Airspeed calibration on moving platform

ArduPlane VTOL Plane
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1

Hello.

I’m onboard vessel and operating VTOL.

I found that airspeed calibration is not possible on moving vessel(about speed 13kts, about 26 km/h)

Because ship is moving, although I blocked airspeed sensor with cotton glove, It seems that air comes in airspeed sensor. Even though I dont feel wind blows in airspeed sensor.

The ground speed on mission planner was 8m/s and wind velocity on portable meter was 8m/s, but in the mission planner the airspeed indicates 2~4m/s after preflight calibration.

I believe the zero point was matched to 4-5m/s.

Is there way to manually calibrate airspeed sensor with portable wind velocity checker?

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Get an airspeed sensor based on a DLVR sensor.
the DLVR type airspeed sensors do not require calibration at initialization and allow ARSPD_SKIP_CAL to be set to “1”, avoiding the need to cover the pitot during initialization.

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You could try using a shunt valve to make sure that both.aides of the sensor see the same pressure during calibration.

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Thank you for all the answers.

I found “ARSPD_OFFSET” parameter in parameter list.

can I change this for zero adjustment for my airspeed sensor while moving?

for example, if portable wind meter is “8m/s” when the ship is moving,

can I adjust “ARSPD_OFFSET” and make airspeed sensor value to “8m/s”?

I wonder which parameter is changed by PREFLIGHT_CALIBRATION.

if only ARSPD_OFFSET changes while PREFLIGHT_CALIBRATION, I can adjust it only. but if complex things happens while I do PREFLIGHT_CALIBRATION, I will study into it.

as I’m on the ship for long time it is not possible to get new type airspeed sensor, I have to use this type of airspeed sensor(need calibration at start-up) anyway.

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Sorry, could you explain more detaily? Im beginner here…

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do anyone have solution on this??

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hi @Truth_T ,
allow me to make a few remarks:

I have doubts that you can reliably windproof the pitot tube with a cotton glove. I use shrinktubes (sealed on one side) for example.

However, you may have been able to completely eliminate the influence of the wind, since 2-4 m/s is still a normal preflight calibration result at 0 m/s windspeed. That sounds a lot, but it’s not:
According to Bernoulli’s principle, for example an error of 5 m/s in differential pressure while preflight calibration at 0 m/s corresponds to an error of only 0.8 m/s at a wind speed of 16 m/s. (Due to differential pressure is proportional to velocity squared).

Not a good idea, among other things because of the quadratic dependence. The preflight calibration has to be done with both dynamic and static aperture covered.

Only ARSPD_OFFSET changes while PREFLIGHT_CALIBRATION

Goto the wiki:
https://ardupilot.org/plane/docs/calibrating-an-airspeed-sensor.html

Good success
Rolf

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Thank you for your remarks.

To clarify once more:

It was successful when I calibrated sensor with true wind speed of 6~8m/s, so I believe this is not the problem of the way of blocking winds. The issue arises with the relative wind experienced on the moving platform.

When the ship is moving at full engine speed, approximately 8m/s, the moving platform generates airflow on the sensor, and it affects the airspeed sensor even when covered with cotton gloves. It cannot be eliminated by gloves.

[1]Regarding calibration method, I experimented with silicon tubes in the past, but they caused the sensor to behave strangely, I guess it is because it blocks sensor entirely. Consequently, I have ceased using silicon tubes for calibration. Instead, I use transparent silicon tubes solely to protect the sensor during aircraft storage. Am I making any mistakes?

[2]I have come to understand that a 5m/s error at 0m/s wind translates to only a 0.8m/s error at a wind speed of 16m/s. Thank you for your explanation.

but, I already tried twice with this calibration. even if the difference looked zero,
calibration during moving caused “unhealthy airspeed” message after 10mins of flight and make aircraft speed to maxiumum speed(30m/s), for safety. I guess the speed was changed to maxiumum speed for preventing stall.

If the ship’s speed is 8m/s and the wind is 4m/s in the same direction, the total relative wind speed becomes 12m/s. This occurs even when the aircraft is on the deck and has not taken off.
so the calibration zero speed is not 0m/s as you supposed, it is 16m/s at bad situation. at worst, it can be 18m/s or 24m/s

Therefore, the calculation does not seem to apply in this situation(as the calibrating wind speed is not 0m/s), but I was unaware that the difference would be so small. That is valuable knowledge.

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You need to shunt static and dynamic ports for calibration. If you have pitot-static tube the easiest way is putting a loose windproof cover over it. If you run the stupid setup with pitot tube and internal static port it may not work as well. You can also use an internal shunting valve between the pipes.

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this setup was done by professional and I bought this drone about 3 months ago.

it is rather expensive thing, although I don’t trust this very much, it is built by professional,

before saying other’s setup stupid, do you understand my question? I want to ask one thing.

are you saying about particular setup on moving platform,

or are you saying about basic setup for all environment?

It seems that you are saying about latter(saying about basic setup for all environment),
you didn’t understand what I question.
the calibaration run well in the ground with excessive winds.
it is problem of the static wind comes to pitot tube when platform moves. The air moving by inertia would be generated in air hose also.
different from external wind, it can’t be blocked by cotton gloves.
blocking hole is not proper way. with opening hole, any pitot tube can experience same problem.
bring your well-setup aircraft here, and I bet that you will have same problem if you use pitot tube.
it is problem of inertia, and physics problem.

If you can calibrate your airspeed sensor while you run very fast, I will admit your saying but maybe you can’t

I guess your saying is about “how to connect airspeed sensor propely”, general things.
why do you saying about basic setup for all environments?

EOSBandi and Rolf seems to understand my questions well, but, you seems not. it is not good to tell someone stupid if you don’t understand the contents of this article and don’t have experience flying at moving platform.
Have you ever fly on the moving deck? I guess you are not.

and I can’t understand your saying.

your saying is so complex and pedantic.
so I can’t understand your saying.

I can’t google because I’m on south pacific sea. I can’t go to land.

why do you say only “shunt” instead of “covering pitot tube with cotton gloves”

for inconvinience?

it was very hard to understand your saying, and after interpret your saying I understood that it was only time-consuming things, not result in solving problem, It was only trick that saying easy thing to very difficult thing