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Elevator Trim Tab Fold -- Acceptable?

Hey all,

I'm working on the LH elevator and trim tab and have gotten the bends on the elevator itself and the outboard tab pretty well done, but the inboard tab has turned out somewhat "less perfect". That said, I'm not certain that another go at it will necessarily produce a much better outcome, and considering that it will be covered in paint and such, my gut is to just build on. That said, I thought I'd ask your collective opinions before doing so:

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The trailing edge isn't very pretty, I know, but otherwise the tabs seem to come together fairly nicely (when cleco'ed to the spar, the come together even better).

{Also: I'm familiar with the "riblet" method...not looking to change gears at this point, just determine if I should live with what I've got...}
 
It will fly, but what I would not accept are the poor edge finishes and an obvious crack in the trailing edge radius.
The empennage is your practical practice piece. You can learn quality and carry that level through your build.
I would swallow hard and do this again, perhaps with some guidance from an experienced builder. That tab can be tricky but shouldn’t show hammer marks when done although it doesn’t affect air worthiness.
Edges should not show mill marks.
 
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Your next one will be considerably better.

You can avoid the hammer marks by using a wooden block to spread the load.

What I did for the end rib folds was use a 3" metal hand seamer, like this one. It didn't do the bend at the trailing edge well, for that I tapped it locally with a hammer against a block of wood.

The trailing edge can be bent by using the tool that Van's recommended in my RV-3B plans. I don't seem to have a picture of it, but it's two 2x6s, straight, next to each other held together with door hinges. Think of it as an open book, with the hinges located farther apart than the width of the trim tab, so they don't interfere. You simply place the trailing edge in the fold and press the pieces together. Be careful to bend it evenly (it can cause local unevenness) and not to go too far. If you go too far, I've been able to open it up a bit by pressing a dowel in there and unbending it as needed.

With both the wooden tool and the dowel, the key is to work slowly and carefully.

If you don't mind a further comment, you should clean up all the edges. What's shown are not as smooth as you'd like and might well lead to cracks later.

Incidentally, for me, it was the fifth one that will fly. The first four were scrap.

Dave
RV-3B, skinning the fuselage
 
It seems like my unease was justified. I'll put in an order for another two (they're cheaper than the shipping, after all) and give it another go--or two.

I hadn't cleaned up all the edges yet and was probably too eager to try the bends to have done enough job even on those parts...I sort of figured based on everything that I read that I wasn't going to get it right the first time, so I almost mindlessly jumped in figuring it would end up as a learning piece of scrap. But the other side came out so well I felt like I wanted to "make it work". Fortunately, other than time lost in shipping, this isn't a big cost or time in rework to get back to where I was.

The edge bend was done with the 2x6s, but it wasn't quite enough in one spot, so I tried making a small adjustment using a pair of pliers, which led to the roughed up and dimpled end.
 
Don?t be afraid to ?relieve? the corners at the trailing edge. You are doing two bends here that intersect: the trailing edge bend and the bend in the tab. That induces stress. This is a bit exaggerated but the corner is well relieved.
Keep swimming!
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I should have added that for the tip flanges, I made a tapered block of hardwood and clamped that inside the trim tab for backup. I'd put a radius on the edges.

I reserve a large shelf in my garage attic for scrap. I felt bad about the amount that was going up there, until another local builder said that when he was done, he took his scrap to the dealer and got $136 for it.

I figure Van's breaks even on the kits and makes their money on our replacement parts.

Dave
 
If you're not on a first name basis with everyone in the order department at Vans, something is wrong....
 
Trim tab bend

I made a bending wedge. Take a piece of hardwood and cut it the same dimension as the trim tab as if it were a rib. Put double sided tape on both surfaces. That goes inside. The mate goes outside also with tape. Camp it down. Add another two board pieces positioned so the two wedges can't slide out either way. Yes, they will, even with tape and clamps.
As Dave mentioned, use a block of hardwood to spread the load. Hammer or rivet gun works to hit the block. One smooth steady motion is best. You don't want back and forth flexing.
Remember, the part bends at the radius of the block so position it carefully. You can't get 90 degrees till the block is removed. The last few degrees can be done by hand.
 
Took me three tries as well, three seems to be the magical number for trim tabs. I also abandoned the ear folding method and went with the riblet method. Probably just as time consuming if not more though...
 
get a sheet metal bending brake (break??)... great results every time, and all of the bends in the trim
take less than 15 minutes....
 
get a sheet metal bending brake (break??)... great results every time, and all of the bends in the trim
take less than 15 minutes....

Well, every time if you have a finger brake, radius fingers, and/or know the tricks to maintain proper bend radius. Most brakes where designed as production machines and take some time to set up for each task, gauge, material type, etc....
Easy if you know what your doing but they are not fool proof and take some practice.

It is really easy to ruin soft material like aluminum sheet.
 
I have a simple one from Aircraft Spruce that I modified a little... I radiused the back edge of the clamping plate so that it consistently produces a nice 1/8 radius bend, every time. The short, lateral edges needed to be trimmed to accommodate the angle of the trim tab ends, but this can be done without affecting the 'standard' edge of the plate. Images shown in the link below. Not tried using Flikr for this before, so it might not work!

Bending brake was Part # 12-02810 and cost just over $100... the cost of a replacement trim tab, postage, import duty, import handling, and tax to get to the UK is only marginally less, and now I have a great new tool to add to the growing collection!

https://flic.kr/s/aHsmjbaiAk
 
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Bending brake was Part # 12-02810 and cost just over $100... the cost of a replacement trim tab, postage, import duty, import handling, and tax to get to the UK is only marginally less, and now I have a great new tool to add to the growing collection!

https://flic.kr/s/aHsmjbaiAk

Wonderful idea. It looks like the same thing is available on Amazon 18" or 30 for quite a bit less too.
 
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I have family in the HVAC business and have access to brakes. I don?t think there is enough room with the taper to make the break very useful. For me #1 was practice. #2 is airworthy but the hinge is misaligned. #3 will be the money. Vans should ship 3 tabs with every kit. And I did the tinker on the elevator skin.
 
It looks flyable, but lets be honest... the trim tab is pretty cheap from Van's even including shipping, and its not a whole bunch of work to redo. I am a bit of a perfectionist, so on a piece like this, since its so cheap and easy to redo, I'd just redo it.

I redid my trim tab twice :) Nothing to be ashamed about.
 
Take 2

Thanks again for all the feedback, folks. I received the replacement tabs skins from Van's and took another crack at it this morning:

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Certainly came out a lot better! I used the steel bar method both times, but this time I went through great pains to get everything locked down with carpet tape and took my time with the bend, using a rubber mallet and a block of wood. I ordered two trim tabs, so I've got one more crack at it (might as well see if I can do even better), but I'm feeling pretty good about this one being usable no matter how things go the second time around.

Any thoughts?
 
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