THE COANDA EFFECT Ref. Jef Raskin's Webpage Coanda Effect: Understanding Why
If a stream of water is flowing along a solid surface
which is curved slightly away from the stream, the water will tend
to follow the surface. This is an example of the Coanda effect and
is easily demonstrated by holding the back of a spoon vertically under
a thin stream of water from a faucet. If you hold the spoon
so that it can swing, you will feel it being pulled toward the stream
of water. The effect has limits: if you use a sphere instead of a spoon,
you will find that the water will only follow a part of the way around.
Further, if the surface is too sharply curved, the water will not follow
but will just bend a bit and break away from the surface.
The Coanda effect works with any of our usual fluids,
such as air at usual temperatures, pressures, and speeds. I make these
qualifications because (to give a few examples) liquid helium, gasses
at extremes of low or high pressure or temperature, and fluids at
supersonic speeds often behave rather differently. Fortunately, we
don't have to worry about all of those extremes with model planes.
|A stream of air, such as what
you'd get if you blow through a straw, goes in a straight line
|A stream of air alongside
a straight surface still goes in a straight line
|A stream of air alongside
a curved surface tends to follow the curvature of the surface.
Seems natural enough.
|Strangely, a stream
of air alongside a curved surface that bends away from it still
tends to follow the curvature of the surface. This is the Coanda
Another thing we don't have to wonder about is why
the Coanda effect works; we can take it as an experimental fact. But
I hope your curiosity is unsatisfied on this point and that you will
Coanda and Flight
Many scientists have recently begun using the COANDA EFFECT
to at least partially explain how planes fly. Ref .
For a long time many people believed (and many people
still do) that LIFT during flight is achieved due to something called
the Bernoulli Effect. This theory suggest that air moving across a wing
moves more quickly over the top than underneath. This creates an area
of lower pressure on top of the wing in comparison to the underside of
the wing. Thus, less pressure pushes down on the wing and more pressure
pushes up and consequently LIFTS the craft into the air…
However, many scientists disagree with this explanation!
Is it time to say good bye to Bernoulli's principle
while speaking about a lift of wing? My interpretation
can be found here.
Some scientists have suggested recently that due to
the shape of a planes wing, air moving along it due to the COANDA
EFFECT will be deflected downwards as it leaves the wing and thus
push the craft up into the air (due to NEWTONS THIRD LAW OF MOTION)
and consequently assist with LIFT
What is the Coanda effect?
|Displayed above is an image of a girl and a few soldiers. Soldiers
are marching forward in straight line. Each soldier holds hand of
his neighbor. Suddenly outsider soldier caches a hand of a girl standing
on a sidewalk.
See what happens. This is simplest explanation of
Note: it is assumed, that "soldiers" are some fluid
elements, not single molecules.
Very simply, the COANDA (or ‘wall
attachment’) EFFECT is the tendency for a moving fluid (either liquid
or gas) to attach itself to a surface and flow along it.
One way of explaining this effect is to understand that
as a fluid moves across a surface, and certain amount of friction (called
skin friction) occurs between the two surfaces (friction is that force that
slows down or prevents two surfaces from moving across each other). This friction
tends to slow down the fluid as it moves across the other surface. This resistance
to the flow of the fluid will then pull the fluid towards the other surface,
making it stick to it… even as it bends around corners! Ref .
Information courtesy of Saulius Pakalnis, Research Support Technologies (researchsupporttechnologies.com)