RUDDER BENT @ OSH - HELP

[crabandy]

Originally Posted by RVbySDI

I hate to tag onto someone else’s thread. I have a damaged rudder also from last night’s storm at OSH. Attachment 28562

Attachment 28563

Attachment 28564in my case the trailing edge rivets at the bottom of the rudder unzipped.

I am going to need a new rudder if anyone else has a 7,9,14 rudder I would appreciate talking to you. I have talked with Van this morning and discussed my damage. He believes I can repair it and fly home. However, it will have to be replaced once home.

If anyone has a built 7,9,14 rudder they can sell me please call me: four O fife ate 2 two zero six 2 won. You can also find my phone number on the link below in my signature.

I was using the AntiSplat gust lock. The wind pushed the elevator hard enough to pull the stick aft. That allowed the bars to the rudder pedals to fall away and dislodge from the pedals. The rudder was free moving at that point.

If anyone can help please call my cell.

Thanks,

Steve,
I have a completed rudder except for the fiberglass. I called the number above, the mailbox was full and was “Jacob Duncan.” Not sure I got the number.

https://andycrabtree.smugmug.com/RV7-Tail-4-Sale

[pilotkms]

Ok. I talked with Larry and it seems he has action in place to allow him to get home. Thanx for those that are assisting him.
I got the scoop on what his control lock was that DID NOT FAIL. It held the rudder tightly at the top where he had it installed. It was mounted on the rudder portion protruding forward (counter balance) and the vertical stab, using zip ties. It held tightly but the wind forced the bottom of the rudder to the left.
Pix below.
He used 2 “bondo” spreaders on each side with 2 holes drilled in each for the zip ties.
He used a similar setup for the elevators and ailerons, but just 1 “bondo” spreader on each side. They held and had no damage to the elevators or ailerons.
Larry- if I have anything wrong or u can add anything here, please correct me or add info here.

[g zero]

Originally Posted by pilotkms

Ok. I talked with Larry and it seems he has action in place to allow him to get home. Thanx for those that are assisting him.
I got the scoop on what his control lock was that DID NOT FAIL. It held the rudder tightly at the top where he had it installed. It was mounted on the rudder portion protruding forward (counter balance) and the vertical stab, using zip ties. It held tightly but the wind forced the bottom of the rudder to the left.
Pix below.
He used 2 “bondo” spreaders on each side with 2 holes drilled in each for the zip ties.
He used a similar setup for the elevators and ailerons, but just 1 “bondo” spreader on each side. They held and had no damage to the elevators or ailerons.
Larry- if I have anything wrong or u can add anything here, please correct me or add info here.

Curious… if it didn’t fail why all the duct tape ? Was the hole in the rudder previously? Trying to learn something here .

[scsmith]

Originally Posted by g zero

Curious… if it didn’t fail why all the duct tape ? Was the hole in the rudder previously? Trying to learn something here .

No doubt the duck tape was added after the damage incident to minimize continued flopping around of the rudder.

Really sad. At OSH you don't necessarily have the option of tying down pointed into the wind - even if you knew which direction the wind might come from.

The cause of damage here is that if you restrain the rudder motion at either end -- either the top at the counterweight or at the bottom by any control lock that keeps the rudder horn from moving -- either way, the aerodynamic load from the wind is distributed along the whole length of the rudder, so there is a lot of torsional moment put into the rudder. At some load, the rudder skins will buckle in the areas between the stiffeners.
Arguably restraining the counterweight is slightly better than restraining the rudder horn, because the skin bay between the counterweight rib and the first stiffener below it is smaller than the skin bay between the bottom rib and the first stiffener above that. The smaller bay of unsupported skin takes a higher buckling load. Also presumably there is some 'boundary layer' in the wind, so that the wind velocity on the upper half of the rudder is probably a bit more than on the lower half, so the upper restraint is probably closer to the effective point of application of the aero load.

The only way to prevent the torsional moment that causes this is to restrain BOTH the counterweight and the rudder horn. That allows the aerodynamic load to be shared by both restraints.

[Jpm757]

FWIW I have an unboxed RV7 empennage kit, will let it go cheap.

[pilotkms]

The duct tape was added the next morning, after the failure.
Thanx for your opinion Steve.
I will continue to restrain my rudder at the horn because, even tho it is contrary to your theory, it has worked for me thru 2 disastrous OSH storms.

[scsmith]

Originally Posted by pilotkms

The duct tape was added the next morning, after the failure.
Thanx for your opinion Steve.
I will continue to restrain my rudder at the horn because, even tho it is contrary to your theory, it has worked for me thru 2 disastrous OSH storms.

Yeah, I think the distinction between restraining upper or lower might be splitting hairs. But if you already have a good restraint on the bottom (at the horn) then it is pretty fast and cheap to add the additional restraint at the counterweight as well - use an AirGizmo one, or roll your own. I think something maybe stiffer than bondo-spreaders though. I think having both restraints would give me a lot of peace-of-mind overnight when a storm is pounding away.

[sprucemoose]

Originally Posted by RVbySDI

Jeff, I would welcome a conversation with you. I am at the homebuilt pavilion most of today, or call my cell. Thanks.

I do have an RV9A so not sure if that would work for me or not. Anyone else please keep me in mind.

My rudder wouldn’t work on a 9, sorry.

[BillL]

I have a DIY (aluminum) restraint for my 7 rudder that is between the rudder and HS. I have wondered about it slipping to the pivot and allowing movement.

That could have happened here . . . where the nylon stretched as the parts displaced and pushed the "lock" closer into the pivot until the nylon stretch allowed sufficient rudder displacement to make contact. Make sense?

Also, I have wondered about the calculated torque that could be generated to test the lock. Steve (Smith), is there a straight forward - worst case angle for the wind to calculate the torque vs gust velocity? This might help understand the design requirement.

Edit: Steve, I looked at a NASA L/D curve for a thin flat plate and it had a .7 CL at ~10 deg. Using that and an online lift calculator, 936 in2 for the rudder (7/9) and 12" from area center to the pivot line. The "lift" calculator yielded 42 lbf at 53 kt (88 ft/s). Is this in the ball park? I don't know the 14 rudder dimensions.

[LJackson]

Hi VAF community! This is Larry (aka the guy with the twisted rudder). It's been a sleepless night and a busy day, but things are looking better thanks to all of your help.

The damaged rudder has been removed from the plane. Confirming our original assessment, the broken trailing edge and buckled skin resulted in a complete lack of torsional stiffness. I am grateful for all of the help. Updates will be coming.