The Role of Gyroscopes in Ship Motion: Understanding the Basic Concept

[Urmi Roy]

I've understood the basic idea of why a gyroscope behaves as it does-- which is easily demonstrated by spinning a bicycle wheel about an axis and the exterting a turning couple to rotate the entire wheel about an axis perp. to the axis of spinning...I got the explanation from http://science.howstuffworks.com/gyroscope2.htm .

However, when we apply the same idea to real life, like a ship, how do we exactly describe what's happening? (In my book, they just draw vector diagrams, without explaining what's what)

So starting off, suppose there's a ship, with its rotor spinning clockwise ...and now it decides to steer to the left (all of this is viewed from its rear end)... then the rotor is analogous to the spinning of the bicycle wheel about an axis passing through its centre, perp. to the plane of the rotor...but what happens after that? How do I describe what happens by comaring it step by step with the bike wheel?

Similarly, what happens in case of pitching motion of the ship?

Also, is it the gyroscopic couple of the reactive gyroscopic couple that actually causes motion of the ship?

In case of rolling of the ship, there's supposed to be no gyroscopic couple, in the book, they calculate a couple,and at the same time they mention that its not gyroscopic couple...then what is it?

 

[Cleonis]

I've understood the basic idea of why a gyroscope behaves as it does-- which is easily demonstrated by spinning a bicycle wheel about an axis and the exterting a turning couple to rotate the entire wheel about an axis perp. to the axis of spinning...I got the explanation from http://science.howstuffworks.com/gyroscope2.htm .

In my opinion the gyroscope story presented on the howstuffworks site doesn't add up. I mean, the writer knows the end result, so his story ends up describing how gyroscopes actually move, but that is the only correct thing of his story.
If you're interested I can tell you why I think so.

However, when we apply the same idea to real life, like a ship, how do we exactly describe what's happening?

As I understand it there have in fact been ship designs that included giant gyroscope wheels as a means of active stabilisation.
These active stabilizing gyroscopes were mounted with their spin axis vertical.

I don't know the naval terms for motion of a ship, so I will use aviation terms:
- Rolling
- Pitching
- Yawing

The way I use those three terms can refer to motion of the ship as a whole, or to motion of objects inside the ship, moving with respect to the ship.

The way the active stabilizing gyroscopes where suspended was that the gyroscope wheel spinning was a yawing motion. Hinges allowed pitching of the gyroscope wheels, but no rolling relative to the ship

With that in place then on a calm sea you can cause roll of the ship by way of a pitching motion of the gyroscope wheels.
The recurrent theme is that the response of a gyroscope wheel to an applied torque is at right angles to it. When the actuators exert a torque that pitches the spinning gyroscope wheel then you get a roll torque upon the ship.

Now the case where a sea swell tends to build up oscillating roll.
With powerful actuators (hydraulic machinery for instance) the gyroscope wheels are pitched up and down in such a way that the tendency from the sea swell is counteracted.

Note especially that such a setup is an active stabilisation setup. To counteract the influence of the sea swell the gyroscope wheel must be actively pitched. That pitching motion takes a lot of force, and it must be timed perfectly.


Earlier discussion (by me) on physicsforums:
A post from november 2010 about https://www.physicsforums.com/showpost.php?p=2992527&postcount=3". Illustrated with images. Just a qualitative discussion.

More detailed discussion (including math) is in the http://www.cleonis.nl/physics/phys256/gyroscope_physics.php" article on my website.

 

[Urmi Roy]

Hi Cleonis, just wanted to thank you for your response...I have two exams over the next two days, so I look forward to reading all your material on gyroscopes on Friday and over the weekend...thanks for your input, I will let you know if I have any additional queries :-).

 

[Cleonis]

As I understand it there have in fact been ship designs that included giant gyroscope wheels as a means of active stabilisation.

How about that: use of active gyroscope stabilisation on ships has reemerged in recent years. Wikipedia:
http://en.wikipedia.org/wiki/Anti-rolling_gyro"

 

[Urmi Roy]

Firstly, excellent website!

...now, from your explanation, there does not need to be a constant applied force/ couple to make the gyroscope work...you just make the wheel of the groscope spin, it does the rest on its own..then why do they mention a gyroscopic couple and a reaction couple in many texts?

What is the role of the reaction couple in functioning of the gyroscope? (I'm referring to this in regard to suppose a plane...from the way its written in the book, it seems that when the plane is pitching, there'll be a continuous oscillatory motion...the plane will not settle into equilibrium like the gryroscope in proffessor Lewin's experiment did when a weight was applied...

 

[Cleonis]

Firstly, excellent website!

...now, from your explanation, there does not need to be a constant applied force/ couple to make the gyroscope work...

It's not clear what you are referring to here.

Gyroscopes are used in two ways:
- one where torque upon the gyroscope rotor is prevented, allowing use as navigation aid
- one where a torque is allowed to act on the gyroscope rotor, and some freedom of motion for the gyroscope to respond to that.

Both are examples of gyroscopes doing their thing. Presumably you are referring to one of them, but its not clear which one.

Gyroscopes in sensors
Gimbal mounting of a gyroscope has the purpose of preventing any torque being exerted upon the gyroscope rotor. In the absence of a torque the gyroscope rotor keeps pointing in the same direction.

Today's navigation systems use other methods to detect rotation, but for example the 1960's spacecraft s for the flights to the Moon used gimbal mounted gyroscopes to find their bearing. If those gyroscopes would lose their orientation then the astronauts would be left unable to execute a plotted course back to Earth accurately enough

Those types of gyroscopes are small.


Gyroscopes for attitude control
Then there are gyroscopes that are designed to receive a torque, because of the way they respond to it.
I think the Hubble space telescope also has some gyroscope rotors for the purpose of actively reorienting the spacecraft . Those gyroscopes can be powered with electricity from the solar panels. That way the thrusters that use propellent have to be used only rarely.

And of course the application that to my surprise is back again: gyroscope setups on ships for the purpose of anti-roll stabilisation.

 

[Urmi Roy]

It's not clear what you are referring to here.

I mean like the one in Proffessor Lewin's experiment...the weight...it's always there in the same magnitude...unlike in a case where we just apply a momentary force to initially spin the gyro into motion...

Could you just tell me , when we apply the weight to the spinning wheel as in the experiment,is the reason as to why the wheel starts swivelling the same as why pitching occurs in the case described on your website? i.e why does the wheel start swivelling?when we apply weight?

 

[Cleonis]

I mean like the one in Proffessor Lewin's experiment...the weight...it's always there in the same magnitude...unlike in a case where we just apply a momentary force to initially spin the gyro into motion...

Could you just tell me , when we apply the weight to the spinning wheel as in the experiment,is the reason as to why the wheel starts swivelling the same as why pitching occurs in the case described on your website? i.e why does the wheel start swivelling?when we apply weight?

Well, I can only repeat information that is in the article on my website. The information you seek is present there.

The demonstration setup that Professor Lewin is using is the most vivid one that I know of. It was natural to me to follow that demonstration in my diagrams, including the colors (yellow housing, red housing).

[...]is the reason as to why the wheel starts swivelling the same as why pitching occurs in the case described on your website? [...]

The short answer: Yeah.

Ignoring the green arrows for now:
- If you grab the yellow housing, and you move it (which is swivel), then in response the spinning will will pitch.
- If you pull at the red housing (making it pitch) then in response the spinning will swivel.

As you ask, the mechanism underlying the response is the same each case.
The general rule is: turn the spinning wheel around one axis, then in response the wheel will turn around the axis perpendicular to that. (Swivel gives a pitching response, pitch gives a swiveling response.)

 

[Urmi Roy]

Thank Cleonis, nice to know I'm finally getting there :-)...

Okay, here's my last question...while considering the motion of an aeorplane, would it be correct to say the rotor of the propeller is the blue spinning wheel, the plane itself is the yellow swivelling part (in case of steering motion) and the rotor develops a pitching motion inresponse to the other two motions?

Sorry for the bother, Cleonis!

 

[Cleonis]

...while considering the motion of an aeorplane, would it be correct to say the rotor of the propeller is the blue spinning wheel, the plane itself is the yellow swivelling part (in case of steering motion) and the rotor develops a pitching motion inresponse to the other two motions?

Yes.

Look up 'rotary engine'.

With a rotary engine the cilinders are arranged in a star pattern, and they are whizzing around. A rotary engine is cooled by the air it moves through.

In the Wikipedia article about the rotary engine design, in the section about http://en.wikipedia.org/wiki/Rotary_engine#World_War_I" I read that for some aircrafts the weight of the engine was so large in proportion to the aircraft as a whole that the flying was strongly affected.

In left-turns, for example, the aircraft had a tendency to nose up. The pilot had to anticipate that. From the information I gather that if the pilot would try to turn too sharply he would lose control over the aircraft.

 

[Urmi Roy]

Thanks Cleonis :-) ...I'm beginning to get a feel for it now...you've been an excellent teacher!

 

[Cleonis]

Thanks Cleonis :-) ...I'm beginning to get a feel for it now...you've been an excellent teacher!

OK, I'm real pleased to hear that.

I'm curious: with what you understand now, what do you think about the things that are said on howstuffworks?

http://science.howstuffworks.com/gyroscope2.htm"
There's a lot of good stuff on howstuffworks, I often visit that site, but the gyroscope story there doesn't make any sense. Remarkably, the picture that accompanies that story says 'copyright 2000'.