Monthly Archives: May 1998

Turbulence

Overview of Turbulence Graph on EFIS

 

In order from left to right…

 

Code      Description

_____    _______________________________________________________________________

 

PiMo      Currently experienced pitch oscillation is causing this longitudinal axis modification

YaMo    Currently experienced yaw oscillation is causing this directional axis modification

RoMo    Currently experienced roll oscillation is causing this lateral axis modification

F_Ai       Air turbulence factor currently being experienced by the vessel’s aggregate                                                            accelerometer input

I_Ce       Estimated turbulence that should be expected at current level based on meteorological                                     data

PiOc        Currently experienced pitch oscillation varies with air density and wind shear intensity

YaOc      Currently experienced yaw oscillation varies with air density and wind shear intensity

RoOc      Currently experienced roll oscillation varies with air density and wind shear intensity

 

 

Typically, the thicker the cloud layer, the more intense updraft and downdraft activity will be experienced.  The computer then bases its estimate of the expected air turbulence (I_Ce) based on the current cell activity (I stands for Intensity and Ce stands for Cell).  These thicker cloud layers forming cells show up on the meteorological information available on the EFIS.  One should not expect to experience the full effect of the expected I_Ce in all situations.  Some cells may be building intensity and others may be diminishing and there is no display representing that stage change.  One should, however, never experience turbulence greater than the estimated I_Ce (F_Ai should never exceed I_Ce in normal conditions) otherwise an error should be reported with the EFIS.

 

The nature of wind shear is that it most greatly affects the longitudinal and lateral axis.  The directional axis experiences an average of 33% that of the other two axis.  This is due to a predominantly vertical exchange of air due to uneven heating of the planetoid.  This may be uneven between the port and starboard sides of the vessel causing a lateral oscillation, or more commonly during forward movement a differential between the bow and stern of the vessel causing longitudinal oscillations.  The longitudinal commonality does not increase the intensity of the oscillations but increases the structural strain exponentially as the vessel increases velocity through rough weather.

 

Verbal notifications only include a hull ionization report which is usually experienced in larger storms (I_Ce of more than 75%) due to the exchange of electrical charges between the clouds and the vessel.  Lightning strikes on the vessel are rare but can happen.  During flight through violent storms, non-extensionary shielding should be raised as a effort to discourage the ionization from forming.