's not a terminology issue, its a factual one.

FS:

Whether it's academically, holistically, or cosmologically correct to refer to mass resistance to change in velocity or direction as a "force", I don't know.

It's not a force. You have labelled it effectively many times when you call it inertia, mass resistance, etc. Why not, therefore, continue to label it correctly? Why attribute a new "engineer only" label that everyone else uses to describe something totally different and thus serves only to confuse and impede understanding? (and isn't this discussion proof of that?)

I think there remains one central issue here for both flight safety and Lu:
Centrifugal force is not a real force. It is, however, a convenient (but technically incorrect) term that can be used as a tool to help simplify otherwise technical explanations.

[Lu Zuckerman]

How to stop this argument

To: helmet fire

If you want to end this argument just let me and any supporters wallow in our own ignorance.