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RV-7 #75069

idubrov

Well Known Member
Started building an empennage kit of RV-7. Made some progress working on the vertical stabilizer.

And this is my damaged front spar assembly for the vertical stabilizer:

VS-705-damage.jpeg


Lesson? Don't try to fix what is not broken :rolleyes:
 
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After many working sessions, getting to the point of no return: this nose rib is going to be hidden inside the part!

hs-nose-rib.jpeg


Looks good to me. Couple of rivets are not exactly straight, but this should do. I noted that I instinctively tend to get shop heads on a smaller side. There was one head ~0.126" (which is still good according to the spec, which gives ~0.122" minimum for 3/32" rivets), but I hit it few more times.

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Ha! Small world, I'm RV7 75070! I'm a long way behind you thanks to Vans loosing my final payment for a month and living in the UK so no doubt further shipping delays there!

I'll follow you with interest if for no other reason than your builder number and for knowing what's next in my build!

S
 
I'll follow you with interest if for no other reason than your builder number and for knowing what's next in my build!

Welcome-welcome!

Meanwhile, horizontal stabilizer is complete! Turned out, I was intimidated by the rivet gun for no reason. Running 3/32" rivets with the mushroom set is nothing to be scared of (I am still intimidated by the universal head -4 rivets, but I'm sure, I'll get there).

hs-complete.jpeg


I was thinking to show my rivets to somebody before I close the part, but I couldn't hold myself from finishing it. Not much to see there anyways, all the rivets are perfect :D

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...and vertical stabilizer is finally complete, too (after rebuilding the whole front spar assembly).

vs-complete.jpeg


Some random rivets inside the vertical stabilizer (I think, they look worse than the horizontal stabilizer ones, but hey, it took me much less time!)

vs-random-rivets.jpeg


Does not look like my dimples are crisp enough! However, I think, truly crisp dimples are a myth :D

dimples-are-not-crisp.jpeg
 
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Okay, so the empennage parts are somewhat complete (except for the fiberglass and fitting parts together).

Still debating if I want all fairings to be removable or just the rudder bottom one (and maybe the elevator ones, so I can keep additional counterbalance weights inside them).

the-empennage-parts.jpeg
 
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You can get crisper dimples.. they aren’t a myth. Cleaveland tool has a great YouTube video you can check out showing the difference between under dimpled and right ones. You either need to squeeze or hit harder, but also check the brand dies and if they aren’t quality ones such as brown, Avery or Cleaveland, you might find a difference there too.

https://youtu.be/DxQwh-X8gOc

https://youtu.be/Qo9QCMaNSoA
 
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You can get crisper dimples.. they aren’t a myth.

I know, I was being a bit sarcastic, given all the discussions about "crisp dimples" I've seen. I primarily use DRDT-2 which I think I set up properly (lots of pressure).

I'll try more pressure (or maybe buy Cleveland dimple dies).
 
Buy Cleaveland dies….I have others but only use them on non visual stuff and grinding the edges on them. I have three sets of 3/32 Cleaveland dies. One has been ground. My fav set and a backup set in case. I have 1/8” dies and all the screw dies from them. They make the best dimples from my testing.
 
Finishing

The pull rivets can be removed if you really want to remove a tip. That also means they can't be covered or the seam bonded or sealed.
The other method is to add a nutplate to the forward tooling hole on the elevators.
The rudder has a counterbalance but the part is not balanced before finishing.
 
The other method is to add a nutplate to the forward tooling hole on the elevators.

Yes, this is what I want to do. Add a nutplate and use a bolt with a stack of washers for the weight. I wanted to put it inside the fairing, for a bit of extra safety. However, now that I think about it, the bolt could be safety wired.

Meanwhile, I got my fuselage kit (took only 2.5 months from the date I ordered it :eek:)! Now this is mean, find those 4 CS4-4 rivets out of 148 LP4-3 and 28 MSP-42 (well, MSP-42 are easy to tell by their mandrel):
 

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This was "I cannot be that stupid moment".

I was about to drill the holes in the F-661EF flap bearing blocks. I measured the blocks and found that even though they are exactly the same dimensions, the bearing hole was offset from the center of the block (which would be top to bottom in the installed configuration). It was something like 0.620" one side and 0.6 50" the other side (edge to the edge of the hole).

So I thought I will machine an aluminum "plug" that will go in the hole and will connect two bearing blocks together. This way they will be perfectly centered one to another and I will see how offset is the hole (and also so I could locate all four holes precisely on a milling machine).

I machined the plug, put it in the block ... and got the following:

IMG_6095 copy.jpeg

I forgot to multiply the depth of the hole by 2 :rolleyes:

Luckily, the plug was thick enough that I could drill it, then use the hole to pull it out.
 
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The Dragon:

IMG_6483.jpeg

The Corner of Despair:

IMG_6485.jpeg

The deadly Hero:

IMG_6486.jpeg

And a somewhat happy ending:

IMG_6488.jpeg

What else did I try:

1. "Fuel tube" trick. Did not work. I think, the tubing I use is too soft. It worked previously in less challenging cases, but here flanges are actively pushed apart to get access for a rivet gun / squeezer / backing bucking bar / etc.
2. "Drawing" the flanges after a few taps. Wasn't able to get good results from it. Perhaps, a skill issue.
3. "Backriveting" using a universal dimple set inserted in a backing bucking bar. This worked well where I was able to use it. However, it did not work well in cases where I need to bend parts away to get access (the spring is not strong enough, I think). That top rivet is the worst -- thin flanges on both sides and limited access from the front due to the seat rib profile.
4. Using piece of lead to push the flange. Worked really well, was able to squeeze the rivet. Lead seems to push the flange really hard, which is what I wanted here. Also, it is soft, so it does not scratch anything. I think, it is the most bullet proof method, since lead changes the shape as needed when a rivet is being set?

I didn't have rubber grommets, so haven't tried this variant. I think, those should work well. I'll try them next time so I don't get exposed to lead unnecessarily.
 
Okay, so I needed to drill the F-715 seat ribs for the bolts going through the F-704. The tricky part here is that holes in F-704 are somewhat valuable. Even though they are not "close tolerance" holes, they still are in the part that is kind of expensive.

And on the opposite side you have a sheet metal rib, which is not friends with regular drill bits. So you cannot really run a full-size drill bit (seems like the holes in F-704 are already #10 holes). The drill will grab and tear the hole in the sheet metal and in the process of doing so, it might also damage the F-704 with its side cutting edges.

It might be a less of an issue if used in an air drill as these turn fast, but I have a slow electric drill.

So, what would a reasonable person do?

Well, one advice I saw was to use brass tubes as bushings so you can drill a small hole first. Then you can upsize the hole using unibit or carefully with the twist drill bit.

Another option is to use a transfer punch to locate the hole on the rib, remove the F-704 then drill.

There are probably some other reasonable choices as well.

What did I do? I made my own tool, of course! Another D-bit. Possibly, less controversial than the one I used for the wing spars. :eek:

Same idea, the cutting edge is at the tapered part, but with taper going all the way to a sharp tip (so it can "drill"). This time I did harden it.

Of course I broke the tip on the second hole, which I kind of expected, but since the tip is not an important part of the tool (it is only used to punch the hole, the most important cutting is done by the wide taper), it still worked fine. I probably should have made a small flat "spade" end from the get-go. I smoothed and sharpened the new "cutting edge" to help it go through the aluminum.

The tool (with the broken tip).

IMG_6785.jpeg

The hole after some deburring. The tool leaves a lot of burrs on exit (I think, it's because it has a neutral rake angle / no relief angle, so it pushes the chips rather than cuts them), but the hole looks good (technically, this tool is also a reamer, cutting very round holes).

IMG_6791.jpeg
 
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