Removing and Replacing the Left outboard rib of the ecenter section on a 415C
The following procedure describes the tools, materials and procedures required for changing the Left End Rib, Univair part no. 415-13135-L, on a 1946 415C. The subject airframe is a 1946 415C #2514.
Introduction
I discovered that the Left End Butt Rib on my 415C was patched when I removed the wing to install the Butt Rib Repair Kit. This kit is a re-enforcement gusset to strengthen the connection of the forward top of the rib to the center spar cap. The rib is subject to fatigue cracking at the forward top corner. The Butt Rib Repair Kit is the usual way to patch the rib when it cracks in that location. In my case, after removing the wings, I found the left rib had a patch in that location which prevented the installation of the kit. The best repair was to install the gusset kit on a replacement rib and then install the replacement rib. This paper describes the procedure used to replace the Left End Rib on my 1946 415C #2514. All work was supervised and approved by a licensed mechanic.
Special Tools and Parts
Riveting Tool
A pneumatic riveting gun was required for this procedure due to the limited access. An assortment of rivet sets for the gun and bucking bars was also needed. A supply of Clecos and clamps was also required.
Parts
New or Serviceable Rib, Univair End Rib-Left 415-13135-L
Gusset Kit, Univair SK-48-R and/or SK-48-L Ercoupe Butt Rib Repair Kit
Fasteners, a few AN3 screws and nyloc nuts will be needed
Rivets, various sizes of rivets, including some flush rivets
Lifting Equipment
The main landing gear leg needs to be removed to allow access for riveting. This will require lifting the airframe. The airframe can be lifted using an overhead hoist or an engine lifter using a nylon strap on the forward wing attach point. I did not have the cowling off, so in my case, the airframe was lifted on the forward wing attachment point or with a jack from the bottom, as needed.
The Procedure
Removing the Wings
The wings will need to be removed to provide access to the rib. The process of removing and replacing the wings is not difficult and will be described elsewhere. With the wing removed, the Butt Rib Repair Kit can be installed if the rib is serviceable. In my case, the End Rib-Right was in good condition so the gusset kit SK-48-R was installed at that time. The End Rib-Left had a patch applied in the past which prevented installation of the gusset kit.
Removing the End Rib-Left
After removing the wing, the aileron bellcrank was removed and the airframe was lifted and suspended from the forward wing attachment using an engine lifter. The rivets were removed from the old rib and the rib was removed from the airframe.
The three gear leg bolts with nylocs were removed to allow the gear leg to hang, supported on long screwdrivers, while the rib was installed. The brake line remained connected, but the brake line clamps were removed to allow positioning the gear leg for riveting. A floor jack supported the airframe for part of the procedure to allow removal of the overhead lifting strap which blocks access to the forward row of rivets on the rib. Another way is to lift the airframe at the engine mount firewall location.
Preparing the Replacement Rib
There are some attachments to the rib. In my case, I used a serviceable rib which had the attachments intact except for the lower re-enforcement angle. The attachments were transferred over or removed as needed. The rib was cleaned and painted as needed. The inside of the wing root area was cleaned. The gusset kit, Univair SK-48-L Ercoupe Butt Rib Repair Kit, was installed on the rib.
Installing the Rib
The rib was placed in location and secured with Clecos in all rivet holes. The rivets were installed using various rivet sets and bucking bars. The wing rib reinforcement gusset assembly is fastened to the center spar cap using AN3 screws and nylocs.
Final Assembly
The gear leg was bolted on and the aileron bellcrank was re-installed with a new bearing. The wing and fairings were installed and the brake lines secured to complete the procedure.
Conclusions
For those contemplating this repair, it will help to have good lifting equipment and a good assortment of rivet sets and bucking bars. In a few locations a rivet squeezer will work, but most of the rivets will need to be driven. An assortment of rivets will be needed a few of which will be flush rivets.
John Earl