Why does an airplane stay in the air?

X3 Skier

X3 Skier

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Since this a topic that always pops up on POA, It’s good to know everybody is correct.

Not even experts can explain why planes stay in the air
At this point in the history of flight, it shouldn’t be that hard for scientists to say what keeps birds — and aircraft — airborne. But the question remains puzzling.

Read in Scientific American: https://apple.news/A0Zc9zaiHRXqIyH2c_aHCtQ

Cheers
 
X3 Skier said:
Since this a topic that always pops up on POA, It’s good to know everybody is correct.

Not even experts can explain why planes stay in the air
At this point in the history of flight, it shouldn’t be that hard for scientists to say what keeps birds — and aircraft — airborne. But the question remains puzzling.

Read in Scientific American: https://apple.news/A0Zc9zaiHRXqIyH2c_aHCtQ

Cheers
Click to expand...

Troll. -Skip
 
Even Chewbacca, despite his limited technical grasp and conversational challenges is scratching his head over this one.

Flight? What is the state of non-flight?
 
@Sac Arrow - Why do you think Chewbacca has limited technical grasp? Also, he's probably very conversant in his own tongue, just not in English. Seemed that R2D2 and C3PO understood him just fine.

I'm gonna check the RoC's. If it's not already in there, I'll petition @Ted DuPuis to add "No disparaging Wookies"!
 
If one is having trouble with an airplane staying in the air then I would suggest reducing throttle. Or wait until it runs out of gas.
 
The thread title nearly reads like a "...crossed the road?" bit of humor
 
X3 Skier said:
Since this a topic that always pops up on POA, It’s good to know everybody is correct.

Not even experts can explain why planes stay in the air
At this point in the history of flight, it shouldn’t be that hard for scientists to say what keeps birds — and aircraft — airborne. But the question remains puzzling.
Click to expand...

after taking aerodynamics in college I came to the conclusion that airplanes are able to fly because for some reason wing generate high pressure below the wing and lower pressure above it. I never found a satisfying answer that went any deeper than that.
 
As soon as you think you have figured out how Bernoulli makes an airplane fly, then explain a fully symmetrical wing.

:)
 
FastEddieB said:
A brick - or Snoopy’s doghouse - or a symmetrical wing - will fly with the right combination of airspeed and angle of attack.
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Give me enough thrust and I can make anything fly.

There seems to be a groundswell of anti-Bernoulli schools of thought out there. Try goooogle "how is lift created" and most of them are giving 100% credit to Newton. Even NASA has turned on Bernoulli.

https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html

:eek:
 
I had it figured out as a child the first time I stuck my hand out of a car window at 60 miles an hour. It doesn’t have to be an airfoil to produce lift.
 
The problem with the Bernoulli principle is that there is no law of physics that causes two molecules that separate at the leading edge to arrive at the trailing edge at the same instant, which was the basis for claiming that one molecule had to go faster and therefor cause a lower pressure on top of the wing.
 
smv said:
As soon as you think you have figured out how Bernoulli makes an airplane fly, then explain a fully symmetrical wing.

:)
Click to expand...
Easy peasy, mac and cheesy. Use the actual Bernoulli equation and not some fairy tail about curves or distances or "it looks like a venturi"...

A symmetric wing works exactly the same as an asymmetric wing. Same laws of physics (both Newton and Bernoulli) apply to both the top and bottom, symmetric or not.

 
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smv said:
There seems to be a groundswell of anti-Bernoulli schools of thought out there. Try goooogle "how is lift created" and most of them are giving 100% credit to Newton. Even NASA has turned on Bernoulli.
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A Newtonian explanation is significantly more straightforward.
Bernoulli gives us the relation between pressure and velocity which is accurate (outside the boundary layer), but leaves us with the question about why the average velocity on top f a wing is faster than the free stream velocity while the average velocity on the bottom is typically slower than free stream. To do that, you have to go back to Newton. So, why not just start with that?
 
Oh, and the FAA is still telling fairy tales...

https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/media/amt_general_handbook.pdf page 5-38
"In Figure 5-56, the air reaching the leading edge of the wing separates into two separate flows. Some of the air goes over the top of the wing and some travels along the bottom. The air going over the top, because of the curvature, has farther to travel. With a greater distance to travel, the air going over the top must move at a greater velocity. The higher velocity on the top causes the static pressure on the top to be less than it is on the bottom, and this difference in static pressures is what creates lift."

But then, the Church sentenced Galileo to house arrest for claiming the earth revolved around the sun, so why should we expect anything different from the FAA?

;-)
 
dbahn said:
The problem with the Bernoulli principle is that there is no law of physics that causes two molecules that separate at the leading edge to arrive at the trailing edge at the same instant, which was the basis for claiming that one molecule had to go faster and therefor cause a lower pressure on top of the wing.
Click to expand...
Except, of course, that there is a lower pressure on top of the wing. Even on a symmetrical airfoil, which is only symmetrical in cross-section, but not in practice.
 
dbahn said:
The problem with the Bernoulli principle is that there is no law of physics that causes two molecules that separate at the leading edge to arrive at the trailing edge at the same instant, which was the basis for claiming that one molecule had to go faster and therefor cause a lower pressure on top of the wing.
Click to expand...

I think that’s always been a simplistic explanation.

What the principle needs is for a fluid to accelerate, with an associated pressure drop. It will do so if it meets a constriction in flow, as in a venturi. This is established.

In the case of a wing in flight, one “side” of that venturi is the wing. The other “side” exists somewhere above the wing, where eventually you meet a layer of undisurbed air. Between the two, air accelerates. The associated pressure drop on the upper surface of the wing is trivially easy to measure.

I’ll stipulate that is only part of the “mystery” of lift, and simple Newtonian physics can also play a part. But no mysterious “bonding” of two air molecules needs to be invoked. It’s nonexistent, shows a misunderstanding of the physics involved and just confuses things.
 
Curiously, this was the first hit that came up searching “wing lift Bernoulli”:

wrong1.gif


Note the “Incorrect Theory” label. The red underline is in the original image.
 
FastEddieB said:
Curiously, this was the first hit that came up searching “wing lift Bernoulli”:

Note the “Incorrect Theory” label. The red underline is in the original image.
Click to expand...

See post #16 above.

;)
 
I go by "more molecules going the same speed are hitting the bottom of the wing than the top of the wing" concept (like a big sail over powering a small sail). You could turn that airfoil upside down and have a similar effect, which is what happens when you fly something like a Decathalon upside down.

upload_2020-1-19_9-21-9.jpg

And I think it's fair to say that if air is lifting the wing then the pressure opposite the lifted surface will always be lower, no matter whether you subscribe to a goofy theory or a sound one.
 
Planes don’t stay in the air, duh.
 
FastEddieB said:
A brick - or Snoopy’s doghouse - or a symmetrical wing - will fly with the right combination of airspeed and angle of attack.
Click to expand...
The US Air Force has always claimed that given the appropriate (translation: huge monster) engine, it can fly anything. The Shuttle is proof.
 
murphey said:
The US Air Force has always claimed that given the appropriate (translation: huge monster) engine, it can fly anything.
Click to expand...
The Israelis demonstrated that with an F-15 after a midair collision ripped a whole wing off and the pilot still landed it.
 
smv said:
As soon as you think you have figured out how Bernoulli makes an airplane fly, then explain a fully symmetrical wing.

:)
Click to expand...
Bernoulli is only part of the equation. Newton’s third law is also an essential component. Action: Air strikes the bottom of the wing and Reaction: airplane is lifted upward. Incidence in the wing is there for this purpose. Well explained in “Stick and Rudder”
 
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