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Still dreaming about the trim, but it can become a nightmare soon...

W

WVM

Well Known Member
Hi,

I am currently working on the legendary trim. It appear to be one of the most redone parts in the kit. And that doesn't surprise me at all...

I have put a circular metal bar of 4 mm (about 0.157 inch) in the corner. This was a tip from a fellow builder. But how far can I bend this part without damaging it? I don't really dare to bend over the point that I feel resistance, fearing for a cracking sound... It is also unclear to me how far the trim edge should be from the corner on the "brake". (red arrow). I also hope that the metal bar isn't to big...

Any advise? Thanks!

trim1.jpg


trim2.jpg


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trim4.jpg
 
It's a relatively thick bar I wouldn't use it. The trailing edge of your trim would be larger then your sharp edged elevator. A show plane judge will notice it :) You can use a leftover wedge instead or nothing at all as per plans. It won't slide out if the blue plastic is still over it.
 
I put mine right in the corner of the brake and squeezed a littie at a time until it held the shape I wanted. If you do it in stages and don't squeeze it tight it should not crack...

I don't know about the metal bar though, I would worry it might flex in the middle and result in varying sharpness along the trailing edge. Why not try it both ways on a piece of scrap and see which turns out better?

You want the trim tab to match the elevators, so you should use the same technique for both...
 
Bending

It's pretty much like any other trailing edge bend. I start with a 1/8" (.125") wood dowel then remove it and finish the bend without one. It really helps to have a target. Make a wedge the shape of the end of the trim tab edge or chord. Get a block of hardwood like oak and cut it diagonally the dimension of the interior of the trailing edge. Remember to cut the correct side of the mark or the kerf will make the inside block too small. The finished product should fit together as a rectangular block when done. You'll need them to bend the ends of the tab anyway. Squeeze till the bend matches the wedge.
To bend the end tabs, get some double sided tape. Put tape on either edge of the interior wedge and insert it into one end lined up with the bend line. Place tape on the mating wedge on top of the trim tab also lined up. Place the sandwich on the end of the bench and clamp it down. Place a block against the end so the two wedges can't slide apart and clamp it to the bench. The top wedge will try to slide downhill. The inside one may also try to slide out. Use a block to keep it from moving too. Now just use a block and hammer to bend the tiny tabs against the wedge. Finish the bend with the mushroom set on the gun with a piece of tape to keep from scratching. Sounds more difficult than it is.
 
For the trim tab you really don't need the hinged press (or for the rudder and elevators actually). I just put a 1/4" diameter wooden dowel inside and squeezed the tab between a piece of wood and a flat bench top with some c-clamps. You will squeeze it flat (with the TE radius) to get the proper angle with spring-back (and flat skins). Use the trim tab spar to check the bend.

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1) ditch the metal rod.
2) don't worry about a "cracking" sound - you won't hear one and you won't crack the sheet.

Bend a little at a time until it's where you want it. You'll be fine.
 
It looks like I need to find a smaller the rod. Maybe ditch it, but still most builders that I know of have had cracks when they didn't use one... I am stunned by the pictures where it is bend flat on the table... I continue to learn... will have another attempt when I am home.
 
Hi,

I think that I'm nearly at the point that I can stop bending, but I notice that especially the middle section of the skin remains more open then the sides. I always used a rod of 3 mm (0.118 inches). The hinged press was nearly completely closed.

In an attempt to get the middle section correct, I tried to bend it by pushing on both sides by hand without the rod.

When I put a ruler on the skin, I notice that it is still ballooning in the middle. But as the press was closed, it is difficult to judge what should be done next to get the ballooning out of the skin.

trim2-1.jpg


trim2-2.jpg


trim2-3.jpg
 
You've gotten to the hard part. Folding the ends can be a problem. Make sure the wedges Yor make / use will make the bend and not result in a bend inbound. Don't ask how I know. Just had to order a new trim pice.
 
Bending

Take the rod out and squeeze it. You want to creep on it till the edges touch the forward spar at rest. Take your time. Squeeze, check, lather, rinse, repeat, drink beer.
 
wirejock said:
Take the rod out and squeeze it. You want to creep on it till the edges touch the forward spar at rest. Take your time. Squeeze, check, lather, rinse, repeat, drink beer.
Click to expand...

So basically the skin should be closed so that the spar just fit in without any cleos?
 
Squeezing

Yes, it's mentioned in the manual when squeezing the elevators and ailerons. If it's not squeezed enough, the skin will bulge because it's trying to spring back. Squeeze too much and it goes inward. Creep up on it. Skin should barely touch the spar flange.
 
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wirejock said:
Yes, it's mentioned in the manual when squeezing the elevators and ailerons. If it's not squeezed enough, the skin will bulge because it's trying to spring back. Squeeze too much and it goes inward. Creep up on it. Skin should barely touch the spar flange.
Click to expand...

Yes, but I think that this is the point where the trouble starts. When your bend is getting nearly fully closed, it tends to close (and crack). That is the reason that I am not keen to remove the rod. But I guess I have to do it anyway... maybe with a smaller rod?

Note: The reason that I am not really keen to do so is because this skin may be very light but when they have to send me a replacement part it will be costly on the shipping. I once asked for a replacement of a skin and it was over 300$ shipping only, while the skin was not a fraction of that amount.

Thanks!
 
Squeezing

Wim
I might consider calling it good at those shipping costs.

Other ideas...
Smaller dowell rod.
A bead of proseal along the trailing edge. Let it cure good then squeeze.
YMMV
 
This is how I done mine once clamped I knocked the ends up with a rubber mallet then a hard block to tighten the bend! It worked out perfect.

Gibbo



20121016_164747.jpg
 
The Van's method was too complicated for my simple brain, and left too much room for error with bits of wood slipping around all over the place etc.
I used two peices of 80mm x 200mm x 8mm thick steel with 1 bolt at the outside as a clamp, and a conventional clamp inside the skin. Overkill maybe, but zero slip while bending, and nice clean bends.

Good luck - not that you will need it!

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photo3-2_zpsbef770c1.jpg.html
 
I am almost over the first milestone... I think :eek: Should I really have it flat straight all over? The manual seems to advice to use two wooden blocks and compress it with a pliers. Tips and tricks?

trim3-1.jpg
 
Wim,

This is definitely one of the areas that is potentially frustrating. I'm a bit OCD, but I did one side 3 times, the other twice until I was happy:eek:. Bending the ends gave me fits. I used scrap wood and painters tape initially; results were ok, but I decided to try again using a hard wood wedge and carpet tape as called for in the plans - that was actually worse!! I finally bent the ends around my back rivet plate held in my table vice - worked nicely. Like Riley said, keep going. Just snapped a similar pic for comparison:
ab9b62e1973f83d88ad57bd0c4b6e047.jpg


I did the starting bend with the brake as Van's suggests in the plans, but I wasn't happy with using the brake. I actually fine tuned the bend using seaming pliers - bending little by little down the length of the tab.

My pile of shame filled with trim tabs!
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60av8tor said:
Wim,

This is definitely one of the areas that is potentially frustrating. I'm a bit OCD, but I did one side 3 times, the other twice until I was happy:eek:. Bending the ends gave me fits. I used scrap wood and painters tape initially; results were ok, but I decided to try again using a hard wood wedge and carpet tape as called for in the plans - that was actually worse!! I finally bent the ends around my back rivet plate held in my table vice - worked nicely. Like Riley said, keep going. Just snapped a similar pic for comparison:
ab9b62e1973f83d88ad57bd0c4b6e047.jpg


I did the starting bend with the brake as Van's suggests in the plans, but I wasn't happy with using the brake. I actually fine tuned the bend using seaming pliers - bending little by little down the length of the tab.

My pile of shame filled with trim tabs!
0c17f9296f556dfaa475b61c1474c16c.jpg
Click to expand...

Hi Jon,

So basically you suggest to stop bending with the brake and switch over to the method VAN's explaining with the pliers? I guess it is 'just' putting the edge in between the blocks and compress it with the pliers. Or did I get it wrong?

LifeofReiley, the rod is already ditched...

Thanks
 
WVM said:
Hi Jon,

So basically you suggest to stop bending with the brake and switch over to the method VAN's explaining with the pliers? I guess it is 'just' putting the edge in between the blocks and compress it with the pliers. Or did I get it wrong?

LifeofReiley, the rod is already ditched...

Thanks
Click to expand...

I didn't use the blocks - only the pliers. I went very slowly - bending just a bit at a time - down the length of the tab. I judged the amount of the bend by sight and, as Wirejock said, by inserting the spar in the skin. You know you have it about right when the skin lays on the spar flanges without any compression.
 
Hi,

I think that I have the intended bend now. This is what I did to correct it.

Used a 0.125 inch dowel in the hinged press to bend the skin so both sides touch each other in the corners. Calm and always monitor the dowel and the skin. Do not bend all at once, but release pressure and continue.

Then I checked with a ruler to check the result like explained with the pictures on the last page of the empennage instruction manual.

To correct the under bended area I took the skin in one hand and squeezed it between my fingers so the both sides touched each other.
trim5-2.jpg


Finally I put pressure on my fingers as close to the bend as possible with the other hand. When I feel that the tension is off when I release my fingers, then bend should be OK.

trim5-1.jpg


The final result.

trim5-3.jpg


What do you think? Enough of do I need to correct it more? When I now put the spar in, the upper skin is just above the spar without any pressure.
 
About the trim bend on the sides... The molds that are used to lock the skin in place, are they having a straight/sharp edge? The results of most trim tabs seems to have some larger radius. I was wondering that maybe beveling the side of the mold may be a good idea to prevent it from breaking?
 
Trim tab

It looks good. The test is to cleko in the spar and lay a straight edge on it.
On the tab bending blocks, mine were sharp edge sanded smooth. The plans may have a bend radius listed. You could radius the edge to the dimension but I would shoot for a tighter radius than the target or you will end up with a bigger radius than you want.
One other posted using the back riveting plate. Pretty good idea. Try it with some scrap first.
 
nzrv8 said:
The Van's method was too complicated for my simple brain, and left too much room for error with bits of wood slipping around all over the place etc.
I used two peices of 80mm x 200mm x 8mm thick steel with 1 bolt at the outside as a clamp, and a conventional clamp inside the skin. Overkill maybe, but zero slip while bending, and nice clean bends.

Good luck - not that you will need it!

photo2-4_zps64eb0731.jpg.html


photo3-2_zpsbef770c1.jpg.html
Click to expand...

I learned by experience that it is an understatement what you told about the wood slipping around... Luckily I tried it with some scrap material.

I was planning to try your suggestion, but noticed that I have to bend the skin open to get the back rivet plate in. Did you do it before you did the final bend? I think it is best to avoid to open and close the skin too much because that's the point where I expect the trouble...
 
About two weeks ago I finally finished the trim. I used double sided tape to keep the wood in place. I pain to remove after completing the bend, but finally I noticed that ACETONE removed the glue very well.

I thought it would be nice to share the result. I am so happy that this is all over. This week I will prime all parts and put them together. Case closed. Thanks all for your help!

trim-bend.jpg

trim-final1.jpg

trim-final2.jpg
 
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