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View Full Version : Pile of hair on the floor (Gyro theory)

Nishko
27th Apr 2001, 15:10
So far so good, averaged 93% on all of my mock tests for far - until that is...
Gyroscopes. I am doing the BGS JAA dist course, and although the material they have supplied is fantastic, I can't help feeling that there must be a better and more comprehensive source of information regarding calculating DI wander etc. I don't know what's wrong with me, but I'm finding something isn't clicking here...

Please, any help appreciated (before I go bald).

Nish.

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"...Don't bother arguing with an idiot, he will only bring you down to his level and then beat you with experience...."

Superfly
27th Apr 2001, 17:32
Nishko, I'm preparing the JAA theory too but with OATS , if you're talking about apparent wander here are things how I understand them:
1) axis of a gyro is fixed in space
2) any point on earth will rotate with it and therefore will rotate relatively to gyro
2) Any object/person staring at indicator ring of gyro will move around it therefore the reading will increase at a rate of 15 degrees/H in the northern emisphere and decrease the same amount in southern emisphere.
3)wander is max at north/south poles 360 deg/24 hour - 15 deg/H and nil on the equator so apparant wander is function of lattitude
4)formula to find wander:15 x Sine (latitude)
so at equator&gt; 15 x SIN 0 = 0
at pole &gt; 15 x SIN 90 = 15 deg/H
&gt;&gt; let's say you're at 45 degres N of latitude then your Gyro compas will experiences a drift of + 10,6 deg/hour, so correction has to be applied on the gyro in accordance of local apparent wander.....

Hope it made it clearer..... SF

Skycop
28th Apr 2001, 03:42
Yeah, right.

That'll come in handy next time I'm flying.

411A
28th Apr 2001, 05:41
Huh? All this, grid navigation and, best of all, pressure pattern navigation (most young guys have NO idea about this), will make it easier for that handflown ILS to 200 agl. Whats next, four course LF radio range orientation? :)

OzExpat
28th Apr 2001, 07:48
There was a sh!tload more rubbish involved when I did my ATPL. This stuff is really simple by comparison.

And, yeah, just about totally irrelevant, but that's not the purpose of a theory exam, is it! :)

Theory exam candidates always have my sympathies.

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Dispela olgeta samting i pekpek bilong bulmakau!

Superfly
29th Apr 2001, 00:01
OzExpat
As you say there is sh.t load more than that but we're not rocket scientists, just pilots or wanabee pilots... so I think it's better to say less and understand it fully !!! by the way I agree there's a lot of rubbish with the theoritical part of the ATPL ! :)

Blacksheep
29th Apr 2001, 07:44
See what happens when us Avionics chaps make the navigator redundant. We're already working on the pilot thing by the way ;)

More seriously, this is a question of when old questions in the syllabus should be considered redundant. Once upon a time pilots needed to be able to cope if their direction indicator failed into DG mode. They didn't have Inertial Systems and VORs are all referenced to magnetic North. It was a good idea to be able to work out just where that was if something like, say a lightning strike for instance, knocked out all the magnetic compasses and left you with just a couple of DGs. I don't suppose there are many D.G. equipped aircraft that need an ATPL to fly them, but there still are a few about. To the unitiated GPS seems to be the fail-safe and foolproof way to find your way around but I'm afraid that it still isn't good enough for primary navigation. If you fly a non-inertial aircraft above 80 degrees north, you really do need to know how to do the DG corrections. Or hire a navigator :)

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Through difficulties to the cinema

411A
29th Apr 2001, 11:10
Personally, would opt for the Navigator. Always good for another round....

Nishko
29th Apr 2001, 13:56
A half decent GPS kit must surely be a more reliable primary instrument these days than a highly complex gyro based instrument that requires constant re-interpretation to be used accurately...? Not to mention the fact that it is full of moving parts.

Anyway, my original post was never meant to start the debate about what ATPL questions are irrelevant! That subject could be subjectively debated until the cows come home (if they ever will that is).

Nish.

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"...Don't bother arguing with an idiot, he will only bring you down to his level and then beat you with experience...."

Superfly
30th Apr 2001, 01:20
Hummmm , well you're wright the debate is not with unnecessary ATPL subjects... but you brought up another hot matter &gt; GPS. Well to be honest I've never used any as I and always found my way around.. Thanks to my map ! I'll always be sure that it doesn't run out of battery or decide to stop working well in the middle of a long X-country to an unknown area ! altough the GPS can be a saver when flying in marginal WX conditions... SF

Nishko
30th Apr 2001, 02:22
SF, I think we're both in the same camp here.

GPS is one of many navigational tools available to a pilot, and I guess it must always be the case that the PIC should use the tools that he/she sees as most appropriate for the job, and under the circumstances that prevail at the time. By definition, where one tool may gain, another may lose - and visa versa under different circumstances.

My personal pref is to use a combination of the two when appropriate to do so. Regardless what your choice of *primary* navigation tool may be - you should always have some level of backup and redundancy. It makes no difference which is primary and which is secondary, and as you rightly point out, GPS is an excellent tool, particularly under marginal VFR conditions where it could be argued as being the most appropriate primary method.

Then, it could be argued that marginal conditions for a VFR flight ought to be avoided as a product of good judgement on the PIC's part. But who knows, much of it must hinge on the Pilot's judgement, judgement that in many cases is learned through experience!

Nish.

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"...Don't bother arguing with an idiot, he will only bring you down to his level and then beat you with experience...."

ShyTorque
1st May 2001, 02:15
411A,

I too prefer to fly with a navigator. In the unfortunate circumstance of a ditching, they improve your chances of not being present for the shark attack by 50%.