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I'm working on flight sensors for a project and I'm supposed to model noise in the Static Port, Pitot tube, and TAT probe measurements. I looked a lot for it online and could not get a convincing answer.

I need the uncertainties of Static port, Pitot tubes and TAT measurements. By uncertainty, I mean + or - certain pascals for Static port and Pitot tubes and + or - certain degree Kelvin for the TAT probe. Is there a typical uncertainty value for these, say for example a Boeing 747 and I guess a digital sensor as the worse case? I don't know much about the companies supplying these sensors or the installation method on the aircraft.

It would be great if someone could help me! Cheers!

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  • $\begingroup$ This question is really too broad, as the answer would be affected by all sorts of factors: Which aircraft, which pitot tube/static port, the actual installation of the aircraft. Are you using an analog or digital sensor. Digital sensors would have their own noise you would need to filter out. $\endgroup$ – selectstriker2 Sep 11 '17 at 15:27
  • $\begingroup$ I have modified the question to make it easier. Thank you! $\endgroup$ – controlfreak Sep 11 '17 at 15:46
  • $\begingroup$ I'm also confused as to what the purpose is of modelling "noise" when you don't have a defined sensor, pitot tube, static port, or outside air temp probe. Each one is going to be different. $\endgroup$ – selectstriker2 Sep 11 '17 at 20:51
  • $\begingroup$ It is for demonstrating noise effects in an ADIRU algorithm. All I need is a typical value of uncertainty in each of these sensors for a wide body jet, as I couldn't find those. My noise model is ready and I all I need to finish them are these uncertainty values. $\endgroup$ – controlfreak Sep 11 '17 at 21:14
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The pressure and temperature measurement devices are analog instruments, extracting parameters that are of value to pilots from physical phenomena. Unfortunately, the physical world throws in a variety of effects, linear and non-linear, that make it difficult to extract the parameter of value. Noise is one of them, but in a way that is exactly what we want to measure since pressure is just the average value of noise in the speed of gas molecules in air.

In the pitot tube there are a couple of effects that make the measurements non-trivial:

  • Friction between the air and the tube causes a velocity distribution that varies with flow radius relative to tube radius.
  • Fluid mechanics causes different behaviour at different conditions, such as laminar or turbulent flow, or supersonic shock waves.
  • Inertia of the particles creates a time delay in pressure measurements as a function of airspeed and could can cause back pressure surges.
  • Old fashioned thermodynamics such as the ideal gas law impose non-linear functions on the relationship between pressure, volume and temperature.

enter image description hereFrom Wiki

All these effects need to be considered in order to measure just the total pressure and the static pressure, and then to extract the airspeed, altitude etc from these.

If it is calibration data of the sensors that you are after, that science is fortunately over 100 years old.

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  • $\begingroup$ I'm sorry, maybe the word model was confusing. I know the modelling part in a way but I'm stuck as I need some typical/realistic values of measurement uncertainties for these three. $\endgroup$ – controlfreak Sep 12 '17 at 8:41

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