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Flight Test Results from Two Total Temperature Probes for Air-Data Measurements up to 2014°K (3625°R)

Measuring air-data parameters is one of the difficult tasks associated with flight-test
programs on research aircraft. Flight measurements of velocity, Mach number, total tem-
perature, and other parameters are needed to plan and conduct research flights as well as
to evaluate research findings. In the X—15 program, a combination of data from onboard
sensors, ground-based radar, and meteorological soundings was used to obtain the needed
air-data parameters (ref. 1). One of the onboard sensors which proved to be particularly
useful was a shielded thermocouple probe which measured free-stream total temperature.

Interest in techniques of measuring free-stream total temperature beyond the present
capability of thermocouple probes led the NASA Flight Research Center to install a piggy-
back temperature probe package on the X—15 airplane for several flights. The experimen—
tal package contained a fluidic oscillator temperature probe and the previously tested
shielded thermocouple probe (ref. 2). These probes were exposed to the large range of
total temperature and the accompanying variations of airplane Mach number, altitude, and
angle of attack which occur over a flight range extending from subsonic to hypersonic
speeds.

This report presents and analyzes data from the fluidic oscillator temperature probe
and the shielded thermocouple temperature probe from four X-15 flights. Total temperature ranged
from approximately 244° K (439° R) to approximately 2014° K (3625° R), with an accompany-
ing Mach number range from approximately 0.8 to approximately 6.7. The altitude range extend-
ed from approximately 13,700 meters (45,000 feet) to approximately 81,500 meters (267,500
feet), although probe data were not obtained over this entire range. Data were obtained under
rapidly changing flow conditions because of the rapid accelerations and decelerations encountered
in the X-15 flight.

In the analysis, the total temperature measurement from each probe was compared
with free-stream total temperature. Free-stream total temperature was calculated from free-
stream velocity and ambient temperature, obtained from ground-based radar and meteor-
ological soundings. In addition, velocities and Mach numbers derived from probe temper-
atures and ambient temperatures were compared with free-stream values. Differences
between total temperature, velocity, and Mach number derived from each probe and the
corresponding free-stream parameters are shown for a range of free-stream and local flow
variables.