Main Spar
Installation and Reinforcement
It holds the wings on, so it's kind of a big deal
Since the main spar supports were already installed during the bulkhead installation, this step starts off quite quickly. The fist thing was to make sure the spar sat perfectly level and square with the fuselage.
Due to the extreme importance of getting the wings as perfectly level as possible, I did not use the little sprit level installed on the front bulkhead, instead opting to put levels on both the main spar resting in place and the front bulkhead, which the canard wing rests on.
Despite my perfect intentions, the spar supports were not perfectly installed; fortunately, this is 100% expected and easily accounted for with structural adhesive during installation.
Next was getting the center spar truly center, and square. It came with a center reference line, to get it close at first. I put a line at the exact measured center of the firewall to line up the spar's center line with.
Then the REAL measuring started... I measured everything short of the distance to the moon here, making sure it was as square in all directions as possible. Here, I measured from the firewall to the wing attach holes in the spar. Note, for best practice, always use the same side of the ruler, so in this case for the right spar the ruler was upside down. That got the spar centered. Next I measured from the nose to the spar ends, so get it squared.
I "pre-wedged" everything, so that when the structural adhesive was added, I knew exactly what I needed to get everything perfectly centered and squared back up.
And time for structural adhesive! I really wanted to completely cover the back side of the spar with structural adhesive, but decided I'd follow the instructions, especially since I would run out of structural adhesive that way! No Velocity has crashed because the center spar came off, so I just followed the instructions on how much adhesive to use. Two sections like this on the back, and completely filling in the top of the spar supports.
Then, it was just a matter of realigning and fine tuning the spar as the adhesive set.
With the spar adhesive set, it was time to reinforce it.
Every edge where the center spar touched the firewall, spar supports, and fuselage body gets bonded with epoxy and filler.
Along the top and bottom of where the spar touches the firewall a fiberglass reinforcement gets installed, so the adhesive should be a tight fillet as small as possible, but rounded enough for the fiberglass to follow.
Here the fiberglass reinforcement strips are show along the top seem of the spar.
Then we get to the transverse bulkheads, which connect the top of the spar to the top of the gear legs to hold everything in place during rough turbulence and hard landings.
You start out by cutting out a piece of factory supplied foam.
Next, cutting to size, and shape. While the cut COULD be straight with extra filler to make up the difference, this method of cutting at an angle made for a much stronger support.
With the transverse bulkhead fitted, it was just a matter of bonding them in place. At this point the panels are just soft foam with no structural integrity at all; however, that is about to be changed.
With the transverse bulkheads in place, it is time to prep some fiberglass layups. These go EVERYWHERE around the transverse bulkhead, to make a secure connection to everything. I did these layups as plastic transfer layups, due to the angled application of them. I cut out and wetted the layups, as specified in the instructions and let them sit for 2 hours to get partially set up. This reduces the amount of epoxy running out of the fiberglass cloth and down everything else. I actually started these before beginning to bond in the spar, so they would be ready now.
Two more step were required before the reinforcement layups could be placed on the transverse bulkheads. First, I covered them in epoxy, partly to make them stiffer, and partly to make a sticky surface for the layups to better stick to. Secondly, was to reinforce the corner of the seems between the spar and firewall with thick fillets.
Here you can see the foam has changed color with the wet epoxy on it, and the fillet at the top. The top layup goes all the way up onto the firewall, to make a secure connection, so the fillets have to go in first.
In order to make my fillets quick, easy, and even, I made this fillet tool out of a plastic putty knife. Well worth the $3 putty knife and 5 minutes to shape!
Here you can see how the fillet re-radiuses the seem and the fillet tool really makes it even.
As with any layup proper surface prep is essential, so a last minute sanding to smooth rough edges and rough smooth surfaces for optimal layup bonding.
Then the top layup goes on as one giant wet rug from nearly the floor to nearly to the top. At this point it sticks out quite a bit and has rough edges; these will all be cleaned up after the epoxy dries.
A total of 4 layup go all around the transverse bulkhead, including one underneath the bottom side of it. This layup really needs to be done as a plastic transfer, and excess epoxy should be cleaned up regularly as it cures.
Once the layups fully cure, they can be trimmed up and sanded down.
With that the center spar is 100% completely and permanently attached to the fuselage.