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AOA confession

sailvi767

Well Known Member
As a Navy trained pilot I have had AOA available in most aircraft I have flown. My first RV was a RV6 with AOA. I liked it but never had a occasion where I felt it provided any type of save or a warning that the aircraft was not in the state I wanted it at. Still I liked having the extra level of protection.
I purchased a F1 Rocket that did not have AOA or any stall warning. That bothered me a bit but I quickly found the aircraft to be very honest and easy to fly in the patten at the proper speeds. I had planned a panel upgrade shortly after purchasing it that would include AOA. In Nov when the aircraft was getting a new panel I considered dropping the AOA option to avoid a pitot change and cost. In the end I kept the AOA. (Dynon HDX system with Dynon pitot)
On Tuesday I was out flying after a frontal passage. On return to my home field which involves a slightly overshooting approach as the norm to avoid tall trees I needed to also compensate for a strong overshooting crosswind in the pattern. (30 Kts at 1000 ft). On base to final I found myself with more overshoot than planned and wrapping the turn up. Normally I would have been at 75 knots at this point but was actually targeting 80 knots with the bumpy conditions. Just after crossing the gap in the trees still turning to align with the runway at about 250 AGL I got a beep from the Dynon AOA. Unloaded, leveled the wings and went around. Glancing at the airspeed I was at 67 knots. In one G flight I get the first AOA beep at 56 Kts. I was slow, wrapped up and visually 100% outside watching the trees. I should have abandoned the approach prior to that point and gone around. I now embarrassingly have my first AOA save in 7 years of flying RV’s.
I don’t know how much margin was left but I am now very glad I went with the AOA option. I fell into a trap many pilots get into and needed the AOA tone to jolt me back into reality. Spend the money and put a AOA system into your aircraft!
George
 
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Great story. I?m also planning a glare shield mounted AoA display. Much more useful than the antiquated stall warner.
 
Great story. I?m also planning a glare shield mounted AoA display. Much more useful than the antiquated stall warner.

I'd love to have this, but unfortunately it's not an option with the Dynon system I'm going with. I suspect I'll make out fine with the progressive aural warning, but having that visual cue would still be a nice addition.
 
Thanks for posting! Always great to hear others experiences. I too have an AOA going in my SuperSTOL.

Clark
 
Speed

In a plane I fly for my job that has 3 different pitot tubes a pilot i work with managed to lose all 3 airspeed sources (it rained inside the hangar and water got inside the pitot lines and when they got above the freezing lvl all the lines froze solid) and ended up having to use their AOA as their only real way to tell airspeed. So I am very much with you on AOA being an important back up for multiple reasons.

I am new to the RV world (I am close to ordering my first kit). but in some planes ive flown you can also use AOA to fine tune best glide speed in an engine out situation, since in reality best glide will change with weight. though from what I have been told that change is minimal in an RV.
 
I'd love to have this, but unfortunately it's not an option with the Dynon system I'm going with. I suspect I'll make out fine with the progressive aural warning, but having that visual cue would still be a nice addition.

I really wish Dynon would offer a glareshield option. One thing I will add. With the first AOA tone coming on 6 knots above stall in my aircraft in 1 G flight I made it my SOP to do a immediate go around if I get a AOA tone and I am not in the flare 1 foot above the runway.
 
On return to my home field which involves a slightly overshooting approach as the norm to avoid tall trees I needed to also compensate for a strong overshooting crosswind in the pattern. (30 Kts at 1000 ft). On base to final I found myself with more overshoot than planned and wrapping the turn up. Normally I would have been at 75 knots at this point but was actually targeting 80 knots with the bumpy conditions. Just after crossing the gap in the trees still turning to align with the runway at about 250 AGL I got a beep from the Dynon AOA. Unloaded, leveled the wings and went around. Glancing at the airspeed I was at 67 knots. In one G flight I get the first AOA beep at 56 Kts. I was slow, wrapped up and visually 100% outside watching the trees. I should have abandoned the approach prior to that point and gone around. I now embarrassingly have my first AOA save in 7 years of flying RV’s.
I don’t know how much margin was left but I am now very glad I went with the AOA option. I fell into a trap many pilots get into and needed the AOA tone to jolt me back into reality. Spend the money and put a AOA system into your aircraft!

George’s post, and the replies to it, show a wide range of responses with a similarly wide range of validity. (My qualifications to pontificate on the subject include four years of work as a contestant in the EAA Founder’s Innovation Prize on loss of control, and that work included studying 700 NTSB report narratives and dozens of dockets, watching a dozen accident videos over and over, flight tests and videos in my RV-9A, etc. All told, much more work and discovery than went into my Ph.D. from MIT… The result of all this is the Expanded Envelope Exercises (E3) so that pilots don’t lose their cognitive availability to process all of the information available when they get stressed. E3 has been written up a few times on line already.)

A number of points arise:
* Kudos! “Unloaded, leveled the wings and went around.” It doesn’t make a lot of difference in RVs with the abundant low speed control authority, but unloading the wings first before leveling is good form and can be crucial in other planes. Going around is good form;
* Hmm. “On base to final I found myself with more overshoot than planned and wrapping the turn up.” In the same way that going around is an under-practiced escape, so is tolerating a runway overshoot. Who says that overshooting a single runway is taboo? I used to train my primary students **NEVER** to tighten up the turn to final but to accept the overshoot and to learn from it and do better next time. And if there are closely space parallel runways, fly final at maybe 15° offset from the runway centerline for extra margin. Shucks, there are even ILS and localizer approaches with offset lateral guidance;
* One of the Extended Envelope Exercises is a deliberate runway overshoot to demonstrate that a strict psychological need to keep on the centerline at all costs can is a learned inappropriate reaction. Pilots tend to get comfortable on the centerline and, after a while, think that it is essential;
* Gusty winds can induce stalls. In my old Cessna, I once was flying with an extra 10 MPH in the pattern at an airport with known gusty conditions. Turning base in a shallow turn, the plane hit a gust and stalled. I did not hear the stall horn till after the recovery. Another man who posts here regularly had a similar experience. There are numerous examples in the literature where stressed pilots did not hear aural warnings…;
* Human factors – “visually 100% outside watching the trees.” This is one reason why visual AOA displays don’t live up to their promise. BTW, when this happens with even the fanciest head up displays (not heads up, please!), this phenomenon is called cognitive capture. Stressed pilots can spend so much attention on the outside world or on the symbology that the other gets ignored, even when watching both is essential;
* AOA limitation – All of the textbook illustrations of AOA at work assume that the AOA is constant. I did the flight test in the -9A (and presented at Oshkosh) that AOA can either lag (follow) pitch like airspeed does, or if there is a g load applied, AOA can lead pitch. Nobody talks about this, and nobody (that I know of) has researched the operational significance;
* I made a video of an approach and landing with winds 9G14. The AOA was all over the place and did not provide usable data all by itself. This is the same result as NASA report TN D-6210 from 1971 (!);
* Human factors – there are accident videos and multiple NTSB reports that indicate that lateral control and longitudinal control are separate tasks. This in turn suggests that problems turning base to final can be because the pilot was focusing on alignment and neglected pitch (and airspeed). The narrative above is consistent with this hypothesis. Interesting statistic: in 47% of the runway excursions on landing in RVs (running off the side of the runway after touchdown), the plane was first in trouble longitudinally, such as bounced landing, flat approach, etc;

I’ve now owned six airplanes in my career (four were RVs), and only the Cessna came with an aural stall warning system, a vane type. Haven’t really missed a stall warning system in any of 'em. When I was instructing in C150s, I really liked the vibrating reed stall warning with its progressive warning. When teaching slow flight and stalls, I’d tell the students to make the baby cry louder…

When I was rewiring the RV-9A and adding a Garmin autopilot and already had the wing open, that’s when I installed an AOA pitot tube. What did I learn?
* Visual AOA never got looked at in normal operation. And when I did look, just to see what it was showing, I had no frame of reference to know what it really meant when I had one or two or however many bars showing;
* It was a surprise to see that on a normal climbout, there were a few AOA bars showing.

Bottom line, and trying to keep it really short, get with a good CFI and learn to tolerate runway overshoots. Don’t be dying to avoid the overshoot. And don't count on some trendy gadget to save your bacon, because when you get really stressed, it will be just one more thing that gets ignored.
 
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George’s post, and the replies to it, show a wide range of responses with a similarly wide range of validity. (My qualifications to pontificate on the subject include four years of work as a contestant in the EAA Founder’s Innovation Prize on loss of control, and that work included studying 700 NTSB report narratives and dozens of dockets, watching a dozen accident videos over and over, flight tests and videos in my RV-9A, etc. All told, much more work and discovery than went into my Ph.D. from MIT… The result of all this is the Expanded Envelope Exercises (E3) so pilots don’t lose their cognitive availability to process all of the information available. E3 has been written up a few times on line already.)

A number of points arise:
* Kudos! “Unloaded, leveled the wings and went around.” It doesn’t make a lot of difference in RVs with the abundant low speed control authority, but unloading the wings first before leveling is good form and can be crucial in other planes. Going around is good form;
* Hmm. “On base to final I found myself with more overshoot than planned and wrapping the turn up.” In the same way that going around is an under-practiced escape, so is tolerating a runway overshoot. Who says that overshooting a single runway is taboo? I used to train my primary students **NEVER** to tighten up the turn to final but to accept the overshoot and to learn from it and do better next time. And if there are closely space parallel runways, fly final at maybe 15° offset from the runway centerline for extra margin. Shucks, there are even ILS and localizer approaches with offset lateral guidance;
* One of the Extended Envelope Exercises is a deliberate runway overshoot to demonstrate that a strict psychological need to keep on the centerline at all costs can is a learned inappropriate reaction. Pilots tend to get comfortable on the centerline and, after a while, think that it is essential;
* Gusty winds can induce stalls. In my old Cessna, I once was flying with an extra 10 MPH in the pattern at an airport with known gusty conditions. Turning base in a shallow turn, the plane hit a gust and stalled. I did not hear the stall horn till after the recovery. Another man who posts here regularly had a similar experience. There are numerous examples in the literature where stressed pilots did not hear aural warnings…;
* Human factors – “visually 100% outside watching the trees.” This is one reason why visual AOA displays don’t live up to their promise. BTW, when this happens with even the fanciest head up displays (not heads up, please!), this phenomenon is called cognitive capture. Stressed pilots can spend so much attention on the outside world or on the symbology that the other gets ignored, even when watching both is essential;
* AOA limitation – All of the textbook illustrations of AOA at work assume that the AOA is constant. I did the flight test in the -9A (and presented at Oshkosh) that AOA can either lag (follow) pitch like airspeed does, or if there is a g load applied, AOA can lead pitch. Nobody talks about this, and nobody (that I know of) has researched the operational significance;
* I made a video of an approach and landing with winds 9G14. The AOA was all over the place and did not provide usable data all by itself. This is the same result as NASA report TN D-6210 from 1971 (!);
* Human factors – there are accident videos and multiple NTSB reports that indicate that lateral and longitudinal flight are separate tasks. This in turn suggests that problems turning base to final can be because the pilot was focusing on alignment and neglected pitch (and airspeed). The narrative above is consistent with this hypothesis. Interesting statistic: in 47% of the runway excursions on landing in RVs (running off the side of the runway after touchdown), the plane was first in trouble longitudinally, such as bounced landing, flat approach, etc;

I’ve now owned six airplanes in my career (four were RVs), and only the Cessna came with an aural stall warning system, a vane type. Haven’t really missed a stall warning system in any of 'em. When I was instructing in C150s, I really liked the vibrating reed stall warning with its progressive warning. When teaching slow flight and stalls, I’d tell the students to make the baby cry louder…

When I was rewiring the RV-9A and adding a Garmin autopilot and already had the wing open, that’s when I installed an AOA pitot tube. What did I learn?
* Visual AOA never got looked at in normal operation. And when I did look, just to see what it was showing, I had no frame of reference to know what it really meant when I had one or two or however many bars showing;
* It was a surprise to see that on a normal climbout, there were a few AOA bars showing.

Bottom line, and trying to keep it really short, get with a good CFI and learn to tolerate runway overshoots. Don’t be dying to avoid the overshoot. And don't count on some trendy gadget to save your bacon, because when you get really stressed, it will be just one more thing to get ignored.


Well said Ed:) The critical word to take away from all that is "unloading", few understand that.
I've got an AoA in my 8, a set of vertical lights on the panel, I didn't put it there (bought the plane built) I've never really looked at it much and sure as h ell would never rely on it! My whole attention is devoted to one single guage inside my plane when landing, the ASI, the rest of my attention is outside. Even flying the early Lears many years ago my head was on a swivel between the ASI and the outside cues despite a crude AoA on the glare shield.
 
In a plane I fly for my job that has 3 different pitot tubes a pilot i work with managed to lose all 3 airspeed sources (it rained inside the hangar and water got inside the pitot lines and when they got above the freezing lvl all the lines froze solid) and ended up having to use their AOA as their only real way to tell airspeed. So I am very much with you on AOA being an important back up for multiple reasons.

I am new to the RV world (I am close to ordering my first kit). but in some planes ive flown you can also use AOA to fine tune best glide speed in an engine out situation, since in reality best glide will change with weight. though from what I have been told that change is minimal in an RV.

In most light plane AOA systems, AOA is measured with differential pressure between the Pitot tube and another tube, offset from straight ahead. In other words, if you lose airspeed, you've also lost AOA. The systems are not independent.

As for best glide speed -- one commercial vendor of a calculated AOA does not use weight in their certified device because it makes so little difference, they told me at Oshkosh. And don't forget that best glide over the ground depends on wind.
 
Thanks for sharing

Glad you made the right call and thank you for sharing.

Can someone explain to me how the AOA or a Stall Warning can be accurate when it is only located at the pitot at one location? the pitot doesn't know what the other wing is doing. So how does that work? Is there a reason why almost all planes have them on the left wing? (if to much of a thread drift just PM me)

thanks.
 
Well said Ed:) The critical word to take away from all that is "unloading", few understand that.
I've got an AoA in my 8, a set of vertical lights on the panel, I didn't put it there (bought the plane built) I've never really looked at it much and sure as h ell would never rely on it! My whole attention is devoted to one single guage inside my plane when landing, the ASI, the rest of my attention is outside. Even flying the early Lears many years ago my head was on a swivel between the ASI and the outside cues despite a crude AoA on the glare shield.

The unloading is easy for me as it was drilled into me from my first flight and I taught out of control flight. A AOA indexer on the glare shield is a great tool and I probably have a 1000 landings using nothing but that. I will check out the post talking about a option!
G
 
Nice writeup George!

This one time at Band Camp, I was on short final with a CFI in the right seat, doing my BFR. He asked me to show him a minimum approach speed landing.

We were steady at 55 knots (This is an RV-9), airspeed good, AoA good, all is good.

That is until we dropped below the tree line and the wind stopped at the same time.

The AS and AoA both dropped out instantly and at the same time.

At tree top height (30 to 50 feet?) we went from being in the Green on the AoA to it screeching just as I felt the plane nibble at the stall, with no warning tone, like George had. We went from flying to falling in a blink of an eye.

I went full throttle and held it level. The plane hit hard on the mains (this is a taildragger, not tricycle) just as the throttle hit the stop and bounced what seemed like straight up. No prop strike, nothing but it was an experience I never want to have again.

My point is, that our RV's are light and they can bleed speed VERY fast. On the positive side, they can gain speed equally as fast.
 
Can someone explain to me how the AOA or a Stall Warning can be accurate when it is only located at the pitot at one location? the pitot doesn't know what the other wing is doing. So how does that work? Is there a reason why almost all planes have them on the left wing?

You're right, of course, the sensor only gives information about airflow at the sensor location.

The short answer to why just one sensor is, "close enough." What the pilot will normally care about is the stall break, and it's easy enough to calibrate the sensor just ahead of stall break, or for full scale to occur at break. And from a human factors point of view, would stall information from both wings be useful information or would it be information overload, distracting the pilot from flying the plane? How would the pilot use that information in real life, approaching an inadvertent stall? Dunno.

However, on the Beechcraft Duchess twin, there are two stall warning vanes, one for flaps less than 16°, the other for flaps more than 16°.

As for both wings, usually the stall is pretty symmetric so again, the short answer is, "close enough." I have seen some writeups that talk about how on some airplanes with some sensors, it may be possible in a spin, where the sensor is on the outer wing with a lower angle of attack in the spin, to spin without setting off the stall warning. Dunno.

Last year at AirVenture, Ron Blum gave (twice) an excellent forum on aerodynamics of AOA. And Mike Bromfield from the UK has published a series of excellent articles on light plan handling and all kinds of related topics. There's lots, lots more to stalls than what's in the private pilot books but then again, the private pilot books are written for private pilots.

One thing (of many) I learned from Ron's talk is that while the AOA probe measures AOA *at*the*sensor*, and calibration takes it from there, there's a lot of variation in AOA measurement with probe location. The best AOA measurement is a few feet ahead of the wing, where the local AOA will change more than the "real" AOA, making the instrument more sensitive. The worst location is near the wing's rear spar, where the local AOA hardly changes at all.

Why on the left wing? Dunno, but that seems like an invitation to all kinds of political jokes. Not going there...
 
Why on the left wing? Dunno...

Perhaps a conservative choice? With most circuits being left-hand, that means the left wing will always be the slower one in the turn when you need the AOA information the most... AOA will be higher on the inside wing, right?
 
I'd love to have this, but unfortunately it's not an option with the Dynon system I'm going with.
It is an option, just not one they sell. AOA data is available on the Dynon serial bus, if you have something to display it with.
 
Well said Ed:) The critical word to take away from all that is "unloading", few understand that.
I've got an AoA in my 8, a set of vertical lights on the panel, I didn't put it there (bought the plane built) I've never really looked at it much and sure as h ell would never rely on it! My whole attention is devoted to one single guage inside my plane when landing, the ASI, the rest of my attention is outside. Even flying the early Lears many years ago my head was on a swivel between the ASI and the outside cues despite a crude AoA on the glare shield.

I should print and frame Ed's comments.

I discontinued my AOA glareshield display product 10 years ago because it did not solve the problem. I then developed a stick shaker that provided physical cues to AOA, which I provided to an FAA research program. In the end, I find the audio tones to be OK.

I am experimenting with an AOA autopilot, but before I do that, I need to work with the OnSpeed team.

IMHO, I think the missing link is training. Just adding a device to the panel is not enough. Learning to fly AOA is what the OnSpeed folks are all about.

V
 
I don't know if this is the real reason for mounting them on the left, but it's what I was taught.

Since most patterns are to the left, most low-speed turns are, too. The left wing has lower velocity in a left turn than the right wing and that translates to a higher angle of attack. Which is what you want to detect.

Dave
 
Van's AOA Kit

Van's sells an AOA Kit for installation in the RV-12. Mine is hooked up to the ADAH-RS unit which reports to the Dynon. Don't know if the would work with other AC but guess that it would. YMMV
 
* Kudos! “Unloaded, leveled the wings and went around.” It doesn’t make a lot of difference in RVs with the abundant low speed control authority, but unloading the wings first before leveling is good form and can be crucial in other planes. Going around is good form;

Could someone elaborate a bit more on "Unload prior to leveling the wings".
I would insert my guess here but why prove my ignorance. :)
Honestly I hesitated on asking but decided I would rather show my ignorance than continue on without understanding. Might save my life one day!

Thank you,
 
X2 here to piggyback on what zazoos said, what exactly is meant by "unloading"? I assume relieving backpressure applied for the turn? I plead ignorance as well and am curious to know.
 
X2 here to piggyback on what zazoos said, what exactly is meant by "unloading"? I assume relieving backpressure applied for the turn? I plead ignorance as well and am curious to know.

Correct, it simply means "stop asking the wing to make so much lift," aka relax whatever backpressure you're applying.
 
I'd love to have this, but unfortunately it's not an option with the Dynon system I'm going with. I suspect I'll make out fine with the progressive aural warning, but having that visual cue would still be a nice addition.

Why ?

We have a 2008 Dynon D100 that has AoA on it.

Calibrating was most excellent fun ;-)

I use it all the time and the OP is very wise to have it hooked up to an aural warning.

Much, much better than a vane stall warner.
 
Could someone elaborate a bit more on "Unload prior to leveling the wings".
I would insert my guess here but why prove my ignorance. :)
Honestly I hesitated on asking but decided I would rather show my ignorance than continue on without understanding. Might save my life one day!

Thank you,

Never be hesitant to show ignorance. Good pilots actively look for places they are ignorant and try to fix it. And no good pilot should take offense or look down on someone who is doing that.
 
Could someone elaborate a bit more on "Unload prior to leveling the wings".
I would insert my guess here but why prove my ignorance. :)
Honestly I hesitated on asking but decided I would rather show my ignorance than continue on without understanding. Might save my life one day!

Thank you,

Also Unload is a lessening of backstick pressure. This does not mean push the stick forward. Its similar to if you overbank, you do not necessarily need to go wings level to fix overbank, you just need to lessen some of the roll. its the same thing, just for pitch, just to bring your wings a little away from the edge of the envelope.
 
Unloading before leveling wings

Let me try an answer that.
In the case of you are in a left descending turn, the inboard wing has a higher angle of attack, if you then attempt to lift the wing first by rolling to the right before unloading, you will be lowering the left aileron, increasing the angle of attack on the left outboard section of the wing, and raising the aileron on the right wing, reducing the angle of attack on the right wing. If you are close to the stalling angle of attack on the left wing already, you run the risk of stalling the left wing, while still producing lift on the right wing. Not a good place to be, especially since you are close to the ground with limited height for recovery. The reason you unload first, is to reduce the angle of attack on the left wing, and take it away from being close to the stall, which then will give you some margin to roll and not stall the low wing.
 
AOA saves lives

Why ?

We have a 2008 Dynon D100 that has AoA on it.

Calibrating was most excellent fun ;-)

I use it all the time and the OP is very wise to have it hooked up to an aural warning.

Much, much better than a vane stall warner.

Dynon has AOA on the screen but no output to a repeater on the glareshield where it would be more handy just like all Navy planes have. Properly calibrated it works good with the background tone but a visual >o< would be nice. Standard Navy scan, meatball, lineup, AOA. That?s it, no airspeed, no power, all outside. Just remember to lower your hook :D

On base to final I found myself with more overshoot than planned and wrapping the turn up. Normally I would have been at 75 knots at this point but was actually targeting 80 knots with the bumpy conditions. Just after crossing the gap in the trees still turning to align with the runway at about 250 AGL I got a beep from the Dynon AOA. Unloaded, leveled the wings and went around. Glancing at the airspeed I was at 67 knots. In one G flight I get the first AOA beep at 56 Kts. I was slow, wrapped up and visually 100% outside watching the trees. I should have abandoned the approach prior to that point and gone around.

Nice break, overshooting high start, low, slow flat in the middle, go around. As heard from a blind and deaf LSO somewhere :D
Thanks for sharing.
 
There's really no significant difference in local true airspeed across the wing during turns, because the turn radius is much greater than the wing span.

For example, a standard rate turn at 65KTAS has a nominal radius of 639m. On an RV-8, the design pitot location is about 2.5m outboard from the aircraft centreline. The difference in airspeed at the pitot location is about +/- 0.25KTAS, which is less than the accuracy to which many light aircraft PEC calibrations are performed and much less than the accuracy to which most pilots fly (present company excepted, of course).

A similar argument applies to local AoA in steady turns (where roll rate is zero).

So, feel free to put the pitot wherever you want, as long as it is fairly well aligned with the freestream, and nothing upstream of it is contributing to a change in total pressure from freestream conditions.
 
AOA Stall warning

Most AOA systems are really no more than glorified stall warmers. To get the real benefit out of AOA you need an instrument that reads out in degrees AOA. NOW you have a useful instrument. A good AOA instrument will NOT lag and will instantly display the angle between wing chord and relative wind. Now you assign all your V speeds to specific AOA values. Want to depart a short grass strip on a hot day with trees at the end, you can lift off go to 7 degrees AOA (or whatever corresponds to Vx in your airplane) and FORGET the airspeed indicator. Maintain that AOA and the wing will be doing exactly what you need it to do. MUCH better than chasing an airspeed needle with pitch changes while those trees fill the windscreen, and so much more useful than just a stall warner. Unfortunately no one seems to appreciate this aspect of having AOA information in the cockpit.
 
"Unloading" is just that. Reducing lift by reducing AOA. Sometimes releasing some back pressure is required, sometimes full forward stick is required. Depends on what you are doing. You are unstalling the wing, or getting the wing further from stall AOA.

Airspeed/attitude/angle of bank etc do not matter. You can be wrapped up trying to not overshoot the runway, or at the top of a loop and accidentally got too slow. Reduce AOA to below that of stall, and you are not stalled, and have better control authority.

After many decades of unusual attitude training in the 121 world, somebody finally clued in the FAA. The Feds actually have forced standardized upset recovery training on aircrews.

The first step, action and callout, is "Push".

Navy flight school has taught that for decades, and flying AOA as a performance instrument, not just for stall warning.
 
It?s not about AOA or Airspeed; it?s about energy?

90% of what we are doing with the FlyONSPEED project is trying to provide high quality training resources to the EAB community. Lots of these are concepts that we were taught as fighter pilots in the military. Fighter pilots lose control of airplanes too, we just don’t crash very many in the process. Why? Training. The OP reacted just the way he was trained to the stall warning/critical energy cue: unload for control. RV's don't always provide good buffet cues approaching the stall. I first heard the expression "unload for control" as a nugget pilot in the USAF and had to endure regular viewing of a movie by the same name that was part of an Air Force training program for F-4 pilots. One of the young engineers that helped run that flight test and develop those training resources for the USAF was Burt Rutan, fresh out of college.

We’ve put a lot of resources on our web site (www.flyonspeed.org) for anyone that wants to learn more. Under the tab “How to Use the AOA Tone” are four essays that cover the topic in some detail with lots of illustrations and videos. We are always trying to improve those; so any feedback or critique is always welcome.

So, from 30K feet…energy management in one picture:

3c039a_102a063af3e04eb7bcd0f6a31f19ff2a~mv2.png


Let’s talk approach and landing first. To land any airplane, you configure, slow to ONSPEED, and maintain ONSPEED until it’s time to flare and touch down. It’s really the old 1.3 Vs you learned in private pilot training, but AOA doesn’t care about G load (bank angle), gross weight or density altitude. This is why it’s such a nifty cue (assuming you have a system that accurately measures AOA, damps the signal and gets the info to the pilot in a usable manner). Any good engineer will tell you that ONSPEED is just an AOA that is a surrogate for a “kinetic parameter” (i.e., airspeed in this case) which is why we’ve been able to come in land for years without an AOA system. What AOA brings to the fight is that it eliminates math…all the pilot does is push or pull (unload or load) the stick to stay in the Goldilocks zone. Warning: “Push” and “pull” are strong terms! That’s why they are lined out in the picture and marked “ease” and “squeeze,” a much better way to think of making those corrections. All US fighter aircraft have used AOA as a primary reference for landing for over 50 years. Oh, and there is some outstanding discussion in this thread: go arounds are free! Silly to die trying to salvage a bad traffic pattern no matter what equipment you have or what your experience is. Again, training and mindset are the key--far more important than equipment.

Now let’s talk maneuvering flight, because it’s some of the most fun we have with our clothes on…Refer to picture one above. Don’t pull any harder than ONSPEED when maneuvering. Why? In simple terms, when the airplane is ONSPEED, energy is “neutral” (thrust and drag are balanced for a given power setting, including full throttle). If you pull any harder (get a slow tone in our example), energy is “negative,” i.e., you’ve got more drag than thrust. That means you are going down, slowing down or both in that condition. To maintain aircraft control means more than just not stalling, it means having sufficient energy to maneuver as well.

Here’s a video that I recently posted over on the Safety Page that has a good, constant AOA maneuvering set in it (along with some other maneuvers that illustrate AOA in action). You need to crank the volume to hear the tone clearly. The tone is low because I had it turned down to normal levels (I usually crank it up for videos so it comes through loud and clear). This was a flight test and wasn’t intended as a training video—it just illustrates the key concepts in this post in six minutes or less: https://youtu.be/Hav7LMIeBFo. Remember how we learned that an airplane can stall in any attitude and at any airspeed? The accelerated stall occurred at 5.1 G’s and the airspeed is right around maneuvering speed (132 MPH IAS ish on the stand-by ASI visible in the video). Also listen to the instances of slow tone, even with my nose and lift pointed down at the same time.

To summarize, all of the above in three words or less: “unload for control" :)

Yes, you can accurately measure absolute angle of attack (the difference between zero lift and the chord line of the wing) with a coefficient of pressure system to with a 1/4-1/2 of a degree and have that system provide a damped cue at high G onset rates (that’s just a fancy way of saying it works in turbulence or if you pull on the stick hard). Turns out all you need are some great test airplanes (RV’s), good engineers with a sense of humor, 100LL, patience and great community support from the VAF family to do that.

Last item: any AOA system can be helpful, even if all it does is provide progressive stall warning. It needs to be properly calibrated and you need to understand how it works in an operational environment. Keep in mind that AOA systems are like a pitot/static system, i.e., calibration dependent and unless you have an identical, tested calibrations, take any specifics you hear (or read online) with a grain of salt since there is variation from airplane to airplane (i.e., just like you can’t directly compare IAS). This is why we are experimenting with automating the AOA calibration to make sure that an orange is an orange—remains to be seen if we’ll be able to pull that off; but it won’t be for a lack of trying!

v/r,

Vac
 
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GRT synthetic AOA

Vac, great info, as usual. Have you or any of your comrades had any experience with the GRT synthetic AOA? Paul Dye seemed to feel it was pretty good for pattern/landing back in the day, but not sure if that view still holds. If it's good, I can remove 3 or 4 ounces of plastic tubing. :D
 
Unloaded = 1G (Some may argue 0G is unloaded. OK. However 0G is not relevant to normal motoring around the sky, more aerobatics. I do aerobatics and never am at 0G doing my normal +G routine except momentarily. Bottom line AOA and stall is relevant to G loading and 1G is the bench mark for stall speed.)

AOA vane (like a weather vane) is actual angle of attack. The ones Garmin and Dynon and GRT use are differential air-pressure and is "derived" AOA (an estimate). There are AOA indicators (derived) that do not use either vane or pressure. It uses airspeed, pitch, G's, VSI and software to estimate margin to critical angle of attack... Call it electronic seat of the pants.

On Jets besides the AOA they have a Flight Data Computer that takes in all parameters and limits and warns the pilot. Although no direct visual AOA bars are shown may see a stall limit indication on airspeed tape and stick shaker.... among other warnings.

For most flying GA or commercial we don't work close to stall (except right before touchdown) but AOA indicator is a powerful tool. However if your RV has no AOA we know the stall speed of our aircraft "unloaded", giving you a margin of safety to stall.
 
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What Vac said...

I have been flying with his Gen 1 tone generator for nearly 2 years now and I freaking love the thing...

Have used heads-up display in USAF (indexer) and AOA gauge (also USAF and Part 121), so I am familiar and have flown with some of the mentioned systems.

I like the tone soooooo much better. Immediate feedback loop on what the wing is doing with no “eye distraction/heads down” inside to look at indexers, gauges, etc. Intuitive. Easily learned.

Valuable feedback not only in pattern work, but in maneuvering flight as well. Also, I learned that most of the speeds I was using in the pattern were too fast...I find my touchdown points more accurate and landings more consistent when flown using the tone vs a straight airspeed reference.

For example, in the OP’s case had he been flying with Vac’s system, he would have been getting AOA trend info all the way as he slowed on downwind, around the final turn, and not just an alert when getting slow on the overshoot. In any case, if flying the On Speed tone won’t give you a safe final turn without an overshoot, you’ll know to take it around early enough to not be hazardous.

Takes a few flights to get used to, but am totally addicted and would not be as comfortable now without it.

EAA Innovation Award winner year before last...great system Vac!

Rob
 
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Van's sells an AOA Kit for installation in the RV-12. Mine is hooked up to the ADAH-RS unit which reports to the Dynon. Don't know if the would work with other AC but guess that it would. YMMV

I will let you know in a week or so. I made an AOA installation with a simple rivet in the leading edge, like the 12 setup, on my 10. I hope to calibrate my AOA on the next flight; That could be a week given the @#$% weaher we're getting now.

Larry
 
my AOA helps in other ways too

As a Navy trained pilot I have had AOA available in most aircraft I have flown. My first RV was a RV6 with AOA. I liked it but never had a occasion where I felt it provided any type of save or a warning that the aircraft was not in the state I wanted it at. Still I liked having the extra level of protection.
I purchased a F1 Rocket that did not have AOA or any stall warning. That bothered me a bit but I quickly found the aircraft to be very honest and easy to fly in the patten at the proper speeds. I had planned a panel upgrade shortly after purchasing it that would include AOA. In Nov when the aircraft was getting a new panel I considered dropping the AOA option to avoid a pitot change and cost. In the end I kept the AOA. (Dynon HDX system with Dynon pitot)
On Tuesday I was out flying after a frontal passage. On return to my home field which involves a slightly overshooting approach as the norm to avoid tall trees I needed to also compensate for a strong overshooting crosswind in the pattern. (30 Kts at 1000 ft). On base to final I found myself with more overshoot than planned and wrapping the turn up. Normally I would have been at 75 knots at this point but was actually targeting 80 knots with the bumpy conditions. Just after crossing the gap in the trees still turning to align with the runway at about 250 AGL I got a beep from the Dynon AOA. Unloaded, leveled the wings and went around. Glancing at the airspeed I was at 67 knots. In one G flight I get the first AOA beep at 56 Kts. I was slow, wrapped up and visually 100% outside watching the trees. I should have abandoned the approach prior to that point and gone around. I now embarrassingly have my first AOA save in 7 years of flying RV?s.
I don?t know how much margin was left but I am now very glad I went with the AOA option. I fell into a trap many pilots get into and needed the AOA tone to jolt me back into reality. Spend the money and put a AOA system into your aircraft!
George

sailvi767,
My AOA- a Lift model Aircraft & Spruce P/N 05-14964 is a gauge with no aural warning. I look at it during my "normal carrier type approaches" and confirm my margin above stall.
The additional benefit is that I have reduced my grass landings to ~500-550ft no brakes needed when flying the AOA.
Really think it was worth $312 for the added safety.

Also use it during engine out practice.

Safe flying

Daddyman
 
Never heard the phrase "unload for control" but I realize this is what I've been doing instinctively. Granted I've been using the stall horn as the indicator so I figure that's leaving a much greater margin than if I had an AOA, but is this not something everyone does?
 
More points to ponder

From the "it depends" department: "Unload" is a relative term, it just means less G than required for whatever it is you are trying to do. In most civilian flying, that means "something less than 1." For example, if I'm pulling a bit too hard in the final turn (riding the "slow" tone), easing the stick forward may induce a .9 G condition. In a more graphic example, if I'm in a 6G turn and want to grab some energy (go faster), 3G's is an "unload." A perfect unload may, in fact, be zero G since an airplane cannot stall at zero G. That recovery trick only works if the ground doesn't get in the way :)

Vanes vs Pressure. It depends on how well the computer algorithm works. A vane has the potential (pun intended) for better overall performance; but a good piece of software can match that performance for all intents and purposes. For example, at an L/Dmax condition (a critical performance parameter that a good AOA system should capture, our Gen 2 shows in absolute AOA of 7.54 degrees in the RV-4 with a standard deviation of .04 deg and standard error or .00 deg. At the same condition, the calibrated vane on the test boom shows a raw alpha of 4.41 deg, with a standard deviation of .03 deg and .00 error as well. The difference between angles is the delta between effective geometric AOA (what we learned in pilot training) and "absolute" AOA (what the wing sees in flight). We are seeing a worst-case error of about .2 degrees using pressure and .1 degrees on the calibrated boom; close enough for government work using a differential pressure source. We are testing with Dynon, Garmin, Alpha Systems, pop rivet, homemade and AFS style differential pressure sources and will publish results as we get 'em. Any of those configurations will work, but may require a different math technique to derive AOA.

Visual vs Audio. Ergonomics and "egonomics" at play. For eyes out, you can't beat an audio cue; but there are limiting considerations. For example, if task saturated, "tuning out" audio is a normal response. On the other hand, it's a pain in the butt to use a visual cue when you're looking over your shoulder. Perfect world, one of each can't hurt; so we are working with Vern to incorporate his nifty, inexpensive visual display. 2 "displays" (audio + visual) may also provide a degree of redundancy. Our system can display raw AOA in degrees (either absolute or geometric); but a graphic display makes more sense for the stick monkey. I'm a fan of the "standard" military configuration (doughnut + chevrons) because it's caveman simple. We added a simple floating bar with an intuitive L/Dmax cue; but totally get that some folks prefer chevrons so it'll have that capability as well. However, the audio capability will remain the heart of the system...you can bolt it into a round dial airplane. I don't have a visual display in the RV-4, but that's simply a personal preference.

Electronic vs air data AOA solution. You can derive AOA from an INS (accelerometers), i.e., you can remove the pounds of extra tubing in the airplane ;) We have an INS platform in Gen 2 for that purpose, but are using that primarily to automate the calibration process and, potentially, integrating that into the AOA algorithm for normal use. We are already integrating lateral G: the tone moves in the headset (sound field) with the ball providing a 3D audio yaw cue. This works with a stereo intercom or via bluetooth to a stereo headset. We learned in the military that directional audio cues work really well and it's nice in the base turn in the RV-4 to get a gentle nudge from the tone to adjust rudder pressure as well as stick pressure when I'm not looking inside. Our objective with Gen 2 is to demonstrate the utility of having intuitive AOA, sideslip and energy cues available to the pilot.

Stall warning. FAR23 stall warning requirements stipulate a minimum of 5 KTS of warning (natural or artificial cues). ANY calibrated AOA system will provide better progressive stall warning than a simple stall warning system. Actual "warning" with an AOA system is essentially pilot selectable. Since I fly a lot of aerobatics, I prefer an accurate slow tone with warning occurring about 2-3 KTS above actual stall so I can "ride" the aerodynamic limit if I want--purely a personal preference and since my airplane doesn't have to conform to FAR23, nor do I in this case. However, reaction to stall warning should always be the same, regardless of system installed or natural cues: unload for control.

Optimum turn performance. "Optimum" turn (best balance of turn rate, turn radius and energy) occurs ONSPEED. In real life, there are only two times when it makes sense to pull harder than ONSPEED. One occurs in combat; and since we don't face that unless the traffic pattern is really busy, the only other time I can think you want to approach the aerodynamic (stall limit) is in an emergency dive recovery close to the ground. In that case, it is appropriate to select maximum power, get the lift pointed 90 degrees to the horizon and pull right to the aerodynamic limit (stall warning) whilst hoping the ground doesn't get in the way. Since hope is never a good strategy, follow Ed's sage advice earlier in the thread to not get there in the first place by exercising good flight discipline. In general, don't ever pull harder than ONSPEED unless you're having some fun upside down.

I understand there's a lot here, so just refer back to the picture in my previous post--it's really that easy; don't pull harder than ONSPEED.

v/r,

Vac
 
Never heard the phrase "unload for control" but I realize this is what I've been doing instinctively. Granted I've been using the stall horn as the indicator so I figure that's leaving a much greater margin than if I had an AOA, but is this not something everyone does?
Well not all stall horns are equal, but stall horn means in general stall is about to occur. It may be conservative or not. Go up and practice some slow flight and nip at the stall horn. Then pull back and note when it breaks.

Every pilot at some point should have done slow flight or "min control" speed maneuvers and stalls and stall recoveries (including accelerated stalls) during training and check ride. GA, commercial and even military, have flown with out AOA.... Airspeed is our indication of stall or angle of attack (to critical) at 1G. Unloading is not a common term but it means 1G. Once you "pull G's" your stall goes up...

AOA calibrated and accurate is a great tool. If you can put it in your plane, it does add a bit of safety or situational awareness, but it is not required to fly safely.
 
Degrees AOA

This is the AOA system that is now made by Advanced Flight Systems that displays degrees AOA. Again stall warning is just one SMALL reason to have AOA information, but without a degree readout all you have is a stall warner. AOA is about knowing precisely what the wing is doing in all aspects of flight.

AFAOApro-2.jpg
 
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Performance Cuing

Any AOA system that can be calibrated to provide performance cues (L/Dmax and ONSPEED) in addition to "slow" cueing is going to be more useful than simple, accurate progressive stall warning. The ability to ACCURATELY capture the aircraft curve (i.e., measure AOA) depends entirely on the sensor and processing that the computer does. AFS has multiple set points and the ability to capture two curves (flaps up/flaps down) I believe. For truly accurate AOA performance you need flaps up/flaps down curves, although, ultimately if the only use you have for AOA is approach and landing an accurate calibration in normal landing configuration is doable (with degraded performance at other flap settings). The type of flap fitted will really define the requirement for multiple curves. The plain flaps on the RV-3/4/6/7/8 have less effect than the split flaps on the -9/-10 and -14. Here's the difference between a two-point calibration and a multi-point calibration:

3c039a_6ddfc4ac5f524ababf208133b857a5f5~mv2.png


The shaded area is potential error. Vcc is Carson's speed. L/Dmax is best lift to drag ratio (bottom of the drag curve). Vprmin is min power required speed (ONSPEED, or bottom of the power required curve) and 1.1 Vs is where stall warning is set in this diagram. Note that each of these calibration points is a key performance parameter. This sketch is for a 23-series airfoil (RV-3/4/6/7/8).

If you have flight test data for your airplane and know what geometric or absolute alpha you are looking for, then a digital display can be helpful. If you don't have data; but have an accurate percent lift calculation (i.e., stall = 100%), then L/Dmax will occur at 50% lift, and ONSPEED will occur at 60% lift. Many systems have some sort of % lift calculation; but keep in mind that is calibration dependent and the 50/60% rules require that the system accurately measures 100% lift at stall. It also requires that the system accurately maps the aircraft curve which it may or may not do. Only way to determine is flight test.

The reason some AOA systems are simply good progressive stall warning is because even a basic, not-quite-right calibration will capture stall accurately although it may not express it properly in terms of % lift or actual AOA.

v/r,

Vac
 
Wow my head is spinning. Math and charts and graphs ugh. I guess many are interested in the details but after flying with the Onspeed Beta box for 18 months All I care about are the tones I hear ...Slow...Onspeed...or fast. This AOA is fantastic. I do not have ANY visual for the AOA other than airspeed so when I pull power fully off and put my flaps on I trim for the Onspeed tone. I do a quick check of the airspeed to make sure I am in the ball park and then fly the tone looking out the window until I grease it in. I love aural AOA.
 
I fly both my -10 and Rans with Dynon systems. The audio AOA is good but their on screen indicator is worthless. The wigit is so small that you can?t see it in a glance.

I have suggested the following firmware change several times, so here it is again.

When airspeed drops below a user selectable value, or when the aural warning is about to automatically come on, the AOA on screen expands to the size of the airspeed tape and is placed just to it?s right. It returns to normal size when airspeed drops below another user selectable speed, well below stall.

Or better yet, a remote indicator on the network for glare shield mounting as others have suggested.
 
I've been pondering the flight safety issues for a long time, and have experimented with visual, audible and haptic indicators for AOA.

Under the assumption that I don't trust the automatic attitude recovery systems that are available (different debate), so how can we use technology to provide the pilot with the critical information, at the right time and elicit the correct response?

I think the OnSpeed technology comes the closest to fulfilling the requirement, primarily because it can be used in normal flight manoeuvres. This allows the pilot to develop good habits that will prevent upset situations, and should one occur, the instincts to recover.

Visual or Audio... how about both? Different people respond differently to audio or visual cues. For sportplanes, where we may be doing aerobatics or formation flying, or a full slip landing on a sandbar or short field, the visual indicators are less useful than the audio. However, many people disagree.

On my list of things to do is build a HUD laser-based AOA indicator. For straight-ahead landings, this may be useful. I have a long list of gizmos I want to build before I die, so give me some time for this. I will be collaborating where possible with the OnSpeed folks.

V
 
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