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Mysterious Case of Rudder Dimples

PandaCub

Active Member
Greetings, all:

A few days ago my RV-14A was tied down on a Wyoming ramp under some pretty strong surface winds (30 knots or so). While I did have redundant gust locks in place (Airgizmos, Anti-Splat, and Pad-Lock), they popped off a few times and I had to reattach them.

Everything seemed OK on inspection this morning, but I noticed three curious dimples just about where the rudder might contact the elevator if the RV-14 rudder stop weren't in place (see Photo 1 attached). As it is, the rudder stop prevents these surfaces from coming anywhere near each other (I measure a full inch between a pegged rudder and the elevator surface - see Photo 2).

For the rudder to override the stop and whack the elevator hard enough to cause these dimples seems unlikely, and I find no obvious sign of wrinkles/deformation/flex on the rudder.

I suppose these dimples could be totally unrelated (hangar rash, etc) but the location, shape, and circumstances have me very suspicious.

Opinions appreciated.
 

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Yes, if the rudder isn't secured, this could result... The rudder WILL warp that much in gusty winds.

Many threads on VAF on this subject.
 
The rudder WILL warp that much in gusty winds.

I just wonder if this single gust warping episode might have permanently weakened the rudder - or is it like the aluminum wings of an airliner that we commonly watch flex through the window.

Should I be worried about doing snap rolls and such from now on?
 
Nothing mysterious about it... Your rudder has contacted your elevator, more than once. If you look carefully you'll probably see impact marks on the edge of the elevator as well, but they'll be harder to see. The rudder *will* flex that far.
 
I just wonder if this single gust warping episode might have permanently weakened the rudder - or is it like the aluminum wings of an airliner that we commonly watch flex through the window.

Should I be worried about doing snap rolls and such from now on?

Well, Van's doesn't endorse doing snap rolls in any RV model, but it should be fine for any of the flight operations that are recommended.

Having said that, a detailed inspection of the entire rudder and hinge area on the rudder and vertical stab. is prudent.
 
And speaking of snap rolls.......

If I remember correctly the two maneuvers Van EXPLICITLY does not recommend is "snap rolls" and "tail slides"!
 
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a detailed inspection of the entire rudder and hinge area on the rudder and vertical stab is prudent.

Thanks, Scott. I've now spent about an hour inspecting and strategically pressing on my RV-14A's rudder assembly and don't notice any permanent deformation (other than the cosmetic skin dimples). Even so, I'm having an A&P go over it next week before I fly again.

I never imagined the rudder could flex so much that it would contact the elevator. Upon searching other threads, though, I saw a case (RV-7, I believe) where the elevator actually poked holes in the skin!

The discouraging part is I'm very diligent about gust locks. In this case I had an Anti Splat Ultimate Gust Lock (which tends to pop off my rudder pedals without supplemental locks) as well as AirGizmos clamps (which work their way loose in a stiff wind) on the left aileron and elevator. Also installed a new PADLock on the rudder, which I sorely regret: its thru bolt acts like a rasp and put a nasty dent aft of the vertical stabilizer rivets. Not recommended at all.

Photos below (of gust lock products in theory vs in practice on my airplane). And look for my other thread entitled Subterranean Gustlock Blues.
 

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Where are those recommendations? I didn't know they existed!

Off topic, but ...

In general, the aerobatic RVs are not specifically designed for snap rolls, and certainly not for tail slides. But note that there are several very experienced and qualified pilots who snap roll their RVs successfully, including Van himself, and in competitions. But they are very careful and know what they are doing.

See the article "An Aerobatic Epistle", by Van himself:


Another article by Van himself on competition aerobatics, "IAC Aerobatics in RVs", with a good addendum on preparing your RV for aerobatics by Ron Schreck. Van again addresses snap rolls and tail slides in the article:


And note the "Aerobatics" section on Van's website:

 
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My apologies for using the term "snap roll" (I don't do those); what I really meant was spin recovery or any other aerial maneuver that requires full rudder deflection.

I'm simply wondering if the ground gusts that evidently flexed my RV-14 rudder could have weakened it to a degree that I'd have to worry about anything down the road.

Again, I don't see any signs of wrinkling, warpage, buckling or other damage except for a couple cosmetic dimples on the rudder skin where it apparently blew against the elevator.

I'll see what my A&P has to say next week, but as always your opinions are welcome.
 
something is bent somewhere…

Those dimples were caused by the rudder skin smacking into the elevator corner. I don’t there’s much doubt there.

Having just built a 7/9 rudder (similar to 14), that structure is fresh in my brain; am concerned about what bent/had to give for the rudder to move the additional 1.5” a 2” beyond the stop impinging upon the rudder stops.

Thinking aloud - once the rudder horn (or front spar web, in the case of an internal stop) stops the movement of the rudder assembly, the momentum would cause the skins to stretch/shrink. The skin that contacts the elevator would need to shrink and buckle the stiffeners. The opposite skin would stretch and impart shear loading on the rivets attaching the skin to the spar flange…

I’d look very carefully at the whole assembly for deformation and damage along the aforementioned areas.

edit: The RV-14 stiffeners are tied together which serves to limit the amount of movement of the skins relative to each other, so the shear loading of the rivets along the spar flange opposite the “dimples in the skin” are going to be subjected to more energy than in the -7/9 rudder case.

more edit: Inspect the rod ends and the rear spar of the vertical stab as well. That energy had to go somewhere…
 
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When a counter weighted control surface slams full range from one side to the other and comes to a sudden stop on the control stop, the inertia of the counter weight at the opposite end from where the control stop is in parts a lot of torsional load on the control surface.
The torsional load is imparted along the entire length of the control surface and can deflect it a surprising amount without causing any permanent deformation. It is this deflection that allows the writer to get closer to the trailing edge tip of the elevator, and if it moves far enough contact occurs.
 
Gust locks RVPlasticParts

I went with the RV Plastic Parts gust lock system for my rudder, elevators and ailerons and felt pretty protected but to date have not "tested" the system with decent winds. (Probably gusts to 20 knots so far) I would feel pretty bad if my airframe got damaged by the wind. I know it's never certain, but I would hope these could withstand 30 knot winds from any direction. Anyone tested theses to higher wind loading?
 
Also installed a new PADLock on the rudder, which I sorely regret: its thru bolt acts like a rasp and put a nasty dent aft of the vertical stabilizer rivets. Not recommended at all.Photos below (of gust lock products in theory vs in practice on my airplane). And look for my other thread entitled Subterranean Gustlock Blues.

I do not like "through the hinge line" gust locks like the ones you mention. The control surface has so much mechanical advantage over those locks that the locks themselves are as dangerous to your control surfaces as the winds they are designed to fight.
 
I do not like "through the hinge line" gust locks like the ones you mention. The control surface has so much mechanical advantage over those locks that the locks themselves are as dangerous to your control surfaces as the winds they are designed to fight.

I agree.
My DIY rudder gust lock installs at the fwd end of the counter balance arm.
 
The "stock photo" of the airgizmo gust lock you show has additional tabs that are on the gust locks that allow the tail of the nylon strap to be put into them so the wind does not blow the strap causing the latch to open. The picture of the gust lock on the plane does not have this updated design. The new ones work better. You may be able to buy a new one and swap halves with the old one so you have two with the updated design on one half to catch the strap's tail. I always put one airgizmo gust lock on each aileron and one on each elevator half so if one gust lock gets free the other is there as backup.

I too have the anti splat gust lock and find that I only "trust" it at fuel stops or dinner etc where the plane does not see significant wind for hours on end while "unattended". When I tie the plane down for an extended period of time I tie a rope around the elevator that ties to a piece of aluminum angle that catches the back of the rudder before connecting to another rope on the other side elevator. This takes all of the mechanical advantage away from the wind and has yet to come loose.
 
Snap Rolls

If I remember correctly the two maneuvers Van EXPLICITLY does not recommend is "snap rolls" and "tail slides"!

Odd because section 15 of the RV-8 Manual includes entry speeds for Snap Rolls. There is a disclaimer about snap rolls at the bottom but it just says that most RV pilots avoid them and doesn't actually state that Van's doesn't recommend them.

FWIW, I've done some snaps rolls in mine and can get a very clean snap at 85 knots entry using some techniques recommended by Eric Sandifer.

Skylor

RVManual Image.jpg
 
Try Putting a long Straight Edge Along the Trailing Edge

A Texas thunderstorm some years ago broke my gust lock and pushed/deflected the rudder far enough to cause the elevator to pierce a pretty large hole. It also caused a permanent “warp” in the trailing edge of the rudder as well as a wrinkle on the corner of the elevator. Both parts have been replaced.
Today, my gust lock is a length of heat treated drill rod with two 90 degree bends - fits thru holes in the rudder horn and the stop on the fuselage. A “strap” is fitted on the underside to ensure the rod can’t flex open. Light, small, cheap, and effective.
Terry, CFI
RV9A N323TP
 
Secure those rudders at the peddles ailerons and elevators at the stick !!

Unfortunately doing so will allow the wind to thrash back and forth at the slop in your controls... Rudder cables, aileron and elevator pushtubes and linkages, etc., and you'd never see any damage that would cause as it'll be hidden inside your fuselage, wing, etc. At least a free rudder shows dimples so you *know* there's been a problem.

The best is to secure the part the wind is moving so it doesn't move. External locks that positively prevent movement and are visually prominent so they aren't forgotten.
 
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That energy had to go somewhere…

OP here.

Brian was right. My A&P inspected the rudder and empennage this week and found deformation and a 1/8" crack on the rudder horn brace (see Photos 1 & 2). A call to Van's support told us to stop-drill the crack and continue to monitor it. If it grows at all we need to replace the part.

So, it seems this gust induced rudder-elevator strike was not as bad as it could have been, as the marks in the rudder were "dimples" and not holes and there appear to be no further signs of deformation (wrinkles, buckling, etc).

That said, in my opinion the free-swinging rudder on the RV-14A is one of the bigger challenges of long cross-country trips. I have yet to find a way of effectively securing it so I can sleep without visions of slamming rudders dancing through my head.

Based on experience (and a few of your posts), my current plan of gust lock redundancy is:

• Any "thru the hinge line" gust locks go in the trash (see Photo 3)

• Clamp new AirGizmo locks (with tabs) on aileron, elevator, and top of rudder if I can reach it

• Antisplat Ultimate Gust Lock on copilot stick

• Seat belt around pilot stick

The Antisplat shows promise but I've found it can slip off the rudder pedals with full aileron deflection, so obviously it's important to lock the ailerons. I thought I'd done this with my old AirGizmos but found they also worked loose in strong gusts, setting up a chain of events that leaves the plane with little gust protection other than the seatbelt.

Thanks to all who weighed in here. Will update as appropriate.
 

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Rudder lock

I built an effective rudder lock for my 9A by heat bending ¼ in steel rod into a square U then drilling holes in the rudder stop and rudders horn.

It has held well in up to 70 MPH winds directly at the tail.
The important thing is to put a substantial flag on it


Jim Frisbie
RV 9A 900 hrs
RV 10 in process
 
Maybe look at the RV plastic parts rudder lock?
My hangar mates 10 has something similar. Grabs the trailing edge and has a bungee and hook on each side that hooks under the trim tab arm/clevis on each side.
Has a little bit of give in it in each direction. He swears by it.
 
I wish “Gustbusters” was still around, a great setup IMO.
Rudder lock is spring loaded to allow for progressive energy absorbing.

https://vansairforce.net/community/showthread.php?t=97734


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Is it not common practice with the -14 to drill a hole in the rudder stop and rudder horn and put a bent pin in the two locking them together? Surprised no one mentioned it here yet.

Also, I think that maybe the antisplat gust lock is not being used correctly in some cases. When you engage the main lock on the gust lock it should be extended enough that when you bend it into place there should be a good amount preload placed on the rudder pedals and stick. I have had my -7 in some pretty significant gusts before and the gust lock never comes off. I also use a bent pin for extra security.
 
Is it not common practice with the -14 to drill a hole in the rudder stop and rudder horn and put a bent pin in the two locking them together? Surprised no one mentioned it here yet.
It is as common as any other model and as reliable as any other model. I had two pins (one on each side) during a trip and they were both bent/broken with a couple of good size ding in my rudder. So I never relied on those alone anymore.

[/QUOTE]
I have had my -7 in some pretty significant gusts before and the gust lock never comes off. I also use a bent pin for extra security.[/QUOTE]

That may have been the reason. I had the same gust lock in my RV7 and found it to be barely OK but not reliable enough to be used as the only means.
 
RV Plastic Parts +1

To date mine have worked well albeit not tested in anything over 20 knots. Does look like they can do the job as intended.
 
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