Tail Spar Inspection

[Paul]

Hello

I'm new to the Culver Club and not very knowledgeable about these wooden aircraft. How do you inspect the tail spar on a Culver Cadet?

Thanks

Paul

[JoeB]

Hi Paul,
Without some surgery you're not really able to inspect anything on the vertical stabilizer, I have not heard or know of any issues there. 

You will want to inspect the longerons in the fuselage where the horizontal stabilizer attaches.  These longerons can have broken glue joints from handling or even be broken from over-torquing of the horizontal stabilizer attachment points. Reference Service Memo #12 found here: http://www.culvercadet.com/servicememos/servicememo12.pdf

While the stabilizer is off the airplane you'll want to inspect/feel the 1/16" plywood bond to the ribs with gentle squeezes and light taps with your knuckles.  Also rotating/shaking the horizontal stabilizer around while off the airplane listening for loose glue rattling around inside there.  If you hear rattling, hopefully it is just the drips of glue that have broken loose from the sides of the ribs.  On my airplane I removed the lower plywood skin to inspect and found loose drips of dried glue and two ribs that had broken glue joints to the plywood. 
Easily repaired but the process is a little time consuming with cleaning, replacing all the loose gussets and everything.  Do it right, when it goes back together it needs to be good for another 80 years!

I hope that helps answer your question!
Joe

[Paul]

Joe, thanks for your information. I was wondering how the horizontal stabilizer spar is inspected while on a flying Cadet, does it have to be removed? Have there been accidents due to rear spar failures?

Paul

[JoeB]

There are two 7/8" thick spars in the horizontal stabilizer, ribs are located as follows: rib 1 centered , rib 2 6” from center, rib 3 11” from center, rib 4 22” from center, rib 5 33” from center, rib 6 44” from center, the leading edge is a 5-ply lamination and then the entire upper and lower surface is covered in 1/16" plywood and fabric.  The horizontal stabilizer is very strong and I have not heard of any failures.
During a thorough inspection of an airframe, the horizontal stabilizer can be fairly easily removed as it is bolted to the fuselage. Remove the elevator trim, trim cable cover and the stabilizer fasteners and off it comes.
I would not open the stabilizer up for inspection unless it sounds (glue rattling around inside), or feels (spongy plywood bond at the ribs), suspicious.