Gyros's

[maxdrypower]

Guys and Gals
I am about to start and IMC :} and as such am hitting the books again.
One thing I have always struggled with and never understood is Gyros .They are my nemesis.
Does anyone have any links to graphic demonstrations of how these things work . I dont want an explanation I want to actually see a visual representation of them working , whether it be a cartoon or moving diagram . These things do my nut in
Told ya I was thick :confused::confused:

[BackPacker]

Go and borrow a power tool which has something serious spinning in it. A circular hand saw or an angle grinder or something. Turn it on, then try to move it through various axis. Very illustrative. (Safety first though.)

Just remember - a gyroscope is something that spins and thus resists movement. If you nevertheless force it to move, it will react with a predictable force in another direction. Depending on how you mount it (and thus limits movement in certain axis) you can use it for various purposes, three of which are typically present in an aircraft.

[maxdrypower]

Thanks for that but again I need a working diagram . I have read all the bumpf necessary buu just cant relate it to a gyro . Unfortunately a power tool doesnt have a aeroplane symbol on it etc etc

[Slopey]

Presumably you've already looked at Wikipedia ?http://en.wikipedia.org/wiki/Gyroscope

And theres http://www.gyroscopes.org/movies.asp which have some video files.

[maxdrypower]

Never presume :} Ive never heard of wikipedia but thanks very much Ill have a look

[sunday driver]

You could take a trip to a decent toyshop - toy gyros have been around for decades - saw one a few weeks ago. Will cost very little and will give hours of amusement.
(Transair don't keep them)
SD

[maxdrypower]

I want a demo of a gyro as it would be in an aircraft ie with the AI or TC card on it so I can see what is happening

[Slopey]

As I understand it (and I'll be rapidly corrected if I'm wrong) - think about a "toy" gyroscope.

The big metal disk big in the middle is in the same plane as the horizon, so if you're in the cockpit, you're looking towards the spinning bit at the thin edge.

(cue very crude picture)

http://www.slopey.com/download/gyro1.gif

Now, imagine that the horizon indicator on the AH is attached to the the spinning disk along the thin edge.

As the aircraft rolls left or right, the housing round the instrument will move but the spinning disk doesn't - it ALWAYS spins "flat" - so the horizon appears to tilt in line with the roll of the aircraft.

In reality the spinning disk inside is still level, but the aircraft has rolled around it, and as the instrument casing is attached to the aircraft (and the disk is spinning freely within it), it indicates the roll attitude.

Same for pitch in that the aircraft rotates around the spinning disk in the up/down sense.

Does that help?

[BackPacker]

Google also came up with www.howstuffworks.com/gyroscope.htm. Unfortunately site seems to be down but I remember it's a great site in general.

[maxdrypower]

Nope guys your really not getting just how much I dont get these things
I need to to see one working as it would be in an aircarft , dont worry Ill find another way , ill delete this thread when I find out how
Thanks anyway

[slim_slag]

Consider it a black box, you will live longer and be happier :)

[tow1709]

Folks on the other flying forum have said good things about this series of Royal Society Christmas lectures given by Prof Eric Laithwaite.
http://www.gyroscopes.org/1974lecture.asp
I don't know if they will explain what you want to know, but they are certainly very entertaining
EL was one of my tutors at Uni a couple of years before these were filmed, when he was working on magnetic levitation trains

[BRL]

Don't delete it Max, there will be other people in the same boat who could use the links here for future reference!

Have you tried going to an engineering place at your airfield and asking someone there if you can have a look at one?

I think that is what you need to do, it is pretty difficult to explain things like this online.

[maxdrypower]

Thanks BRL that may be what I need to do , Cheers all , Ill have a look at those lectures as well

[Fly-by-Wife]

If your budget stretched to it, you could buy one (2nd hand) and open it up...

FBW

[Squawk7143]

Here is a link to a full motion mpeg of a bicycle wheel used as a gyro mass. This is the howstuffworks like. It shows the effect very nicely

http://science.howstuffworks.com/gyroscope1.htm

[stickandrudderman]

And if you still don't get it you should give up and go and become.......




A lumberjack!

[IO540]

Is Eric Laithwaite still around? I went to a great lecture of his in 1975 and he looked about 60 then.

To be honest, very few engineers understand from first principles how gyro work. It's pretty damn complicated.

A pilot should not need to know this stuff. What he needs to know is the characteristics of his instruments and their limitations and failure modes. Anything else is a waste of time learning.

[maxdrypower]

Tell the bloody caa that , damn exam questions .
SARM your dicing wih danger here we dont want to be excluded AGAIN
personally lion taming has more appeal :):)

[Pilot DAR]

Ask around and a maintenance or instrument shop will probably give some junk ones. They'd work well enough for what you want, particularly if you have some compressed air to blow into them. I've got some junk ones here if you want to pay the shipping from Canada!

When you get one apart, you'll be surprised how simple they are!

Pilot DAR

[coodem]

If you dont get any joy, try get out to a company that repair them, No doubt they will show you what its doing with the cover removed. There is a repair place at Cranfield

[tow1709]

IO540

Eric died about ten years ago. He got into a bit of trouble with his gyroscope work, as some of his claims were perceived to contravene Newton's laws of motion!

TOW

[IO540]

I do recall him claiming that gyros did things which were (at the time, 1975) not fully understood.

Whether he was correct I have no idea.

[likair]

Hello


Is a 2 axis-gyro, that measures vertical change has;
1 degree of freedom at the horizontal axis?


Thanks

[Gertrude the Wombat]

Gyroscope physics and mathematics is bad enough. What you do to them to make useful aircraft instruments is worse. And what happens when people who don't understand them write "model" answers to sample examination questions in "confuser" books is worst of all!

(Example: a question about whether your "gut feel" goes in the same or opposite direction to a gyro. Long involved ramble about inner ear hairs and air vanes on gyro rotors and so on. All complete bollocks - all you need is a one-sentence understanding of general relativity which enables you to say "neither your body nor the instrument can tell the difference between gravity and acceleration".)

[SNS3Guppy]

Understanding gyroscopic principles is important, and is NOT a waste of time. What applies inside the instrument in your cockpit applies to a spinning wheel after takeoff, and applies to the forces acting on your propeller, too.

What isn't needed is an indepth knowledge of the physics involved. The principles, however, are important.

Inside your gyroscope is a heavy piece of metal that spins. It may spin due to an electric motor function. It may spin by air being introduced on one side of the case and and sucked out the other...blowing on a wheel that spins. It may even be done in another manner using advanced systems that acutally replace the gyro, or use lasers...but those aren't applicable here. A basic vacum powered gyro, which is nothing more than air blowing on the gyro internally to make it turn, is what you'll find in most light airplanes.

An object in motion tends to resist changes to that motion; this is the case with the gyroscope. It tends to stay rigid in space...it resists being turned or moved. It resists so well, in fact, that when put inside an instrument, the instrument turns around the gyro. The gyro serves as a stable reference...so that it can be used in a simulation of a compass, for example...always keeping a stable reference as the airplane turns and climbs and dives. The gyrocompass, or heading indicator, is one such instrument. An attitude indicator is another. By using internal gearing, a pictorial representation of the airplane can be attached to that gyro. the gyro maintains it's relationship to the horizon or the sky, depending on how it's designed, by simplying staying spinning all the time...and as the instrument is moved about, the picture on the instrument appears to show what's going in the world outside the airplane.

The reality? the gyro is the world...the gyro is what is stable and stays in it's relative postion...not the airplane, not the instrument case...we simply use mechacal linkages to help produce a picture, based on the stable gyro, of the world around us.

You say you don't understand the gyroscope, but I'm sure this much you get, already. What you may not get is how gyroscopic precession works.

If you really want to get a good example of how a gyro works, take the front wheel off a bicycle. hold it with the axle vertically, one hand one each side, so you have a hand on top holding one end of the axle, and one hand underneath, holding the other end of the axle. Then have a friend spin the wheel quickly. Once the wheel is spinning, attempt to rotate the wheel slowly so that it's oriented up and down, and the axle is oriented horizontally. You'll feel the rigidity of a gyroscope, and you'll get an instant understanding of the principle in a more sure way than reading about it or even watching a video.

Gyroscopic precession works in a way you'll see with the bicycle tire. If a force were imposed on the wheel at the rim, such as pushing on the wheel as it spins, you wouldn't see the wheel moving where it was pushed. If you're holding the spinning wheel with the axles horizontally, for example you might try to move the wheel so that the top end, held at eye level, moves to your left. That's not how the wheel will react, however. A property of a spining mass, when a force is exerted upon it to turn it, is precession. Instead of that wheel moving to the left, it turns in a different direction.

Imagine that wheel being held with the axle horizontally, parallel to the floor, one end in each hand, and the top of the wheel at eye level. It's spinning away from you, with the top of the wheel spinning away, and the bottom end toward you. Imagine that, if you will. Applying a force at the top of the wheel (you can do it using your hands on the axle, if you will...you can feel it just as easily like this by tipping or attempting to tilt the wheel) will make it move. In this case, you're attempting to make the top of the wheel move left. Instead, the forward part of the wheel, farthest away from you, moves left. The wheel moves in the same direction you tried to push it, but 90 degrees forward in the direction of rotation. You pushed at the top, and 90 degrees ahead is the part of the wheel opposite your chest. There, the wheel moves left.

You can study the math to learn why, or simply accept that it does this. I suggest the latter. This explains the forces on your crankshaft and engine mount when making turns and violent maneuvers. It is a basic principle that the designers of a gyro use to make the instrument work. It's a force that affects the tires or an aircrat during retraction when spinning (considerably more on big airpanes than small, of course), and even the rotor of a helicopter or gyroplane.

What's more important for you to understand is that the gyro needs to spin fast to be rigid enough in space to work. When we say rigid enough in space, we simply mean rigid or resistant to tipping, tilting, wobbling, etc. The bicycle tire or the toy gyroscope will be turning at a few RPM's, but an aircraft gyro is spinning between 18,000 to 36,000 rpm's. It's pretty darn rigid in space, and if in good shape, very stable, too.

If you've ever spun a child's top, the little toy that spins and stays stable, you know gyros. And you know precession. Take a child's top, spin it, then touch one edge. There you go.

Most gyroscopes work up to a point. Tilt them too far, and they "tumble," or tip over internally and take a while to set themselves up with proper orientation again. Setting up for proper orientation is referred to as "erection" or establishin the gyro in a stable manner in the direction it needs to be to do it's job. In most attitude indicators, the gyro is oriented vertically, and in most heading indicators, it's oriented horizontally. These are sometims referred to as the vertical and horizontal gyros...though the direction of motion and of the axis really isn't important and can be either way...it's all inside the instrument and what needs to concern you is what you see on the outside.

What's important for you to know as you view the instruments are what happens when they're not properly powered, what they tell you when they're working, and what they don't tell you, or tell you incorrectly, when they're not working.

Gyros are typically either vacum (air, pneumatic) powered, or electric. Some gyros will have a flag which drops down in front of the instrument when the power source is lost...this is generally the case with electric gyros, but not air driven gyros. In an air driven gyro, a suction source is created either at the side of the airplane (venturis) or in the engine area (vacum pump, manifold tap), and this suction source draws air through the vacum system. It's air being sucked through the case of the instrument that makes it work. We will see a vacum gauge which tells us what the value of the air passing through the instrument is...or more specifically, the value of the suction. Not enough suction, and we don't get enough air through the case, and the gyro won't spin fast enough...the instrument isn't reliable.

Too much vacum usually means some kind of a blockage in the system...which ironically means not enough air flowing through the instrument...the gyro won't spin fast enough, and the instrument isn't reliable.

In a light airplane, most often the gyros are pneumatic powered. Most of the time this is with a vacum pump, driven from the engine, and most of the time it's a dry pump made of fragile carbon vanes, internally. These break easily, and it's not uncommon to have a vacum pump fail. I've probably seen 50 or more of these fail in flight over the years, and long ago lost track of the number of vacum pumps I replaced. What this means is that your instruments shouldn't be counted upon, especially in the case of a single engine airplane with but one vacum source. For this reason, it's important to keep the vacum gauge in your scan as you look over the instruments...make sure you have a valid source of vacum to keep those instruments flowing.

Next you need to know what the instruments tell you...for this you don't need to understand much of gyros, other than to know they're working in your favor.

Next you need to know what the gyros aren't telling you. All aircraft instruments lie, and using them is as much knowing that they can't do or don't tell you, as what they do. You've likely already seen this as you come to understand compass errors, altimetry, etc.

Your attitude indicator will show a slight climb when increasing forward speed, and it will show a slight descent when slowing down. I always remembered this the same way I saw it in a car; step on the gas pedal at the stoplight and the front of the car would rise up. Step on the brakes at the next light, and the front of the car goes down. Why does it do this...precession, but don't bog yourself down trying to understand why...it's precession and it has to do with the internal construction of the instrument.

Your heading indicator will drift with time...the heading will change and becomes less accurate as time goes by. The heading indicator isn't a compass (in most cases), it's just a stable reference that's easier to read than a wet compass...because it's gyro stabilized. You do need to check it against the compass and reset it frequently. The amount it drifts in heading depends on the condition of the instrument (worn bearings, for example affect the rate and manner in which the instrument precesses), as does the type and amount of maneuvering you're doing. In straight and level flight, the instrument doesn't precess nearly as much as it might if one were doing roll reversals and steep turns.

Your turn and bank indicator, or turn coordinator (different instruments telling you similiar things) works because of precession. The instrument measures the rate of precession through mechanical linkage, and this is used to tell how fast you're turning. The way in which the gyro is oriented in the instrument determines whether it's a turn coordinator or turn and bank indicator...a turn and bank indicator provides information only regarding the rate of turn, while a turn coordinator provides information about rate of turn and the rate of roll. Neither one tells you about angle of bank....because these aren't set up mechanically to do that. (That's what the attitude indicator is for).

Once you've seen the basic principles at work for yourself, such as with the childrens top, the toy gyroscope, and the bicycle tire, then you need to get familiar with the instrument indications. With this knowledge in hand, you know most of what you need to know. Any deeper you delve may satisfy curiosity, but won't help you fly the airplane. Knowing those basics will also help you understand why the airplane behaves the way it does during pitching motion or turns, as a function of propeller gyroscopic action.


A few pictures, and some explaination:

Precession - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Precession)

[youngskywalker]

Guppy, you have far too much spare time to be a Pilot! Doesnt your local FBO have a decent coffee machine and cute girls behind the counter?

[SNS3Guppy]

Probably, but I never make it to the FBO these days and the cute girls could be my daughters...and I'm married. My wife doesn't even have to be there and I can still feel myself getting cuffed upside the head just for looking. It tumbles my gyros...

[Crash one]

Guppy
I have a question, Why is it necessary to reset the gyro direction indicator periodically due to precession but it is not required to reset the attitude indicator?

[Keef]

You should be able to scrounge a defunct electric turn coordinator from a maintenance outfit. Take the back cover off so that you can see the innards, then shove 12 volts into it.

Watch the gyro spin up, then turn the thing and observe how the rotating bit doesn't want to turn, so the spring stretches and the little aeroplane leans over. Turn it the other way and see the other spring get pulled and the aeroplane lean the other way.

If you've got one that's still got some life in it, you'll find it difficult to turn it past "max rate" on the scale while holding it in your hand.

An AI would need a supply of "suction" to make it spin, and there's more going on in there. Get your head round the turn coordinator, and then use that understanding to do the AI.

Or, if you're near Southend, pop in and I'll demonstrate a TC.

[SNS3Guppy]

I have a question, Why is it necessary to reset the gyro direction indicator periodically due to precession but it is not required to reset the attitude indicator?

That's an excellent question, and one that really needs a diagram to properly explain. Mike Busch does a good job in the following article:

The Gyro with an Attitude (http://www.avweb.com/news/avionics/183240-1.html)

The attitude indicator has a different function than the heading indicator. it's job isn't just to be stable in one plane, like the heading indicator. The only job of the gyo on the heading indicator is to maintain a stable platform to give a reference better than the compass...one that doesn't lead and lag and have acceleration and dip errors. The drawback is that it needs to be reset occasionaly, and the amount is owing to it's condition, the condition of the bearings, it's speed, the amount of maneuvering and precessive forces applied to the gyro, etc.

The attitude indicator must remain erect or upright, all the time. It's sole purpose is to give a true picture of the world outside, around the airplane. It's got to have a way to find up...not such an easy thing to do, if you think about it. It's got to have a way to stand that vertical gyro up, or "erect" itself, without any pilot input. the pilot can always refer to the wiskey compass to set up the heading gyro (and in more advanced aircraft, flux gate compasses do this automatically).

Some attitude gyros incorporate a "fast errect" mechanism using electrical input, others use a mechanical pull knob to "cage" or fix the gyro in an erect position...useful when doing aerobatics, and also for quickly erecting the gyro. Once it's up to speed and upright, it needs to stay that way. The gyro uses a weighted gyro gimbal, as well as "pendulous vanes" which direct the flow of air through the gyro case, to force it upright.

A pendulous vane is just what it sounds like. it's an exhuast port through the gyro assembly, which is covered by a pendulum. The pendulum hangs down, blocking the exit. If the gyro is tileted in a manner that causes the pendulum to swing free of the exhaust port, the airflow out the exhaust port creates a force, a "jet" if you will that helps upright the instrument internally.

This can only protect against so much tipping...if the instrument is tipped too far, it may "tumble" and then have to erect itself again.

Attitude indicators do precess, however. As mentioned before, acceleration errors cause the attitude indicator to show a slight climb when increasing forward speed, and dip a little to show a slight descent when rapidly slowing. Other fairly insignificant precession errrors also occur with the attitude indicator.

The short answer to your question is simply that the heading indicator and the attitude indicator are designed for differrent purposes, and act differently becase of their internal mechanical construction.

The following link contains a number of different instrument explainations, which may be useful:

attitude indicator (artificial horizon) (http://www.pilotfriend.com/training/flight_training/fxd_wing/attitude.htm)

The following link contains some good diagrams of pendulous vanes at work:

4-4 (http://dauntless-soft.com/PRODUCTS/Freebies/Library/books/IFRH/4-4.htm)

Another powerpoint presentation on instruments. Gyro information and diagrams begin on frame #21:

freegroundschool.com/Free%20Ground%20School/Files/Aircraft%20Instruments.ppt

[Tinstaafl]

Find an instruments repair shop - they nearly always have a box full of old, defunct and unrepairable out-of-tolerance instruments. Beg them for a suction driven AI, suction driven DI and a TC or T&B. Remove the casing screws so you can remove the gubbins and also attach a piece of tubing to the air intake. Blow through the tube and watch the magic occur!

A suction driven gyro will work just fine for demonstration purposes. I used to have one of each in my instructing days. Wish I still had them but they're long since lost now. :(

[IO540]

Why is it necessary to reset the gyro direction indicator periodically due to precession

Most of the time, the answer is that the DI is a piece of crap which has not been serviced in decades, and it suffers from excessive friction. Precession doesn't come into it.

Precession does account for a gradually accumulating error (due to the earth rotating so the N pole shifts as you are flying along) but from my recollection is it very small - far smaller than the kind of drift one sees on the training spamcans which would often lose 10 degrees every 10 minutes. The schools blame it on 'precession' because it looks better.

[SNS3Guppy]

Any force bearing on the operation of the gyro induces precession. Friction from uneven ruby bearings in the gyro gimbal mounts and pivot points is one such force; this force imparts precessive action on the gyro during routine operation, and it drifts. This is precession.

The single most common source of uneven gyro bearing wear? Sitting in the tie-downs on the ramp (or apron, if you will). As the gyro sits, not being moved, and the airplane rocks in the wind, the bearings wear unevenly, and this does more to damage the gyro than many hours of operation. Another source of damage is moving the airplane before the gyro has stopped spinning down. If the airplane is moved while the gyro is destabilizing after the airpalne has been shut down, it imposes significant forces on the bearings, which dramatically increase bearing wear and cause instrument damage.

In any event, the end result of such wear and damage is increased rate of precession.

[maxdrypower]

Thanks very much for the replies guys , but look at date of post Ive done the ATPL's and the CPL since then .
And no im still not 100% Sure of bloody gyros
1 _ R T
2 i E A
2 i S X
2 _ T D

This table told me all I needed to know . (for certain questions anyway)

[Fuji Abound]

Guppy

Understanding gyroscopic principles is important, and is NOT a waste of time.

Any chance of the in a nut shell version please?

:)

[SNS3Guppy]

That was the nut shell version.

[Crash one]

IO540
One of these days, perhaps when the Taliban discover a means of directly targetting a seleted GPS receiver, someone is going to pull the plug on your all singing & dancing GPS glass wondership & without steam driven, olde worlde, days of yore, technology you are going to be in the **** big time.
Please stop stuffing it down our throats that GPS is the only way to navigate, or remain upright.

[IO540]

One of these days, perhaps when the Taliban discover a means of directly targetting a seleted GPS receiver, someone is going to pull the plug on your all singing & dancing GPS glass wondership & without steam driven, olde worlde, days of yore, technology you are going to be in the **** big time.
Please stop stuffing it down our throats that GPS is the only way to navigate, or remain upright.Calm down, old boy. What's your problem? I never said any of the above. Anyway, if you actually knew what you are talking about, you'd know that GPS is nothing to do with attitude (aircraft attitude, not your attitude :) ).

I can navigate right across Europe perfectly well on VORs etc and have done so. It's completely feasible. You just have to keep telling ATC that you don't have RNAV. But these words are lost on you because you obviously never do any of this.

Back to the topic, a clapped out DI isn't suffering from "precession". It is simply clapped out. The flying schools call it "precession" because it sounds like it is unavoidable. Same reason they say a plane has "gone tech" when there is a queue of punters within earshot waiting to book a pleasure flight :)

Real precession is caused by the earth rotating while one is airborne. The rate of this precession is something of the order of 1 degree every few minutes, and nothing can be done about that. The traditional solution is to slave the DI to a fluxgate magnetometer, usually mounted in a wingtip, which transmits a continual correction. Planes with a slaved DI/HSI are much easier to fly straight because the heading indication is right even when the DI is clapped out.

[SNS3Guppy]

No, real precessive action is a result of any force applied to the gyro which results in displacement, or instability. Precession is used to produce useable instrument indications, as in the turn coordinator, and countered to produce a stable gyro in an attitude indicator, with pendulous vanes.

Instrument gyro precession has nothing at all to do with motion of the earth, particularly for an aircraft in flight. Gyro precession takes places as a function of forces out of the plane of rotation, and as discussed previously, occur in the direction of the force, 90 degrees ahead of the applied force, in the same direction as the direction of rotation.

An uneven gyro ruby bearing applies such a force, and the end result in a horizontal gyro such as the heading indicator, is the gyro drifting.

Brand new heading indicators drift including electric ones. This has nothing to do with unscrupulous flight schools renting clapped out airplanes. In aircraft where gyro drift is considered unacceptable, flux gate compasses and other updating systems are used to stabilize the gyro instrument, which is itself serving to stabilize the compass indication.

If you want to get away from gyros that drift, then you have to go a gyroless system. Even advanced INS units and laser gyros drift...even IRS and INS updated gyro systems drift...and these are a little more advanced, and a little more expensive, than what you see in the local flight school. We use triple INS units which most definitely do drift, each updated with independent GPS inputs, plus separate GPS units, and all updated by external ground based navaids as well, where able. This capability isn't available in a rented Cessna...one has a simple gyro on the panel, and it has it's limitations...brand new or well used. The rate at which the gyro precesses and drifts may vary somewhat with age and wear...but it's most definitely a function of precession.

Gyros drift.

[ShyTorque]

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?

[Crash one]

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!

[BackPacker]

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.

That's not the definition of precession. That's just bad engineering or maintenance.

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?

You are flying relative to the surface of the earth, not flying relative to a fixed dot in space. What you call a "straight" track is actually a curve across the surface of the earth - simply because the earth is round not flat. If the earth rotates and you don't rotate your DI with it, your DI will be off after a while. Well, not "off" in the absolute sense, but it will no longer be aligned with the earths grid (or magnetic north). That's precession. (Well, not quite, but close enough.)

[bookworm]

Precession is a change in the direction of the axis of rotation. Such changes induced by friction or mechanical imperfections certainly counts.

but it will no longer be aligned with the earths grid (or magnetic north). That's precession.

That's usually called "wander". It's not precession just because your reference direction changed as the earth rotated!

[ShyTorque]

That's precession. (Well, not quite, but close enough.)

I think that's actually "apparent drift".

[Crash one]

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.

[effortless]

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.