Dynamic Pressure

• Full Name: Dynamic Pressure

• Short Name or Acronym: QCF, QCR (also QCFR on the C-130)

• Measurements Provided: Dynamic Pressure

• Manufacturer or Builder of the Instrument: Honeywell / Rosemount

• Operational Status:

  • Requestable, ready for deployment.

• General Description:

  • The “dynamic pressure” is the pressure that develops if air is compressed and adiabatically brought to rest relative to the aircraft. This is normally sensed using a pitot tube, a tube pointed in the direction of the relative airflow and specially designed to be relatively insensitive to small-angle changes in the direction of the relative airflow. The excess pressure above the ambient is equal to 0.5 times the air density times the airspeed squared, so this excess pressure can be used to determine the airspeed of the aircraft. On RAF aircraft, the measurement of dynamic pressure is made by combining a measurement of static pressure with a measurement of the difference between static pressure (at the static buttons; cf. the section on static pressure) and dynamic pressure (at a pitot tube). The latter difference is measured by a Honeywell digital transducer on the GV and by a Rosemount Model 1221F transducer on the C-130. Because any errors affecting the measurement of static pressure also affect the difference between dynamic and static pressure, the same corrections that are applied to static pressure (for errors in the pressure delivered by the static ports) are also applied to the measured difference between static and dynamic pressure. See the discussion of processing algorithms in the “Documentation” section at the end of this page.

• Measurement Characteristics:

  • GV: Range: 0 - 5 PSI, Accuracy: 0.001 PSI Typical, Response Time: 0.05 s
  • C-130: Range: 0 - 125 mb; Accuracy: 0.7 mb; Time Response: 0.02 s
  • Overall estimate of uncertainty: 0.001 PSI
  • Response time: 50 ms / 20 ms
  • Precision:
  • Other measurement characteristics (comments on signal/noise, bias limits, etc):

• Lead Contact: Allen Schanot

Documentation

• Operating Manual (GV): PPT User Reference Manual

• Descriptive Publications
• Documentation of the Processing Algorithm(s): See the Technical Note on Processing Algorithms at this URL (fix when available)

  • Memo regarding corrections ("PCORS") applied to dynamic and static pressure

  • Presentation used for discussion of the above memo

• (Other)