Top rudder skin and rib-rudder tip
Please reference the parts manual figure 7 for the items below.
I found item 10 (Rib-Rudder Tip) cracked in two pieces right at the rudder to vertical stabilizer hinge line. After removing the rudder and drilling out the upper tip skin/rib rivets I discovered a lead weight about 4” long, 1.5” to 1” wide and contoured to fit forward of item 9 (Spar-Rudder Auxiliary) and the interior skin. It’s held in place by one #6 screw & nut passing from the outside skin, through the lead weight and through where items 9 and 10 meet.
Question is, does that lead weight belong there? I don’t see it nor the screw & nut in the parts book. I’m thinking that weight cantilevered 10” forward of the rudder/vertical stabilizer hinge line creates quite a load on the rib that cracked and then the skin. The skin was cracked at the hinge line rivet holes both sides.
John 108-2 N2721L
Here’s a photo showing the cracked rib and lead weight next to were they go. Guess that lead caused a good bit of corrosion too.
my 108-2 also has that weight. I believe it is part of the design to prevent flutter.
It may not be in the parts book, but it should have a Stinson part number on it. Definitely supposed to be there for flutter, but also hard on the structure up there. Just part of the deal.
Johnm930: That lead weight is absolutely supposed to be there. It is to balance the rudder. Higher speed aircraft are very sensitive to control surface balance. There are balance weights in tips of the Ailerons and in the tips of the elevators. Airplanes like Bonanzas are extremely sensitive to proper control surface balance. Our Stinsons are not as sensitive but the weights are there to prevent flutter at high speeds in case someone exceeds the red line. I called Univair some 45 years ago trying to find a spec on the balance or the weights. They could not find anything in the drawings that specified the weight. All we can do is keep the weight in there properly.
I doubt that the weight caused your rudder rib to crack. What probably caused it was perhaps the airplane sat out in the wind for years and the wind was flopping the rudder around. especially if the tailwheel guidance springs were the wrong ones or not on the rudder at the time it was stored outside. That is more likely the cause of the cracks and yes, the balance weight contributed, but in normal operation it would not be a problem. Only if stored outside for long periods in windy locations and unsecured.
Thanks Larry and to the others that responded also. I just wanted to make sure it wasn’t someone’s good intention idea to put a weight there. Great information about weights in the other control surfaces to Larry, good to know. I’ve owned and flown this plane for 20 years, always hangered except for overnights on trips, fair weather as far as I can remember. Just found the crack on a post flight the other day. I do slip to landings almost always and sometimes quite aggressively. Wonder if that practice might have helped the rib to crack?
Yes, aggressive slips might contribute to the cracking but a doubt it. You have been flying this plane for 20 years, but some time before you owned it it may have had something that happened that helped start the crack but did not show up until now. These airplanes are 75+ years old now and it is hard to tell what may have happened to them in the more than 30 years prior to 2000. I have only been flying mine for 53 years and have slipped it sometimes but not very often, less now that I am on a longer runway than I had back 40-50 years ago. I keep minw at my Airport, Flying W, XS56 in deep south Texas since 2001. Prior to that I had it in Indiana on a short, side of the hill, one way strip.
I am right now in Indiana for the summer and will try to go to OSH next week in our motorhome. Last time I flew the Stinson to OSH was in 1991 and I quit because they moved the classic camping away from the woods to make way for non-camping expensive planes like Howards and Staggerwings.
I have a '65 Mooney M20C (manual gear and hydraulic flaps) that I keep in Indiana since 1990. I now have the same 180 hp Lycoming O-360 A1D in both the Stinson and the Mooney, but with the constant speed prop the Mooney is much faster. The Stinson did not gain any speed with the larger engine, but it climbs a lot better.
Where are you located?
Florida, east coast by the Space Center, Arthur Dunn Airpark, X21. I normally land on the shorter grass strip rather than the 3000 foot paved runway and there’s trees on both ends of the grass. That’s the reason for slipping most of the time plus, I like to stay high on the approach in order to make the runway in case the Franklin has an issue, then come down like an elevator for the threshold once clear of the trees.