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Technical Alternatives for Pitot Tubes?

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Technical Alternatives for Pitot Tubes?

Old 23rd Jun 2009, 17:55
  #81 (permalink)  
 
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Estimating the aerodynamical efficiency of the control surfaces

Hi there
There are multiple projects of airborne [email protected] anemometers, some are used by Airbus on a plane to study the turbulences in the wake of its airliners, so, provided it can be certified for commercial usage and proven reliable, maybe a different technology like [email protected] velocimetry can be goog for the overall navigation chain of airliners.
Speaking about the anemometry, I have a question for those who knows in flight mechanics/control and navigation: if the autopilot has the slightest doubt about the reliability of the airspeed measurements or AoA, would it be possible for the autopilot to add to the normal law/orders, very small predefined orders on the control surfaces (the goal is not to induce an upset) to see how they translate into load factors (linear/rotational accelerations via the IRUs) and estimate in another way via a numerical model of the flight mechanics of the aircraft, these suspicious air parameters (airspeed, AoA,...) ?
Jeff
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Old 23rd Jun 2009, 19:24
  #82 (permalink)  
 
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Quote:
Originally Posted by Graybeard
Why is it only Airbus receiving attention for multiple pitot problems?
-------

Mad Flt Scientist:
"In industry terms, it isn't "only Airbus"."

"EASA Safety Information Bulletin 2009-17, issued June 09, contains "recommendations" to operators regarding unreliable airspeed procedures and the applicability is:

Quote:
"All aeroplanes operating in commercial air transport."
-----
Now obviously the more general media are concentrating on AB because that's the simple story. And to be honest, would it really help matters if the press started harping on "it could happen to Boeing too, or Douglas, or ..."? There's enough unnecessary anguish already."
--------

The generic safety memo aside, I guess I should be more blunt: Is there a history of Boeing or McDouglas multiple pitot icing problems?

GB
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Old 23rd Jun 2009, 20:54
  #83 (permalink)  
 
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Cars use MAF sensor. It measures amount of the air getting into the engine and probably this is the speed of the air. They are cheap and uses different methods. My Toyota Supra 1988 has an optic one. I think there are dozens of other ways to measure air speed without mechanical devices.
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Old 23rd Jun 2009, 21:01
  #84 (permalink)  
 
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pleeeease..

we need no alternatives to pitot tubes..

just well heated ones..
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Old 24th Jun 2009, 13:08
  #85 (permalink)  
 
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falconer 1

the voice of reason. Could not agree more.

Its not airbus its a vendor and airline issue.
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Old 24th Jun 2009, 18:47
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Would a database-driven approach do?

I've lurked on this forum for years, but for the first time I think that I might have a valuable idea to contribute. (I'm just a PPL, but as this conversation is more about engineering than pilotage...)

In regards to the idea posited by bob.arctor and commented on by Mad (Flt) Scientist - if I understand it correctly - to take a model-based approach to determine airspeed, I have this to suggest. Instead of building a complete flight model, or using a new sensor technology (eg. covering the skin of the aircraft with piezoelectric devices), why not just create an database with prior good data?

Presuming that you've had at least a few minutes of reliable indication off of a pitot source, you now have some reasonable data on aircraft performance. Put another way, on any given flight, you know what airspeeds have resulted with recent combinations of AoA, power, vertical speed, and temperature. That should be sufficient to backdrive at least an approximate aircraft mass. If you wanted to get fancy you could incorporate flight control positions as well, but I'm primarily thinking about level, unaccelerated flight.

If airspeed data then become unreliable due to any factor - sensor failure, icing, impact damage, whatever - you should already have a reasonably close estimation of present aircraft mass (perhaps supplemented with data from a fuel totalizer) and, if I'm not mistaken, should then be able to calculate airspeed given present AoA, power, vertical speed, and temperature. This system should also make it possible to resolve disagreement between multiple pitot / static systems.

If each airframe had a onboard database of prior combinations of the same types of data, then it should be possible to deal with the failure of one sensor, whether it was an AoA vane, pitot tube / static port, thermometer, or whatnot. This strikes me as something that would be quite valuable for pilots, especially because it would eliminate a lot of guesswork as to what sensor or system was providing bad data. It such a system was incorporated into flight logic, it might have prevented recent upsets due to sensor or software failures. (And no, I'm not just referring to AF447, I'm also thinking of the Malaysia Airlines 777 upset over Perth in 2005.)

Obviously, for a system such as I've described to be useful, a single sensor failure should not make two variables unknown. For example, you'd want vertical speed to come from a gyroscopic source, not from the static system, since static port blockage could simultaneously render both airspeed and vertical speed unreliable.

Also, it's worth noting that I'm not sure how good the temporal resolution of this sort of system would be, but I'm reasonably certain that it would be good enough to avoid overspeed / stall during cruise and to maintain Va on approach. If its response were made fast enough it might also be able to take care of cruise gust load alleviation.

Perhaps someone's already implemented such as system? Thoughts and comments would be appreciated.

Cheers,
Alex
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Old 24th Jun 2009, 19:09
  #87 (permalink)  
 
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Originally Posted by falconer1 View Post
we need no alternatives to pitot tubes..

just well heated ones..
Ok, but it's been nearly two decades that the EASA has been issuing airworthiness directives to replace Pitots by Pitots: the problem is still here and seemingly worsening, more and more frequent. If it was just about augmenting the efficiency of the heaters of the Pitot probes, why hasn't it been done in two decades ? When the responsible of the EASA is being asked why the last Pitot replacement was not mandatory, he suggests that there is no point to replace Pitots by other Pitots which will not offer any improvement over the previous ones. And even after Air Caraibe or the AF447, the Pitot replacement is not mandatory (even given the suspected consequences of a loss of the flight assistances and alternate law 1 or 2). About responsabilities: when air transport companies ask their aircraft manufacturers about more resilient Pitot probes, the manufacturer answers that their probes are up to the specifications and even beyond. They don't improve their products in that direction since they are already compliant to the spec. : isn't it the responsability of the regulatory bodies (EASA, BEA,...) ?
When an inconsistancy is detected on air references (a doubt arises), what about testing the authority of control surfaces as previously suggested ? It does not require any new instrument (or the instrument is the entire airframe)
Jeff
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Old 24th Jun 2009, 19:36
  #88 (permalink)  
 
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well Hyperveloce,

first, for better or for worse, EASA did not exist two decades ago..it is a fairly recent "invention"..but that's besides the point..

1) The way I understood it, and worldwide the media has not reported correctly on that, it was in fact operators like Air France and others who confronted the manufacturers and demanded a "better" probe for the A330 / A340 family..

the probe upgrade for the A320 was not originally done for the same reasons as was deemed necessary by the operators for the A330/340 family..

so obviously the manufacturers seem to have told the operators that they don't believe the A320 probe upgrade would help with the A330 situations..

(that's why it obviously was not classified mandatory, but sort of optional, like in "nice to have" but not that necessary..)

at least that's the way I understand it from our industry media reports..

2) specs......well you can design a no nonsense old fashioned probe that is glowing like a frying pan, and it would fulfill those specs probably to the point..only problem, as a manufacturer, what do you want to charge for that?? it does not cost that much and the OEMs would not pay that much..

then again, if you design a super - duper space shuttle type probe, that has all kinds of technology in there, it may not be a common sense product, but it would still be up to specs... and guess what, for what that probe is sold for and for what the OEMs are ready to pay for it, you probably could buy a real nice 4 seater private airplane...we are talking big bucks here..

a product with "value added".. so to say...

3) regs.. well I am of the old fashioned variety in that I DO NOT believe that more regs and more mandatory stuff actually will improve a product, nor will it ultimately improve safety..

so maybe I'm wrong, but once you start to make some wild high tech thing out of a pretty basic pitot tube, well, it WILL fail more often, simply because more failure modes are designed into it..

look at an old 737 probe, or from whatever 60's or 70's era plane and look at the new stufff

times are a 'changin..

the only thing that still is fairly predictable and has not changed for a long while, guess a couple of million years by now, ( contrary to what all the climate change folks want you to believe ) IS the weather..

so maybe we should revert back to old "cheap" probes for the same old "expensive" weather..
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Old 24th Jun 2009, 21:30
  #89 (permalink)  
 
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Originally Posted by falconer1 View Post
first, for better or for worse, EASA did not exist two decades ago..it is a fairly recent "invention"..but that's besides the point....
True, but the BEA and other regulatory bodies did exist:
_______________________
AIRWORTHINESS DIRECTIVE
released by DIRECTION GENERALE DE L’AVIATION CIVILE

Translation of ‘Consigne de Navigabilité’ ref. : 91-227-021(B) R1
In case of any difficulty, reference should be made to the French original issue.

AIRBUS INDUSTRIE
A320 aircraft
Pitot tubes

The present Airworthiness Directive applies to AIRBUS INDUSTRIE A320 aircraft, MSN 002 to 122, 124 to 179, 183 to 194, 196 to 228, 230 to 245 and 247 to 255 included without AIRBUS INDUSTRIE Service Bulletin A320-34-1024 R3.
In order to prevent wrong speed indication - one or several speed indications lower than the real aircraft speed - due to water accumulation in flexible hoses betweeen pitot tubes and air data modules (ADM), the following measure is rendered mandatory on the effective date of this Airworthiness Directive :

accomplish AIRBUS INDUSTRIE Service Bulletin A320-34-1024 R3 at first opportunity or before
January 31, 1992 at the latest.
Ref. : AIRBUS INDUSTRIE Service Bulletin A320-34-1024 R3
EFFECTIVE DATE : JANUARY, 03 1992
_________________
And I don't have the means to make a more comprehensive search in the BEA archives.

the only thing that still is fairly predictable and has not changed for a long while, guess a couple of million years by now, ( contrary to what all the climate change folks want you to believe ) IS the weather..

so maybe we should revert back to old "cheap" probes for the same old "expensive" weather..
Well, I don't want to debate about the climate change and about the GIEC, but a pilot (now being a specialist of aeronautics consulted by most of the French TV) mentionned the effect of climate change at high altitudes to try to explain why the frequency of Pitot problems seem to increase. I am not a met specialist, but Pitot problems have been here for long and it is not only about Airbus.

But maybe prevention/maintenance can also help: between two flights in the airports, are there systematic inspections of the pitot drain hole and of the static pressure lines ? (drainage of water/humidity/moisture in the pressure lines)
Jeff
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Old 24th Jun 2009, 22:38
  #90 (permalink)  
 
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Synthesized IAS

* Sorry for going on about this *

Here follows some more on the 'synthesized IAS'. The software could work much like in face recognition, assuming that every [relative speed level vs altitude] make its own distinct pattern.

The noise could possibly be attenuated by incorporating broad audio spectrum analysis in addition to the accelerometer and piezo-electric readings from points within the main carrying structure.

About cost, the computing could possibly be done on an affordable modern server, and the software could be open sourced.

Mac OS X and Linux are solid operative systems and not prone to crash / output BSOD's.

The system structure could be made to accept multiple failures and still output reasonable data.

THAT is what causes the bending.
I meant the full motion of the wing, not just the vertical.

Last edited by bob.arctor; 24th Jun 2009 at 23:35.
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Old 24th Jun 2009, 22:53
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well Hyperveloce,

sorry, but you are proving my point, maybe without wanting to..

the story about the A-320 probes seems to have been about water drainage..

(stuff that could affect the pitots when flying in heavy rain for instance in an approach situation..)

The problems that Air France and Air Caraibes for instance have had with the A-330 /340 probes seems to have been during "dynamic convective" situations at high altitude...and that does not seem to be related to the water accumulation as such in the probes but seems more related to sudden freezing of the probes by super cooled droplets..so seems to be related to the heating elements..

That's the reason, according to what I have heard, that Airbus themselves had been skeptical whether the updated A-320 probe would solve the A330/340 issues..

and in regards to any reports that may correlate the high altitude freezing issues with any "new" climate we may experience..

well, I would be very careful with these theories..

the simple reason may well be that we have a lot more long range flights today which cross well known convective zones on a regular basis, and therefore we may see a significant increase of such incidents / accidents..

and like some others here in the radar threads maybe rightfully suspect, that we may not be as conservative in regards to heavy weather avoidance as in earlier times, maybe because some new high tech stuff in the cockpits, while being an enormous improvement in many regards, on the other hand may lead to a false sense of safety at times..

and may have changed in ever so subtle ways our threat perceptions..
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Old 25th Jun 2009, 00:28
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... as this is the Pitot Tubes Alternatives thread

One very good place to put piezo-electric sensors for the 'IAS Synthesizer' would be at the engine mounts.

This [synthesized] reading could be thought of foremost as complementary to the conventional old-school and normally reliable pitot tube-based meter.
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Old 25th Jun 2009, 22:45
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well, Bob..

One very good place to put piezo-electric sensors for the 'IAS Synthesizer' would be at the engine mounts.

This [synthesized] reading could be thought of foremost as complementary to the conventional old-school and normally reliable pitot tube-based meter.
grand idea, how about if we'd also couple it to the N1 indicator or EPR then subtract the ITT and put it into relation to the pressure altitude corrected by the "freezing point" of supercooled water droplets, if present, and divide it by the mean aerodynamic cord of fan blades and finally subtract the thickness of the windshields..and then

the EAS could determined with a poll in the cockpit taking into the equation the tilt of the engine mounts and the age difference between PF and PNF..

man, how about we stay with straight ( don't even mind if they're bent) PITOT TUBES..nice hole up front and a short circuit built into them that draws MEGAAMPS for a real nice hot temp at the hole..??!!

just my two cents..
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Old 26th Jun 2009, 05:13
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@alex_ledin

What you have described, calculating with tedencies could certainly purposefully be incorporated in the IAS Synthesizer

@falconer1


The concept of an IAS Synthesizer apparently sounds far fetched to you.

I'm quite sure that such a device can be built, although maybe not exactly the way I have described it (The story about the car Homer Simpson designed for one of the Big 3 comes to mind). Some uni could possibly make it work.

About the new weather, flying trough strong turbulence in an airplane today can well be likened with traveling in a speeding bus on a very neglected dirt road, with no suspension and all tires blown.

If the cockpit, cabin and baggage compartment together were made floating in relation to the airframe (as with electronic F1 car suspension technology), the general safety and comfort could be way much better.

Last edited by bob.arctor; 26th Jun 2009 at 05:30.
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Old 28th Jun 2009, 15:18
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Code:
THAT is what causes the bending.
About the vertical motion / wing oscillation, analyzing vertical accelerometer data over the wings alone should give an IAS reading as air speed and air density are two main parameters affecting the wave damping.

Surely the analysis would be complex in turbulence conditions but then there'd be all the other data.

Last edited by bob.arctor; 28th Jun 2009 at 15:35.
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Old 28th Jun 2009, 19:25
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Goes to show there are a lot of complicated ways to measure airspeed.

GB
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Old 28th Jun 2009, 23:01
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Just my 2p:

Alex_ledin - Like the idea of a database-driven approach, but it's maybe susceptible to other inputs giving false readings and exacerbating the feeling of a loss of control of your senses (no pun intended).

bob.arctor - Linux and MacOS don't crash?? Don't make me laugh!

"Laser" anemometers - good idea for a backup that works in a totally different way - shouldn't be too expensive to mass-produce either? Also, if you have a problem with finding particles that far up, create your own! Just stick a smoke generator a few feet in front if necessary.

And now on to my off-the-wall idea for measurement:

Sensors in each jet engine in the compressor stage, measuring the amount of air resistance occurring at the fan blades.

Not sure how sensitive it might be (or rather how insensitive the jet engine is for a given state of fuel entry), but it's one place to try?
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Old 29th Jun 2009, 09:40
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Mike,
most engines have their own pressure and temperature sensors in the intakes already - but I guess they are pitot/statics too!.

The A380 has all the engines reporting their parameters to the central system which then sends information back to the other engines as well as the airframe values.

More use might be made of all this data, but certification of any computer system on an aircraft is not like releasing it to normal users. It takes much time and effort to be sure that it is as safe as possible (ALARP) and will not interfere with the safe conduct of the flight.

Mac-OS and Linux would struggle to conform, specialist OSs are needed for safety.

VnV
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Old 29th Jun 2009, 23:26
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The real question: flying with 1 type of sensor inop.

Mike-Bracknell: I agree that you'd have to do input checking, but even this would probably have positive safety consequences. For example, if the pitot gets plugged and your airspeed goes from M.80 to M.27 in less than a second, you know that something's gone wrong, and it's overwhelmingly likely to be related to the pitot / static system if there's little or no recorded vertical acceleration. (Again, this presupposes that you're getting VS from a gyro or accelerometer and not your static source!) I don't know quite what you mean about loss of control of the senses: are you concerned that pilots would lose the ability to determine which systems had failed?

bob.arctor: A synthetic IAS / TAS system would require a purpose-built real-time OS that was far more reliable and rigorously tested than a general purpose operating system like Linux or most versions of BSD, including the Mac OS. Thankfully, such RTOSes already exist. Additionally, if a synthetic IAS system were to be implemented, it would have to function with the limited computational resources that are available on an aircraft. That's why I suggest that using a database with known-good data would be a better approach than some sort of real-time modeling. Any system that requires heavy analysis (say, finite element analysis) is almost certainly inappropriate for in-flight use, at least right now. I can imagine that in ten or twenty years we'll have the computational horsepower to alter airfoils in-flight to achieve whatever results are desired.

Given recent rumor and information about similar problems with A330s at TAM, NWA, Qantas, and Air Caraibes, it's tempting to focus on pitot/static system-specific problems. I would suggest that the bigger issue is how to keep a computer-controlled aircraft flying safely with persistent bad data from all of the sensors of a single type. Since we cannot reasonably build aircraft with three different designs of pitot tube (for example) from three different vendors, we have to prevent an unanticipated design flaw in that one pitot tube design from delivering fatally bad data. There’s no reason for that bad data to cause a loss of control, never mind a bunch of bent metal and lost lives. This goes for all sensor subsystems: accelerometers, AoA vanes, engine performance monitors (FADECs), etc., and not just pitot / static systems.

Cheers,
Alex
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Old 30th Jun 2009, 00:27
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I don't know quite what you mean about loss of control of the senses: are you concerned that pilots would lose the ability to determine which systems had failed?
Got it in one...well almost - I was also including the computers, as with more than one failed component you would deviate from the known failure for one axis of the plotted database, thus leaving your computers scrabbling for knowledge of which system had failed and where exactly it was supposed to be in this database.

Trend analysis would have to be a feature of the database I think, and I also think you do computational power a disservice as nowadays there's a hell of a lot of number-crunching can be done with a lowly PC processor. Certainly enough to give a *rough* estimate of flight parameters i'd assume.

I do think there's mileage in trying to apply modern techniques as backups to firstly augment (and then maybe replace) the systems that have done well up to now on aircraft though. Having watched Wimbledon tonight, and seen how well Hawkeye does nowadays with line call predictions purely from camera data, there's an example of something that wouldn't have been possible 20 years ago, but works well enough now that the line judges are almost redundant.
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