Internal Wing Panel Structure

last update - 6/22/18

Jigs

1. 15.5 degree ramp and guide bar jig used for final finish sanding of LE and TE rib ends.
2. Hollow rib jig from 1/2" plywood used for locating through holes for internal strut clearance.
3.  Clamshell form to fabricate ribs.
4. raw foam blank template for hot knife cutting rib foam cores.
5. 15.5 degree rib gusset jig to set rib gusset offset.
6. rib slab cutting board used for cutting all slabs (minor & major ribs and foam fairing slabs.
7. chord dimension jig (2 each mounted on either side of each rib as they are riveted to the frame) They lock in the outside wing chord dimension of 39 7/16.

Changes needed to be made to the original kit plans to allow me to solve the severe fabric pull down between the ribs that was so hard to avoid with the original rib layout.  The lower wing panel originally had 6 ribs.  My current approach involves using 1 extra main rib on the bottom wing panels making a total of seven 1/2 inch foam/spruce cap strip main ribs.  In addition to the extra main rib, I've added 6 minor ribs constructed of 1/4 foam and balsa wood cap strips with a single side gusset to mate with the leading and trailing edge spars.  The other change I am including is the replacement of the filament tape with pinked, 1.0 inch Poly tape from Aircraft Spruce.  I am running 5 lengths spanwise with a 2" spacing on the leading edge section.  I found that strapping tape is not compatible with the application of PolyBrush fabric sealant as it causes trapped bubbles that cannot be removed.  The tape MUST be shrunk prior to covering to avoid unrecoverable puckers in the main fabric.

I have witnessed 3 partially assembled kits that all had a different chord dimension, none of which came in at the plan spec of 39 7/16.  Hence the inclusion of a chord dimension jig above.

Changes From Original plans;

Both panels:

1. Replace strapping tape with 5 spans of 1 inch Poly Tape (Aircraft Spruce)

Bottom Panel:

1.  Add one main rib for a total of 7 (spaced evenly)
2.  Add 6 minor ribs (1/4 inch) between each main rib

Top Panel:

1. Currently added 3 additional main ribs evenly spaced to avoid bracket locations.
2. Added full-length minor ribs (1/4 inch thick with a single LE & TE gusset)
3. Added 3/4 inch .035 internal strut midway between the original internal diagonal strut and the tip to help alleviate spar bowing during the covering process.

Locating holes in foam for internal struts

This was originally a challenge and now. with the addition of several minor ribs I found it necessary to come up with a process to bore these through holes.

Fabricate a template rib. Cut a scrap piece of 1 inch tubing at the angle the strut will go through at. Trace the angle cut tube end onto a 3x5 card and cut out a bit larger than the tube outline. Make two of these cards. Remove the strut and thread the first cut out card onto the strut. Next thread the template rib onto the strut and lastly thread on the second card. Tape in place after the strut is re-located to it’s installed position. Carefully remove the strut far enough so that the rib template can be taken out. Transfer the hole location onto the rib to be bored out and cut out the foam. Fine tune with half round file and/or sandpaper.

The photo here shows the template rib (this one is made from 1/2 inch plywood) located at the position of a minor rib (1/4 inch thick vs main ribs that are 1/2) that will be bored using the template rib and cards taped to it.  (notice the two temporary, removable rivets called 'Clecos" commonly used in aircraft construction).

TO BE CONTINUED