Hi DaveS,
"
Remembering a prime source of "twist-force" is wind turbulence, which
would set swinging and even swat the Z-frame HAWT into a jump-rope
loops. PeterS can always add more stability if he underestimated the
need, “
Yes, the
stability can be increased by changing the relative lengths of the Z
frame triangles so as to increase the pendulum effect and the damping
effect of the tension in the tethers. And, as you observed, a tail vane
could further increase stability. I’ll add a tail vane to my next
iteration just to give the kite some greater margin of stability.
You
are anticipating a galloping effect due to some sort of resonant
condition, perhaps like the Tacoma Narrows Bridge. But you need to
explain the precise physics of how that could happen – otherwise, your
concern is too vague to do anything about it. You need to show
precisely why galloping would be likely. I don’t think that you can. If
you have seen it happen somewhere, please show me.
“
but there are other tricky details to resolve, many hidden
complications. For real pesky examples, the secondary drive-loops on
Peter's HAWT rotor would tend to soon relax, elongate and slip, if not
provided with a tensioning feature; and If the primary loop is a belt,
it will tend to strum strongly in wind, causing lots of excess drag and
negative lift. “
It
would be easy to add tensioners to the belt loops from the ram air
rotors. But I specified using shock cords for those loop belts so as to
keep them tight. I would try those first before adding tensioners so as
to try to keep the weight to a minimum.
“
kPower intends to acquire a KiteWinder unit for testing and collection
by the American Wind Power Museum. It would be great to test KiteWinder
against Peter's version, to settle his open claims. The cheaper lighter
AWES will indicate the better way forward for the small dive-loop HAWT
AWES class. Its hard to imagine a serious fly-off against Makani will
occur. Testing remains core validation best-practice. “
My
goodness! You certainly are being competitive. I just introduced the
concept and already you are challenging me to a “fly off” instead of
trying to improve my design to make it superior to other energy kites.
A
“fly off” is an inadequate comparison because it doesn’t include many
important variables that determine the cost of the energy over the
lifetime of the WECS, such as durability, required maintenance,
production costs, insurance, land use, visual impact, noise, bird and
bat deaths, etc., etc., etc.
---------
"Twist force" is any force that tends to flip over the frame. You seem to relying on tip-rotors to cancel normal HAWT torque, “
Thanks
for defining what you mean by your term “twist force”. Now it
would be helpful if you were more specific about what you mean by “flip
over the frame” since there are various ways for the frame to rotate
(“flip”).
I am
not relying on the tip-rotors to cancel normal HAWT torque. I am using
the tip rotors to avoid creating, in the first place, the usual high
torque that a HAWT rotor creates when it spins its central shaft. But
maybe that is what you meant to say. There is almost no torque created
by the large rotor. The only torque that the large rotor creates is
when energy is transferred to the central pulley to spin it at a high
rpm. But note that none of that torque is transmitted to the Z frame
(except for bearing friction). Wind turbines don’t always need to
create torque in order to capture and transmit energy. Another example
is the Bird Windmill; it can function normally without producing torque.
“
but even if that pans out, I am warning here that there are other
twist-forces, like a simple swinging jump-rope effect, where weak
pendulum or windvane stability is chaotically over-whelmed and the
drive-loop twists. “
You
are again expressing concern that the large rotor will experience a
galloping effect, and that that effect could not be controlled, with
the result that the drive-loop would be twisted. If you can show a
physical mechanism that could cause that effect, please do so, so that
I can solve the problem. Otherwise, you are merely stating the obvious:
that there are usually unexpected dynamics to deal with when a
mechanism has many degrees of freedom. Do I expect unexpected problems?
Of course. Might they be unsolvable? Probably not. But thank you for
the warning.
“
A real prototype of your design would settle if the Z frame as drawn
has adequate stability, and does not tend to flip. “
Again,
instead of a careful analysis, you wish to prematurely rush to testing.
Obviously, like other kites, this kite would need to be tested. But it
is still in the design stage. Why do you have a bee in your britches?
If
a device is tested before it is adequately analyzed, then negative test
results could be misleading because they would suggest the design
doesn’t work well, whereas a slight adjustment, based on an adequate
analysis, might be all that is required.
And
conversely, if an analysis is incomplete, positive test results could
be misleading. Examples are the experiments by K Lab. You assume that
if you can get something to work as a proof of concept model, then that
substitutes for analysis. But it doesn’t. There may be, and probably
are, inherent limitations that the demonstration does not test because
you haven’t analyzed the potential limitations.
For
example, will a short-pull kite work just as well if the length of the
tether is far longer than the length of the tether in the test, or will
the slack in a longer tether reduce the efficiency of the energy
transfer from the kite to the ground? Is there, therefore, a desirable
minimum ratio between the stroke length and the tether length? Does
each type of short-pull kite have a different minimum ratio? Does a
longer pull-stroke allow a higher short-pull kite? Does that make some
types of short-pull kites inherently more efficient than others? Maybe
so.
“ Another issue
is how you find those tricky-looking secondary rotors and drive loops
as simpler than just using their extra mass applied to a thicker slower
drive-loop from a single HAWT rotor, and let groundgen gearing do
standard rpm step-up. “
The
issue seems to be that you do not yet understand the concept. So let me
try to clarify. The primary goal is to minimize weight and cost, which
is something that you have emphasized many times. Your approach does
not minimize the weight, and as a result, will likely not minimize the
cost. That is because torque requires strong parts and therefore
heavier parts. And a slower circulating loop tether must be stronger
and heavier. Your approach is also more expensive because it requires a
transmission with a high step-ratio on the ground.
A
flaw inherent in most wind energy conversion devices is that they use a
fast moving blade tip to slowly turn a central shaft to spin a
high-step-up transmission in order to spin a generator at a high rpm --
or they substitute a large, low rpm generator for the gearbox. That is
all very expensive to do, and for a kite is also very heavy.
So
I’m trying to bypass that problem of high weight and high cost. My
design does so. Of course there are still many unknowns about the new
idea. But it has great potential. You seem to not understand that
potential, and see only vague problems.
Is my use of loop belts from the ram air rotors to the central pulley
simpler than using a gearbox. I think that most people would agree that
it is simpler. But the answer depends upon how one wishes to define
complexity. If you wish to present a definition of complexity that
supports your claim, please do so, and I will consider it.
“
There is an old AWE debate over whether conventional gearing in surface
applications is proven enough by success in autos, bikes, etc, and
gearing as applied in many historic windmill and aviation types. By
comparision, any camparatively Rube Goldberg approach at least needs to
be shown in practice, to convince third-parties effectively. “
The
current assumption among wind turbine designers is that gear boxes need
to be eliminated because they are expensive and problematic. They
prefer large, direct-drive generators, even though they are expensive.
I agree that gearboxes should be eliminated. But I disagree that
direct-drive generators must be large and low-rpm.
Most
kite designers, due to the kinds of kites they are developing,
currently take for granted that gearboxes are necessary. I say they are
wrong. My design eliminates the need for a gearbox (it also eliminates
the need for a large, low-rpm generator).
The
Makani kite eliminates the need for a gear box, and it also eliminates
the need for large, low-rpm generator. So the Makani kite is a
significant conceptual advance. As a substitute for a gearbox or a
large, low-rpm generator, they use many, small, direct-drive, ram air
turbines (RATs). That is an important conceptual advance because it can
potentially save weight and cost. I’m trying to further simplify so as
to reduce complexity, weight, and costs. My system requires only one,
generic, high speed generator -- not many of them like Makani uses.
(And it requires no gearbox.)
You characterize my design as a “Rube Goldberg approach”. That is
gratuitously pejorative. Why? What are you mad about? RG devices are
humorous because they include a great many additional and unnecessary
intermediate mechanisms to accomplish a simple task, such as breaking
an egg. That is not true of my design, so your analogy is
inappropriate, and in more ways than one.
And again, you insist on immediately testing instead of understanding the concept and the design strategy behind it.
“
Note that all existing AWES drive-loop HAWTs are very lightweight
already Yes, your design will weigh less than a Makani equivalent, but
there is no major weight advantage seen over similar HAWT AWES
experiments. “
My
design strategy of saving weight by minimizing torque indicates that
you are wrong, and that my design will have an even greater advantage
at larger scales. You are insisting that minimizing torque cannot
minimize weight and cost. I have presented evidence that it can. So
please submit your evidence that it cannot. No evidence; no credibility.
“
In Makani's defense, they have a working prototype (Wing7), compared to
your paper scheme, if evidence-based criteria is required. “
You
are denigrating my very new concept for being a very new concept, and
for not already being developed and tested against the Makani kite, as
if R & D requires no time at all. That is absurd.
PeterS
