4 ms·

I wonder if it's feasible to build a guard to cover the AoA sensor to mitigate the ability of foreign objects damaging the vane. Clearly it'd need to be very t

I wonder if it's feasible to build a guard to cover the AoA sensor to mitigate the ability of foreign objects damaging the vane. Clearly it'd need to be very transparent to airflow—something like the face guards of an NFL player—a heavy gauge titanium cage or something like that. Btw, the Wright Bros knew the importance of AoA and included one on the Wright Flyer. Implementation? — a length of straight stick parallel to the wing chord with a bit of ribbon affixed to the end :-D (KISS at work!)

subb 8y ago
I wonder if they could take the mesure from the underside of the plane (90 degrees difference from the front)? It might help for bird strike, not much for ice.
- CamperBob2 8y ago
  I wonder if a small array of microphones couldn't be used to accomplish the same thing by cross-correlating the sound made by airflow hitting adjacent surfaces at different angles. Seems like a bad idea to use mechanical vanes for this, especially if you're going to bet the whole farm on a single instrument as Boeing seems to have done.
lawlessone 8y ago
>omething like the face guards of an NFL player it would probably just get blocked then by bits of bird.
VBprogrammer 8y ago
AoA sensors are sensitive to very minor deviations in the surface they are mounted to, there are aircraft which don't allow any minor damage in that area because it can cause misreadings.
- HeyLaughingBoy 8y ago
  You seem to have a pretty high level of knowledge of avionics. Do I remember correctly that you worked in the field? If so, do you have any idea of what the allowable range of an AoA sensor might be? i.e., on some systems I've worked on, we had a range that a sensor was expected to be in (normal, just do regular control loop), an outer range that was unlikely (stop reporting for a while/hold control output constant to see if it gets better or worse before warning operator), and a narrower range that was flat out impossible (notify operator of sensor failure/put system into a graceful shutdown). I assume that the engineers designing this system had something similar, but given that MCAS activated with an AoA indication of 80 degrees (IIRC) and that's essentially impossible on a 737 (or at least would correlate with a hell of a lot of other warnings), was there anything they could do to warn the operator (pilot) that there was likely a bad sensor input?
  - VBprogrammer 8y ago
    Not me. Humble student pilot and aviation enthusiast. Not sure if you caught this post https://philip.greenspun.com/blog/2019/04/08/boeing-737-max-crash-and-the-rejection-of-ridiculous-data/ https://philip.greenspun.com/blog/2019/04/08/boeing-737-max-... which I think is basically the same idea as you are suggesting. From all outward appearance it appears they failed to do any kind of range check On the data. Although people were quick to point out that AF447 had a situation where the airspeed decreased to such a low level that the warnings stopped (because it was outside of any normal flying range) which was implicated as a source of confusion.
HeyLaughingBoy 8y ago
My general practice is to assume that the engineers in a highly regulated field are competent and have good reasons for the things they do/don't do. If there isn't a guard, then it's likely that having one would cause more problems that leaving it off or it would be ineffective. e.g., hitting a bird at 100+ kts would damage both the guard and the sensor anyway, rendering the guard useless.
- peteradio 8y ago
  Engineers can have their hands tied as well, limiting their options to doing the job or resignation. Perhaps putting a guard on the vane would have only been necessary if it was considered an intolerable failure and being flagged as an intolerable failure would have required a recertification of the plane or something. Just a guess.
- noir_lord 8y ago
  Given they test aircraft canopies by firing frozen (after defrosting) chickens at them it's usually a safe assumption. Air travel is very safe because of literal generations of engineers working hard to make it safe, in this case the failure is one of procedure and people been people (cutting close to the wind on what was allowed). Things usually tighten up after this kind of thing and then gradually loosen until the next disaster that could have been preventable.
laydn 8y ago
I was thinking whether they can "hide" an extra AoA sensor under the hood for emergencies. Just like a landing gear can be put down or retracted, an AoA sensor can be kept inside the fuselage, and brought out only when necessary. Maybe this one sensor will have better lifetime/reliability since it is not exposed to outside conditions.

subb 8y ago

I wonder if they could take the mesure from the underside of the plane (90 degrees difference from the front)? It might help for bird strike, not much for ice.

CamperBob2 8y ago
I wonder if a small array of microphones couldn't be used to accomplish the same thing by cross-correlating the sound made by airflow hitting adjacent surfaces at different angles. Seems like a bad idea to use mechanical vanes for this, especially if you're going to bet the whole farm on a single instrument as Boeing seems to have done.

lawlessone 8y ago

>omething like the face guards of an NFL player it would probably just get blocked then by bits of bird.

VBprogrammer 8y ago

AoA sensors are sensitive to very minor deviations in the surface they are mounted to, there are aircraft which don't allow any minor damage in that area because it can cause misreadings.

HeyLaughingBoy 8y ago
You seem to have a pretty high level of knowledge of avionics. Do I remember correctly that you worked in the field? If so, do you have any idea of what the allowable range of an AoA sensor might be? i.e., on some systems I've worked on, we had a range that a sensor was expected to be in (normal, just do regular control loop), an outer range that was unlikely (stop reporting for a while/hold control output constant to see if it gets better or worse before warning operator), and a narrower range that was flat out impossible (notify operator of sensor failure/put system into a graceful shutdown). I assume that the engineers designing this system had something similar, but given that MCAS activated with an AoA indication of 80 degrees (IIRC) and that's essentially impossible on a 737 (or at least would correlate with a hell of a lot of other warnings), was there anything they could do to warn the operator (pilot) that there was likely a bad sensor input?
- VBprogrammer 8y ago
  Not me. Humble student pilot and aviation enthusiast. Not sure if you caught this post https://philip.greenspun.com/blog/2019/04/08/boeing-737-max-crash-and-the-rejection-of-ridiculous-data/ https://philip.greenspun.com/blog/2019/04/08/boeing-737-max-... which I think is basically the same idea as you are suggesting. From all outward appearance it appears they failed to do any kind of range check On the data. Although people were quick to point out that AF447 had a situation where the airspeed decreased to such a low level that the warnings stopped (because it was outside of any normal flying range) which was implicated as a source of confusion.

HeyLaughingBoy 8y ago

My general practice is to assume that the engineers in a highly regulated field are competent and have good reasons for the things they do/don't do. If there isn't a guard, then it's likely that having one would cause more problems that leaving it off or it would be ineffective. e.g., hitting a bird at 100+ kts would damage both the guard and the sensor anyway, rendering the guard useless.

peteradio 8y ago
Engineers can have their hands tied as well, limiting their options to doing the job or resignation. Perhaps putting a guard on the vane would have only been necessary if it was considered an intolerable failure and being flagged as an intolerable failure would have required a recertification of the plane or something. Just a guess.
noir_lord 8y ago
Given they test aircraft canopies by firing frozen (after defrosting) chickens at them it's usually a safe assumption. Air travel is very safe because of literal generations of engineers working hard to make it safe, in this case the failure is one of procedure and people been people (cutting close to the wind on what was allowed). Things usually tighten up after this kind of thing and then gradually loosen until the next disaster that could have been preventable.

laydn 8y ago

I was thinking whether they can "hide" an extra AoA sensor under the hood for emergencies. Just like a landing gear can be put down or retracted, an AoA sensor can be kept inside the fuselage, and brought out only when necessary. Maybe this one sensor will have better lifetime/reliability since it is not exposed to outside conditions.