32

Stalls occur based on a wing's angle of attack rather than the aircraft's airspeed. (In fact, one of the basic facts that all pilots learn in their initial training is that an airplane can stall at any airspeed). The A330 measures angle of attack using vanes mounted on the fuselage: However, below 60 knots, these vanes become ineffective. During the ...


23

There are several reasons to have the pressure sensors in the front section of the fuselage. The further aft the more turbulent the airflow is and the thicker the boundary layer caused by the fuselage. This would cause strong fluctuations of the measured pressure and the reading could be inaccurate. Far forward the boundary layer is the thinnest because the ...


22

Captain Bill Palmer, in his book "Understanding Air France 447" has a section dedicated to answering that very question as it pertains to AF447. Although there is no way to know for certain he puts forward some possibilities. He quotes a commenter on a website: One commenter on the Weather Graphics website’s AF447 article provided this interesting ...


21

Airliners do generally have GPS receivers, but GPS doesn't give you the information that's needed in this case. In AF 447, the primary consequence of the blocked pitot tubes was that the flight envelope protection system couldn't do its job properly and therefore automatically disengaged together with the autopilot. The subsequent crash was caused by the ...


18

who was responsible for ATC relaying false altitude information to the pilots Not an easy question mostly because it asks (even if not directly) to put the blame on someone. And although there is not an explicit rule for not doing this, I prefer avoiding it in respect to the dead and the ATCOs doing their job as good as they can. I will focus on the reason ...


17

Technically speaking, inertial measurements are not sufficient to derive airspeed. You need pressure measurement (or airspeed measurement, see LIDAR). Pitot-static probes are the most usual and conventional devices to measure pressure. However, several researches have been conducted, to replace pitot-static tubes with different technologies. These ...


17

The comment: In fact, the pressure at the static ports will drop as the aircraft's speed increases (Bernoulli principle) is not exactly accurate. The aircraft is a complex aerodynamic shape and static pressure distribution across the fuselage is not linear. An example is provided by the following figure from NASA Technical Memorandum 104316: [...


16

Some aircraft DO heat the static port, if only by side effect: Piper PA28 aircraft (Cherokee/Warrior/Archer/Arrow ) for example have the static port located on the pitot mast. When pitot heat is turned on in these aircraft the entire mast heats up, including the static port. This characteristic would be the same on most aircraft with a combined pitot/static ...


15

You'll find your answer if you take a look at the form of a pitot tube or other kinds of ducts where pitot (or total) pressure is taken and compare it to the parts of the aerofoil where ice is prone to accumulate. Ice will most likely form on the leading edge of thin surfaces in the airstream but not on the side of the fuselage. If ice would built up there ...


15

I'm not sure what kind of airplane that you are flying in the simulator, but the checklists for jets typically do have you turn the pitot heat on just before takeoff and leave it on until after landing, just so that this is less likely to happen. Update: I found a French checklist for the Caravelle and it says to turn on the pitot heat before takeoff: ...


14

Though it's often omitted from diagrams, most pitot tubes have one or more drain holes connected to the pressure chamber, and are essentially "self-draining" (water doesn't make it into the lines): In addition to drains on the pitot tube itself some aircraft have separate "drip chambers" and drains for the pitot (and occasionally static) system to remove ...


14

There are five sets of pitot tubes on the 737, organized into two groups, the pitot tubes on the nose are used for airspeed measurements, independent for the pilot and copilot and one as a backup. There are two pitot tubes on the tail that are for the "elevator feel and centering unit" (pdf; page 8). The elevator feel computer provides simulated ...


14

The linked article says that an HWA (hot-wire anenometer) is fragile and requires complex equations to relate the sensed value to the fluid speed as well as correct for inherent, unavoidable nonlinearities as well as external factors such as fluid type, ambient temperature, humidity, and angle between the flow and the sensor. Conditions in a wind tunnel or ...


13

A pitot probe strictly measure ram air pressure, commonly called "pitot pressure" or Pt pressure. A pitot tube measures pitot pressure and pitot pressure only. A separate static port is required to measure static pressure (Ps) and will usually be located on a section of the fuselage where airflow is minimized. A pitot-static port is a combination pitot AND ...


11

I can generally only speak for commercial aviation. The reasoning is probably the same or similar for General Aviation, but seeing as that is such a wide and varied field, with a tremendous number of different aircraft, probe types, etc., someone somewhere could probably find some niche corner-case to dispute the reasoning. My guess would be that, generally ...


11

Airspeed - not reliably under all circumstances. You need to feel that wind somewhere in order to get a direct and accurate measure of the speed of it, and the pitot tube is an accurate and proven instrument to measure total pressure. Other possible methods: Laser based(LIDAR). A 20 year old NASA report can be found here. It mentions at the end that the ...


10

The aircraft checklist will determine when the pitot heat should be on. Strictly speaking, if the checklist says it should be on, the only reason it should not be on is if the system is inoperative or is causing some issue (if the generator system fails it will drain the battery, as falstro commented). The checklist linked by Lnafziger has the pitot heat ON ...


10

There's much simpler and safer logic. Most modern Western transport aircraft automatically switch the pitot heaters on when in flight mode or at least one engine is running. Pilots can manually force pitot heat on, but there's no direct option to switch them off. Normal procedure is to leave it in auto. Boeings since the 757/767 are automatic (exception: ...


9

At our airclub, the checklist for C172 shows: ... stuff ... Pitot heat on, check tube warm, turn off. ... complete the walk-around... start... taxi to engine run-up... do run-up... Do final pre-take-off checks, one of the last of which is "pitot heat: ON". I've seen some C172 checklists that say "as required" instead of "on" near the end. There are no ...


9

What caused the ATC to pass incorrect information to the flight crew was that they had no reason to mistrust their own instruments. The altitude information displayed to the controller was transmitted from the aircraft itself, and at the time the controller was no more aware of the issue on board the aircraft than the flight crew were. The NTSB, although ...


9

Autopilot vs FMS vs protection The autopilot does not prevent a nose down, this task is done by the envelope protection, which is a different flight computer. The FMS is what sends the autopilot commands, i.e., the autopilot is part of the FMS. The pilot interface with the autopilot is the CDU (which is basically a keypad and a screen), and the FCU (the ...


7

You're correct that there are a number of parameters that influence the measurement of air data in general. For example, the total pressure measurement (as done using the Pitot tube) is influenced by, Angle of attack Reynolds number Mach number Velocity gradients Proximity to surfaces (wings, fuselage etc.) Flow steadiness Probe geometry Compressibility and ...


7

The first thing to have in mind is that a pitot tube is NOT measuring speed: the pitot tube measures pressure and later on the airplane (flight management system in a modern airplane) calculates the speed based on pressure. More specifically the pitot tube calculates the stagnation pressure which is the sum of static pressure (what you show in your picture) ...


7

The B-2's pitot plate has actually been the cause of an accident in conditions that may or may not have had the same effect on aircraft with pitot tubes. Pitot plates work much like pitot tubes; they measure the pressure of incoming air. The main difference is just how they measure it: pitot tubes measure the ram force of air while pitot plates measuring ...


7

The pitot tube is not much of a problem - it's your typical pitot tube, pointing forward (toward the nose of the helicopter) to measure forward airspeed. Airspeed is somewhat less important to a helicopter pilot than it is to a fixed wing pilot since lift is generated by swinging the rotor around instead of moving the whole vehicle through the air. The ...


7

The crew checks the pitots and static ports before the flight to ensure they are in good condition and not blocked by objects or insects. Pitot tube (pitot-static) can be obstructed in-flight. Static ports are less affected. Detecting a blocked pitot or static port: This is not done, but is possible (e.g. send some air from the back of the tube in a pitot, ...


7

A number of systems are under development- most are optical systems- determining airspeed using LiDAR. NLR, for example has developed an Optical Air Data System for this purpose: The developed system applies the LiDAR technique to measure air speed in four different directions. The aircraft’s TAS (True Air Speed), AOA (Angle Of Attack) and SSA ...


7

Depends on how much blockage. If fully blocked, as in air tight, the pitot side becomes like the sealed aneroid side of an altimeter and it only reacts to changes in static pressure, indicating the difference between ambient static and the pressure trapped in the pitot side. If the blockage is not air tight, like you usually get with bugs, somewhere ...


7

If the pitot tube gets blocked in flight, such as by icing, the airspeed indication is maintained at first. Note that the indication is still subject to changes in static pressure as long as the static port is not blocked as well, effectively turning the airspeed indicator into an altimeter. If only the static port is blocked, the airspeed indicator shows ...


7

The boundary layer grows in thickness as you move aft on a fuselage. It is thinnest near the nose. A pitot tube near the nose only has to protrude a small distance away from the fuselage skin in order to extend out of the boundary layer and into undisturbed air.


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