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RV-9A Rudder Jam

Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
I was sent this picture by Ed Wischmeyer, who asked me to share it here in the hopes that it might make folks go have a look at their rudder cables to make sure they don?t have a similar problem. This was on the -8A that he bought (he didn?t build it) ? apparently, the front of the cable end barrel jammed on the rudder stop in flight. Ed says he tested both left and right rudder before flight, and this happened in the air.
IMG_1946.JPG


Curious about how this could happen, I stepped out to the hangar and took a side-on shot of my RV=8?s installation:

IMG_1461.JPG


I instantly saw the problem ? Ed?s rudder stop is installed quite low, putting the stop directly in the path of the cable. I didn?t go look up the -8 plans, but I am pretty sure mine are installed per the drawings (although shaped to actually work right). Something folks should check ? I am sure Ed?s airplane has flown for many, many hours this way ? but it only takes once to get an exciting ride into the nether regions of your airport if the rudder jams.
 
Thanks for the heads up Paul. I'll be looking at the -8 tonight.

One area that caught me on the -8 was the screws securing the counterweight started to loosen up, and the screw head started to catch on the top of the vertical fin. That is now a significant area of interest on preflight.
 
self edit

Edit: I just saw that the reference image is of a -9A, not a -8. The stop is in the correct orientation for a -9A per plans, just very low. It should have used that upper rivet location that it is half hiding.
 
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Seeing the chipped paint on the trailing edge of the rudder stop I'd say, it's been hanging up and/or scoring there for quite some time. Good catch and glad to see it was discovered.
 
Looks like his stop was set to contact the horizontal of the rudder horn. That is too low.

The pilot should be able to dislodge this jamb by just pressing firm on both pedals then applying more right rudder.

Looking a 7 plans, dwg 27A..... it does show the tab to be mounted down to tie in with the lower J stiffener.
I don't know how the 8 goes. But, one of the above pictures are wrong. It is a simple measurement from the top of the longeron.
 
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Interesting. I wonder if the builder decided to lower the rudder stop so it was more in line with the rudder horn. I would be curious to see what part of the rudder horn contacts the rudder stop. It looks like the stop is now on the longeron so maybe the thought process was to lower it so it was more "structural". Seems like a relatively easy thing to fix though.

I always worry when I go off plans that something like this will come down the road years from now. I guess that is why I spend so much time thinking about it and holding parts in place to see relationships etc.
 
Per plans it looks far from jamming on 9A. If there is no wobble in cable attach holes of course.

 
Toobuilder said:
Thanks for the heads up Paul. I'll be looking at the -8 tonight.

One area that caught me on the -8 was the screws securing the counterweight started to loosen up, and the screw head started to catch on the top of the vertical fin. That is now a significant area of interest on preflight.
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I had that issue too! And yep I always look up at those screws/ bolts. Pre flights can be life savers for sure.
 
It would seem to me if ever there was a good spot for pre-punched holes, this would be it.

I remember spending a long time trying to figure out where to drill for the rudder stops when i was building my -8. The plans in the late 1990s didn't show where to drill, just said mount them where they won't interfere with the cable. For a newbie builder, little items like that can drive you crazy as you worry about how to avoid snagging the rudder cable. It all worked out for me but the photo shown in this thread reminded me of one the frustrations of building. I hope the plans today are better.

Good catch Scott on observing the stop was mounted upside down.

Chris
 
Another thought?

It seems to me a little improbable that the catching was indeed the rudder stop. My eyeballing of a straight line between the rudder horn and the fuse exit point does not seem to intersect the stop at a point where it would actually catch. Certainly could be the culprit, but:

I don't know about the -9's, but the -6 I built had another catch point up towards the front. There is a fuse bulkhead forward of the main spar, which (on the -6) is in a perfect position to catch the aft end of the cable end. It catches on the aft-going side, meaning apply left rudder and the right cable catches. I fixed it by fastening a slit pvc tube over the cable, and cable end, for the entire length which travels back and forth in this bulkhead.

Maybe it was the aft end, but this forward end is worth a look.
 
I noticed this too when building my -6

I initially installed the stop so that the horizontal flanges of the stop and the horn aligned - thinking that this was the most robust structural solution - and being comfortable that the cable and clevis were outboard of the stop - at least on the "tension" side. Fortunately however I noticed that on the "slack" side the cable swung inboard and was rubbing on the stop and for this reason I moved the stop up to clear. I didn't consider that the sleeve of the clevis on the "slack" side could also possibly jam on the stop.

Can't remember what the -6 plans show.

Jim Sharkey
 
AlexPeterson said:
It seems to me a little improbable that the catching was indeed the rudder stop. My eyeballing of a straight line between the rudder horn and the fuse exit point does not seem to intersect the stop at a point where it would actually catch.
Click to expand...

I thought that, too. One thing I would check is to be sure the bolt is not over-tight and pinching the clevis. If the clevis cannot rotate freely, then it could actually be 'aiming' the clevis end at the rudder stop or, worse, at the aft fuselage.
 
flion said:
I thought that, too. One thing I would check is to be sure the bolt is not over-tight and pinching the clevis. If the clevis cannot rotate freely, then it could actually be 'aiming' the clevis end at the rudder stop or, worse, at the aft fuselage.
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Very good point.
 
internal rudder stop

There's an internal rudder stop that eliminates this issue. I believe that it is available through Flyby Accessories.
 
DanH said:
But it is a fine way to overstress the structure.
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Yep. Nice unintended torque moment on the aft spar of the VS every time the rudder contacts the stop. Whether or not it actually causes overstress, though, requires some more information to calculate.

My rudder doesn't hit the stops all that often in regular use, and if I'm able to control it the contact is gentle. However a nice ill-timed wind gust that forces the rudder hard over as you're getting out of the plane at a fuel stop will really make you cringe.
 
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