Wayne,
The pendulum topic is not your strongest contribution (I like Antarctic
Ice-Pack Blow-Molded Wings).
Rather than being overlooked, pendulum stability is almost universal in
aircraft design. Obviously all helicopters, autogyros, trikes,
paragliders, and hang gliders have inherent pendulum stability designed
in. Most small aircraft are high winged, with decided pendulum stability.
Ordinary single line kites require only a bit of pendulum-based yaw
stability; kite pitch and roll are effectively constrained by just split
bridling (triple bridle). Even low-wing aircraft are actually
pendulum-mass stabilized, the dihedral angle selects whichever is the
lower wing to act as a pendulum rod. Only extreme aerobatic designs
deliberately avoid pendulum stability.
That is, until now: Our latest kite energy arrays, "staked-out" crosswind,
simply have no need for any pendulum mass/moment for attitude control.
Each kite sail in a dense array is constrained stably by the lattice. The
pure "rag and string" school has triumphed over ordinary instability and
especially pendulum uncertainty and mass requirement. No more chaotic
flying pendulums run amok. Its really a revolution over the dependence
existing aviation has on pendulum stability.
Consider how simply anchoring across the wind is the most inherently
stable basis for "crosswind power" harvesting,
~daveS
Subject: Re: Pendulums or Gondolas
as pendulums for Passive Attitude Control
Dave and friends,
What I wrote was really a simplicity to say the heart of the matter
without disclosing all details. Actually, pendulums were suggested early
on in aeronautics but they were rejected when it became evident that
aircraft were making accelerations of their own that swamped out the
accelerations due to gravity. Even so, I am told that one aircraft
successfully flew by using a pendulum for attitude control. That is
because it was designed to always fly on a steady course and not generate
accelerations of its own. But the point you make Dave is right, pendulums
can benefit from damping and I should have pointed out that such damping
can easily be achieved in this design simply by making the shaft that
connects the wings with the pendulum/gondola as long as designed --
increasing the length of the shaft increases the amount of damping -- at
the cost of some extra wind drag. If the shaft is too long then the craft
would act like it is in "leg irons" in that it would too greatly resist
intended changes in direction -- unless the angle of the
shaft/pendulum/gondola with respect to the wings is what would determine
the pitch and roll over-all of this tethered craft -- hopefully tethered
to a submerged hydrofoil for the fastest sailing possible.
Actually Dave, I had no thought of who might "own" the concept of using a
pendulum to achieve such simple Passive Attitude Control. I never thought
of claiming it as my own idea though looking back I can see where you
might have thought that I was claiming it as my own. But now that you
mention it, I know, as I mentioned that pendulums were suggested early on
for aircraft in general -- and shortly abandoned in general. But I did not
know of anyone else suggesting them as perhaps the one simple device that
would enable kites in general to attain much more of the stability of
airplanes in general -- and therefore able to due useful and reliable work
as a result of it. Also, at Chico I presented one model of this pendulum
kite to you and the other to Dave Culp. I do not think that Dave ever
realized what it was that I gave him. I think that is the method that he
could use to obtain the stability that would make his ship propulsion
kites possible in the simplest way.
But again, if you thought that I was claiming the most fundamental uses of
pendulums myself in aeronautics then I apologize and should be more
cognizant of what I intend to say, but also what other people might
reasonably hear as well. But the question really is Dave (and friends): if
it is true that pendulums could so easily and simply stabilize kites
shouldn't our fraternity consider them as a normal and expected part of
tethered craft unless a more sophisticated method of attitude control is
used instead? Frankly, I think this point, that I made at Chico also, is
that pendulums may provide a simple and direct method of stabilizing kites
that most everyone has overlooked in our fraternity. I would appreciate
kind discussion by all of you regarding this matter and I am inviting Dave
Lang, as "Mr. Tether" to comment also -- as he knows much about tethered
systems.
-- Wayne German
Wayne,
While you are right to count on pendulum-stability as a useful principle,
keep in mind that it is an old standard concept in aeronautical
engineering (eg. high-hat wing). It does not seem possible your FRI
friends did not know this. Also remember that pendulums are unstable, and
"pendulum stability" is mocked by common turbulence, in any chaotic
aeroelastic inertial kite event where the kite starts by swaying wildly
like a swing (pendulum), then orbiting as a stable (falling) flywheel. If
you will make some simple kites with a pendulum attached (just as Hargrove
over a century ago), you will find just how weak dependence on (undamped)
before our time seem to cover virtually every concept we think of. Name
any kite idea you have ever thought totally original to you, and some
close prior art can likely be shown by Joe or me. We should be glad to be
humbled by such amazing predecessors.
So keep up the great real work. I think there must be a way to make a kite
fly just like the falling seed heli, where the mass helps maintain
rotation, thanks for that sort of insightful clue,
dave
PS Thanks for the kind words. Culp was the name you wanted to remember.
Joe,
Here is the concept 3d drawing I made in Rhino and gave to the Drachen
Foundation and gave to
Dr.
Breidenthal from the University of Washington. Then I made models of
the concept and passed them out to Dave S. and Dave ??? (I forgot his last
name. He made the spinnaker that won the America's cup that year).
Suppose the first couple of feet of the tether from the kite was actually
rigid. Then it would stabilize the pitch and yah of the kite. And the
pendulum or gondola (which is way too big and bulky here) would stabilize
the pitch and roll of the kite. So between the tether and the pendulum or
gondola the kite should be stabilized in pitch, yah, and roll -- the three
directions necessary to fix the attitude. Please see the picture that is
attached.
-- Wayne
Dave, I welcome your opinions as I do
Joe and others. I think a free and lively interchange of ideas helps us
all because we all see some things that others don't so together we can
progress further than any of us could individually. And the reason I sat
down to write again was to tell you that you were apparently the first who
realized the potential of a "maple seed" rotating kite to maintain
rotational momentum and thus lift during variable winds.
But I do not understand your comment about kites as arrays generating
power cross-wind. Isn't that the whole nature of the "vertical blinds"
that I discussed with you? Don't they form an array of wings that are
vertically oriented -- like a stack of kites that lift sideways rather
than up to spin one or more generators on the ground?
And in the event that the winds should die down the bottom of the vertical
blind array could be let out faster than the top of the vertical blind
array and each of the vertical blind wings that would have symmetrical
cross section could be inclined somewhat to not only provide traction to
make the ground based generator(s) spin but also to provide lift for the
vertical blind arrays so they could fly dynamically by some of the power
that they themselves would generate.
But in the event that most or all of the winds should die the generators
could really be generator/motors acting as motors and some power could be
used to keep the entire array aloft dynamically by pulling it back and
forth across the Great Plains using power from the grid.
In all these situations the altitude that the vertical blind arrays would
fly at would be a function of how fast they were lifted to the side either
by the winds blowing cross wind or the power from the grid.
But Dave, it sounds like you are saying that kites for generating
electrical power across great expanses should necessarily eliminate all
needs and desires for simple kites to generate wind power with. How about
for generating power over single farms all across Amercia!!! Surely, the
large massive array power generators do not meet all needs. How about for
on-board power for ships and freighters -- particularly at anchor?
But what I was really trying to say is that I am beginning to think that
all kites could benefit from the Passive Attitude Control that pendulums
would provide. After all, isn't that the main problem that faces all kites
-- that they eventually lose control over their attitude and crash? The
point is that I do not often see even your basic ordinary toy kite come
down just for lack of sufficient wind. Almost always, it seems to me, that
the kites get into an attitude that they cannot get out of and the kites
streak to the ground and crash -- rather than just go limp and sag to the
ground.
On the other hand, if you have been pursuing these objectives or promoting
these objectives without including me in your discussions it leads me to
believe that I have been freely including you in discussing my ideas but
you are not reciprocating. If you would rather pursue tethered flight
projects as competitors that's fine. But if that is so, I would ask that
you not use my ideas as your own then. But if you can show that your ideas
are significantly different that's fine. All I ask is that you be fair and
reciprocate as much or as little as you want and let me know how you would
have each of us interact. I am happy discussing tethered flight issues
with you or Joe or anybody -- providing they are willing to reciprocate --
and providing they do not take my ideas as their own and share them with
just anyone who choose not to reciprocate either. I honestly think Joe and
I have had a great relationship as of late, but I do not remember when you
have volunteered to give me any information either technically or
regarding the politics in our fraternity Dave. If your intention is to
give me the brush off Dave I would appreciate it if you would be up front
about it rather than acting like a one way gate for knowledge and input.
-- Wayne
PS: Aren't you talking about the idea of using "vertical blinds"
that are arrayed like stacks of kites sideways to generate power
cross-wind -- such as places like the Great Plains where in the low level
jets that form there generate maximum power at a thousand feet above
ground and therefore these "vertical blinds" at a thousand feet in the
peak of the low level jet that is present there the stack of "vertical
blinds" pulling sideways as an array could sweep power all across
-- Wayne |