Airspeed calibration and daily use questions

I’m sure I had read in several places that a major difference between an analog vs a digital airspeed sensor was that the digital sensor does not need calibrated. But now I’m not so sure.

So a few questions from a long time Arducopter user, but a new Arduplane (quadplane) user:

  1. Do I need to calibrate the digital airspeed sensor? Just once, using ARSPD_AUTOCAL = 1? And then turn ARSPD_AUTOCAL off? It sounds like some folks keep it on all the time.

  2. Do I need to make sure I cover the airspeed sensor on bootup for each flight?

  3. How does the above integrate with using the PREFLIGHT_CALIBRATE --> DO ACTION? Do I need to do that for each flight? Doesn’t that mean the ARSPD_AUTOCAL will be over-written? Or perhaps I’m just recalibrating the ZERO number?

  4. Are we saying then that if I boot up the airplane on the ground on a windy day (say 15 knots/whatever), that Pixhawk will think 15 knots is actually zero?


  1. yes if done right only one time.
  2. yes. but there are some very new airspeed sensors that “claim” to need no calibration. not tested.
  3. best practice, start the uav, wait 5 minutes until the electroniks heat up. then cover the airspeed sensor and press “preflight_calibrate”. airspeed should be (with cover on around 0-3m/s) it just resets “zero” not the tune.
  4. yes. that would be very bad :wink:

analog vs a digital
analog has lower resolution and is more prone to noise if the signal wires are long.
both work fine if installed correct.

that’s why you need to have it covered on boot and Calibrate

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aamadeuss and yak…

Thanks very much.

When I put my finger over the sensor, the sensor reads 5-15 miles per hour…goes up and down quickly/randomly…shouldn’t it read zero when my finger is over the end? Or do I need to cover the static port as well?

Thanks again.

if you put your finger on the hole on the front you will trap and compress air. this will lead to a reading about 15ms/s. that correct.

if you want to test the senor. calibrate it (i use a thick glove for covering it. or some plastic pipe)
remove the cover. with no wind it should show around 0-4m/s and if you blow directly in the sensor from the front the number should go higher to 15-10m/s.

I think a piece of open cell foam should work well too.

What is the type of AS you´re using? I use this SDP33 on my Zeta FX61 with Pixracer clone. I skip offset calibration (set to 0) and do a constant calibration without problems - the airspeed ratio is always 3.0. So I think there is really no need for offset or ratio calibration.
I test my sensor with mission planner connected by blowing into the tube and looking at the AS. When i put my finger on the hole it still shows 0.0-0.3 m/s.