transport wander
 

hi...

i'd highly appreciate anyone who could help me understand transport wander and apparent wander.


also... how exactly the ins finds true north

thank you

hey mate,

Gyro wander divides into 2 types.Real wander and apparent wander.
Real wander is any physical deviation of the the gyro axis from a fixed direction in space. Due to diff.forces acting on it (friction of gimbals,spin axis,turbulence...) the errors in precessing rate will slow down or accelerate the rotor of the gyro.

Apparent wander states that NO physical movement in gyro itself takes place.It appears to an observer that there has been a change in direction due to movement of earth rotation.Be
aware that the gyro still maintains its direction with reference to space as we rotate with the earth!Therefor "apparent "wander.

The formula for Total Drift (TD) =

TD=RW + LN + ER + TW

RW= Real wander , LN= Latitude nut
ER= Earth rotation , TW=Transport wander (watch out for TW east or west depending on Northern or Southern Hemisphere)

The LN only compensates if stationary on the Ground at the Latitude to which it is set up for!
Purpose:compensates for apparent wander by making the gyro process in the horizontal plane about the vertical axis.

If working on example this may help:

Northern Hem. / Southern Hem.
ER - / +
LN + / -
TW east - / +
TW west + / -

TW can also be calculatet:G/S * tan. latitude
--------------------------
6o


hope this helps,greets andi:E

addition!
 

2red2white,

just remembered that for calculating TD (total drift),
u need to put ALL the presigns (ie. + or - in brackets otherwiese
u will get wrong answer!!!

Example:

a perfect gyro is set up to give 0 degrees drift when stationary
on the Ground at 54°N.
You are at Ground at 54°N!
Calculate rate of drift and state if reading is increasing or
decreasing.

TD= RW+LN + ER+TW
As there is no Real Wander in this Question,put a cero or/
below position of RW.Then u put + and then put LN with presign
+ or - in brackets! ( )
Means : RW= 0
LN=(+15°*sin 54°N)
ER=(-15°*sin54°N)
TW=0
PS: 15°are used nml for calculating those questions (its 15.04° to be precise) and gives the rate of drift of the earth in 1 hr!)

Result: 0 {RW} +(+15°*sin54°N) {LN} + (-15°sin 54°N) {ER}+0

=0+12.35° - 12.35°+0 ==cuz of presigns drift cancelles out!!

Remember the Northern and Southern Hemisphere Presigns !!!
for this example the LN in NH is + (in SH would be -)
ER in NH is - (in SH would be +)
Hope not to have confused u more my friend! let me know please
and good luck!!!

right,as i understand it,
1/transport wander is the amount of change from its initial state caused to a gyro when it is being TRANSPORTED (ie flown,as i an installed gyro in a plane,such as the one on your DI).

2/Apparent wander is the APPARENT amount of change from the initial state,whem a gyro is stationary,ie in a plane with instruments running,but on the ground,not moving.

A gyro aligns itself with a fixed piont in space,and will remain fixed and aligned to that piont unless diosturbed.However,the earth rotates.This rotation means you'll soon find the gyro changing its alignment in relation to the initial point it was set up on.this is compounded by the fact that they actually put them in planes and fly half way round the globe...meaning much more changes.

Hope you're not too confused mate! Good luck.:cool:

Transport wander and earth rotation wander are both types of apparent wander, you need to look at some pictures to understand this.

Have a look at this page for some pictures

Real wander you get from imperfections in gyros, or from the lat nut, which corrects for apparent wander with real wander.

Finding true north, the INS does not find true north, it aligns itself with true north only if it is north-pointing inertial navigation system. A north-pointing inertial navigation system has a north gyro, this gyro once aligned with true north will tend to remain pointing to true north. As the aircraft moves from its position, the departure is used to align the north gyro with true north (15 Sin lat). The north gyro sends siglnals to the platform gimbal motors that "tilt" the platform in space to keep the platform level with respect to earth but aligned with true north.

There is some feedback via the accelerometors to the gyros if the earth rate, is not calculated accuratly, the accelerometors will sense some acceleration due to gravity and this will be fed back into the azimuth gyro to keep the platform level.

Have to be off...migh re read this later and add to it

:ok:

real wonder
 

thanks guys for helping me out with this one!