Category Archives: flaps

Finally Flaps…

It took awhile, but the flaps are finally closed up and done.  I’ve been spending a lot of time on my job search.  I’ve got quite a few leads and have had a few interviews, but no offers yet.  I’m interviewing with a big California tech firm in early June.  That looks very promising!  I’m also looking at some finance and fintech jobs here in NYC.  Hopefully I’ll have a better idea of where I’m going when the ailerons are finished.

On the last post, I had finally gotten the flaps assembled for the first time.  I always like that part, as the skeleton gets put together and the real shape of the part emerges.  Alas, that is typically short lived as the next step is to take it all apart, deburr, prime, etc…

Normally, I use my DRDT-2 to do the dimpling work on the skins.  That tool is still in the hangar in Chicago, so I used my backup C-Frame for the first time.  I was extremely careful because I’ve seen all the pictures of the “extra” holes people have managed to poke into their skins.  It was a bit tough getting the inside of the nose skin even with the reduced profile dimple die, but I managed.

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Doing the top and bottom skins was a lot easier than the nose skin!

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The next step was to prime all of the internal ribs and doublers and hinge plates.  Everything was carefully marked so I could reassemble it.  The blue tape is there because I only wanted to prime the internal area of the hinge plates.  I’m using Comet cleanser and a scotchbrite pad.  It really cleans nicely, leaving a dulled finish ready for paint.

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I also scuffed and washed the skins and spars.  They were a lot more awkward to do in our kitchen sink!  The blue tape covers the part of where the trailing edge wedge goes.  It is cleaned and scuffed right before installing the wedge.  Primer would effect the adhesive, so it remains bare aluminum. After cleaning and drying the parts, I lay down some paper in the garage and primed them (with a blockade in place so that my wife would not return and drive over the parts!).

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Some of the nose ribs get doubles and nut plates (not shown, but they are installed!)

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The hinge brackets are similarly riveted to some nose ribs.  Then the matching pairs are riveted together.


Then the flap skeleton is riveted together and the top skins are put back into place so they can be riveted (and back riveted) onto the ribs.

But… there was a small problem!  Apparently, I missed a couple of dimples in the nose skin of one flap.  So I had to take it all apart again.  This is why I like to do one last scan before putting that first rivet in place.

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With the top skin in place, you first rivet the top skin, nose skin, and spar together.  Pretty easy since you just need to reach over the top of the skin to get a bucking bar in place.  All but the last two rivets in each rib are driven (or squeezed on the ends).  For the last two, the gap is too small for a bucking bar, so they are back riveted.  My 5 foot back rivet plate was very handy here.  You also pull and squeeze the rivets for the top of the nose ribs here.


The next step is a bit tricky.  It is easy to introduce a twist into the spar when closing up the D-cell that makes up the nose.  The instructions recommend using a digital level to check the hinge brackets.  When the angles match, the box is squared up.   I had to play around with each flap for a while to get them lined up.  In the end, they were only .2 degrees off.  It will have to do.

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With that done, you can reach in through the (tight!) opening and rivet the bottom skin, nose skin, and spar together.

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Next, you get the back sides of the nose ribs and the two rivets that are close to the hinge brackets.  These are blind rivets because either they are so close to the bracket that there is no room to get the rivet gun in place or (for the nose ribs), you have no access to buck them.  The plans noted that using the pull rivets is optional for the spar rivets.  I figure that these are on the bottom, so they really aren’t a “beauty” item and also, they form a nice line with the nose rib rivets that have to be pulled.  It looks fine.  I do have some dings from squeezing the bracket rivets to buff out though 😦

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The trailing edge wedge is done in the normal way.  After pulling the tape that masked out the primer, I just had to scuff and clean the edge with some scotchbrite and acetone before adding the adhesive tape to the wedges.  The wedges were washed with Comet cleanser and scuffed as well.

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Once the wedges were clecoed in place, I let them sit a couple of days so the adhesive set would set.  Then it’s the normal double sided rivet thing.  Here, I first squeezed the rivets part way and then finished the back side with my mushroom head set.  They came in pretty flush as you can see in the picture below.  Finally, you pop rivet the bottom skins in place.

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Next I’ll start in on Section 22 — Ailerons!   Their construction is similar to the flaps except it uses stiffeners instead of ribs, so everything is back riveted.  Hopefully I  have all the pieces here in NY.  Otherwise, it will all have to wait until I can get out to Chicago in a couple of weeks.



Flap Therapy


I’m looking for a new job.  The old one in Chicago just didn’t work out, so my employer and I have parted ways. For now, the majority of the project will stay in Illinois until I figure out where I’ll be working next. I did keep some parts to work on at my NY home, so at least I can make a little progress!

So, I got started on the flaps.  I figured that they would be pretty easy to build in my basement shop.

I made the brackets earlier.  They were pretty easy to make using my table saw and band saw.

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Like most sections, this one starts with lots of parts preparation.  There’s a little fluting to do on the nose ribs (made harder by the fact that my fluting pliers are still in Illinois) and some burnishing of gaps to prevent faceting, but the annoying part is cutting a bunch of tabs off the flap ribs.  They’re easy to identify (no problem with Left and Right parts) since the tab has no hole.   I cut these off using metal snips and then used a file to carefully trim the edge down.  The snips did cause the edge to bend a bit, so I had to carefully straighten them with some smooth nosed pliers.

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Similarly, each of these rounded cuts caused the ends to “pucker” out a little bit.  It’s not noticeable until you look carefully.  But as I applied the same smooth pliers to each, I could feel the pucker straighten out.  Then, there’s lots of deburring.  The edges and holes on all these ribs were a little rough.  Lots of hand work with sandpaper and files to get the edges prepped.   I don’t have pictures here of the hinge plates and doublers, but they too required a lot of hand work to smooth out cut marks.

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Then, you assemble the flap skeletons.  This is one of my favorite parts of building… when a “real” airplane part suddenly starts to emerge from the pile of small parts!

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Here’s a close up of the inboard and outboard rib assemblies.  At first, I though that the inboard one was for the inboard most position, and the outboard one was for the outboard most rib.  No….  They work together to hold a rod that will eventually connect to the flap control system.  A bit of squinting at the diagram made this all clear.

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The joggled hinge brackets line up very nicely.  There are holes in just one of the joggled parts.  Later, when everything is lined up, I’ll match drill and rivet them together.

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I’m working on both flaps at the same time to help make sure that I get the right parts in the right assembly!  The two are mirror images, so it helps to see both at the same time.

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Next, you cleco together the skeleton with the skins.  It takes a bit of finesse to get the nose skin in place.  It has to be fitted over the flap hinge brackets and then worked around the nose ribs.  Two of the nose rib holes are not pre-drilled.  We’ll get them in the next step.  I just kept working the clecos around the edge and eventually got the whole thing put together.

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I match drilled the “missing” holes in the nose ribs pretty quickly.  The only real problem I have is that I only have a small compressor at home.  The air drill quickly runs through all my air, so I have to wait occasionally for the compressor to catch up.

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You need to be careful drilling the trailing edge.  The instructions make it quite clear that you must drill perpendicular to the cord line not perpendicular to the edge.  It’s a 84 degree angle.  I used to have a block cut to that angle (from previous trailing edge work), but it is lost somewhere either in Illinois or in the scrap heap.  So, I just downloaded a paper protractor and taped it to a square.  This provided enough guidance to final drill without enlarging any of the holes.

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So, here’s two flaps!  Of course, now the real work begins.  I have to deburr, dimple, and prime all the parts (and match drill the hinge brackets) before putting this all back together.

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Lots of work upcoming.  The big one, of course, is to get a new job!  I have some leads and have done some interviews.  I’m hoping to hear soon what’s up with that.

I have enough parts to work on for the next month or so (flaps and ailerons) and may bring back the tanks when I go back out to Chicago to move out of my apartment.

I’m hoping the next couple weeks will bring some better direction.