I teach that acceleration error is mainly caused as a direct consequence of hanging the needle on a pendulous pivot, (to minimise the angle of dip, of course) thus separating the needle's CofG from the pivot, creating potential for a turning moment to be created. I don't have a problem with that, my query is more to do with the uncommanded deflection of the needle when the aircraft is banked. I don't believe this has anything to do with a turning moment as for acceleration error, but is created when the needle banks with the aircraft and is therefore taken out of its best alignment with the gauss line. You can demonstrate this by taking a broomstick, facing your class/student with one end of it on the floor pointing to them, the other on your shoulder/chest/paunch/nether regions. This simulates the gauss line, dipping down toward the nearer pole. Now take a model and point its nose at them, in front of the broomstick and with your fourth hand (it can be done!) use a marker pen above the model as a compass needle with it pointing at north. I am in the southern hemisphere (NZ to be exact) so I will tell the students I am therefore facing south. With the wings level, it is easy to show the needle, pointing behind the aircraft, maintains alignment with the broomstick/gauss line. Now, bank the model, (maintaining heading, yes I know this is impossible without crossing the controls, but ..) AND THE NEEDLE WITH IT, and you can see the needle will be taken out of alignment albeit only slightly. See if you can move the needle to improve the alignment. If you have done it correctly, you will see that there is a swing, in this case, against the movement of the aircraft, and this is what causes the needle to lag. The students get a simple visual demo, without verbal diarrhoea or histrionics on the whiteboard.
This error is absent on east and west, since the needle lies athwartships in both these cases, maintaining best alignment with the gauss line/broomstick and therefore cannot improve its alignment any more. The error is also absent on the ground, since the aircraft is not banked. (Try it!)
My question is that, I can't readily explain why the movement should be the opposite on north as it is for south. Every time I try to demo it the swing seems to be against the movement of the aircraft in both cases.
I was wondering if anyone was familiar with using this method to teach this. I abandoned the pivot-point CofG method when I discovered this error does not occur on the ground.
In NZ this is required to be taught at all levels. The PPL requirement is identical to the CPL, ATPL, IR and instructor rating requirements. The only difference is in the flight tests, where the professionals are required to hit the correct headings first time (or have a good reason why not and explain exactly what happened) whereas there is a bit of give and take at PPL level.
Cheers
DH
[This message has been edited by deadhead (edited 27 January 2000).]
[This message has been edited by deadhead (edited 27 January 2000).]
[This message has been edited by deadhead (edited 27 January 2000).]