Turbine D
I am not a pilot but an engineer.
Me too, and I find myself in complete agreement with what you say.
In designing a devise of any sort, the design engineer has to know as much about the parameters the devise is going to experience and operate within.
Yep!
What could go wrong with a pitot tube where the basic physics and general design has been known dating back to the late 1700s? And why is it that one manufacturer's design seemingly has less problems than another manufacturer's product when both met mandatory testing and certification requirements? Why is it that when the devise is used on one aircraft, it is more susceptible to non-performance than on another aircraft?
Or that one manufacturer’s product will work, but another’s won’t, both at the same location on the same aircraft? Or that the one that didn’t work was OK for seven years?
I would postulate to you all, there is nothing wrong with the basic concept of the current day pitot tubes, they will and can work successfully across the total flight envelope without any new bells and whistles.
I completely agree!
The reason they may not is because the parameters used in the design and testing did not and for that matter, do not match what is experienced across the total operating envelope, particularly at high altitudes and high speed in icing conditions.
Again I agree completely
I have thought about this for some time and wondered in the instance of Airbus aircraft, could there be a difference in pitot tube performance verses that of Boeing aircraft? Could it have something to do with installation or location or shape of the fuselage forward of the mounting point or how the air passes into it or the actual testing and certification requirements? Was Boeing lucky and Airbus unlucky?
I have wondered about that also, and it is interesting that Airbus themselves, when commenting on the proposed TSO, say:
These conditions are free-stream conditions and do not consider the effect of the potential installation effects. Depending on the probe design and aircraft installation these installation effects can lead to the Liquid Water Content (LWC) at the probe location several times greater than the free-stream conditions. The TSO should at least highlight the potential installation affects to applicants
And
Furthermore a probe designed and tested in liquid icing conditions only may require a significant redesign to meet the ice crystal and mixed phase requirements.
It should be noted that recent evidence indicates that the ice crystal and mixed phase conditions defined in AMC 25.1419 may not be adequate for pitot and pitot-static probes
Max intermittent icing conditions that are considered below JAR25/CS-25 Appendix C requirements. Accounting for installation effects on A330/A340, local LWC at –30°C should be 1.5g/m3 for maximum intermittent icing (without safety factors). The TSO C16A recommendation is 1.25g/m3, which therefore does not cover installation effect on Airbus A330/A340.
But the newly proposed Appendix P to CS25 gives the TWC at -30oC to be 4.5 g/m3 BEFORE any installation effects are included. So the requirements against which the A330 was designed are miles too low against the possible ice particle exposures now envisaged.
[I should have added that Airbus say they test to their own internal requirements that exceed the JAR 25 variety, so we don't really know what theA330 probe capability was]
Worth noting also that the research and analysis work that led to this conclusion was not started until 1998, four years after the A330 went into service.
So I think with proper design parameters, proper mating with the aircraft and proper testing requirements pitot probes from any manufacturer can be designed that work throughout the flight envelope.
I agree with you there, with one proviso, and that is there has to be a suitable facility for testing the probes.
In AIAA 2006-206 they point out that:
Once the atmospheric threat is known, the next challenge to the industry is to develop test methods that properly simulate the engine operation at high altitude in this environment. Icing wind tunnels and icing test facilities available to the industry nowadays are mainly designed to simulate supercooled liquid droplets depicted in the FAR Part 25 Appendix C icing envelope23. These droplets are produced by nozzles spraying water initially at above freezing temperature into the cold working air stream of the test facility, and targeting the same particle size range as in the natural cloud conditions. The droplets lose temperature as they travel down the cold air stream, and in most cases achieve a supercooled state before they reach the test article. The spray particles are generally spherical in shape as they would be in a natural supercooled cloud. Ice particles, on the other hand, occur naturally in many different shapes and they generally span a much larger range of sizes than the supercooled droplets depicted Appendix C envelope
We are not there yet in full understanding, but it is not hard to imagine the icing problems can and will be solved very soon.
Let us hope so