Prepping and Installing the Keel
It's the backbone of the plane...
My plane is the first SE-2 RG model, and this is the first place it deviates from the standard SE. The SE-2 includes the cut down keel upgrade, which makes installing it much simpler. Mostly because most of it is cut off!
The first step was the front keel access hole.
Note: I later realized that the cut out is needed now, but making the cover should wait till after the keel is fulling installed and reinforced.
First I cut it out, using the cut lines, then I prepped it just like the lower cowl. Duct tape to act as a release agent, and popsicle sticks to hold the cover panel, during construction.
The cover panel was then hot glued to the popsicle sticks.
Finally, the fiberglass layers up and over the cover, to make the attachment flange. If I were to do this again, I would either use a second BID layer, or use TRIAX, to make the flange instead. The flange seams a bit flimsy to me, but for now I will keep it as is.
The instructions say to trim the flange to 3/4", so that it comes down 1/2" down the side of the keel; therefore, I trimmed it to 3/4". Unfortunately, 3/4" flange does not equal 1/2" down the side of the keel. Cutting them a full 1" would have worked much better.
Next was the installation of the nut plates, as per the instructions. Getting the holes drilled perfectly spaced was a challenge, and a few of the pop rivets ended up a bit crooked, but eventually all nut plates were installed securely. I found going back and squeezing the rivets with pliers, really helped the rivets secure better.
This photo shows the nut plates installed with screws from both the front and back.
The final step was to ensure all went well, by screwing the cover panel on. It would have been nice if the flange went down onto the side of the keel; however, it appears to be fine a bit higher up too.
The cover screwed on for the first time, to make sure it works correctly.
The next step was to prep and install the wood hard points inside the keel.
First, I sanded the wood pieces and put good bevels on the edges, to better facilitate the fiberglass to go over them.
These went in pretty simple, just mixed a batch of epoxy adhesive, and "glued" them where the marks on the keel were. The hard points were all much larger than the indicated size and shape, so there is good leeway, making it that all the much easier to locate them. I then put clamps on them and let them set.
The 3 hardpoints being glued into the keel. Can't have too many clamps!
Next was the fiberglass layers over the hardpoints. This time, I had to do one side, then the other, so they could be done flat.
This step went quite smoothly. The bevel on the edge of the wood pieces was not quite enough, so there is some delamination around the edges, but I'm sure its plenty secure enough.
The instructions say to cut a piece of PVC pipe to make sure the keel bottom is open at least a set amount, with the allthread to hold it in place. I quickly realized the PVC was pointless, and the spacing could be set much more precisely using four nuts and washers instead.
Since this is the SE2 model, the aileron control linkages are not installed till after the fuselage top is installed. Also, since the keel is cut down, there is no reason to install the main hydraulic cylinder before the keel.
There are not any actual instructions in the build manual, for actually bonding in the keel, so this is what I did.
I decided to install it, like I did the bulkheads. First I measured and got the keel just where I wanted it. Then, I clecoed it in place, so I could trace an outline of it on the floor, on both sides of the flange.
Next I sanded the keel flange bottom, and the area the keel was attaching to, to ensure a strong bond.
Next, I made up a large batch of structural adhesive and applied it to the keel bottom and fuselage attach area. And placed the keel in and used the clecos to relocate the keel in the proper place.
The ribbon of structural adhesive on the fuselage floor.
When I set the keel in, it was easy to put it at almost the perfect placement, due to matching the ribbon of structural adhesive with the keel flange.
Pushing the keel down and then placing pop-rivets in the cleco holes, did a good job of squeezing the keel down tight, and pushing out any excess structural adhesive. I then used the excess structural adhesive, which had been squeezed out, to create fillets all the way around, and back fill the inside edges. With that, the keel was initially bonded in.
The next step was to apply the keel stiffening and reinforcing layers. This went pretty smoothly; however, this is one place having waited to make the front access cover till later would have made things easier.
I came up with two ideas to make these front lay ups go in better. First was to trace the shape of the wood hard point onto the lay up, so I would easily be able to get it perfectly placed. The other was to cut out the bottom corner, where the floor, keel, and bulkhead met up. This would allow the corner to sit cleanly.
So as to not loose the location of the gear mounting hole, I drilled out the outside layers, before applying the inside layers. That way I always had a clear path to one side of the hole at a time.
The right angle drill adapter was very awkward, but got the job done. If I had the money, I would just buy a right angle drill, they work much better.
For now, I just didn't want to loose the holes, so I stuck with the original 1/4".
Next, for the inside lay ups.
Of course, the manual does not say to, but you always need to put in a good fillet, especially for TRIAX, so it does not delaminate from the corners. I made a custom fillet tool, by shaping a 2" plastic putty knife. It took a while to get the shape right, but it has been amazing! For BID fillets, I find the popsicle stick's natural curve makes a perfect fillet.
Here is my custom TRIAX fillet tool. It makes doing these fillets almost effortless. I highly recommend doing this.
There are two inner lay ups, a large one covering the majority of the space from from the sides of the keel, around the bulkhead, and onto the other side. Then a small thick one, where the front gear captivator will be mounted. These also went without a hitch, as described by the manual.
First, the narrow working space of the keel, forced me to create my own modified tool for applying the epoxy. To this end, I cut the end off a paintbrush
My cut down paintbrush was perfect for applying epoxy and working the fiberglass in.
Using the plastic transfer technique, I installed the two lay ups. For doing vetical and upside down layers, I have come up with a very good technique. First, I apply a thin layer of epoxy 4 hours before I apply the lay up. Then two hours before, I wet out the lay up, and let it sit till time to install. In my workshop, air conditioned to around 75 degrees, 4 hours is the right amount to get the epoxy to get very thick and become almost like contact cement. This is great holding the lay up, so it doesn't fall, then the 2 hours set up time of the actual fiberglass, thickens the epoxy enough that the epoxy does not seep out the bottom too much.
The first inner keel reinforcement installed. Not the fillets allowing a smooth gentle transition to the different surfaces. It is also marked with the location for the next layer.
Here is both inner reinforcement lay ups. Yes the small one is not quite level; however, it is more than close enough to support the gear captivator.
Finally, after reading about how drafty the planes are, when the landing gear are down, I decided to beef up the front access hatch cover. Using the same techniques, as the original flange, I made larger flange that went well down onto the side of the keel. I then drilled holes to regain access to the old nutplate holes, and installed a few new lower nutplates, to hold it better. I have to admit, I do really like the extra long cover flanges. By moving them down onto the sides, the whole piece is much more stable, and I hope less drafty.
Here is the new access cover. I actually did not do this till after I installed the front landing gear retract system, but this is a more appropriate time to show it.
With that, the keel was fully installed. Next, installing the front landing gear retract system...