Phase II Final Report - NASA's Institute for Advanced Concepts

Planetary Exploration Using Biomimetics
An Entomopter for Flight on Mars
3.4.2 Fourth-generation Concept
Figure 3-140 shows how this concept works. A split piston that moves in opposite directions
under the influence equal pressures from the same source provides a reactionless opposing
motion. The mass of the spool is negligible compared to the overall mass of the entire assembly
and its vibrational contribution will be of little effect. The concept relies upon the fact that pressure
cannot build up as long as there is gas flow into an expanding volume. As soon as the volume
becomes a fixed value, continued flow will result in a pressure rise. This pressure rise can
then act upon a pressure-triggered spool valve to redirect the flow into a different (expanding)
volume. The process is regenerative.
In Frame 1 of Figure 3-140, the split pistons are located at their innermost positions and gas
flow is directed toward the inner faces of each piston, inducing them to move away from the
center as shown in progress during Frame 2. In Frame 3 the pistons have reached their outer
limit and the volume between the inner piston faces can no longer expand. As a result, the pressure
at point A begins to rise and the slight flow-restricted pressure at point B drops to zero
when all expulsion flow ceases.
Frame 4 shows static motion of the internal pistons and spool valve as the pressure continues to
increase. In Frame 5 the pressure at point A has risen to a point that is sufficient to overcome the
spool valve holding force (represented in these frames by a spring-loaded ball detent). When this
pressure is reached, the spool valve will begin to move as shown in Frame 5. The intent is that
the force be “explosive” such that when the holding force is suddenly overcome, he spool is
driven to the right. Inertia of the spool carries it past the all-ports-closed dead point.
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Phase II Final Report