Hi Joe,
Thanks very much for the great video of the Magnus Effect cylinder balloon kite for producing a pumping motion.
I can explain how to possibly improve that concept.
I
invented a 3-sided, self-spinning rotor called a Sharp Rotor. It
requires no motor or windmill to spin it. Each of the three sides is
shaped like the top surface of a very thick wing, with a great deal of
camber at the leading edge, and reverse camber at the trailing edge. It
uses two end discs to increase the lift coefficient. Basically, it is a
3 sided version of a flip-kite (rotor kite; Donaldson rotor, etc.) It
creates high lift at a spin ratio of 1. (A spinning cylinder creates
little lift at a spin ratio of 1.) If spun faster using external power,
it will increase its lift like a Flettner Rotor (spinning cylinder with
end discs). In free flight, it flies twice as far as it falls, so it
has a lift to drag ratio of 2 to 1 in small sizes. In larger sizes, the
L/D may improve. I have made and flown a lot of paper models and the
lift is impressive; it may be higher than I’m guessing (Cl = 2). I have
a whip-stick model that demonstrates that high lift, and when I can
walk easily again, I’ll make a video of it.
At
a spin ratio of 1, the lift of a Sharp Rotor is due to the Katzmyer
Effect rather than to the Magnus Effect. When a wing is increasing its
angle of attack, the stall angle increases. For the Sharp Rotor, the
stall angle of the top surface is always increasing, so the rotor
doesn’t experience any stall. Most two-sided rotors experience a
momentary stall during part of their rotation, and a loss of lift.
That’s why they vibrate so strongly when tethered.
My
paper models can be thrown upward underhand, and they do a forward loop
and come back to me so that I can catch them. The diameter of the loop
is bigger than for a two-sided rotor, and that seems to be due to the
difference in weight. (I patented a 2-sided rotor with dihedral to give
it some increased stability in free-flight. It was much thicker at the
ends than in the middle, so from the front it had an hour-glass shape.
It demonstrates the much greater lift due to the top of the wing than
the bottom of the wing. A similar model with the opposite dihedral
(thick in the middle) is completely unstable. (Yet somebody patented it
as a flying toy, apparently without ever testing it.)
When
pre-spun using a rubber-band launch, the distance a Sharp Rotor can fly
is just a bit farther than a Flettner Rotor launched the same way. They
both initially do a fast, tight back loop before beginning to glide
forward. My paper models are about 11” wide, with end discs made of
paper.
A
Sharp Rotor could be used as shown in the case of the motorized tube
balloon – to create an oscillating pulling force. The lift of the Sharp
Rotor can be eliminated by braking it to stop its rotation. It produces
very low torque, so it is easy to brake. Because it does not require
anything else to rotate it, it can be cheaper, safer, and more reliable
than a motorized tube balloon.
However,
there are other ways to use Sharp Rotors as kites that should be much
more efficient. It’s main advantage is that it can create very high
lift while also providing high buoyancy if filled with a tube bag or
multiple, round, balloons, filled with helium. If the end discs rotate
independently of the body of the rotor, the rotor can take off from the
ground, and land on the ground (or the surface of a body of water if
the end discs provide enough flotation). That means that, on water, it
need not be lighter than air, because it can orient to the wind and
launch and land itself.
Another
advantage is that it does not vibrate when rotating -- like two-sided
rotors. So, for example, it can be used as the blades of a buoyant horizontal axis windmill
(no need for a supporting kite). In order to generate electricity,
small HAWT could be mounted out beyond the outer tips of the blades.
Those HAWT would function as an “aerodynamic transmission”, as they do
on the Makani Power Kite. When forced through the air, they would
produce a great many times as much energy as they would if they were
stationary. And due to their very high rpm, they could be small and
light.
A simpler and cheaper approach to using Sharp Rotors as the blades of a buoyant horizontal axis windmill
would be to cause the windmill to twist the cords of a
twist-cord-accumulator/transmission, or TCAT. The twist cords would
double as the tether. When the torque of the twist cords became high
enough to overcome the resistance of the magnetic release catch on the
generator shaft, on the ground, the generator would briefly spin at a
high rpm. The rpm of the generator would be the same regardless of the
wind speed. It would just spin more often in higher wind speeds. A TCAT
is not efficient, but it is dirt cheap, and the bottom line is the cost
of the energy. In high winds, the rotor blades could be allowed to tip
away from the wind to lose power and lower the total rotor drag. So the
windmill could remain aloft during high winds.
Sharp
Rotors might work well to create a practical version of something
closely similar to the original ladder-mill concept. Sharp Rotors would
be mounted on a loop, like the stairs of a ladder. Small, horizontal
tail vanes could be mounted at both ends of each rotor. When the rotor
was rising, the tail vane lever would move downward and release a brake
so as to let the rotor spin freely. Once the rotor passed the top of
the tall ladder-mill loop, and started to be pulled downward, the
tail-vane lever would move upward and apply a brake to stop the rotor
from rotating, thus eliminating its lift. The rotors would all be
slightly more than neutrally buoyant. I’m not yet sure how to provide
safe overspeed control, but I have some ideas.
The
rotor’s blade skin could be fabric stretched over a frame made of bent
wood, fiberglass, or carbon fiber. Inflating the internal balloon would
be used to provide rigidity.
The
smooth curves of the rotor surfaces could probably be replaced with
straight sections, thus further reducing the cost and further
simplifying construction.
A
Sharp Rotor toy (maybe 3 or 4 feet wide) filled with helium would be
great fun because it could glide extremely slowly, and it could glide
on the updraft from a single hand moving along beneath it. Blowing on
it from behind would cause it to sink quickly. On a windless and sunny
day, it could probably glide along in level flight from the air rising
off of an asphalt street. It would look like a very strange drone
flying down the street, with no apparent means of propulsion.
Here
is an interesting physics factoid. If a DWFTTW land yacht uses a
propeller that has Sharp Rotors for blades, the horizontal axis rotor
will function as a windmill initially to spin the wheels and accelerate
the land yacht from a standing start just like a normal windmill
vehicle sailing directly downwind. Then at a downwind speed of roughly
0.6 times the speed of the wind, the wheels will begin to spin the
horizontal axis rotor. So the horizontal axis rotor will function as
both a windmill and a propeller simultaneously. The Sharp Rotor blades
need not make any pitch changes because they are always at their
optimum “pitch angle”. As the land yacht exceeds the speed of the wind
(if it can do so given the high drag of the Sharp Rotor blades), the
horizontal axis rotor functions as a pure propeller. Everything would
be automatic because no changes would be needed to the “pitch” of the
Sharp Rotor blades.
Best Regards,
Peter A. Sharp
From: AirborneWindEnergy@yahoogroups.com [mailto:AirborneWindEnergy@yahoogroups.com]
Sent: Sunday, August 28, 2016 12:33 PM
To: AirborneWindEnergy@yahoogroups.com
Subject: [AWES] The search for a high flying clean energy generator
