AoA data: can you fly without it?
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AoA data: can you fly without it?
I ask this here so as not to impede the more informed discussions elsewhere. Question I have is, could you design a modern passenger transport flight control system, including info to crew, that didn't use AoA data. Introduction of AoA data seems a rather modern idea and I wonder if it isn't just to enhance economies or allow envelopes to be pushed out ( with whatever that implies about margins and fail safes). Anyone know?
Last edited by Mr Optimistic; 25th Nov 2018 at 09:32. Reason: Usual collection of typos
Not an airliner I know but Mr Macs F-4 (first flew in ‘58) was AOA equipped and large portions of the flight regime were or could be flown flown with reference to AOA, rather than IAS .....I’ll put money on that not being the first aircraft so equipped.
There is no absolute reason why AoA is necessary, it’s value is relative to the source of alternate data and information provided.
Arguing the reverse, in commercial aircraft AoA has piloting value at low speed, usually at values which should be avoided; however at other times it provides little information relative to structural or performance limits dependent on speed. For modern auto-controls, AoA provides better precision and reaction to the dominant flight control parameter.
Desperately trying to recall an aircraft without AoA; Comet, Dove, … Gnat - except the Bedford resident festooned with probes and vanes !
Arguing the reverse, in commercial aircraft AoA has piloting value at low speed, usually at values which should be avoided; however at other times it provides little information relative to structural or performance limits dependent on speed. For modern auto-controls, AoA provides better precision and reaction to the dominant flight control parameter.
Desperately trying to recall an aircraft without AoA; Comet, Dove, … Gnat - except the Bedford resident festooned with probes and vanes !
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Hmm, and what if after Step 1 all you see is grey in grey? Or dark with little sparkling lights both below and above you? Not that uncommon, both scenarios. However, Step 2 is even recognized by Airbus, if you read their golden rules. And if you look at their recent airplanes, they are bristling with probes and AoA vanes.
Hmm, and what if after Step 1 all you see is grey in grey? Or dark with little sparkling lights both below and above you? Not that uncommon, both scenarios. However, Step 2 is even recognized by Airbus, if you read their golden rules. And if you look at their recent airplanes, they are bristling with probes and AoA vanes.
As for a serious answer to an interesting question: if you mean without using an AoA at all as a concept then, I guess, no - for all the reasons you mentioned. That would require some serious thought - and questions about what kind of envelope protection, if any, we require etc etc.
If you mean without using AoA vanes, but artificially creating a figure we could refer to as AoA which we could use to keep us away from the trees - then yes. Using modern INS data in 3 axes you could artificially derive a sensible figure for AoA.
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If you mean without using AoA vanes, but artificially creating a figure we could refer to as AoA which we could use to keep us away from the trees - then yes. Using modern INS data in 3 axes you could artificially derive a sensible figure for AoA.
I might be wrong, but i believe currently there is no better way, same as for pitot tubes where we always search for something else whenever a plane crashes because of a pitot malfunction.
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Needs to be a type with acceptable natural stall characteristics, hence no need for artificial stall enhancement (which almost inevitably means AOA, though there are ways to sense the stall that don't directly sense AOA of course)
I don't recall Hawk having one, but the T-45 did, so it might have. Not sure what we used it for, if so.
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Yes, the original curiosity was about using AOA data in the control laws. The actual devices look pretty basic to the untaught eye and sit in the airflow next to the fuselage. If there is an upset you can imagine the airflow getting a bit dynamic affecting the response of the vane. I hadn't realised they were the inputs to the stick shaker. But I was surprised by the apparent reliance on AOA data to allow flight stability augmentation and in doing that allowing less margin in the flight characteristic than perhaps would previously been the case with just the natural, passive, characteristics of the airframe and control surfaces.
So thanks for the info, looks like I am behind the times!
So thanks for the info, looks like I am behind the times!
Of course you can fly without AOA data. Just keep the plane above stall speed. The problem is when the AOA system fails and it's tied to warnings or worse to an automatic trim system like the 737 Max. I flew the KC135 for years. It has an AOA indicator, but it isn't coupled to anything else and was seldom even looked at.
Interesting idea, but how would the INS, which by the way is standard for the last 40 years or so, know about airflow? The position of the aircraft in space is known and not questioned, however, relative airflow is a different matter and i do not know any other means of measuring it except by some device like a vane. That is not saying much as i am not aircraft design engineer or something like that, just a pilot.
I might be wrong, but i believe currently there is no better way, same as for pitot tubes where we always search for something else whenever a plane crashes because of a pitot malfunction.
I might be wrong, but i believe currently there is no better way, same as for pitot tubes where we always search for something else whenever a plane crashes because of a pitot malfunction.
In general I think the OP’s question about removing AoA vanes is giving too much weight to the very rare failures and not enough weight to the vast majority of the time when the system works properly. Instead of scrapping it all together, we should probably be working towards improving it.
You may be right that there is no “better way” but if you consider aircraft with a flight path vector display, such as the Airbus “bird” then you can get an approximation of angle of attack from the difference between the flight path vector, where the aircraft is going, and the attitude, where it is pointing. This is, as far as I know, all done using the IRS, it doesn’t need to know the relative airflow.
In general I think the OP’s question about removing AoA vanes is giving too much weight to the very rare failures and not enough weight to the vast majority of the time when the system works properly. Instead of scrapping it all together, we should probably be working towards improving it.
The results were positive and the INS calculations were reliable. Even if not as a primary source of AoA data, it would be good as sense check data.
It does seem rather odd that the one thing to be avoided in flying is stalling yet no a of a indication is usually fitted.
People glibly say, "Just keep ablve stall speed" wgule completely ignoring (or forgetting) that stall speed is a variable figure and an ASI cannot ever tell you what it is. Only in some limited circumstances can an ASI even give an approximate suggestion that a stall is approaching. As the primary thing a wing 'sees' in this illustration is angle of attack it is indeed strange that we approximate out knowlege of this by use of a secondary indication, speed which take no account of wing loading.
I'm sure it is done this way mainly for historical reasons and most of the time the system works fine, but it isn't ike aviation to rely on a secondary source and inaccurate approximaton to asess something as critical as stall speed.
People glibly say, "Just keep ablve stall speed" wgule completely ignoring (or forgetting) that stall speed is a variable figure and an ASI cannot ever tell you what it is. Only in some limited circumstances can an ASI even give an approximate suggestion that a stall is approaching. As the primary thing a wing 'sees' in this illustration is angle of attack it is indeed strange that we approximate out knowlege of this by use of a secondary indication, speed which take no account of wing loading.
I'm sure it is done this way mainly for historical reasons and most of the time the system works fine, but it isn't ike aviation to rely on a secondary source and inaccurate approximaton to asess something as critical as stall speed.
