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Tail Surfaces Layout and Jigging for Welding

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  • Tail Surfaces Layout and Jigging for Welding

    Carlo is getting close to needing the tail surfaces to get his aft fuse control runs done (avionics and interior already done on his bird... too cold to weld = not too cold to wire or set nut plates), so he asked me to block time to fab the stab/elevator and rudder jigs. The stab and elevator layout are detailed, but the same approach handles the elevator and any full scale layout jig needed for the vertical stab. Worth a couple shots to capture the approach we used... if you have a better/different method, please feel free to add to the thread or link to your post here.

    Job One was figuring out a reference line, and our decision was to use the LE of the elevator for fore and aft ref and elevator forward extension for the lateral ref. We gridded off the plans page in 1/2" increment for the elevator and stab using those references, then added some 1/4" increment gridding at the elevator tip to fine-tune the shape there. Once that was done, I laid out and cut two pieces of plywood to nest together along the reference line and duplicated the grid layout using 2" squares (1" at the tip). We added the plan stab and elevator centerline, hinge centerlines, and a few other control points based on that fuselage CL (ends of the T13/14 leading edges and aft T14 stab spar).

    Nested Ele and Stab Laout.jpg

    With just a 4x increase in size to handle, a good pair of dividers handles the transfer of plan to jig grid intersection, and some thin box nails at about every 3rd or 4th grid line give me the ability to wrap a plastic spline (an 8' x 1/2" x 5/16" piece of cellular PVC offcut... Azek or Veranda) around those initial control points, then adjust the nails for a fair curve (plus add additional nails to keep the baton in place). For stuff like this, an eye-sweet curve is important - any up-scale always introduces some measurement error, so it is worth understanding what has to be dead-on (e.g., tubing cut-off for interface to fuselage mounts) and what just needs to be a fair curve that is reasonably close (+/- 1/4") to Bob's layout (e.g., elevator tip shape). A fine Sharpie allowed us to trace the applicable edge of the baton for the outside of the tubing, and a carefully selected washer handled the offset to lay out both sides of the T3 (3/8" offset) and the T13/14 (7/8") stab leading edge tubing.

    Elevator Spline.jpg

    We decided to use a 1" vertical lift for the T13 and T14 tubing to allow room for the airfoil-shaped stab ribs plus some room to allow back-side tacking. A little arithmetic give us blocking height for the T1, T3, and T5 tubing. Other than that, we added vertical reference blocks on one side of the blocking with the intent of using steel spring clamps to keep things aligned and allow easier adjustment where necessary. For the ribs and the T1 stuff, we cut a number of blocks from scrap to allow temporary squaring of ribs, etc. using clamps or hot glue gun for temporary tack of block.

    Stab Blocking.jpg Elevator Blocking.jpg

    Will post on actual construction if there is anything to add to the convo.
    Last edited by SpruceForest; 06-05-2025, 10:49 AM.

  • #2
    Nice job, the more images the better.
    Gerry
    Patrol 32#30

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    • #3
      Tail feather jigs completed with the rudder jig...

      Rudder Jig Layout.jpg
      Rudder Jig Blocking.jpg

      Lots of minor tweaks on this airplane - such as saving some weight by a 'Y' in the T1 versus two full-length pieces... these braces keep the inner-most stab rib from bending due to covering loads, and a single piece of T1 is plenty strong enough to do that... a short 'Y' saves an ounce back where it matters. Elevators in progress, with Carlo using a single larger tab versus the plans split tab based on his experience with his Patrol flights (plenty of pitch trim authority) and experience on the two Hatz biplanes built. With electric trim, he's focused on some weight savings by putting the servo in the elevator itself. Note the lack of the elevator trim structure, as that disappears with servo-driven electric trim in the elevator. Carlo is thinking some scrap tungsten embedded in the elevator horn weights as far forward as possible to reduce overall mass balance weight and 'pay' for that HD trim servo.

      Hor Stab Welded.jpg
      Last edited by SpruceForest; 09-28-2025, 04:54 AM.

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      • #4
        Forest--- I did about the same thing you are doing except I didnt make a grid on the table. I drew a center line down the spar. The perp. lines at each rib location. Established the depth at each rib location with a scale ruler. Then I used a long stainless ruler to flex and laid out intersecting curves for the trailing edge. took a few draw/erase repeats to get the curve I liked. Then I made wood pedestals- each having a half circle notch--- so they held the tubing perfectly elevated but parallel to the table surface. Each tube diam. had a different height to make all the tube centers coincide. Then I took galvanized pipe strapping and made straps to apply downward pressure to the tube at each station using to screws to pull the strap down. That was a very sturdy setup. I did a wood tower about every 12 inches. more in certain spots. It held the whole assy good and stout.

        I drew out a big rectangle with one side being the spar tube. That helped keep the ribs square .

        Rudder done.... doing horizonal stab now-----

        Tim
        image.png
        Last edited by fairchild1934; 09-19-2025, 11:10 AM.

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        • #5
          Originally posted by fairchild1934 View Post
          Forest--- I did about the same thing you are doing except I didnt make a grid on the table. I drew a center line down the spar. The perp. lines at each rib location. Established the depth at each rib location with a scale ruler. Then I used a long stainless ruler to flex and laid out intersecting curves for the trailing edge. took a few draw/erase repeats to get the curve I liked. Then I made wood pedestals- each having a half circle notch--- so they held the tubing perfectly elevated but parallel to the table surface. Each tube diam. had a different height to make all the tube centers coincide. Then I took galvanized pipe strapping and made straps to apply downward pressure to the tube at each station using to screws to pull the strap down. That was a very sturdy setup. I did a wood tower about every 12 inches. more in certain spots. It held the whole assy good and stout.

          I drew out a big rectangle with one side being the spar tube. That helped keep the ribs square .

          Rudder done.... doing horizonal stab now-----

          Tim
          I think as long as you can make x-y measurements and check with a second method (either off grid or from an x-y baseline), it works. Grid helps prevent any massive measurement error (allows quick reference re: which grid square/where), but it is more work and subject to the same mental confusion/measurement error we see in any plans-to-the real measurement. I've also seen photo projection used for this sort of thing, and realistically, being a half inch off in shape due to lens distortion is not going to matter as long as the hinge lines are correct (there is at least that much slop in the ribs).

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          • #6
            Just noticed that you dont have a tip rib on your stab. Looks like you used tubing instead. Do your plans show a tube there ? Mine show a sheet metal rib--- my plans are about 1-2 years old----- Wonder if that makes your structure more rigid torsionally ?
            Tim

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            • #7
              There is a tip rib, but it cannot be airfoil-shaped if we want to transition from the airfoil-shaped stab to tapered slab -style elevator horn profile at the tip of the stab. The tip rib is the same straight line tapered construction as the elevator ribs, but a bit deeper flange at 9/16", with taper to match the elevator horn (and the T13 leading edge on the stab must be flattened near the outboard rib to match the 1/2" horn LE diameter). In the plans shot below, you can see the flange direction and size call-outs and the note to flatten the T13 over the last couple inches of stab LE outboard of Stab Rib 4. So to summarize, Stab Rib 5 and Elevator Rib 6 have the same taper, (7/8" to 1/2") but Rib 5 has wider flanges to handle the loads there.

              My plans are a year or so older than your set, (end of 2022) so if Bob has since gone to an airfoil-shaped elevator rib 6, that might be another way to handle the transition.

              Stab Ele Horn Detail.jpg
              Last edited by SpruceForest; 09-19-2025, 10:01 PM.

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              • #8
                I think I mistook your rib for a tube in the picture. I remember now some of the slightly older kits did not have lofted ribs in the tail. We are prob more or less the same. I will check your pic against my plans and see if it looks slightly different-----
                Tim
                Last edited by fairchild1934; 09-20-2025, 12:55 AM.

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                • #9
                  spruce----
                  I checked my plans-- and I have the 3-rd revision - which is dated 6-28-20. I think my plan was to make rib 6 have a slight airfoil shape--- but have it in between rib 5 and rib 7. But I had not really thought about it since I have not gotten to the elevators yet. I measured the max thickness of my tip rib-- and its quite a bit thinner than the inboard ones-- its max thickness is about 1.4 inches -- at about the 50% chord point----- which looks like will make an OK transition to rib 6 in the elevator. HOWEVER--- you did induce me to catch a mistake----- i made my stab ribs have a 1/2 inch flange.( slightly wider than the 7/16 call out on plans) I had NOT noticed that the plans call out for a 9/16 rib at the tip. Is that wider for the purposes of the fabric glue-on area ? Or is it because Bob wanted it to be stronger for some reason. ?

                  My ribs are so far soft steel. However I also have a sheet of chrome molly I have not tried using to form ribs yet.
                  do you think I should remake the tip ribs because of the missing 1/16 on that flange ?( 1/2 vs 9/16)
                  I COULD try them out of the stronger 4130 sheet too ?????

                  What do you think ?

                  Here is a pic showing my tip rib---- thinner and more symmetrical end to end than the other plumper ribs.


                  IMG_20250919_021710.jpg
                  Tim

                  Attached Files
                  Last edited by fairchild1934; 09-20-2025, 04:07 PM.

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                  • #10
                    This is pretty much a Bob question, but I am guessing there are torsional loads that the wider flanges address. Given the bracing inboard, he may tell you it’s all good without further change. The bigger issue is that ribs 5 and 6 need to be the same profile to avoid a stepped edge... aerodynamically, I think the consequence would just be some added drag, but pretty disturbed area back there already, so again Bob is the go-to for seeing if what you have is acceptable and if not, what is the work-around.
                    Last edited by SpruceForest; 09-20-2025, 09:13 PM.

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                    • #11
                      I'm pretty sure that my factory tip rib on the h-stab has no airfoil shape. I'd say with 90% certainty is straight and fabricated from steel sheet, and is a mirror image of the adjacent elevator horn. I'm not home right now to see and I cant find data in the plans to back up my belief.
                      Brooks Cone
                      Southeast Michigan
                      Patrol #303, Kit build

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                      • #12
                        Here's mine.
                        Cheers
                        Gerry 20250923_152430.jpg

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                        • geraldmorrissey
                          geraldmorrissey commented
                          Editing a comment
                          That rib was very fussy. I ended making 3 to get 2. The fwd end needs some fancy filing to fit the squashed leading edge tube.

                      • #13
                        here is what I did to try to get the holes for the trim shaft in near as perfect alignment as possible. I cant think of how to do it any better. I can measure front-to-back between the TE and the shaft and make that constant--- and between the table and the shaft for the up-down. Anyone have any better tips for locating the holes in the ribs ?
                        here is a pic----- Tim

                        IMG_20250923_004422.jpg

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                        • #14
                          I think I will just go simple and do a flat rib on the end. The factory built stab is like that---- so it should be good ! I will make it out of 4130 for a little better stiffness and maybe put a 30 degree bend at the edge. (as well as making it a bit wider- per the plans----)

                          Tim

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                          • #15
                            I called Bob about that rib and he recommended .025 4130 cond A stock.

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