Why isn't AOA on the panel?
 

Reading through Adrian's post on Vx and Vy speeds got me thinking.

A whole lot of the numbers that we try to remember when flying a new type are much more to do with angle-of-attack than they are to do with airspeed.
Vs, Vx, Vy, Vref are all functions of load, power and load factor though if represented on an AoA instrument they would be (almost) constant.

I spoke to someone who had put a modern AoA gauge on a homebuilt RV-8, and he now flies all his approaches and climbs using AoA, and also uses it for reference during aerobatics.

I guess that a stagnation point type sensor wouldn't compensate for flap position, though that could be easily accommodated.

Would you like one on your panel?

An angle of attack guage would be useful and I wish I had one.
But most pilots are not concerned with AOA as they shoud be, rather they think in terms of airspeed. They would need to learn (or remember) more advanced facts. The fact that a wing stalls at a lower angle of attack with the flaps or aileron down is forgotten by most pilots.

Please correct me if I'm wrong.

I've always thought a wing would stall at the same angle of attack (give or take) regardless of flap.

AoA is the angle between the freestream airflow and the chord line (effectively a straight line between LE and TE). By lowering flaps and maintaing the aircraft pitch you are automatically increasing the AoA. And hence it is at a lower pitch attitude that an aircraft will stall.

If, as has been mentioned, they can compensate for flap settings then yes it could be useful.

An airfoil will always stall at the same AoA. That does not mean any airfoil; different airfoils will stall at different AoA. Adding flaps alters the chord, camber and size of the wing; it may alter the flow over the wing (as in slots energizing the boundary layer etc), and will definitely change the critical AoA.

Reference any decent principles of flight book; it will have graphs of CL plotted for different AOAs in different configurations. Without having access to any at the moment; I believe the general tendency for extending flaps is moving the graph up and to the left; ie increasing CL for any given AOA, but dereasing AOAcrit. Adding slots, either by slats or slottet flaps, will extend the graph up and to the right; ie not provide any significant increase in CL for a given AoA, but increase the AoAcrit. These two used together, as in a flap+slat combo or even a decent fowler flap, will increase CL, and may increase or decrease AoAcrit.

But don't shoot me if I got it wrong either. 11 months ago I had never even touched a yoke; now I'm a CFI, so there might be some gaps here and there ;)

If a pilot flying in a turn about on the edge of stalling and close to the ground gets scared and suddenly applies full aileron control to level the wings, the down going aileron may stall that wing and instantly put him in a spin.
The pilot is trying to level his level wings but the opposite occurs. The aileron control reverses when it is stalled.
An AOA instrument might help, but the angle of attack of the aileron can be changed very abruptly. The pilot should be looking out instead of looking at the panel, so an audio AOA device might be good. I have an audio variometer that works well.

Wings stall at about 15 degrees angle of attack without flaps.
Wings stall at about 12 degrees with the flap down. The aileron is the same as a flap with regard to how it changes the angle at which stall occurs. It would be more difficult to monitor the ailerons rapid movements with a gauge.

Which angle of attack shall we present? The local one sensed by the probe, or a corrected value to fuselage AoA based on flight test with a noseboom, itself subject to corrections. Shall we correct for pitch rate induced alpha, or not?

Then things which you think are "almost constant" often are not. What about variations with altitude, or Mach number? Or cases where scheduled speeds are determined by other criteria - like VMC, for example. Your Vref-alpha chart would be no simpler than the Vref-speed chart.

It's also common to have more redundancy in the airspeed system than in AoA systems - 2 AoA vanes, but 4 airspeed systems, for example.

And to reinforce the previous point - trailing edge flaps (including ailerons) do influence the stall AoA - using a constant fuselage reference for AoA, not accounting for theoretical chordline changes.

In Serial 25 of http://www.pprune.org/forums/showthr...=223467&page=2 , Mr Farley sums it up very well.

Unfortunately, there is no single AoA for a pilot to remember. For a useful display of 'AoA' for a pilot you'd have to provide some kind of normalisation to account for configuration, Mach number, altitude, load factor, all of which CAN affect stall or similar behaviour.

To a reasonable extent thats what the 'low speed cue' and 'green line' on airspeed tape aircraft displays - speed adjusted for AoA and config, which is much the same as AoA adjusted for speed and config - but even these can present misleading info and there's no practical way to make them perfect.

It would be pretty simple for an AOA display to be biased appropriately by flap position, so that the indicated value for Vso remains constant.

I can't help disagreeing with M(F)S just a little bit.

Whilst it's true enough that stalling AoA, and by relation the preferred AoA for approach, manoeuvre entry, etc. is affected by altitude, configuration and so-on, it should be less affected than airspeed since for a start weight and g are removed from the equation. PEC also shouldn't be as big an issue one might hope.

So, it should for most aeroplane types be possible to schedule (for example) a single approach I_alpha per configuration which may lead to significant simplification of operating limitations and advice.

It'll never replace airspeed - Vne and VMC for example are inavoidably functions of EAS, but it might help make life a little simpler and easier.
Maybe.

It would certainly be an interesting thing to look at seriously in regard to an example aeroplane for which both IAS and I_AoA correction and operating data are available.

G

Actually, it wouldn't be (and indeed, isn't!)

The first question is: what stall AoA do you want to display - the one you would achieve if you were to conduct a 'standard' 1 kn/sec slowdown from your current speed, or the one you'd achieve if you were to pull a wind-up-turn at your current speed? Because they won't be the same, and the latter may be noticeably less than the former. If you display the 1'g' stall AoA then you may be giving the pilot a false sense of confidence in manoeuvring flight; if you display the manoevring stall AoA you will find that the displayed AoA moves around as you speed up and slow down (anyone who's watched their "low speed cue" or "green line" has probably seen it moving around on some aircraft, where the input data are Mach-dependent).

There are also issues with the accuracy of AoA sensing at low angles/high speeds, compared to high angles/low speed - as one gets faster the intrinsic accuracy of the airspeed system improves relative to the AoA sensors - for things like stall or shaker speeds the AoA system is generally more accurate than the airspeed system, when the two are compared, but the AoA resolver accuracy becomes more and more significant as the AoA drops. You'd have better luck trying to fly a precise cruise speed than a cruise AoA I expect.

John Farley's remark that automated systems expect AoA as an input is correct, but FBW systems also can have gains and such as a function of AoA; most autopilot systems don't, to my knowledge, use AoA as a control parameter.

Let's not forget that there are many aircraft - high performance jets, notably, that fly their approach using AOA as the primary reference.

If we had our choice I imagine that we would choose to fly solely AOA on approach, as it is the most appropriate measure of both aircraft performance and safety margin. Conventional aircraft are AOA stable, and as such we choose an airspeed that results in a given AOA - important point here...in a given configuration, at a given weight, the AOA is known, constant, and stable for any given airspeed (and vice-versa). The weakness that we have today is in the method of displaying AOA, and the smoothness of the data.

Previous posters are quite correct in that the AOA can vary with different wing configurations at a given airspeed; however, this can be easily compensated for procedurally. If standard procedure is to fly an approach with full flap at 9 degrees AOA on the guage one can easily accomplish this. Adjustments can be made for different configurations, either by aircraft systems or procedures. The important point is that the pilot has an appropriate target to fly to, and that he or she is capable of maintaining the target.

As an aside, when flying the Alpha Jet I would always cross reference my approach AOA to an airspeed once configured. Flying AOA was great until there was turbulence or gusty wind conditions, at which point the airspeed indicator would tend to jump around less than the AOA guage, and was therefore a better instrument to use.

Several autoland systems, to the best of my knowledge, use AOA as a control parameter and adjust descent rate using direct lift control methods. Carrier based systems (present and future) are predicated on AOA, although I suspect I'm diverging from the 'civil' nature of the thread... :>

The military flew indexed ‘AOA’ which accommodated configuration changes – the doughnut chevron system. In later years indexed systems were produced for civil aircraft, mainly in corporate operations. Both of these systems focussed on safety, providing approach speed / speed margin and guidance for keeping out of trouble, stall, windshear etc.

If the full value of AOA is to be realised then more sophisticated calculation is used, but then the dominate problem in civil operations is the acceptability of a display. A standalone advisory system can be certificated on the basis that it is not misleading. Using AOA as primary the primary ‘speed’ reference would present significant problems in certification, but probably the issues of training and standardisation costs to the operators would prohibit this option. A counter example is the use of HUD, where the costs have been offset against the Cat3 capability.

On a point of standardisation, speed or AOA, I was always impressed by the US Navy system of colour coding ASIs. This provided speed bands for flap (gear) speed and the range of approach speeds; each aircraft type was calibrated / marked accordingly. Thus it didn’t matter which type you were current on – flying the approach in the ‘green’ band provided a significant degree of error proofing.

Civil flight tests (1970’s) experimented with AOA for auto thrust control with little success, but the military IIRC, were more successful – A7.

AOA on the panel.
 

Lest we forget??

CONCORDE.

The Rocket had it and the crew used it all the time.

Most flight data recorders log AOA as a parameter and AOA features in a lot of accident investigations. All airliners have a AOA vane as part of the stall warning system and certain FBW aircraft use it's input as part of the control law configuration. Accident reports frequently mention high AOA, but wht don't we get a display on the flight deck?

Cost! My A320 FCOMs show an optional AOA guage on the instrument panel, but to my knowledge no operator has ever fitted one. And until enough reports state that one factor of an accident was an increasing AOA which the pilot wasn't aware of and they become mandatory, they won't be fitted.

The Tucano in RAF service has an AOA guage and an AOA indexer. Unfortunarely, the indexer is not calibrated to the approach speed of the Tucano in RAF service and is not much use. And use of the guage was not taught. But after losing my ASI during an inverted spin one day (a regular problem until a restrictor was fitted in the pitot line) I was forced to use AOA against power as an approach reference. This made me realise the value of the instrument and I used it regularly from that point.

Some airliners have the ability to display a Flight Path Vector on the Primary Flying Display. The difference between your attitude and the FPV is you angle of attack. The A320 SOPs for my airline requires use of the FPV for visual flying and Non Precision Approaches. It's a very useful tool.

Cost might a reason why an operator might not choose an option. But the reason why it's not even offered as an option is FEAR - fear of what it will be used for by pilots, fear by the engineering and design people. And the second part of your post shows why we FEAR installing AOA gauges. You had a system that you know isn't much good and which you were never taught to use, but now you've decided to "use it regularly".

One of the biggest hurdles to implementing ANY new display device - not just AOA - is a fear that it will be misleading, or misused. Even if we don't take cert credit for a display, it has to pass the "causes no hazard" test, and agencies will generally assume that if its there and misleading, people will be misled.

Turn things the other way round for a moment; suppose you had an aircraft which was flown with AOA as primary, and then we decide to add airspeed as a "nice to know" secondary display. Without knowing about PEs and SSECs and reversionary systems and redundancies and all the other things we have to do right now for airspeed displays - would you just fly based on an unapproved display?

For those advocating use of AOA for approach instead of airspeed. If the aircraft weight is correctly known, they amount to the same thing. Consider, though, what happens if the weight is wrong.

Assume the aircraft is 5% heavier than calculated (a pretty gross error, but its just a number...)

For an aircraft flying airspeed, it will be flying at a higher AOA than it should (effectively flying at 1.20 Vsr instead of 1.23Vsr) and it will also have 5% more energy/moment to bring to rest - say 5% more landing roll required (though in fact the brakes will work better, so it'll be less in practice)

If instead the aircraft flies AoA, it'll be at the 'correct' 1.23vsr, and consequently 2.5% faster than the book says for the weight. Therefore it'll now have 10% more enegry/moment to bring to a halt.

Flying AoA protects more in terms of stall speed margins, but puts all the error into the landing distance, unless you recalculate based on the actual speed flown (which would seem a bit of an imposition)

There already is an audio angle of attack indicator and it's in just about every fixed wing airplane. It's the stall warning. If you're approaching the critical angle of attack, it kicks in. Even better, it works no matter your weight, balance, wing loading, airspeed or configuration. Is is as effective or complete as a nifty visual indicator that displays in all regimes of the flight envelope? No, but it does tell you what's most important - when you're running out of angle. 'Member, stalls aren't a function of airspeed, just AoA. Go slow enough and there isn't an AoA that won't stall you, but it's still angle of attack.



I would imagine also that a visual angle of attack indicator would also introduce an unnecessary incentive to keep one's eyes on the panel.



Or I could be talking out of my ass. I haven't slept for thirty hours.

What Traffic Several RN aircraft used ‘indexed’ audio AOA for Carrier approaches.

MFS IIRC there is a clever method of using AOA to display (overlay) AoA related information such as stall margin or approach speed on EFIS airspeed scales.
I believe that the technique required knowledge of CL polars etc, and on some aircraft a trim input as an approximation of cg. As I understand this overcomes the problems of weight; are we discussing similar concepts?
I am confident that this was used on the Avro RJ – it used a Honeywell algorithm, which may have originated from the MD11, as both these aircraft had Honeywell EFIS speed computation. The Avro RJ did not provide any FMS derived aircraft weight input to the system.

It's the use of normalised AoA; we use it too. It depends on having a very good understanding of your lift-curve slope, as you note. It (invariably) assumes this to be linear (which it usually ISNT) which means its an approximation. Because the prime use of normalised AoA on the airspeed scale is to get the "low speed cue" aligned with shaker activation, it's "tuned" for that case; it can be CONSIDERABLY in error under other conditions.

(What you do is define an AoA for "zero lift" and an AoA for "CLmax" for each configuration, then you assume the relationship between CL and AoA is linear, and that the AoA for CLmax corresponds to stall speed.
So, "normalised" AoA is then defined as:

AoA(n) = [ AoA - AoA (zero lift) ] divided by [ AoA (CLmax) - AoA (zero lift) ]

With the assumption of linear CL variation, you can show that the square root of normalised AoA is proportional to the inverse of your stall speed ratio, that is, for
AoA (n) = 1, V/Vs = 1/sqrt(1) = 1.0 (naturally)
AoA (n) = 0.5, V/Vs = 1/sqrt(0.5)= 1.41 Vs
and so on.
If you know your shaker stall speed ratio (and hence AoA(n) for shaker) you can use this to display shaker info.

To put it onto an airspeed tape involves a bit more messing around, to account for current conditions, but not much.)

Normalised AoA would work exactly the same as flying to a dimensional AoA in terms of weight - you end up at the "right V/Vs" but the "wrong Vref" compared to what you work out from the 'book'. As I suggested, that's good for stall speed margin, bad for landing distance margin.

Every Citation flying has AoA displayed, both as a guage and a reference on the ADI or PFD depending on age. Similarly the L1011 has it, and upon selection of landing flap the speed selector on the MCP is hashed out and the AP/FD targets AoA whether you like it or not (If I am recalling correctly - it was 25 years ago!). And as has been pointed out Concorde had it.
Therefore all this discussion of why it can't be done is some 35 years behind the times - it can be done, but as usual cost comes before mere usefulness until there is an accident.:ugh:

Is it primary, secondary or advisory on the Citations? (sounds like it's primary for a phase of flight for L1011).

The manual says it's secondary, however on the older ones the fast/slow pointer on the left of the ADI is purely referenced to 0.6AOA which is Vref in all configs as the system is compensated for flap position etc. In the newer ones the same info is displayed on the speed tape on the PFD as a white circle.

dunno about the new citation but on the old one the "AOA" was calibrated for clean and full flap. On full flap and gear down you would have the Red / Green / Amber Light repeaters on the glareshield. On clean it shows the best L/D at .55

On the Falcons AOA are used to trigger the stall protection ie extending slats at 17° and retracting the inboards at 19° for example (depending on model of course)

Safe Flight manufacturer of those kits got a lot of info handy if you ask them.

Mad (Flt) Scientist

I always look to your posts to sort out most threads and have never disagreed with your many positions…...until here.

While I do not disagree with your technical comments on detailed aspects of AOA I do feel you are rather missing the main point behind the debate.

Surely it is about whether it is easier to glance at an AOA indication and at once have a reasonable feel for your margin from the stall or whether you would do better to direct the glance towards the ASI?

Looked at that way it is no contest as far as I am concerned as the ASI reading is no help without in some way taking into account the current weight, bank angle and g loading – the effects of which on the ASI indication at the stall as we all know can be large.

By way of light relief I was one day flying the final approach in a CN-235 twin engine transport on behalf of the Captain who was busy trying to calculate the speed we should use. He eventually announced a speed and I suggested he should check his sums. This he did and after quite a while came up with a new number 11 kts faster. He was extremely apologetic (we were less than two miles out by now) looked at the ASI and saw I was already flying at the higher speed. ‘How did you know the correct speed John?’ I was not qualified on type but the aircraft had a really excellent AOA gauge as standard fit which of course I was using. To my undying shame in response to his question I merely gave the wheel a twitch and said ‘Don’t worry X -after a while one develops a feel for such things’.

JF

...and if the pilots are briefed properly on where the real limits are, and if the gauge is reliable, that's fine. We routinely flight test with a boom (as does most everyone) and the AoA is displayed prominently in the cockpit, and limits are briefed for various tests. I'm sure our TPs wouldn't fly without it.

BUT, for routine line use, unless you generate the same level of briefing knowledge in line crews, then it's not so useful. The fear - to use that word again - among the design/engineering community is that an AoA gauge will either mislead or be abused or both.

"raw" AoA would be difficult to justify in a line operation - stall angles are too dependent on config and on speed to expect anyone to remember the values. So some form of indexing/normalisation is required. But even that can't be made "right" and sometimes is downright misleading. For example....

Suppose the stall AoA is 10 deg at M0.6, and the zero lift AoA is 0, to make life simple. A plane dawdling along at 8 deg AoA at M0.6 will displane a normalised AoA of 0.80, and would appear to show a stall speed of sqrt(AoA-n)*0.60=M0.54. But as you slow down, let's say by M0.55 the stall AoA has increased to 11 deg; the plane will be somewhere near 9.5AoA at this slower speed, but AoA-n will now be 0.86, and the stall speed will now appear to be sqrt(0.86)*0.55=M0.51.

This Mach-dependency effect is real and confusing, especially to crews who've never seen it before. So predicting what our hypothetical crew might do with this imperfect information is hard. Similar examples can be shown for things like contamination/anti-ice failures, OEI operations, sideslip conditions. There's a lot of compensation going on the stall computers to address all these kinds of things, but since AoA itself isn't being displayed it's possible to be conservative in applying corrections (one example might be deliberately mis-compensating for sideslip to provide more stall protection in sideslip cases); if it were displayed we'd have to make it "right", whatever that means.

Citation had AoA indicator
 

Many years ago I flew a Citation 500 / 501, and this has an AoA gauge on panel, this was coupled to flap setting.
Part of the test flight was to calibrate this gismo.

Later in life: the Gulfstream 550, has an eyebrow indicator that shows the stall barrier on the attitude indicator, this I hope is also config adjusted.

Windy

It appears that Boeing offer it as an option on 737NG, 767-400 and 777 aircraft. A document explaining the philosophy and the system is at www.wingfiles.com/files/instruments/aoa.pdf

The NG has it as a option and some companies use it .Pegasus was one of them,on the 738 (last I know of).It appears on the EADI instead of RA indication(upper right side) ,which is displayed then on the lower part of the EADI .
It's a nice tool,but you have to learn to use it,and most of the experienced pilots will find it difficult to accomodate with.
The same with the NG FPV. When we asked about it's use,we were told to forget about it,just a new gadget.Anyway,without a cage...:hmm: good in wxr radar use,though.

The new Embraer Jets have a Pitch Limit Indicator. Its a mustach type symbol that is displayed with reference to the aircraft pitch symbol and uses the adi pitch scale to show margin in degrees to the AOA limit. Its colour matches that of the Low speed awareness tape and when you reach the AOA limit it would be in line with the pitch symbol and the stick shaker will fire. This will also trigger AOA limiting in the fly by wire system to prevent any increase in AOA. The nornal flight referance symbol is a Flight Path Angle used in all phases of flight except take off. so AOA can be seen as the diffrence between FPA and Pitch.

Honeywell EFIS.

There's a big conceptual difference between providing an indication which is driven from AoA (in whole or part) such as 'eyebrows' or a 'low speed cue', and actually providing an AoA indication itself.

With the former options, it can be pretty accurately determined how these will be used, and they can be presented - or not presented! - in the appropriate circumstances, and even manipulated in some circumstances. (On one of our types the 'eyebrow' feature appears during windshear alerts, but not otherwise, IIRC)

A 'pure' AoA display is far more prone to abuse, and makes the designers far more nervous about its presentation, reliability, veracity. And raises more certification issues, too.

I was a passenger on the jumpseat of a Delta 767-400 a few years ago and noticed that an AOA indication is provided on the PFD.

We operate the same aircraft but do not have this option.

It would appear quite a handy piece of kit though.

For the (US) FAA certification, were cost and maintenance complexity the original reasons for the avoidance of designing an accurate indicator in the first generation and later jets etc? Possibly the older generation of pilots from WW2 and Korea preferred what they were familiar with? The T-38 had a fairly good system and could not have been very complex. Of course you could feel a high angle of attack in the short, stubby wings when "rocks" then feel like "bigger rocks".

Our 60's generation jet has them on the right side of the ADI, but there are no accurate markings and no training or limitations for them. A good system would probably have saved hundreds of lives in the US, i.e. New Orleans, DFW and at other places.

Sadly, the one Citation that arguably needed it the most, the Citation X, (C750) offered the panel mount as an option. The airspeed indicator has a "low speed awareness tape" which is, in effect, an AOA but only displays AOA information at low speeds. It was quite disappointing to be up high trying to determine max endurance or estimate climb performance and having to either get the book out or make an educated guess. A simple AOA guage would have been quite useful. IMHO, all aircraft should have full-time AOA info available to the pilot for certification.

Perhaps Cessna are denying you the gauge by default because they WANT you to use the data from the manual, perhaps because it isn't just a simple function of AoA.....

We used ADD (Airstream Direction Detector) to land Sea Vixen and Buccaneer aboard ships. ADD removed the need to adjust approach airspeed to cater for different landing weights. It was always sensible to check that the target approach ADD against the ASI/AUW was as expected. Both Vixen and Bucc had audio ADD which allowed the pilot to concentrate visually on the centre-line and mirror info, which were as vitally important as the speed. The audio signal was: short high interrupted tone for too fast, (peep peep peep) long, low, interrupted tone for too slow (burp, burp, burp) and a steady note for on target ADD. I only once met an ADD system that was sticky and therefore gave an innacurate reading,--and that caused loss of the aircraft.
So I remember being unimpressed later at Warton, with the recommended take off procedure for a heavy Jaguar, which was to rotate to, and climb out at, a high ADD reading, for guaranteed best performance. I remained uneasy about putting reliance on a simplex instrument that couldn't be properly checked on the ground before each flight. (You could twiddle the probe and see the gauge move, but you couldn't assess stiction).
In the military, returning to land with underwing stores, (in some cases with hangups which the pilot didn't know were there), use of ADD guaranteed stall margin on the approach.
When later, watching daughter flying 767s for BA, I was surprised that they didn't use AOA for the approach, with such a huge variation in possible landing weights. But she assured me that AOA was indeed measured and was contributing to the safety systems, such as stall warning.

I guess it depends on where your priorities lie. Given worst-case scenarios, would you rather stall on final, or overrun the runway? I'm pretty certain of my answer.


Perhaps. But perhaps not. But pray tell, if it's not a simple function of AoA, then just what exactly else do you suppose is figured into a climb calculation when you're already at max power?! Last time I checked, there's only 2 things can determine climb performance: pitch and power.

Alpha display
 

Given that, how about a reliably informed & programmed ( ie. by Test Pilot / Flt. Test gen', not avionics types with computers in bedrooms ) - a decent Stores - ( weight / fuel Mangagement System, with civilian equivalent ?

Along with suitable decent sensors.

Seems to a pleb' like me a much more user - friendly way to do things, after previous users & systems required a lot of heads-down deciphering...

DZ

The problem being, that the existing certification margins for both apparoach speed and landing distance are designed, however empirically, around the CURRENT design assumptions i.e. that the consequences of a weight error are equally distributed between risk of stall and risk of overrun. (If anything, service experience would seem to indicate that risk of overrun is actually far greater, but it is as you note generally (but not always) more survivable).

Changing to a system where all the risk is loaded onto the overrun side of the equation would represent a net REDUCTION in safety unless the conservatism in the current landing distance calculations were increased to account for the increased risk.

Also, give the 'worst case scenario' of being grossly overweight, there are warning systems or characteristics which will alert the crew to a too-slow approach; there's nothing to warn you that your calculated landing distance is too short (that I know of) except indirect clues. So to stall on approach requires the weight error and failure to respond to warnings. With an AoA approach, what's going to protect against overrun?

Is it not significant that many of the military types which use AoA for approach are CARRIER aircraft - a case where landing distance considerations DONT have much significance.

Scheduled speeds can also be affected by, amongst others, VMC (a, l or g), VMU or variations in stall AoA with conditions; none of which will be captured by a simple AoA target.