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How to use an AOA indicator?

KazooRV-9A

Well Known Member
Patron
I was at Oshkosh this past week, and had opportunity to look at the Alpha Systems AOA indicators which I was/am possibly considering for my RV-9A build. (I currently fly a Cessna 120)

But even after talking with the salesmen, I can't understand how to use the AOA for landing?

The salesmen kept saying that you wouldn't be looking at airspeed, but would be keeping on the AOA "Donut" (optimum AOA) as you approach, adjusting throttle for hitting the touchdown point. I don't understand how airspeed is associated/coordinated with using an AOA indicator for landing. How is it, that you wouldn't still be looking primarily at the AI, on landing?

-Can someone describe exactly how to set up and execute an approach and landing, utilizing an AOA indicator? Is it truly useful for this?

-What other flight conditions, do GA pilots actually use/rely upon an AOA indicator for?

-Is a $2000.00+ AOA indicator, a great investment for an RV-9A?

The salesmen kept stating that "all US service pilots are taught to fly with the AOA". What does this mean to me vs. an F-14 pilot? Why did the salesmen think that would help convince me to buy one? (Note that my C120 doesn't even have a stall warning horn)....

I enjoyed the demo and discussions with the salesmen, they were very nice and the equipment looks very well made, but in the end I couldn't/didn't plunk down that many AMU's $, for the device.

Thank you!

AC.
 
Take a look at these videos:

https://www.youtube.com/watch?v=ajOd0Rh8Bcc

https://www.youtube.com/watch?v=0XFhNmCvcC8

These are for the AFS AOA, but the operating principles are the same for any AOA that uses a doughnut and/or chevrons as a display.

Mine has saved me one more than one occasion. It allows you to fly just above the stall speed very precisely. Imagine having to follow that Cub from Ripon, that decides to slow to approach speed at Fiske. It also helps when you are low and slow to determine the appropriate course of action to take.

Hopefully you talked with Dynon and/or AFS about how you get their AOA for their EFIS significantly less expensive than the one you mentioned.
 
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AOA vs airspeed

One way to think about it is airspeed is always affected by weight, altitude, and temperature. The angle of attack is not affected by any of those three. When he is saying fly the green donut he is saying that will give a constant angle of attack. By approaching landing at that constant angle of attack you can vary the decent rate by increasing or decreasing power. Thus you never need to look at the airspeed. Typically, you would calibrate the green dot to 1.3 time stall speed once - at any weight, altitude, and temperature - and forget about the speed after that.
The advantage to this type of flying is you no longer care if you are at the beach or a high mountain airport, at gross weight or minimum fuel, in a steep bank or level flight, the green donut is a constant and your landings will become more consistent. Does that help?
 
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But even after talking with the salesmen, I can't understand how to use the AOA for landing?
AC.

Thanks for asking this question. Ive felt like a dope for a long time on understanding how to use AOA in the flight regimes - just didnt get the explanations.

And thanks to Bob Leffler for the videos. I think I finally get it now, esp the last link.
 
If you buy an EFIS, most likely it will have an AOA display. I know Advance and Dynon do. $2000 for a stand alone unit is nearly 40% of the cost of an EFIS. Dan from Reno
 
Flying AOA in an RV

Here's a demo video of AOA maneuvering, including approach and landing in an RV. The video uses an aural system that lets you hear the angle of attack in lieu of looking at a graphic display. "ONSPEED" is simply optimum AOA--the same as a "Green doughnut" on a conventional display. The video includes an airspeed indicator, so you can see how IAS varies while AOA remains constant during different examples of maneuvering flight. Any calibrated AOA system really helps with proper energy management when you are flying on the back side of the drag curve ("region of reversed command"), as we do every time we take off and land.

There are lots of excellent systems available, and many of them have some sort of progressive stall warning that can help determine when you are approaching aerodynamic limits, and may also allow you to hear ONSPEED or other useful aerodynamic AOA (e.g., L/Dmax).

https://youtu.be/-kbA6NxMpmQ

Fly safe,

Vac
 
Possibly look at Dynon's AOA system via their pitot tube. I installed it on my RV-8 after phase 1 and wished I had it sooner. I use the aural tone to determine precise approach AOA to avoid float, yet still have enough energy to make a nice wheel landing on a short runway.

Friday night I got stuck following a Piper Cherokee between RIPON and FISKE. There has been lots of discussion about using flaps or not while flying the 90 kt profile into Osh. I started off flying comfortably at 90 KIAS with no flaps while maintaining visual spacing with the Cherokee....I started to hear my AOA chirping and noticed I was down to 64 KIAS while trying maintain spacing. I added 10 deg of flap and it made flying at 65 KIAS behind that Cherokee a bit easier.

The take away is that the AOA tone gave me a warning sooner than I may have sensed my higher AOA and lower airspeed since I was 100% heads up trying to maintain visual separation.

A good AOA system is worth its weight in any precious metal...
 
I have two AOA systems, one from my GRT HX, one from the Dynon D6 backup. I really like the aural warning tones if approaching a stall. That said, I still fly approaches to landings by indicated airspeed. The only unaccounted for variable is weight, and in practice that doesn't vary that much. I use the gross weight speed, and if I'm light the landing is a bit longer. (If it's a really short runway, some thinking is needed). But it's not the same as for an F-14, where the weight difference between heavy and light is substantial, and every (carrier) landing is a short field landing.
As others have noted, you can get a complete EFIS with AOA for less than $2K.
 
Possibly look at Dynon's AOA system via their pitot tube. I installed it on my RV-8 after phase 1 and wished I had it sooner. I use the aural tone to determine precise approach AOA to avoid float, yet still have enough energy to make a nice wheel landing on a short runway.

Friday night I got stuck following a Piper Cherokee between RIPON and FISKE. There has been lots of discussion about using flaps or not while flying the 90 kt profile into Osh. I started off flying comfortably at 90 KIAS with no flaps while maintaining visual spacing with the Cherokee....I started to hear my AOA chirping and noticed I was down to 64 KIAS while trying maintain spacing. I added 10 deg of flap and it made flying at 65 KIAS behind that Cherokee a bit easier.

The take away is that the AOA tone gave me a warning sooner than I may have sensed my higher AOA and lower airspeed since I was 100% heads up trying to maintain visual separation.

A good AOA system is worth its weight in any precious metal...

What generated your AOA chirping? Was it the Dynon AOA built in or do you have Vac's most excellent "ONSPEED" audio warning?
 
What generated your AOA chirping? Was it the Dynon AOA built in or do you have Vac's most excellent "ONSPEED" audio warning?


It is built into the Dynon system. I have a D-180 with a Dynon pitot tube in my -8 as well. I would not purchase an AOA system unless it had an aural tone. Vac should market his AOA as it is mimics the F-4 which had an outstanding aural tone system.
 
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Others have given an answer to your question "how do you use AoA" - and by now, you probably realize that it is simple. And yes - it IS that simple. No matter weight, G-Load, etc, just keep it on the donut. Suddenly have to break out in a tight turn to avoid traffic or a bird? Keep it on the donut and you won't stall.

The remaining question then, is "how do I use the Airspeed indicator?" For me, the answer is - to make sure I am below the top of the white arc to lower the flaps. That's the last time I look at airspeed on approach. And while I used to use AoA in very advanced flying in my old job, I only started using it for light airplane flying about six or seven years ago. Before that, it was all airspeed based. I still have to do that when flying demos in lots of different craft, but ALL of my airplane's have AoA, and I wouldn't build one without it.

It's easy to learn, far superior, and don't let the old guys tell you it isn't. You CAN teach an old dog new tricks!

Paul
 
I've been using my GRT Sport AOA indicator for over a year and I love it.

I've been flying Cessna140s, Taylorcraft, Champs, etc exclusively prior to finishing my RV, so I've never used a stall warning device before- it was all seat of the pants and airspeed.

I notice that it gives me confirmation of turbulent conditions on landing as well as a slight compensation in approach speed based on actual loading.

I didn't buy my EFIS because I needed an AOA, and I've never felt it was truly needed for safe flying, but I can appreciate how it let's you minimize landing rollout without using brakes.
 
Great video's and thank you all for the information.

I have an older Sport EFIS that I spoke to GRT about at Airventure last week.

If I have it correct, it can be modified to add AOA and I see on their website, that it also has an aural tone.

I think that this may be the option to choose. (Although the Alpha Systems unit had a cool heads-up display, for just money....)

I believe that I will include AOA in my build. Wonder how well I currently fly "On Speed" at approach,,,

I think that through the video's and in reviewing the theory behind the AOA indicator, that I better understand the "Can stall at any speed and any attitude" training!

Thank you,

AC.
 
Onspeed AOA. Great teaching tool

Recently The Onspeed (OS) showed me what a powerful flight tool it is.

My son Ian, 25yrs, has grown up flying with me numerous hours. He recently started down the road to pilothood. He has been taking lesssons in a Light sport Pipestral. He told me that the pipestral flys very much like The 7a and the 12 I now own. Extremely light on the controls, same rotax power plant but has a high wing. I had never let Ian take off or land previously but yesterday I deceided to give him a try. Ian recently soloed the pipestral.

I flew up to 3500 feet and gave Ian a lesson on how the AOA OS works and sounds. There is nothing to look at only aural warnings. He flew simulated single turn approaches. He is being taught a rectangular pattern so this was new to him except he has been in my plane dozens of times while I land with a single turn approach. Our ten minutes of training was over and we headed back to land. My RV12 does not have dual screens so Ian had no instruments in front of him. After he arrived at the proper pattern alt he throttled back and set up a glide with trim OS. With his head out the window the entire time he nailed his first landing. It was a right hand pattern but he was on the right side of the aircraft. He had never landed a right hand pattern. He made another right hand landing again nailing it. There was no wind so we decided to use the other runway which is a left hand pattern. He again nailed two more landings without ever looking at the instruments as I told him to trust me and AOA OS will do the work for you.

I had a blast doing this with my son. I think he is hooked on the AOA OS.
 
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One point on using AOA. AOA should be cross checked with the airspeed. It becomes your primary scan for landing but like everything else it should be cross checked with the airspeed at least once after slowing to approach speed to insure its functioning properly. I check on base and again final.
 
The Emperor's New Clothes

AOA visual indicators are the emperor's new clothes of GA flight instrumentation. I've got about 200 hours with it in my RV-9A, done flight tests, have made videos, plotted data, the whole nine yards.

There are basic problems with visual AOA:
1. You can't adjust target AOA in advance for reported gusts and winds, although you can adjust airspeed. (To be complete, you do have to adjust airspeed for gusts and winds). If you fly the same AOA regardless of wind, that's the same as flying an approach with no wind compensation;
2. "On speed" varies a lot, unless you are the only plane in the pattern with all the runway you need. If you are told to keep your speed up, or to make the first turn off, those will require a different approach speed and hence a different AOA. And how do you calibrate for on speed, or do you just take what the vendor gives and check it against airspeed?
3. If you fly a slow vertical S and plot IAS, G, and pitch, you can see how noisy the recorded AOA is. Sometimes you can set a filter ringing (you engineers know what I'm talking about) with even simple, smooth maneuvers. I've got data from two different vendors, both show lots of noise in the plots;
4. Recorded video in very light chop shows my AOA flickering by +/- two bars, so that disqualifies it from being a precision, general purpose instrument. The airspeed indicator in my system is heavily damped and hardly budges, but to be fair, the mechanical airspeed indicator in my RV-8 flickers by about +/- 2-3 MPH in similar conditions to the AOA flickering by two bars;
5. For a given weight, the airspeed band corresponding to each displayed AOA bar is not constant, but gets narrower at higher AOA. One bar of AOA variation is more airspeed variation than you'd get watching the airspeed indication;
6. If you're turning base to final and looking at the runway, an AOA indicator atop the panel is out of your primary field of view.... especially if you are fixated on the runway;
7. I know one vendor who will not say exactly what their AOA shows, how it calculates how many bars to show, or what compensating is done in the display processing. I've asked;
8. And of course, different vendors use umpty gazillion different displays, so learning one AOA system doesn't necessarily mean that you know **exactly** what the next system you fly is showing, even if you know how it is calculating the display.

Aural stall warning? Absolutely. Aural AOA cues for speed? Fuhgeddaboutit.

And I did get a chance to try out AOA in an F-18 simulator last month. The speed band corresponding to the on speed bug being illuminated is about +/- 6 knots, and, making the appropriate conversions, this is a little fatter than +/- 1 bar AOA on my plane. The F-18 AOA did not flicker, but who knows how much compensation was in that system, probably from a computer that cost more than my whole plane. And F-18 pilots don't compensate for winds and gusts on approach. My nephew flies F-22s and he says almost all those pilots fly approaches using airspeed based on weight and ignore AOA.

Bottom line? Attitude flying still rules!

Ed Wischmeyer

PS. I'm going to apply to present these findings at Sun 'n Fun and Oshkosh. Bring your tomatoes, I'll bring my helmet...
PPS. Who are you going to believe, me or the recorded flight data?
PPS. For you classical control theory types (a la Bode plots), you can get some really interesting lead/lag phenomena, and those have implications for piloting technique. AOA can lose big there under the right circumstances, but that's a longer explanation for a limited audience.
 
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FYI...

Recently The Onspeed (OS) showed me what a powerful flight tool it is.

My son Ian, 25yrs, has grown up flying with me numerous hours. He recently started down the road to pilothood. He has been taking lesssons in a Light sport Pipestral. He told me that the pipestral flys very much like The 7a and the 12 I now own. Extremely light on the controls, same rotax power plant but has a high wing. I had never let Ian take off or land previously but yesterday I deceived to give him a try. Ian recently soloed the pipestral.

I flew up to 3500 feet and gave Ian a lesson on how the AOA OS works and sounds. There is nothing to look at only aural warnings. He flew simulated single turn approaches. He is being taught a rectangular pattern so this was new to him except he has been in my plane dozens of times while I land with a single turn approach. Our ten minutes of training was over and we headed back to land. My RV12 does not have dual screens so Ian had no instruments in front of him. After he arrived at the proper pattern alt he throttled back and set up a glide with trim OS. With his head out the window the entire time he nailed his first landing. It was a right hand pattern but he was on the right side of the aircraft. He had never landed a right hand pattern. He made another right hand landing again nailing it. There was no wind so we decided to use the other runway which is a left hand pattern. He again nailed two more landings without ever looking at the instruments as I told him to trust me and AOA OS will do the work for you.

I had a blast doing this with my son. I think he is hooked on the AOA OS.

Just an FYI regarding Jeff’s post...

He (and I) are using an AOA system described by Vac in post #6 on Page 1 of this thread which is an aural-based system vs the visual one being considered by the OP in Post #1. Similar outcomes desired in both cases (using an AOA system to enhance SAFE flying in our RV’s) but a different manner of approaching that goal.

I have been flying with Vac’s system 4-5 months and am completely addicted to it now...it has allowed me to more completely utilize my RV’s flight envelope, allowed more consistent approach/landings, and keeps me from pulling on the pole too hard on the occasional overshoot from base to final.

I. Love. It!! D-I-Y/built it yo’self approach keeps it easy and cheap, too. I have a Dynon Skyview system and after getting it tweaked and dialed in for my aircraft, it has been invaluable.

Research is on-going for the Gen 2 system, but Gen 1 is available now by searching for Vac’s “On Speed” thread over on the “Safety” forum on this website. Lots of info, data and links to relevant websites found there...

Rob S.
 
Questions.

AOA visual indicators are the emperor's new clothes of GA flight instrumentation. I've got about 200 hours with it in my RV-9A, done flight tests, have made videos, plotted data, the whole nine yards.

There are basic problems with visual AOA:
1. You can't adjust target AOA in advance for reported gusts and winds, although you can adjust airspeed. (To be complete, you do have to adjust airspeed for gusts and winds). If you fly the same AOA regardless of wind, that's the same as flying an approach with no wind compensation;
2. "On speed" varies a lot, unless you are the only plane in the pattern with all the runway you need. If you are told to keep your speed up, or to make the first turn off, those will require a different approach speed and hence a different AOA. And how do you calibrate for on speed, or do you just take what the vendor gives and check it against airspeed?
3. If you fly a slow vertical S and plot IAS, G, and pitch, you can see how noisy the recorded AOA is. Sometimes you can set a filter ringing (you engineers know what I'm talking about) with even simple, smooth maneuvers. I've got data from two different vendors, both show lots of noise in the plots;
4. Recorded video in very light chop shows my AOA flickering by +/- two bars, so that disqualifies it from being a precision, general purpose instrument. The airspeed indicator in my system is heavily damped and hardly budges, but to be fair, the mechanical airspeed indicator in my RV-8 flickers by about +/- 2-3 MPH in similar conditions to the AOA flickering by two bars;
5. For a given weight, the airspeed band corresponding to each displayed AOA bar is not constant, but gets narrower at higher AOA. One bar of AOA variation is more airspeed variation than you'd get watching the airspeed indication;
6. If you're turning base to final and looking at the runway, an AOA indicator atop the panel is out of your primary field of view.... especially if you are fixated on the runway;
7. I know one vendor who will not say exactly what their AOA shows, how it calculates how many bars to show, or what compensating is done in the display processing. I've asked;
8. And of course, different vendors use umpty gazillion different displays, so learning one AOA system doesn't necessarily mean that you know **exactly** what the next system you fly is showing, even if you know how it is calculating the display.

Aural stall warning? Absolutely. Aural AOA cues for speed? Fuhgeddaboutit.

And I did get a chance to try out AOA in an F-18 simulator last month. The speed band corresponding to the on speed bug being illuminated is about +/- 6 knots, and, making the appropriate conversions, this is a little fatter than +/- 1 bar AOA on my plane. The F-18 AOA did not flicker, but who knows how much compensation was in that system, probably from a computer that cost more than my whole plane. And F-18 pilots don't compensate for winds and gusts on approach. My nephew flies F-22s and he says almost all those pilots fly approaches using airspeed based on weight and ignore AOA.

Bottom line? Attitude flying still rules!

Ed Wischmeyer

PS. I'm going to apply to present these findings at Sun 'n Fun and Oshkosh. Bring your tomatoes, I'll bring my helmet...
PPS. Who are you going to believe, me or the recorded flight data?
PPS. For you classical control theory types (a la Bode plots), you can get some really interesting lead/lag phenomena, and those have implications for piloting technique. AOA can lose big there under the right circumstances, but that's a longer explanation for a limited audience.

Hello Ed,
When I fly an approach at increased speed due to a controller request, by definition the approach is no longer stabalized at the briefed approach speed or AOA. However, somewhere between the final approach fix and 500’ (VMC) and 1000’ (IMC) I will be stabalized as briefed. As for making a certain taxiway, I only comply when it is safe to do so and I never adjust my approach based on that request. The AOA calibration portion should have been done during initial equipment installation. “On Speed” is typically calibrated at 1.3VSO. For the F-18 you found a calibration of +/- 6 knots, but you do not specify the actual speed. Lets assume it was 140 kts. That is well within the 1.3 calibration.

As for the flicker you see in your AOA. Remember your training, “don’t chase the needle”. Set your AOA and hold it. Make slow determined adjustments.
 
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Hello Ed,
When I fly an approach at increased speed due to a controller request, by definition the approach is no longer stabalized [sic] at the briefed approach speed or AOA.

Thanks for your comment.

I spent a year studying unstable approaches at Boeing and presented results at an international conference, so I've paid those dues. The short answer is the GA aircraft do not always fly stabilized approaches VFR -- I often get the automated 500 foot callout when still on base, and I did not find a minimum distance on final in the Airman Certification Standards. Sometimes the tower requests a short approach, sometimes thermals, downdrafts and gusts require substantial corrections. GA flies safely in these "unstable approach" conditions because the aircraft have more control authority, higher roll rates, faster throttle response and shorter time constants than airliners.

And there has been a lot of politics within the airline community regarding whether 500/1000 feet makes sense universally. Some airlines do not follow subscribe to the 500/1000, and indeed, since the advocates were unable to get the automated 500 foot callout into the FARs, they put the 500 foot callout requirement into the TSO. (Not sure about the Gastineau Channel approach at Juneau, as it's not published, but I doubt that it would meet standard stabilized approach criteria.) Frankly, the 500 foot callout is an irrelevant PITA for my flying, and when I'm IFR, I care much more about 500 feet above minimums. Even the Flight Safety Foundation finally changed its tune and no longer looks at go around criteria as driven by stable approach criteria, IIRC -- but I've not been in that arena for some years now.

As for averaging out the flicker, part of the lead/lag answer has to do with what you suggest, not chasing the AOA. Unfortunately, there are other factors at play that can render that strategy infeasible. And telling the pilot to manually filter noisy data is high workload, splitting attention inside and out. etc. You can read the airspeed right away, but averaging AOA noise is heads down, inside the cockpit -- or maybe cognitive capture if displayed heads up.

AOA guidance can work in benign circumstances, but so what? Accidents don't happen in benign circumstances.

Best,

Ed
 
Thanks for your comment.

I spent a year studying unstable approaches at Boeing and presented results at an international conference, so I've paid those dues. The short answer is the GA aircraft do not always fly stabilized approaches VFR -- I often get the automated 500 foot callout when still on base, and I did not find a minimum distance on final in the Airman Certification Standards. Sometimes the tower requests a short approach, sometimes thermals, downdrafts and gusts require substantial corrections. GA flies safely in these "unstable approach" conditions because the aircraft have more control authority, higher roll rates, faster throttle response and shorter time constants than airliners.

And there has been a lot of politics within the airline community regarding whether 500/1000 feet makes sense universally. Some airlines do not follow subscribe to the 500/1000, and indeed, since the advocates were unable to get the automated 500 foot callout into the FARs, they put the 500 foot callout requirement into the TSO. (Not sure about the Gastineau Channel approach at Juneau, as it's not published, but I doubt that it would meet standard stabilized approach criteria.) Frankly, the 500 foot callout is an irrelevant PITA for my flying, and when I'm IFR, I care much more about 500 feet above minimums. Even the Flight Safety Foundation finally changed its tune and no longer looks at go around criteria as driven by stable approach criteria, IIRC -- but I've not been in that arena for some years now.

As for averaging out the flicker, part of the lead/lag answer has to do with what you suggest, not chasing the AOA. Unfortunately, there are other factors at play that can render that strategy infeasible. And telling the pilot to manually filter noisy data is high workload, splitting attention inside and out. etc. You can read the airspeed right away, but averaging AOA noise is heads down, inside the cockpit -- or maybe cognitive capture if displayed heads up.

AOA guidance can work in benign circumstances, but so what? Accidents don't happen in benign circumstances.

Best,

Ed
Hello Ed,
I don’t understand your point. I think your saying that looking at AOA is a distraction, yet would not looking at airspeed be similar? I understand you have a preference for airspeed and that is fine; however, if your going to advocate a position in a paper or presentation why would you ignore that another instrument has similar characteristics? I think the real issue is quality and calibration whether it be airspeed or AOA. I appreciate that you want to help educate pilots, thank you for that. As for me, I will continue my stabalized approaches. I believe the quality of the landing starts during the approach.

https://m.youtube.com/watch?v=8JcjWnAJGKQ
https://m.youtube.com/watch?v=qF9E3eOibNI
 
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Interesting thread, just came across it -:)
I have an AoA ind (series of vertical lights) just next to the speedo, was already installed on my 8 when I bought it. Read the manual that came with it, experimented with it on a few approaches when I bought the plane, now I rarely look at it. Why? Simply not needed, in nearly 40 years of driving planes inc heavy metal I use my hard earned skills to keep my ride going where I want it👍
$2000 dollars buys a lot more fun/interest than some 'Christmas decoration'😉👍
 
Yesterday I was out in our Glasair Sportsman doing practice approaches. Sure it's not an RV, but this discussion is about technique so it's pretty much aircraft agnostic.

The Sportsman features a full-flap stall of 42 knots. I typically fly approaches to paved strips at 60 knots. I know that's a little more than 1.3 Vso but 60 knots just feels good in this airplane so I use it.

Yesterday's landing practice was to sharpen my skills at flying behind the power curve, flying at 50 knots to make landings on a predetermined spot. I've found that at this speed I can be a knot or two fast or slow and I can't really feel the difference with "seat of the pants" sensing.

The aircraft is equipped with a GRT HX EFIS with the new Adaptive AHARS with AOA sensing with both on-screen visual AOA presentation as well as aural AOA tones.

I made three approaches "behind the power curve" and found myself flying almost entirely with reference to the aural tones, keeping my eyes out the windshield in order to accurately judge/control touchdown point. In each of the three landings the wheels touched within less than one airplane length of the intended location.

While I'm reasonably good at controlling airspeed on approach with this airplane, I find the added feedback of the AOA tones and the large on-screen AOA indication gives me a significant confidence boost while allowing me to spend more time with eyes looking outside.
 
Part 1

In 1907, Orville and Wilbur discussed an “angle of incidence” device to assist with energy management…’course that discussion predates the term “energy management” or even bolting an airspeed indicator into an airplane (that happened in 1912 at Farnborough). So, it appears the roots of some of the discussion in this thread may have been started about 111 years ago…

AOA and airspeed are complimentary concepts. Either airspeed or AOA (or a combination of the two) will work as a reference if properly engineered, tested, and applied by a knowledgeable, trained pilot. In a dynamic, maneuvering environment, AOA can be an easier to use and a more precise energy reference, depending on how accurate the information is, how it’s conveyed to the pilot and what the airplane’s energy state is (e.g., if I'm going fast, I'm probably more concerned with G or airspeed limits).

In the Boeing 777 I fly at work, there is a nifty computer program we call the Aircraft Performance System (or “APS”) that is full of data for all phases of flight. APS derived or cross-checked airspeed for takeoff, approach and landing are entered into the flight management system by the pilots (note: the system requires the input of the primates in the cockpit). These airspeeds are then displayed on the airspeed tape. The utility of the display is further enhanced by a dynamic “foot” that shows what the energy (airspeed) margin is when we maneuver (bank the airplane). It also has a nifty cue at the top end of the airspeed band we call a “zipper” that lets us know where the Mach limit is (or the flap speed limit if those are deployed). Airspeed data are derived from extensive performance engineering and validated by thorough flight test and displayed in a user-friendly format on the primary flight display. The airplane is equipped with calibrated pitot, static and AOA sensors installed and maintained in a certified configuration. Precise data are available for static source pressure error, etc. It doesn’t matter what the gross weight; density altitude or CG condition is—there are reference airspeed data for everything that’s within the usable flight envelope. We fly the airplane by reference to IAS/mach. The 777 has an AOA gauge as well. We use that to make sure that we didn’t screw up programming the airspeed cue for approach, since approach AOA is always the same value, regardless of other parameters (no cockpit math or pilot input required!). We learned to cross-check the “always the same approach AOA” on final after we almost lost an airplane when the crew accidentally mis-programmed the gross weight of the airplane, which provided an erroneous speed cue. AOA cues provide a great “trust but verify” of the programmed airspeed cue. Boeing academics and design philosophy regarding the use of AOA cues can be referenced here for folks that want to learn more: http://www.boeing.com/commercial/aeromagazine/aero_12/attack_story.html. Some EFIS systems available for EAB airplanes have similar airspeed displays, and if accurate flight test data is available, can provide much of the utility of the Boeing airspeed display logic

I also have some experience flying upside down and exploring the G and aerodynamic limits in fighters equipped with hydro-mechanical flight controls…that means that the only “limiting device” was the pilot—which is the same as flying an RV. All of the flight control logic resides between the pilot’s ears. Turns out, if I can fly some key AOA’s in my RV-4, properly modulate power and G; and respect airspeed limits, I can operate throughout the usable envelope of the airplane in any attitude and any energy condition, even if I don’t have extensive performance, static source pressure error or CAS correction data available for the airplane. If I can listen to the AOA, this becomes a caveman simple, “how hard to pull on the pole" cue, and I don’t even have to be looking in the cockpit to do it. One reason so many of us washed-up fighter pilots fly RV’s is because, well, they fly like a fighter (on a beer budget :)). It turns out, if you adapt some handling techniques that work well in fighters, they also work well in RV’s.

The key AOA’s that we care about when we fly a straight-winged propeller driven airplane are stall, ONSPEED, L/Dmax and Carson’s Speed. If we have a properly calibrated system and the pilot can either easily see or (better yet) hear these AOA’s, we can use them for many energy management tasks in an RV.

Let’s start by using AOA to land an RV…since we all have to land, regardless of what kind of flying we like to do in our RV’s. To land using AOA: slow to ONSPEED, configure the airplane and maintain ONSPEED until landing. That’s it. There is no gust correction (not required), and if you change bank angle (G load), gross weight or density altitude, it doesn’t matter; ONSPEED AOA is always the same. If you are ONSPEED, you have sufficient energy to land (i.e., not too fast or too slow, no math required). Now the Lieutenant Neanderthal lobe of my brain still has a ballpark 1G IAS reference for approach and landing, so I always “trust but verify” proper AOA operation before I go eye’s out (just like I cross-check airspeed in the 777 using AOA or an F-22 pilot verifies the accuracy of the displayed approach AOA cue using IAS). But once I’ve got a warm fuzzy the system is working, it’s all about aim point and AOA. In small airplanes, it’s a good idea to be stable 10-12” prior to touchdown. It actually takes longer to read this paragraph than it does to demo how to fly the tone in flight :) (See post 13 in this thread)

Some AOA rules of thumb: L/Dmax for maximum range glide, maximum endurance (time aloft), and best rate of climb. ONSPEED for approach/landing, best angle of climb on takeoff, maximum endurance glide and optimum turn performance. Since L/Dmax is pretty slow in RV’s, I like to use Carson’s for holding (best MPG) and as Vz reference for optimum climb performance. If you know actual AOA for L/Dmax (flight test, engineering math, or wind tunnel test), then ONSPEED occurs at 1.73 x L/Dmax AOA and Carson’s occurs at .58 x L/Dmax AOA. If you know CAS for L/Dmax, then ONSPEED occurs at .76 x Velocity L/Dmax and Carson’s occurs at 1.32 L/Dmax. For our purpose, we adjust the ONSPEED cue to be about +/- 1 degree, which works out to about a 5 Knot speed band in an RV. We bias ONSPEED slightly to the right of max power available on the thrust/power required curve for reasons that are a bit too long to get into here, but I’m happy to discuss in a PM, email or phone call. Of note, at a 1G stable (no bank) condition, ONSPEED is about 1.3 x stall speed (which should sound pretty familiar).

We’ve built a demonstration system that uses the calibrated AOA output from a commercial EFIS to generate a simple tone pattern that lets the pilot hear L/Dmax, ONSPEED and stall. Our first-generation system, for which we received the EAA Founder’s Innovation Award this year, works at up to 2G’s per second onset rate and is damped to mimic the response characteristics in similar systems equipping fighters. It is possible to “beat the system” if the pilot applies 3 G’s per second or greater, but the system catches up prior to secondary stall. Here’s a video demonstration of a rapid pitch input exceeding system capability: https://youtu.be/DLtamTAh-Is. Our “next generation” system is equipped with indigenous pressure sensors and samples at a rate of 50Hz with an accuracy of ¼ to ½ degree. This eliminates the need for a source of AOA signal and allows installation in any airplane. One of our objectives with the new design is to increase high-gain input response rate to handle an onset rate of 3-4G’s per second in addition to simplifying AOA calibration with the new design. This ability to accurately process AOA data and provide a pilot-usable cue that is appropriately damped is why no gust correction is used flying AOA for approach. If the pilot wants extra energy during approach, the low inertia and rapid power response rate of RV’s make flying a “slightly fast” cue easy until it’s time to slow to ONSPEED for landing transition.

Here’s a short, five-minute overview of the aural logic in flight: https://youtu.be/48ZgOYDQUfk

Here’s a long “how to” video that discusses flying AOA using aural cues for ONSPEED, L/Dmax and stall: https://youtu.be/-kbA6NxMpmQ

Here’s an unedited and unnarrated software validation test flight video that has numerous closed patterns and air work using aural AOA cues as a primary reference: https://youtu.be/-iudL-gAL5E

Detailed discussion about how to fly AOA in an RV in different phases of flight as well as pilot aero academics are included in the RV Transition Training Manual (reference the sticky at the top of the VAF Safety page for a link to the most current version).

Full disclosure: I don’t have a PhD in aeronautical engineering, but here’s a great paper by someone that does that explains the science behind our AOA development work: https://drive.google.com/file/d/1WELUD--STAb77zxNegIGNXtFioI3IFmX/view?usp=sharing and here’s the short, three page version that summarizes all of the basic relationships: https://drive.google.com/file/d/12dCY5b0jFgEn3G-J8d0ZgIwf7IJB1tci/view?usp=sharing. The author, Dr. Dave Rogers, also graciously helps with our AOA project, making sure that we are always coloring between the lines.
 
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Part 2

Because Paul hit the nail on the head in post 11 in this thread, we are adding some additional capability to our next generation AOA system that will also provide aural logic for overload (G) and airspeed as well—effectively letting the pilot listen to the entire flight envelope. Short of fully-automatic flight controls, this logic should provide robust energy management cues for semi-thawed caveman pilots like me.

We’ll publish test data and share it via VAF and our new website at FlyONSPEED.org (which is still under construction and not ready for prime time!). All of our work, including flight test data, engineering information, code and training materials are “open source” and available to anyone that is interested. Also, if you are absolutely convinced the green eggs and ham taste bad, come and fly with one of us or our beta testers to try the aural logic for yourself. If you know any old or young fighter folks, hit them up in the bar and pick their brain about how you can apply AOA in your daily flying. If you know a glider pilot that’s flown with a veriometer—ask them to explain how they do that (not AOA but using an audio cue to manage energy). If you know a fixed-wing Navy pilot, ask them about the approach technique they use to come aboard the boat. If you know any corporate or airline pilots that fly an airplane with and AOA system, ask how they use that information in flight. Although relatively new to GA, we’ve got over a half-century of collective aviation experience with angle of attack systems.

As for the Alpha Systems AOA referenced in this thread: it’s one of the best systems on the market. Very well engineered, mature and tested. The quality of the components is outstanding, and system reliability is quite good. It is completely independent of the aircraft pitot/static system and can also function as a backup in the event of a pitot/static malfunction. Multiple display configurations are available to suit individual taste. It’s one of the commercial systems available that uses the aural AOA logic discussed in this post—a great way to fly ONSPEED accurately without having to engineer, build or test your own equipment. If you read the technical paper in the link above, you’ll learn a lot about the Alpha Systems probe as well as everything you wanted to know about coefficient of pressure AOA sensors in general.

Nothing wrong with the old light bulb, but the new one works pretty well too when a) it’s properly calibrated; and b) the pilot knows what to do with the information. And it’s not even a very new bulb ;)

Cheers,

Vac
 
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I've been flying with my AFS "Sport" AoA for over four years now and don't use it much for approaches any more. I glance at it occasionally, but mostly just use airspeed. I would be hesitant to fly my Lancair without the audible "Angle Angle Push" warning though. That's the primary reason I installed the unit: To keep me from falling out of the sky in a moment of inattention. Also, I get the warning in my flare, just before touchdown. The secondary reason for the AoA is it could be a life saver after an engine failure. It would show me my best glide speed, and guide me around the "impossible turn", should that become necessary. Since my plane has retractable gear, the unit will also give me a "Landing Gear" warning whenever I get below 90 Kts with the gear still up. Whichever AoA you decide to purchase, get one with audible warnings.
 
Have been using my Alpha System AOA for several years. Have horizontal led bar located just under the top panel lip so peripheral vision reads it without looking at it. Use it on every landing. Sure, i glance at airspeed but just prior to touch down i am paying attention to the blue light only.
 
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