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How airplanes fly
Posted by: Don C
Date: April 18, 2009 10:52PM
I pretty much understand (at a very basic level) the concept of lift on a wing as air flows different across the top of a curved wing vis a vis across the flat bottom of the wing. Plane goes forward, airflow crosses the wing, lift develops (or "happens") and the plane can fly.

So today I am watching the air show at Thunder over Louisville
[www.thunderoverlouisville.org]
[www.visualpresentations.com]
and any number of fighters zoom into the show box and then turn straight up. Afterburners are roaring, of course, but my understanding of lift fails to explain how that happens.

Then the F-4 comes in, goes straight up, and "floats" down looking like a leaf with no forward motion. He finally goes nose down and does his parabolic pullout shortly before diving into the Ohio River. I cannot begin to understand the physics of this!

This is more of an exclamatory note than a request for what to me must be advanced physical science.

It was an afternoon of fine aircraft, but one flyover that was particularly fun was the "Heritage Flight" with a P-51 propeller driven plane, and four jets, F-4, F-16, and F-22 flying by in formation. I could just imagine that the pistons in that P-51 were turning as fast as they can and the four jets were barely above stall speed. (Maybe not true, but a cartoon image of Felix the cat turning the propeller came to mind.)

The C-47 Chinook dipped its tail in the Ohio River in a precision move I'd not seen before.

Anyway, I am absolutely amazed at what these plane can do.



Edited 1 time(s). Last edit at 04/18/2009 11:04PM by Don C.
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Re: How airplanes fly
Posted by: mikebw
Date: April 18, 2009 11:03PM
This brings back memories of my hours at the computer playing Chuck Yeager's Air Combat. The P-51 mustang was a fun plane, but I would always end up in an F-4 or F-16 hunting down a bunch of B-17 bombers for fun.
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Re: How airplanes fly
Posted by: Don C
Date: April 18, 2009 11:12PM
Incidently, local news his week showed video of setting up the Command Center with the director under a desk wiring his Mac. It would be interesting to know just what function he was using if for. There is a photo of him in photo section of the link with several images on the screen so he might just be monitoring live camera feeds, but it was definitely a Mac he was using.
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Re: How airplanes fly
Posted by: birdmanjeff
Date: April 19, 2009 12:06AM
Only one thing explains this accurately, Pure power.
if you have more power than weight the airplane is closer to a rocket.



Birdmanjeff


www.magfundraising.com/faleofamilyadoption
www.cafepress.com/aviary
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Re: How airplanes fly
Posted by: Doc
Date: April 19, 2009 12:19AM
Dunno about stunt flying, but came across this fascinating discussion with a little Googling.
[64.233.187.99]
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Re: How airplanes fly
Posted by: Filliam H. Muffman
Date: April 19, 2009 12:30AM
Poking through airplane specs, the P51 has a takeoff/approach speed of about 95 MPH and a top speed of 360 MPH at sea level (edit: for the original ones). Most jet fighters designed for Carrier operations have a takeoff speed of around 140 MPH. Air Force versions can be expected to be a little higher.

One of the strangest things I have experienced at an airshow was a SR-71 doing a pass at low throttle after building up some speed. Seeing something go by at over 200 MPH and making almost no noise was very eerie.



In tha 360. MRF User Map



Edited 1 time(s). Last edit at 04/19/2009 12:42AM by Filliam H. Muffman.
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Re: How airplanes fly
Posted by: Carnos Jax
Date: April 19, 2009 12:46AM
The pilot pulling back on the control stick causes the (horizontal) tail to induce a nose up pitching motion which in itself induces a large spike in lift generation by the wing. As the aircraft continues to rotate in a nose up fashion, engine thrust starts becoming the dominant form of opposition to the aircraft's weight, until at vertical where it is the sole protagonist while lift generation by the wing is no longer.

At least that answers the first part of your exclamatory exposition.



Edited 2 time(s). Last edit at 04/19/2009 12:53AM by Carnos Jax.
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Re: How airplanes fly
Posted by: Article Accelerator
Date: April 19, 2009 01:40AM
Quote
Don C
I pretty much understand (at a very basic level) the concept of lift on a wing as air flows different across the top of a curved wing vis a vis across the flat bottom of the wing. Plane goes forward, airflow crosses the wing, lift develops (or "happens") and the plane can fly.

Maybe, maybe not. Bernoulli's Principle is an incomplete explanation for airfoil lift:

[academic.evergreen.edu] (PDF)
[en.wikipedia.org])
[en.wikipedia.org]

Note that Jef Raskin, one of the original Macintosh development team, is cited.
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Re: How airplanes fly
Posted by: M>B>
Date: April 19, 2009 02:13AM
And don't overlook what came before the Zip drive...

[en.wikipedia.org]
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Re: How airplanes fly
Posted by: AAA
Date: April 19, 2009 08:38AM
OH!

Are there clear skies today? You might have given me an idea of how to fill my day today.
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Re: How airplanes fly
Posted by: cbelt3
Date: April 19, 2009 08:44AM
Nice. You see, as noted, there's a a point in modern jet fighters where the aircraft actually stops flying and, essentially, becomes a rocket. Watch an F-15 go from takeoff to 30K feet straight up. No flight, just plain thrust from a couple of big honkin engines. Suckers can break Mach 1 straight up.
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Re: How airplanes fly
Posted by: flareslow
Date: April 19, 2009 09:47AM
In jet aircraft, it's all about energy- maintenance of, conversion of, addition of (from engines)- managing. Usually kinetic to potential and vice-versa.
Sometimes its a regular airplane and sometimes its a rocket and sometimes its a rock.
The F-4 was described by a friend who flew them as a "barn door with big motors." One of my rotorhead friends would point out that an H-53 could beat an F-4 to 10K feet from takeoff. I saw it demoed at one air show.
There is no ride at Disney or Six Flags that compares to the fun you can have in a military jet. And thats not even getting to shoot the guns!
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Re: How airplanes fly
Posted by: Blankity Blank
Date: April 19, 2009 10:18AM
Quote
Filliam H. Muffman
One of the strangest things I have experienced at an airshow was a SR-71 doing a pass at low throttle after building up some speed. Seeing something go by at over 200 MPH and making almost no noise was very eerie.
That is exactly how I felt when I saw the B-2 Stealth bomber at an air show once. It felt like I was watching a UFO pass by.
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Re: How airplanes fly
Posted by: AAA
Date: April 19, 2009 11:39AM
When I saw the B2, it was very low cloud cover. They had one on the ground, and this one flew overhead, dipped below the clouds VERY CLOSE to the ground, and took off back into the clouds. So freaking eery.
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Re: How airplanes fly
Posted by: Craig
Date: April 19, 2009 12:23PM
Quote
Article Accelerator
Quote
Don C
I pretty much understand (at a very basic level) the concept of lift on a wing as air flows different across the top of a curved wing vis a vis across the flat bottom of the wing. Plane goes forward, airflow crosses the wing, lift develops (or "happens") and the plane can fly.

Maybe, maybe not. Bernoulli's Principle is an incomplete explanation for airfoil lift:

[academic.evergreen.edu] (PDF)
[en.wikipedia.org])
[en.wikipedia.org]

Note that Jef Raskin, one of the original Macintosh development team, is cited.

Actually what Don said is absolutely correct. The lift is caused by the difference in the way that air flows across the top and bottom of a wing. He said nothing about how the effects are modeled or what fluid forces are dominant at what speeds, etc. Just that the top of the wing is different than the bottom. And that the difference causes lift.

I love airshows. I once saw an F/A-18 at an airshow produce a vapor cone very similar to the one seen here: [www.youtube.com]



Edited 1 time(s). Last edit at 04/19/2009 12:23PM by Craig.
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Re: How airplanes fly
Posted by: Article Accelerator
Date: April 19, 2009 01:53PM
Quote
Craig
Quote
Article Accelerator
Quote
Don C
I pretty much understand (at a very basic level) the concept of lift on a wing as air flows different across the top of a curved wing vis a vis across the flat bottom of the wing. Plane goes forward, airflow crosses the wing, lift develops (or "happens") and the plane can fly.

Maybe, maybe not. Bernoulli's Principle is an incomplete explanation for airfoil lift:

[academic.evergreen.edu] (PDF)
[en.wikipedia.org])
[en.wikipedia.org]

Note that Jef Raskin, one of the original Macintosh development team, is cited.

Actually what Don said is absolutely correct. The lift is caused by the difference in the way that air flows across the top and bottom of a wing.

Ah--so that's all there is to it, eh?

So, airplanes cannot fly inverted then? I could swear I've seen one or two actually do that...

Quote

He said nothing about how the effects are modeled or what fluid forces are dominant at what speeds, etc. Just that the top of the wing is different than the bottom. And that the difference causes lift.

And I said that's an incomplete explanation of airfoil lift generation. And I provided links that discuss the various mechanisms involved. I think you'll find them to be informative and thought provoking.

Quote

I once saw an F/A-18 at an airshow produce a vapor cone very similar to the one seen here: [www.youtube.com]

That's an interesting phenomenon. It's caused by an effect known as the Prandtl–Glauert singularity:

[en.wikipedia.org]
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Re: How airplanes fly
Posted by: Carnos Jax
Date: April 19, 2009 02:13PM
I'm not sure he wasn't implying that was the technically simple answer (because there isn't one), rather that lift results from differences in the way air flows above and below a wing.

Though an upside-down wing generates lift, it's much more inefficient doing so. Aerobatic airplanes usually have a symmetric airfoil. The horizontal stabilizer of most airplanes have an upside down airfoil, because it's generating a down force throughout much of the flight.

Quote
Article Accelerator

Quote

I once saw an F/A-18 at an airshow produce a vapor cone very similar to the one seen here: [www.youtube.com]

That's an interesting phenomenon. It's caused by an effect known as the Prandtl–Glauert singularity:

[en.wikipedia.org]

It's amazing how most people confuse this phenomenon with an aircraft 'breaking the sound barrier'.



Edited 1 time(s). Last edit at 04/19/2009 02:15PM by Carnos Jax.
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Re: How airplanes fly
Posted by: Craig
Date: April 19, 2009 03:30PM
Quote
Article Accelerator
Ah--so that's all there is to it, eh?

So, airplanes cannot fly inverted then? I could swear I've seen one or two actually do that...

I am quite aware that planes fly inverted. And again, simplistically stated, this is due to the fact that the air flows differently across the top and bottom of the wing. In the case of inverted flight the top and bottom are reversed but as Carnos Jax points out the wings in aerobatic planes often have little to no camber. The asymmetrical airflow over the wing is due to the angle of attack.


Quote
Article Accelerator
And I said that's an incomplete explanation of airfoil lift generation. And I provided links that discuss the various mechanisms involved. I think you'll find them to be informative and thought provoking.

Believe me, I understand that the Bernoulli principal is an incomplete explanation for the complex mechanisms involved in lift. I have had coursework in fluid dynamics. In fact, there are different theorems that can be used to estimate lift depending on what is known/unknown, but ultimately everything goes to a wind tunnel. Experimental testing is required in this engineering science more than almost any other. As smart as we are about fluid dynamics, and as good as computer models have become nothing beats an actual scaled test. And I stand by Don's explanation that at a very basic level air flows different across the top of wing than the bottom of the wing and as the plane goes forward, air crosses the wing, lift develops, and the plane can fly. He didn't mention anything about common misconceptions such as equal transit time.
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Re: How airplanes fly
Posted by: Psurfer
Date: April 19, 2009 04:48PM
Cool thread.

I've had my own B-2 close encounters: Once roaring over my backyard on it's way to an air show. Like it was right over my head. Low, loud, and definitely one of those "that thing could kill me right f-ing now and there's not a damned thing I could do about it" moments.

The other time, I caught an amazing but terrifying glimpse of one seen between downtown buildings, maneuvering to make another pass at an air show. This gave me the chill that I imagine most of the rest of the world feels when they think about (or unfortunately, See) our airpower meaning business low over their city.
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Re: How airplanes fly
Posted by: Craig
Date: April 19, 2009 05:56PM
Quote
Psurfer
Cool thread.

I've had my own B-2 close encounters: Once roaring over my backyard on it's way to an air show. Like it was right over my head. Low, loud, and definitely one of those "that thing could kill me right f-ing now and there's not a damned thing I could do about it" moments.

The other time, I caught an amazing but terrifying glimpse of one seen between downtown buildings, maneuvering to make another pass at an air show. This gave me the chill that I imagine most of the rest of the world feels when they think about (or unfortunately, See) our airpower meaning business low over their city.

That reminds me of one odd close encounter that I had. I used to be a camp counselor in the late 80s in the mtns of western North Carolina. We had an overnight trip that we used to take the campers on where we would lash 12 canoes together into a barge and spend the night on lake Fontana sleeping in the canoes out on the lake. We pulled our barge up into a finger of the lake and anchored up for the night. About 9 PM just as it was getting dark and we were settling in, one of the campers turned and yelled "LOOK!"

As we whipped around we saw the first of 2, F-15s (I believe) dipping down over the trees and heading towards us up the canyon that we were camping in. Followed about three seconds later by another. They buzzed us at what seemed like 50 ft although in reality it was more like 300 ft I am sure. They went straight over head and then the sound hit us. It was like nothing I had ever heard. Reflecting off the water and reverberating in the canyon it was deafening even with your fingers in your ears. As they sped away from us down the lake we saw them turn to climb and light the after burners. Absolutely amazing and one of those times that I was awestruck by human accomplishment. We had to convince some of the campers that they weren't UFOs. 20 years later and I remember it like it was yesterday.
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Re: How airplanes fly
Posted by: Don C
Date: April 19, 2009 08:10PM
Actually, I was telling you everything I know about how airplanes fly, which makes REALLY CLEAR how little I know about how airplanes fly. The fact that the planes in the show were doing things that I cannot explain makes it perfectly clear how little I know!

The B-1 and B-2 bombers have visited this show in years past and they definitely are impressive. A couple of years ago, a plane flew in from North Carolina (maybe), did a couple of fast passes, then a couple of slow passes, then headed down to Dallas to do the same thing. Pilot was probably back in the barracks before dark.

Our technology is truly amazing and I am SO glad that we have people who know how to do these things! Between the bombers, warthogs, gunships, and helos I am very pleased to have them on MY side.
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Re: How airplanes fly
Posted by: mrbigstuff
Date: April 19, 2009 08:27PM
Once upon a time in the early or mid 1990s, near Otis Air Force base on Cape Cod, the sky turned black for a few seconds, a deafening roar was heard, bags being held were dropped, ears covered - and it was all over in a matter of seconds. It was no more than a few hundred feet above ground. To this day, I do not know what plane that was overhead. But, it was huge. I believed it was flying so low as to be less visible to the public. Speculation was a stealth bomber, but it seemed larger than that.
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