Chapter 20 – Winglets
In this chapter we get to make more moving parts that get the plane that much closer to flying one day. The winglets are attached to the ends of each wing and perform the same duty as the vertical stabilizer on a conventional plane.
The construction of the winglets are identical to the wings with the exception of there are no spars that have to be fabricated. The winglets are made in two pieces, an upper surface that houses the rudder and the comm. antenna. The lower surface provides an aerodynamic fence to stop the span wise flow of air under the wings. This provides greater stall margins regarding the canard/main wing relationship.
The first step is to micro a small piece of urethane foam to the top of the winglet so it can be better shaped in a rounded fashion. Next, the comm. antenna is fabricated out of the same copper tape that is used for all the antennae and is laid out on the foam. I checked the antenna for continuity and allowed sufficient cable length to run to the wing root. Once this was accomplished it was just a matter of doing the lay-ups per the plans schedule.
This picture shows the upper winglets. The one on the right is glassed. The one on the left is getting the comm. antenna installed before glassing.
Once the winglets were laid up, a paper template is placed along the bottom of the upper winglet. This template provides a line to cut the bottom of the winglet so it matches the contour of the top of the wing where it attaches to the wing.
The next step involved placing the winglet in the proper location on the wing. This was another step that requires a lot of maneuvering around and you wish that you had a third hand to hold things in place while measuring. There a 3 key measurements that need to be made and they all start at the leading edge of the inboard aileron cut out. The first measurement is to the leading edge of the winglet. The second is to the trailing edge of the winglet. These first two measurements ensure the winglet is placed properly on the wing in the horizontal plain, sort of like setting the proper toe in on your car. The last measurement is to the trailing edge of the top of the winglet, this ensures the proper vertical placement (the winglets lean in from the top slightly) of the winglet.
Once again, you change one measurement and the other two change as well. After chasing things around for a while, the winglet is properly placed and a line is traced on top of the wing and the portion of the wing that is under the winglet is removed. This provides additional area for inside lay-ups to attach the winglet to the wing.
Here you can see the amount of wing that is removed under the winglet. The plastic tube at the trailing edge of the wing is the rudder conduit that the rudder cable is routed through.
Next, the wing is turned over upside down and foam is removed from both the winglet and wing so the first inside layup can be done. Once that layup has been completed, a second layup is done to the outside bottom of the winglet and side of the wing.
The picture on the left shows the foam removed for the first layup, the picture on the right shows the completed layup and foam reinstalled. The black cable is the comm. antenna cable that is routed to the wing root.
This picture shows the second inside layup.
Next, A urethane foam block is microed in place and shaped before the final bottom layup is applied. Here the foam has been shaped and the last layup applied to the wing. The pocket in front of the tan foam is for installation of the internal belhorns that were added later.
Flipping the wing back over again, the last structural layup is applied to the top, inside portion of the wing/winglet area. The winglet is now structurally attached to the wing and the plans state that the winglet can now withstand a 170 mph 90 degree cross wind. Sounds pretty strong to me.
The next step involves shaping and installing the bottom portion of the winglet. This is not structural and is only held on by one layer of bid glass. The original design didn’t even have the lower winglet. It was found that during flight testing that after the canard stalled, the main wing could be stalled also without an ability to recover and the plane would pancake into the ground. Adding the lower winglet stops the span wise flow of air from escaping from underneath the wing and keeps the main wing flying long after the canard has stalled.
I used pour foam from a can to fill the space between the upper and lower winglet. This picture shows that operation.
The last step involves fabricating the rudders. This is done much like the ailerons were done in chapter 19. They are measured and cut right out of the winglet. Once they are removed, reinforcing lay-ups are done to the trailing edge of the winglet, and the leading edge of the rudder.
Once these lay-ups are complete, hinges and return springs are installed.
In the left picture, I am routing out the foam of the winglet before doing the reinforcing lay up. The picture on the right shows this layup before trimming the glass.
The plans call for an external bracket to be attached to the rudder. Burt Rutan had drawn up some supplemental plans for internal belhorns that eliminate the external bracket. The plans were only $14.00. I opted for this modification because of the cleaner look and less chance for damage from hanger rash. It takes about an extra week or two worth of work to fabricate them, but when you are looking at a project this big, what’s another week?
The last two pictures show the fabricated belhorns on the left and their installation into the rudder on the right.
