To accurately test the effectiveness of a ram air system put a selector
valve on the pitot port of your airspeed indicator allowing you to switch
between pitot pressure and manifold pressure. Compare the two indicated
speeds. If there is no change you have a great ram air system.

Use a suitable orifice in the manifold pressure line to avoid pulsing the
indicator. The orifice will not affect the reading as long as there are no
leaks in the system.

Switch to manifold pressure only at wide open throttle. Try varying the
RPM over the full range to asess induction efficiency as function of flow
rate. This will give a clue on inlet size requirements,or possible
separation on a sharp edged inlet. Try it at different altitudes and
airspeeds.

Indicated airspeed is proportional to the square of dynamic pressure. To
calculate pitot pressure multiply indicated manifold pressure by the ratio
of

(Indicated pitot speed squared) / (indicated manifold pressure speed
squared)


BILL HANNAHAN
WFHANNAHAN@YAHOO.COM



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