NACA-TN-4122

Abstract

Wind-tunnel tests have been made to determine the static-pressure error resulting from external interference effects of flow through the static-pressure orifices of an NACA airspeed head at a Mach number of 3 and 0⁰ angle of attack. <br>The results indicated that the static-pressure error increased almost linearly with increase in mass flow through the orifices. At a mass-flow rate corresponding to that which would be obtained at high altitudes for an airplane in a 45&#176; climb and for which the airspeed installation incorporates an airspeed indicator, a Mach meter, and altimeter, the error in static pressure would be about 6 percent with a corresponding error in Mach number of 3 percent. In a vertical climb with this airspeed system the error would be 8 percent in static pressure and 4 percent in Mach number. The static-pressure error of the forward set of orifices was not influenced by varying flow rates through the rear orifices. However, varying flow rates through the forward orifices caused a small effect of 1 percent or less on the static-pressure error of the rear set of orifices.