A couple of questions
 

OK, I'm wrong and you are all right however I would like to pose the following questions to the pilots out there and not the engineering graduates although you are involved in this also.

I have a couple of questions.


1) When you learned principles of flight for helicopters did your instructors use the term centrifugal force when addressing the loads on the blades or rotorhead or, did they use the term centripetal force?

2) If you attended higher level classes in engineering and / or physics you most likely learned about centripetal force? If this is the case and your POF instructors addressed centrifugal force as opposed to centripetal force which theory do you embrace in your daily operations of your helicopter or if you are a mechanic when you work on the helicopter?

This poll will be on PPRuNE as well as on this forum.

Please no sarcastic responses. Just respond to the questions.

I thought centrifugal and centripetal forces were just the same thing, depending on your frame of reference.

i.e., from an external observer's viewpoint, a rock on a string being whirled in a circle is being dragged away from what would otherwise be a straight line path by a centripetal force acting through the string towards the centre of the circle.

From the rock's point of view (sentient rocks - now there's a novel idea!), it feels an apparent force, centrifugal force, towards the outside of the circle, again because if left alone it would move in a straight line but this damn string keeps pulling it elsewhere.

Or have I just butted in to the continuance of some previous and more complex argument here? Sorry, if that's the case.

Arm out the Window,

Yes and yes. They are essentially the same and this is a part of a more involved discussion.

Refer to Aerodynamics ~ Phase Lag if you're interested.

Well..errrr...actually...as long as all the forces more or less balance....I nip into the break room and have a cuppa. I have enuff to ponder without worrying my alcohol ravenged brain (whats left of it) about which terms of reference my POF instructor used over thirty years ago. Where do you come up with these issues Z-man? You really need to examine an unclad female form or something at night....or take up Spider Solitaire on the four suit setting.

Could you be just a bit more specific in your frame of reference...which bit on the aircraft are we talking about....and in what context are the terms to be used...aerodynamics, physics, stress analysis...control dynamics....vibration resolution? We talking blades, bearings, spindles, rotor dynamics, performance?

Lu,
Yes you are right, you are wrong!
1.I was taught an example that stated a merry go round with a rim on the edge of it. Depending on where your'e looking, on the merry go round or on the ground, the marble will have no motion or a circular motion. If the marble is stopped from rolling off the side of the merry go round by a rim, the rim is exerting centripetal force on the marble. With no rim the observer on the merry go round would say that the outward force on the marble is centrifugal. It depends on where you are, on the merry go round or looking from the ground. Centripetal force describes the behaviour, or to use another example, the piece of string holding onto a rock, the elastic string is providing the elastic force INWARD toward the centre, the centripetal force. If you cut the string at the rock, the rock would move in a straight line in a tangent from the point from which it was cut. So to keep the rock MOVING in a circle, the inward FORCE required to pull it is centripetal force.

2. How in the daily use of a helicopter does it matter which force works? I always adopt the Zuckerman theory, "I don't know, but lets argue the point anyway"

Lu, who really cares........ :)

As I understand it- motion in a circular path requires a constant acceleration towards the centre of the circle. A constant acceleration towards the centre requires a constant force towards the centre.
That force is centripetal force and is applied by the piece of string on the stone or whatever. Centrifugal force is the 'reaction' to centripetal force (As in "every action has an equal and opposite reaction")and is the force felt by your hand when you are spinning the stone round. Now I can't remember what the question was!!!

1) They used the term "Centrifugal Reaction", which is technically correct while avoiding having to explain Newtons Laws to a bunch of chaps who would rather fly than study physics (with the odd exception ;) ).

2) See 1.

See it's easy if you ask the right questions.

I have to agree with TeeS. That is exactly what I was taught.

In the case of "which theory do I embrace when I work on the helicopter?" I would have to agree with Geronimo 33, I can't say that I actually think about it whilst in the working environment.

I actually recall, whilst being taught the theory, being told that it was just one of those things you had to learn for the exam, and then would be highly unlikely to need again if pursueing a career on the hangar floor.

Yes heedm, I had a look at that thread you mentioned...holy tamale! Talk about arguing about nothing.

Who would have thought that such a straightforward issue could be made so complicated? Amazing.

Lu,
Answers for you:

1) Centripetal from day 1

2) Centripetal because I teach, i.e. I have to use the correct terminology.

I would like to add some questions:

3) Should the majority view be right, or should the scientifically accurate view be right? (Remember we used think the world was flat, the sun revolved around the earth, and porpi were smarter that octopi)

4) When you have effectively been shown to be wrong in a subject, should you always create another thread to remove the background of the discussion whilst creating a thread you can delete at will?

5) Is obscuring the arguement with reality a poor substitute for opinion?

6) Why is it called "Seven Eleven" if it is open 24 hours a day?

:D :D

http://www.7-eleven.com/about_us.html

For the answer to the question .
I guess 24/7 is probably already taken by someone.

Another question :-
Why does buttered toast when dropped always land butter side down ?. Is it aerodynamic force at play ?.

To: helmet fire

I wasn’t trying to do anything other than asking two questions. I just wanted to know what the pilots and mechanics were taught relative to POF. I was not trying to gain support for my opinions. Having read the various posts condemning me for my stupidity and ignorance I was curious what other people were taught because, I learned it was centrifugal force and centripetal force was never mentioned. I posted these same questions on Just helicopters and a pilot by the name of Butch Grafton emailed me some information taken from the FAA mechanics manual and he pointed out one area of the FAA Rotorcraft handbook. These two manuals identified both forces and in the explanation they indicated both were real forces that acted in opposition to each other. Now I don’t know if it is technically unsophisticated to have referenced these manuals but they are major teaching tools in the USA for pilots and mechanics.

By stating that centrifugal force is a non force can cause problems in the minds of technically unsophisticated individuals like myself. That is why this argument has gone on so long.

If 7-11 is open 24/7 then why do they have locks on the doors?

If the sun doesn't orbit the earth then why does the sun trace an arc in the sky?

and finally,

Octupus's are smarter than porpoises? Really?

Lu,

If we could go to one central issue with your discussions, it is that you have believed in what a basic text has told you for a very long time (I think you mentioned fifty odd years).

You need to grasp that occaisonnaly books are written to give a BASIC understanding of a subject to a BASIC user. Keep It Simple Stupid. Good principle. BUT, if you want to know how it ACTUALLY works, you would need to get some post basic course education. in other words - believe everything you read in DAY ONE texts and you will only ever achieve a DAY ONE understanding.

Think of it thus: Is there ANYTHING you have learned outside of your basic engineering course?
Answer Yes: Then maybe not everything on the basic course is all there is to know.
Answer No: You only need to listen to newly graduated mechanics because they have the most recent understanding of the basic texts.

Heedm,

Suprisingly, I am "reliably" told by a slightly nutty relative that the latest experiments have begun to show that Octopuses can recognise individual scientists by their face and can react differently to different known faces (i.e. a personality)!! Apparently they have demonstrated that they are smarter than pigs (the smartest farm animal) This is leading to SPECULATION that they are/might be more intellegent than porpoises, but probably not dolphins. But I bet the greenies wont save them because they are not majestic like whales, nor cute and playful like porpoises.


But (are you listening Lu) if they can prove this intellegence is there, maybe I will no longer believe my high school text book that says dolphins, whales and then porpoises are the sea's most intellegent animals...
:cool:

To: helmet fire

Aside from the experiments above that prove the Octopi (SP) can recognize a scientists face as described in your post they are now conducting experiments to see if animals have self-awareness. They experimented using primates and porpoises and it turns out that porpoises have self awareness and can recognize their own”face” which is is better than recognizing the face of the scientist because all scientists do not look alike but porpoises do.

Lu, I'll bring this back on topic.

"1) When you learned principles of flight for helicopters did your instructors use the term centrifugal force when addressing the loads on the blades or rotorhead or, did they use the term centripetal force?"

I can't remember. I would hope that they would have used centrifugal force and understood centripetal force, in case anyone asked. The point of a principles of flight course is not to make pilot wannabes into physicists. It's give them enough background so that they can understand what happens in flight.


"2) If you attended higher level classes in engineering and / or physics you most likely learned about centripetal force? If this is the case and your POF instructors addressed centrifugal force as opposed to centripetal force which theory do you embrace in your daily operations of your helicopter..."

The theory I use in flight is, "cylic forward, houses get bigger....". I'm not kidding. For day to day operations, neither arises. If we need to get into technical qualities of the helicopter, I think centripetal, but translate if required.

Just to stir it up a bit :D

2.5.2.4.0.A.1
Coning is caused by the combined forces of
a. lift and centrifugal force.
b. flapping and centrifugal force.
c. drag, weight, and translational lift.

Nothing like 'technical unsophistication' from the FAA :p

A little fuel for the fire.

From the Rotorcraft Flying Hand Book.

CENTRIFUGAL FORCE - The apparent force that an object moving along a circular path exerts on the body constraining the object and that acts outwardly away from the center of rotation.

CENTRIPETAL FORCE - The force that attracts a body toward its axis of rotation. It is opposite centrifugal force.

From the dictionary of aeronautical terms.

Centrifugal Force. A force that acts outwardly on any body moving in a curved path. Centrifugal force tries to move a body away from the center of its rotation, and this force is opposed by centripetal force.

Centripetal Force. The force within a body that opposes centrifugal force as the body rotates or spins. Centripetal force acts inside a piece of rotating machinery and tries to pull the rotating object in toward the center of its rotation.

An FAA test question.

R.8.8.8.2.A.1 R01
How is anti icing fluid ejected from the slinger ring on a propeller?
A. By centrifugal force.
B. By pump pressure.
C. By centripetal force.

Happy Holidays

Butch

Butch

With all due respect sir, you have missed an awful lot of discussion around this point. It has never been in contention that the FAA (and others) talk about centrifugal force, but thank you for repeating the point. What has been in contention is that centrifugal force is an EASY way to understand the dynamics, but not an ACCURATE way. See the corriolis thread, the Aerodynamics - Phase Lag thread, and the Icing/Wx nasties thread to give you a bit of background (particularly pages 4 & 5 of the Aerodynamics - Phase Lag thread).

I understand Lu has got you to post your two cents worth by raising the topic on Justhelicopters, but you should get in on the background. Hence my earlier question to Lu on page 1 of this thread:

>>4) When you have effectively been shown to be wrong in a subject, should you always create another thread to remove the background of the discussion whilst creating a thread you can delete at will?<<


A central theme in our discussions with Lu is that he (selectively) quotes BASIC text books (such as the FAA ones) as an authoratative source on complex subjects such as aerodynamics, despite the fact that they have been written to promote a quick user friendly understanding, not to further research or design. The resulting discussions have been challenging, educational and highly amusing.

Read the other threads and tell us what you think.
:D :D

Too many beers - had to correct twice.

[ 03 December 2001: Message edited by: helmet fire ]

[ 03 December 2001: Message edited by: helmet fire ]

Actually I wasn't trying to make any point. Rather, I simply wanted to post the information from the FAA pubs covering the two terms for those who may not have access to it.

By the way, I did read all of the posts under both topics and was unimpressed with the entirety of it all. It ended up in the standard name calling contest as so many of these potentially good discussions do. I'll go back in my cave now and leave you to your devices. <:O)

Butch