Thomas Lukasczyk
Member
Hi all
Recently, I discovered cracks in the rudder-skin of my RV-4. The cracks occur at the forward most rivet of various stiffeners.
If you push the skin slightly and watch the surface move, you will know why.
I kept stop drilling them and patched them up with small pieces of 0.020 Alclad attached with high-performance metal adhesive.
None of the cracks ever grew, but when there were three patches on the rudder, it was time to do something about it. I have done "left-rudder-aerobatics" lately and I assume that has caused the cracks. The plane has 200 hours TT now and I feel certain maneuvers do accelerate this problem.
Although it is a small, rather cosmetic flaw, it still bites you and you wonder whats up next.
Long story short, I am going to build a new rudder.
As far as I know, these are the most common countermeasures against cracks. Are there others?
-Use 0.020 skins (already had them)
-Put RTV between stiffeners at trailing edge (done that, no cracks there)
-Use Pro-seal or Sikaflex to "wet-rivet" the stiffeners on
-Use small RV-10 type angles to attach the stiffeners to the spar (Rivets, Sikaflex or Pro-seal)
I am also considering a way to omit the stiffeners completely.
What about a blue-foam core that fills the inside of the rudder? I would glue it in using a special (aluminum to PU-foam) adhesive for aluminum-sandwich components for freeze trucks.
This stuff works pretty well and it will not come of ever again. It does not age and temperature is a non-issue. It is even suitable for structures of aluminum vehicles, like busses, railway-waggons and RVs (the bulky ones without wings).
Everything else is going to be per the plans.
The main concern so far is weight. It is probalbly going to be a little heavier than the stock-rudder (not necessarily). I do not worry about CG but I fear the flutter characteristics might change.
The RV-4 does not have a counterbalaced rudder so my plan is to not exceed the residual momentum of the old rudder. (I hope to have translated "residual momentum" correctly)
Has anybody done something similar? Is there anything you can think of why I should not be doing it this way? (other than "never change a running system").
Thomas, RV-4 http://www.rv-4.de
Recently, I discovered cracks in the rudder-skin of my RV-4. The cracks occur at the forward most rivet of various stiffeners.
If you push the skin slightly and watch the surface move, you will know why.
I kept stop drilling them and patched them up with small pieces of 0.020 Alclad attached with high-performance metal adhesive.
None of the cracks ever grew, but when there were three patches on the rudder, it was time to do something about it. I have done "left-rudder-aerobatics" lately and I assume that has caused the cracks. The plane has 200 hours TT now and I feel certain maneuvers do accelerate this problem.
Although it is a small, rather cosmetic flaw, it still bites you and you wonder whats up next.
Long story short, I am going to build a new rudder.
As far as I know, these are the most common countermeasures against cracks. Are there others?
-Use 0.020 skins (already had them)
-Put RTV between stiffeners at trailing edge (done that, no cracks there)
-Use Pro-seal or Sikaflex to "wet-rivet" the stiffeners on
-Use small RV-10 type angles to attach the stiffeners to the spar (Rivets, Sikaflex or Pro-seal)
I am also considering a way to omit the stiffeners completely.
What about a blue-foam core that fills the inside of the rudder? I would glue it in using a special (aluminum to PU-foam) adhesive for aluminum-sandwich components for freeze trucks.
This stuff works pretty well and it will not come of ever again. It does not age and temperature is a non-issue. It is even suitable for structures of aluminum vehicles, like busses, railway-waggons and RVs (the bulky ones without wings).
Everything else is going to be per the plans.
The main concern so far is weight. It is probalbly going to be a little heavier than the stock-rudder (not necessarily). I do not worry about CG but I fear the flutter characteristics might change.
The RV-4 does not have a counterbalaced rudder so my plan is to not exceed the residual momentum of the old rudder. (I hope to have translated "residual momentum" correctly)
Has anybody done something similar? Is there anything you can think of why I should not be doing it this way? (other than "never change a running system").
Thomas, RV-4 http://www.rv-4.de