Hi JoeF,
Let
me try to explain with more detail the “definitive test”. First, it is
necessary to understand the different dynamics of DS and of
cycloturbines. They don’t work the same way.
DS
works best when a glider (no tether) uses a ridge line or hill to block
air from reaching the bottom part of its vertical back-loop orbit so as
to create the largest possible “wind gradient” (which is actually just
blockage and not a wind gradient as commonly understood). The reason
for that is that is that the glider has no tether. Its looping orbit would be carried downwind
if the hill did not block the wind while the glider was flying in the
upwind direction while on the bottom part of its loop. Because the hill
blocks the wind, the glider can fly forward toward the wind with very
little drag, and while producing enough lift just to support itself. It just glides without capturing wind energy during the lower half of its loop.
So it can glide all the way back to the hill and then swoop upward
above the hill. At that point, the accelerated wind hits it and the
glider develops high lift. That high lift propels the glider both
upward and downwind. Once the glider reaches the top of its orbit, it
starts diving downward. The high lift on the wings propel it downward
and downwind. So by the time it at the level of the hill again, it has
been carried a considerable distance downwind. But it can manage to
glide all the way back to the hill because it is moving at a high
speed, and because it is creating only enough lift and drag to fly back to the hill.
If
the hill were not there, and there were no wind gradient, the DS glider
would not work at all. To work, it would have to be a perpetual motion
machine. That is because it would be blown downwind faster and faster
until it was moving at the speed of the wind, and then there would be
no source of energy to propel it in loops.
If
the wind gradient is steep enough, without a hill, a DS glider can fly
in loops without being carried downwind. But it needs to be a big
difference in the speed of the winds lower down and higher up.
Albatross use DS by flying toward the wind when they are just above the
sea where the wind speed is the lowest. And albatross get some addition
help when near the surface of the sea by using the Katzmayr effect, but
that is another story. As I recall, there is now a drone glider that
can fly like an albatross using DS near the surface of the sea.
Cycloturbines
are stationary, not free flying like a DS glider. So they cannot be
blown downwind. Consequently, they do not require wind blockage on the
advancing side of the rotor. In fact, they produce especially high lift
and torque from the advancing blades. If the wind were blocked from
those blades, there would be a large loss of power.
The
Bird Windmill blade/kite is a cycloturbine with its central axis
horizontal, and with the advancing side of the rotor on the bottom of
its orbit. It uses elastic cords to suspend the blade. Those cords
store and release energy during each revolution, and by doing so, they
significantly increase the efficiency and power. The blade/kite will
still work without elastic cords, but less well. And the blade/kite
will still work if the direction of rotation is reversed with the upper
part of the orbit heading into the wind, but noticeably less well.
Will
a wind gradient increase the power of a Bird Windmill blade/kite? The
answer is yes and no, depending upon what is being compared. Assume a
steady wind speed with no wind gradient and use that as the starting
point. Then, if the lower wind is slowed to create a wind gradient,
that will lower the average speed of the wind, and there will be less
energy. So the blade/kite will produce less power. On the other hand,
if a wind gradient is created by increasing the speed of the wind at
the top of the blade’s orbit, that will increase the average wind
speed, and that will increase the power of the blade/kite.
Now
let’s consider a third option. Keep the average wind speed the same at
10 mph, but make the upper wind faster than the lower wind. What
happens then? Due to the way the blade/kite works, there will be a loss
of power. That is because the blade/kite produces more power from the
lower, advancing side of its orbit than from the upper, retreating side
of the rotor. The reason is that the advancing blade develops more lift
and thrust than a retreating blade, and that is because the apparent
wind speed on the lower part of the orbit is much higher than on the
retreating side of the orbit. People who understand conventional
cycloturbines know that the retreating and advancing sides develop
roughly equal power, but the windward side of the rotor develops 2/3 to
more than ¾ of the power because the upwind blades extract most of the
energy from the wind and slow the wind. But the Bird Windmill is
different from most cycloturbines because it has a very low solidity
ratio and because the blade is suspended on elastic cords. The very low
solidity ratio allows lots of wind energy to reach the downwind blade
pass. In fact, the downwind blade pass produces much more power than
the upwind blade pass. The orbit quadrant that produces the most power
is the downwind, advancing quadrant. That is because, in that quadrant,
both the blade speed is highest and the apparent wind speed is highest.
(The least efficient quadrant is the upwind, upper quadrant.)
So
if the wind is blocked from reaching the lower half of the blade’s loop
orbit, there will be a large loss of power. In lower wind speeds, the
blade will stop altogether because there won’t be enough energy for the
blade/kite to complete its loop. The wind speed needs to be 7 to 8 mph
for the blade/kite to start galloping and then convert to orbiting.
What
this means is that the blade/kite does not work like a DS glider.
Explaining its behavior as due to dynamic soaring is completely wrong.
But
DaveS believes that using a large wind gradient will increase the
power, and thereby prove that the blade/kite operates like a DS glider.
He is entirely mistaken. As compared to the same average wind speed
with no wind gradient, a large wind gradient will reduce the power, not
increase the power, and that is the exact opposite of what to expect
from a DS glider.
So
the “definitive test” I proposed to DaveS is to use a fence or some
other large obstacle to block the wind from reaching the bottom of the
blade/kite’s orbit. If the blade/kite functions like a DS glider, then
it will work much better. But if the blade/kite functions like a type
of cycloturbine, it will work much worse. Simple test with a clear
result.
DaveS
is making an extraordinary claim for which extraordinary evidence is
required. But now DaveS, who never admits when he’s wrong, wants to
change his claim rather than do the test. So rather than do the test
and discover that he is wrong, he now claims that a wind gradient will
increase the power of the blade/kite, and that makes it similar to a DS
glider. But all he is actually saying is that if the average wind speed
is increased, then the blade/kite will work better. But that’s obvious,
and it has nothing to do with the physics of a DS glider. He ignores
all of the other considerations and distinctions that should be part of
the analysis.
The
Bird Windmill is extremely complicated. It cannot be mathematically
analyzed or simulated without spending millions of dollars of human and
computer time. There are still aspects of it that I do not understand.
So casual theorizing about it, based on close to zero knowledge about
cycloturbines, is likely to be way off the mark.
PeterS
From: AirborneWindEnergy@yahoogroups.com [mailto:AirborneWindEnergy@yahoogroups.com]
Sent: Friday, June 21, 2019 6:14 AM
To: AirborneWindEnergy@yahoogroups.com
Subject: RE: [AWES] Peter Sharp's Looping Arch (reposting video link to new topic)
PeterS described a test and write "the definitive test."
As
described, I am holding out and keeping a doubt over whether or not the
described test will be definitive on whether or not dynamic soaring
plays a part in the dynamics of the orbiting arch-held wings. My
reasons for keeping a glob of doubt are not fully settled yet in me;
for one starter: there will be significant rotor wake from the blocking
wall or curtain that will disturb the scene for the arch-held
wings.
