Rudder Repair - 5/1/2008 to 5/3/2008
During strong gust the rudder lock failed. As a result the rudder horn impact the stop, the twist force acted on the trailing edge popped the trailing edge open. The shop head of rivets are too small. The skin pull right though the shop heads.
Similiar problem was reported four months ago by a 7 builder: Click here to see the report
Trailing edge after the wind gust hit.
Damage to the trailing edge includes a bend to the wedge.
Shop heads were insufficiently set. The small size of the head made it pull through rudder skin easily.
Bend the wedge straight then drill bad rivets out.
Apply JB weld to both sides of the wedge. Wrap the trailing edge with plastic film, then clamp it with two pieces of wood. After the glue dries, I will get a friend to help set the rivets.
This afternoon I got a helper to buckle rivets. First we used the factory specified 426-3x3.5 rivet. The shop head was way too small to fill the dimple. I drilled it out and put in a 426-3x4 rivet. The shop head looks much better. We finished all the rivet and the trailing edge looks good.
I decided to put a pin strip over the rivets instead mix two different paints and touch up over the rivet heads. Now the repair is done.
The damage to the rudder must have twisted it. Since I fixed rudder the ball has moved to the left by one. During cruise I have to apply a lot of force to the left rudder to keep the ball centered. Again I made a wedge using Bersa wood and duct taped it to the trailing edge of the rudder. During my Florida trip in June, the wedge flew away. I finally decided to make another one and glass it in. I applied one layer of glass and put some Icing (see painting page) over it. After several icing layers and sanding, I applied primer then using an air brush painted it. The new trim tab is more than three times the length of the old one. Well, I am not ready to build a new rudder of obvious reason (I am too lazy!). An ugly rudder is the punishment.
Rudder Lock
Here is a photo of the rudder lock in place (after the damage I bent it back to shape):
When I think a little deeper about why it failed, I realized that the stop and the honr are at different height. The rod can slip down the hole on the horn, thus, be slanted. This makes the rod much weaker (bending force).
In order not for the rod to slip down the hole, there must be something to keep it up there. I will post my solution here when I build one.
In this picture you can see the height difference (3/4") between the stop and the horn.
5-5-2008. After pondering the issue for a few days, finally I decided not to use a very rigid lock. A rigid lock will constrain the bottom of the rudder. Yet, the top is not constrained. When wind gust hit the rudder, the top will turn thus generate a twist force on the trailing edge. A little flexibility of the lock will absorb this force, thus, reduce the twist on the trailing edge. My final decision is to use two 3/16" mild steel U-shaped lock, one on each side of the rudder. Each will give a little during strong gust, but, probably will not fail like the single 1/8" lock did.
8-14-2009. I noticed after awhile the lock has a tendency of getting pushed out of the holes. During my last trip the wind was strong, I had to tie the end of the lock together to prevent it from popping out of the holes. This morning I cut the legs of the lock a little shorter then put on #10-24 thread on them. I went to Lowes and brought two stainless steel wing nuts. In the future after inserting the lock, I will put the wing nuts on. This way I am sure the lock will not slip out of the holes.
Go to the homepage