Pew, pew, pew!

Just when you thought matters chez Airball could not get any more ridiculous, there's this:

So let's back up a little. On the front, there's the thru-bolt style probe prototype that we've been working on. Nothing new there. But the things with the spirit level are way weird, and the mounting stuff in the back is just zany. Let's take it one by one. First the mounting.

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The RAM ball mounting is very versatile and strong. But, if you apply pressure to a RAM mount, it will slip and move to a new position before it breaks. For a mount for an iPad or something, that's a a feature. But for something where alignment is important, I'd actually rather the mount break first, to make it clear that it's been misaligned!

To that end, I've been thinking of making a more rigid mount. Because many wing struts are not necessarily perpendicular to the direction of airflow, I need at least 2 degrees of freedom to adjust, which I have chosen to be: rotating around the axis of the probe, and rotating side to side. The result is this mounting:

The verdict: Way too wobbly. The design needs to be more rigid. But the idea seems sound, and we'll keep plugging at it.

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Next, there's the matter of the gunsights. This is part of a procedure to boresight the probe. First, we sight down the fuselage of the aircraft at a distant object:

Then we look down the sights, which are arranged somewhat similarly to a tang sight (as popularized on the Sharps rifle) and are to be attached temporarily with rubber bands and aligned with the keel line of the probe:

We level the probe with the bubble level, and align it with the distant object. The slit design of the sights allows us to move our line of sight up and down as needed:

The result is that the probe is aligned in a vertical plane parallel to the centerline of the fuselage:

If things are reasonable, it should also be aligned along the angle-of-attack axis in a reasonable direction. It need not be perfectly "horizontal" relative to the wing because -- well -- there is not such thing really (what do you pick? zero-lift line? chord line? ...?). From that point on, we do a test flight to calibrate the important AoA points, like stall, best climb, best glide, etc.

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Stay tuned as we work out the kinks from the mount design. We will likely maintain our RAM mount adapters because they are so darned convenient. But the more rigid mounts are, in our view, also promising.

And of course, with the probe mounted on the end of a "tube", for experimental airplanes, we can use Adel clamps to clamp the tube to the wingtip screws, as shown in this schematic:

And that is of course a bridge to a permanent, wired-in solution for experimental airplanes!

Progress with probe kit build

It's been a while since I've posted an update. Rest assured we've been working massively hard. :) For now, here's a bit of news about work I've done to -- hopefully ;) -- improve the way the probe is built and make it easier to put together.

The "new" design is a throwback to some of our earlier work, using four thru-bolts to hold the whole assembly together. The bolts are #4-40; previously we were using #6-32, which is honestly way too big. This solves a number of problems with previous designs --

1. Building 3D printed parts to axially locate the internals made these parts complicated.
2. Relying on the outer polycarbonate tube to hold things together meant that, during assembly, everything flopped around.
3. Drilling holes in the polycarbonate tube is nontrivial -- easy for a well-equipped shop, but not something that's easy for a kit builder to do.

The result is as you see. Meanwhile, notice that our new material of choice is translucent blue PETG, which has proven to be extremely good at reproducing detail. We have high hopes for this stuff.

These renderings show the probe from the outside, from the "top" and "bottom" (the battery is now on the bottom):

You can see how we have preserved the previous method of attaching to the mount, with the two screws with standoffs coming off the back -- except now, these screws are part of the continuous thru-bolt assembly going the entire length of the probe. Next, here is a detail of the temperature sensor board, which sandwiches in the 3D printed parts and will now be wired to a screw header terminal:

The pressure sensors are pretty much as before. Note that we are relying heavily on the plastic threaded and barbed connectors you may have seen us using previously:

The sharp-eyed among you might notice we only have 5 holes in the probe nose now; no "static" hole or static probe. This is a new result and one which we hope to talk more about soon. For the moment, we note that this is a really promising direction.

The assembly sequence is shown in the below photo album. Note how, once the thru bolts are assembled, the entire circuitry and plumbing are exposed to be worked on, after which the outer tube can be installed.

Assembly photo album