The top side of the center section is ready! It was a long and difficult path to get there…
We tried to prevent some problems we had last time with the lower side. Most prominent is that we produced a left and right side for the inner face sheet. Last time we had problems with wrinkles while draping the geled sheet. Using two halves reduces the risk substantially and is much easier in handling.
Production of the inner face sheet started with a dry layup on top of the pattern. Last time we used a drawed tamplate while laminating the sheet, which was difficult to set correctly up. It is much easier to make a dry layup on the pattern.
Originally we wanted to vacuum infuse the face sheet and join it with the honeycomb core when geled. However, we had massive problems to get a sealed bag and the infusion of one half failed. I think the following picture shows my mood that night:
Already here it showed that having two halves is better than one, as we lost half of the sheet instead of all. The problem was that the bag was made of the wrong material: Never use a single layered PA bag for infusion, use a three layered PE/PA/PE bag. No matter if the PA bag is slightly cheaper. Usually a small leak is not a problem, as long as the part produced is not something like a visible carbon surface. But, this time the leak was directly at the suction line, so that the resin was not sucked properly and the laminate was not wetted. Anyway, we made the dry layup of one side again, we wetted the old way with a roller and vacuum pressed them for about twice the resin’s pot time.
After having glued the geled face sheet with 3M 9323 epoxy-resin on the honeycomb:
The whole thing was cured in moderate vacuum for 24 hours and then heat treated for 15 hours at 60 °C (140 °F):
We are proud of the result: very light and extremely nice
We have to cut and level the joining edges of both the upper and lower sides. Also some ribs are needed to support the shape, in particular where the pilot will walk on top to enter the plane. Having done this, we’ll be finally able to join these into one piece. I guess the picure above gives anyway a good impression of how it will look like.