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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

#171

Post by MaxBarraclough »

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.

You might get something out of this 2013 talk by former Boeing engineer Doug McLean on misconceptions about lift. [0]

[0] https://youtu.be/QKCK4lJLQHU?t=834 (watch for 5 minutes to get some idea of his main points, or 35 minutes to watch in full. The link will skip the introduction.)

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

#172

Post by Retric »

slipframe wrote: post #163
Retric wrote: post #80

Earlier quoted context omitted.

Yea, start throwing around enough thrust and you can fly just about anything. The F-15 got to the point where one wing was optional: https://theaviationist.com/2014/09/15/f-15-lands-with-one-wi...

There is more to that F-15 incident than just incredible thrust; the F-15's wide fuselage provides significant body lift. https://en.wikipedia.org/wiki/Lifting_body#Body_lift

They can also fly sideways. Body lift is why it can land, thrust is why it could fly.

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

#173

Post by lowkey »

benhurmarcel wrote: post #154
lowkey wrote: post #56

Can confirm. I worked at Pratt & Whitney testing jet engines early in my career. At the time I read a similar article and spread it amongst my colleagues - the cognitive dissonance was palpable. As engineers we had been taught that lift was due to air above the wing traveling faster than air below the wing and thus creating lift by way of a pressure differential. The more accurate answer as seen in the article is tha…

> a re-vectoring of horizontal thrust in a downward direction. Literally the engine pushes horizontally accelerated air downward and the action-reaction mechanic causes an equal but opposite upward force lifting the plane. You mean the wing, not the engine. But even then that doesn't answer the question. It's just another way of looking at the effect, but it doesn't explain the cause. The question is then why/how doe…

> You mean the wing, not the engine.

Yes, clarifying I meant the wing not the engine.

> The question is then why/how does the wing pushes that air downward?

Fair point. I honestly didn’t expect this quality of analysis on the topic.

I believe that another phenomenon is required to complete the explanation in addition to Newton. Couette flow explains why streamlines closest to the wing tend to follow the shape of the wing. Hence the vectoring effect. I’m sure a better article exists but Wikipedia is a bit lacking unfortunately.

[1]Couette Flow - https://en.m.wikipedia.org/wiki/Couette_flow

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

#174

Post by smusamashah »

ec109685 wrote: post #160
8bitsrule wrote: post #153

As a kid in a car, when I stuck my arm straight out the window at speed, it got pushed backwards (in my frame) by the airflow. Keeping the arm rigid took effort. If I tilted the front of my hand in a clockwise direction, my arm was pushed upwards. It took more effort (rigidity) to stop that considerable force. That's the observation. Clearly my rigid arm/hand was accelerating some air downward. Like a gun acceleratin…

That only (intuitively) explains lift generated by a positive angle of attack. As shown here, you can get lift with a flat angle of attack: https://www.wolframalpha.com/input/?i=NACA+6409+airfoil&assu...

The upside is curved pushing air upwards reducing the pressure hence generating lift from below. Isn't it just that?

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

#175

Post by hollerith »

smusamashah wrote: post #174
ec109685 wrote: post #160

Earlier quoted context omitted.

That only (intuitively) explains lift generated by a positive angle of attack. As shown here, you can get lift with a flat angle of attack: https://www.wolframalpha.com/input/?i=NACA+6409+airfoil&assu...

The upside is curved pushing air upwards reducing the pressure hence generating lift from below. Isn't it just that?

If the plane is pushing the air up, then by Newton's third law, the air is pushing the plane down. Also, pushing it up would not reduce the pressure of a parcel of air.

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

#176

Post by perryizgr8 »

JasonFruit wrote: post #84
tdy721 wrote: post #67

Rocketry is heavier than air flight. I submit we discovered it before lighter than air flight. I will hazard that I do have a nice understanding of how it works. I learned it from media like this: https://youtu.be/X4iMeKif488 I do think you’re dead wrong!

Many people would object that rockets don't fly , they are hurled .

A hurled object would decelerate from the moment it is thrown. Its fastest speed is at launch. Rockets have their slowest speed at launch, and they continuously accelerate. So they are definitely not "hurled".

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

#177

Post by AstralStorm »

tomsto wrote: post #36
AstralStorm wrote: post #30

Earlier quoted context omitted.

Correct. Still incomplete. Angle of attack causes a vortex at the trailing edge which has nothing to do with raw air speed and everything to do with fluid dynamics (which involves speed but is much more complex) Short version is that you created a hole (lower pressure area) in air which it now tries to fill. Air and gasses have finite limited velocity known as speed of sound, which is why you get these pressure diffe…

I’m not sure I fully agree. Do you not get this trailing edge vortex with an asymmetrical aerofoil at 0 angle of attack? (Just less strongly because less pressure difference between suction and pressure sides)

You do. And you get small vortices on wing surfaces too.

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

#178

Post by tdy721 »

perryizgr8 wrote: post #176
JasonFruit wrote: post #84

Earlier quoted context omitted.

Many people would object that rockets don't fly , they are hurled .

A hurled object would decelerate from the moment it is thrown. Its fastest speed is at launch. Rockets have their slowest speed at launch, and they continuously accelerate. So they are definitely not "hurled".

Disagree. It could be seen as one very long hurl? Or you know, stages of them?
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