Sun Sep 20 2020

Forward fuselage and canopy structure

I made a decision today to re-do the forward fuselage structure. Why? Several reasons:

  • With the inclusion of wide UHMW blocks, the pivot bolts need to be substantially longer than as originally specified by Van's.
  • These ribs started out as Van's factory ribs, with their associated lightening holes. Unfortunately, those holes are located in non-ideal locations with respect to the modifications I'm making.
  • Because the canopy structure is a formed and welded structure, I have far less ability to make that conform to the required shape. However, I can easily (?) fabricate new ribs and bulkheads. Essentially, I think remaking these ribs and bulkheads is going to be the path of least resistance to achieve a sufficiently good fit.
  • The existing forward fuselage ribs extend far enough aft to support the panel. However, the location of these ribs is designed for a six-pack layout. If I install a glass panel (which I plan to), these arms will be in exactly the wrong position. So, I would have to cut these off anyway and find a different position for support of the panel.

Because this is a kit-built airplane rather than a plans-built airplane, there aren't a lot of dimensions available to determine the "right" position for various parts. I checked the plans and they state that the roll bar which is part of the canopy structure should have it's flanges 1/4" away from the face of the roll bar. So, I placed the canopy side rail in position, spaced appropriately from the roll bar, and marked the forward edge...27 1/2" from the forward edge of the side skin.

That side rail is supposed to be 1/8" off the top of the longeron. But since the side rail extends forward about an inch and a half beyond the point where the longerons take a downturn, the spacing of the WD-716 canopy forward structure / weldment actually needs to be spaced up about .272" above the longeron.

I made up some .272 thick spacers from a piece of oak on which to rest the canopy structure.

Then, in order to sort out the warped shape of the forward canopy weldment, I ran over to Home Depot to pick up a piece of very flat 1/2" thick plywood. I cut a piece of it and drilled and clecoed to the longeron gussets.

Slots are needed to allow the canopy pivot arms to pass through.

Slots added. After this photo, I cut and glued a doubler (3/4" particle board) to this plywood. BTW, the reason for using 1/2" plywood is that it replicated the space required between the aft face of the forward fuselage structure and the forward face of the canopy structure.