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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

#151

Post by na85 »

hattar wrote: post #138
PaulHoule wrote: post #134

Earlier quoted context omitted.

We understand flight well enough to make highly optimized airplanes. There are some old controversies that are largely settled. The Microsoft Flight Simulator manual in 1980 "teached the controversy" but it was really settled decades before that. People still remember the controversy from back then and keep repeating it and probably will still do it when people are living in space colonies. The Bernoulli effect expla…

> The Bernoulli effect explanation is bogus. I hear this but never seem to get any further info. Why are wings shaped with a curved top and flat bottom? Is there a good summary I can go read to understand this all?

>Why are wings shaped with a curved top and flat bottom?

Most wings aren't shaped like that.

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

#152

Post by exporectomy »

tsimionescu wrote: post #18
exporectomy wrote: post #9

Earlier quoted context omitted.

Though I don't know what idea he was referring to, tides can be pretty hard to predict accurately. Obviously nothing to do with God, but it's probably fair to say there are aspects of them we don't understand or at least can't simulate arbitrarily far into the future. "In an analysis of the tides in Venice Lagoon, at the head of the Adriatic Sea, where the tides seem to pick up because of near-resonancy of the basin,…

This was the video in question: https://m.youtube.com/watch?v=HABNe7_D22k?t=1m52s . It's not about predicting the exact movement of tides, he's arguing science fundamentally can't explain the regularity of tides...

Oh, well that's different.

Funny though, the guy he's interviewing said Islam is a scam and Muslims are suckers who have fallen for it. Funny what you can get away with if you couch it right.

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

#153

Post by 8bitsrule »

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 accelerating a bullet, there's a recoil (but a continuous one). That's Newton: conserving momentum. Maybe not a complete explanation, but it's the bulk of one.

Here's how NASA puts it:

https://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html

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

#154

Post by benhurmarcel »

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 does the wing pushes that air downward?

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

#155

Post by [deleted] »

Cogito wrote: post #7

The continued assertion that "we don't understand heavier-than-air flight" is a weird one. The article even skates around this, saying (essentially) "well maybe we do understand it, but chaos theory!" If you're in the sky and you want to stay there, you have to counteract gravity. Heavier-than-air flight does this by pushing down on air. Want to stay in the sky? Push down on enough air, fast enough, and you will stay…

[deleted]

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

#156

Post by benhurmarcel »

jeffreyrogers wrote: post #132

This is silly. We know why: the wing pushes air down and as Newton taught us, every action has an equal and opposite reaction. To push air down the wing must be feeling a force up on it, which causes lift. You can also see the same thing with a helicopter flying over water: the water is affected in a circular region fairly close to the rotor itself, indicating that there is a large downward force being exerted on the…

Obviously lift is produced by pushing air down. The question is why/how is the air pushed down.

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

#157

Post by jeffreyrogers »

benhurmarcel wrote: post #156
jeffreyrogers wrote: post #132

This is silly. We know why: the wing pushes air down and as Newton taught us, every action has an equal and opposite reaction. To push air down the wing must be feeling a force up on it, which causes lift. You can also see the same thing with a helicopter flying over water: the water is affected in a circular region fairly close to the rotor itself, indicating that there is a large downward force being exerted on the…

Obviously lift is produced by pushing air down. The question is why/how is the air pushed down.

The wing directs the flow of air downwards. The flow doesn't separate except at high angles of attack (stalling). You can go into arbitrary levels of detail (why doesn't the flow separate?, how thick is the affected layer?, etc.) but it doesn't change the fact that mostly we know the answers to all those questions.

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

#158

Post by PaulDavisThe1st »

a1369209993 wrote: post #150
beckingz wrote: post #70

Earlier quoted context omitted.

Turns out, the world is really really complicated. So it's better to say that our models are simplified, not lies.

> So it's better to say that our models are simplified, not lies. To be fair, for most purposes (atoms, molecules, metals) there usually (very-) technically aren't any electrons, just configurations of the relevant quantum fields (eg in the form of electron orbitals) whose asociated conserved quantities would allow them to convert into a certain number of free-flying electron particles if you dumped in enough energy…

More generally: we have stories that say that "things behave as if they are made of ..." but too many people misread or mishear them and think that the form is "things are made of ..."

There are no quantum fields either, just as there are no atoms. Things (of the right size) behave as if there they were composed of quantum fields (or electrons or atoms), and the less we have to say "... except that ...", the more comfortable we are with the story.

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

#159

Post by dogma1138 »

chasd00 wrote: post #77
anvandare wrote: post #60

Earlier quoted context omitted.

I usually just answer Socratically: "So how can (some) planes fly upside-down?" whenever I encounter the Bernoulli-adherents.

Has someone taken an rc airplane and turned the wing upside down and flown it? It should be pretty easy to demonstrate.

RC airplanes have insane thrust to weight ratios, with enough thrust a brick can fly.

That said with my historic experience with single piston RCs if you didn’t compensate for the upside down flight with your ailerons you would nose dive.

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

#160

Post by ec109685 »

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...
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