HN39
Originally Posted by TU114
Also, why not turn the pitot tube around? Then, Ptot will no longer be Pstat+Pdyn but Pstat-Pdyn
I wonder what an aerodynamicist would have to say about that assumption.
An aerodynamicist would say that you won't measure Pstat- Pdyn but Pstat-base pressure on a rearward facing step - say about -0.15*(0.5 rhoV^2).differential.
A machmeter indeed, measuring the local Mach close to the airplane. But staying airborne has to do with pressures, so you still need ambient pressure (Pstat) to have something that relates to lift.
I fully agree, with the emphasis on local Mach, and close to the airplane. Unless it sticks well out into the flow it will measure the Mach Number in the boundary layer. If you stick it well out you may have a devil of a job calibrating it. The device, so far as I can see, measures Mach number along its "line of sight" which in general will not be aligned with the local flow (AoA or sidewash or both). I also wonder about sound waves "bounced" off the aircraft skin and how that might interfere with the received signal