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• June 15, 2016 Create Date
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Wind Tunnel Calibration of a 40° Conical Pressure Probe at Mach Numbers from 3.5 to 7.4

A wind-tunnel calibration of a 40° included—angle flow-field cone probe was made
over a Mach number range of 3. 5 to 7. 4. The cone probe was designed and fabricated
by the NASA Flight Research Center to obtain flow —field data on the X—15 airplane.
Estimated accuracy of the calibration was 5:2 percent in Mach number and 40. 2° in flow
angularity at a Mach number of 7. 4. Reynolds number effects were negligible over the
test range of 0. 65 million to 3. 25 million per foot (0. 20 million to 1. 0 million per
meter). A rake designed for flight on the X-15 was used to mount two cone probes.
Slightly different calibrations resulted for the two cones because of differences in
the cone afterbody configurations.

A conical pressure probe for surveying the flow field beneath the fuselage of an
X-15 aircraft has been developed by the NASA Flight Research Center. The flow field
in this region is of interest because of the possibility of mounting an airbreathing
engine on the X—15 and flight testing it over the Mach number range of 3 to 8 (ref. 1).
Design and operation of the engine and evaluation of its performance would require a
knowledge of the flow—field Mach number, total, static, and dynamic pressure, and
flow angularity. Since these parameters vary considerably with free—stream Mach
number and angle of attack, wind-tunnel and theoretical studies (refs. 2 to 4) of the
flow field were performed. However, full-scale flight data are also desirable.

Previous studies (refs. 5 to 7) showed the feasibility of using conical pressure
probes for surveying flow fields. The cones used in these investigations were designed
for wind—tunnel testing and so were small in order to minimize flow disturbances.

Also, to minimize pressure lag, pressure orifices on the cones needed to be as large
as possible. As a result, the cones were small with relatively large orifices, which
caused the cone probes to deviate from a sharp-cone theoretical calibration. The small
size of the cones also made accurate fabrication difficult.