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Jul 03, 2017, 01:12 AM
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Speed estimation with Doppler effect.

First you need a sound file of your flight. Remember that the closer the pass to the microphone the more precise will the estimation be. If the passes are too far from the microphone the frequency analysis (and therefore the speed result) will not be real.
Second you need a spectrogram progam, which can be downloaded from internet, but you can also find as app for android in the playstore. With this program you will see graphically (and read) the incoming (higher) and outgoing (lower) frequencies (remember that the more preccise the reads will be the more real the result will be).
Third you need to calculate the sound speed, which depends on local temperature (C) and humidity (%) of the moment (this latter is not much effective and could be ignored, but temperature is important as it could change results significantly), but this is included in the datasheet supplied herebelow. I suggest to separate the single passes audio and produce multiple frequency readings in order to have more speed computing which can give an idea of your model speed (input data are to be placed in the orange columns).
Hope this will be helpful for all those that do not want to put a gps data logger on the plane.
Finally remember that all the apps using Doppler effect to compute the speed of your model ignore the humidity datum and get the local temperature datum from the meteo system, that is why they require the gps to be on, therefore they can not be used on a second moment. If they do not ask the gps to be on do not trust their results.
Last edited by eagle60; Aug 16, 2017 at 12:33 AM.
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