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Technical Alternatives for Pitot Tubes?

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Technical Alternatives for Pitot Tubes?

Old 8th Jun 2009, 09:59
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Technical Alternatives for Pitot Tubes?

Given that pitot tubes apparently play some role in the Air France accident,
I was wondering if there are technical alternatives to pitot tubes.
To the non-expert it's rather surprising that redundancy for measuring such
important parameters is not implemented via at least one additional device
that uses a different technique and may be less susceptible to
icing/contamination etc.

So my question to the tech gurus is whether there exists an alternative.

Thanks
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Old 8th Jun 2009, 10:59
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Piezo-Electric?

I wonder if it would be possible to measure the dynamic perssure using some sort of piezo-electrical device; a flat patch head-on to the slipstream on the airframe somewhere where the airflow is clean?

I frankly have no idea wether anybody ever considered searching for an alternative to the pitot, which is tried and tested technology, and does not go wrong a lot.

Regards!
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Old 8th Jun 2009, 11:39
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Pitot tubes, properly heated, have worked for nearly 100 years so why change now? But I agree, an alternative method of measuring pitot pressure wouldn't be a bad idea.
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Old 8th Jun 2009, 11:57
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Measuring airspeed through the GPS could be another alternative although it's accuracy at such high speeds has not been validated, AFAIK. Another alternative is to put a small propeller in the windstream and get the airspeed through the propellers rotation. Not very accurate as the windspeed could mess it up, but better than nothing.
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Old 8th Jun 2009, 12:44
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How would you like to measure airspeed with GPS? You can calculate GS, i don`t really see the technical possibility to get airspeed with GPS. The propeller method was already used, I think even Wright Flyer had one I guess it didn`t proove accurate and reliable enough.
You can measure airspeed with variety of means, some aircrafts had Venturi airspeed indicator,
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Old 8th Jun 2009, 13:23
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Some modern anemometers use ultrasonics for measuring wind velocity - perhaps that techology could be applied to the problem.
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Old 8th Jun 2009, 13:28
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How about measuring doppler shift from a [email protected] aligned to the aircraft centreline? Should work well in IMC and hence as a backup for iced up pitots but would probably be ineffective in a clear sky.

Regards

csd

Why is PPRuNe putting a "@" in [email protected] instead of an "a"?
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Old 8th Jun 2009, 20:21
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I agree with the need for a pitot tube alternative. While the pitot tube may have been around for a 100 years, and works without incident most of the time (esp. with pitot heat), when conditions for icing, etc exist, all the redundant pitot tubes on the plane are susceptible to the the same kind of failure.

It would be great if aircraft, in addition to the pitot tube, had some other mechanism (as suggested by posters earlier) which can be used to cross-verify pitot tube readings in failure scenarios.
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Old 8th Jun 2009, 21:48
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A mandatory AOA indicator as apart of stby instruments can be a solution.

If you lost everything fly the AOA.

In fact, a version of this is in use and can be purchased as an option for A 330.

If All ADRS are gone, PFD displays a green band, simply adjust speed to fly within.

Ironically, T 38 Talon manufactured 1968, we used to fly green AOA light on approach regardless weight and Flap.

Last edited by JABBARA; 9th Jun 2009 at 08:52.
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Old 9th Jun 2009, 05:06
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There is no other method to read actual airspeed. Most above posters negate the factor of air pressure. GPS etc,etc calculates ground speed only, not the speed of air in relation to the aircraft.

All other options would have to be mounted on the aircraft and be subject to the environmental forces a pitot tube is capable of reading.
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Old 9th Jun 2009, 08:31
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It is possible the ultrasonic devices mentioned above might be adaptable to aircraft use. The ones I have seen on sailboats have 3 vertical probes oriented in an equilateral triangle that measure wind speed as well as direction. I suppose a static input could be mixed in with it to get an equivalent "indicated" or true airspeed readout...

I don't know if such a system is adaptable to high airspeeds or if it would be more or less susceptible to icing, though...
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Old 9th Jun 2009, 08:49
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Isn't it possible to get the airspeed via GPS through calculations or through the known windspeeds or air pressure from ATC or the MET chart ? I'm not saying GPS should be the primary means of measuring airspeed but as a backup, it's better than flying blind. Morever, most commercial a/cs are fitted with GPS, so not much of a retrofitting to be done.
I wonder what the QRH states for in case the pitots fail ?
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Old 9th Jun 2009, 14:33
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To calculate airspeed with GPS you would need PRECISE wind data. And you don`t have it.
In small airplanes I was told if you experience pitot tube failure you need to fly the aircraft with the seat of your pants and use the power setting to guess the airspeed, but obviously you need to know the aircraft you`re flying pretty well, and be lucky
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Old 9th Jun 2009, 15:47
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How about a venturi system? The surfaces around the throat could be heated to ensure ice does not build up, and the system built large enough to ensure that water and other debris do not cause difficulties. I know some (older?) light aircraft use a venturi to drive the suction driven instruments, surely the pressure in the venturi could be measured (and a correction applied) to give dynamic pressure - or would this be subject to the same issues as a pitot tube?
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Old 9th Jun 2009, 15:56
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Venturi system was used in old aircraft. It is susceptible to many problems. Of course icing is the issue, just the same as carburetor icing. Then comes the accuracy. It is dependent on geometry of the whole system more than pitot tubes. You have to keep the surface smooth or large error will build up.
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Old 9th Jun 2009, 16:00
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Or even a calibrated plate acting against a spring of known strength.
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Old 9th Jun 2009, 16:18
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leewan

I wonder what the QRH states for in case the pitots fail ?
In the cast of pitot failure all you have other than GPS for G/S ref. are usually a set of generic power settings for each phase of flight. This is an extremely rare case.
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Old 9th Jun 2009, 16:21
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Stormin

Or even a calibrated plate acting against a spring of known strength.
Ice is still a factor in both weight and now friction.
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Old 9th Jun 2009, 16:33
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Sorry to take the wind out of the sails of the venturi enthusiasts, but at typical Jet Transport aircraft speeds, the venturi would "choke" with supersonic flow.

OutOfRunWay, the last flat plate airspeed indicator that I saw was on a Gipsy Moth (DH60), even it's successor, the Tiger Moth (DH82) had Pitot tubes.

The AoA indicator is the only suggestion that bears some merit.

Regards,

Old Smokey
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Old 9th Jun 2009, 17:38
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Given that pitot tubes apparently play some role in the Air France accident,
I was wondering if there are technical alternatives to pitot tubes

YYYEEESSSS of course there is an alternative:


BOEING AIRPLANES !!!!!!!!!!!!
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