TWL: Bernoulli effect is not why wings fly
Subject: Re: TWL: RE: Bottom Effect
To: elnav@uniserve.com, trawler-world-list@lists.samurai.com
Message-ID: 12a.2fa2755d.2c6d1291@aol.com
Content-Type: text/plain; charset="US-ASCII"
I will go with the Bernoulli principle as an explanation.... This is also
the same thing that makes an airplance fly and is applicable to all fluids.
While this is the most popular reason given as to why an airplane flies
(it's easy to understand) the Bernoulli principle actually has very little
to do with why a wing flies. A wing flies because it pushes air down. It
flies for the action-reaction reason. Bernoulli's principle contributes a
bit in some wing designs as to why the wing pushes air down, but it's
actually a very minor contributor.
If you doubt this, then ask yourself why the totally symetrical wings of an
aerobatic airplane fly. There is no Bernoulli effect at all on these wings
as the upper and lower surfaces have equal curvatures, and equal chords
(wing widths). But the wings of aerobatic airplanes generate as much lift
flying upside down as they do rightside up. They have to, otherwise the
airplane could not maintain level flight upside down, which of course, they
can.
I once saw a diagram as to what shape of a 747 wing would have to have in
order to fly using the Bernoulli effect. The upper curve of the wing stood
up nearly as high as the top of the tail. This was what the distance
difference would have to be between the upper and lower surfaces to
generate enough pressure differential to support the airplane. Of course,
such a wing would't fly for a lot of other reasons, the largest being the
stupendous amount of drag it would generate which could never be overcome
by the engines. So you'd never push the wing through the air fast enough
to generate sufficient pressure differential to get the thing off the
ground anyway.
So as much as many physics books and the accepted theory of flight preach
the Bernoulli effect as the reason wings fly, it is in fact not why wings
fly at all. They fly for the simple reason that they push air down. A 747
that weighs 800,000 pounds pushes air down with a force of 800,000 pounds.
That's why it flies. It does not generate 800,000 pounds less pressure
above the wing as below it.
The reason wings push air down is extremely complicated and the aerodynamic
forces that combine to do this have a very complex relationship, some of
which are still not fully understood. But the bottom line is that a wing
flies for the same reason that if you stand next to a table and push down
on it with your hand, if you push down hard enough, you will lift your body
off the floor. Advanced aerodynamicists knew this as early as the 1930s,
but the Bernoulli thing is easier for everyone to understand, so that's
been the common explanation used. But it is, in fact, incorrect.
C. Marin Faure
GB36-403 "La Perouse"
Bellingham, WA
You are correct! This is one of the most mis-stated explanations in the modern world.
Richard Kumferman
"C. Marin Faure" wrote:"
the Bernoulli principle actually has very little
to do with why a wing flies. A wing flies because it pushes air down. It
flies for the action-reaction reason. Bernoulli's principle contributes a
bit in some wing designs as to why the wing pushes air down, but it's
actually a very minor contributor.
Am I to understand that my high school science teacher
was wrong when he stated that the reasons planes fly
is because of the low pressure area on the top of the
wing lifts the plane. Now if I understand this
correctly, that is not the case, (or only a minor
reason) in reality the wing pushes the plane up into
the air?
Where's Mr. Wizard when we need him?
Leo
--- Richard Kumferman rpkesq@earthlink.net wrote:
You are correct! This is one of the most mis-stated
explanations in the modern world.
Richard Kumferman
"C. Marin Faure" wrote:"
the Bernoulli principle actually has very little
to do with why a wing flies. A wing flies because
it pushes air down. It
flies for the action-reaction reason. Bernoulli's
principle contributes a
bit in some wing designs as to why the wing pushes
air down, but it's
actually a very minor contributor.
To Unsubscribe send email to
trawler-world-list-request@lists.samurai.com
Include the word "Unsubscribe" (and nothing else) in
the subject or body of the message.
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software
http://sitebuilder.yahoo.com
Ooo I can't ignore that one.
ALL the technical literature and airfoil profile design techniques are based
on the Bernoulli principle. The early days of cambered wings to "push air
down" died about the time of the Wright brothers experiments. The
inefficiency of dragging a wing tilted sideways to give lift means you only
use it if you have to, like when the flaps are extended on take off or
landing and overall efficiency is not so important.
The actual fact is that lift is created by suction above the wing, NOT by
pressure below as you are proposing. The bottom of a typical wing is flat
and HORIZONTAL while there is a convex curve to the top. This means the air
passing over the top has to travel further to arrive at the trailing edge so
it travels faster and the reduced pressure creates a SUCTION on top of the
wing.
And I did stay in a Holiday Inn last night.
Andina Foster,
tech@yandina.com
You are correct! This is one of the most mis-stated explanations in the
modern world.
Richard Kumferman
"C. Marin Faure" wrote:"
the Bernoulli principle actually has very little
to do with why a wing flies. A wing flies because it pushes air down.
It
flies for the action-reaction reason. Bernoulli's principle contributes
a
bit in some wing designs as to why the wing pushes air down, but it's
actually a very minor contributor.
snip> Now if I understand this
correctly, that is not the case, (or only a minor
reason) in reality the wing pushes the plane up into
the air?
Where's Mr. Wizard when we need him?
Leo
Try http://science.howstuffworks.com/airplane2.htm. Poor Dr. Bernoulli, so
misunderstood. Your going to need a lot of math. C. Marin Faure gave a
great and accurate overview may be easier to re-read his post.
And for my part, all boats exhibit the "Banks" effect to some degree in any
depth of water. Its most pronounced when in shallow water because the water
cannot fill in fast enough. Watch a Hatteras Sport fisherman at full plane.
They dig in pretty deep and you can hardly see the transom viewed from the
side. Many displacement boats when over powered and pushed beyond the hull
speed begin to squat down considerably while trying to get over the bow
wave. It not just the bow being pushed up. Even when I start my dinghy to
get up on plane, it digs in (I understand there are planes that fit around
the outboard that help this)
Skooch
Hatteras LRC 42
Worton Creek MD
David Stahl
Beacon Technologies Inc.
Serving The Delaware Valley
Business and Residential Internet Services
Not "all" the technical literature and airfoil design technique are based on this. It is a
combination of two actions. First and foremost, "angle of attack" is required. This is the
angle of the wing centerline cord to the relative airflow. Without a proper "angle of
attack" the wing cannot "bite" into the airflow. This then allows a pressure gradient to
develop, higher on the bottom and lower on the top surfaces of the wing. (unless we are
flying inverted!) Airfoil design has much more to do with maximizing the lift vs. drag than
creating the lift in the first place. Most wings on all but the simplest aircraft are not
flat on the bottom, but subtly curved to increase efficiency. One cannot create a suction
above without a push from below in the earth's atmosphere (normal air pressure is the push
from below), without the angle of attack to cant the wing in to the airflow this will not
happen. When a plane is flying at a constant altitude inverted, note that nose must always
point slightly "up", (away from the earth) in order to have this angle of attack. The slower
the airspeed the further the nose must point "up". You might try a different hotel in the
future :)!
"Andina@yandina.com" wrote:
Ooo I can't ignore that one.
ALL the technical literature and airfoil profile design techniques are based
on the Bernoulli principle.
The actual fact is that lift is created by suction above the wing, NOT by
pressure below as you are proposing. The bottom of a typical wing is flat
and HORIZONTAL while there is a convex curve to the top. This means the air
passing over the top has to travel further to arrive at the trailing edge so
it travels faster and the reduced pressure creates a SUCTION on top of the
wing.
And I did stay in a Holiday Inn last night.
The Bernoulli effect helps wings fly, but, it is not the only thing that
helps. How can a plane fly upside down? It's the angle of attack of the
wing. To make the plane efficient, since fuel is limited <grin>, you
design a wing to take advantage of the Bernoulli effect and design the
plane to take advantage of the angle of attack of the wing.
Now one thing I am not sure of is this: if the plane flies slower,
Bernoulli's principle plays a greater role than angle of attack. And if
the plane flies faster, etc..........
Now if someone can convince me that Bernoulli's principle still does not
contribute to the plane flying............... Bernoulli's principle is
essential to the operation of many internal combustion engines!
And, why are we talking about planes??
Regards, Bob Rapasky
The opposite is true. The faster a plane is flown the more Bernoulli has affect, the slower
it is flown the more affect angle of attack has.
Bob Rapasky wrote:
Now one thing I am not sure of is this: if the plane flies slower,
Bernoulli's principle plays a greater role than angle of attack. And if
the plane flies faster, etc..........
Andina@yandina.com wrote:
Ooo I can't ignore that one.
ALL the technical literature and airfoil profile design techniques are based
on the Bernoulli principle. The early days of cambered wings to "push air
down" died about the time of the Wright brothers experiments. The
inefficiency of dragging a wing tilted sideways to give lift means you only
use it if you have to, like when the flaps are extended on take off or
landing and overall efficiency is not so important.
The actual fact is that lift is created by suction above the wing, NOT by
pressure below as you are proposing. The bottom of a typical wing is flat
and HORIZONTAL while there is a convex curve to the top. This means the air
passing over the top has to travel further to arrive at the trailing edge so
it travels faster and the reduced pressure creates a SUCTION on top of the
wing.
And I did stay in a Holiday Inn last night.
Andina Foster,
tech@yandina.com
So how did all those model planes with wings of perfectly flat balsa
(with a shallow angle of attack) that I bought as a kid manage to fly?
KP
Count not the authorities, but weigh their truth.
- St. Thomas Aquinas
Ooo I can't ignore that one.
ALL the technical literature and airfoil profile design techniques are
based
on the Bernoulli principle. The early days of cambered wings to "push
air
down" died about the time of the Wright brothers experiments. The
inefficiency of dragging a wing tilted sideways to give lift means you
only
use it if you have to, like when the flaps are extended on take off or
landing and overall efficiency is not so important.
The actual fact is that lift is created by suction above the wing, NOT by
pressure below as you are proposing. The bottom of a typical wing is
flat
and HORIZONTAL while there is a convex curve to the top. This means the
air
passing over the top has to travel further to arrive at the trailing edge
so
it travels faster and the reduced pressure creates a SUCTION on top of
the
So how did all those model planes with wings of perfectly flat balsa
(with a shallow angle of attack) that I bought as a kid manage to fly?
KP
I didn't say it wouldn't work. I just pointed out that the principle was
primitive and inefficient.
Andina Foster,
tech@yandina.com