Rudder Damage and Cure

sjhurlbut · #1 12-02-2007, 08:20 AM

During a recent trip we encountered very gusty winds on the ground (30G50 kts). With the airplane tied down (no hanger space) we had some damage happen to the rudder. I use a common home made rudder lock that others employ as well that bolts the rudder horn to the rudder stop using 0.125 alum and AN3 bolts. I wanted to share this with others because I believe in high winds, this type of rudder lock is not sufficient. The rudder is held at the hinge but is allowed to "twist" at the trailing edge causing compression on one side of the rudder and tension on the other. The effect was the split rivets at the bottom of the rudder. It also just so happened that with the wind shift that day, the airplane ended up in the worst 90 degrees to wind position.

So if you encouter any strong winds, consider a full rudder lock that entends from VS leading edge to rudder trailing edge and move the airplane to face into wind.

Steve
RV7A

lrfrey · #2 12-02-2007, 08:58 AM

Wow! That's amazing Steve. Sorry for your damage. I'm still trying to figure out how a "full rudder lock" you mention would prevent the damage though.

Larry

AlexPeterson · #3 12-02-2007, 10:34 AM

Wow is right! I am really having trouble imagining just how this happened, with only that damage shown. Just to be clear, you locked the rudder with a fore/aft piece of aluminum, from the stop to the bar that the rudder control cables connect? Were additional rivets above what is shown in the picture sheared? Is the damage confined to what we see in the picture?

LettersFromFlyoverCountry · #4 12-02-2007, 03:35 PM

This is amazing! It's almost as if someone took a flat head screwdriver and just worked their way up. Is there damage forward of what's shown here?

DanH · #5 12-02-2007, 03:53 PM

You sure you didn't get hit by something?

kevinh · #6 12-02-2007, 03:59 PM

Quote:

Originally Posted by DanH

You sure you didn't get hit by something?

Yeah- that's what it looks like to me.

robertahegy · #7 12-02-2007, 04:15 PM

I use a 1/4" U shaped pin in the rudder horn and stop, which is basically the same. I don't see how this would cause damage as shown, either. That part of the rudder can not hit the elevators, at least not on a 7.

I think that damage was done by something other than wind, unless the wind blew something into the rudder.

Roberta

Mike S · #8 12-02-2007, 04:35 PM

Sorry to be the voice of disagreement, but to me, it sure looks like the rudder failed exactly where/how I would have expected it to.

The rudder lock holds the bottom of the rudder in a fixed position, and the balance of the rudder is trying to move with the wind. This will induce a torsional force into the rudder, as the majority of the surface tries to pivot on the hinge line, and weathervane.

The locked bottom is resisting this, and the farther away from the hinge line, the greater moment arm. Thus, the failure at the trailing edge, at the bottom where there is not only a stiffener, but the bottom rib also.

But, it could also have been flying debris, from the wind, not just the wind. However, the forces involved from either debris, or just wind, still reach max force and max resistance right where the failure occurred.

Paul Thomas · #9 12-02-2007, 04:57 PM

I agree with Mike which. Van locks the rudder using the same system by the counterweight, put some remove before flags on it and you're good to go... the only reason I know of their rudder lock is that it was not removed during preflight on my demo flight, luckily the control check caught it.

robertahegy · #10 12-02-2007, 06:31 PM

I guess I was mistaken. The damage, at first, looked like impact. But the twisting-tearing could be from the sideload force of the wind. Must have been quite a wind storm, though. These same forces are encountered during low speed flight and rudder operation.

I arrange for a hangar wherever I go, or I go somewhere else. I don't need to see that kind of damage anywhere. Ruins the day.

Roberta