What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Rudder twist....

sloengineer

Active Member
We hit our first "full stop" moment today. When we finished riveting the rudder spar to the skins, we seem to have a twist. When laid on the right side, it lays flat on the table. Laid on the left it rocks.

I found a really old thread but never saw a resolution to the original posters question. I couldn't figure out if it's a normal condition, abnormal, maximum deviation allowed per side, etc.

What are the latest thoughts on rudder twist?
 
Rudder

If memory serves, it's a 7 rudder?
Since it tapers to a sharp edge, the only way to know for sure is to clamp it or hang it so it's perfectly vertical with a plumb bob through the bearings. Then use the plumb bob on the trailing edge to compare. I suspect Vans would say, "Build On". Call after measuring the twist, if any, and ask.
 
Alignment

Is the table top perfectly flat? Try checking the rudder on a different flat surface, just in case it is the table that is out of plane.

If the rudder is actually twisted, by 1/8" or less, then I wouldn't worry about it too much. If it's 1/4" or more then I would want to investigate and understand how and why it got twisted.

I had this concern early on in my build and an airframe mechanic advised the above tolerances.
 
Last edited:
This most likely happened during riveting the trailing edge, there is a part in the plans that warns about this. I don't know if a way to fixe this and considering the parts are not that expensive, you might consider rebuilding one. I know people who this happened to them and they rebuilt a new one.
 
The rudder is tapered both in chord and thickness. If riveted on a flat table, a twist will be built in.
 
To accommodate the rudder’s tapering spar, I would fabricate 2 angle brackets that would temporarily bolt the rudder hinge rod end bearings parallel to the table surface. Than I would cut a board spacer that would bring the trailing edge to the same height & also parallel to the table. With skins & trailing edge all cleko’d together, the rudder would have the proper geometry.

Personally, to fix the twist (I would not settle for the twist) I’d drill the trailing edge apart & re-rivet it while properly jigged.

Also, not part of the OP’s questions (but thought I’d mention it) I would squeeze all the trailing edge rivets in place partially while jigged (so not marking the skins with smileys), than after all the rivets are in and the geometry is locked, than finish them off with the normal back riveting technique.
 
Listen to Mel.
If you don't check with a plumb bob, you're herding cats.

As Mel & I were likely typing at the same time, note that I agree with him, but go further and describe a jigging procedure that has worked (I forget how many rudders...) for me to produce straight rudders.
Hinge line & trailing edge both spaced parallel from work surface = straight rudder. I like cats too but know not to chase them.
 
Jig

To accommodate the rudder’s tapering spar, I would fabricate 2 angle brackets that would temporarily bolt the rudder hinge rod end bearings parallel to the table surface. Than I would cut a board spacer that would bring the trailing edge to the same height & also parallel to the table. With skins & trailing edge all cleko’d together, the rudder would have the proper geometry.
<snip>
.

That would work well and pretty quick to set up for riveting the trailing edge.

Let's hope he has no issue and may "Build on".
 
Go to Big box store buy two sections of angle bar stock aluminum. First insert 3 or 4 clecos.

Then rest the aluminum angle stock against cleco's

Clamp on both sides of the trailing edge.

Cleco the rest of the trailing edge.

rivet away.
 

Attachments

  • Angle alum.png
    Angle alum.png
    34.1 KB · Views: 204
  • 20210307_114230.jpg
    20210307_114230.jpg
    187 KB · Views: 296
  • 20210307_114217.jpg
    20210307_114217.jpg
    131.6 KB · Views: 283
Last edited:
current sitrep

Good afternoon, guys, OP here! Thank you all so much for the quick replies. We were on the road all day so I'm just getting to the computer.

So we have not riveted the trailing edge yet. We rolled the left skin onto the right, pop riveting the stiffeners to the shear clips, and we used the 3M transfer adhesive on the TE extrusion (section 7-9). Then riveted the rudder spar skeleton to the skin assemble (section 7-10). When we were positioning the rudder to start on the trailing edge riveting we noticed the flat and rocking side. Looks like about 5/16 on the left and nearly flat on the right or maybe 1/16.

I am very interested in the v-blocks or rigging that you guys mention to hold it while riveting the trailing edge and the angle iron to back rivet. I think I will get the angle iron as well. Could someone give some dimensions on the v-blocks for a 14? Or some reference dimensions so I can fixture it before nailing down the TE? It sounds like proper fixturing before riveting the TE would fix us up.

Thanks again for all the feedback!
 

Attachments

  • rudder2.jpg
    rudder2.jpg
    258.3 KB · Views: 186
  • rudder1.jpg
    rudder1.jpg
    229.7 KB · Views: 195
Just a clarification. The angle aluminum stock is not for backriveting. its to hold the rudder straight while you squeeze the rivets.


.
 
I've been waiting on tech support to advise, but no response. I guess I'm going to have to make a decision one way or another and get going. Can anyone provide guidance on the fixturing that used to be called out on older model rudders? My idea is to make some wedges that will split the difference between the left and right sides, then clamp the TE as I back rivet.

Thoughts?
 
A few thoughts.

1) This can happen if you weigh down the rudder on a flat table. A properly built rudder will rock back and forth on either side because it doesn't lay perfectly flat. Side note, Elevators, Ailerons and Flaps are symmetric in coord so you can weight them down. Using a steel angle to make the edge straight works great, even as part of a backrivet process. The key is that you will need to shim the rudder a little bit in one of the corners so it doesn't lay flat. This sounds hard/scary to figure out, but its not bad when you actually look at it on your table.

2) Start working on the next section. There is no reason to stop with this right now. Your rudder will sit in the corner well into after you have mated your emp to your fuse.

3) Once you hear back from Vans, or you get an idea of how to check how much twist there is, you can check your rudder and choose what to do after that.

4) Don't do any of your fiber work on the rudder in case you rebuild it.

With that said, if you rebuild it, wait until you order the wings, then you can have all the rudder parts included in that shipment. There is no rush to get the rudder specifically done.

Something I learned eventually on my slow build. If you let the little things freeze you up, you loose so much time where you could be deburring, priming, or assembling other parts. And when you do move on, it was surprising how many little things that I didn't like eventually became acceptable (not saying your twist will be acceptable, just saying don't freeze up!).
 
I've been waiting on tech support to advise, but no response. I guess I'm going to have to make a decision one way or another and get going. Can anyone provide guidance on the fixturing that used to be called out on older model rudders? My idea is to make some wedges that will split the difference between the left and right sides, then clamp the TE as I back rivet.

Thoughts?
If I understand it correctly, you have not riveted the TE yet. How confident are you that your table is flat in all its surface area?
I am not aware of any wedge that can be used to split the difference and not even sure how that would work.
At this point, if it was me, I would push forward to rivet the TE taking my time and making sure I have a flat surface for back riveting. I have a good size table saw and have used as my back rivet plate multiple times with great success but on my first plane I used a long 3" x 4' long iron from scrap metal shop as my back rivet plate which was recessed into appropriate size plywood for a flat surface. This way, I did not need to move the rudder much to get it position on the back rivet plate.
 
Twist

See a Ralph's post #6 in this thread.
Honestly, I would wait for Vans reply.
If the trailing edge isn't riveted, use Ralph's method or the angle aluminum method.
I used the latter with proseal. Leave it clamped or clekoed till it fully sets then rivet.
 
To accommodate the rudder’s tapering spar, I would fabricate 2 angle brackets that would temporarily bolt the rudder hinge rod end bearings parallel to the table surface. Than I would cut a board spacer that would bring the trailing edge to the same height & also parallel to the table. With skins & trailing edge all cleko’d together, the rudder would have the proper geometry.

First, I would separate ONE side skin from the glued trailing edge wedge.
Install the hinge rod end bearings in the spar.
Fabricate 2 metal angles that you can attach to the table, drill a hole in both 2 1/2" above table height so spar will hinge parallel above the table.
Cut a board about 5' long and 2 1/2" so you can suspend the trailing edge parallel above the table.
Cleko the skins to the spar and trial align/fit the trailing edge rivet holes and cleko. (at this point, if things don't line up, call Vans)
If everything aligns, now gently position & clamp an angle straight edge above & below the trailing edge & squeeze the rivets (partially, avoid smiles in the skins) to join the trailing edge.
Finish up with (gentle) back rivetting.

Good luck
 
Ralph has an excellent suggestion and I would offer another method that is similar.
Wait until the tail surfaces are mounted on the aircraft. When all the tail surfaces are mounted you can mount your rudder on the vertical stab. Take some long strips of wood, think yardsticks, and clamp the strips on the top and bottom of the vertical stab and rudder assembly. Now hanging a plum bob aft of the rudder and see what you have. Take the opportunity to swing the rudder side to side to check clearances with the elevators. Now you can make a real world estimate of the error. Heck the fuse itself might have a minor twist, working this way you can adjust the rudder trailing edge to fit the airplane in it’s final assembly.
 
Last edited:
See a Ralph's post #6 in this thread.
Honestly, I would wait for Vans reply.
If the trailing edge isn't riveted, use Ralph's method or the angle aluminum method.

First, I would separate ONE side skin from the glued trailing edge wedge.
Install the hinge rod end bearings in the spar.
Fabricate 2 metal angles that you can attach to the table, drill a hole in both 2 1/2" above table height so spar will hinge parallel above the table.
Cut a board about 5' long and 2 1/2" so you can suspend the trailing edge parallel above the table.
Cleko the skins to the spar and trial align/fit the trailing edge rivet holes and cleko. (at this point, if things don't line up, call Vans)
If everything aligns, now gently position & clamp an angle straight edge above & below the trailing edge & squeeze the rivets (partially, avoid smiles in the skins) to join the trailing edge.
Finish up with (gentle) back rivetting.
Good luck
At this point, Ralph seems to have the most recommended suggestion. I'll get the bearings in and level it out as suggested and re-evaluate the situation.

Is the table top perfectly flat?
We do a lot of woodwork, so I've measured using the ole winding stick method. It's the EAA standard size table. I would say twist under 1/8 total measuring the full 5 foot length.


2) Start working on the next section. There is no reason to stop with this right now. Your rudder will sit in the corner well into after you have mated your emp to your fuse.
Not a bad suggestion, but I'm trying to protect me from myself. :) If I start allowing myself too many "do it later" projects, I'm afraid I'll end up with too many loose ends of which to keep track.
 
I've been waiting on tech support to advise, but no response. I guess I'm going to have to make a decision one way or another and get going. Can anyone provide guidance on the fixturing that used to be called out on older model rudders? My idea is to make some wedges that will split the difference between the left and right sides, then clamp the TE as I back rivet.

Thoughts?

The older model (non pre-punched) rudder and elevators were held in alignment for drilling and final riveting using a jig. The jig comprises a couple of rectangles of particle board with a vee cut into them. The vee matches the full size profile of the control surface and they are mounted vertically with the narrow end of the vee pointing down, one near each end of the rudder. Alignment is set by carefully plumbing the centre line of the vees before putting in the rudder skin and spar. The old model rudders have the trailing edge bent rather than riveted with a wedge.
 
True after all!

I really can't thank you guys enough for all the input on my rudder questions. Using the input from Ralph, et al., I constructed a pair of fixtures to align the heim bearings at the same level from the table. Then poppa ripped a 2x6 down with a 6 degree bevel such that the TE was also the same plane from the table top. We now have a perfectly planar rudder!
 

Attachments

  • 20210311_184618.jpg
    20210311_184618.jpg
    166.5 KB · Views: 197
  • 20210311_184632.jpg
    20210311_184632.jpg
    280.5 KB · Views: 226
  • 20210311_184646.jpg
    20210311_184646.jpg
    88 KB · Views: 194
  • 20210311_184745.jpg
    20210311_184745.jpg
    85.1 KB · Views: 208
Back
Top