Saturday, May 18, 2019

Data analysis from previous flight

I analyzed the data from the flight with Airball and the MEMS accelerometer. First the major airdata variables:

This looks like reasonable data and fits with what I recall of the flight. Next let's look at the entire period of data collection (not just the flight) and compare Y acceleration (the lateral acceleration which we hope to correlate with yaw) with measured altitude:
We see that the acceleration jumped to 0.2g for no reason while sitting on the ground, then bounced back and continued with a really weird bias. This is clearly junk data; I don't know what went on but I need to fix it before we can draw any conclusions. Using the accelerometer on the workbench, it seems to work fine, showing +/- 1 g as it is tilted vertically one way or the other, so we have no explanation.

Finally, a few cute plots. Ever wondered about the correlation between IAS and AoA? Well here it is:
 and for good measure, here is the correlation between dynamic pressure and AoA:

Stay tuned; a friend has very kindly agreed to lend me a high-quality accelerometer....

Sunday, April 28, 2019

Accelerometer and airdata comparison flight on N291DR

Today I did a quick (0.6 hour) flight on N291DR to compare accelerometer data with the airdata probe. The idea is to see if the angle of yaw measurement from the probe is consistent with "ball" coordination or whether it changes with airspeed / AoA / .... The setup involved a data logging laptop strapped in with the seat belt into the passenger seat:

The probe itself should surprise no follow of this blog but it was on the pax side this time, to be closer to our receiver:

As for the accelerometer, this was an interesting challenge. :) I had a SparkFun ADXL 345 breakout board requiring I2C or SPI connections. I found an I2C to USB adapter I could use with my PC. However -- that requires knowing all the setup of the ADXL 345 chip and writing a "driver" for it from scratch. Meanwhile there's already a driver library written by SparkFun ... but it is for the Arduino. Perversely, therefore, the "easiest" way to get data out of the thing was to run a tiny program using the SparkFun library on an Arduino, and send the data via the Arduino's serial to USB connection to the PC. This is the accelerometer board, clipped to the glareshield in the center of the airplane:

Bonus points, I say, for finding a way to include an actual breadboard and jumper wires on the "avionics" of a flying aircraft. :)

For the wireless connection, I used a simple USB adapter to the XBee module, and clipped it to the glareshield:

We have a total of 1 hour of logged data, where the actual Hobbs time on the flight was 0.6 hours, and the actual flying time somewhat shorter. We will be crunching through this and reporting back. Meanwhile enjoy the pictures of the pretty Airball test ship:

Sunday, April 14, 2019

First flights on N291DR

Yesterday I flew our first flights on our new test ship, N291DR. We are already geared up to mount on a RANS S-6S so it was pretty easy. Here are some pictures of the setup:

We need a better place to mount the display -- we have a RAM mount on the upper framework but that's hard to see. In any case, though, we did make a few important observations:
  1. Basic operation of the probe is good.
  2. Our altitude math is totally off. Need to figure out what's up.
  3. The air was quite turbulent and the ball jiggled a lot; maybe we need some filtering after all.
  4. For some reason, the wireless connection kept cutting out.
I was doing takeoff and landing practice, and using my store-bought ASI as my primary reference but every once in a while peeking out of the corner of my eye. From that quick observation, it does appear like the AoA and yaw information is pretty useful and sensitive and I could, if I wanted (and if the system were more reliable, and mounted more in my field of view) fly using it.

I'll be trying to fix our altitude math and then doing some post-analysis of the data in the coming days.

Saturday, March 2, 2019

Airball has a plane and a posse

Greetings! Watching this blog, you might think that Airball is somehow pickled. Nothing could be further from the truth.

So far, we have been flight testing on certificated aircraft, relying on the kindness of friends and trying to make our mountings as temporary as possible. This has limited what we can do. So for the past few months, I have been arranging access to an Experimental Amateur-Built (E-AB) aircraft we can really do some serious testing on.

I am proud to offer you the Coyote Valley Sport Flyers, a new flying club based in San Jose, CA (KRHV), which owns N291DR, a Dave Rigotti RANS S-6S "Coyote 2". At this point we are 4 pilots with an equal share in the airplane.

Our club motto is adverso vento ululantes, which means, "howling into the wind".

You can follow our adventures on Facebook at:

I have been getting my tailwheel endorsement in the plane and I can say it is the perfect testbed for Airball. It's a very predictable, simple rudder and tailwheel bush plane with lots of power and climb, and excellent glide performance.

Due credit goes to Dave Rigotti, of Chesterland, Ohio, who did an amazingly great job building the airplane. We cannot thank him enough for his care and attention to detail.

Stay tuned for some awesome developments as we get used to the plane and start doing Airball experiments on it!