Rudder Trim Tab – Additional Details

2-14-2018 – 3.5 hours and 2-15-2018 0.5 hours.  Total 4 hours.

Confession time – I’m just guessing at hours.  It isn’t simple, because I am also teaching full time while I am working on the plane.  So I just guess at the number of hours I got in, and the number of hours that were spent answering student questions and keeping students from chopping fingers off.

So let’s get on to today’s work – completing the rudder trim tab from the parts I made yesterday…

The first thing I had to work on today was adding a way to remove and install the hinge pin.  This involves drilling 2 holes in the rudder – one through a stiffener and one through the bottom rib.  Note the sheet of folded 0.060 aluminum also in the picture.  This is what I intend to make the control horn from.  It has a wide radius bend, as this has a large minimum bend radius.

Here is the route plan for the hinge pin install/removal holes.

Here you can see the hinge pin emerging from the holes.  Now it is on to making the control horn for the tab.

Here is my first attempt at the control horn.  It is folded from 0.060 2024-T3, and looks great.  The only problem is that I would have to cut into the rudder spar to make it work properly.  FAIL.

Another view of my failure.

Here is the control horn 2.0 being planned.  I used another one of the 2024-T3 fittings that I had.  It has a sharper bend, so I can tighten up the location and make it open and close.

Here is the completed control hon, with most of the riveting done.  (Picture out of sequence.)  The horn should be aligned/streamlined with the direction of travel.

And now its time to talk about riveting.  I planned my riveting poorly, and ended up having to set the rivets with odd shaped bucking bars – one at a time.  I have all but three of the rivets set now, and will bring a thin bar clamp to use as a bucking bar for those last three rivets tomorrow.  (See the picture of the complete trim tab control horn with its missing rivets.)  I will not cut in the access panel for the servo or the control arm slots until I have the servo in hand.

Just a little more piddling around, and I will have my first trim tab completion done.  The extra dimpled holes in the skin will have to be filled before paint.

So I went back in today (2/15/2018) and got those last 3 rivets.  Here is the bar clamp I referred to.  Note that it makes a long bucking bar that covers the entire rivet seem.  It did take quite a few more blows to buck the rivets, but they went in.  Rudder trim tab is done except finishing!


Adding Rudder Trim

2-12-18 and 2-13-18 – 4.5 hours spent

So here is the trim tab I decided to add to my rudder.  Note the holes in the corners of the cutout.  I cut the skins with a Harbor Freight “High Speed Panel Saw.” It worked fairly well after I re-tightened all the loose set screws that it came with.

Here is the trim tab spar.  It extends about 1.5 inches past the trim tab on each side.  This was a complicated fold, as the rudder tapers, so the spar lines are not parallel.  I was pretty happy with how the spar folded and went together – nailed it on the first try!

I drilled the stiffeners off the inside of the trim tab, but cutting away the stiffeners on the inside of the rudder was tricky.  I borrowed a dremel with cut-off wheel, and sliced through the bent portion of each stiffener.  I also ground halfway through the flat portion.  After folding the bent portion relatively flat, the stiffeners could be bent the other way.  A couple of back and forth bends, and they snapped neatly off.

Here are the cut stiffeners.  No damage to the inside of the skins.

Here is the hinge going onto the spar and into the opening.

Spar, hinge, cut/broken off stiffeners, and the c-clamps to get them into position to drill.

So I was so proud of myself when folding the rudder trim tab spar.  Folding the spar for the other side did NOT go well.  The Z-fold didn’t work on my brake, and I ended up trying 5 times before I finally got it right.  Here are 4 failures.  The final one that did work is not in this pile.

The trim tab going together.  You can really see the Z bend in the spar.  I’ll fill the rivet holes before prep and paint.

Trying to dimple inside the tiny spar openings was hard.  I eventually had to build my own very low profile female dimple die.  I chucked a unused rivet set in my drill, and profiled it on the grinder while spinning.  Next, I drilled the hole with a #40 drill bit.  Finally, I finished the countersunk portion with a standard #40 100 degree countersink.

Zinc Chomate on all the new parts.

Next up – forming a control horn and riveting the hole thing back together.