Comments on: How Planes Fly: What They Taught You In School Was Wrong

By: BuLLDoSer

BuLLDoSer — Mon, 25 Jan 2010 18:24:29 +0000

Hi there! I really like your article it has many interesting things very useful and attractive.Keep up the good work.

By: PaperAirplanes

PaperAirplanes — Sun, 13 Dec 2009 13:26:45 +0000

Thanks for clarifying that. The title grabs attention too.

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By: Kevin

Kevin — Tue, 17 Nov 2009 02:07:43 +0000

Yay! At least one person has it right! This would be my comment, but “Name” beat me to it.

By: ckenterprises

ckenterprises — Thu, 29 Oct 2009 14:45:12 +0000

This post seems to make sense, however it does not explain the lift v/s drag curve for airfoils. If lift depended only on the angle of attack then the lift should not go down after fifteen or eighteen degrees (Angle of attack).

By: cabrinha

cabrinha — Fri, 04 Sep 2009 22:44:52 +0000

Its the same thing.Wings force air downward(Hence creating more pressure on the bottom), which in turn force the wing (and therefore the plane) upward.That's it so what's the big deal?

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Osas_Odeh — Tue, 01 Sep 2009 01:09:06 +0000

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By: Name

Name — Tue, 28 Jul 2009 12:02:46 +0000

The lift generation comes out from the mathematical solution of the differential equations that describe the flight phenomenon. These are the so called Navier-Stokes equations. The Bernoulli principle is an ideal subset of Navier-Stokes that cannot fully describe the actual phenomena in a lifting body or airfoil or 3D-wing. By solving the Navier-Stokes in 2D or 3D one can actual see how pressure side and suction side of a wing co-operate in order to produce lift, together with the remaining aerodynamic field (temperatures, vector velocities, entropy etc. etc.). So, in conclusion there is no straightforward explanation of “how planes fly” and no wrong or correct school explanations, but incomplete explanations. Only by solving the above mentioned differential equations in an appropriate grid and with the appropriate solid & boundary conditions will understand flight.

By: Name

Name — Tue, 28 Jul 2009 08:02:46 +0000

By: Susan Pinochet (spinochet) 's status on Monday, 27-Jul-09 12:38:08 UTC - Identi.ca

Mon, 27 Jul 2009 12:38:18 +0000

[...] Why Planes Fly http://danielmiessler.com/blog/why-planes-fly-what-they-taught-you-in-school-was-wrong [...]

By: Tim

Tim — Mon, 27 Jul 2009 08:33:06 +0000

"Ask yourself why planes can hang tons of massive crap (engines, bombs, etc.) off of the bottom of their wings if the bottom of the wing is so important for flight."

Engines take up only a small fraction of the underside area of the wing, and are much easier to reach for service there. Bombs -- well, where else would you put them? on top of the wing? :-) Besides, no matter what you do, no matter which theory of flight you believe, or where you put it on the airplane, "tons of massive crap" is both (a) not going to increase lift, and (b) necessary for the aircraft to do its job. Observing that your 767 has a giant engine under the wing does not, alone, contradict Bernoulli.

"This also explains how planes can fly upside down."

Not really -- unless I'm mistaken, the Bernoulli theory can also be applied here.

"wings have a downward slope at the rear of the wing, which forces large amounts of air from the top of the wing downward"

Practical experience shows me the opposite: a paper airplane with a downward sloping wing dives straight into the ground. Every paper airplane I've ever seen that's flown more than 2 feet has had either an upward-sloping or level wing. Where's Coanda now? :-)

I'm not saying you're wrong, or that Coanda isn't true, or that Bernoulli is, but I don't find the evidence you've presented to be compelling. (I don't know what to believe, but I'm not an aerospace engineer so I don't think it's important for me to believe in one theory. I have no strong feelings on the matter.) But "extraordinary claims require extraordinary evidence", and contradicting all of my physics textbooks is, I think you'll agree, a rather extraordinary claim.

By: What You Learned About How Asparagus Works Was Probably Wrong « Joe Doliner

What You Learned About How Asparagus Works Was Probably Wrong « Joe Doliner — Mon, 27 Jul 2009 08:22:05 +0000

[...] This post was inspired by an old Daniel Miessler post which surfaced yesterday on Hacker News entitled “ Why Planes Fly: What They Taught You In School Was Wrong .” [...]

By: Esteban

Esteban — Mon, 27 Jul 2009 02:52:23 +0000

I always thought it was like you say, never heard of the Bernoulli Effect maintaining planes in the air.

By: Jordan Bettis

Jordan Bettis — Mon, 27 Jul 2009 02:28:58 +0000

Not only is the Coanda effect largely irrelevant to the aerodynamic lift produced by wings, but water following a curved surface has nothing to do with Coanda (it's caused by surface tension).

You're guilty here of doing the same thing the Bernoulli explanation does: taking a partial truth, and papering over the gaps with untruths.

By: SciTech

SciTech — Sun, 26 Jul 2009 22:23:11 +0000

I don't see how this explains upsidedown flight. Won't he invertd wing force air up and push the wing down only the the angle of attack will stay the same?

By: ack

ack — Sun, 26 Jul 2009 21:07:57 +0000

from the flu.edu link:

"The role of the angle of attack is more important than the details of the airfoil’s shape in understanding lift."

kinda sums everything up neatly in my book

By: Name

Name — Sun, 26 Jul 2009 19:01:59 +0000

I'd like to make it plain, before replying, that I am not an aerodynamicist, and am therefore attempting to referee a "battle of experts" from a position of student rather than teacher. This raises a significant danger of this becoming a typical Internet physics debate. Nevertheless:

1) [the "appeal to experts" part] I will note that both pages you linked use only the briefest references to Coanda, whereas See How It Flies spends several pages discussing it. In particular, SHIF lists a series of predictions that "Coanda causes lift" would imply, and the the evidence to the contrary (18.4.4 "Fallacious Models of Lift Production"). When one teaching source mentions something superficially in one diagram, and another spends several pages exploring it (including examining predictions, etc), it is circumstantial evidence that the second may be a fuller explanation.

2) [the "appeal to common sense" part - Danger, Will Robinson!] As the Coanda effect relies upon the existence of a curved surface, it does not explain why the proverbial flat barn door actually performs as a pretty decent wing. At very least, then, this would suggest that Coanda is only a minor part of what makes some wings fly.

By: Daniel Miessler

Daniel Miessler — Sun, 26 Jul 2009 18:35:25 +0000

I see your av8n.com link, and raise you an Aeronautics Learning Laboratory link:

http://www.allstar.fiu.edu/aero/airflylvl3.htm

You'll find that the link above, combined with the physics lecture
done at Fermi (also linked in the article) will contradict the link
you posted. I think you should reconsider.

By: Name

Name — Sun, 26 Jul 2009 18:09:36 +0000

Sorry to rain on your parade - but the Coanda effect isn't the real cause of aerodynamic lift either. There's a reasonable-but-very-accessible explanation in the (online) pilot's textbook I use:

http://av8n.com/how/htm/spins.html#sec-coanda

The author is a flight instructor and physics professor. Take a look - the whole book is free online, and very engaging. (The main "how a wing works" section is in chapter 1)

By: Daniel Miessler

Daniel Miessler — Sun, 26 Jul 2009 17:01:11 +0000

Not as sorry as I am.

By: rajneesh

rajneesh — Sun, 26 Jul 2009 16:33:53 +0000

well, what about rudders, aren't they curved as well?

By: moschops

moschops — Sun, 26 Jul 2009 16:32:40 +0000

A plane with a flat wing will also fly; it is all about pushing air downwards at the wing, but the air above the wing is not being pushed down by the wing, but by the air above. The underside of the wing is doing very serious business in the field of pushing air downwards.

By: EvilCON » Why Planes Fly: What You Learned in School Was Probably Wrong

EvilCON » Why Planes Fly: What You Learned in School Was Probably Wrong — Sun, 26 Jul 2009 15:31:59 +0000

[...] is quite interesting. The reason planes fly is different from what most of us were taught in school. It’s not totally different but enough so that it fills in the gaps in my understanding of [...]

By: mr Swordfish

mr Swordfish — Wed, 24 Jun 2009 02:48:26 +0000

This pretty much nails it. Air goes down, plane goes up. It's really very simple.

The same thing happens with sailboats - air goes backwards, boat goes forward.

Of course, to do serious engineering you need a more sophisticated model - Partial differential equations in three dimensions, vector fields that solve those equations, boundary conditions such as the Kutta condition, surface integrals to compute the total force, and yes the Bernoulli's principle to convert the velocity vector field to pressure. But all this complicated math can obscure the simple physical principle - the wings generate lift by forcing the air downward.

By: mr Swordfish

mr Swordfish — Wed, 24 Jun 2009 02:47:52 +0000

By: Seun Osewa

Seun Osewa — Fri, 19 Oct 2007 13:42:08 +0000

Not convinced. Sorry.