Alpha Systems Angle of Attack video

[pfactor]

I did a bunch of looking at angle of attack systems at Oshkosh this year, and finally decided on the Alpha Systems AOA Eagle display. I just had it installed, and I'm extremely pleased with the results. Having the display up on the glareshield is perfect, and it's mounted to the center bar just below the compass. It's easily in my peripheral vision and can be seen from either pilot seat.

Big thanks to Fred Scott for his AOA articles which I found extremely helpful. I calibrated my system in the landing configuration (the manual says to do it clean). Here's what I did.
1) Do a power-off stall in the landing configuration, note the actual stall speed.
2) Multiply that by 1.3, and that's the OAA (optimal alpha angle)
3) Fly that speed to calibrate the blue donut
4) Fly at Va adjusted for weight to calibrate the cruise speed.

Here's a video of my installation where I do a short-field take off, power-on stall, accelerated stall, power-off glide, power-off stall and a couple of landings. I calculated the actual speeds for Vs0, Vs1, Vx, Vref, Vy, Vglide and Va based on the actual aircraft weight that day.
http://youtu.be/hRmKkxSpu9E

 

Phil

[carusoam]

Phil,

Welcome aboard.

Please introduce yourself. It would be most proper if you are commercially related to the AOA equipment that you are demonstrating.

Very interesting level of technology in and on your panel.

One of our discussions today is related to touch and go landings. Your video and instrumentation are an excellent demonstration of the challenges a Mooney pilot encounters during the higher brain level activities that occur during the landing phase.

Thank you for sharing the timeline and what to expect in the video.

I look forward to your next video. The one where the checklist is moved out of the way so we can see the runway. I am also looking forward to seeing less sun glare. The AOA matching to the Aspen is good, but seeing out the windshield would be the best!

Best regards,

-a-

[Marauder]

Phil, Welcome aboard. Please introduce yourself. It would be most proper if you are commercially related to the AOA equipment that you are demonstrating. Very interesting level of technology in and on your panel. One of our discussions today is related to touch and go landings. Your video and instrumentation are an excellent demonstration of the challenges a Mooney pilot encounters during the higher brain level activities that occur during the landing phase. Thank you for sharing the timeline and what to expect in the video. I look forward to your next video. The one where the checklist is moved out of the way so we can see the runway. I am also looking forward to seeing less sun glare. The AOA matching to the Aspen is good, but seeing out the windshield would be the best! Best regards, -a-

Pretty picky! Let's see some of your videos!

[jrwilson]

I don't think he is commercially related to the AOA. I think he works for google, he has done formation training with the mooney caravan and is a nice guy.

[Gone]

Cool video Buzz:

 

"Buzz" is Phil's Caravan call-sign and he was Element Lead of Kilo Element for the 2014 Caravan.  This is a big video file though and it takes a little time to download here in Myanmar.    I too am looking at one of the options for an AOA in my E model next year as well.

[Piloto]

Nice video Phil. Does the Alpha AOA comes with a voice annunciator? Stalls are more prone to happen when turning from base to final (low speed and high bank angle). At this point I am more focused on the runway than looking at a gage. At this point I can get either a stall warning or a landing gear warning. To differentiate them I installed a voice warning for the gear and left the buzzer for the stall. Worth it every penny ($200). The problem is that if you hear an alarm thinking is the stall you may push the throttle slightly forward thus deactivating the gear alarm and end up doing a belly landing.

 

José    

[Danb]

Jose, I have the King Klr model and keep the voice annunciator turned off it was driving me crazy and with it mounted on the glare shield the picture and frame of reference is awesome, I'm sure everyone is different re: the voice, also when I have a passenger on board they probably think we're always slow since the aoa does not know where the runway is and we need to stall that puppy on and I wonder what's going through the pass mind when it's barking to slow...no kidding we're landing....

[flyboy0681]

It's interesting how Mooney is sometimes featured as the testbed. In addition to this video, Garmin used it for development of the GTN.

[carusoam]

Chris,

My last video I produced was for industrial printing machinery at vandammachine.com. Printing drink cups in eight colors at 600 cups per minute. I was a technical marketing and sales guru for industrial machinery.

Now, I struggle with posting still photos on MS.

My intent was to welcome the original poster on board. Anyone with a first post that includes a picture of their mooney deserves that!

Realizing he had a few skills higher than an ordinary pilot with an iPhone, I requested the introduction.

I liked the detailed use of V speeds. I got a little wary because he was giving detail of his air speed that I could not get from his ASI. Of course, the detail was coming from that little ribbon on the Aspen...

There was so much detail delivered in a usable way. I was hoping to find that he is a CFII working directly with the AOA manufacturer.

My second time through the video I was pleased to see things like clearing turns, GUMPS and other necessary details that are proper for GA. That's when I realized the darned checklist is hanging in my line of sight and I can't see the runway he is landing on.

I am cautious about promoting TNGs in complex AC. It is too easy for ordinary people to make an expensive mistake. I don't believe the TNG adds any value to the video either. If it did, I missed it.

Of course, it was after midnight, while I was getting caught up on my daily reading. That was the time I got your invite to the EAA event today.

I hope you are there now!

Ned, on the home wifi using a new imodem the video feed is flawless in NJ. Thanks for the intro detail.

Best regards,

-a-

[Marauder]

Chris, My last video I produced was for industrial printing machinery at vandammachine.com. Printing drink cups in eight colors at 600 cups per minute. I was a technical marketing and sales guru for industrial machinery. Now, I struggle with posting still photos on MS. My intent was to welcome the original poster on board. Anyone with a first post that includes a picture of their mooney deserves that! Realizing he had a few skills higher than an ordinary pilot with an iPhone, I requested the introduction. I liked the detailed use of V speeds. I got a little wary because he was giving detail of his air speed that I could not get from his ASI. Of course, the detail was coming from that little ribbon on the Aspen... There was so much detail delivered in a usable way. I was hoping to find that he is a CFII working directly with the AOA manufacturer. My second time through the video I was pleased to see things like clearing turns, GUMPS and other necessary details that are proper for GA. That's when I realized the darned checklist is hanging in my line of sight and I can't see the runway he is landing on. I am cautious about promoting TNGs in complex AC. It is too easy for ordinary people to make an expensive mistake. I don't believe the TNG adds any value to the video either. If it did, I missed it. Of course, it was after midnight, while I was getting caught up on my daily reading. That was the time I got your invite to the EAA event today. I hope you are there now! Best regards, -a-

Thank you Roger Ebert... I'm just happy people are posting things with videos that show details about what they post.

[carusoam]

I'm still composing that response...

Had to add a thank you note for Ned. Wifi speeds in Myanmar are a bit slow...

Wondering if anyone at Google could help a brother aviator out???

Best regards,

-a-

[pfactor]

Please introduce yourself. It would be most proper if you are commercially related to the AOA equipment that you are demonstrating.

I'm a long time lurker, and I didn't even think about the fact that this is my first post. Happy to introduce myself.

I'm Phil Verghese, flying N201UT out of RHV in San Jose, CA. I've owned this plane since 1998 and earned my commercial, CFI, and CFII certificates in this baby. I've been flying with the Mooney Caravan formation arrival to Oshkosh that last two years, and I think it's the safest way to get to Oshkosh. I've got a bunch of formation flying videos on my YouTube page.

I have zero commercial interests in the AOA equipment or anything else in my panel. Sorry if my post sounded like it could have been commercially motivated. I'm just a very happy customer and think more pilots should be installing AOA systems in their airplanes.

 

Very interesting level of technology in and on your panel.

Yeah, I'm really pleased with how my panel has turned out. I'm almost done with it

 

My wife is a pilot too, and we decided a few years ago that this is the right plane for us. We're keeping it forever, so we're making the upgrades that make it more safe and enjoyable for us to fly more often. The money we put into this airplane makes no financial sense, but makes us both happy.

 

One of our discussions today is related to touch and go landings. Your video and instrumentation are an excellent demonstration of the challenges a Mooney pilot encounters during the higher brain level activities that occur during the landing phase.

I agree that touch-and-go landings are more challenging than a full-stop landing. I can see both sides of the discussion on that accident thread where touch-and-goes came up. I do not think they are a good idea for pilots new to the airplane. But I do think that a pilot who maintains a high level of proficiency can do them safely. I routinely practice both full-stop landings, touch-and-go landings and go-arounds. I have over 1700 hours in this particular airplane, and over 2200 total time.

 

I look forward to your next video. The one where the checklist is moved out of the way so we can see the runway. I am also looking forward to seeing less sun glare. The AOA matching to the Aspen is good, but seeing out the windshield would be the best!

Yeah, unfortunately it's hard to get the camera to correctly expose the outside view and the inside view. You have to pick one or the other, so I set the GoPro up to do spot metering and pointed it centered on the instrument panel. That makes the outside view very overexposed. I wanted to show the relationship between airspeed & AOA in this video.

 

If someone knows of a way to get the video to work for both the inside and outside view, please let me know.

 

Phil

[pfactor]

I don't think he is commercially related to the AOA. I think he works for google, he has done formation training with the mooney caravan and is a nice guy.

 

That's me. Hi John!

[pfactor]

Nice video Phil. Does the Alpha AOA comes with a voice annunciator?

Thanks José. Yes, you can configure 4 different audio annunciations. I have mine set up to play through the overhead speaker rather than through the intercom. I had the GoPro wired up to the intercom, so you couldn't hear the AOA beeps in the video but they were there.

 

Here's the 4 options you can set up:

• 3 beeps the first time the bottom-half of the blue donut shows up. Only happens once.
• A two-tone warble (more attention getting than the beeps) at the same situation as above. Only happens once.
• The same as above. Then when the red chevrons are illuminated, a female voice says "Too slow" every 2 seconds.
• Female voice says "Getting slow" when the bottom-half of the blue donut lights up (happens once). Then the same "Too slow" repeating when the red chevrons come on.

I chose the first option (which is the default). My primary purpose of getting the AOA was to help me fly the correct speed on final based on weight. I don't want to have to do math to figure out the correct Vref -- I want a heads-up indication of being on the correct AOA.

 

I've got enough warnings of an impending stall that I don't really need the voice warnings. I like the subtle 3 beeps. I don't want to make passengers feeling uncomfortable hearing "Too slow" as we're just about to touch down. But if I chose that option, I'd let them know to expect it.

 

Stalls are more prone to happen when turning from base to final (low speed and high bank angle).

 

You don't want to have a high bank angle or low speed on your base to final turn. If you do, then it's time to go around. I limit my pattern turns to about 30 degrees of bank. Some pilots are even more conservative than that.

 

I don't know if I'd say that stalls are more likely on base to final, but I understand what you're getting at. If you overshoot final and try to fix it with an uncoordinated turn, and pick up a high descent rate, then try to fix that by pulling back on the yoke, you're set up for the classic base-to-final stall/spin accident. You won't have time to recover.

 

I would say that one of the most dangerous times to stall is on the base to final turn if you get into the situation I described above.

 

At this point I am more focused on the runway than looking at a gage.

 

That's why I mounted the AOA above the glare shield. I'm looking at the runway. The AOA indicator is in my peripheral vision. Another aspect of being safe on landing is flying the correct approach speed (or even better, correct AOA). I think many pilots of high performance aircraft are adding a few knots for mom and the kids, and end up coming in way too fast. That's also a contributing factor to landing accidents. Being too fast on final can be just as bad as being too slow.

 

Fred Scott wrote an excellent article on this topic. Please give it a read and see what you think. He's got a bunch of stuff about AOA indicators and extensive documentation on test flights done by very experienced pilots.

 

At this point I can get either a stall warning or a landing gear warning.

 

I'm going to reference one of Fred Scott's pages again. Here he's quoting from Flying Magazine November 1971.

"Stall warning devices are …binary or 'On-Off' devices that give the pilot no indication whatever on how close his wing is to stall….one or two degrees [of angle of attack] below stall, a [stall warning device] is still speechless, mute. It is at its most awkward, tongue-tied phase just when the pilot needs it most..."

[pfactor]

I got a private message asking how I adjusted the V speeds for weight. I figured I'd share with the group in case others were wondering.

 

For the V speeds that vary by weight (Vs0, Vs1, Vref, Vx, Vy, Vglide, Va) you can correct the speed for your weight with this formula.

 

V' = V * SQRT(actual weight / max gross weight)

 

To give a concrete example from one of the speeds in the video, let's say Vref is 71 (at max gross), my actual weight is 2319 and max gross is 2740.

 

Vref' = 71 * SQRT(2319 / 2740)

        = 71 * SQRT(.84635)

        = 71 * .919973

        = 65

 

So for this weight, Vref is 65 knots.

 

But I don't want to do this math for every flight. Instead, I flew the calculated V speeds and noted the AOA indication for each one. For this airplane with this instrument, it works out like this:

 

Vso is the red triangle

Vs1 is the red triangle plus red chevron

Vx is the red chevron and top-half of the blue donut

V ref is the blue donut

Vy is the bottom-half of the blue donut plus the yellow chevron

Vglide is the yellow chevron

 

I can't really use the AOA indicator to know exactly where Va is. For me, the green bar shows up around 100 knots and Va is generally above that.

[ArtVandelay]

I liked the detailed use of V speeds. I got a little wary because he was giving detail of his air speed that I could not get from his ASI. Of course, the detail was coming from that little ribbon on the Aspen...

 

I notice that too, the Aspen was displaying 90 and his ASI was indicating 107...

[ArtVandelay]

You need the light level inside and out to be the same, try shooting early or late in the day, with interior light on, or mount a couple of lights on the headrests (need 2 to cut down on the shadows).

 

 

If someone knows of a way to get the video to work for both the inside and outside view, please let me know.

 

Phil

[pfactor]

I notice that too, the Aspen was displaying 90 and his ASI was indicating 107...

 

The outer scale of my mechanical ASI is in miles per hour. The inner scale (hard to see in the video) is in knots.

 

107 mph is 92 knots

[ArtVandelay]

The outer scale of my mechanical ASI is in miles per hour. The inner scale (hard to see in the video) is in knots.

 

107 mph is 92 knots

Thats right, I forgot about that.

[carusoam]

Phil,

With all of the technology /data collecting that you have...

How closely does your airplane match the various published V speeds? I have some speeds published with 0.5 KIAs

Some of our members report that their ASI is good enough (for them) and don't want an AOA.

My ASI is a standard device that requires interpolation between lines. This gives me the tendency to bulk up the safety margins...

I see plenty of value in what you are portraying.

- Higher precision data delivery. Airspeed accuracy to 1KIA...

- graphic interpretation. In case my math skills decline under higher work load, or O2 depletion after a long flight.

- voice warnings of critical points minimizes chance of error of misinterpretation.

My interest is generally improving the consistency of my flying from T/O to landing. I ask a lot of questions...

Hope you are not offended by my accidental aggressive nature.

Best regards,

-a-

[MooneyCFII]

Having lived with AoA on other aircraft I thought I would make a comment. 

 

The problem with ASI is that it lags, it has installation error, and marked stall speeds are only valid for steady state flight at one weight (max gross). You can invoke a sudden change in AoA to stall the wing without a corresponding change in AS. Also, stall "speed" changes with loading. Stall speed is increased in a level turn and can result in an accelerated stall. (I like to take my students up, configure the airplane for landing, and demonstrate how one can invoke a stall at speeds well above the indicated stall speed in the base-to-final turn.) So an AoA indicator is really useful because it gives instantaneous indication of the state of the wing relative to stall. An airspeed indicator doesn't even come close. (But every airplane has an ASI so you still have to know how to use it and what its limitations are.)

 

On my last AoA equipped aircraft I had it configured to indicate from zero-lift (zero alpha) to critical AoA for both "clean" (gear and flaps up) and "dirty" (gear and flaps down) configurations. it was calibrated for both and therefore I always knew how far I was from stall and how far I was from best L/D, always useful in an engine-out situation. (I tested it from 0.5G all the way up to 5G and it was dead-nuts on.) It was even useful in a botched aerobatic maneuver as I could just pitch to zero alpha and then recover without having the airplane depart in an undesired snap-roll or spin regardless of whatever airspeed I was flying at. (It is really useful to be able to fly the airplane well below "stall speed" without stalling.)

 

So, yes, I am a CONFIRMED believer in AoA indicators in aircraft. Everyone here should have one in his or her aircraft.

 

Now for the problem: the current crop of "easy-to-install" AoA indicators that have been approved for aircraft flying with a standard airworthiness certificate have no way of automatically adjusting themselves for flap deployment. (The FAA would not approve them if they had any connection to the flight controls.) Extending the flaps changes the effective AoA of the wing and produces erroneous readings. So you have a choice: configure the AoA indicator to read correctly flaps-up, or configure the AoA indicator to read correctly flaps down. If you are like Phil and are specifically addressing the issue of the infamous base-to-final stall-spin event, configuring the unit in the landing configuration is probably the better approach. If you want a more general indication then you probably want to configure with the airplane "clean" and then re-mark the instrument to show the error when "dirty". That seems like a kludge to me so I have decided to wait for the availability of an AoA indicator like the one I used to have, which worked in all configurations. 

 

I know of one AoA manufacturer who has an AoA indicator that takes in flap position information to correct the AoA readings, making the unit usable and accurate in all flap configurations. The only problem is that he is still awaiting FAA approval for his new device. Once he gets approval I will probably purchase his units for all my airplanes. 

 

Brian "Pinky" Lloyd

[pfactor]

How closely does your airplane match the various published V speeds? I have some speeds published with 0.5 KIAs

I'd say my plane was right on the speeds I could directly measure as indicated on the Aspen. The only two speeds that I could directly measure are Vs0 and Vs1. The stalls with flaps down and flaps up were right at the book numbers (adjusted for weight). I have no way to measure accuracy at any of the other speeds.

 

Some of our members report that their ASI is good enough (for them) and don't want an AOA.

If those members are flying the same airspeed regardless of aircraft weight, then they are probably flying too fast on final. If they are doing the math and adjusting their Vref for the actual aircraft weight, then that's fine. They should  also do that for other performance-critical speeds like Vx and Vy.

 

I don't want to do the math on every flight, which is why I chose to install an AOA.

 

My ASI is a standard device that requires interpolation between lines. This gives me the tendency to bulk up the safety margins...

 

I read "bulk up the safety margins" as "flying at a faster approach speed than Vref". That's not great. At best it will result in a longer float, but not a huge deal if you have a long runway. At worst, pilots who fly too fast sometimes try to force the nose down if they feel they are running out of runway.

 

I see plenty of value in what you are portraying.

- Higher precision data delivery. Airspeed accuracy to 1KIA...

- graphic interpretation. In case my math skills decline under higher work load, or O2 depletion after a long flight.

- voice warnings of critical points minimizes chance of error of misinterpretation.

My interest is generally improving the consistency of my flying from T/O to landing. I ask a lot of questions...

Hope you are not offended by my accidental aggressive nature.

No worries. I was put off a bit when I first read your reply, but I'm over it now. Thanks.

Phil

[pfactor]

Thanks for sharing your experience and thoughts Brian.
 

On my last AoA equipped aircraft I had it configured to indicate from zero-lift (zero alpha) to critical AoA for both "clean" (gear and flaps up) and "dirty" (gear and flaps down) configurations. it was calibrated for both and therefore I always knew how far I was from stall and how far I was from best L/D, always useful in an engine-out situation. (I tested it from 0.5G all the way up to 5G and it was dead-nuts on.) It was even useful in a botched aerobatic maneuver as I could just pitch to zero alpha and then recover without having the airplane depart in an undesired snap-roll or spin regardless of whatever airspeed I was flying at. (It is really useful to be able to fly the airplane well below "stall speed" without stalling.)

That sounds like a good system. Who made it?
 

If you are like Phil and are specifically addressing the issue of the infamous base-to-final stall-spin event, configuring the unit in the landing configuration is probably the better approach.

Actually the reason I calibrated by AOA in the landing configuration is that I want to use it fly the correct speed on final. I'm really not too worried about the base-to-final stall. I've received and given enough training that I know to go around if things don't look right when turning final.

The difference between the AOA indications with flaps up vs flaps down are just 1/2 a donut. In my plane, with the flaps down, I see the full donut when I'm on the correct AOA on final. With the flaps up, I see the bottom half of the donut. It's not too hard to handle.

 

Plus 99% of my landings are with full flaps anyway.
 

I know of one AoA manufacturer who has an AoA indicator that takes in flap position information to correct the AoA readings, making the unit usable and accurate in all flap configurations. The only problem is that he is still awaiting FAA approval for his new device. Once he gets approval I will probably purchase his units for all my airplanes.

Which manufacturer is that?

When I talked to Alpha Systems at Oshkosh, they said they've already got the software configured to handle a flap position sensor as an input. They are hoping to have that out soon, and it will be possible add that input to the system I bought at Oshkosh. I'm not sure I'll bother doing that since I'm fine with how it works even without that sensor.

 

Phil

[MooneyCFII]

Sorry, I tried to figure out how to interleave my responses with the quoted text but couldn't figure out how. And the message that came in email had all the quote levels stripped out. So I am just sending out a straight-forward reply.

 

The system that I had in my Nanchang CJ6A was from Advanced Flight Systems. See:

 

http://www.advanced-flight-systems.com/Products/AOA/aoa.html

 

The problem with the systems that use a differential pressure probe (like the Bendix/King or Alpha Systems units) is that they don't actually measure AoA. A differential probe *can* be used to measure AoA but only if the differential pressure is corrected for dynamic (pitot) pressure. That means the calibration will be correct at only one flap position AND only one aircraft loading, or only one AoA. The Advanced Flight Systems unit has the static/dynamic pressure correction which is why it gives proper indications at all speeds and loadings. (Like I said, it was dead-nuts accurate from 0.5G to 5G.) But because it connects to the pitot/static system and doesn't carry the FAA Seal of Approval, you can't install one in an aircraft with a standard AC. I have heard of this unit being granted a field approval if the owner mounts a second pitot tube on the aircraft just for the the AFS AoA indicator. 

 

Given that many of the low-cost, easy-to-install system are differential pressure only (the most popular was the Lift Reserve Indicator) you really don't know what they are telling you other than some kind of relative sort-of, kind-of, AoA-like-but-not-really indication. They will give accurate information over a wide range, but only at one loading. IF you adjust the probe position correctly you can get it to tell you one particular AoA at any dynamic pressure (airspeed). I believe that the original Lift Reserver Indicator (LRI) had you adjust the angle of the differential probe to show critical AoA so it did show critical AoA at any speed or loading. It was just that the scale was compressed at higher airspeeds and wing loadings. 

 

But don't take my word for it. Here is a very interesting paper that describes how all this works:

 

http://www.nar-associates.com/technical-flying/angle_of_attack/DeltaPAOA_wide_screen.pdf

 

I believe this paper is actually addressing the errors specifically in the Alpha Systems unit. (I am guessing at this based on the photos.)

 

Vane-type sensors, if properly placed, do read AoA for whatever configuration they are calibrated for or, if they have some way to sense flap position, can be calibrated for all flap positions. This is pretty straight forward. Personally I just don't like having a vane out there where it can ice up or get damaged. (OTOH, if your wing is iced up, your AoA isn't going to help you at all because your wing now has a completely different airfoil making the AoA indicator useless. So maybe a vane isn't so bad after all.) But a vane does respond to incident wind independent of airspeed and so can provide accurate relative AoA indications across a wide range of airspeeds. Add correction for flap position and you have a useful AoA sensor. 

 

BTW, the unit that will be adding flap correction is from RiteAngle. 

 

I'm sorry if I appear negative. I just find it so frustrating that the FAA inhibits technology that really could make our flying safer. When I went looking at AoA 15 years ago, the unit from Advanced Flight System (then Precision Flight Controls if I recall correctly) was the hands-down winner. Today it still appears that way. I would have one on every one of my airplanes if I could get away with it. But a differential pressure unit without dynamic pressure correction just doesn't really tell you what you want to know no matter how fancy the display is. So it looks to me like the vane-type indicator is the best we are going to get in the near term. 

[rq3]

Sorry, I tried to figure out how to interleave my responses with the quoted text but couldn't figure out how. And the message that came in email had all the quote levels stripped out. So I am just sending out a straight-forward reply.

 

The system that I had in my Nanchang CJ6A was from Advanced Flight Systems. See:

 

http://www.advanced-flight-systems.com/Products/AOA/aoa.html

 

The problem with the systems that use a differential pressure probe (like the Bendix/King or Alpha Systems units) is that they don't actually measure AoA. A differential probe *can* be used to measure AoA but only if the differential pressure is corrected for dynamic (pitot) pressure. That means the calibration will be correct at only one flap position AND only one aircraft loading, or only one AoA. The Advanced Flight Systems unit has the static/dynamic pressure correction which is why it gives proper indications at all speeds and loadings. (Like I said, it was dead-nuts accurate from 0.5G to 5G.) But because it connects to the pitot/static system and doesn't carry the FAA Seal of Approval, you can't install one in an aircraft with a standard AC. I have heard of this unit being granted a field approval if the owner mounts a second pitot tube on the aircraft just for the the AFS AoA indicator. 

 

Given that many of the low-cost, easy-to-install system are differential pressure only (the most popular was the Lift Reserve Indicator) you really don't know what they are telling you other than some kind of relative sort-of, kind-of, AoA-like-but-not-really indication. They will give accurate information over a wide range, but only at one loading. IF you adjust the probe position correctly you can get it to tell you one particular AoA at any dynamic pressure (airspeed). I believe that the original Lift Reserver Indicator (LRI) had you adjust the angle of the differential probe to show critical AoA so it did show critical AoA at any speed or loading. It was just that the scale was compressed at higher airspeeds and wing loadings. 

 

But don't take my word for it. Here is a very interesting paper that describes how all this works:

 

http://www.nar-associates.com/technical-flying/angle_of_attack/DeltaPAOA_wide_screen.pdf

 

I believe this paper is actually addressing the errors specifically in the Alpha Systems unit. (I am guessing at this based on the photos.)

 

Vane-type sensors, if properly placed, do read AoA for whatever configuration they are calibrated for or, if they have some way to sense flap position, can be calibrated for all flap positions. This is pretty straight forward. Personally I just don't like having a vane out there where it can ice up or get damaged. (OTOH, if your wing is iced up, your AoA isn't going to help you at all because your wing now has a completely different airfoil making the AoA indicator useless. So maybe a vane isn't so bad after all.) But a vane does respond to incident wind independent of airspeed and so can provide accurate relative AoA indications across a wide range of airspeeds. Add correction for flap position and you have a useful AoA sensor. 

 

BTW, the unit that will be adding flap correction is from RiteAngle. 

 

I'm sorry if I appear negative. I just find it so frustrating that the FAA inhibits technology that really could make our flying safer. When I went looking at AoA 15 years ago, the unit from Advanced Flight System (then Precision Flight Controls if I recall correctly) was the hands-down winner. Today it still appears that way. I would have one on every one of my airplanes if I could get away with it. But a differential pressure unit without dynamic pressure correction just doesn't really tell you what you want to know no matter how fancy the display is. So it looks to me like the vane-type indicator is the best we are going to get in the near term. 

 

I build the FAA approved CYA-100, and you've discussed just about everything applicable to an AoA display.

 

The only thought I can add is that if a vane type indicator is calibrated for stall in the landing configuration (flaps down), then you have a "buffer" against stall with the flaps up. It's hard for many folks to wrap their head around the fact that most (including the Mooney) airfoils stall at a LOWER angle of attack with flaps deployed.

 

Rip