G Tolerance

Forces of 3-4 G during Spiral Dives and up to 7 G in Acro

Jim Nougarolles Acro Sequence Accelerometry data (Free Flight Physiology Project)
3-axis accelerometer data during an acro sequence by Jim Nougarolles.

At the peaks of his infinity tumbles, our acro pilot Jim Nougarolles transiently reached approximately 7 G. However, more usefully for the rest of us regular pilots, we found that a consistent spiral dive of -10 m.s-1 descent rate led to sustained acceleration forces of approximately 3-4 G in multiple axes and required three times as much oxygen and energy as normal flight.

Our findings were similar to the G forces measured in an investigation by a group of Dutch pilots in 2008. Bear in mind that acceleration forces as low as 2.6 G in a single axis have been known to cause loss of consciousness and G forces in multiple axes are even harder on the body.

Key Messages

Spiral dives generate sufficient G force to cause loss of consciousness in some individuals. Everyone’s G tolerance will vary during the course of their flying career.

  1. Be aware of the factors that can reduce G tolerance, including hypoxia, low blood sugar, infection, dehydration and time away from flying.
  2. Learn techniques to improve blood flow to the brain during high G manoeuvres.
  3. The additional oxygen requirements of spiral dives may mean that lower energy manoeuvres like big ears are a safer and more sustainable way to descend from extremes of altitude.

This is a summary of one of our key findings from Phase I of the Free Flight Physiology Project. For a full write up of our methods and results, please see our our Cross Country Magazine article or our scientific paper in High Altitude Medicine and Biology.