Monday, April 23, 2018

It happened, the moment...

As I blogged previously, last weekend, I did a couple of test flights with CFIs. On the last one, we were returning to the airport when the following happened --
  • I am not used to the C172's glide (I usually fly an Evektor SportStar) so I was too high on approach and had to cut power and burn altitude to get to pattern altitude.
  • The pattern was very busy.
  • The controller told us to make right traffic for runway 31 right, which seemed ok.
  • He also told us we were #3 behind a Citabria on 3 mile final.
  • And finally, to extend downwind, and he would call our base.
  • The CFI pointed out to me a water tower that was a 3 mile landmark out at our airport.
  • I squinted desperately wondering, which of these is the bloody water tower?
  • And I squinted some more wondering, where in the heck is the bloody Citabria?
  • We flew on and on, and I started wondering if the controller had forgotten about us.
  • I transmitted "Tower, Cessna 123, sequence" and hoped for the best.
  • I was (if I recall correctly) asked to remain on downwind.
  • I continued wondering where in the heck the bloody Citabria was.
  • Now we were approaching rather uncomfortably close to some hills, and the CFI pointed out that maybe it would be best not to fly straight into them, so perhaps I'd better turn base.
  • I started my turn right as the controller asked me to turn base.
  • And in so doing, the controller asked me to switch to runway 31 left.
  • I puttered along trying to make the turn, expecting the kind of performance I get from my usual Evektor SportStar.
  • I overshot base to final.
  • I had plenty of distance (I extended downwind halfway to the next county, if you recall), but I still needed to be careful to do it right.
Within all this commotion -- I think during my downwind to base turn -- I asked myself the quintessential question:

How am I flying the airplane?

And I glanced at the Airball on the panel and right there was my answer. Indicated airspeed where I expect it to be, AoA where I need it, and coordinated. One glance.

A couple of test flights

Over the past week, I did two test flights with two different CFI friends in Cessna 172s. The goal was to use the Airball system (V3 board, Raspberry Pi display) in a "real" flight setting and see what the CFIs reaction was, and how they thought it would help them teach.

CFI #1

This CFI was like, ok, this is great but what does it do? :) He noted that he usually teaches attitude flying. I replied, well, think of all the times when your attitude is not a good indication of your AoA. This lit a fire in his brain.....

The first thing he did was to completely botch a stall recovery, where he pointed the nose down at the ground, "panicked" that he ground was coming up at him, then pulled up again. And there we were, with the nose pointed down towards terra firma yet the AoA was right down in the stall region. Hah!

Next he proceeded to do a steep turn. And this was definitely within utility category limits and non-aerobatic, but it was steep. My jowls felt like they were going to sag down into my lap. And lo and behold, a "fat" airball that "sagged" down to a high AoA, which if we were not careful could lead to an accelerated stall. Hah!

He also tried some more commercial maneuvers including wingovers (half of a lazy-8) and noted that it was interesting to see the yaw in the maneuver very clearly displayed, without having to look down at the laggy, slow inclinometer ball.

We also did some more regular things like slow flight and stalls, and observed how the ball changed position.

CFI #2

This CFI is all about teaching AoA, and was quite happy to finally have an instrument that visualizes it. Thus enthused, we launched for a jaunt.

We spent a long time trying stuff out with the AoA monitor. He came up with the idea of using the ╬▒REF marker (the split circle) to mark a given flight condition, then try variations from that. This was brilliant and allowed us to figure out, for example, how the AoA changed when flaps were deployed, or observe the phugoid oscillation of the airplane if we pulled up flaps without trimming. We spent a long time messing around with the flaps and observing their effect on AoA and theorizing about what was going on.

Overall, he was excited about the possibilities and planned to try it out with some of his students.

On our return from this flight, something happened that is worthy of its own blog posting. Stay tuned....

Tuesday, April 3, 2018

Airball Probe v4 is alive – and flying!

A new version of the Airball Sensor Board

In Oopsie – but it's alive! back in January, I described the process of producing the Airball Sensor Board v3 (and the "oopsie" in the short-lived v2), which made a number of improvements from Ihab's initial design (retroactively named v1).

While Ihab has been busy testing the v3 boards, I've now produced Airball Sensor Board v4, which made a handful of important improvements and made the boards a LOT better:

  1. Integrated all necessary components from the Sparkfun Fio v3 which we were carrying on the previous boards in a socket. This allows us to reduce the size of the overall board stackup quite a bit and allows us to fix a number of issues with the Fio, and gives us more flexibility in laying out the board as well.
  2. Relocated the pressure sensors and re-arranged them.
  3. Replaced the (very tiny) TI TMP102 outside air temperature sensor with a bigger and more manageable TI TMP275.
  4. Integrated all battery charging and voltage regulation on the board (instead of the Fio) and added a new battery monitor chip to provide accurate voltage and charge/discharge rate from the LiPo battery, which I wrote about recently in Validating air data probe battery life – with data.
This is what the new boards look like when populated:


It takes a number of parts to assemble one:


When assembled with the new mechanical parts, it looks pretty nice! I hope you'll agree:


The internal plumbing is quite clean with the new design:

Flying my DA40 with my new Airball probe!

I took my DA40 up for a short flight to validate the probe (and the probe mount) that I built, to test radio reception, and to see if I couldn't collect some data to add to our growing data set and provide some new insights through analysis.

Here's a close up mounted to the plane:


And a glamor shot of the first Airball-equipped DA40 (at Carson City Airport):


Onwards and upwards!