Wednesday, February 10, 2021

N291DR is re-balled!

There has been a bit of a hiatus when we were in between old and new designs for the probe and display, and our test ship N291DR was devoid of an Airball.

One of the issues was electrical interference. We were powering our Raspberry Pi display from a USB adapter plugged into the 12V "cigarette lighter" port in the plane. We discovered that the Waveshare LCD panel in our display for some reason backwashed enough noise into the airplane that it defeated the squelch on our radio!! So we were trying to think of solutions.

Now meanwhile we have a new display being built by PCBWay in China as we speak, but this is not here yet.

What we now have is the display wired into the same breaker as the power to our removable GPS. These are now both non-critical devices sharing a 1 amp breaker. All seems well:

The probe is now mounted as you would expect, GoPro style:

So how did it all work out? So far so good. The new probe, with the bogo-calibration we did a while ago using the car on the highway, actually displays a much more "reasonable" IAS than the old one, and I suspect it's more accurate than the ASI in the plane.

There are two main problems we need to work on:

The first is that the Wi-Fi connection from display to probe takes a long time to be established. This is just a need for wpa_supplicant tweaking on the Raspberry Pi. This is super minor.

The second is more annoying. For some reason, our probe "bottoms out" in its AoA measurement before our plane gets to stall AoA. That's super annoying, and also sad because it could be solved with proper calibration had it not been for COVID. But these are the breaks.

We had more "straightforward" calibration and performance with the old probe geometry that had the static pressure "tube" sticking out of it. If we need to go back to that, we will. The actual sensors and electronics will be exactly the same. We'd make a slightly different 3D printed blue part and stick the same hoses into that.

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