Technical Alternatives for Pitot Tubes?
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From: Orbit 5
it seems we have left behind good simple thinking for all of the wonderful 'new ideas' in aviation like that bring'em down year after year for the same old reasons since 1903 
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From: Netherlands
To come back to the original question are there ttechnical alternatives for pitot tubes...The answer is yes, optical air flow meters have been developed and tested on aircraft with success. They accurately measured the airspeed of the aircraft. It could take some time until they become available on the commercial market.
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From: Orbit 5
A few nanometers thick layer of piezo-resistive skin could perhaps also be seen as an alternative 
Processing the data would require some dense continuous computing but this method should give a very reliable and precise IAS reading.
Processing the data would require some dense continuous computing but this method should give a very reliable and precise IAS reading.
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From: SoCalif
Until the present Thales/Airbus situation, pitot tubes have been very reliable.
It just shows that manufacturing even the simplest device can be screwed up. What could possibly go wrong with making and maintaining piezo-electric skin?
GB
It just shows that manufacturing even the simplest device can be screwed up. What could possibly go wrong with making and maintaining piezo-electric skin?
GB
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From: Bedford, UK
vortex shedding
a few years ago I believe work was being done on speed sensors which relied on 'vortex shedding ' (why telephone lines 'sing' in the wind). These don't rely on dynamic pressure. Don't know what, if anything, became of them.
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From: Bedford, UK
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From: Orbit 5
What could possibly go wrong with making and maintaining piezo-electric skin?
2) Paint job
The sensor surface shouldn't require any more maintenance than say a carbon fiber airframe.
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From: Orbit 5
...As a secondary and auxiliary meter, the IAS could be derived from an internal 3D reading of the wing geometry together with weight, static pressure and accelerometer data.
Last edited by bob.arctor; 22nd June 2009 at 02:25.
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From: La Belle Province
Are you seriously suggesting to try to back out the external wing loading from FEM type measurements within the structure? That would require a degree of accuracy that simply does not exist, and may not feasibly ever exist in any cost-effective sense.
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From: Orbit 5
Are you seriously suggesting to try to back out the external wing loading from FEM type measurements within the structure? That would require a degree of accuracy that simply does not exist, and may not feasibly ever exist in any cost-effective sense.
There would be a combination of inputs needed, with advanced realtime computing involved, surely. A carbon fiber airframe would have more flexing / movement that would make the measurements more 'visible' to the various sensors.
The main 3D physical motion of a wing could be measured from one strategic single point, affordably.
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From: La Belle Province
You can't deduce airspeed from the data you are suggesting, though.
At least, not with any expectation of accuracy.
A wing flexes the same under load to support the same weight, independent of airspeed (to a first approximation). So the wing shape at 100knots and the wing shape at 200knots would be essentially identical for the same weight. Even then, backing out the weight would not be trivial, especially given the unknowns of the inertia distribution due to fuel and payload distribution. (The wing flex for a heavy a/c with low fule state will differ from that with a high fuel load but correspondingly lower payload)
So, let's assume nevertheless that somehow we back out a reliable estimate for the weight. What's left in the lift equation - 1/2 rho V squared, S and CL. OK, S we can define, but to get closer to V we need CL. For that we're going to need an accurate model of the aerodynamics - not at all trivial, especially for an in-service aircraft not given the TLC a test vehicle gets. (Indeed, this methiod has been used with a KNOWN V to estimate degradation of CL compared to standard, and it's not always small).
I think if you do the error budgets in that process you struggle to get any kind of accuracy for airspeed - especially given that we have a pretty good way of measuring it right now that's a great deal simpler.
The alternative - Well, you could attempt to deduce the airspeed by looking at very small differences in wing loading due to low order Mach effects - not something terribly accurate at low Mach numbers. But that's even more error prone I suspect.
At least, not with any expectation of accuracy.
A wing flexes the same under load to support the same weight, independent of airspeed (to a first approximation). So the wing shape at 100knots and the wing shape at 200knots would be essentially identical for the same weight. Even then, backing out the weight would not be trivial, especially given the unknowns of the inertia distribution due to fuel and payload distribution. (The wing flex for a heavy a/c with low fule state will differ from that with a high fuel load but correspondingly lower payload)
So, let's assume nevertheless that somehow we back out a reliable estimate for the weight. What's left in the lift equation - 1/2 rho V squared, S and CL. OK, S we can define, but to get closer to V we need CL. For that we're going to need an accurate model of the aerodynamics - not at all trivial, especially for an in-service aircraft not given the TLC a test vehicle gets. (Indeed, this methiod has been used with a KNOWN V to estimate degradation of CL compared to standard, and it's not always small).
I think if you do the error budgets in that process you struggle to get any kind of accuracy for airspeed - especially given that we have a pretty good way of measuring it right now that's a great deal simpler.
The alternative - Well, you could attempt to deduce the airspeed by looking at very small differences in wing loading due to low order Mach effects - not something terribly accurate at low Mach numbers. But that's even more error prone I suspect.
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From: Orbit 5
The model would be complex, and this 'synthesized IAS' could be thought of as a complementary reading, used when there was an eventual problem with the main meter.
The resistance will here be quadrupled and this will bend the wing accordingly.
The accelerometer data is meant to make the reading / the modeling more accurate.
(I dropped out of school long before any of the above and we only had access to an ABC 80 btw
So the wing shape at 100knots and the wing shape at 200knots would be essentially identical for the same weight.
The accelerometer data is meant to make the reading / the modeling more accurate.
(I dropped out of school long before any of the above and we only had access to an ABC 80 btw
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From: Bedford, UK
A friend, John Talbot, has designed a simple system where a valve shuts off the ASI from the pitot tube and engine bleed air is blown back through the pitot system to the pitot head, clearing any ice, moisture, insects, etc. If this is done on each pitot head one at a time by a sequence system of some kind the ASI reading will not be lost.
The patent for this is now in the public domain so a developer would not have to pay royalties, etc. but I`m sure John would appreciate an acknowledgement. We have tried sending the idea to most of the manufacturers but no luck so far.
Publication number:
GB2418739
Publication date:
2006-04-05
Details can be found on
http://v3.espacenet.com/textdes?DB=EPODOC&IDX=GB2418739&F=0&QPN=GB2418739
The patent for this is now in the public domain so a developer would not have to pay royalties, etc. but I`m sure John would appreciate an acknowledgement. We have tried sending the idea to most of the manufacturers but no luck so far.
Publication number:
GB2418739
Publication date:
2006-04-05
Details can be found on
http://v3.espacenet.com/textdes?DB=EPODOC&IDX=GB2418739&F=0&QPN=GB2418739
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From: La Belle Province
No. Although the dynamic pressure is 4 times greater at 200knots compared to 100 knots, the wing loading is actually the same. Because the wing is supporting the same aircraft weight, and THAT is what causes the bending.
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From: UK
xMillion dollars worth of electronics being fed information by a couple of holes in the side of an aircraft.
I know its not as simple as that but its a question of balance.
Takes me back to my days in industry when the time and motion engineer would measure operations to the nearest minute then produce costings to a thousanth of a penny! He didn't understand the problem but common sense......
It is actually quite serious because we now have a very good indication that something wrong with these 'holes' can totally disable a large aircraft and that 'something' can be a problem encountered regularly by all pilots i.e. ice.
I know its not as simple as that but its a question of balance.
Takes me back to my days in industry when the time and motion engineer would measure operations to the nearest minute then produce costings to a thousanth of a penny! He didn't understand the problem but common sense......
It is actually quite serious because we now have a very good indication that something wrong with these 'holes' can totally disable a large aircraft and that 'something' can be a problem encountered regularly by all pilots i.e. ice.
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From: Somewhere out there
l@ser...
laser l@ser l@ser l@ser l@ser l@ser
funny...
Is it because l@ser is a trademark?
funny...
Is it because l@ser is a trademark?
P.S.: I wonder if it could be applied to machines somehow...
Last edited by augustusjeremy; 23rd June 2009 at 16:03.
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From: La Belle Province
EASA Safety Information Bulletin 2009-17, issued June 09, contains "recommendations" to operators regarding unreliable airspeed procedures and the applicability is:
All aeroplanes operating in commercial air transport.