Repairing a broken T-28 foam wing

[Frank v B]

A member's plane suffered significant damage because a sudden unanticipated gravity reversal. 
The plane cartwheeled on take-off.  The foam wing ended up in 3 large pieces with severe cracks in the center section.
This post will go through the repair and re-maiden of the plane.

Frank

[Knightlite]

Gorilla Glue now makes a white expanding foam glue now. Make repairs almost invisible.

[Frank v B]

Approach:

step 1: assemble the wing parts one at a time with 5 minute epoxy so it holds together.
step 2: reinforce the joints with round toothpicks dipped in 5 minute epoxy.  They are poked into the wing across the joints (both ways).  Then the back ends of the toothpicks are cut off with side cutters.  Once cut off, I push them into the hole further so the spackling filler can fill the hole.
step 3- make the crack disappear with white filler and paint.
step 4- re-attach the aileron with proper pin hinges. This wing had one aileron completely broken off at the hinge line.

I use Bob Smith 5 minute epoxy because it stays clear.  Other ones seem to yellow.

Frank

ps: Colin, thanks for the advice on the Gorilla Glue.  Will buy and try it.  I have a personal principle in repairs- I never experiment on a customer's repair unless there is nothing to lose.
Lots to lose here. 

[Frank v B]

Gluing the last large crack.

04- glued crack with round toothpicks inserted.
05- the toothpicks cut off with a side cutter.  Then the toothpicks are pushed in below the surface before the glue dries.

Frank

[Frank v B]

Installing hinges.

The port aileron was ripped off.  The hinge point was in the middle of the aileron,
I used 3 hinges, removed the pin with a side cutter.  For purposes of this demonstration I have inserted a length of piano wire the width of the aileron.  The purpose of the wire is to show that the hinge pins of all 3 hinges need to be exactly in line on all dimensions.

Step 1- remove the pins from 3 hinges
Step 2- cut off the remaining foam that used to be the hinge on both the wing and the aileron.
Step 3- cut slots where the hinges are to be installed.  Note: I install the hinges on one side (wing), glue them in and let them cure.  Then do the same on the aileron side (tomorrow).  This allows everything to cure on one side.
Step 4- add a drop of oil on the hinge points.  This is so epoxy will not cure on it.  I spread it on the small hinge tabs with a toothpick.
Step 5- push 5 minute epoxy into each slot in the wing.  Wipe off excess.  Put glue on one half of the 3 hinges and insert them into the wing.  Make sure the piece of piano wire is absolutely straight.

So much for one side of the hinges.  Tomorrow the same will happen to the aileron.

Photos:
06- 3 hinges.  The right two have had the pins partially removed.
07- 3 hinges with a piece of piano wire holding them in place.
08- left hinge installed, middle hinge ready to be installed with glue.
09- 5 minute epoxy pushed into the last hinge slot.
10- all three hinges perfectly lined up.

Frank

[Frank v B]

Finishing the hinging

- cut 3 slots in the aileron to match the hinge position.
- cut the hinge pins.  Note that the pins are long so they can be cut and slipped apart. Photo 56.  Note in photo 57 where to cut the pin if you ever have to take it apart.  It is left long so it can be pulled up above the wing and cut with a side cutter.
- added 5 minute epoxy to the three slots
- added epoxy to both sides of each plastic hinge.  Only on the ends.  It spreads towards the hinge pin when it is pushed into the final position.
- added tape to hold it tight while the glue dries*. Photo 58

Frank

* I used JB Weld 5 minute epoxy.  It starts to harden in 5 minutes but takes an hour to cure...lots of time for the hinge to slip and cure in the wrong position.

[Frank v B]

Everything glued and sanded.  The aileron push rod was missing.  There was one hiding in my collection the exact length.

Last job- use light weight spackling (filler).  It dries a dull white.  It is available at the box stores like Home Depot.  There are about three or four types.  Pick it up.  If it feels empty you have the right one.  All others have significant weight. The one I use is DAP Fast'n Final.

Done.

The owner has been contacted.  The wing is awaiting a date with the fuse.

Frank