24th Feb 2002, 21:01
According to my JAR Instrumentation course notes the sign convention for an aircraft flying east would be negative and the opposite for west. That is, the gyro would drift by e.g. -7.94 degrees per hour for an aircraft flying East at 400 kts along 45N. Now, with a different set of notes the sign convention has changed and I'm struggling to visualise the mechanics of Transport Wander.
Any gyro boffins out there?
24th Feb 2002, 22:32
Is it not -6.66 per hour.
I thought it was Ground speed X Tan 45n divided by 60 = answer.
East in northern hems = -6.66.
Please someone correct me if Iam wrong.
26th Feb 2002, 06:58
Transport wander is negative for East in the Northern Hemisphere, and positive for the Southern Hemishpere.
Capt Pit Bull
27th Feb 2002, 05:46
You can learn signs by rote if you wish. Alternatively:
Most people know where the sun rises and sets. This tells you direction of Earth Rotation.
That is all you need to figure out sign of earth Rotation. If you can't figure it out, with a sketch if necessary, then there are all sorts of compass / instrument / navigation things that are going to be hard work.
(If stuck, I can tell you how to visualise this in a simple and effective way).
Once you've sussed out Earth Rotation for one hemisphere, the other hemisphere will be opposite.
As far as transport wander is concerned, the basic mechanism is the same as Earth Rotation. We have changed the angle between the gyro datum and the compass datum. How this happened is irrelevant. I.E. the effect is the same whether the earth rotated us around through space, or whether we flew round the Earth, or a bit of both.
Any time you fly the same direction as the Earth rotates, Transport Drift gives you more of the same (so same sign as Earth Rotation in that hemisphere).
Any time you fly in the opposite direction as the Earth rotates, Transport Drift causes the reverse effect, so opposite sign to Earth Rotation for that hemisphere.
Take that on board and you'll never need to memorise another table of plus and minus signs again! And you'll be able to recreate it from scratch should your brain dump in the middle of an exam.
28th Feb 2002, 04:52
Well thats cleared that up then.I would advise getting thru the exam by hook or by crook and if yu are a pilot ,land at the nearest airport if all yer nav stuff packs up and go to a hotel as soon as posible till its fixed.
The only transport you should need to "wander" about is "wanderng" where the hotel shuttle bus is.. .Hope this helps.