Gyros's
Avoid imitations
Joined: Nov 2000
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From: Wandering the FIR and cyberspace often at highly unsociable times
mdp,
I'm not sure if you worry most about a lack understanding of the basic principles of a gyro, or how the principles are used inside the instruments.
Some years ago I spent some time worrying about how to teach what a gyro is actually doing and how it's characteristics can be explained in very simple terms. It dawned on me one day that it's actually all down to the phenomena we know as inertia, often noted as "Newton's First Law". Namely, a moving body will tend to continue in a straight line unless acted on by an external force.
The "moving body" in the example of a gyro is the mass of the "flywheel". It helped me to understand what is happening when I considered each molecule of the wheel as an independent moving object wanting to continue in a straight line, but can't because it's forced to turn in a circular path instead. Suddenly I saw why the flywheel has rigidity.
Imagine heavy washing in a spin drier, or a conker on a string being whirled around a boy's head. These objects want to continue in a straight line due to inertia, but are forced to follow a circular path instead. On a gyro/flywheel, the intermolecular bonds replace the washing machine tub, or the string.
Can you understand this so far or is this too basic?
I'm not sure if you worry most about a lack understanding of the basic principles of a gyro, or how the principles are used inside the instruments.
Some years ago I spent some time worrying about how to teach what a gyro is actually doing and how it's characteristics can be explained in very simple terms. It dawned on me one day that it's actually all down to the phenomena we know as inertia, often noted as "Newton's First Law". Namely, a moving body will tend to continue in a straight line unless acted on by an external force.
The "moving body" in the example of a gyro is the mass of the "flywheel". It helped me to understand what is happening when I considered each molecule of the wheel as an independent moving object wanting to continue in a straight line, but can't because it's forced to turn in a circular path instead. Suddenly I saw why the flywheel has rigidity.
Imagine heavy washing in a spin drier, or a conker on a string being whirled around a boy's head. These objects want to continue in a straight line due to inertia, but are forced to follow a circular path instead. On a gyro/flywheel, the intermolecular bonds replace the washing machine tub, or the string.
Can you understand this so far or is this too basic?
Last edited by ShyTorque; 27th November 2008 at 14:28.
Joined: Sep 2006
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From: Scotland
I am perfectly calm thank you, old boy, & I am, & have been for some time, well aware that GPS has nothing to do with attitude, I am also aware that you never said any of the above, in this thread. What you do seem to be saying is that most club a/c have clapped out instrumentation fit only for the bin. Your "attitude" seems to be that to fly using anything other than state of the art kit is a waste of effort. OK so you can navigate without it, so can I, so can many. But we don't all think we are flying something inferior at the time. As for how far you have flown compared to how far I have? You have flown far, far further than I, should I feel bad about that?
As for precession, I'm not so sure about that explanation, how does the planet have anyting to do with it if you are not in contact with said planet? The gyro is not a magnetic force thing. I also don't really believe that magnetic north moves very far as I "fly along", a few minutes per year if I remember right. I think precession occurs to a greater or lesser degree depending on the amount of friction caused by worn bearings, weight of rotor, drag from surface finish of the rotor, out of balance etc.
The fact that flying school a/c DI's are wore out & need reset more often is actually a good thing, as a learning tool it shows the student what is happening, no use if it only needs reset at 50hr checks!
As for precession, I'm not so sure about that explanation, how does the planet have anyting to do with it if you are not in contact with said planet? The gyro is not a magnetic force thing. I also don't really believe that magnetic north moves very far as I "fly along", a few minutes per year if I remember right. I think precession occurs to a greater or lesser degree depending on the amount of friction caused by worn bearings, weight of rotor, drag from surface finish of the rotor, out of balance etc.
The fact that flying school a/c DI's are wore out & need reset more often is actually a good thing, as a learning tool it shows the student what is happening, no use if it only needs reset at 50hr checks!
Joined: Feb 2007
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From: Amsterdam
I think precession occurs to a greater or lesser degree depending on the amount of friction caused by worn bearings, weight of rotor, drag from surface finish of the rotor, out of balance etc.
As for precession, I'm not so sure about that explanation, how does the planet have anyting to do with it if you are not in contact with said planet?
Joined: Aug 2000
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From: UK
Precession is a change in the direction of the axis of rotation. Such changes induced by friction or mechanical imperfections certainly counts.
That's usually called "wander". It's not precession just because your reference direction changed as the earth rotated!
but it will no longer be aligned with the earths grid (or magnetic north). That's precession.
Avoid imitations
Joined: Nov 2000
Aviation Qualifications: ATPL
Posts: 15,116
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From: Wandering the FIR and cyberspace often at highly unsociable times
That's precession. (Well, not quite, but close enough.)
Joined: Sep 2006
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From: Scotland
Backpacker.
That wasn't meant to be a "definition" of precession rather the cause of it. The more restriction to the rotation of the rotor the greater the rate of precession.
Also, precession will affect the accuracy of the DI a lot more than the mathematical problems associated with great circle tracks. I am aware of, but not all that used to, spherical trigonometry but I don't think it is just a case of resetting the DI! Precession is the result of attempting to change the freely spinning motion of the rotor, whether that is caused by friction or by numerous changes of direction or whatever, it's not to do with planetary action. If a gyro is spinning in deep space away from gravitational influence, does it precess or not?
I think SNS3Guppy has it sown up pretty well. I don't profess to be an expert but I do think gyroscopic precession is a self contained, self controlling thing, not something controlled by an outside influence like a compass.
That wasn't meant to be a "definition" of precession rather the cause of it. The more restriction to the rotation of the rotor the greater the rate of precession.
Also, precession will affect the accuracy of the DI a lot more than the mathematical problems associated with great circle tracks. I am aware of, but not all that used to, spherical trigonometry but I don't think it is just a case of resetting the DI! Precession is the result of attempting to change the freely spinning motion of the rotor, whether that is caused by friction or by numerous changes of direction or whatever, it's not to do with planetary action. If a gyro is spinning in deep space away from gravitational influence, does it precess or not?
I think SNS3Guppy has it sown up pretty well. I don't profess to be an expert but I do think gyroscopic precession is a self contained, self controlling thing, not something controlled by an outside influence like a compass.
Joined: Dec 2004
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From: Under the clag EGKA
I the dark ages I had to demonstrate a gyro to a load of sprogs. I used a bicycle wheel. Let them hold the spindle and get the bugger spining as fast as pos. They then felt the forces involved.
