The Use of Pitot Tubes
Joined: Jul 2001
Posts: 1,611
Likes: 0
From: Gold Coast
On the Citation I used to fly many years ago there was an excellent AoA meter and we found that with a little practice we could determine the weight of the plane in-flight to within 100kg, and by using the meter the other way we could get our speed accurate to within a few knots as well on departure and approach.
I'd love to see them fitted and used more often in larger aeroplanes, and also used in the sim in emergencies. They take a little getting used to, but once you do they are fine.
I'd love to see them fitted and used more often in larger aeroplanes, and also used in the sim in emergencies. They take a little getting used to, but once you do they are fine.
Joined: Mar 2006
Posts: 1,115
Likes: 86
From: England
Thermostat, “Ice would also affect the angle of attack vane just as it would the pitot tube”.
Not so for ice crystal icing – probably a significant feature in AF447.
Ice crystals would more likely bounce off an AOA vane (as for wings etc), because there is little forward facing heated surface area to give partial melting, a requirement for this type of ice to form. Also the free stream air-flow angle and particle speed around a vane would make adherence unlikely, whereas crystals being 'trapped' in a partially closed heated tube provides ideal conditions, particularly if the crystal mass flow is high.
Conventional icing appears to be well contained by existing pitot heating.
Not so for ice crystal icing – probably a significant feature in AF447.
Ice crystals would more likely bounce off an AOA vane (as for wings etc), because there is little forward facing heated surface area to give partial melting, a requirement for this type of ice to form. Also the free stream air-flow angle and particle speed around a vane would make adherence unlikely, whereas crystals being 'trapped' in a partially closed heated tube provides ideal conditions, particularly if the crystal mass flow is high.
Conventional icing appears to be well contained by existing pitot heating.
Joined: Dec 2002
Aviation Qualifications: ATP+Mil
Posts: 3,985
Likes: 568
From: Where the Quaboag River flows, USA
Thermostat
Ground speed, whether derived from IRS or GPS inputs, would have to have an air data input i.e a pitot and temp probe input to produce CAS/EAS. Your statement answers itself. Without air data, ground speed is useless for what you want. Pitot and Rosemount inputs are not going away.
Ground speed, whether derived from IRS or GPS inputs, would have to have an air data input i.e a pitot and temp probe input to produce CAS/EAS. Your statement answers itself. Without air data, ground speed is useless for what you want. Pitot and Rosemount inputs are not going away.
Joined: Sep 2002
Posts: 2,188
Likes: 6
From: La Belle Province
Yes, ice (outside the design envelope) may affect pitot systems. Ice outside the design envelope may also affect vanes.
But the probability that both systems, which have some significant dissimilarity in their sensing methodology, would be similarly affected by icing is quite unlikely. Even if both systems are affected by "extreme icing", the chances that they start to be affected at the same time, and furthermore in a fashion which is complementary (so that no comparison system could spot an anomaly), appear at first thought to be small.
Joined: Dec 2005
Posts: 247
Likes: 6
From: At home
One could also ask why, after more than a hundred years of technology advances, the aviation industry still uses those big, clumsy, ice-prone things called wings to produce lift. There must exist a better way, yes?
Well, as we know, no. I guess the discussion about pitot tubes comes from the fact that they are used to sense a property which is ultimately displayed on an electronic display. Thus people tend to assume that the sensor could also be subject to the same rapid technology evolution as the digital electronics.
But in fact the airspeed sensor sits as the interface between the physical world, which basically does not change, and the digital world.
AoA would IMO be the closest alternative to measure relevant airspeed or dynamic pressure, but as others have said, it seems its benefits have still not outweighed its disadvantages.
Well, as we know, no. I guess the discussion about pitot tubes comes from the fact that they are used to sense a property which is ultimately displayed on an electronic display. Thus people tend to assume that the sensor could also be subject to the same rapid technology evolution as the digital electronics.
But in fact the airspeed sensor sits as the interface between the physical world, which basically does not change, and the digital world.
AoA would IMO be the closest alternative to measure relevant airspeed or dynamic pressure, but as others have said, it seems its benefits have still not outweighed its disadvantages.
Joined: Sep 2002
Posts: 2,188
Likes: 6
From: La Belle Province
Indeed. And that leaves you and your aircraft exposed to certain common cause failures which could affect not just airspeed and altitude display, but also stall protection and warning. Causing the handling of those failure cases to be significantly more problematic than with reliance on multiple dissimilar technologies.
