Pressure on cockpit window - is it inward or outward?

Question

If you have a boeing 737 flying at 35000 feet at 500 mph then there will be a higher pressure on the front-facing cockpit windows due to the air coming at it at 500 mph and being deflected up and to the side.

However the air pressure at altitude is itself a third of the pressure at ground level and certainly less than that inside the pressurised cabin.

So if you could open the front window, would air rush in, or out.

Are there any modes of flight where the two are equal?

Answer 1

My guess is (an this is just a guess), that given the condition you describe the interior would have higher pressure. I think you need to be closer to the speed of sound to get even a doubling of the outside pressure vs ambient. If the altitude were lower, and the speed faster, obviously at some point the outside (ram) pressure would be higher. I don't know what the threshold would be, though, and it would depend a lot on shape.

Answer 2

The pressure is not greater on the front window, the wind velocity is just increased. Pressure depends on several barometric factors, and wind velocity doesn't affect these factors. For example, on a windy day, the atmospheric pressure doesn't increase.

Also, the pressure inside the cabin is greater than that outside the cabin. The main goal of having a "pressurized cabin" is to make the passengers feel as if they are at sea level, because low pressures can be fatal depending on how low they are.

If you opened the front window, regardless of the inside or outside pressure, air would surge in, since the plane is moving against the wind. However, if you were to open the side window, the air would flow out. Since the pressure inside is greater than the outside pressure, the air would flow out the window into the sky. The reason that this would happen is because the higher internal pressure would diffuse to the outside, so inside the cabin it would seem as if the air is rushing out.

Answer 3

If you could push open the front facing window at that speed the air would come in. If you were in a stationary balloon with a cockpit at that altitude the air would rush out. The pressure of wind on the forward facing glass surfaces are high but some engineering will go into angling them just right to alleviate the huge forces.

Answer 4

The windscreen of an aircraft is angled, like the windscreen of a car, so the air flows over it, not against it. The airflow causes a drop in pressure over the window (Bernoulli's principle) so in fact the airflow over the window is tending to suck the glass out. If you break the window, the glass will fly outwards and the air inside the aircraft will tend to be sucked out. The aircraft is also pressurised of course, so air will rush out both because it is under pressure inside the aircraft and also because the airflow over the open window is sucking the air out.

In the famous case of the pilot hanging out of the window, it wasn't the pressurised air escaping from the inside of the aircraft blowing him out that was the problem, because the pressure inside and outside the aircraft would quickly have equalised. The pilot was being sucked out by the airflow over the open window and so could do nothing until the airspeed had dropped substantially.

Answer 5

Depends on the aerodynimcs of the specific aircraft. Air's not simply slamming into the front of the aircraft, it's flowing over it (laminar flow). The contours of the aircraft will result in high and low pressure zones. With proper design, you could fair the fuselage such that air flow would allow you to open a window into a pocket of still air.

In the case of a front windshield, removing the glass would in all likelieness disrupt the airflow. My instinct is that the air stream would continue to flow past the open windshield, and a vacuum would be created - but that's just a hunch. I couldn't say for sure without doing a computer model (or a realworld test ;-)

Answer 6

That is simply a question of design. Unlike the upper surface of the wings, it's not designed for lift. It's designed for smooth air flow to minimize drag and to minimize structural stresses. But it's also designed so the pilots can actually see what's in front of them. The designers will accept some additional stresses and drag to improve visibility. For that reason, if you could open the front cockpit window, air would almost certainly rush in.

Answer 7

If you could do it, the air would rush out. There's a case where a cockpit window burst in flight & the captain was sucked out, only being saved by the co-pilot & then a stewardess ( I think) clinging grimly onto his legs while the co-pilot landed the aircraft.

Answer 8

While specific calculations are needed to answer your question, any opening of a door or window results in the air of the cabin rushing out.

Answer 9

It rushes out, there is a case of a pilot being sucked out of a front window and then held there on the top frame by the forward pressure, half in half out with a hostess or someone hanging onto his legs. He survived.

Answer 10

planes are pressurised inside