How was the concept of bicamber
technology discovered?
The first discovery was applying the idea of concave
surfaces, both front and back to a canoe paddle.
This was to allow cupping of the water whether the
paddle was being stroked forward or backward. I found
that I could hold the paddle at an angle other than
flat to the stroke and avoid the need for J- stroking
while propelling the canoe straight in winds and
currents. Normal paddles when held at an angle other
than flat to the stroke, stall out; i.e. lose their
grip in the water and forward propulsion is impossible.
It became apparent that my unusual, dog bone shaped
profile was providing aerodynamic performance that
is impossible with typical flat or airfoil shaped
paddle blades. It wasn’t stalling out at angles
of attack around 60 to 90 degrees.
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If a concave surface having
two raised humps can provide improved aerodynamic
performance, would more humps and more concaves be
even better?
Not necessarily. In fact it would likely be worse
because repeated changes in direction will tend to
cause more turbulence. When air flows over a surface
presented at an angle to the air the flow is initially
pulled down toward the center of the surface and
then away from the surface as it passes the center.
This behavior is evident in the fact that leading
edge bubbles will accompany trailing edge separation
just before full separation and stall. It is visible
in flow experiments with dynamic stall, and in the
location of cavitation erosion. Fluid naturally tends
to make this first dip toward the airfoil center,
but subsequent dips aren’t, to my knowledge,
demonstrated in any experiments or observations.
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Is it really necessary to
have a concave on the bottom? Would a concave only
on the top provide the same benefits?
Patents for single concaves on the upper surface
were awarded in the first half of the twentieth century,
about 1930. These were not adopted to common practice
and apparently were not successful for some reason.
We experimented with single upper airfoil concaves
and found they had better lift than traditional airfoils,
but were not stable and seemed to produce a lot of
drag. We concluded that the single concave produced
an airfoil camber that was not beneficial in reducing
drag and had the bad habit of making the airfoil
very erratic as the angle of attack changed. By matching
the upper concave with a lower concave the nice smooth,
single curved camber of the very best traditional
airfoils can be retained for stable operation at
all angles of attack.
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Are there any structural disadvantages
to the thin central portion of the Bicambered™ airfoil?
Structurally, the Bicambered™ airfoil has
as much cross section area as comparable traditional
airfoils. There is less area in the center, but a
bit more in the tail section. Structurally it is
better to locate mass toward the outer extremes which
the Bicambered™ airfoil does. An I beam is
an apt example. The forward thicker portion is closer
to the leading edge and the rear thicker portion
closer to the trailing edge making a stronger frame
type object.
There may be disadvantages of design of a wing, such
as where to locate wing internal parts like tanks and
landing gear, or how to clear the concave upper surface
of water or ice, but these are application design problems
that should be easily solved, and may even provide
unforeseen opportunities.
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