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Why we don’t understand heavier-than-air flight

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Re: Why we don’t understand heavier-than-air flight

#121

Post by mbrameld »

NickNameNick wrote: post #12
jobigoud wrote: post #4

Earlier quoted context omitted.

Air moves faster on the upper side , creating a pressure differential.

Why does the air move faster on the upper side of the wing? It's not because there's a magic force that requires air particles parted be the leading edge to rejoin thier partner at the trailing edge. The air particles on the upper surface reach the trailing edge much sooner than the ones under the wing.

My understanding is that the air moving over the top of the wing is compressed against the air above it in the atmosphere, like a venturi. This may be extremely simplified but it's what we were taught in flight school.

Re: Why we don’t understand heavier-than-air flight

#122

Post by jjk166 »

IshKebab wrote: post #24
jobigoud wrote: post #4

Earlier quoted context omitted.

Air moves faster on the upper side , creating a pressure differential.

A common and wrong explanation. The pressure differential is created by the fact that the air is being pushed into the lower side of the wing. It's much simpler than that anyway. The wing forces the air downward, so the plane must be forced up.

Another common and wrong explanation. The air is pushed down by induced rotation. An inclined wing is one way to do it, but is not necessary.

Re: Why we don’t understand heavier-than-air flight

#123

Post by afterburner »

zazen wrote: post #111
afterburner wrote: post #108

Earlier quoted context omitted.

I am replying to this: "I usually just answer Socratically: "So how can (some) planes fly upside-down?" whenever I encounter the Bernoulli-adherents." Which is a lazy and garbled gotcha attempt.

It is a lazy gotcha attempt. It is a lazy attempt at gotcha-ing someone who believes angle of attack ISN'T important. Unless you think a plane flying upside-down is somehow evidence AGAINST the importance of angle-of-attack? Again: this entire pointless misunderstanding has arisen because you didn't see - apparently STILL HAVEN'T SEEN - which side of the debate the comment you replied to is arguing for.

Oh I see. You think the Bernoulli approach is independent of angle of attack? It's not.

Re: Why we don’t understand heavier-than-air flight

#124

Post by jjk166 »

lowkey wrote: post #106
afterburner wrote: post #82

Earlier quoted context omitted.

Causing a pressure difference is the same as causing a force vector. There's no gotcha here, it's just two ways of looking at the same thing.

See my sister comment. The Bernoulli effect explains the pressure differential by way of an above-wing streamline reaching the back of the wing at the same time as the below wing streamline. Since the upper wing is curved and therefore a longer path the theory claims the pressure differential is caused by the upper streamline traveling faster than the lower streamline. The problem with this theory is that there is no…

> The Bernoulli effect explains the pressure differential by way of an above-wing streamline reaching the back of the wing at the same time as the below wing streamline. Since the upper wing is curved and therefore a longer path the theory claims the pressure differential is caused by the upper streamline traveling faster than the lower streamline.

That's not how the Bernoulli effect explains the pressure differential. The bernoulli explanation is that air builds up in front of the airfoil, creating a high pressure region, while there is a low pressure region created in the wake of the wing. This pressure differential forces accelerates air over the wing. For an asymmetric airfoil, more of this flow is over the top than the bottom, so the airflow over the top is faster, and thus lower pressure, than the airflow under the wing.

The "equal time" thing is a pop-science misunderstanding.

Re: Why we don’t understand heavier-than-air flight

#125

Post by salawat »

laurent92 wrote: post #113
salawat wrote: post #69

Earlier quoted context omitted.

>They were all right. Or rather, they were all wrong: Everyone knows Ariane V exploded because the officer pushed a red button ;) ...and this is why learning the value of drawing the boundaries and selecting stop points in the analysis of complex topics, and the employment of humor is a powerful rhetorical tool. This is why you composition is the most important topic this semester! Sorry... Couldn't resist. Also, wha…

> Also, what school teaches QA These days? Interesting question! INSA Lyon in France, but that was in 2005, you could mock that the Old Continent does a lot of V-Cycle waterfall projects and had missed the Agile turn of 2001. BUT learning how processes help is, instead, a very important step to judge what exactly we give up with Agile. The irony is I went on creating software for requirements, and I can testify that…

That's because QA and Statistical Process Control were born out of manufacturing due to the high stakes with processes and tooling not being able to change on a dime like software does. I'm not surprised at all there.

Software Quality Assurance is much more... Spongey.

Re: Why we don’t understand heavier-than-air flight

#126

Post by zazen »

afterburner wrote: post #123
zazen wrote: post #111

Earlier quoted context omitted.

It is a lazy gotcha attempt. It is a lazy attempt at gotcha-ing someone who believes angle of attack ISN'T important. Unless you think a plane flying upside-down is somehow evidence AGAINST the importance of angle-of-attack? Again: this entire pointless misunderstanding has arisen because you didn't see - apparently STILL HAVEN'T SEEN - which side of the debate the comment you replied to is arguing for.

Oh I see. You think the Bernoulli approach is independent of angle of attack? It's not.

I'm afraid it is most evident that you do not see. Forget trying to guess what I might or might not think about aerodynamics. Just see if you can follow the following recap of the conversation:

1) anvandare says aeroplanes can fly upside down. This is an argument AGAINST a putative person who argues that lift is entirely a function of aerofoil shape, ignoring angle of attack. In advancing this argument, anvandare implies that he DOES understand and contend that angle of attack is significant.

2) You say something unclear about "effective change of shape", apparently attempting to rebut anvandare, who, remember, contends that angle of attack is significant.

3) I say that what you said about "effective change of shape" is unclear, meaning I am rebutting you, meaning I agree with anvandare that angle of attack is significant.

4) You form the impression that I believe angle of attack is not significant, and tell me that if I believe angle of attack is not significant, then I am wrong.

Can you see where you have gone wrong there?

Having written all this, I'm come to the point of actually becoming quite concerned about your neurological state. If you've had a recent head injury or you're old enough that Alzheimers is a possibility, you need medical advice - you've failed to follow the simple thread of a conversation.

Re: Why we don’t understand heavier-than-air flight

#127

Post by WalterBright »

laurent92 wrote: post #64
k__ wrote: post #52

Earlier quoted context omitted.

Reminds me of learning what electricity is. I learned it multiple times. In middle school, in high school, in university, on youtube explained by a quantum physicist. Everytime I understood less of it.

> I learned multiple times. Everytime I understood less of it. Isn’t that how to spot seniority? The junior says “I know ReactJS and SpringBoot!” The senior says: “I don’t know much…” Unrelated, but that reminds me how my Masters Degree teachers touted the importance of their subject in their introduction course, all explaining the Ariane V explosion from a completely different angle: - The measurements professor: “A…

That's why proper engineering is to address all the causes, even if fixing just one of them would have prevented the accident.

You'll see this regularly in the series Aviation Disasters on TV. It has lessons for all engineering projects. I watch every episode :-)

Re: Why we don’t understand heavier-than-air flight

#128

Post by jjk166 »

lowkey wrote: post #107
jjk166 wrote: post #104

Earlier quoted context omitted.

The upper flow does move faster, and must for the sake of vortex production.

Please explain what you mean here in simple language. I don’t understand how you conclude that the upper flow must move faster and I don’t understand how it relates to vortex production.

To get a force acting upwards on the wing, there must be a downward reaction on the airstream.

This downward force on the airstream bust change its direction.

This change of direction is a rotation about the airfoil. Specifically a downwards rotation.

The airstream moving above the centerline of this rotation is moving in the same direction, and thus will be accelerated faster.

The airstream moving below the centerline of this rotation is moving in the opposite direction, and so will be decelerated to a slower speed.

The center of this rotation happens to be along the camber line of the airfoil, so all the air above the camber line (ie over the top of the airfoil) must move faster, while all the air below the airfoil must move slower.

The vortex is just the bulk rotational movement of the airflow. In fact, the airfoil can be replaced by anything that will generate the same vortex, like a rotating cylinder.

Re: Why we don’t understand heavier-than-air flight

#129

Post by yarcob »

oolonthegreat wrote: post #31

I didn't understand what we don't understand about hta flight but maybe that's just me.

I have the same feeling.

I think what people usually mean when they say that we don't understand flight is that there are no simple equations. A lot of physical problems have elegant solutions (eg. the shape of a hanging chain is roughly the cosh function). But there are no elegant equations that describe the profile of a wing, so it's a bit unsatisfying.

Re: Why we don’t understand heavier-than-air flight

#130

Post by IshKebab »

jjk166 wrote: post #122
IshKebab wrote: post #24

Earlier quoted context omitted.

A common and wrong explanation. The pressure differential is created by the fact that the air is being pushed into the lower side of the wing. It's much simpler than that anyway. The wing forces the air downward, so the plane must be forced up.

Another common and wrong explanation. The air is pushed down by induced rotation. An inclined wing is one way to do it, but is not necessary.

I don't know what you are trying to say.
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