Poor filtering is poor

I noodled around with the data from the road test, passing it though a 25-tap lowpass FIR filter. Here are the results -- purple is original, and green is filtered. The X axis is in seconds:

Looking more closely, we have:

Notice the 1 second delay, and the DC bias. Clearly this is not okay.

Now it's true that I studied signal processing at some point in my life, but that was literally 30 years ago. :) So I have a big ramp-up I need to do, and clearly I need to learn about, and implement, a proper Kalman filter.

The data above is nominally at 20 Hz, but because I have had trouble getting timers to work on my Arduino, what this really means is that I acquire data with a 50 millisecond delay in between. This is no way to acquire data. :)

And finally, it's possible that the road environment has more turbulence than flight, so it may be that the filtering requirements for flight are less stringent, which would mean I could defer the fancy filtering until later.

Therefore what I've learned here is:

1. I need to move to flight testing sooner;
2. This means I need to figure out my airplane mounting again -- the mount I bought was a bit wobbly, and maybe I should move to using a Citabria that has 2 struts for more stability;
3. For this testing I need to buckle up and add my 2 other sensors to my probe and hope I don't fry them;
4. I also need to get Arduino timers working so my data is at a consistent sampling rate (no sense paying for a flight test then using crappy sampling); and
5. Meanwhile, I need to start learning about Kalman filtering.

That should keep me busy.