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AOA (Pitot/Static) probe for Glass Survey Accuracy

What Pitot, Static, AOA Used and Accuracy?

  • AOA/Pitot (Off the shelf Dynon/Garmin)

    Votes: 18 78.3%
  • AOA RV-12 wing leading edge

    Votes: 3 13.0%
  • AOA (combined with pitot under wing DIY)

    Votes: 1 4.3%
  • Static Port Per Plans side of Fuselage

    Votes: 10 43.5%
  • Static Port with Pitot Under Wing

    Votes: 0 0.0%
  • Pitot Under Wing Per Van's Plans

    Votes: 5 21.7%
  • Pitot, wing leading edge (retractable boom)

    Votes: 0 0.0%
  • OTHER (please comment, accuracy)

    Votes: 1 4.3%

  • Total voters
    23

gmcjetpilot

Well Known Member
AOA - What are people doing for AOA. Dynon and Garmin offer a Pitot/AOA probe combo for typical underwing mounting. I am thinking of making my own Pitot/AOA probe unheated. How accurate is the AOA using pressure and calibration with the glass. Has anyone one used the RV-12 leading edge AOA port on their RV4/6/7/8/9/14.

STATIC - per Van's side of fuselage left and right. Thinking of having Static with Pitot under wing. Anyone do that and any accuracy issues.

PITOT - Under wing is common and per plans. I am toying with idea of a boom in the wing tip fairing. It would retract (manually). Extended a foot more from wing leading edge it should be accurate at the cost of longer pitot tube plumbing, weight, complexity and possible damage if left extended.

The two in one either Pitot/AOA or Pitot/Static[/] B- are fairly common. I found wind test probes that combines both Pitot/Static where there is a tube in a tube. The pitot center and outer tube had ports for static. Very slick. A variation of this is for RC models. Except they use small pressure transducers to send electrical signal to the on board electronics. That would be slick verses running tubing to the Glass. However not sure how that would work or how to integrate.

All three in one underwing probe, Pitot, Static, AOA under wing. I saw this on a LSA. It was pretty slick.
https://photos.app.goo.gl/sLJmZtyZ55vikjiE9

Thoughts?
 
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On my RV-10, I've got SafeAir static ports in the stock locations on the tailcone sides and a Garmin GAP26 heated pitot in the stock location under the left wing. No accuracy issues.
 
It seems the standard stuff works well.

What are you hoping to gain from a change to tried and true?

Yes stick to plans. Keep it simple, light. Always good advice. What to gain? Well may be more simple. May be less weigh. If you have all three probes (Pitot, Static, AOA) all in one, with three tubes together it may simplify installation and possibly be more accurate.

Accuracy? The tried and true static side of fuselage is a compromise. Selection of static port can cause errors in airspeed and altitude. The AOA probe using differential pressure is a compromise. True AOA computers use AOA Vanes with a flight computer that considers configuration, airspeed (trend) and accelerations in all three axis. A Piper stall Tab in leading edge is an electrical switch to buzzer. It is an AOA device (works on AOA not airspeed). If you don't calibrate your glass AOA it can be useless.

My goal is a thought experiment and learning. My goal would be more accuracy, low weight, simple installation. 3 in 1 (pitot, static, AOA) under wing may be good, or 2 in 1 (Pitot/AOA or Pitot/Static) may be an option. Under wing by combo of 2 or 3 probes minimizing drag would be a goal.

All the "options" I mention are NOT new or my invention. They are used on many planes with great success. Bottom line the VAN'S PLAN for pitot / static are tried and true and good enough. As far as AOA, I am intrigued with Van's RV-12 leading edge port. Will it work on other RV's? Only one way to find out. Flight test.

Last goal to spark discussion, and hear if anyone tried these ideas and what the results were.
 
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Pitot and static as per plans. I saw no need to modify something as important as air data from something that had been already tried and proven.
AOA I have a Proprietary Software system with ports on upper and lower surface of RH wing leading edge per installation instructions.
All were verified and calibrated during phase 1 with no accuracy issues.

(Proprietary Software AOA system was bought by someone a while back but don’t remember who)
 
I have been involved with troubleshooting autopilot issues in several different airplanes that were solved by relocating the static port from under the wing (Piper style) to the fuselage (RV or Cessna style). I wouldn't mess with the location or shape of the stock static ports on an RV.
 
IFR certification required a heated pitot, so previous owner replaced the original Van's pitot with a Dynon...AoA was based on in-wing ports and unfortunately he didn't have the pitot plumbed for AoA. After I bought it, my integrated ADAHRS went TU and the upgraded replacement EFIS required pitot-based AoA so I had to plumb the Dynon heated pitot for the AoA. Static system is what looks like SafAir ports on the fuselage sides. Everything seems to work fine.
 
just me

What I would like to see is Garmin make a heated pitot/static/ AoA probe that interfaces with the Can Bus, much like a remote AP servo. No more plastic tubing. A builder can use one on each wing for redundancy.
 
My goal is a thought experiment and learning. My goal would be more accuracy, low weight, simple installation. 3 in 1 (pitot, static, aoa) under wing may be good, or 2 in 1 (Pitot/AOA or Pitot/Static) may be an option. Under wing by combo of 2 or 3 probes minimizing drag would be a goal.

Last goal to spark discussion, and hear if anyone tried these ideas and what the results were.

I have experience with this, or similar, single probe multiple times over the last 20 years. Of coarse we feed a triplex flight control computer.
https://www.aeroprobe.com/air-data-probe/
They were located 8 feet out in front of aircraft. Accuracy very good with proper software and computer.
It will be a noble effort to get a system like that to be cost effective for EAB but my experience is it requires quite a bit of work to get calibrated unless quite far out in front of aircraft.
 
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IFR certification required a heated pitot, so previous owner replaced the original Van's pitot with a Dynon...AoA was based on in-wing ports and unfortunately he didn't have the pitot plumbed for AoA. After I bought it, my integrated ADAHRS went TU and the upgraded replacement EFIS required pitot-based AoA so I had to plumb the Dynon heated pitot for the AoA. Static system is what looks like SafAir ports on the fuselage sides. Everything seems to work fine.
Just for clarity, FAR's do not require heated Pitot for IFR on Part 23 planes not used for commercial operations, unless it has known ice certification. IS IT A good idea? Heck yeah. But.... Ye thou shall not fly-ith in ice no way no how, heated pitot or not.

Small diameter things like pitot tubes will pick up ice before anything else. One advantage of IFR in a Cessna is you can see the ice first on strut and pitot mast. It is a GREAT idea to have heated pitot but not required. My pitot will not be heated. If I go IMC it will be in temps I am assured not to get ice or in clear air (even if on IFR Flt plan). I like to file to busy airports even if "CAVU". Far easier arrivals than special VFR arrivals with landmarks I never seen before.
 
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What I would like to see is Garmin make a heated pitot/static/ AoA probe that interfaces with the Can Bus, much like a remote AP servo. No more plastic tubing. A builder can use one on each wing for redundancy.

Very good idea. Much easier to run wires than plastic tubes.
 
Re: Piper style static port on mast under the wing. A while ago there was a post here, concerning an unstable in pitch autopilot. When the autopilot company’s rep read that the poster was using the Piper style static port, he said, ‘That won’t work’. Something about very small static pressure changes with pitch driving the autopilot the wrong direction.
 
I have been involved with troubleshooting autopilot issues in several different airplanes that were solved by relocating the static port from under the wing (Piper style) to the fuselage (RV or Cessna style).

STATIC - per Van's side of fuselage left and right. Thinking of having Static with Pitot under wing. Anyone do that and any accuracy issues.

Re: Piper style static port on mast under the wing. A while ago there was a post here, concerning an unstable in pitch autopilot. When the autopilot company’s rep read that the poster was using the Piper style static port, he said, ‘That won’t work’. Something about very small static pressure changes with pitch driving the autopilot the wrong direction.

That was me, and yes I have the Piper P/S mast under my wing on my RV-6. It played havoc with my Trio Autopilot, and yes, Trio said it wouldn't work (they had used an RV-6 as their test bed when developing the Trio apparently). They said the pressure changes, in any pitch change, even small ones, way too much and too fast for it to be useful for the autopilot computer. I ultimately had to mount and plumb the per-plans static port on the fuselage to get my autopilot performance to any where near acceptable (and kept the piper mast for pitot).

This thread
 
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I ultimately had to mount and plumb the per-plans static port on the fuselage to get my autopilot performance to any where near acceptable (and kept the piper mast for pitot).

This thread
THUMBS UP.... Thanks I will learn from your experience gladly. Yep. I will likely make my own AOA/Pitot combo under wing "L" tube. I am still intrigued by the RV12 leading edge AOA port.
 
Here is old VAF thread with reference to successful AOA port (RV-12 style) in RV-4.

https://vansairforce.net/community/showthread.php?t=186185&highlight=aoa+rivet

Based on this, I've installed similar in my -6A to feed the Dynon, but haven't flight tested it yet. I put the rivet at 20 degrees incidence, which is a little further back than 30 degrees on the Dynon probe, so as to locate it out of potential turbulence area (hopefully).
 

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It Depends...

We've tested Dynon, Garmin, Alpha Systems as well dual tube and custom spherical sensors. I've also tested two different static configurations on the mighty RV-4. As folks have pointed out, dialing in a pitot static system is a black art, and once calibrated, best left alone (unless you enjoy the constant experimentation, which is cool--I do:D).

Our test RV-4 has a wireless YAPS (yaw, alpha, pressure, static) boom attached to the left wing:

3c039a_9d1406ccc066417ea89af2737a5cba27~mv2.jpg


The boom is fitted with alpha and beta vanes as well as a Kiel probe for sensing dynamic and static pressure. To mitigate flow effects, any sensor has to be placed at least one chord length ahead of the wing. This boom does not extend that far and we have to compensate for upwash, G and pitch/AOA rate. With a short, tip mounted sensor, you will need to compensate for upwash during calibration.

The best location for a differential pressure AOA sensor is 6" (or more) below the wing, between 25-45% chord. Note the relatively undisturbed flow lines in that "sweet area" under the wing:

3c039a_e4bc62b901734bed95c47b2014f6b4c2~mv2.jpg


The offset (alpha) port on the Dynon and Garmin sensors are a bit of an afterthought, and the commercial sensors have about 5-6 degree beta (sideslip) limit before you run into problems. The Dynon is notable for the lipped, conical pitot port. We've found this configuration performs well at high alpha. Ultimately a spherical head will likely give best overall performance, mitigating sideslip effects. This configuration could have between two and five ports, depending on number of pressure sensors fitted to the computer.

If you experiment, drop a PM or email, and I'll share an assessment tool for deriving static source pressure error without having to use a drogue.

After experimenting with a home made "L tube" configuration, we found it was necessary to damp the offset pressure to mitigate noise effects. A small machined "bullet nose" with a tiny aperture did the trick:

3c039a_edfa4ec667ab40b2bb811c2e2e61c912~mv2.jpg


Overall, this sensor proved to be slightly noiser than the Dynon or Garmin probes, but usable. It has the tactical advantage of being easy to fabricate and inexpensive. We've also found that printing a sensor is a neat way to experiment. We use a common mounting configuration (Alpha Systems) to make it easy to swap probes for testing:

3c039a_319434641f3f45de8884be19293fca7c~mv2.jpg


Any ringing effects will be installation dependent, but we haven't had any issues using standard 1/4" OD flexible tubing with lengths sufficient to reach the aileron actuator from the cockpit on the RV-4 and -8.

Although specific to the Alpha Systems probe, there is excellent information in this paper regarding coefficient of pressure Derived AOA and placement of sensors: https://www.tc.faa.gov/its/worldpac/techrpt/tc18-7.pdf

Another excellent resource: https://www.tc.faa.gov/its/worldpac/techrpt/tc18-19.pdf

Good luck and report back results!

Vac

FlyONSPEED.org
 
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