skin crack on elevator

I just found an aprox. 2 cm crack on my rt elevator just aft of the aft end of the center stiffener. I have heard that this is not uncommon. 77 hours on the airframe. I've stop drilled the ends. I'm considering injecting some RTV into the area to dampen the vibes. Is this a good idea? any other suggestions?

When I built the elev. I encorporated a modification of the stiffener rear end which supposedly would prevent said cracking.(a sl bend up off the skin) So much for that idea.

No to RTV

Bill, do not put RTV in the crack just yet. It would hide it if the crack started propagating further than the stop drills. For the time being put some tape over it and re-inspect every couple of hours to make sure it isn't growing. But eventually you have to repair it. Think probably a small scab patch and pop rivets

Reform the trailing edges.

These cracks are caused by improper formed trailing edge radius. Tape up the jaws of you seaming pliers and gently crimp the trailing edges so that there is absolutely NO bulge aft of the last rivet. The 2 RV-6s that I built 15 years ago are still flying with no cracks. I used no sub ribs, RTV, or anything else. If you do this now the stop drilling should be sufficient.

Yes common, ulitmate repair?

billnaz said:

I just found an aprox. 2 cm crack on my rt elevator just aft of the aft end of the center stiffener. I have heard that this is not uncommon. 77 hours on the airframe. I've stop drilled the ends. I'm considering injecting some RTV into the area to dampen the vibes. Is this a good idea? any other suggestions?

When I built the elev. I incorporate a modification of the stiffener rear end which supposedly would prevent said cracking.(a sl bend up off the skin) So much for that idea.

Click to expand...

Not a lot you can do and your repair is ok if you keep an eye on it, short of some external bonded doubler with may be a few some blind rivets (not pretty). I'll be honest with you the best repair is re-skinning. If its not a pre-punched part just buy all new parts and make a new one. You might be able to save or salvage the steel elevator horn. Not saying you have to make a new one, just that it's the ultimate solution. Mel is right, cracks are from the stiffener not extending to the most they possibly can and the flexing around that last rivet causes the cracks. Silicon in the corner to fill, support and dampen is a common mod people use to shore up this area during construction. The early RV4's where real prone due to the super thin skin they used. Later Van upped the gauge on later models. I am not sure if some early RV6's had the thinner skin or not (0.022).

Early ones...

gmcjetpilot said:

....
Later Van upped the gauge on later models. I am not sure if some early RV6's had the thinner skin or not (0.022).

Click to expand...

Early RV-6s have 0.016 skins here.

One of Van's fixes for the early elevator skins was to inject RTV into the trailing edge angle at the stiffener locations. I'm not sure if Mel's "squeeze it" approach will work in all occasions... the size and shape of the stiffener ends dictate how much squeezing can occur before one stiffener hits the opposing skin... none of these parts were pre-punched or pre-marked in the early kits, so lots of variation exists.

The plans appear to have been re-drawn in 92/93 and changed from sheet 4 to sheet 4a - perhaps the first sheets that were CAD drawn. At this re-draw, the dimension from the last rivet to the fold and the length of the stiffeners was "refined"....

gil A

Gil is correct - mine is one of the last .016 6's. I had cracks in my rudder at the forward edge of the stiffeners. I built the elevators and rudder with rtv supporting the trailing edge, so no problems there. Anyway, I drilled three cracks in the rudder at around 150 hours, no more problems in the next 800. Drill 'em and watch for any more monkey business.

thank you

Thanks to all for the replies. Sounds like I'll just watch closely my mitigation on the crack. It's the price of owning a slow build built by a rank amature, eternal vigilance!

Bill