Is anything happening in this area or LEI manufacturers completely gave up on this idea? Cabrinha Apollo was a half-hearted attempt to make LEIs relevant at the racing scene, but it didn't go far for several reasons:
1. The kite is C shaped, with significant m^2 loss in projected area.
2. The AR is still lower than high performance foil kites.
3. Typical LE tube is too thick, which negatively affects L/D ratio.
Now, it is obvious that rigid wing should have superior aerodynamics to sail hinging on some frame, this is why America's Cup contenders are equipped with rigid wing sails. Therefore, executed properly, rigid inflatable kite structure should be superior to paraglider. This is assuming the aforementioned 3 Cab Apollo issues are worked out.
Problems #1 and 2 seems to be easier to solve, than #3. Not so long, on this very forum, Bruno Legaignoux suggested high pressure kite
. Bruno's kite has inflatable frame so thin that it would be well suited for high performance applications.
However, the inflatable trailing edge has to go. It is the basics of aerodynamics, that while airfoil can have blunt leading edge, the trailing edge should be razor sharp. Can Bruno's design be salvaged so that it would work without rigid trailing edge? One solution is to mimic foil kites and to have elaborate bridle supporting trailing edge. Unlike trailing edge, rigid leading edge distributes the load evenly, so that the LE bridle can be kept minimal -- essentially the same as the existing tube kites.
Elaborate paraglider style bridle is the source of drag. Apparently, it has less effect than LE tube, but maybe foils sit further in the wind window just because of their higher AR? Anyway in this proposed LE race kite design there is only one bridle with nontrivial drag: the trailing edge one.
There is one more advantage of paraglider style trailing edge bridle: it helps for reverse launch. Did I forget to mention that Apollo sucked badly with water relaunch? This is because high AR rendered invalid the traditional LEI relaunch technique. For ultrahigh AR kites the reverse launch seems to be the only option, and with paraglider style trailing edge bridle I suppose the relaunch difficulty should be the same as for foil kites.