On my first attempt trying to bend the end tabs on the elevator trim tab skins, I followed the plans exactly but ran into several issues along the way that resulted in me ordering a new trim tab skin to reattempt the bends.
In Section 9 Page 16 Step 5, I originally cut the V-shaped wedges from pieces of the shipping crates by hand and they matched well to the dimensions given in the plans. However, the issues I encountered while bending the tabs included
- the bend being too tight, increasing the risk of cracking (even though I had slightly rounded the edges of the V-blocks)
- the V-blocks slipping backward while bending, and tapping the bend with the rivet gun resulting in the tab being pushed back and slight denting appearing on the tab near the bend
- denting the trim tab skin while clamping down the inboard end of the skin sandwiched within the V-blocks. The reason for this was that the V-block doesn't extend the full length of the angled inboard end of the trim tab (to the trailing edge), and without realizing I started clamping down over a part of the skin that wasn't fully supported by the V-blocks
I believe these issues are commonly experienced by other builders, and I therefore decided to give some thought as to how I could overcome these issues and making bending the trim tab end tabs a non-event!
It turned out I got so busy working on other parts of the RV-10 build that it took me more than a year to revisit the trim tabs. However, over that time I had gained a lot of additional experience working with sheet metal, and knew far more now about what techniques worked and didn't work than I did when originally working on the elevators.
After some trial and error using the previously damaged trim tab (as well as a replacement trim tab that was damaged during shipping for which I had to request another replacement) I finally came up with some techniques that worked well in practice, and resulted in really nice, easy and repeatable trim tab bends.
The techniques that follow require creating some simple jigs and some prep work, but they are easily made using standard shop tools and scrap pieces of wood.
Clamping the trim tab skin
To get a good trim tab bend, clamping the work piece securely (in this case the trim tab skin) is key. To that end, rather than clamping the skin as described in the plans, I found that I could cleco the skin down to the workbench through the spar holes. This way, there is no way the skin would move or slip out from the clamp.
However, rather than match drilling the cleco holes into my workbench, I instead took a scrap piece of 8" x3/4" MDF about the same length as the trim tab, and proceeded to place each trim tab skin in turn on the MDF board so that the skin lined up exactly with the end of the MDF and the end tab overhung the MDF (see 3rd photo below for illustration). I then marked about 7 on the spar holes onto the MDF spread evenly along the length of the skin. After removing the skin, I drilled the holes where marked with a 3/32" bit to a depth of about 1/2".
I repeated this for each of the 8 end tabs (lining up the skin to the end of the MDF) as you cannot reuse the same holes for other end tabs and still get the skin to line up to the edge.
Creating a wedge to bend end tabs against
Having had no success with the V-blocks, I decided to create a wedge that would fit exactly into the space next to the end tab, and that could be clamped down directly without having to clamp over the skin on top and risking deformation.
To do this, I took a piece of 1"x3" hardwood about 2ft long and cut the ends to an angle that matched the angle of the V-blocks. I also cut one side at each end to the same angle as the inboard end of the trim tabs, and then rounded all edges to 1/16" radius. With the wedge cut this way, I was able to place it in position to bend any of the trim tab ends, and having the wedge inserted all the way to the trailing edge of the trim tab providing maximum support while bending the tab.
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| MDF clamping board on the left with spar holes from the skin match drilled (somewhat visible above) into it. Wedge on the right with angles cut to match trim tab angles |
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| Another view of the wedge. All angles were cut using a miter saw. |
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| Clamping block allows the trim tab skin to be clecoed down using stubby clecoes. Note the edge of the skin is lined up with the edge of the clamping block and the end tab overhangs |
Using the two jigs, I was able to clamp down the trim tab to the workbench using clecoes and several bar clamps as shown below
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| Trim tab skin clamped securely and ready for bending the end tabs |
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| The wedge was offset 1/32" from the end of the skin as specified in the plans |
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| Double sided tape was also used on the bottom of the wedge for additional support in keeping the wedge in place. I found that double sided tape worked better than carpet tape because it was easier to loosen from the skin surface after bending the tab |
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| The initial tab bend was started using a scrap piece of 2x4 |
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| With the 2x4 I was able to get the end tab bent to about 60 degrees |
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| Next I used a scrap piece of 1/4" MDF and a flat set in the rivet gun to gently tap the tab to 90 degrees. The rivet gun was turned down relatively low, but high enough to still affect the bend amount |
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| Tab bent to about 90 degrees. Note that I did also angle the side of the wedge so that the tab could be bent slightly beyond 90 degrees to allow for spring back |
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| Working on the inboard end tabs. This follows the same procedure as above except that the wedge is flipped around to fit right up to the trailing edge of the trim tab, and different holes are used in the clamping block to cleco the trim tab skin |
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| Wedge put in position 1/32" from the edge of the skin, right up to the trailing edge |
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| Inboard end tab after initial bend by hand |
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| Bottom end tabs done. Now to bend the top end tabs. |
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| Wedge used again to bend the top end tab over the bottom end tab |
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| Wedge did not budge while bending the tab by hand or while using the rivet gun, thanks to the additional double sided tape to hold it down inside the trim tab |
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| Same process was followed to bend the top inboard end tabs. By now it was a fairly straightforward routine to create repeatable, uniform tab bends |
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| Once again the wedge was put in place, but for the top end tabs, was offset only about 1/64" from the skin edge |
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| Another tab bent with the bend forming exactly where needed |
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| Another view showing that there was no way the trim tab skin could be dented by excessive clamping as the clamp was never directly on the skin |
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| Both trim tabs with all end tabs fully bent as required by the plans. |
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| I was very happy that the end tab bends formed right in line with the edge of the trim tab skin, and had a roughly 1/16" radius that would reduce any risk of cracking over time |
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| Trim tabs ready to proceed with next assembly steps |
These are the trim tab bending techniques that worked for me, and allowed me to achieve uniform, repeatable bends. As mentioned already, clamping is key to getting good bends. If you're reading this, and having trouble bending the tabs as outlined in the RV-10 plans, try what I have described here. Hope it works as well for you as it did for me!
