Zipping Up the Impossible Rivet Seam

2-18-18 and 2-19-18 – 5 hours

So this session is mostly about closing the impossible back seam on my modified aileron – although my son and I spent also dimpled the second aileron.

He clecos and dimples.  A 13 year old assistant is good news every now and again!  Thanks Jason!  Look carefully, and you can see the laptop playing Pandora tunes in the background.  Also, notice the two flaps and the rudder on the wall.  We’ll be adding to that wall in this post.

Its not a red carpet, but it is a big help.  Here we are assembling the trim tab.

And so we ended up with a dimpled aileron, ready for riveting.

And here is the trim tab, mostly riveted in place on the aileron.

And we ended the day by spraying zinc chromate on the second aileron structure.  KW already got the skin.

And for this act, I will rivet together not one but two impossible rivet seams.  First I have to rivet the trailing rib inboard of the flap.  THer are 7 of these little boogers.  The rib faces into the aileron, so NONE of the rivets are reachable without “going deep” from the other side.  I had a piece of 1″ square aluminum in the shop, and I taped my smallest bucking bar onto a short scrap aluminum.  This will just reach the right area if I can just attach it properly.  It has to be flexible to get into the right spot.

And this, boys and girls, is where to use pop rivets when building an airplane.  Actually, these are worse than pop rivets – they are harbor freight imitation pop rivets.  Think of them as tiny single use clecos.  At a penny each, the cost is right.  These will hold the bucking bar in position, but allow some side to side movement and control.

An here is the jig in use.  I C-clamped the aluminum bar over a 2×4, so it can be shoved into the aileron.

Its hard to see in the photo, but the bucking bar is in there, and in position.  I got 3 rivets without moving the rig.  Riveting like this, you carefully raise the aileron with one hand while you use the gun with the other.  Like any other technique, it takes practice.

Moving up the seam, I withdrew the bucking bar and reattached it – this time in a notch I cut in the aluminum arm.  Electric tape worked well.  This got the last four rivets of the first seam.  Seven rivets in 1.5 hours!  This is why Vans suggests just pulling the back rivets.  About now, I am wishing I had!

Now I’ve switched bucking bars to reach the other (long) seam.  Too bad this arrangement didn’t quite fit due to the height of the stiffeners inside the aileron.

And now I am on to my 4th cantilever bucking bar arrangement for the day.  It looks kind of like a prehistoric spear.  This arrangement worked well.  You can also see the unzipped seam in this photo.

With the right arrangement, it only took a few minutes to zip up the aileron.  I did the previous seam while I was alone in the shop, as I needed to concentrate.  By the time I got to the second seam, class was back in session.  You can see my students busy working on their projects in the background.  This pic shows the seam about 1/4 zipped up.  I kept this bucking bar arrangement taped together, because I’ll use this on the normal aileron tomorrow, DV.

And now I have an aileron to join the “long term storage” wall of parts!  On to the next aileron, which I anticipate will be done MUCH more quickly.

This also is a major milestone.  I have now completed the preliminary structural mods to add my trim tabs.  They say to count on 100 hours per departure from the plans.  I have made two significant departures, and am coming in way under budget on hours according to that math.  Of course, I haven’t added the servos yet, nor have I wired them in to the autopilot, so I still get lots of hours to spend…

Zipping up the Aileron/Trim Tab

2-16-18 – 7 hours spent

So today’s goal was to close the dimpled aileron.  This was a lot of work, because 1) I don’t like pulled rivets, and 2) the internal structure that was added to this aileron to strength it for the trim tab did not lend itself well to using solid rivets.  Still, whats building an airplane for if you don’t like 3D puzzles?

So here is the skeleton clecoed together.  I started with the squeezer, and I wanted the rivet heads (factory) to be facing outward if I ever needed to drill them off and open the rivet.

Unfortunately, the squeezer wouldn’t fit all the locations, so the long #4 rivet set comes out and into play.  And I got out the first bucking bar for the day.

Now its time to drive the skin rivets into the top of the aileron.  This is a relatively simple operation, as the way the skin wraps around the bottom of the aileron, the top rivets are pretty easy to reach.  Other than the need to use LOTS of clecos to keep the dimples nested, it should be pretty straightforward.  And the rivets go in one by one until

Uh Oh!  Somebody (me) screwed up the dimpling.  Here you see the pretty dimple on the skin – but you will notice it isn’t lying flat.  That’s because I didn’t dimple the hole underneath it.

I was going to countersink this hole, because the dimple die doesn’t fit due to the nutplate that is in the way.  There is no way the dimple die would fit before – but now I am up a creek without a paddle.  There is no way I’m drilling out all those rivets and countersinking the hole, and I can’t countersink the hole with the skin over it.  I built that rivet gun dimple adapter yesterday, but that won’t work without a low profile female dimpler.

So its time to modify another bucking bar.  The foot of the standard bucking bar makes a great female dimple die.

And its hard to see in the pic, but now I have ALL the holes dimpled, and the rest of the rivets in the top went in smoothly.

When I say smoothly, that may be a bit of a stretch.  You can see the tools and the coffee mug.  One rivet at a time.

And here is the results on my hand.  Lots stress and one bandaid…

Before zipping up the back, I think that I’d better zip up the trim tab.  It’s going to be a difficult process.

And so I’m motivating by looking at the top surface of the aileron.  I’m pretty happy.

Although if you catch the light right, it isn’t perfect.  Still, it beats a lot of production aircraft…

So before closing the trim tab, I need to add a control horn.  I’m going to put it near the center.  It would be so easy to just make an angle and rivet it on the outside, but I need better than that.  After all, this is probably the only RV6 I’m going to make…

Here is a first try to sketch a control horn that works.  But I really want to catch the front spar and the center rib.  Probably overkill, but I want to make sure that there is no way that fatigue can crack that skin.

So here is the trim tab control horn sitting on the end of the tab.  Of course it needs to be mounted in the middle.

And its going to need a slot cut in the skin.  The most important measurement for this is the alignment with the side of the rib.

Clearing out the slot with 1/8 drill bit.  Then a set of needle files to finish it up.

Here is the control horn sticking out of the slot.  Now I need to ensure that the horn is appropriately situated inside when I drill the holes.  I held the horn against the spar and the rib at the same time, and drilled the angle to the spar.

And here is the horn.  I got the three holes drilled into the spar and the control horn.  I also drilled the back of the control horn, but I have not drilled the rib.  I can do that last – after that aileron is skinned.

Now I have to zinc chromate the control horn.  Back to closing the aileron while I wait until the chromate dries…

Its going to need to be done in the exact right order or there will be no way to git-er-done without those unfortunate “pulled” rivets.  (Spits on floor.)  The good news is that I found the perfect bucking bar.  This little beauty fits exactly in the spot it needs to.

So here goes.  First the underside of the two nose ribs – one faces each direction (outboard).  After I got those three rivets on each nose rib, I had to tuck the rear skin under the front skin.

After tucking the skin in, I used a LOT of clecoes to make sure the dimples align.  Luckily, the trim tab cutout lets me get in there with a long bucking bar.

And here is one side of the aileron closed.  The other side will be a little easier IF I remove the rear rib from the other side, I use my long bucking bar.  But I’m out of time for the day, and its time to quit.

Before I put everything away for the night, I did want to take a picture of all the bucking bars I used today.  So glad that I have a lot of options on the shelf.  There is no way I could do this without pulled rivets if I didn’t have the tools…

I Begin Dimpling the Ailerons…

2/15/2018 – 4 hours.

So here you see the extent that you can reach the rivet holes to dimple with a 3 inch rivet yoke.  This is obviously not going to cut it, and the reason I had to spend money on a long reach dimpler.

More stuff I can’t reach.

I think the ailerons are particularly hard to dimple, because the skin curls all the way around.  I ended up chucking the dimpler in the vice in order to  cantilever over the other side of the skin.  I also set a piece of carpet up  at about the same height to help me not to scratch up the skin as I work.

Here is the dimpler in use.  I personally found it easier to remover the spring from the head.  This helped me find the holes, support the sheet (critical) in a flat level attitude, and then strike the rod with a hammer.

This is as far as my dimpler will reach, and it STILL ISN’T FAR ENOUGH!  Look close, and you will see 3 rivets that could not be reached.  Time for a little creativity.

I had an old #4 rivet set that ruined the rivets each time I used it.  I chucked it in the drill and ground the end off flat, with a nice bevel.

All I need is a 3/16 inch hole down the center to hold my dimple dies.

Luckily, there is a lathe in the building.  I had a bit of trouble with my old drill bit, but got it sharpened enough to do the job.

Here is the new tool along with the rest of the set.  The bucking bar (which I already had) has a hole drilled in it for one side of the set – in this case the female die.  The male die is in the adapted rivet set.

Look at the beautiful uninterrupted row of dimples!  I really can’t tell which ones were made with each tool (Squeezer, Long Reach Impact Dimpler, Rivet Gun Dimpler).  I do have a couple of cautions:  1) make sure you stay perfectly aligned with the gun, and 2) don’t overdrive.  Both will make you regret your carelessness.

So I also dimpled the structure.  I did have to dissasemble several parts, but in the end I was able to dimple all but one hole.  This was too close to the structure for the dimpler to reach, and I countersunk it

Here is a rudder with trim tab ready to rivet together.

Back to the Ailerons…

2/6 and 2/7 – Hours spent 5

So with the new ribs in stock, its time to get back to the ailerons.  Speaking of the ailerons, here is the structure of the trim tab after removing the skin.

Now its time to begin the other aileron.  The only thing that KW has done on this aileron is riveting the stiffeners onto the skin.

KW didn’t drill the optional lightening holes on the aileron spar, so that is a beginning point.  I’m drilling the 15 holes – 2 inches diameter each – in the aileron spar.

Here is the fly cutter in the drill press.  The holes are going in nicely.

I was curious how much I weight I saved, so I weighed the 15 circles.  2.8 ounces.  Not a lot of savings, but between the two ailerons, that should be almost 5 ounces.

Clamping the ribs in place on the spar.

Going back over the other aileron, and cutting the lightening holes in.  I had to use the small fly cutter and the hand drill instead of the drill press, because the structure was already riveted together.

I could not get the last three holes cut in do to the additional structure of the trim tab area.  That’s why I figured 5 ounces instead of a little more than 6!

The ends of the spars have 2 3/4″ by 2 1/2″ plates made from 0.040 aluminum.  These took quite a bit of planning, as the holes have to fit a variety of different parts.

Clamping the pieces in place before drilling.

And all the parts that go on the outboard end of the aileron.

My 13 year old son Jason looking over our evening’s work.  We drilled and clecoed the skin over the top part of the aileron.


Framing an Aileron Trim Tab

First real day of work – 5.5 hours.  ($5.25 spent on drill bits)

These are the ailerons as I got them.  As you can see from the one on the left, it is missing the nose ribs.  I started looking everywhere for them, and finally found them mounted inside the other aileron, along with 2 extra tail ribs on the outboard section.  I really mulled over why this happened and what to do about it until I remembered that KW had told me he was going to add aileron trim (just like me!)  He was beefing up the aileron to accept a servo and be strong enough to separate a trim tab.

While I was figuring out what became of the nose ribs, I looked up the cost to buy new ones from Vans.  In stock, $13 each.  Wow!  I’m used to Cessna prices – and I like this!  I am also missing the aileron counterbalance weight for the left aileron.  It cost $10 from Lowes – its a piece of 1/2 inch galvanized water pipe.

Anyhow, the aileron trim tab KW began is on the outboars side of the right aileron.  I was thinking inboard, but since he began on the outboard, I’ll go that route.  I want to frame up a trim tab not unlike the rudder trim tab as per the plans.

Rudder Trim tab as per Vans Plans

Existing framing.  The two inside nose ribs and tail ribs are extras added by KW.  He already drilled the skins to match the ribs, so I was committed.  Luckily, I already had a length of MS20257 hinge – the same hinge Vans calls out in the plans for the elevator trim.

Frame with hinge.

Fabricating a trim tab spar of 0.032 2024 T3.  Luckily, I had some scrap to do the job.

Folded end of spar clamped on inboard rib.  Outboard rib trimmed, folded, and temporarily clamped in place.  The spar is clecoed to the inboard rib, but the outboard can’t be drilled until the skins are fitted up.

Trimming up the middle rib.  This will also be drilled after the skin is clecoed back on.

Spar clamped in place with skin installed and clecoed.

Cutting off the skin aft of the spar.

Trim tab cutout.  Now I can drill and cleco the joints between the ribs and spar, as the final position of the ribs is set by the skin clecos.

Laying out rivet pattern for spar/hinge/skin joint.  Rivet fans are a great tool.  You can see stools in the background.  I am working in the SIU Aviation Technologies Sheet Metal lab, where I teach aviation sheet metal fabrication and repair.  This is how I just “happen” to have so much good stuff and access to so many nice tools.

Hinge clecoed in position.  Trimmed portions of ribs clecoed back onto the cut out portion which becomes the trim tab skin.

Using one of the rib ends to make a pattern for a new rib.  Don’t try a job like this without a caliper.  I’m old fashioned enough to like my dial version over the more modern (and less reliable) digital versions.

Rib form block cut out of scrap pine and radiused.

Drawing the rib blank.  I used 0.030 aluminum instead of the 0.025 of the other ribs.  That will add a couple grams.  We’ll have to check the balance before we fly!

Hand forming the flanges with a rubber hammer.  This will be followed up with a more precise sheet metal hammer.

My new rib alongside the outboard rib and the pine bending block.

Clamping the trim tab to a straight edge before drilling the new rib to the skin.

Not shown – forming the trim tab spar.

Trimming and folding up the rib to fit the spar.  I’ve cut the triangle forming block to length, and I’ll hammer the flange down.  Notice the relief holes in the corners.  This was done on the 2 outside ribs.  The center rib will not be riveted in to the spar, forming a stiffener instead of a rib.  The full aileron had stiffeners only in the center, not ribs.  My trim tab is fine with a stiffener instead of a rib.

Trim tab set in position.

Drilling the skin/spar/hinge joint.

Tim tab clecoed in place, shown slightly raised.  Raising the trim tab will push the aileron down, pushing the wing up – so the trim tab moves the same direction as the wing travels.

Bottom clecos removed to fit in the bending brake.  Lower skin bent as per elevator instructions.

Completed end view of formed trim tab.  Compare to end view of elevator tab below.  I need to get the servo before I finish the tab.  I have decided to use the Actuonix digital servos because they are light, low cost, and I can hook them to an autopilot as well as a simple trim system.  They are specifically intended to be controlled by Arduino, and that will probably be the brains on my trim computer and my autopilot system.

I’m very happy with the trim tab – it easily moves up and down through an appropriate range – about 15 degrees down, and as far up as I want.  I can control the precise stops when I add the servo.

Reminder of the elevator trim for comparison.