[hankbrown]

I wonder how the FDR would actually record this phenonemon - anybody know?

[ijk]

"I wonder how the FDR would actually record this phenonemon - anybody know? "

It's pretty elementary, actually. If you know the speed of the plane and it's turn rate, then you know it's acceleration (for those that did not realize it, 'gs' are acceleration). The "Indicated Air Speed" is drawn from the same source that the speed indicator in the cockpit draws it from (they used to use "pitots" for that, but I'm sure they've got something fancier now). The turn rate can then be calculated from the combination of the position of the flight surfaces during a turn and IAS (this would be well known for a particular aircraft). The rest is solved with:
F = dp/dt.
In other words, all you really need to know is where the flight surfaces are and the IAS.

[El Gato]

I wonder how the FDR would actually record this phenonemon - anybody know?

Modern aircraft are equiped to measure both accellerations and angular rates. It's how they navigate, along with GPS, Loran or other external navaid, if available. The measurements are also used in the flight control system and/or the autopilot. The FDR merely records these measurements, often at a somewhat slower rate than the navigation systems generates and uses them. Accellerations are measured, not surprisingly, by accellerometers but angle rates are measured by rate gyros (gyroscopes). You need three of each (at least) so as to measure the accellerations in or turn rates about 3 mutual perpindicular directions.