Yes sorry. My fault for using the word 'airspeed' rather than total pressure as created by forward motion. Of course you could get the true airpeed (height corrected) by using the air pressure from the vario (static pressure) sensor which is where we are with our standard vario. My explaination was simplified to try and demonstrate what I was thinking about.RightRudder wrote:An airspeed indicator displays the difference between total pressure (measured at the pitot) and the local air pressure in the free stream (static pressure). The total pressure is the pressure at pressure coefficient Cp=+1. If you use an absolute type pressure sensor rather than a differential type then you are measuring total pressure directly, not airspeed for which you need a differential type sensor.
Okay. So the TEK probe is giving us a lower or higher pressure depending upon the forward speed of the aircraft in addition to doing the calculations to give us the VS. Surely by using an MS5611 to measure the total pressure (due to forward speed) with the resultant output added in some proportion to the output of the static pressure sensor would give us the vertical speed.RightRudder wrote:The TEK probe has a hole at the back in the suction area behind the probe and measures the pressure at Cp=-1. So all you need to do is hook up a pitot to an absolute type pressure sensor and subtract its output from the static pressure measured by the MS5611 in order to compensate the vario. If you scale the value by a gain factor so that you get a compensation value which ranges say between -0.8 and -1.2 you can adjust the compensation to how you like it..
We know that from a null point (different for each aircraft) we have a known forward speed (pressure) with a known sink rate. That in our case could be treated as the zero. From that we know that any decrease in forward pressure will result in a decreased output on both sensors due to the aircraft being in a climb, and the reverse is true with increased sensor outputs. . Now this is where I loose the plot. How to use those two numbers to give us a sensible output of climb and sink due to rising/sinking air.
Yes I like the differential sensor approach. That does beg the question if that worked. Why wasn't/isn't it used in full size mechanical aircraft instruments. Maybe it is as is the possibility that the electronic dual sensor or single differential sensor is already out there.. Think I found one.. It is an Aircotec XC-Trainer vario that you can add a speed sensor to that does the job.
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