Building the Fokker D.VII Bottom Wings
Bent lower wing ribs.
Drilled the spars and assembled both lower wing panels. Not much to show, they go together just like the upper panels.
Aviation friend Greg dropped by and we assembled all spars and compression struts and rigged the drag-anti-drag cables in an hour or so.
The left bottom wing is jigged up on the bench and ribs are being fabricated. The rib tubes were bent in a previous work session so the main tasks are making brackets and riveting everything together.
Left panel ribs are attached. Still need to fabricate the tip bow, attach the leading edge sheeting and design a wing walk for the two root ribs.
I prefer to use a gusset to join the two tubes together instead of having them lay side-by-side per the manual.
There isn't any documentation on how to attach the tip bow so here are some photos of how I did it. Don't forget to bend the bow for the other panel at the same time so they can be identical.
A single rivet attaches the end of the bow to the main spar. A bracket with a stiffening angle is riveted to the forward rib bracket.
Another bracket is located at the rear spar and the tip of the bow is attached to the rib with a gusset. This resulted in a stiff wingtip with minimal added weight.
Leading edge sheeting is supplied in 48" lengths. Because two pieces will cover the lower wing panel, I butt-joined them together with driven flush rivets instead of overlapping per the manual.
The left wing needs a wing walk to assist with entry into the cockpit. I decided to make the entire area between the first two ribs and aft of the leading edge skin a reinforced area so I could "walk" on the wing as necessary.
The first two ribs were strengthened with aluminum webs. Angles parallel to and across the ribs were riveted to the webs to support the wing walk surface.
The wing walk base is 1/2" CD plywood resting on the angles. This makes the top of the walk flush with the top of the rib tubes.
Bottom view of the wing walk showing trailing edge angles. A plywood shim was glued between the ply and rear spar to serve as another support.
The ply is covered with sheeting that is riveted to the ribs and leading edge. The aft edge of the walk was bent 90 degrees to form a reinforced trailing edge. The whole deal feels very stiff and did not add very much weight.
The trailing edge is unusual in that it consist of 1/4" copper water tubing. This is used so the Fokker scalloped trailing edge can be formed. I formed it by hand and eye as I progressed from one bay to the next. It is very soft and easy to form without tools.
The plans call for terminating each rib tube side-by-side, I suppose for speed of construction. But I used a gusset to attach the coped upper tube to the bottom one so each tube would lie in the same plane. A 1/4" hole is drilled in the lower tube, the end of the tube notched, and the copper tube pushed into the notch. The ends of the tube are hammered over the tubing to hold it securely.
Here is the trailing edge terminated at the wing walk.
The aft edge of the leading edge skin wasn't very firm and had minor puckering between ribs. Sheet aluminum angles were formed on the metal brake and riveted to the aft edge to straighten out the edge and make it firmer.
Left lower wing panel finished with exception of cutout in the leading edge for the N-strut. I estimate about 25 hours labor including considerable time figuring out how to build the wing walk.
The next panel should come together considerably quicker.
All the ribs with tip bow have been installed on the right lower wing. No wing walk to construct on this one but I did need to design a means of mounting a pitot/static mast.
Here is the bracket that will carry a cover with the pitot mast attached to it. It sits flush with the lower surface of the wing. I will add nutplates later. 1" PVC pipe provides a way to push the pitot/static tubing down the wing after it is covered.
The PVC terminates at the root rib and is supported by a brace at mid-span.
Both bottom wing panels finished.
Happened to think that we need some way to tie this bird down if the wind comes up. I don't like having tiedowns hanging in the breeze when they aren't needed. Here is the solution--tie downs that screw into place as necessary.
A 1/8" steel angle was attached to the tip of the spar with two AN3 bolts and with a nut welded to the angle. There will be a small access grommet in the covering for the tie down.
The tie down rings will ride in the plane's storage compartment until they are needed.
Building Log for Sam's