Hydrostatic theory and G protection using tilting aircrew seats

Area of Science:

• Aerospace Medicine
• Human Factors Engineering
• Physiology

Background:

• The hydrostatic theory of blackout is widely accepted in acceleration literature.
• Disagreement exists regarding the precise thoracic origin for hydrostatic distance (h) to the eye.

Purpose of the Study:

• To determine if existing published data supports a specific origin for hydrostatic distance (h).
• To validate a refined hydrostatic model for predicting acceleration tolerance.

Main Methods:

• Reanalysis of published data correlating acceleration tolerance (T) with seat-back angle (theta).
• Application of a nonlinear equation: T = Tmin / cos(theta - phi).
• Comparison of derived correction angles (phi) with independently measured hydrostatic distances (h).

Main Results:

• A simple hydrostatic model, with h measured from the aortic valve to the eye, provided an excellent fit to acceleration tolerance data.
• The derived correction angle (phi) from 1975 data matched an independent estimate derived from X-ray measurements of h (aortic valve-to-eye).
• Acceleration tolerance data from two other seats in a 1984 study also strongly supported this refined model.

Conclusions:

• The aortic valve to eye is the most likely origin for hydrostatic distance (h) in the context of acceleration tolerance.
• Future research should standardize the measurement of h from the aortic valve to the eye.
• Utilizing appropriate nonlinear analysis methods and seat-back angle spacing will improve future study designs.