Servers by jDrones

Expected behaviour in case of in flight pitot ice or water ingestion?


(Fredrik Falkman) #1

Can someone enlighten me as to what to expect if my air speed sensor readings were to be affected by ice or water in flight?

Also are there any rc scale ways to cope, like pitot heating? Anything that works well?


(James Pattison) #2

This is a definite problem, and I don’t think there is an ‘off the shelf’ solution. The size of the pitot makes it susceptible to blockage, as you’ve identified. If the airspeed sensor is enabled and used, I actually don’t think the ekf will reject bad data from it, so if you are flying in freezing or precipitous conditions I’d recommend turning it off.

(Fredrik Falkman) #3

So what would be the result in-flight if the air-speed sensor suddenly starts reporting a much lower or zero speed? The AP trying to speed up? Or relying more heavily on GPS speed?

(James Pattison) #4

Ekf_eas_gate is the relevant param. It will reject sudden changes outside the limit set by this param, but gradual changes will be accepted I think, because the gps provides a different velocity so the two aren’t directly compared (except to calculate wind). @tridge?

(Hunt0r) #5

Here’s a fun and maybe-relevant story: I once had an airspeed sensor get clogged with mud on a “unscheduled landing” and didn’t catch it before the next takeoff.

The plane exhibited a VERY odd behavior… it couldn’t turn left! (or rather, left turns were incredibly gentle bank angles) But it turned right “reasonably” well. I could definitely tell something was wrong, but the not-turning-left was severe enough to abort the mission and come land to troubleshoot.

Moral of the story: A malfunctioning airspeed sensor can cause unexpected and strange behavior.

(Fredrik Falkman) #6

I always supposed there was a little bit of magic going on in the EKF…

(Hunt0r) #7

Indeed, the EKF is a mathe-magical thing! But the wierdness that I experienced probably wasn’t caused by it.

I’ve never bothered to dig deeper… but I think one major issue is that the plane scales its control-surface movements with respect to airspeed. Normally this makes sense… as higher airspeed makes a given aileron deflection much more impactful… but in the case of an incorrectly-high airspeed, it kills the control-surface effectiveness.

I still have no idea why it seemed to be asymmetric for me, that day. But the plane was a flying-wing with elevons, no rudder, and small asymmetries in the sensor mounting. So I am not surprised when odd flight behavior happens on this UAS.

(Andre-K) #8

based on my experience, water droplets do not affect the IAS , at least not for planes that never go below 13m/s.
What happens when it freezes, is hard to preedict, it can capture higher pressure if freezing while flying into headwind, or prevent sensing proper speed if it’s just clogged by ice. with results accordingly depending on situation.
it’s fairly easy to use nichrome wire and make a heated pitot.

(Kikislater) #9

What about using AHRS_WIND_MAX parameter?
It seems to solve airspeed issues but forgot once to remove pitot cover and results in a crash with full throttle and plane losing altitude after takeoff. May be I set it to high …