Elevators 9-7-9 to 9-9-8
It was time to start dimpling and countersinking the holes in the rest of the elevator parts.
I began by dimpling the skins using the DRDT-2. This was easy as the skins are flat. I used the Main Squeeze to dimple the holes in the closeout tabs with 1/8" 120 degree dies that conform to the CS4-4 rivets to be used there.
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| Skins dimpled, except for trailing edges to be dimpled later |
I then worked on dimpling the front and rear spars. The front spar is easy to dimple using the pneumatic squeezer. The rear spar took a little more effort as there are 29 holes that need to be countersunk, while the rest are dimpled.
While countersinking the rear spar I ran into an issue with chatter as I was working on the second hole. My initial countersinking setup was as follows.
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| 1st attempt at countersinking the rear spar. |
I had a strip of wood with holes drilled into it onto which I rested the rear spar flange. I used a sheet of aluminum from the empennage trim kit to help support the countersink cage over the edge of the flange. This was clamped down at the edge of the work bench, and the rear spar flange could slide along to position each hole over the hole in the wood strip.
This setup appeared to work well for the first hole, but the second hole resulted in significant chatter and ended up being drilled somewhat square. I cleaned that hole up with a deburring bit, but decided that I needed a different setup to better support the countersink pilot as I was drilling.
I found a left over piece of aluminum from fabricating the horizontal stabilizer attachment brackets, and this was the perfect thickness and size into which I could drill a #40 hole to support the countersink pilot.
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| Countersinking attempt #2 |
By placing this at the edge of the work bench and lining up the spar flange hole to be countersunk with this one, I was able to countersink the remaining holes without any chatter issues.
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| Countersunk holes in the top of the rear spar |
To dimple the holes in the rear spar flanges, I used the hand squeezer as I needed better control of the squeeze due to the small space in which to work in between the flanges. There were no issues with this approach.
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| Dimpled holes in the front and rear spars |
I then dimpled the flanges of all the rib halves. This was most easily accomplished using the DRDT-2, as the squeezer yokes had trouble fitting over the bent parts of the rib flanges. These were not an issue for the DRDT-2 though.
I also dimpled the two holes of the long flange of the inboard shear clip. I again used the 120 degree 1/8" dies as CS4-4 blind rivets will be used here.
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| Dimpled rib halves and inboard shear clip |
Next I had to dimple the tip rib parts. I used the pneumatic squeezer to dimple the counterbalance skins (except for the holes that would hold the fairing), and a combination of the pneumatic and hand squeezers to dimple the holes in the two rib parts.
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| Tight fit dimpling fixture attached to a sturdy cabinet |
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| Dimpled tip rib parts |
While looking ahead in the plans, I noticed that the instructions to attach the trim cable anchor brackets to the access cover plates required the use of LP4-3 blind rivets. Given that I was using the aluminum anchor brackets rather than the welded ones provided in the kit, I decided that it would be easy to modify the attachment hardware to use AN426 rivets which would lay flush against the surface of the cover plates.
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| Countersinking the anchor bracket attachment holes |
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| Brackets and access plates ready for priming! |
The 3/32" vise grip dimpler arrived and made short work of the dimples in the root rib end flanges as well as the tip rib holes where the squeezer wouldn't fit. Only the very last hole at the tip of the tip rib had to be dimpled with the tight fit dimpling fixture. I am very happy with the vise grip dimplers, and am sure they will be useful on other occasions.
After having dimpled and countersunk the spars, I cut an 84 degree wood wedge that would allow me to check the angle of the flanges on the spars. I did notice some minor waviness around 12 dimpled holes on the top flange of one of the front spars, and sure enough when I check the flange angle in that area it was a few degrees off. I used the hand seamers to bend the flange back to the correct angle, and although some waviness still exists it looks much better, and should get pulled tight when riveting. All other parts of the spar flanges were also checked and the angles were all good.
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| Checking flange angle along the spars |
Next I countersunk the trailing edge wedges using the drill press. There were no issues using the Cleaveland Tools trailing edge jig and all countersunk holes turned out great.
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| Countersinking the trailing edge wedges on the drill press |
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| Trailing edge wedges countersunk and ready to attach later |
Before bending the trailing edges and dimpling the holes in the skins, I decided to skip to the next step and scuff the areas where the trailing edges and foam ribs would be prosealed. After carefully measuring the rib locations and marking off the areas with tape, I used 150 grit aluminum oxide sandpaper to scuff the surface, and cleaned off the residue using acetone.
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| Scuffing the foam rib locations and trailing edge |
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| All scuffed and cleaned with acetone! |
I also scuffed the interior flanges of the rear spar where the foam ribs would sit. I did not scuff the spar web in those locations because upon examining the rib templates, I determined that the foam ribs will not reach all the way back to the spar web.
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| Scuffing the inside flanges of the rear spar where the foam ribs will sit |
The final step before priming the elevator parts involved bending the skin trailing edges slightly and dimpling the trailing edge holes.
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| Dimpling the trailing edge holes after adding a slight edge bend |
Build Hints
- When countersinking thinner aluminum sheet, ensure that the countersink pilot is well supported as you are countersinking. If not, you will likely encounter chatter as the pilot moves around, and this will result in a square, ugly looking hole. A 1/8" piece of aluminum with a hole the same diameter as the countersink pilot works well here.
- Vise grip dimplers are very useful for getting into tight spaces where the squeezer yokes will not fit. The dimple is not quite as crisp as with a squeezer, but perfectly adequate especially for internal parts.
- Make sure to properly support bigger pieces while dimpling. I ended up with some minor waviness (<1/32") around 12 dimpled holes of my elevator front spar top flange due to the pneumatic squeezer pulling the spar up while the dimple was being formed. Once I noticed that and held the spar flange perpendicular to the dimple die pilot there were no further issues with waviness.