An Alternate Theory of Lift
Some High School Physics
If you look in high school physics text books
you may find a couple standard diagrams
This diagram supports the theory
that since air flows faster over the top of the wing
and slower under the bottom of the wing.
the pressure on the top falls
and therefore the wing rises.
You may recall seeing this diagram in high school.
You may also recall a feeling of confusion
and having trouble connecting all the dots.
In the same books, we find the large-to-narrow pipe diagram
along with a "proof" that high velocity and low pressure go together.
You can see the math at Note 1, below.
for cases involving air that actually moves around,
attempts to use Bernoulli's Principle
that fast air goes with low pressure
And By the Way,
Bernoulli Theory requirement about constant density,
Radial Momentum Offers a Better Explanation
Radial Momentum Explanation:
as the air fans out radially from the center of the device
it expands into larger and larger volumes
and so it gets less and less dense.
This lower density explains the lower pressure.
The cone collapses and the tube does not collapse.
This indicates that air fanning out goes with pressure drop
and that fast or slow air makes little difference.
The Cone Collapses
The Tube does not Collapse
To further test this out, I construct a more formal levitator table
from a big piece of see-through plastic
with which I can measure the air flow and pressure.
Fancy Levitator Table
See the flow meter on the left
and the pressure meter on the right.
View from Underneath
The air flows through a 1/8" orifice in the table.
I try my
levitator table with various kinds of playing cards
I find they all stick to the bottom of the table
blow air down the hole onto the cards.
The smooth plastic disks stick too.
Then, to test a hunch, I construct some special disks - ones with channels.
The channels can force the air
to flow in different ways.
Detail of the Hourglass-Channel Disk
I then try these disks with my levitator
to see what happens.
All the disks stick to the levitator
when I put the smooth side up.
When I put the channel sides up,
all of them stick - except for one of them.
The one that does not stick
has the parallel channel.
This one, and only this one, does not allow
radial expansion of the air.
This further substantiates my theory
that Radial Momentum, not air speed
The Professor and His Business Card
I show my results to a professor from a nearby college.
He specializes in fluid dynamics and he says he thinks I'm crazy.
He says my theory goes up against 300 years of science
and that there is no way I can have it right.
Furthermore, he shows me a pile of final exam papers
from his graduating college seniors.
out the errors in the exams,
since these errors trace directly back to his teaching.
As I proceed, I notice, he appears to consider me
He tells me, with impatience and disdain,
about high velocity going with low pressure.
He suggests I build a table with a slit, rather than a hole.
The slit would broadcast air in a linear ribbon
that does not expand radially.
He says that when I see the card sticking to the slit,
I would have to abandon my theory,
develop some humility
The Business Card Levitator Experiment
I build the experiment according to his suggestion.
The Slit Levitator
The air enters through the fitting at the right
and emerges out of the slit that holds the card.
In operation, the card sits flat on the bed
between the "headboard and footboard."
To make it all the more dramatic,
I use one of the professor's own business cards
as the test pilot.
I turn on the pump and begin the experiment.
The card does not stick to the equipment.
This lends further evidence that Radial Momentum
and not air velocity correctly explains
lift in the levitator.
I call the professor with the good news
that he and all his students have it wrong.
He does not sound very happy to hear the news.
He does not want to discuss the matter further with me.
I do not know if he still teaches his seniors about the levitator.
Fun with Water
I run further experiments with water.
The results turn out much more vivid.
Parallel Channel Water Nozzle
Hourglass Channel Water Nozzle
The Hourglass Works as a Levitator
Again, the parallel channel does not levitate.
I get a much stronger effect with water
since water has less compressibility,
pulling water molecules apart, even a little bit,
Some Theory: The Ring of Air
The Ring of Air
The Theory of Radial Momentum holds that fluid, once in motion,
expands out radially, by momentum,into larger and larger rings of air.
When the same mass of air occupies a larger volume
its density drops and the pressure goes down with density.
I build a computer model, using Radial Momentum as the organizing principle.
Computer Model Output
The model shows the pressure, velocity, density, mass and mass flux
running from the center of the disk (left) out to the edge (right).
The model shows the pressure drops right around the center
in a region I call the active zone.
The pressure reaches a minimum in a ring around the central orifice.
imparting additional radial momentum to the particles.
As the fluid particles continue radiating outward from the center,
the fluid becomes less dense and the pressure falls.
As the particles flow past the minimum pressure ring,
they experience back-pressure that tends to slow them further.
The velocity continues to fall until the Radial Momentum dissipates,
the pressure rises to slightly above ambient pressure
and the fluid gently drains out at the edge of the disk.
The Cavitation Ring
According to the model, the lift effect occurs
in a small active region around the center of the disk.
I begin searching for evidence of this ring.
I take the equipment outside into my back yard
where I can use water.
Portable Levitator with Water as the Fluid
The jet travels about 30 feet.
If you hold your hand in front of it, it deforms your hand
and feels painful.
Close-Up of the Portable Levitator
The water emerges through a small hole in the center of the disk.
Bringing the Disk up to the Levitator
The stream of water hits the disk and sprays everywhere.
The stream also pushes the disk away with considerable force.
Note: experimenters sometimes have to subject themselves
back splash and other hardships in the pursuit of scientific knowledge.
disk comes flush with the levitator, the levitator suddenly "captures" it.
stick together with several pounds of force.
Consistent with the Radial Momentum model,
the water gently emerges from around the edge of the disk.
Levitation, Another View
I use my left hand only to keep the disk from sliding to the side.
apply little or no upward pressure on the disk.
The stream of water from the hose levitates the disk.
It Works Under Water
I test the effect under water,
and I find the effect still works.
Without the levitation effect holding the disk to the levitator,
the water jet from the hose would shoot back out of the dish.
Looking for the Ring
This Image Shows the Underside of the Levitator (see the orifice above thumb).
I first run the test at low pressure, by crimping the hose.
I notice a faint white ring around the central orifice.
I figure this indicates tiny air bubbles,
emerging from the water as the low pressure sucks them out.
Turning up the Flow
I let the
hose go a little bit, increasing the flow.
The cavitation ring becomes bigger and whiter.
Even More Flow
The ring gets bigger and whiter.
I let the hose go, full on.
The ring gets even bigger and whiter.
Water on the Back of a Dish
You can see a very thin low-lying layer of water
in the "active region" in the center of the dish
and a "hydraulic jump" a couple inches from the center.
This profile matches that of the levitator.
Jet Aircraft with Trailing Ring
According to the Theory of Radial Momentum
divert the air into a radially expanding pattern
that forms an expanding cone along the nose-to-tail axis.
This results in a decrease of pressure and temperature
active regions behind the cockpit and at the tail.
interact momentarily to generate a visible cloud.
Flow Versus Pressure for a 3.9 oz. Disk Using Air
I take some actual measurements on the levitator table
to compile a flow-versus-pressure chart.
For low head pressure (from the pump)
I see a flow of about 2.5 standard cubic feet per minute.
As the pressure rises, the flow actually decreases!
This phenomenon has to do with the levitation effect
as the disk moves closer to the levitator
restricting the flow.
Radial Momentum explains Levitator lift.
Fast or Slow air has little to do with it.
The Bernoulli Equation has to do with energy balance.
It does not apply to the levitator.
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