Conical Probes are generally used for static
pressure, total pressure and direction
measurement in supersonic streams. The straight heads
are usually mounted in a special holder.
As pitch and yaw measuring
probes, they can be mounted in a holder with angular adjustment in two directions and the angles determined by balancing the pressures measured
at opposite sets of holes. The angles can also be determined
up to about 16° with the probe in a fixed position by
reading the pressures
and calculating pitch and yaw angle from the readings. Where
the air stream has a pitch or yaw angle of less than 10°, the average
pressure of the four holes corresponds closely to static pressure of
the same cone at zero angle of attack.
The static pressure measured
on the surface of the cone can be corrected to true stream static theoretically, following curves of the general shape shown in Fig.
1. Total pressure of Types | B and D can also be corrected theoretically to
give free stream values so the
probe is useful as
a supersonic velocity probe. The total pressure
holes in Type B and D give a blunt tip to the
cone, which will affect
the static readings if the
ratio m/n (Fig. 2) is less than 25.
This limits the
minimum size of probe of this type which can be
used
with purely theoretical corrections since
the minimum size of blunt tip
is approximately
.025". However, a smaller m/n ratio can be used
if the probe is calibrated against some other
standard. Types
A and C probes are more
convenient for static pressure measurements in
the smallest sizes.
National Advisory Committee for Aeronautics,
Technical Note 2190, describes tests made on
conical tip probes and gives
references for the
calculations necessary to correct the readings
to stream static and total. Other NACA reports
TN 1428, 2579 and
3213 give further information
on the use of conical probes. |
Type SA:
4 hole tip for static pressure only, straight stem.
Type SB:
5 hole tip total and static pressure, straight stem. |
Type SC:
4 hole tip for static pressure only with 90° bend.
Type SD:
5 hole tip for total and static pressure with 90° bend. |
