My fifth foil is a 4.5m², with (again) a PW99a profile (15.5% à 23%), AR 4.3, D-Ribs, bridle every third rib, twisted. As for the 1.9m², the three last cells are closed, with 3D valves (bellows), with an access to the closed cells to remove sand (see last picture). I've a big mistake when designing this foil and I've done a lot of 'surgery' to make it fly. The vents were badly placed, and I had to shorten the lower skin and extend the upper skin, otherwise it did not inflate. If you look at the pictures, it is the black part at the leading edge. I've also added 'D' lines (3 bridle attachment points per profile was not enough). It flies OK now, but it was very painful.