Angle of Attack
 

Comments please. I think the aircraft is great. I love the AOA device.


https://www.youtube.com/watch?v=2wlvpJLcf-A

100% agree!!

The Wright Bros understood the importance of AOA from the very beginning.

My landings in the 727 greatly improved when I started using the Honeywell Fast/Slow AOA indicator that was equipped on some of our planes.

It proved, often, that our zero fuel weight, as provided by load planning was, indeed, incorrect.

Totally agree and surprised at the lack of AOA in light GA also that A5 looks a great little Sea plane and a lot of fun.

We have an AOA on the Citation and you could disregard the ASI and just fly the gauge for more accurate speeds and approach.

My only concern without reference to another instrument is if the AOA instrument failed or false read which could land you in a dangerous mess
So I would still want an ASi and preferably 2 separate AOA to cross reference

Pace

@Pace

Agreed. Watching the hard pull in the youtube clip at low level had me wishing for a secondary AOA device.

Best,

SSS

I've been banging on about this on here for decades! AoA is what the wing knows - there is NO SUCH THING as stall speed, only stall angle. Yet every time the tired old responses come back supporting use of air speed in stall avoidance.

The GA world does NOT think AoA. The airliner world is obsessed by 'speeds', and the only airliner I know with an AoA indicator is Concorde!

As the video says, the military know better. They always think AoA, just as the aeroplane does.

I've said it before, and here it is again.... I'd trade just about any instrument on the Chipmunk's panel for an AoA indicator!

There's been a problem to date with fitting them to prop singles - the propwash mucks up AoA measurement using conventional sensors. One wonders if it's significant that the aeroplane in the video is a pusher?

I'm a big provisional fan of AoA. Provisional because I think that for GA there are a bunch of best practice issues still to be sorted out and, whilst clearly you can do without AoA, you can't actually do without airspeed - if only to determine the rotate point. You also need speed or altitude in the cruise, as reference solely to AoA is a recipe for phugoids.

The military don't use AoA exclusively - they do usually use it for approaches and some combat manoeuvring in fast jets. For various other things they also use IAS and/or IMN.

Testing out IAoA instrumentation and developing some best practices has surely to be an ideal use of the new CAA E-conditions?

G

Most light GA types don't have a 'rotate point'. They fly when they are ready!

Used to break my heart to watch the Manchester-based flying school PA 38s doing circuits at bumpy Barton - hammering down the runway up to and beyond the point the aeroplane would happily fly, elevator firmly down, nose leg having seven sorts of !!!!!e kicked out of it, until some mythical 'rotate speed' was achieved, way too far down the runway, and the little Tommy gave a prayer of thanks as it left the ground like a cork out of a champagne bottle, at last allowed to take to its natural element!

And this video isn't calling for the abolition of 'speeds', only 'stall speed', which doesn't exist as an absolute.

I had a quaint notion of using a vane/rheostat device under a wing coupled to some modified form of classic, 1950s fuel gauge. However, with respect for SSDs comment above I think two such systems are needed, one for each wing.
I am no electronics person and have little faith in the stuff, but a simple rheostat switch that can move a needle to represent zero to seventeen degrees over an actual needle movement of forty five deg can't be beyond the wit of mankind, at a sensible price?
I wouldn't utter the words "stall speed" in close proximity to SSD as that would equate to invoking the wrath of Khan! I've tried in the past!:{:{

Are the AOA indicators on GA aircraft calibrated to the cruise or landing config ?

The raw data for AoA indicators is from a fixed sensor measuring the angle of the whole aircraft to the relative airflow. (Often referred to as the 'Alpha Angle', or just 'Alpha'.)

This is obviously independent of configuration, and is usually set to show the AoA of the wing with a 'clean' aircraft, but this can be modified by sensors on the flaps, gear, and other adjustable devices, to take into account configuration changes.


MJ:ok:

Ps. Some students just don't seem to be able to visualise the AoA thing at all, and I find that a length of bamboo cane, with a piece of wool on the end, taped to the underside of the outboard section of the wing, and protruding far enough in front to be clear of the effect of the wing on the airflow, works sufficiently well as a crude alpha indicator to get the point across.

An AoA indicator might have prevented AF447 and other stall-related accidents.

I guess I'm the odd man out, I just don't see the point. If you understand basic pilot-level aerodynamics, it's all obvious. And if you don't, all the fancy gauges in the world won't help you. Hence it wouldn't have helped with AF447, because those guys were just totally lost and in tunnel-vision panic mode, to do what they did. (And ditto the recent Air Asia accident). If it isn't obvious to you that keeping the stick hard back while descending at 5000+ fpm is a bad idea, one little instrument among many won't help.

I've been yelled at on here for daring to utter the phrase "stall speed", but actually it's a pretty useful concept. It's extremely rare to try and land (or take off) in a 60 degree bank, never done it myself. And if you can remember some very simple math, the airspeed indicator makes a pretty decent AoA susbtitute assuming you're not trying to do loops.

I hope this doesn't degenerate into a screaming "stair head rammy" (Scottish expression) over stall speeds. Let's just agree that we all are aware of AoA.
SSD, I too would trade a few instruments for such a device, ASI being one of them. Although it may be of some use for Nav in the event of GPS failure.
The wooly stick ahead of the wing? Ok but a little crude. For GA light stuff I don't think sensors on flaps or other configuration changing devices is necessary.
It needs to be neat, tidy, and do a reasonable job on a clean a/c. If it were to read "stall" when clean and the flaps are down it is erring on the safe side.
If such a device could be built at a sensible price I think it would be taken up, especially if it could be retrofitted to anything. An expensive box of electronic junk costing an arm and leg to be certificated will not be.
My daft idea of lashing a fuel gauge tank sender unit wind vane thing to an u/c leg reading to a fuel gauge with instant read out is still on the drawing board, my a/c being permit powered I may try something this summer just for fun if nothing else. Any advice gratefully received.

Back in the '70's, we used the AOA indicator on the KC-135 to tell us our best range angle of attack, best endurance angle of attack, as well as our stall angle of attack.

I never understood why the airlines are so reluctant to incorporate such a useful instrument throughout their fleets.

I assume most of the GA AOA gauges on the market do not have the config sensors, and are either on a fixed calibration for landing or cruise which could lead to some false interpertation at best or conversely encourage a pilot who was unsure of the setup and was flying close to the performance envelope to Stall while they correctly read a gauge that shows they are not near that point.

I don't think there are any on the market.


MJ:ok:

Oops. :O

Yes there are:

Angle Of Attack Indicators from Aircraft Spruce

I think it's a safe bet that these accessory AoA systems do not take into account config. changes, so I imagine you can set them up to indicate correctly in whatever config. you like best, but only one.

As Genghis says, If they become a popular accessory, we will need to establish conventions for what the best config. for that would be, and I imagine that most would agree that calibration in the 'clean' config. would probably offer the safest compromise, in most cases.



MJ:ok:

The Piper Cheyenne II I used to fly had AoA as a part of its type design, and you lived by it, but it was a slinky plane. That said, for GA aircraft, I tend to agree with

I liked the Icon video, and am intrigued by the aircraft. I greatly respect the philosophy and effort toward safety, but if industry makes planes too "safe" pilots may forget to take responsibility for the safety of the flight themselves. If a pilot learns on the super safe Icon, how safe would they be while piloting a more mundane GA aircraft? It might be like getting your multi engine rating in a Cessna 337, should you really have a multi engine rating applicable to the regular fleet?

I installed an Alpha Systems AoA system in a client's Cessna amphibian. I set it all up (which was quite easy), and it worked very well. I even mounted it well forward on the glare shield, so it was more "eyes out". After 60 hours of flying the plane, I could not think of a time I looked at it, other than to confirm it was working. I just had no sense of need.

I had an older "lift reserve indicator" (form of AoA - same function) in my 150 for a while, but found I never looked at it. If I were landing into a place so tight that I would actually need to refer to it, I was much too busy watching where I was going outside, to ever look at an instrument in the panel.

I know that aircraft stall at an AoA, rather than a speed. For me, the stall is warned in the seat of my pants, and I refer to the airspeed if I'm curious about it.

I hope that the generation of pilots who learn on hyped instrumented GA aircraft also learn to fly them well, when the instruments quit, or go kaflooey. The AF447 pilots (for two) seemed to have missed that lesson. We can't be training around basic flying skills, just because there is new tech!

Most so-called 'AoA' indicators for light SEP aircraft are nothing of the sort. They rely on pitot and static pressure sesnsors, from which they 'deduce' AoA - usually on an overcomplicated display unit, to give the impression that they're worth the cost.

The aircraft I've flown with real AoA gauges displayed 'units' on a simple dial and had either an audio tone system (Buccaneer) or simple visual warning display (F-4).

I wouldn't recommend one of the current GA 'AoA' devices until someone has found a way of directly detecting actual difference between chord line and relative airflow and displaying it on a simple indicator.

The Russians have an excellent performance indicator in some of their aircraft - a combined 'g' meter and AoA gauge. Pull to whichever value is the more limiting and you're at your best turning performance!

Another of their very sensible instruments is a combined turn and slip and VSI - excellent for standby instrument work.

AOA indication in the million-dollar cockpit chez Smasher is my butt which also does sideslip. Bargain!

If my bum tells me my ship is languishing and the controls are labouring at the air (ok, my hands are in on this, too) then AOA is high. If my behind says the ship feels tight and buoyant, AOA is low and it's all good. I sense the aeroplane's motion, weight and response through my magic posterior which is absolutely art rather than science.

The further away you get from flying by the seat of your pants the closer you come to flying by numbers. By the time you reach jet fighters, airliners and tankers this justifies investing in a proper AOA gauge, one that gives you useful, calculated metrics like best range and endurance, rather than vague notions like "low" (aircraft feels firm beneath me), "high" (mushing around) and "dead" (clenched.)

FWIW My 1960's Jodel had the perfect aural device for the usually most dangerous deliberate slow phase of flight, i.e. approach & landing.
A simple leading edge vane & buzzer. You didn't have to look away to hear it begin to sound on the sweet spot for finals. After all it's wing airflow break away we're discussing, so it doesn't really matter at what angle.
mike hallam.

I see we're starting to get the 'fly by your bum' and 'de skilling' arguments this subject usually generates. Soon some bright spark will mention 'stick position'.

Pull too hard in a loop exit in a Yak 52 and be even a tiny bit out of balance and BANG, you flick. No time for any info from your bum, and there isn't any anyway. Not all aeroplanes have gentlemanly pre-stall buffet like a Chippy does!

De-skilling? I think not! If you can pull to nearly the stall angle in steep turns and aeros, you are losing no skill but gaining information, maybe life saving information if you're low down, that you didn't have before.

That Russian device Beags mentions sounds the dog's whatsits to me. Sounds typically Russian; elegantly practical. Pity they didn't fit one to the Yak!

The other point worth considering is the rough and ready 1.3 Xs the stall in a given configuration.
That is drummed into pilots as the approach and landing VREF which is not actually accurate. 1.1 1,2 1.3 1.4 1.5 they are all just numbers as is the principal idea that an aircraft has to land at or near the stall. It can be landed way above the stall if your not worried on published stopping distances

The AOA will give you a much more realistic picture

Pace

I do understand the thought behind "rather have AoA than ASI". But in my dotage I tend to drift off a bit......

.............It's a gusty day, maybe 10 Kt to 20 Kt, 30 degree X-wind, and young Lucy, who has been taught to use an AoA indicator from Day 1, and is now flying solo circuits on an aircraft with one, 6 hours after getting her PPL.

Her approach is watched by people who notice that she seems to be over-controlling with the elevator, and that she is having difficulty staying on the centre-line.

At 300 ft or so, the nose drops in a stall from which she does not recover. RIP Lucy.

Now, I wonder what caused that? Would she have been better off watching her airspeed like a hawk, and keeping it a few knots high because of the gusts? Did the AoA indicator kill her? Perhaps she should not have been flying on that day, but she had a PPL and a mind of her own. That's not the point, which is that the AoA indicator is obviously useful, but could be a very false friend if you don't really know how to fly.

Perhaps I'm just over-cynical about magic bullets.

I see your point, true, the butt isn't a precision AOA instrument or even a stall indicator. Listen to your butt tell you your AOA is high, or low, but don't ask it for exact science.

Wing loading decides how much precision you can achieve flying with your bum. A Cub bobbing along like a cork is much better than the big bad Yak slicing through the air.

Yeah there is! You're in a loop, you're under G. Your squashed butt says your AOA is high, right there. About unexpected flicks: see butt sensitivity and aircraft design, above.

Leighton Collins on angle of attack
 

Here's an excellent treatise on the subject of AOA:

FROM THE ARCHIVES: LEIGHTON COLLINS ON ANGLE OF ATTACK, 1965 | Article - Tue 28 Apr 2015 07:02:24 PM UTC | airsoc.com.

I don't understand this. Are you saying every time 'G' squashes your bum you should ease off because the AoA is high? I don't see how you'd ever complete a loop if you did that!

The trick is to pull as hard as you can but not so hard you exceed that stall angle. To do that, you need to know when you're approaching the stall angle. To do that you need an aeroplane that buffets before it departs (the Chippy) or an AoA indicator.

Thanks wannabee for an interesting and illuminating article. I think his final thought is on the button;

Why? Here's the last para of the add-on re flying a twin on one engine (BTW the pic is an Aztec, I think, which I did my twin rating on; I recall that achieving level, and straight, flight on one was a minor triumph at any altitude.)

I would prefer to say "...angle at which the wing meets the air..." because the wing goes through the air (perhaps motionless up to that point) and because I have a tiny mind. I agree 100% with what he says there.

PS; discussions like this always remind me of Alan Bramson's famous description of aircraft that could be flown with outrageous AoA; "Thrust-supported Contraptions". (NB I do mean AoA, as opposed to climb rate and angle.)

Cabot that is the very point I am making regarding 1.3X the stall in a given configuration there are times when 1.3X stall is dangerous on approach and you may have to look at a much higher figure and sometimes a much much higher figure


Pace

BEagle, is this based upon your personal experience with a modern GA AoA system such as the Alpha Systems brand?

Having had experience with "real" (vane type) AoA systems, and earlier pneumatic AoA systems, I was startled to see how well the modern system worked.

That said, after hours of testing, and confirming good function, I was not sold that I needed it - but it worked!

And not all aeroplanes are type certified (for stall warning characteristics) as a Chipmunk is. It seems there is a reason for that! A type certified GA aircraft will give the pilot tactile stall warning in all situations.

thing is shaggy, if you are doing aeros, last place you are looking is inside at the cockpit at gauges!! :)

I do think a properly trained pilot can do with out an aoa indicator and anyone doing aerobatics knows you can stall at any speed - 9g in a extra equates to about 170kts (give or take)

the extra buffets before stalling - just the more G you apply the shorter the period between buffet and departure. To practice finesse I sometimes split s and hold the plane on the buffet at a shade under 5g

but having said that anything that reliably aids safety cant be a bad thing

As I recall, the McDonnell F-4 Phantom had a variable pitch aural AOA indicator (through the headset) which allowed the pilot to give his full attention to his outside combat environment while keeping the plane's performance as close to the "burble" as possible without stalling.

I don't know the G limits, within which, their typical air combat maneuvers were conducted.

PPruner's???

No - sorry - I didn't mean to imply you should ease off - or do anything at all! Except, maybe, to proceed with caution. All I meant was when you've got G, you've got high AOA. That's all! Nothing more and nothing less. High AOA isn't a bad guy by default, you can fly at high AOA all day long and that's OK so long as you know you're doing it. As you say, how else would you do a loop?

Yes, exactly, glad we're on the same page. My bum only tells me roughly what my AOA is. If I want precision I need a gauge or an aeroplane design that tells me.

I could nevertheless see further development in AOA technology from Hud display to autopilot coupling and auto stall avoidance

Pace

AoA triggered stick shaker and stick pushers have been around for years!

The VC10 had such a system (due to ARB issues concerning 'super stall'), which was quite positive in action. During air tests of the VC10K, we took it to the 'stick shaker' stage, but the VC10C could be taken to the stick pusher if an additional AoA display was fitted. Intentional stalling (i.e. at the stick pusher) was prohibited in the VC10K variant though.

There was also a 'lift rate' modifier which ensured that the stick shaker would be triggered at the correct AoA for configuration and would also operate sooner if it detected a rapid change in AoA...

It was quite common to get the odd rattle of stick shaker during flapless or slatless approaches. One reason being that, in one VC10K2, the lift rate modifier wiring was found never to have been connected and was tucked behind the soundproofing....

But on another occasion, I was flying a nice steady flapless approach at exactly the correct speed when suddenly the klazons went off and the stick pusher operated :eek:! It was certainly possible to override the system, so having done so we went around, dumped the stall protection system (it was common to do so when refuelling off another tanker, due to disturbed airflow over the AoA probes) and landed off a normal approach.

The reason for the spurious operation was that the aircraft had been sitting in the grubby, dusty environment of the operational theatre and hadn't had a wash for ages. So the AoA probes had probably been binding until a gust on my approach dislodged one, which then went from the cruise value to the actual value, fooling the stall protection system into premature operation by spurious detection of a rapid AoA change....:\

So no thank you - please do not consider an autopilot with an 'auto stall avoidance' device. Airbus includes excellent envelope protection features in the autoflight system, but if the pilots don't understand them or take the totally wrong action for unreliable airspeed indication, all the clever robots in the world won't guarantee protection.

:ok:All a/c have an angle of attack indicator. It's called the stick/column and when its aft of a point which you can paint on the fus, the wing will be stalled. Don't bother quoting different flap positions etc because it always works out more or less to the same spot. For example if you are tightening a final turn, be very aware of stick position!

Not in single Cessnas, the flap setting will affect the neutral position of the pitch control considerably.

Ha! Didn't take long! As I said in post #22:

Camarque: No, of course one isn't fixated on any instrument in aeros, but one would take occasional glances as one does with the other instruments to confirm that at this speed and this 'G' the AoA isn't too near the top of the yellow arc. In a sustained pull (max performance 360 for instance) one can pull to the limit!

Errr do you want to word this better?? "pull to the limit" of what limit of the movement range of the stick?? or something else?

Oh... probably something else, Pittsextra. :rolleyes: