Angle of Attack on the Dynon Skyview

 
 
The Dynon Skyview is a modular avionics system that easily allows you to add features to your panel. My system consists of a 7 inch display, Engine Monitoring System (EMS), Air Data Attitude Heading Reference System (ADAHRS), and various accessories like the GPS antenna, mapping software “add-on”, and remote mounted transponder. One really nice feature of the ADAHRS is a provision for Angle of Attack (AoA). The unit has three pressure ports designed to be connected to pitot, static, and AoA indication. Dynon sells a variety of pitot probes (heated/unheated, pitot w/AoA or w/o), and they are well-made units, but at $200+ they are a bit more expensive than I wanted.

I love the safety and situational awareness benefits of AoA, and the Skyview incorporates AoA seamlessly into the display and function. It’s a feature that is too good to pass up, so I decided to build my own AoA probe to feed the ADAHRS. I have some experience doing this with my previous AoA projects, and there are other designs of home-made AoA probes available online to consider as well. However, spending some time studying the Dynon AoA probe and its connections to the ADAHRS, I realized that Dynon was using a slightly different principle to gather AoA data. Other units typically use a pair of ports situated on different faces of the probe to generate a pressure differential (delta P) across those ports. Dynon only uses a single port, and uses the pitot-static ports as the second source of pressure information to provide the delta-P.

Studying the Dynon AoA port geometry, the port is situated along a line inclined 30 degrees below horizontal. If we can find a convenient place to stick a pressure port that falls along this 30 degree downward line we can pull AoA pressure. Luckily, such a place is easily found on the bottom of the wing skin. You can visualize this by holding a ruler that is inclined at the 30-degree down angle and matching that to the bottom wing profile. The point of contact is the spot where the pressure port should be in installed.

In practice, this works out to approximately 6 inches aft of the leading edge. From my experiments I found that locating this port too far back changes this angle, but the AoA still works, albeit somewhat less than perfectly. It will still calibrate and will be reasonably accurate at high angles of attack, but will be very ineffective at low angles of attack. Locating the port in the proper location will give you good, linear AoA readings all throughout the range of angles from cruise to stall.

Once the proper location is determined for the AoA port, the next step is to fabricate the port itself. There are a number of ways to do this, from a commercially available static port installed at that location, to a hole in the skin and a port located inside the wing, but the simplest and easiest is to use a regular CCP-46 pulled rivet installed in a #30 hole in the skin. The rivet is already hollow, and has a low-profile head that works well as a pressure port. You simply need to remove the mandrel and slip the rivet body into the hole. Since the rivet will not be set in the normal way, retaining the rivet is accomplished with a drop of glue under the head of the rivet and safety wire inside the wing along the body of the rivet holding it tight to the inside wing skin. The rivet body also serves as a convenient place to attach the tubing that will run to the ADAHRS. Select a tubing internal diameter that will fit snugly over the rivet body and you’re all set. The rest is just plumbing as you route the AoA line back to the ADAHRS, and can be accomplished much in the same way as your pitot-static system plumbing.

The system described above is simple to fabricate, effective, and very inexpensive. For under $15 you can purchase all the materials needed and installation takes only a few minutes, with another 30 minutes or so to route the new AoA line. Probably the single biggest challenge is gaining access to the back of the ADAHRS to install the new fitting (not so if you do this in advance while building).

My Sonex 1374 Tour video has a minute or so explaining this. Please note that the video was filmed with the rivet port in the first location I tried. You can see more on my Youtube video. I later experimented with new locations and suggest placing the rivet approx. 6" from the leading edge in the bottom wing skin (NOT the location shown in the video).

Material List.

The following part numbers are from mcmaster.com:

  • 1 each CCP-46 Rivet (un-set, with mandrel removed)

  • 1 each 5047K12 Moisture-Resistant Acetal Sngl-Barb Fitting Adapter for 1/16" Tube ID X 1/8" NPT Male Pipe. $1.10 each
    This is the fitting that adapts from the tube to the 1/8 NPT female fitting on the Skyview ADHRS.

  • 1 pack 51525K211 Plastic Quick-Turn (Luer Lock) Coupling Nylon, Female X Barb, for 1/16" Tube ID, packs of 10. $3.41 per pack

  • 1 pack 51525K121 Plastic Quick-Turn (Luer Lock) Coupling Nylon, Male X Barb, for 1/16" Tube ID, packs of 10. $3.83 per pack
    This is the disconnect fitting that I used use at the wing root. It was not available in a single quantity you’ll have extra fittings.

  • 25 ft. 5006K51 Abrasion-Resistant Clear PVC Tubing 1/16" ID, 1/8" OD, 1/32" Wall Thickness. $0.15 per foot.

 

AoA Probe Examples:

Air-Soob Home-made LRI

Sport Aviation AoA Meter

 

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Updated: 31 Jan 17