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AOA and steep turns

tomhanaway

Well Known Member
General question and am not sure where to find the answer.

I have my Garmin AOA calibrated and it works great. It was based on stall speed in straight ahead flight. Green center dot shows up at 3 degree slope with approx 500 rpm descent.

I understand that if I'm doing steep turns (let's say 60 degrees or so), that my incipient stall speed increases.

Is the reading from the AOA still valid in the steep turn?

Thanks,
Tom H
 
AOA should be accurate regardless of speed. Your AOA is ehat determines a stall, not your airspeed.
 
I don't think that was his question. The concern was that it would be accurate in a steep turn, which I think I understand it should be. I have kind of the same question though.

I have AOA with my Advanced Flight System EFIS. The ports are way out on the right wing. In a steep turn, is the angle of attack the same across the entire wing, or is it different between the inside wing tip and the outside wing tip? Aren't spins caused by the inside wing stalling first? Wouldn't that indicate that the AOA is different there?
 
I don't think that was his question. The concern was that it would be accurate in a steep turn, which I think I understand it should be. I have kind of the same question though.

I have AOA with my Advanced Flight System EFIS. The ports are way out on the right wing. In a steep turn, is the angle of attack the same across the entire wing, or is it different between the inside wing tip and the outside wing tip? Aren't spins caused by the inside wing stalling first? Wouldn't that indicate that the AOA is different there?

Some wings have a 'twist' so the inboard section does see a higher angle of attack and stalls first (this lets the outboard section - and ailerons - remain unstalled if you approached the stall smoothly and gently, and so the ailerons still work - just in case you don't know that you're supposed to use the rudder). Regardless, you calibrate the AOA device so it hits the 'solid tone' (or whatever indicator) when the wing first stalls (inboard section in this case).
 
I have my Garmin AOA calibrated and it works great. It was based on stall speed in straight ahead flight.

I understand that if I'm doing steep turns (let's say 60 degrees or so), that my incipient stall speed increases.

Is the reading from the AOA still valid in the steep turn?

Thanks,
Tom H

Your calibration was not based on stall speed; rather, stall angle of attack. That's what the device measures.
Yes, it should work in steep turns, more than 1g pull-ups, weight-independent, etc.
 
In ball centered/ rudder co-ordinated flight it should provide data that is accurate along both RV wings(that are straight with no wash out). The sensor however is only measuring AOA at one point along one wing.
 
Local Aoa changes along the span of a wing, and I will also be affected by sideslip. If you were able to move your sensor along the wing spanwise you would see it change. But if you calibrate your aoa sensor to give you a certain reading at stall with wings level it should be repeatable and reasonably accurate in a turning stall. There will be small differences between left and right turns, so you would need to test it to be sure by doing turning stalls left vs right. It depends how sensitive your indication is and how accurately you fly. Also, stall aoa changes slightly with entry rate. If you really pull it in dynamically you can get to a higher aoa.

Stalls, lift measurement and aoa measurement are tricky things that mfgs spend a lot of time and money to get right. In industry we shoot for 1/4 deg accuracy but if you just have a display with green, yellow and red you don't need anything close to that, as long as it is either right or erring on the conservative side.
 
Local Aoa changes along the span of a wing, and I will also be affected by sideslip. If you were able to move your sensor along the wing spanwise you would see it change. But if you calibrate your aoa sensor to give you a certain reading at stall with wings level it should be repeatable and reasonably accurate in a turning stall. There will be small differences between left and right turns, so you would need to test it to be sure by doing turning stalls left vs right. It depends how sensitive your indication is and how accurately you fly. Also, stall aoa changes slightly with entry rate. If you really pull it in dynamically you can get to a higher aoa.

Stalls, lift measurement and aoa measurement are tricky things that mfgs spend a lot of time and money to get right. In industry we shoot for 1/4 deg accuracy but if you just have a display with green, yellow and red you don't need anything close to that, as long as it is either right or erring on the conservative side.

Thank you Scott, I think you're hitting on the grey area in my head about this. (and sorry for the thread hijack folks.)

So in a perfectly coordinated turn, all things being right, a stall, no matter how steep the turn, would not result in a spin as the entire wing would stall at the same time. The full span of the wing is in the same condition and the location of the ports span-wise. matters not. A bit weird to wrap my head around when the spin in a turning stall is something we have drummed into us to avoid.
 
General question and am not sure where to find the answer.

I have my Garmin AOA calibrated and it works great. It was based on stall speed in straight ahead flight. Green center dot shows up at 3 degree slope with approx 500 rpm descent.

I understand that if I'm doing steep turns (let's say 60 degrees or so), that my incipient stall speed increases.

Is the reading from the AOA still valid in the steep turn?

Thanks,
Tom H

My understanding is (and I could be completely wrong here) that your stall speed in a steep turn increases, because you have less length of wing acting against gravity (as it's no longer perpendicular to gravity). Additionally, the inside wing is experiencing a lower airspeed than the outside wing because it's closer to the axis of the turn, so it's likely to stall first.

I expect that your AOA will still indicate angle of attack accurately, but that you'll reach a stall at a lower angle of attack.
 
I expect that your AOA will still indicate angle of attack accurately, but that you'll reach a stall at a lower angle of attack.

incorrect. You will stall at the same angle of attack but you will be at a higher airspeed when in a roll.
 
The full span of the wing is in the same condition and the location of the ports span-wise. matters not?

This is correct for our RVs due to no twist in the wing. Not necessarily true for other airplanes. That said, ports near fuselage or other items that effect local airflow always matter.

A bit weird to wrap my head around when the spin in a turning stall is something we have drummed into us to avoid.

I think the reason this has been taught is that in a banked stall we are more likely to cause a spin because It is more likely not be coordinated with rudder and therefore more likely to enter a spin due to already being in a yaw condition. Also people are more likely to not recover from a stall in a coordinated manner due to the natural tendency for our brain to think in "world" coordinates and not "airplane centered" coordinates. Recovery from a stall is to reduce angle of attack (Push stuck forward) and includes no roll input. When in a banked flight condition, pilots tend to want to roll out of the stall.
 
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incorrect. You will stall at the same angle of attack but you will be at a higher airspeed when in a roll.

It will be a higher airspeed under a higher load factor. Roll/bank angle has nothing to do with it. I can be in an 80 degree bank at 20 knots and not stall; I can also be wings level at 130 knots and stall.
 
It will be a higher airspeed under a higher load factor. Roll/bank angle has nothing to do with it. I can be in an 80 degree bank at 20 knots and not stall; I can also be wings level at 130 knots and stall.

I was referrer to a level turn. Your statement better as we are not necessarily talking level turns. For constant load factor you will stall at the same airspeed regardless of back angle.
 
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aileron usaged increasing AOA

I have always wondered about this and glad someone has asked the question but I'm still confused here.

Let's say our AOA indicator is out on the left wing. We are in a steep descending right turn maybe 60 or 70 degs. So technically the left wing is traveling faster and the right wing is traveling slower but let's forget airspeed at the moment and talk AOA.

Now I'm going to try and stop my roll to the right by applying left stick which will cause the right aileron to drop (increasing the AOA on the right inside wing) while my left one goes up (decreasing the AOA on the left wing.)

So in theory my right wing will be stalled first with the higher AOA with the aileron being down as this is the wing that will drop first.

Will the AOA indicator on the left wing detect this or do we need to install an AOA on the right wing as well?

There must be some Military Pilots that can help out on this?

Tim
 
Now I'm going to try and stop my roll to the right by applying left stick which will cause the right aileron to drop (increasing the AOA on the right inside wing) while my left one goes up (decreasing the AOA on the left wing.)

So in theory my right wing will be stalled first with the higher AOA with the aileron being down as this is the wing that will drop first.

Will the AOA indicator on the left wing detect this or do we need to install an AOA on the right wing as well?

When defecting a control surface (aileron or flap) you are not changing AOA. AOA is angle between flight path and wing chord. Neither changes when deflecting a surface. You are changing camber. Adding Camber increases lift at the same AOA. That is what make one wing go up and other down when deflecting the ailerons. Entire wing remains at same AOA.
 
So it's ok to use our ailerons for stall recovery?

When defecting a control surface (aileron or flap) you are not changing AOA. AOA is angle between flight path and wing chord. Neither changes when deflecting a surface. You are changing camber. Adding Camber increases lift at the same AOA. That is what make one wing go up and other down when deflecting the ailerons. Entire wing remains at same AOA.

So it's ok to use our ailerons for stall recovery?

From anything I was taught, experienced or read is that using our ailerons at a stall to raise the wing will only make your situation worse and if you're close to the ground it will totally spoil your day.

Tim
 
So it's ok to use our ailerons for stall recovery?

From anything I was taught, experienced or read is that using our ailerons at a stall to raise the wing will only make your situation worse and if you're close to the ground it will totally spoil your day.

Tim

Generally speaking, you should not use the ailerons for stall recovery. If the wing is fully stalled the ailerons won't work. Worse, the down aileron will add drag and help rotate you into a spin. The wing twist only helps by giving you some aileron control in an incipient stall.
 
Thank you Scott, I think you're hitting on the grey area in my head about this. (and sorry for the thread hijack folks.)

So in a perfectly coordinated turn, all things being right, a stall, no matter how steep the turn, would not result in a spin as the entire wing would stall at the same time. The full span of the wing is in the same condition and the location of the ports span-wise. matters not. A bit weird to wrap my head around when the spin in a turning stall is something we have drummed into us to avoid.

I would not say that. A coordinated turn means the ball is centered, which means not lateral acceleration. I does not mean no sideslip. Contrary to what most pilots think, there is always small residual sideslip in a coordinated turn. Is this what makes an airplane drop a wing to the outside of the turn? I'm not exactly sure. There is so much going on, like sideslip, aileron deflectio which could be in either direction etc and at high yaw rates some angular flow which could change the stall pattern. But I think that is nit picking

Your aoa probe could be reading slightly high or slightly low, but it should still show you being in the yellow or red arc i.e. close to the stall AOA, which means you should stop pulling. It doesn't have to be perfect to still give you situational awareness, which is it's job. Likely +/- 2 or 3 deg is fine for our purposes. If you are that close you need to take corrective action.

But getting back to the OP, the stall indication should work for straight and turning stalls, theoretically. Some times the local flow near the sensor, or the sensor design itself, makes it really sensitive. The only way to know is to test.
 
Yes we are probably nit picking on this. Whether it is exact or not is probably irrelevant at that point in the flight. Your right, the whole idea is situational awareness.

But on a technical side and we wanted to know exactly, would we in theory need to install an AOA indicator in each wing? There must be someone from Garmin, RITE, Bendix or Advanced Flight that could help clarify this.

Tim
 
1. AOA is defined as the difference in angle between the relative wind and the wing chord. Chord, in turn, is defined as the line between the leading edge and the trailing edge. Deflecting ailerons or flaps changes the (local) AOA, and on some planes (like Delmar Benjamin's GeeBee replica) DOWN aileron at low speed can cause that wing to stall.
2. Whether to use ailerons or not in a stall recovery depends on the airplane. For some planes it's great, for others, you want to use the rudder. On some planes you don't want to use the rudder -- I did a stall in a Skybolt (aerobatic biplane) and tried to pick up a low wing with a rudder and got a beautiful 1/4 snap roll. Generalizations don't work on this point.

In experimentals, the best answer is to practice. That often means with a spin-qualified person on board and that may be you, may be an experienced CFI.

Ed

PS. Due to surgery, my spine is now limited to 2Gs and that means no spin recoveries, which can easily exceed 2Gs, even if the spin itself does not. :-(
 
General question and am not sure where to find the answer.

I have my Garmin AOA calibrated and it works great. It was based on stall speed in straight ahead flight. Green center dot shows up at 3 degree slope with approx 500 rpm descent.

I understand that if I'm doing steep turns (let's say 60 degrees or so), that my incipient stall speed increases.

Is the reading from the AOA still valid in the steep turn?

Thanks,
Tom H

I was up doing 45? level bank accelerated stalls in my Flight Design CTSW this morning. The FD CTSW has a 1.7? dihedral but no washout.

My Dynon AOA is well calibrated and very accurate for level flight. I've done a ton of stalls straight ahead at many flap and power settings and the AOA is right on.

I noted that my AOA and aural stall warnings in the 45? level bank accelerated stalls were exactly consistent with my wings level experiences. The horn was full on and at one (last) red bar the plane stalled.

As you suggested, in this "accelerated stall" the indicated airspeed was notably higher than in a conventional stall. There is a pretty good write up on it in Airplane Flying Handbook. FWIW, AFH recommends 45? bank maximum in training for this maneuver.

To hold the ball in the center at a 45? constant altitude or level bank in my plane takes some upper rudder pressure. It may be that when the stall is broken the rudder pressure is not released at the commensurate rate and thus the plane may roll to one side or the other. FWIW, my plane broke directly "down" in airplane terms and was very well mannered. None of the bad habits I had learned to anticipate in the C-150s may of us learned in years ago.
 
Try listening to the AOA...

The short answer to the original question is that optimum indicated angle of attack is not affected by gross weight, bank angle, load factor, airspeed or density altitude...like an airspeed indicator, if the system is calibrated, stall will always occur at the same indication on the AOA display for a given configuration. If the display is in the pilot's visual cross-check, it can be quite useful when maneuvering the airplane as well as during approach and landing operations.

The VN diagram for my airplane depicts the optimum AOA band as ON SPEED (nominal 60% lift), and you can see how the band follows the aerodynamic (stall) limit and varies with indicated airspeed:

view


Long answer (from the "it depends" department!):

My RV-4 is equipped with an aural tone generator that utilizes the AOA serial data output of a DY-10A that comes from a standard Dynon differential pitot sensor. The tone processor begins a low frequency beeping at L/Dmax with the pulse rate increasing until reaching an ON SPEED (optimum AOA) condition (nominally 60% lift) and changes to a steady tone at that point. As the airplane continues to slow and AOA increases, the frequency changes to a high pitch and begins to beep again, with a high pulse rate stall warning provided 15% prior to stall. This tone allows me to hear the back side of the drag curve, and it will help illustrate how AOA works during maneuvering flight. This video link shows what the back side of the drag curve sounds like using this tone logic:

https://youtu.be/S9H6T_tOLe4

Old F-4 pilots will immediately recognize the tone pattern, and fighter pilots will recognize that ON SPEED provides a basic reference for not only approach and landing, but also best sustained turn performance for speeds at and below corner velocity (maneuvering speed). The tone generator allows me to fly approach and landing and "max perform" the airplane without having to look inside the cockpit and helps me avoid pulling too hard and exceeding the aerodynamic limit (i.e., stall).

Since it's difficult to describe how this all works, it's easier to show you with some basic examples--here are some You Tube video links that might help illustrate the concept. Unfortunately, you can't see the EFIS in the video, but the back-up airspeed indicator is visible and provides a reference point. Also note that the tone has a volume control, but output to the camera is defaulted to maximum volume, so what I hear in the headset is not the same as what comes out on the video. The tone is not as annoying as it comes across in the video recording, but the loud volume on the stall warning is NOT adjustable (i.e., it's designed to be annoying!).

This video shows an ON SPEED base turn and final approach. The change to a high pitch tone indicates a "slightly slow" condition, the steady tone indicates ON SPEED and the change from steady to beeping is "slightly fast." The basic technique I use is adjusting pitch to control AOA (tone) and power to control glide path. It is a fairly wide pattern to provide maximum time ON SPEED for demonstration purposes. The final approach is a 3 degree glide path but may appear a bit drug in due to the distortion of the medium field of view mode on the Go Pro camera used to record:

https://youtu.be/IkuHyUuEB_w

To get to the original question in this thread, the next two videos show steep turns; and note the airspeed at which the ON SPEED tone occurs--quite a bit higher than what you saw when operating in the traffic pattern; but the AOA is the same, optimum, for both conditions. Roll into the second turn is more rapid, and you'll note a momentary AOA over-shoot on the initial pull. If you watch the video carefully, you can see the change of nose track with the change in tone--in other words, I'm reacting to the tone by adjusting G (how much I'm pulling) to keep the turn ON SPEED.

https://youtu.be/BphHzWHbOjo

https://youtu.be/4tvrWWtBEbQ

The next two videos show a 180 degree banked steep turn (i.e., a Split S), again note the relationship between the tone and indicated airspeed, the AOA is constant throughout the pull through:

https://youtu.be/kZJpk_hFIbg

https://youtu.be/nMXvd5MYC8k

The last video is a simple accelerated stall with an intentional secondary stall. The stall occurs when the nose stops tracking across the horizon. Due to the high G onset rate, you'll note that the aural AOA system is a bit pressed to keep up with rate of increase...in other words, if I pull hard enough, it's possible to "beat the warning" just like you can with a conventional stall warning:

https://youtu.be/DLtamTAh-Is

I hope this helps demonstrate some of the basics of what's going on with AOA during maneuvering flight. There's quite a bit of discussion about maneuvering in the training manual that is posted on the safety page that may also be helpful for folks interested in the topic.

Please note that I'm learning as I go with all of the video editing and sharing, so if there are any issues with the links, let me know and I will try to fix it.

Fly safe,

Vac
 
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Dynon AOA Set UP

Mike , Thanks for your very informative information on how you use your AOA. The biggest question I have concerns the Alarm Setup for your Dynon. The Alarm Setup menu lists Audio Start at various levels, Yellow Top, Yellow Mid and Yellow Bottom. Which setting are you using in your Utube video.
Val K.
RV-8
N81VK
 
Hi Val,

It's not a Dynon tone you're hearing in the video. It's a stand-alone tone generator that utilizes the Dynon serial output and processes the message to produce the tone that mimics the logic we had in the F-4, which allows you to hear key points on the drag curve (especially ON SPEED, or optimum AOA) as well as providing stall warning. It's a stand-alone prototype system that we built to demonstrate the concept using a common AOA sensor and EFIS.

Cheers,

Mike
 
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AOA Prototype System

Mike,
It sounds as though your system may be superior to that of Dynon in that it enables you to fly the tone in order to stay on speed. This I think is a better and more usable approach. Would you be willing to share your system?
Val k.
RV-8
N81VK
 
I've been trying different AOA configurations using Dynon's instructions to try to simulate something like that. Different flap settings and different "stall" speeds. Have not been very successful ...
 
Another challenge to using AOA for approach speeds is compensating for winds and gusts. It's easy enough to add half the steady state winds and all the gusts to your approach speed, hard to do that with AOA.

Ed
 
Val,

Here's a link to an open source site that contains information about the code we are using as well as a description of the prototype box:

https://github.com/dinglewanker/aoa-tone-efis-serial

Tom is spot on--calibration is critical to making a system like this work. Currently, we are biasing software settings (based on flight test) to compensate for the baseline Dynon calibration for individual airplanes. But this is a bit like dialing in a pitot/static system and requires quite a bit of work at present. Our objective is to develop a reasonably simple calibration technique, but that requires more experimenting. Ultimately, it may turn out easiest to incorporate sensors in the tone generator and bypass the EFIS signal entirely--again, to be determined by further experiment.

Ed, we've actually found performance in gusty conditions to be quite good, even with a low inertia, light wing-loaded airplane like an RV; but you bring up a great point! A properly calibrated AOA is fine for use in all conditions, but, frankly, a slightly fast approach is usually warranted under those conditions, which is exactly the same as adding half the gust--in other words you adjust AOA just like you adjust airspeed. The tone logic (pulse rate and frequency) is designed to allow you to hear "slightly fast" just as you hear ON SPEED. Obviously it's a good idea to back up AOA with airspeed (or vice versa, depending on what systems are installed).

It may be practical to achieve a somewhat similar effect with the basic Dynon progressive tone and graphic. ON SPEED is essentially the 60% maximum lift point, so if you can download your Dynon data and plot airspeed and % lift over time thru a series of stalls in different configurations, you can determine what the maximum % number for your airplane is (some folks can achieve 100% which makes the math easy!), but each airplane will vary somewhat (just like individual static systems vary from aircraft to aircraft). We think the middle of the yellow Dynon graphic is nominally the 60% lift point (similar to a doughnut on more conventional old-fashioned AOA indicators); but this hasn't been verified. If it is 60%, then theoretically if you can calibrate your airplane to achieve 100% lift at stall, for that configuration the start of the Dynon tone should should approximate ON SPEED. Obviously, it won't help you with L/Dmax, but at least you'll have a workable indication along with excellent stall warning. Unfortunately, I'm not familiar with the Dynon progressive tone, so this is simply best guess based on what we've learned.

If an EFIS or AOA system manufacturer were to adopt the tone logic (or a similar logic that allows the pilot to effectively hear the back side of the drag curve), then a stand-alone tone generator would not be required.

One of the purposes of this experiment is to demonstrate what is, in fact, 50 year-old technology so that folks can determine if there's any utility in this type of system for airplanes like our RV's. We'll keep the shareware site updated, and eventually post more details on the Safety page as we learn more.

We are discussing the ergonomics of this type of system, and are interested in feedback from anyone that has thoughts.

Forgive the long post; but I'm always happy to answer questions.

Cheers,

Vac
 
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