ASI differences

[matherp]

Is there anything in the D10A which compensates for position error on the pitot using the AOA input? The reason for asking is that I am seeing differences between the airspeed reading on my RV9A on the Dynon compared to the mechanical ASI - but only at lower airspeeds. Above about 90kts they are identical but below that the Dynon reads progressively more than the mechanical as speed reduces. Both are fed of identical static sources and both use the same Dynon pitot/AOA probe

Any other suggestions? The mechanical seems more like other RV9As in terms of readings.

 

[dynonsupport]

There is no correction for position error, either by using AOA or other method. But, you can set the "zero airspeed" pressure as described in the latest manuals if you have newer firmware. This is meant to fine tune the performance of the ASI at the very low end of the range.

 

[matherp]

Thank, I'll try recalibrating.
Just a thought - if I had connected the AOA and pitot tubes the wrong way round what would I expect to see?

Thanks

Peter

 

[dynonsupport]

Generally, airspeed that under-reads and varies strangely with AOA changes.

 

[Mel]

My old D10 showed about 1-2 mph faster than my analog ASI. The new D10A indicates about 5 mph faster. All other factors (pitot, static, etc.) are the same. Is there any calibration to fix this?

 

[dynonsupport]

At what speeds is it off that far?

You can try the "zero airspeed", but this will only help with lower airspeeds.

Also, you should really check to find out which one (Analog or EFIS) is correct. We've become better at all of our calibrations over time, so there's a real chance that your new D10A is actually more accurate than the old D10. Given that both are above the analog ASI, I'm guessing the analog isn't exactly dead on either.

To answer you ultimate question, there is no way to adjust the displayed airspeed on the EFIS. We would need to re-calibrate it here at the factory if you are convinced that it is off. We can't adjust it away from reality either- when we calibrate it, X PSI = Y Airspeed. We can't make it match something else if that something isn't accurate.

We are of course happy to look at it here for free.

 

[Mel]

I'll be busy for most of December and my transponder is due in January. I'll look at calibration comparison at that point. But I like your solution that my airplane is actually 5 mph faster than the analog ASI is showing.
Thanks