[EMAIL PROTECTED] wrote:
But it may very well be a very important issue. In particular the strength to weight ratio of the cable may be a paramount concern because of its indirect impact on the _footprint_ of the kite.Hi Robin and Stephen,
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Actually that's wrong. Because of the way in which tensile strength is measured, the force pulling up on the cable can equal the weight of the cable, so even at maximum length, almost any upward force can be maintained, simply by making the cable thicker, until the weight of the cable equals the lifting force.
Of course, it's going to be a lot easier on the kite, if the cable is lighter. It would also mean that a better compromise between lift and drag can be used. BTW drag in this case is what is responsible for energy production, so you want it maximised.
Regards,
Robin van Spaandonk
If tensile strength is a real issue (which I suspect it really isn't) but if it was:
The problem is that the cable is going to hang in a catenary. If it's at a 45 degree angle at the kite, it's going to be at some much smaller angle relative to the ground. In order to avoid having thousands of feet of cable strung out near the ground before it climbs to some reasonable height, and in order to avoid making the no-fly zone really huge, it may be necessary to put a great deal of tension on the cable unless the material of the cable is very very light, or some other method is used to support the middle of the cable.
Another approach might be to strategically place a series of "support lifter wings" that run all the way up the tether to the kite. While wind drag itself would not be eliminated (in fact it would increase, see below) it seems to me that a certain amount of downward tensile stress brought on by the downward pull of gravity would be alleviated by the lifter wings. For example: Every 500 feet a computer controlled support wing calculated to the right square footage might be attached to the tether and repeated all the way up to 15,000 feet. You would need 30 computer controlled support lifter wings to make it all the way up to 15,000 feet. The trick however might be to determine whether there is significant tensile strength savings using this approach as stress may simply be transferred from the downward pull of gravity to the accumulated sideway wind friction the result of the all the attached lifter wings.
Another thought that I'll bring up again within Vort is whether it might be economically advantageous to gang up multiple power generator kites on a single tether. When you get up to 14 - 15 thousand feet it might turn out to be useful to stack 2,3, perhaps 5 kites or more on a single tether - perhaps separated every 300 - 500 feet. It seems to me that potential instability introduced by attaching several power kites on a single tether could be controlled by sophisticated computer s/w that carefully monitors the lift-flight characteristics of individual power kites making necessary adjustments every microsecond.
Regards,
Steven Vincent Johnson www.OrionWorks.com
