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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

#81

Post by rkique »

anvandare wrote: post #60
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…

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

But the "true" explanation given above is that the engine pushes the horizontally accelerated air downwards (with respect to its own orientation). Wouldn't that also lead to the conclusion that upside down flight is impossible?

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

#82

Post by afterburner »

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…

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.

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

#83

Post by afterburner »

anvandare wrote: post #60
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…

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

Changing the angle of attack effectively changes the shape of the airfoil. No gotcha here either.

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

#84

Post by JasonFruit »

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.

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

#85

Post by formercoder »

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…

Same as sailing, does the airplane have an equivalent of the keel?

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

#86

Post by afterburner »

DangitBobby wrote: post #55
hamilyon2 wrote: post #51

Earlier quoted context omitted.

So, people answering on quora for example, are wrong? https://www.quora.com/Can-a-helicopter-having-a-power-to-wei... I am even more confused now.

No, I have to conclude that the previous commenter didn't understand your point, which was the observation that heavy aircraft with very low sustained forward thrust (thrust that would not be sufficient for a helicopter to hover) results in sufficient upward lift to suspend the aircraft indefinitely, which is very surprising.

A helicopter doesn't rely on the forward thrust of the chassis, it relies on the forward thrust of the helicopter blades in rotation. Those blades are wings.

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

#87

Post by zazen »

afterburner wrote: post #83
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.

Changing the angle of attack effectively changes the shape of the airfoil. No gotcha here either.

I'm not immediately convinced that "effectively changing the shape" is a coherent idea. The lift effect either crucially depends on the actual, unchanging shape of the aerofoil or it doesn't. Flying upside-down proves that it doesn't. Maybe all we're disproving is a straw-man of a "Bernoulli-ist" position, but we're disproving it all right.

EDIT: trying to think what you might mean by "effectively changing the shape". Do you just mean that an upside-down aerofoil is a reflection of the aerofoil the right way up? Because that's the entire point of the argument you seem to be trying to rebut.

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

#88

Post by foobiekr »

krisoft wrote: post #49
parineum wrote: post #14

Earlier quoted context omitted.

Knowing Newtonian physics doesn't mean we understand all things that move. The point about "not understanding" flight is that, if we truly understood it, we could design the optimal aircraft from first principles before it ever entered a wind tunnel. Instead, we work based on incrementally improving tribal knowledge of what has worked in the past and try to make something similar to fit our desired flight envelope. C…

You have an unduly rosy picture of rocket science. The turbopump used in most liqued fueled rockets to presurize the fuel is notoriously complicated. Small changes to the design can result in a dramatic loss of efficiency, or even worse if it starts cavitating the pump can eat itself. For this reason nearly nobody designs turbopumps from scratch and first principles, they take a well understood design and maybe tweek…

I can’t think of a technology sector where this logic isn’t true.

I also can’t think of a technology sector where the naive/new/low level/clueless don’t also assume this is not true.

Even manufacturing. ASICs. Software. Everything.

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

#89

Post by clairity »

sigmoid10 wrote: post #47
Someone1234 wrote: post #34

Earlier quoted context omitted.

If an aircraft flies level upside down it will lose altitude towards the ground (as opposed to right side up wherein given adequate thrust it should keep its current altitude). In order to stay at a fixed altitude upside down you have to bring the nose of the aircraft up several degrees (increasing based on air speed).

If wings only generated lift in one direction (i.e. towards the curved side), then even flying with your nose up would pull you down if you are inverted. What people here are missing is that curved wings in level flight generate lift, but any shape of wing can generate lift with a positive angle of attack. Just stick your hand out the window while driving on the highway and tilt it slightly, you'll see.

> "Just stick your hand out the window while driving on the highway and tilt it slightly, you'll see."

this is really all the intuition most people need to understand flight, even if it leads to an incomplete understanding. it's easy to feel the air pushing on the bottom of your hand when you tilt it up (or top, when tilted down). what's not obvious is that there is also lift created on the top side at the same time, but that can subsequently be learned in high school physics (or fluid dynamics in college, which is where it really stuck for me).

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

#90

Post by foobiekr »

jessedhillon wrote: post #22
parineum wrote: post #14

Earlier quoted context omitted.

Knowing Newtonian physics doesn't mean we understand all things that move. The point about "not understanding" flight is that, if we truly understood it, we could design the optimal aircraft from first principles before it ever entered a wind tunnel. Instead, we work based on incrementally improving tribal knowledge of what has worked in the past and try to make something similar to fit our desired flight envelope. C…

Almost nobody understands software then, by this definition.

I can’t tell if this is meant as a counter or not. Literally the pool of people who really understand capital S Software is tiny.

I’ve worked with thousands who don’t and maybe two dozen who do.

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