Flight 587 destroyed by a charge sheath vortex
Flight 587 didn't stand a chance. Its tail fin can withstand the buffeting of a turbulence vortex from a preceding jet, but the dry air delivered something far more deadly.
Flight 587 wasn't buffeted by the swirling winds of turbulence. It was ripped apart by forces that far exceeded its design limits.
Under normal conditions the wings of a large jet produce swirls of air from each wing tip that continue rotating for some time after the jet has past. Under humid conditions these can be visible as moisture condenses inside theswirl, and a long tube of swirling air is left behind as the aircraft passes.A small aircraft may be flipped by a large swirl, and a larger aircraft maylose lift as the aerodynamic flow of air is disrupted if it flies through a swirling vortex. But the airflow of such a vortex has little structural impact.
The dry air that morning (dewpoint 19F, Temp 37F) produced something much more intense and dramatic. As the preceding aircraft took off an electric charge developed on the wings as it moved down the runway, and the flow of dry air over the wings increased. This electrical charge was continuously discharged into the vortex on the wing tips.
This electrical charge changed the trailing vortex from a turbulence vortex of spinning air into something far more deadly: the charged sheath vortex that powers the core of the tornado tube.
A simple turbulence vortex cannot transmit forces along its length. It is simply swirling air, but the charged sheath vortex behaves like a rigid tube, transmitting force along its length with ease. The tail fin of flight 587 wouldn't have experienced the force of a swirl of air, it would have been ripped sideways by the core of a tornado expending the energy developed along its entire length. The engines may also have been ripped sideways as they moved through the charged sheath vortex.
A charged sheath vortex produced in this way by electrical discharge into the wing tip turbulence is likely to persist very much longer than an un-charged vortex.
The charged sheath vortex is only likely to develop from wing tip turbulence under dry conditions (the sort of condition that makes your clothing cling and crackle with static)
Smoke should be discharged into wing tip vortices to make the vortex visible under at risk conditions.
The following plane should not take off until the vortex structure has dissipated or blown clear of the flight path.
This information is copyright Peter Thomson 2001-2004