Re: Questions to PierreB? //
- Since we are best advised to deal only in tension structures...
Furling may be best achieved by tension difference control, ...
decreasing the gap of the C shape of inflated ram air parafoils, kites or paragliders.
In the case of my spinning kite set; Having a more elastic tether on the outer tethers of the kites set on the ring.
As wind increases, the extra stretch on the outer lines makes the outer extent of the kite tip fold back and central to the axis of rotation.
A similarly more elastic back than front line promotes automatic sheeting out.
So as the wind increases the amount of sail presented to the wind decreases and the angle of attack lessens.
A self limiting power set-up is really quite simple and elegant.
Now if you want to totally kill and bring down the stack... Force the generator which normally points downwind at the stack to rotate off the wind. This will make the rotating kites snake and whip around, jerk, skew, slow their rotation and crash... probably.. I'm willing to try it.
And if you think that's ridiculous...
You should see the design I have for one of those funny wave power clams using underwater kites.
--- In AirborneWindEnergy@yahoogroups.com, Bob Stuart <bobstuart@...> wrote:
> In a large kite array, there may be an advantage to furling some
> kites in stronger winds, to keep the forces and power more constant.
> This action might be triggered by spars which bend in use, up to the
> force that causes them to fail. If the failure mode is like the
> buckling of an over-extended tape measure, it causes no damage, and
> lets the structure pop open again when loads are reduced. Tree
> leaves are notable for being inflated structures (by sap) which
> collapse to a low-drag form under high aero loads. The tricky bit is
> probably to avoid flapping.
> Bob Stuart
> On 19-Dec-11, at 12:27 PM, dave santos wrote:
> > Pierre,
> > We can rejoice that the paraglider service-life figure of 1000hrs
> > mainly reflects a super-conservative safety margin for human
> > flight. AWES multi-kites with no human aloft can use a far more
> > liberal service life specification. Any failure of the fabric is
> > likely to be local, easily repaired, and not cause immediate
> > disruption of a whole kite network. Peter Lynn does make clear the
> > gradual degradation, with long use, of kite fabric's initial zero
> > porosity, so a hot parafoil becomes "soggy" with age, but a pilot
> > kite is better for some porosity (a stability factor). Resizing by
> > a quick spray coat of the upper surface during a parafoil's life
> > might be useful.
> > Unlike a conventional turbine, fabric kites must depend on avoiding
> > storms by being furled away. In many ways the simplistic kite v.
> > tower comparison breaks down. For example Doug would hope to
> > compare an AWES at 120 feet with a windtower at the same height, so
> > the AWES loses by every measure except capital cost, but the same
> > AWEs allowed to go up to 500ft, by adding a bit of kiteline,
> > accesses winds almost twice as strong and consistent,
> > daveS
- thanks for the feedback Doug.
I'm using "beginner" kites. Because the chord length is so long, I'm hoping for beginners luck and intuition in finding their top speed and balancing that with the right amount and length of bungee to give at the right time. It will be a total fluke and it's a ballance between the centripetal acceleration of the air inside the wing cells ballanced against the relative drag rearward as it starts to oversspeed.
I'm probably being foolish not looking for the fastest kites. I'm hoping, against all advice from solid systems to develop a usefull high torque, many vane more like a let turbine model.
I tested new needles in my sewing machine today. Cutting old sails soon. It's got to be worth a go.