Aoa

[Flybyjim]

Hi folks,

Who is using an AOA in their planes?, How did you do the calibration, with/without flaps and what AOA system are you using. Would you install one again, same one?

Jim

[Av8r3400]

I have a Dynon D810 in the Mangy. It uses one of their "double" pitot tubes.

They have a procedure to calibrate both with and without flaps. I have been very happy with the performance. There is a visual display on the Dynon screen and had an audio output that I put into the intercom system.


I would install it again.

[PapuaPilot]

I did the Garmin AOA with the G3X Touch display and I really like it. It displays on the screen and has an aural warning too that goes from slow beeping to full on sound as you approach the stall. The AOA was very easy to calibrate.

Normally I just use the aural warning to give me an idea of how close the wing is to stalling when I am doing STOL landings.

[n85ae]

https://www.youtube.com/watch?v=_42g25oTC7g

[neville]

I have the Advanced 5600 with AOA. Cal proceedure is straight forward. AOA is a welcome addition to flight safety and makes for better landings. Would miss it if not there.

[Av8r3400]

You can hear mine in this video at the 17:30 mark.

https://youtu.be/HEJNI77TZFg

[av8rps]

This may sound a bit strange to some, but I've always wondered if you just kept really good notes on your planes stall speeds as if you were calibrating an AOA, and then you put your findings somewhere on your panel as a reminder of speeds to use, wouldn't that be just as effective as an AOA?

I'm not trying to be a smart ass, just wondering if someone can convince me how wrong I am?

[Av8r3400]

A wing can stall at any speed but has only one critical angle of attack.

[av8rps]

Yeah, I agree. But when you calibrate it you are primarily identifying at what speed and angle the wing begins losing lift, right? Again, maybe I'm still missing something? But with such a docile airfoil as the Kitfox has that gives you a shaking and shuddering prior to stalling, isn't that much like having an AOA alarm going off, telling you the wing is about done flying?

For the record, I would see an AOA as a huge benefit to a fast aircraft like a Glasair 3, a F-18, with a stall that is abrupt. Without one it's likely the average pilot is going to fly it at the lower speed of the envelope much faster than is really needed, in fear of a stall close to the ground.*

But heck, I've been flying like that for the last 40+ years. As I tell my friends, unless I need to get into a super tight strip, "I give it an extra 5 or 10 mph for Mom as she appreciates that" ;)

But to go into a super short strip I fly just above the stall (onset of airframe buffeting) and carry power to control descent. And of course that airframe buffeting happens at a different speed when heavy verses light, etc. So you have to learn your airplane well, as those numbers change based on a bunch of variables.

Would that be different if I had an AOA? Again, I'm just curious to learn what I might not understand...

[av8rps]

Yeah, I agree. But when you calibrate it you are primarily identifying at what speed and angle the wing begins losing lift, right? Again, maybe I'm still missing something? But with such a docile airfoil as the Kitfox has that gives you a shaking and shuddering prior to stalling, isn't that much like having an AOA alarm going off, telling you the wing is about done flying?

For the record, I would see an AOA as a huge benefit to a fast aircraft with a stall that is abrupt. Without an AOA in those aircraft it's likely the average pilot is going to fly it at the lower speed of the envelope much faster than is really needed, in fear of a stall close to the ground.* But heck, I've been flying like that for the last 40+ years. As I tell my friends, unless I need to get into a super tight strip, "I give it an extra 5 or 10 mph for Mom as she really appreciates that" ;)

But to go into a super short strip I fly just above the stall (near onset of airframe buffeting) and carry power to control descent. And of course that airframe buffeting happens at a different speed when heavy verses light, etc. So you have to learn your airplane well, as those numbers change based on a bunch of variables.

Would that be different if I had an AOA? Again, I'm just curious to learn what I might not understand...

[n85ae]

Exactly what av8rps says here.


Yeah, I agree. But when you calibrate it you are primarily identifying at what speed and angle the wing begins losing lift, right?...

[jiott]

There are many places on the internet where you can read really good explanations of AOA and measuring systems. In a nutshell what I have gathered is that stall has very little to do with airspeed but everything to do with wing chord angle to the relative wind direction. If all conditions remain the same as is true in many landing approaches, then yes airspeed can be a good indicator. But if things change such as bank angle, flap configuration, control coordination, and some other things I can't remember now, then airspeed is no longer an accurate measure; however AOA instrumentation is still accurate. You and only one other guy I know has the balls to actually fly a short field approach with the wing starting to shudder. Since all AOA instrumentation is progressive rather than singular, you can fly a short field approach as close to or as far away from stall as you feel comfortable. I like my Dynon system that starts a slow beep in my headphones and progressively gets faster until the beep becomes a steady tone immediately before stall buffet. This progression is programmable during the setup and calibration. It also allows you to keep your eyes outside where they belong.

[Floog]

AOA in a KF is a waste of $$.

[Esser]

I like the idea of an audible alert so your eyes are outside.

[Floog]

Good point. I just rely on seat of the pants and sink rate. Below 45-50 mph sink rate increases proportionally. When you're falling like a rock, you're probably stalled....:)

[Av8r3400]

I like the idea of an audible alert so your eyes are outside.

I do too. Having the Dynon in the panel, it wasn't a big leap to get e dual pitot tube and hook it up.

Many people don't understand this isn't just a speed warning, it is a differential pressure measurement by two differently angled pitot tubes giving the angle of the relative wind to the wing chord.

[jiott]

Floog you are one of the guys I mentioned who flys landing approaches in an early stall condition. Not for everyone, including me.

[aviator79]

There are many places on the internet where you can read really good explanations of AOA and measuring systems. In a nutshell what I have gathered is that stall has very little to do with airspeed but everything to do with wing chord angle to the relative wind direction...

This.
To placard your panel in lieu of an AOA indicator, you'd have to have a multi-dimensional lookup table with at least bank angle, weight, CG location, and you'd have to cross-reference several instruments with that table to know at what speed your plane will stall. A common stall/spin LOC scenario is pulling too hard of a bank to compensate for overshooting final. I very much doubt you'll take the time to figure out your stall speed in that scenario, but an AOA indicator can let you know how much margin you have at a glance.

You may or may not find that AOA information is necessary or useful the way you fly your airplane, but making a table is definitely not the same thing as having a calibrated AOA indicator.

[Floog]

Jott, How did you know I was 'one of those guys??? :)

1.3Vso is not an 'early stall' or even an 'imminent stall'. That's a normal safe stabilized approach airspeed for many aircraft including Kitfoxes. 45-50 mph is in that range and it's a safe margin above the stall in smooth air. As I mentioned, a slower approach speed gives a greater sink rate (steeper angle) that allows me better short field landing performance. "Slow down to go down."

I'll admit that in 'feeling out' the slowest possible approach speed, I have, on two occasions, unintentionally stalled less than a hundred feet from the ground! In one instance, I thought I was too high to make the intended touchdown spot: the leading edge of the numbers on an 8,000 ft runway. I slowed even more, stalled, then recovered with a blast of power and made one of my finest landings and on that spot! In the other instance, a headwind to tailwind shear on short final sent me down like a falling elevator (stalled). It was again a full power recovery. In both cases, I had to change out my underwear....:( But I did land SHORT. Ha, ha! Love the Kitfox!

[av8rps]

Ok, I'm learning more about why some of you like an AOA. And hey, in aviation the more tools you have the better off you are. So please understand that I'm not dissing anyone for having one.

Part of my reason for questioning an AOA was based on an experience I had helping a friend calibrate one on his Highlander. By the time we were done I felt it was as if we just installed a stall warning horn (which I also did on another friends homebuilt previous). Of course, while I truly felt both had over-killed their simple and super docile airplanes, they both felt better having their new gadgets. And what the heck, if it improves safety for them, more power to them. I just never felt the need as I find Kitfoxes, Highlanders, and Avids just so easy to fly. It's almost as if they talk to you when they get close to stalling.

But to further improve my understanding of an AOA I'm going to take the advice given earlier and cruise the internet on AOA's to see what I can learn. I'm actually still curious about what I might be missing? I'll report back if I have an epiphany. :)

And for the record, I don't fly approaches with the airframe buffeting in a stall. But I am confident I could if needed to. I generally don't even use the standard 1.3 x stall speed for landing approaches as I learned back in my early Avid Flyer ownership days that while my 360 lb Avid stalled at only 22 mph, the sink rate was incredible under 30 mph due to the super high lift but draggy airfoil, so a 45 mph (or more) approach worked much better. It would interesting to see how an AOA would suggest landing that Avid?

With all that said, I feel our Kitfoxes are just so docile and predictable that an average pilot should easily be able to understand what the plane is telling you as it approaches a stall, regardless of all the variables like weight, speed, bank angle etc, etc.

[aviator79]

About a year and a half ago, our local pilot community lost two experienced, conscientious pilots to a departure stall accident. There are kids here in our small town growing up without their mom. According to the NTSB, in the decade between 2001 and 2011, 40% of fatal fixed wing GA accidents were due to Loss of Control Inflight (LOC-I), with the deadliest phases of flight being approach, departure, and maneuvering when the bottoms of the white and green arcs become meaningless. LOC-I accidents caused almost four times as many fatalities in 2014 as the next deadliest category (powerplant malfunction).

Chuck Yeager probably has an AOA indicator built into his rear end as a result of flying many different airplanes to every corner of their flight envelopes. But none of us is Chuck Yeager. I can't speak for all of you, but I make mistakes when I fly. I get a little slow or steepen up a little to roll out on centerline because I didn't compensate for that tailwind on base. Maybe it makes sense to install an instrument specifically designed to help us avoid the type of accident that kills the most of our fellow pilots.

I'm not criticizing anyone for not having it. I fly a certified aircraft without one, and certainly don't feel unsafe. But given the accident statistics, it's hard to call it a waste of money if you're building new and the cost is marginal.

[Floog]

I should have said, AOA is a waste of money FOR ME. I'm one of those people who run with scissors, drink from garden hoses, and sometimes drives a car without a seatbelt!

[jiott]

Hey Floog, sorry if I attributed something to you that is not quite true, but you did tell me once that you could make real short landings by coming in on the edge of stall and it was controllable. Coming from such an experienced guy I figured you must do this fairly often. Anyway, glad to find out you are more normal (except that drinking from a garden hose) than I thought.

av8rps, the AOA instrument won't suggest anything about how to land your Avid. It only gives you a reliable progressive warning when you are approaching a stall condition. At your own discretion it just makes it possible for you to come in on a stabilized approach at some point just above stall (which you can choose for your own comfort level) without ever having to glance down at your airspeed indicator.

[southwind32]

Simply put...........Stalling airspeed is a variable................AOA stalling is a constant.
Hence an AOA indicator is a better reference in ALL flight attitudes regarding relationship to stalling.
With that said.........probably 99.9% of general aviation pilots learned to reference airspeed on approaches, flight at minimum controllable airspeed and other flight conditions............it obviously works..........most of the time............but that doesn't mean it's the best either.
Brian

[av8rps]

Ok, I've been doing my research on AOA and have some further thougts:

In the mid 80's when I was flying my super light Avid Flyer, using the airspeed indicator in the stall speed range was generally useless as it bounced around A LOT in the mid 20 mph range, probably due to the high angle on the pitot tube. So the more I flew it (I used to average 250 hours a year) the more I developed that built in AOA that someone suggested earlier Chuck Yeager had in his butt. Heck, I pretty much never looked at the panel to land my plane as I could feel the plane more than an airspeed indicator would help me by knowing the numbers. I didn't need to read numbers to know what I had to do with the throttle or the stick. So maybe I flew enough to develop a sense that many may never get?

I will admit that when I fly with other pilots in all types of airplanes it seems that many fly their plane as I describe as "Mechanical, or by the numbers". By comparison, I typically fly by attitude, using numbers only as a reference. I believe flying by the numbers is probably the number one reason so many are having loss of control issues these days, and feel strongly that somehow we need to get back to training pilots to fly by attitude, not just numbers. I learned in a J-3 Cub as a teenager and was taught seat of the pants flying. I obviously will fly a high performance airplane with more respect of numbers, but the last time I was in a Glasair 3 I still flew it a lot by attitude. I'm guessing if I had a chance to fly the Space Shuttle I'd be watching the numbers close, but still looking out the window a lot :D (not expecting NASA to call me anytime soon)

With all that said, my research along with the great discussion we have had here led me to this position;

Maybe if every plane had an AOA gauge in it with audible warning in your headset, maybe more pilots would learn to fly by attitude easier?

So after thinking about it a lot, I agree that having an AOA gauge would be good to have in any plane. I particularly like the audible warning part, as I doubt I would be looking at the gauge any more than I look at my airspeed indicator. I would be surprised if I would fly my plane any different than I do currently, but I do agree it would be one more safety device, and the more tools you have at your disposal for safety the better off you always are. Maybe it could help pilots develop a better feel for their planes and help to reduce the LOC accidents?

And there is also the added benefit of helping out the next guy that ends up owning the plane. Maybe he won't have a lot of hours in type, or have that seat of the pants feeling that those of us that learned how to fly in Cubs have? Of course I doubt I will ever be able to part with my Kitfox, so I'm probably not going to rush to install an AOA anytime soon. But if the opportunity arises, I'd most definitely put one in.

So thanks everyone for helping me to understand the benefits of an AOA more than I did when this discussion started :)

[Av8r3400]

We should get together sometime so you can try the Mangy...

You'll kick that cry-lander to the curb.

[av8rps]

...You'll kick that cry-lander to the curb.

Careful, careful...you know there is a less complimentary name for a Kitfox ;)

[Av8r3400]

Yes there are. But we all know they are untrue... :D


Just funnin' ya.

[av8rps]

Good catch Larry :)

[N981MS]

I do not think anyone has mentioned this but we all fly AOA.

In cruise we maintain altitude/level attitude by referencing the cowl to the horizon.

I do the same in climb, descent, and on approach. On final I regularly check airspeed and/or AOA meter if I have it.

My Kitfox instructor had a phrase on approach that I found excellent. "That's the picture". Meaning that is what the approach should look like in the frame of the windshield.

[aviator79]

I do not think anyone has mentioned this but we all fly AOA.

In cruise we maintain altitude/level attitude by referencing the cowl to the horizon.

I do the same in climb, descent, and on approach. On final I regularly check airspeed and/or AOA meter if I have it.


What you describe here is flying by pitch attitude, not AOA. (Which I agree is how it should be done.) The way we teach and practice stalls really enforces the idea that a stall happens at a certain pitch attitude and creates this false equivalency between pitch and AOA. Without the indicator, there is no single reference, in the cockpit or outside, that gives you AOA information. We develop some sense of AOA, and the ability to synthesize AOA information from several indicators simultaneously only through experience and training. Unfortunately, when we look at accident data, we find that many of us aren't as good at it as we think we are.

[N981MS]

I should have been more clear.

With wings level, in relatively stable air, and in a relatively stabilized condition (ie not in a turn) the pitch information we get from referencing over the cowl is directly related to angle of attack. Therefore we are all using a secondary reference to angle of attack to fly even without an AOA gauge.

My point was that we all fly in reference to angle of attack even without an AOA gauge. I am not against AOA gauges and in fact think it is an excellent addition.

[Av8r3400]

Max, you are very much correct. But...

As your airspeed changes, that point on the cowl, attitude reference, is at a different angle of attack, relative wind to wing chord. You can hold that same point on the cowl to the horizon and as your air speed slows, the AOA will go from very shallow to full stall.

This is where the AOA instrument shows its value and what aviator79 was saying.

[n85ae]

In my airplane an AOA is really just a toy, which is mostly just fun to
play with, but I don't need it.

I have had two AOA systems on my airplane, one was similar to the old
fashioned Bacon Saver, and a more recent with a floating dot. My feelings
with my airplane, are that my control stick gives me as much information
as I ever need so I really don't use the AOA system.

A different airplane it probably makes sense, but my Kitfox really gets
very soft a long ways before it's even close to a stall when I'm landing.
For climb under power I watch airspeed only.

Jeff

[jiott]

For those of you who don't feel the value of an AOA indicator, how about the next low time pilot you sell your airplane to, or your brother-in-law who just got his ticket and wants to borrow your airplane. With most glass panels nowadays the AOA feature is already built-in and it is quite easy and inexpensive to add the sensor port on the wing to activate the feature.

[jiott]

Or maybe one of these days you might decide to get IFR rated. I think the AOA feature may be even more beneficial in IMC conditions.

[neville]

equating pitch attitude directly to AOA is a good way to perform the " loss of control maneuver". Go flying and at altitude simulate overshooting the turn to final. While doing so watch the AOA indicator. As the bank increases in your shallow descending turn you see the AOA increasing from 3 deg to 8 or 9 deg and the pitch angle has not changed. Your still in that shallow descending turn. Increase the bank a little more because your still overshooting and AOA jumps to 11 deg and pitch angle has not changed. The only thing that might save the day is that in your primary training you learned that those real sluggish controls are not an indication of normal flight. Nearly all of my flight time is spent looking outside of the aircraft and sensing what the machine is doing by sound and attitude in reference to the horizon (and to the RPM indication because I have this very nice Rotax 912iS which will be at overspeed in a heartbeat if not watched closely). But when doing any maneuvers AOA is scanned frequently and on approach to landing carries more weight than airspeed. Since having an aircraft with AOA I would really miss it if flying a plane without one.

[aviator79]

If you don't have an AOA indicator, and you think you know your AOA by other means, you're almost certainly wrong. Look in any flying handbook worth the paper it's printed on and you'll find something very similar to "An airfoil can stall at any airspeed and any attitude." Even "control mushiness" is not a reliable indicator. We only think it is because the airplane is usually slow with minimal airflow over the control surfaces when we practice stalls. By the time your AOA is causing your controls to be ineffective, airflow has separated and you are already stalled. I realize I'm beating a dead horse here, but as a CFI I feel obliged to point out that most of the surrogate indicators for AOA that have been suggested simply aren't. They are secondary indicators that depend upon a lot of other factors. It doesn't mean that maintaining a stall margin by referencing those indicators is unsafe, or color me guilty every time I fly our club plane. But we do need to be honest about how much information we really have in the cockpit, especially given the accident record.

I'm sure many of you are better pilots than I am, and yes, the Kitfox is pretty docile. But there have been LOC fatalities in Kitfoxes, and I'm sure those pilots would have told you that they knew their airplanes quite well.

[aviator79]

I guess the point I'm trying to state rather poorly is this:

If you don't install an indicator because you're comfortable flying safely without the information it provides, then go forth and enjoy.

If you don't install an indicator because you believe you already have the information it provides, you might want to think about it some more.

[av8rps]

Very well said.

Thanks for taking the time to educate all of us skeptics, or in my case, previous skeptic :)

[rv9ralph]

To add to this discussion. There is an article in the October edition of Sport Aviation on page 34. It is Charlie Precourt's column titled "Demonstrating Ingenuity". The core of the article discusses the pros/cons of a squared vs. rounded traffic pattern. The interesting part is a reader providing data from his aircraft while flying both patterns. The data on AOA and Bank Angle is very interesting, it shows that the AOA increases more that you may think when making square turns from downwind to base and then to final.
It is a good read and shows that AOA display shows your margin of safety, regardless of other factors you may feel are giving you good information (i.e. airspeed, but feel, deck angle)

Ralph

[av8rps]

Yeah, I've always wondered why if everyone is so concerned about stall/spin accidents, and we know the majority happen in the landing phase, then why doesn't the FAA change (or at least suggest) a rounded corner approach to landing?

Whenever I fly a "Hot" airplane I do round corners rather than square, just to give myself a bit more safety margin. It only makes sense, much like Precourt proves.

I also would like to see takeoff procedures changed to help engine failure on takeoff concerns. For that a slight bank angle to the right immediately after takeoff (or left as needed to alleviate flying into downwind traffic) so if the engine were to quit you could bank slightly left and intersect the runway rather than going straight ahead (as taught currently) which typically puts you into neighborhoods, highways, water, etc. Landing at the airport is always preferable but under the current methods taught unlikely.

Just my two cents worth...

Sorry about the thread drift.

[Flybyjim]

At my own airfield, a grass field 1200 feet long I always make a right turn once air born climbing out at 60mph with one notch of flaps, this rounded turn is to about 30-45 deg to the runway. If I have an engine issue I have a much better option than landing straight ahead, I practice this turn back to the runway often by cutting the throttle, I know it is not the same as if the engine stops but I have a plan each time I take off. I apply this same turn on departure where ever possible at other airports. I am flying a Rans S7 while building my Kitfox SS7. I have used rounded corners, turns for a long time, even during flight reviews with discussions with the instructors. I have never had one disagree with the reasoning of this practice of rounded turns.
I have never flown using as AOA, I would like to after all this discussion. I have been looking online at the different options, stand-alone AOA's are pricey like most things aviation.

[av8rps]

FlyByJim, great comments. Glad to see others doing much of what I do.

[n85ae]

I have built several iterations of AOA systems, using microcontrollers and my
first system was based on the good old bacon saver. Mostly since I like
hobbies, I like building and programming them.

I've spent a lot of time flying around using them, and done a lot of airwork
with it.

I find no real value for them in N85AE. It is a Series 5 with an IO-240B,
my stall speed is at about 35 mph, and at an indicated AOA about 25-30
degrees

If you fly AOA, and believe in it as a panacea for stalling, you will learn a
hard lesson in a Kitfox.

Fly an illusionally safe AOA on final, can lead to a quite slow speed ... Let's
say 1.3 x 35 mph stall = 45 mph ... This is ONLY like 15 degrees AOA, which
seems very safe, until you hit a summer time burble, and with a 10 mph
wind shift. Then you will see the little AOA indicator go from safe to near
vertical in the blink of an eye.

Not that AOA is bad, but honestly I have never found anything in flying my
airplane where the AOA told me something I didn't already know, and
I have found situations where flying AOA can lead to inadvertent danger.

On a summer day, or any day when there's any chop I'm watching the
runway, carrying a safe buffer of airspeed, and I have my hand on the
throttle and I see the AOA bouncing up and down as I punch through
thermals and turbulence off of trees, etc.

So I do see AOA as an extra thing to look at, and it gives me "some"
information, but definitely not something that is in my opinion high value
in my airplane. I personally use airspeed, control feel, and seat of pants
a LOT more for telling me what's going on.

I also feel that if somebody stalled, and spun a Kitfox, that an AOA system,
airspeed indicator, or BRS would not have saved them either.

Ok, flame away now :)

Jeff

[Guy Buchanan]

When I fly low wing aircraft, I tend to do a round pattern. When I fly high wing, I square the corners so I can see what's going on in and around the runway.

[jiott]

I agree with what you are saying, basically that having AOA indication does by no means allow you to disobey all the normal common sense rules we all were taught in our flight training, such as extra speed in windy, shifty, turbulent conditions. I really do like the way that it instantly warns me by screaming in my ear when, as you say, a completely unexpected "burble" occurs on an otherwise calm approach. I do believe that it warns me a little quicker than my own senses would react which allows me to take corrective action somewhat sooner. Certainly as you gain many hours of familiarity with your plane, your own senses will tell you most of what you need to know, EXCEPT in those rare circumstances of unusual or more extreme attitudes which most of us never encounter enough to become familiar with; in these cases the old needle, ball & airspeed and seat of the pants may not be good enough. Also, an AOA indicator you have to LOOK at is nearly worthless unless you have a Head-Up display.