Here is a link to the recent speedweek results and photos. Would it be possible to somehow construct an r/c version of the kite sail?
http://www.speedsailing.com/speed_week_2003_pics.htm
Best, Michael
Sailing a kite is quite similar to sailing a windsurfer. Body weight (leaning) is used to balance against the pull of the sail/kite and the resulting force is transmitted into the board. The force of the sail/kite needs to be modulated to keep the system in a state of dynamic balance.
On a windsurfer, small trim changes are used to keep the body in balance with the sail. If the sail force is too strong, you ease out a small amount, let your body lean back a small amount and then trim back in. If the wind starts to die, you can either over-trim to pull your body back upright, or bend your knees to reduce your lever arm a small amount. Similar dynamics take place with the kite ski (I used the windsurfer as the example because it is easier to explain heeling force in terms of sail trim than it is to explain how you generate more or less force with a kite…).
Translating this into a RC model would be tough (the windsurfer or the kite). It is not something that could easily be controlled from shore. The dynamics need to be felt, not seen. You would really need an on-board automatic control system with sensors and actuators. The response time would have to be very fast (think of this as the inverted pendulum problem in 2 dimensions turned sideways). Perhaps with the proper application of gyros or strain gages it could be done, but it would take a lot of work.
Once you have the basic stability problem under control, you need to tackle starting (anyone who has windsurfed of kite skiied will tell you that mastering the water start takes years of practice) and gybing. The mechanics alone of these two problems, regardless of the control system is quite daunting.
Perhaps if you were winning to get in the water and assist the start sequence and really did not care about gybing, you might be able to pull it off… Of course for the same amount of money and time, you could buy a windsurfer and learn to sail and be having a hell of a lot more fun than just wiggling your thumbs…
- Will
Will Gorgen
Will ,
you are so right…i just love my flexifoil 
but i do love my rc sail-boats as well
wis
if it isn’t broken, don’t fix it!
wismerhell,
I love my flexi’s (2 Pro-team 8’s) too, but, my Force 10 is still the BOMB! See one at http://www.bfk.com/kite/ki49039.htm
Ahh back to the boats…[:-bigmouth]
Fair Winds,
David Goebel
and i thought i was an oldtimer with my nasa wings
i used to test these things…way toooooooo dangerous…but funny
as you said back to boats 
wis
if it isn’t broken, don’t fix it!
I’ve always been a bit partial to windsurfers.
I had the opportunity to meet Bill Roesler at the Atlantic Ctiy Boat Show about 12 years ago. He was a classmate of my thesis advisor so I was able to maintain a technical discussion with him over the years. I have several of his conference papers on the original KiteSki concept.
I now work quite closely with the company that his son Cory works for out in Hood River. Cory and many of the guys at that company are big into both windsurfing and kite skiing. So I have gotten an earfull about the relative advantages of each. I think if I lived in Hood River, I would have to live in a van down by the river just to give me enough time to do both…
Although I think I would still prefer windsurfing…
- Will
Will Gorgen
Just had a chat with Cory Roesler. winds were only 15 to 25 all week. not great for setting records.
Aparently he had a GPS strapped to his arm during his runs. He was having problems keeping on course and ended up sailing about 20 - 30 degrees off of the course line. So he was sailing quite a bit more distance between the gates. According to his GPS, he was over 40 knots on several runs. I told him he needs to work on his equipment so that he can hold better lines. He agreed.
And aparently, Bjorn never took out his speed equipment all week. He set the top mark for the fleet with his slalom gear!
Just an update…
Aren’t we supposed to be taling about RC sailing or something like that around here???
- Will
Will Gorgen
just one thing[^]
Aren’t we supposed to be taling about RC sailing or something like that around here???
YES
but its nice to talk about windsurfing as well…hhehe
wis
if it isn’t broken, don’t fix it!
Alright, well, since we are talking about it and everyone is enjoying themselves.
This month’s Sailing World has an article on Robby Naish who aparently decided to retire from competition at the age of 40 after 27 years on the circuit (you do the math). He is spending his new-found free time pursuing the 50 knot barrier on his windsurfer. He and his buddies have spent $40,000 building a contraption that is supposed to suppress the waves so that they can set up a nice flat-water speed course anywhere they want to. In his first attempt at speed trialing with the system, he broke the 40 knot barrier. Dunkerbeck, who is part of this same effort, hit 43 knots on the same day. So it sound like those two will be chasing each other around a new kind of course.
Any bets on who will break 50 knots first?
My money is on Robby…
- Will
Will Gorgen
Will, I’ve noticed that most the “peaked up” square top windsurfer sails have zero shape in the upper third of the sail: the top three battens are straight-and the leach at that point is without tension. Seems like it generates no power at all but perhaps has an effect similar to an endplate? I spend most of the day at least on Sundays at Kelly Park in Merritt Island where Tinio and the Caleema people have a shop and school. When theres wind(almost always) there are 20 to 40 boats out.
A 10 boat fleet of cats sails there too and several of them have square top mains that twist nicely going up but the camber seems to get larger closer to the top of the sail which seems appropriate.
Can you shed any lite on the windsurfer sail theory-or can anyone?
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing
Here is a link to another kite-propelled person, this one on Good Harbor bay in northern Michigan.
http://www.leelanau.com/backgrounds/waves2-800.jpg
I used to keep a white water kayak on this bay as a beach plaything, and I tested kite propulsion with an ordinary borrowed bat kite – just by sitting in the kayak and letting the kite pull me along.
The simplicity of it, and the surprising speed it achieved (downwind, bien sur) is what makes me think an r/c model would not be entirely far fetched.
Next to the r/c boat pond in Humber Bay Park in Toronto there is an active kite flying and fighting club. From watching them work, it seems to me the warping controls, which are done with a twist of the wrist, might be replicated with servo arms pretty readily.
As noted above, however, and in various postings here, standard servos have slow reflexes.
On the other hand, it seems like a pretty simple system from a vector standpoint. A pull on a string. In other words, perhaps it would be less difficult to achieve, technically, than a remote controlled model sailboat.
I meant to conclude:
“…easier to achieve than a remote controlled model sailBOARD.”
mcg.
Michael, I think it would be technically possible to make a kite boat work but assuming it was how would you handle the rules problems? Or would you envision racing differently than most rc sailboats?
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing
Hello Doug. Surely you jest?
Okay, it is not an entirely serious idea, but anyway:
Here is a link to a fascinating slow flying r/c plane that uses “warperons.” There is an animation of the wing about mid-page. Perhaps one could adapt from this to build a kite sail.
I guess what you could start with is an airborne r/c kite towing a surface bound boat, perhaps passive, perhaps with rudder control.
Best, Michael
Doug,
The “limp” top of the windsurfer sails came about through extensive research and development by several of the major sail companies during the late 80s and early 90s. One of those was Aerotech near Daytona (your neck of the woods?) I have a full quiver of their race sails and they are all limp like that. I don’t think much science went into it, but I can tell you that from an evolutionary standpoint, that those sails are a lot faster than the onse that came before it which had a more traditional look and feel to them.
About that time (eraly 90s), I was making annual pilgramages to the mecca of flat water windsurfing - Aruba - with a bunch (by a bunch I mean 20 to 30) of MIT students and alumni. One night during a pool game with no less than 5 MIT PHDs in attendance and several Master’s Degree Candidates, we tried to figure out why that limp topped sail was so fast. Here is what we came up with (mind you, there was a lot of beer involved, but even so, I think the usable brain power brought to task on that question was still quite impressive):
Given that the top of the sail is not doing much by way of lift generation, the aerodynamic center of effort is lower on the sail. Since this reduces the heeling moment, you could carry more power in the sail for a give body weight and lean angle.
So why would you bother to carry around the top part of the sail any more? The answer we came up with is that the extra sail area up top maintains the high aspect ratio of the planform. This has the effect of moving the tip vortex further up and thereby reduces the induced angle of attack and the resulting induced drag.
Given the high planing speeds that windsurfers sail at drag angles on the hull is quite low. Thus the top speed of the windsurfer is limited to a speed just below the speed where the aparent wind angle reaches the drag angle of the sail (resulting in no forward force from the sails). Therefore any improvement to the induced drag angle of the sails can be directly translated into top speed potential.
To think about it another way, that limp part of the sail is doing a similar job as winglets on an airplane wing - Spreading out and moving the tip vortex away from the body of the sail. Boeing believes that winglets are no different from adding wing span (hence their blended wing designs). Winglets have the advantage of not inceasing the span of the wing (which would affect how closely they could be parked at the gate) while reducing the drag in the same way that more span would. Windsurfers don’t need to worry about parking at a gate, so they add span rather than winglets.
That’s the best theory we could come up with, but I have never heard a better one…
- Will
Will Gorgen
to mcg
for sure some servos are slow…if so, jump to digital servos…fast and strong …a bit expensive…but the response is much better
http://www.futaba-rc.com/servos/futm0211.html
just for info
wis
if it isn’t broken, don’t fix it!