Hi DaveS,

Your analysis is incorrect. You ignored what I said about how both craft will use the maximum wind speed they can handle. The wingsail cart can handle a higher wind speed. So it will use that higher wind speed when that higher wind speed is available on the record course. The kite cart does not have the advantage of a higher wind speed. You are incorrectly assuming a race in the same wind, where a kite would have access to the faster wind up high. In that case, the kite would have the advantage. But that is not how top speed records are done. The craft do not race against each other using the same wind. They race against the clock. The sailwing cart has better traction, so it can handle a higher wind speed than the kite cart. It also has less drag, so it can point closer to its apparent wind and achieve a higher speed ratio. Higher wind speeds due to the wind gradient are not relevant in this case.

There are ways to make kite carts and wingsail carts much faster and I discuss some of them as part of my Metatheory of Sailing. But not all are legitimate for setting top speed records. One simple way to make a kite cart go over 150 mph is to connect the kite reel to the wheels of the cart by using a clutch. Use a very long tether. The torque created by the wheels will wind in the kite at a high speed, At the same time, the cart is pulled forward by the kite at a very high speed that can be multiple times the speed of the kite relative to the ground. There is no inherent limit on the top speed of the cart. However, this type of kite cart is a "limited distance device". It can’t sustain that very high speed because it must let out the kite tether before it can make another high speed run. I show that it differs from true sailing craft that can sustain a high speed for an unlimited distance in a given wind condition. So it couldn’t set a top speed for sailing craft. But it could set a record for its own type of craft. It would be fast as hell.

There is a way to increase the top speed of a wingsail cart, but it is very difficult to do from an engineering perspective and so it may never be done. It's too complicated to fully explain here. It involves circulating a row of wingsails aft while they are producing thrust, and circulating them toward the bow while they are horizontal and shielded from their apparent wind. It could add maybe another 20 mph to the top speed in the same wind speed, depending upon how fast it would be possible to circulate the wingsails.

Something to keep in mind is that top speed sailing records cannot involve any stored energy. For example, a wingsail kite that dived to increase its speed would be using stored gravitational potential energy. Similarly, any kite that crossed the finish line at a lower altitude than when it crossed the starting line would be using stored energy.

Top speed records tend to be based on sustained speed. For a kite cart, I would expect that the both the time of the kite and the cart would be measured over the course (probably 200 meters for the time trap) and the slowest time would be taken as the official time. It would be fun to have a different contest to see what the highest momentary speed could be, and set records.

But please describe the technique you have in mind for creating a burst of speed for a kite cart. It might be a technique I am not aware of. Are you thinking of some sort of slingshot technique?

Here is an idea for a fun drag race: Use your two kite on a Y tether that fly away from each other to create a pull on the bottom of the Y tether. Attach the bottom of the Y tether to a kite cart and see how fast it could cover a distance of 100 or 200 meters. Thrill ride!

PeterS