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Silly question for today


GordonD

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I know that the curved cross-section of an aircraft wing means that the airflow on top is moving faster than that below, resulting in a higher pressure underneath, which provides the lift so that the plane can fly.

But then how can it fly upside-down? :shrug:

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Because it is not just the shape of the wing section, but the angle it makes with the airflow. This is called the angle of attack - the more nose up the more lift until the wing stalls. So an aircraft flying upside down has a rather inefficient aerofoil and so has to fly at a greater angle of attack to get the same lift.

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Yes indeed angle of attack

I know that the curved cross-section of an aircraft wing means that the airflow on top is moving faster than that below, resulting in a higher pressure underneath, which provides the lift so that the plane can fly.

But then how can it fly upside-down? :shrug:

Yes it's all about angle of attack. Almost any surface can produce lift if the angle of attack is sufficient. For example there are symmetrical wing cross sections, typically on aerobatic aircraft which works the same inverted, vertical or upright as long as the angle of attack to the oncoming airflow is correct. Another example of how lift can be produced is to put your hand out the window of a moving car. Hold it horizontally and it will remain steady, incline the palm slightly and it will tend to lift. Clearly it's not wise to do that while driving the car!

But controversially your description of how lift is generated is incorrect! Don't feel bad because in fact exactly how lift is generated almost defies simple explanation.

Despite the fact that this method of generating lift is that most often taught to new pilots. In fact this subject has generated more controversy than Luftwaffe colours or the interior colour of early Spitfires. There were many arguments between the proponents of the Bernoulli method of producing lift and Isaac Newton's theories. In reality it's a combination of both. Here's a webpage with some good examples including inverted flight.

http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/airfoil.html

All I know for sure is that it works. I've been flying for over 34 years and every time I look out at the wing I think. 'I have no idea how that plank like thing is keeping us in the air.'​

​

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Another example of how lift can be produced is to put your hand out the window of a moving car. Hold it horizontally and it will remain steady, incline the palm slightly and it will tend to lift. Clearly it's not wise to do that while driving the car!

Unless your indicators have failed - and you are turning right..... :whistle: :whistle:

Sorry..... I'll get my coat.

Ken

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Because it is not just the shape of the wing section, but the angle it makes with the airflow. This is called the angle of attack - the more nose up the more lift until the wing stalls. So an aircraft flying upside down has a rather inefficient aerofoil and so has to fly at a greater angle of attack to get the same lift.

Some aero focussed aircraft (eg Extra 300) have symmetrical wing profiles and only generate lift via AoA so their wings work equally well (or badly) in any orientation.

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The definitive answer can be found in the excellent BBC radio series Cabin Pressure. It's in the episode called "Abu Dhabi" and pops up throughout the episode. Although the audio recording is difficult to find online, the script is readily available.

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I know that the curved cross-section of an aircraft wing means that the airflow on top is moving faster than that below, resulting in a higher pressure underneath, which provides the lift so that the plane can fly.

But then how can it fly upside-down? :shrug:

Pure magic.

Everyone knows planes can't really fly.

It's an optical illusion.

Rick.

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The definitive answer can be found in the excellent BBC radio series Cabin Pressure. It's in the episode called "Abu Dhabi" and pops up throughout the episode. Although the audio recording is difficult to find online, the script is readily available.

I have all the audio recordings, but listening to the first episode is not a good idea. Because then I'll feel compelled to listen to the second one, and then the third...

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Actually this video provides the 'best' explanation of how lift is generated that I have ever seen. It starts about 3:30 into the video. But the video is worth watching in full for it's terrific insight into the life of an airline pilot.

It was produced by the BBC in a series called 'People like us' which came out in 2001.

​

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Just in case anybody didn't realise, this was an episode from a sitcom - a spoof on those fly-on-the-wall documentaries. The unseen presenter went round various places interviewing people about their jobs. I remember one set in a police station, where the fax machine had run out of paper and they asked another station if they could fax over some more...

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Just in case anybody didn't realise, this was an episode from a sitcom - a spoof on those fly-on-the-wall documentaries...

It's still the most accurate portrayal of airline pilots I've ever seen 😊

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