Horizontal Stab Bolt Holes, '41 LCA

[Keith U.]

I am just getting into my fuselage rebuild and while the woodwork generally seems in good shape, the forward horizontal stab mounting bolt holes in the fuselage are elongated, one even had a bushing in it.  It seems like a weak area.  Has anyone seen this or had any experience with this area?

[Brett Lovett]

Check Service Memo 12:  http://www.culvercadet.com/servicememos/servicememo12.pdf

The factory became aware that some airplanes were experiencing crushed longerons at the front stabilizer mount and issued this service bulletin to address the issue.  Part of the recommended alteration is to install a steel bushing.  The text suggests that some airplanes were originally equipped with steel bushings in these mounting holes and some weren't.  I would recommend fully complying with Service Memo 12 while you are doing the fuselage rebuild.

[Brett Lovett]

I also suggest paying close attention to Service Memo 5, whether it applies to your Culver by serial number or not.  This service memo does not apply to my airplane, s/n 329, built well after the service memo alteration was incorporated into production starting with s/n 179.  However I found out the hard way that someone in the airplane's past didn't like those big pulleys sticking up out of the floorboard (even with the cute little covers on them), so they re-drilled the pulley brackets and installed small pulleys that would not extend through the floorboard, thus doing a very good job of recreating the issue and events that resulted in the service memo, an experience that I could have easily lived without.

[Keith U.]

Thanks Brett,
The Service Memo is exactly what I needed.  The longerons are not crushed, and both holes have bushings, but I still plan on following this letter.  I have #117, So I will look at SM#5 also.
Thanks again...

[Culver Dreamer]

Can someone take and post a picture of the "fix"   I'm not quite getting my head around how ,what I am imagining the part to look like, makes the area stronger.
Mark

[Keith U.]

Here is a picture of the stab. attach bolt holes.  The metal bracket ties in the vertical fin and horizontal stab. to the fuselage.

[Brett Lovett]

Can someone take and post a picture of the "fix"   I'm not quite getting my head around how ,what I am imagining the part to look like, makes the area stronger.
Mark

Mark,

I don't have a picture, but I can give you a description that hopefully will help you visualize it.

A 3/16 inch thick plywood block is glued to the underside of the longeron at the bolt hole.  A 1-3/16" long bushing (the thickness of the longeron plus the block) is placed around the bolt in the hole, through both the longeron and the block, to prevent the bolt from crushing the longeron and plywood block.  A .049 thick tab of 4130 sheet is soldered to the bolt head to serve both as an anchor for the bolt head and as a washer to spread the load of the bolt head.  The end of this tab being bent up over the front of the plywood block keeps the bolt from rotating when the nut is installed. 

The bushing provides the primary strength to prevent crushing from excessive tightening.  The 4130 sheet tab serves as a washer to reduce the likelihood of crushing (by spreading the load of the head) from "improper handling" (lifting by the leading edge of the stabilizer).  I also suppose the plywood block also serves a bit as a doubler for the longeron adding a bit of strength and thickness to the original 1" longeron and possibly can take some crush from the bolt head without damaging the longeron itself.

At least I think this is right. 

Brett