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• December 16, 2016 Create Date
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National Advisory Committee for Aeronautics, Technical Notes - Wind Tunnel Investigation of Six Shielded Total Pressure Tubes at High Angles of Attack

The effect of inclination of the air stream on the measured pres-
sures of six shielded total-pressure tubes (all designed for end—mounting
on a horizontal boom) has been determined for an angle-of—attack range
of approximately -30° to 65°. The tests were conducted at a.Mach number
of 0.26 in the Langley stability tunnel and at Mach numbers of 0.50, 0.70,
0.90, and 0.95 in the Langley high-speed 7— by 10—foot tunnel.

The results of the tests showed that curved venturi entries are less
sensitive to inclination of the air stream than the conical entry of the
standard Kiel design. 0f the three curved entries tested, the tube having
the bluntest entry proved the least sensitive to inclination. The
critical angle (that is, the angle at which the totalppressure error
equals 1 percent of the impact pressure) for this tube was i63.2° at a
Mach number of 0.26.

The tests also showed that the critical angle of a shielded tube
could be extended to higher positive angles of attack by means of a
slant profile. The critical angle of a tube having a conical entry with
a 100 slant profile, for example, was found to average 9° greater than that
of a similar tube having a square profile. Although the critical angle
of this tube at angles of yaw was less than that at angles of attack,
the critical angle in yaw was equal to that of the tube with the square
profile.

Tests of the effect of varying the position of the total-pressure
probe in the shield showed that, in general, no advantage was to be
gained by changing from the position used in the standard Kiel design.
Idmited tests of the effect of varying the internal diameter of the shield
showed that an increase in the diameter of the throat corresponding to
an increase in the internal area of 50 percent resulted in a relatively
small increase (2.50) in the critical angle.

The effect of Mach number on the sensitivity of the tubes to incli-
nation was shown to be appreciable. An increase in Mach mmber from 0.26
to 0.90, for example, resulted in a decrease in the critical angle of most
of the tubes of about #0.

The National Advisory Committee for Aeronautics is conducting a
series of wind—tunnel investigations to determine the effect of inclina—
tion of the air stream on the measured pressures of a number of total—
pressure tubes through a wide range of angle of attack in both the sub-
sonic and supersonic speed ranges. These investigations are being con-
ducted for the purpose of providing fixed or rigid total-pressure tubes
for use on present—day high-performance airplanes having the capability
of maneuvering to high angles of attack at supersonic speeds.