On short notice, I took a week off of working on the Defiant project. A friend of mine was coming to Phoenix to do a commercial glider add-on, so I invited myself along on the adventure. It was about a week of really fun flying. I highly recommend it.
After my soaring sabbatical, it was time to get back to work on Brian’s Defiant. As luck would have it, I had a friend decide to come to Phoenix to help work on the airplane. For those of you who followed along with Betty’s build, you will recognize Greg.
Greg is a friend of mine from St. Paul, MN and a Long Ez builder/owner/pilot. His Long EZ has been flying for 32 years. For the last several years of building Betty, Greg came over at least one day a week and many times two or three times a week to help me get Betty flying. His building experience and dedication are a big part of the reason why Betty is flying.
On the Defiant, we left off with the lower cowl mold halves laid up. When Greg got here, we started by building a wood structure around the mold halves. This not only gave it extra rigidity, but also allowed us a couple bolt holes to repeatably re-align the two halves together.
Then it was time to release the molds from the plug. Unfortunately, this didn’t go as smoothly as I would have liked. We ended up pulling quite a bit of the primer off the plug when they separated. Good news is there was a good coat of PVA on the plug so the primer came off the mold easily. I am not quite sure why the primer came off, but at this point no harm, no foul.
After a bit of clean up, we did the usual wax and then clay along the center seam. In addition to that, there was one area where we put 1/16″ sheet wax. The sheet wax is there to create a joggle, or offset. This will allow the top cowl to come down over top of the aft flanges of the bottom cowl and will make an integral mounting flange in the initial layup. It is hard to see in the photos, but it is the rectangular yellow opaque area on the aft vertical surface. Then it was 5 coats of PVA.
Since I am still trying to learn resin infusion and vacuum bagging, we decided to try resin infusion with the first part from this mold which will be a fiberglass tool cowl. Greg and I took our time cutting 1 ply of deck cloth and 4 plies of BID. These were arranged dry into the mold. Then it was all of the infusion consumables including peel ply, flow media, and then bagging film.
Unfortunately, the best we could get after hours of trying to fix our setup was 10″ of HG vacuum. We had major leaks. We tried everything we could think of. We went around the bag perimeter multiple times looking for leaks. We painted the outside of the mold with flex seal thinking there may be a dry spot with pin holes. We trimmed the centerline flange for access and bagged the exterior of the centerline flange/mold split. We put tacky tape on suspect areas on the outside. We put tacky tape along the sharp edges of the flow media. We added bags on top of the bag. We got a stethoscope out and listened for leaks. We blew smoke at the mold looking to see if we could find where the leak was.
None of that was successful. So we took the bag off the mold. Our plan was then to do a wet layup and try one new bag over top of that as a wet layup vacuum bag. We didn’t expect it to perform much better than the first bag (unless it was in fact the flow media that punctured the bag), but 10″ was at least some kind of vacuum and would give some of the benefits of bagging to the part. But this round of bagging went sideways too. The seal was non-existent and didn’t pull any vacuum on the part.
To make matters worse, I was frustrated enough with the time spent and lack of fixing the problem that I convinced myself to take a shortcut with the wet layup. The mold was already packed with our 5 plies very nicely. I was concerned about getting the plies out and back in the mold without distorting the fabric to the point where we would end up short of material in some dimension. So I reasoned if I could wet out a 5 ply stack on the table reasonably well, we could do that in the mold. (BTW, never do this with a flying part… it is very bad technique, heavy, and you cannot ensure the each layer of the laminate is wet out appropriately.)
As all of you have done composites work know, this was a major mistake. It was not only probably more time consuming in the end, but ended up producing an abysmal part. There are dry areas. There are inter-laminate bubbles. There are places where the cloth didn’t lay against the mold and it is not representative of the shape. etc.
There are 3 good things to come out of that mistake. The first is that the perimeter of the part is wet out sufficiently well to use the tool cowl as intended. It will allow me to precisely trim to fit the firewall and wing roots, etc and transfer these features to the mold. The second good thing is it will give us a part to use to ensure things like the exhaust are located inside the cowl with plenty of spacing, etc. Lastly, I was able to remove the part from the mold without splitting the two halves. The fiberglass tool cowl is a bit more flexible than the final carbon cowl will be, but I think I could get away with bonding the two halves of the mold together and still get a part out. This will remove one major area that is likely the major cause of our leaks.
All in all there was a lot of learning that went on with this part, mostly what not to do. I will end up with a good part out of this mold eventually, but for now we are going to switch gears to something else.