Twice Shy. I am going to skip right to the end of the story since the last few posts have been pretty long. Since my morning got consumed and I changed my mold plans, I wasn’t ready to spray my new PVA on the mold until almost 6 PM. This time I looked at the radar and we were primed for another dust/monsoon storm. So instead of spraying, I put plastic over my mold to minimize dust and will spray first thin in the morning.
Last night, while I was sleeping (or trying to), I was thinking about my cowl mold. I was wondering why I wasn’t adding flanges to the mold during the initial layup. The mold needs flanges no matter what if I am going to vacuum bag. It was just a matter of whether or not it would be during the initial layup or as a secondary operation.
The plus of doing it as a secondary operation is the initial mold layup is easier without need to jig flanges onto the airplane. The disadvantage is there is more work to be done on the mold which increases the chances of damaging it. It also makes locating flanges and trimming the mold more difficult.
Integrating flanges in the initial layup of the mold has the disadvantage of having to create and jig flanges onto the airplane. It also creates challenges in the prep and layup of having to work into corners. But if done right, I think it creates a superior mold and will allow use of the mold quicker after release from the airplane.
I decided to add backer board flanges to the airplane before I did my mold and will do it all in one layup. I made poster board templates to find the flange shapes. These were then traced out on the backer board and cut out with a circular saw and jig saw. They are 4″ wide. Plenty enough to give a sealing surface and place to put tacky tape.
Jigging these flanges onto the airplane was more of a challenge than it should have been. It took Brian, Travis, and myself well over an hour to get them glued in place. I started with hot glue beads in multiple places. This seemed to work, but the weight of the backer board was enough to break the bond of the glue in places. So we had to also use bondo and struts as well. We used popsicle sticks that braced the flange. Of course that was challenging because it was hot enough that the bondo was almost liquid and flowed so it didn’t stay where we wanted it to. It also was hot enough it kicked off before we could get it where we needed it. With a little stubbornness, we were finally able to get a stable flange structure.
The backer board I got had a shiny white surface, which is a good molding surface. Therefore it only required one coat of wax. Even so, I was very careful not to apply too much force when applying or buffing wax.
I also added clay in the corners of the mold between the flanges and the tool cowl. Not only does this fill gaps, some of which were bigger than I liked, but it gives a fillet that will create a nice rounded area for the fiberglass cloth to transition from the cowl to the flange. It also will prevent a sharp corner in the mold which could tear vacuum bags.
I put plastic over the cowl to prevent dust from building up in tonights storms. Tomorrow, first thing, I will spray 3 coats of PVA. Then cut cloth and layup my mold.
I guess now would be a good time to tell you that this really will be my first mold. Of course, I did make the mold of the induction inlet less than two weeks ago. But that was a simple small part. A cowl mold is larger and more complicated. I can’t wait to see how it goes.