Using a barometer to record aircraft cabin pressure?

littleshrimp

Using a barometer to record aircraft cabin pressure? [Copy link]

 

Yesterday I made an air pressure recorder using SensorTile.box. It is simple and low-power, and can work for about 12 hours on a full battery.

The firmware that comes with the SensorTile.box supports data logging, but because Bluetooth is always active, it is not suitable for use on an airplane.

In fact, this idea has been around for many years, because when an airplane takes off and lands, the ears often feel uncomfortable due to changes in cabin air pressure, which can usually be solved by swallowing saliva.

A few years ago, I fell asleep during a plane landing and didn’t swallow in time. As a result, my ears hurt for a long time. It was a very uncomfortable feeling.

Later I figured out a way. I closed my mouth, pinched my nose and blew hard into my ears. I felt a stream of air coming out of my ears and the pain went away.

So the question is, using the pinching nose method to expel the gas in the ear when the air pressure in the ear is higher than the ambient pressure, so that the air pressure in the ear can be balanced with the ambient pressure.

But I have tried this method and it works whether the plane is taking off or landing. If the outside air pressure is dropping when the plane takes off, the air pressure inside the ear will be greater than the ambient air pressure.

But why does this happen when the plane is landing?

I guess it may be that the pressurization system in the cabin is sometimes not well controlled during takeoff and landing, which causes the air pressure in the cabin to suddenly rise and then drop, resulting in the air pressure in the human ear being higher than the ambient air pressure.

But think about it carefully, is the air pressure in the cabin really that difficult to control?

Next, I plan to bring this small box with me the next time I fly and record the air pressure in the cabin for analysis.

Below is the air pressure and room temperature curves I recorded overnight from 4 pm yesterday to 4 am this morning using SensorTile.box. You can see that the air pressure is gradually decreasing and the room temperature is basically stable at above 25 degrees. It is still quite comfortable to be indoors in the Northeast in winter.

chunyang

In order to comprehensively consider operating costs, safety, and comfort, the cabin of an aircraft is only pressurized to an altitude of more than 2,000 meters when flying at high altitudes. Some low-cost airlines will even relax this to around 3,000 meters. Only some new aircraft models will be pressurized to within 2,000 meters on mainstream routes, but they will not be pressurized to the altitude corresponding to most plains. Therefore, the cabin pressure of most aircraft from the departure point will gradually decrease when ascending, and will gradually increase when landing. The entire pressurization process is linear and will not change suddenly, so the situation described by the original poster will never occur, which is determined by the cabin pressurization principle.

After a short-term change in air pressure, the difference between the air pressure inside and outside the ear reaches a certain level, and the deformation of the eardrum will cause discomfort. The fundamental reason for this phenomenon is the physiological structure of the human ear. The Eustachian tube is long and thin, with a narrow part of only 1-2mm, and there is no bone support, and sometimes there is mucus, which can easily cause the narrow part to close, resulting in the closure of the inner ear, and then the deformation of the eardrum due to the air pressure difference. The solution is either to swallow or yawn frequently, or to close your mouth, pinch your nose, and exhale suddenly, relying on the sudden increase in air pressure in the lungs to open the Eustachian tube. Generally speaking, the pressure in the ear is high during the decompression stage of the aircraft's climb, and swallowing and yawning are easier to open the Eustachian tube, while it is easier to exhale hard during the pressurized stage of descent, which is also commonly used by military aircraft crew members. Because I fly quite often and it is related to my major, I have mastered the method of using yawning and exhalation to actively balance the air pressure inside and outside the ear in stages. That is, I balance the pressure inside and outside the ear several times before the ear feels uncomfortable, so I rarely encounter ear discomfort, but sometimes I still encounter it when I fall asleep. The greater the difference in air pressure inside and outside the ear, especially when the air pressure inside the ear is low, the more difficult it is to balance it by movement, so you have to take the initiative to move in advance.

chunyang

The consequence of not properly controlling the cabin pressurization of an aircraft is not just a matter of ear discomfort, but a matter of life and death. In the past, aircraft did not have sufficiently obvious pressurization control warnings, and pilots sometimes forgot to turn on the automatic pressurization switch, resulting in serious consequences. There was once a Boeing 737 aircraft of Cyprus Helios Airlines that caused all passengers to become unconscious due to lack of oxygen because the pilot forgot to turn on the automatic pressurization switch, and the aircraft eventually ran out of fuel and crashed. The aircraft has an independent cabin air pressure detection system. Once decompression occurs, the alarm system will immediately activate and automatically pop up the oxygen mask, and the pilot will immediately fly the aircraft down rapidly to a safe low altitude.

littleshrimp

chunyang published on 2020-11-25 16:46 In order to comprehensively consider operating costs, safety, and comfort, the cabin of the aircraft is only pressurized to an altitude of more than 2,000 meters when flying at high altitudes. Some low-cost airlines even...

I tested it today and indeed there isn't much change. But I don't know if it's because I flew well or the pressurization system was well controlled. The whole process was quite comfortable, only a few times the sound got louder after swallowing.

chunyang

littleshrimp posted on 2020-11-26 14:38 I tested it today and it really didn’t change much. But I don’t know if it’s because I flew well or the boost system was well controlled. The whole process was quite comfortable, with only a few swallows...

It's not about how well you fly, nor how well you control the boost; it's all determined by your physical condition.

It seems that we have to talk about the aircraft's pressurization system. First of all, the entire cabin is a huge hysteresis system for the pressurization mechanism. If we compare it to an electric circuit, it is an RC loop with a very large time constant. The rapid change of the input voltage will not cause a significant change in the output voltage. It is easier to understand with an example from daily life: in winter, in a room with closed doors and windows, if you burn an electric stove to keep warm, will the temperature in the room suddenly rise? Obviously not, because the heating power of the electric stove is very small compared to the specific heat capacity of the entire room space, and there is also heat dissipation from the room to the outside, so the temperature of the room will only rise slowly. As long as the doors and windows are not opened, the room temperature will never change suddenly. The cabin pressurization system is completely similar to this situation, so the cabin pressurization system is not even a closed loop, that is, it does not use the feedback of the cabin air pressure to adjust the output of the pressurization mechanism, but is related to the altimeter, which controls the pressurization mechanism with altitude data. This is simpler and more reliable, because the aircraft altimeter is one of the most important instruments for the aircraft, a highly reliable device, and has redundancy from multiple different data sources.

chunyang

Cabin pressurization is actually a major threat to the structural safety of the aircraft, and the air pressure outside the cabin is mainly determined by the altitude, so maintaining a stable cabin pressure makes passengers comfortable but is not conducive to flight safety. In order to ensure flight safety and take into account the comfort of passengers, reducing the cabin pressure change rate rather than stabilizing the cabin pressure itself is the design goal of the cabin pressurization system.

Civil aircraft have specific routes, including take-off and landing routes. Due to geographical differences and differences in aircraft take-off and landing density, route planning may vary greatly at different airports or even at the same airport at different times. That is, the flight altitude changes per unit time are different, corresponding to different air pressure change rates. If the aircraft is scheduled for a route with a large altitude change per unit time, the passenger comfort will obviously be relatively low.

However, on certain routes, comfort is largely related to the physical condition of the passengers. If there is fluid in the Eustachian tube, especially when there is local inflammation, the Eustachian tube is obviously more likely to close, resulting in excessive pressure difference between the inner and outer ears and causing discomfort. Therefore, when flying, taking the initiative to balance the air pressure inside and outside the ear can greatly help reduce discomfort.

freebsder

Awesome, you know a lot.

littleshrimp

chunyang posted on 2020-11-26 17:45 Cabin pressurization is actually a major threat to the structural safety of the aircraft, and the air pressure outside the cabin is mainly determined by the altitude, so maintaining a stable cabin pressure makes passengers...

I compared the data from two flights. The ear discomfort should be related to the aircraft's descent speed (the rate of change of air pressure). If the aircraft descends too fast, the ears will be particularly uncomfortable, so that swallowing will not work.

But there is one thing I don't quite understand. From the recorded data, it can be seen that the air pressure is indeed increasing when the plane descends, which means that the air pressure outside the ear is higher than the air pressure inside the earphone. But the method of pinching the nose to blow air seems to release the air in the ear to the outside. Is it actually pumping air into the ear?

chunyang

littleshrimp posted on 2020-11-30 12:21 I compared the data from the two flights. The ear discomfort should be related to the aircraft's descent speed (the rate of change of air pressure). If the aircraft descends too fast, the ears will be particularly...

Whether you feel uncomfortable is determined by the rate of change of air pressure rather than the air pressure itself. Slow changes in air pressure, such as taking a car to a plateau or climbing a mountain, will not cause ear discomfort, because the Eustachian tube is always unobstructed and the air pressure inside and outside the ear is balanced.

Close your mouth, pinch your nose (or block your nose, I make a fist and use the back of two fingers to block your nose) and exhale sharply, which will increase the air pressure in the entire respiratory tract and pharynx, force open the closed Eustachian tube, and increase the air pressure in the inner ear. When the plane is descending, the external air pressure will quickly exceed the air pressure in the ear in a short period of time, which is more likely to cause the Eustachian tube to close, so this trick is often more useful than swallowing when the plane is descending, and yawning is also more useful than swallowing. Swallowing is still effective during the ascent of the plane, because the air pressure in the ear is higher, and the position and degree of Eustachian tube closure are different from those during descent. I usually don't use the swallowing method. If I feel it is obvious, I will use the exhalation method, otherwise I will use the yawning method, but both methods need to be practiced. I mastered it after about two times, but if you are not feeling well, the effect will be greatly reduced or even completely useless.

To sum up, the yawning method is mainly used in the ascending stage, and you can also exhale with your mouth closed and your nose blocked. After the Eustachian tube is opened, breathe normally, and the air pressure inside and outside the ear will be balanced. If the yawning method is ineffective in the descending stage, close your mouth and exhale with your nose blocked as soon as possible. The best way is to do multiple air pressure balancing actions in advance. When you feel it clearly, the Eustachian tube has been closed for a period of time and the air pressure difference inside and outside the ear is too large. The greater the pressure difference, the more difficult it is to deal with.

littleshrimp

chunyang posted on 2020-11-30 12:41 Whether you feel uncomfortable is determined by the rate of change of air pressure rather than the air pressure itself. Slow changes in air pressure, such as taking a car to the plateau or climbing a mountain, will not cause ear discomfort, because...

If you close your mouth and pinch your nose, it will increase the air pressure in your ears. It is probably easier for air to go out than to go in, so it will be more uncomfortable when you descend.

chunyang

littleshrimp posted on 2020-12-1 09:17 If closing your mouth and pinching your nose increases the air pressure in your ears, it is probably easier for the ears to exhale than to inhale, so it will be more uncomfortable when descending

After the Eustachian tube is closed, the internal air pressure is higher than the external air pressure, so it is easier to open. However, even if the internal pressure is high, the Eustachian tube can be opened by exhaling, the only difference is whether it is opened from the inside or the outside.