It's been a while that I have been reporting progress. Some of you might have thought that I gave up. Nothing is less true.
I came to a part in the building process that is know as been the most difficult and most boring part of the empennage kit : bending the trim tab and elevator tabs.
Don't panic, it's not mine but I just wanted to illustrate that the trim tab is the most replaced and most hated piece among all RV builders.
The trim tab is the only piece that also occurs in the Van's catalog. You can imagine How many of these they must be producing.
The following work sequence is the summary of 3 weekends of work. Not very fast but accurate and patiently. And I would advice these 2 simple principles to all new builders starting the bending of the trim tab. Be patient ! Do it slowly! Measure and measure again.
You start of by bending the trailing edge of the trim tab. It's a small part and thin skin sheet so be gently on it. No brute force.
Also note that I have used the same metal dowel inside de bend to avoid cracks. Don't even think of trying this without one ! I have seen many pictures of cracked bend ends on other websites of people who had different ideas.
The process is the same as with bending the elevator trailing edges. Insert the part in the bending brake. Make sure the hinges are close to eachother to avoid bulges. Start close to the trailing edge, close to the closing point of the bending brake.
The start squeezing. This makes a first squeeze close to the bending point. Once it's been closed almost completly, you can move the part forward and squeeze more. Constantly check height with the rib and check on the end points in the bends.
I closed mine just a little too much on one side because I gave it a last squeeze without the dowel. I managed to get it back up, it proofs once more the theory I gave before: don't remove the dowel until finished.
This is how it looks like with the E607PP rib in place. Nicely connected without stress.
And no bulges and a nice radius in the bend. Perfect !
I then started to draw the lines on the trim tabs ears. The idea is that these ears will be bend over, over eachother and that you close them up later with pop-rivets.
On the outboard side, some pilot holes are already punched in the kit and you need to draw the bend line parallel to the unbent part. This is really easy. Do the same on the inboard side.
Don't worry too much yet on distance here for seperation from the left elevator trim tab ears. That misery comes later.
Then the stress starts. It's tab ear bending time. The manual explains this process in a lot of detail. Follow it in all it's detail. Think of the picture with the garbage bin I started this article with, we don't want that!
As a summary: put strong two sided tape on the edge of a table. remove the vinyl to the same width as the tape.
Then position the trim tab with the bend line(bottom side) aligned with the table.
Now put some tape on the block that will be inserted in the trim tab and also glue it into position. As the manual says, put the block +-1/32" to the outside as the block will shift a little during the bending process.
Put tape on the top side.
If you decide to follow this sequence, make sure the top side of you trim tab is facing down on the work bench. The top side ears will go over the bottom side ones to avoid water entry places.
Put the second block on top of the trim tab and clamp the complete structure very tightly on the work bench.
A word of caution here. As you can see in the picture below, the top block is almost aligned and far away from the bend in the trim tab.
This is a must ! I you put it too close to the bend, you will get a small dent in a hard to reach and repair place (ask me how I know).
Another fact: the top block will move downwards in the direction of the bend line of the trim tab. Watch for this as you proceed with bending and reclamp the block if needed.
With a small wood block, start tapping parallel to the top clamp block with light taps and working progressively over the complete range of the trim tab ear.
When the tab is completely bent and almost completely against to block, you can use your rivet gun (I used the flush swivelhead) to tap on the aluminum.
Caution ! Low pressure only. Set the rivet gun against a table and adjust the pressure as you tap. You should hear the tapping at a very low frequency.
Keep tapping and work progressively from one side to the other.
As you can see, there is plenty of clearence on the bottom of the bent ear. You won't be so lucky on the other side.
Now do the same on the other side. I couldn't get it too close perfectly with pusing together. You would need to overbend this second ear slightly if you wanted to achieve that (remember: aluminum, spring back).
It fitted well and the pop rivets will pull this together so I didn't worry too much about this. I might be trying to close this up once more when I get to rivet them.
Now do the same thing on the inboard side (narrow end).
The radius is a bit different here so you will need to make a new bending block.
In the picture below you can see where my dent got created, the blow was over the trailing edge and slightly pushed in the aluminum as it slipped down. Very small and fortunatly on the bottom side.
As you start bending, you will immediatly notice the problem here. As I wanted to make sue I had sufficient clearence space later between elevator and trim tab, I decided to bend as far as possible inwards.
The results is that the tab ear is a bit too long on the trailing edge side. I was able to use a small file and remove the excess material.
I also found that the water escape hole and bending near the trailing edge was getting to small and would get too much stress concentration around too many bends.
I used a small round file to open this up again as you can see in the picture below
The picture below is the finished product after working it with the rivet gun. It closed up very nice on this side.
If you got to this point, you can cast a big sigh of relief. The most difficult part is over. Chances are about 80% you won't end up like my first picture.
Now it's time to matchdrill the E607 bottom flange to the trim tab
Then clamp the 2 trim attach horns together and run a clevis pin the attach hole to align. You may be a little confused as you have to get the pieces from the remaining stock. These horns also come with the electric elevator trim kit.
It is better to use those as they are already pre-trimmed to exact size.
Clamp in place on the bottom side of the trim tab. Notice the hinges are a bit too large on the bottom side according to my bend. So I will have to grind it down a bit. Be carefull not to grind too far. Keep the minimum edge distance rule in mind for those rivets.
Here all holes have been drilled and the horn is in place.
Now comes the part where you can still mess up. So pay attention.
First make a marking of the dimensions on DWG 4 for installing the piano hinge to the trim tab. Vans calls for 1/4" to the inboard and 3/8" from the trim tab forward side.
You will notice as you do so that the alignment of the hinge is good but the edge distance on the piano hinge is far far far from sufficient.
I decided to draw a center line on the hinge and use this line to test-fit the hinge to the tab. I also marked the distance of 1/4' from the side of the hinge to mark the position for the first hole alignment on the outboard side of the tab;
When the hinge is aligned, you will notice it's too longe on the outboard side. This is normal.
Since I have been closing in the hing into the trim tab, the ends of the fix bar are a little inside.
When I installed the hinge to the elevator for testing, I noticed I can still clearly move the elevator more then 90° up. It will never need that but it proofs my decision to move the hinge a little inside for edge distance has no effect on the motion of the hinge.
In the picture below, you see the blue line through the holes.
Take your time again before drilling the first hole ! Use the depth measuring side of a caliper to measure how far the hinge is in on the trim tab and make sure it is to some thousands close equal everywhere.
You don't want a twist in the hinge. It has to move freely.
Drilled the hinge in place. I reinstalled the pin and other side and the fit is perfect. Very smooth motion.
From the bottom side.You can see here the hinge is about 1/32" in on the end of the tab (about 0.040")
Then time to countersink the E607PP on the top flange. The other side will be dimpled. I first countersinked to have a test rivet flush but after putting the dimpled skin in, the dimples didn't sit flust so I went 2 clicks under on the countersink cage as most do and the fit was much better.
Then you trim the hinge to align with the outboard side of the trim tab.Mark and cut, then grind away the rest of the excess material.
Then we jumped into the last major problem of the day.While dimpling the skin, you notice that the holes closest to the tab bent for the elevator attach horn are not reachable by the yoke because the ears are now bent and the area is too thight to pull open without damaging the bend. Also the pop rivet dimpler doesn't fit in there (the dies are too wide and the nail too long.
Jaqcues came up with a great idea to countersink a small iron flat bar and lay this on top of the inner forming block we used before.
Slide it in and make sure it fits thightly. You don't want to make dents as you hit the male dimple in.
I then used the top bar of the C-frame with the male dimple attached and gave it a couple of good hits. It worked fine. No dents and a good dimple.
Oh nooo... more bending !
Time to bend the ears of the left elevator. You can use the same clamping blocks you used for the small side of the trim tab.
I made a construction that supports the inboard part of the left elevator so the tab could end over the edge of the work bend.
Same procedure as with the trim tab. Tap gently with a wooden block.
I forgot to take a picture of the finished product but it came out nice without a dent.
This concluded the bending part of the assembly process. I am now waiting anxiously for my two re-orders. I should have them monday so it will soon be priming time again.