Drift

[radeng]

How do you measure drift on a transoceanic flight? Does the Doppler nav look sideways as well as forwards, thus calculating drift? GPS would do it, but I don't see how inertial could. I know smoke flares aren't dropped any more........Over land, the VOR or even an NDB would tell you, but way out at sea, how's it done?

[Rainboe]

Come on lad, jerk yourself up to date! You seem to be locked in 70s thinking. I hope you haven't got hippy hair and flares still, and listen to New Seekers and Bay City Rollers music!

Inertial knows heading (input from servo compasses). It knows track- it works that out itself. Therefore difference =drift. Doppler is history by 30 years now! VOR/NDB only lets you assess drift to an approximation of a couple of degrees. Inertial even has input into memory a worldwide grid of iso......iso......(lines of equal magnetic variation) so when variation changes between you and VOR stations (as it does over short distances in Canada and the US), it knows to allow for them. But we don't use VOR anymore anyway (next paragraph)

It's quite a thought, but most airline flights with GPS/Inertial never even make use of VOR or NDB, at all. They are doomed. When you can go out and buy a car satnav for less than £60, what is the point of maintaining into the future a worldwide network of expensive ground based radio systems? The age of satnav/mini inertial for aviation is coming.

[radeng]

OK rainboe, I must be thick. How does inertial know it? The gyro tells you change of heading, but assuming no or minimal precession, surely you can be on a constant heading with a cross wind drift? Why do you not need an external reference?