How to form sharp the radius in fwd fuse side skins

[tims88]

I need everyone's tips on how to form the sharp radius at the aft end of the F-1069 side skins. I can't seem to get a nice round bend when it gets to the point of twisting the skin with the aft vice grip and hitting the roll construction angles with a rubber mallet (29-11 step 5). Based on what is shown in the picture I've attached of one of my attempts, I'd say I'm probably hitting the construction angles too hard with the mallet which is causing the indentation in the skin but anything less doesn't seem to do anything. Also in that picture the bending block has slid a little bit but I can fix that with more clamps

The third picture is what my best attempt so far looks like when it is attached to the fuselage.

[Auburntsts]

So the idea isn’t to bend the skin at the block like if you were using a bending brake. Rather the idea is to try and curl the free edge of the skin in on itself so you end up with a more gentle vs sharp radius. You have to massage into shape with multiple “curls” and not attempt a quick brake like bend. Kinda hard to describe

[Carl Froehlich]

Just finished this today - and it is a royal PITA.

Some tips:
- The hardest part is getting edge distance on the floor panel to F-1041 L&R. To do this first make sure your have enough twist in the F-1041. Next step is to cleco in the F-01050 floor boards. Mark with a sharpie the holes from the F-01050 floor boards to the F-1041 to verify adequate edge distance on the F-1041. If good, drill the common holes and cleco the floor boards to the F-1041. This is needed to fit the F-01069 sides skins so they do not pull the F-1041s out of position.
- it takes an extra set of hands to bend the F-01069 side skins. The crital part (as you found out) is the aft part of the bend. With your helper holding the twist in the skin use a hammer with some tape to carefully conform the aft portion of the bend. Be careful to not get carried away and start a crack.
- Don’t forget to slightly break the skin edge that butts up to the bottom skin.
- Cleco the skin in place. The skin will not conform to the F-1041 until you have a boatload or clecos in place.
- Only after all this are you ready to drill the 1/8” holes into the engine mount weldments.

I was please with the end product. The skin came around the fire and clecoed to the bottom rib, flush with the bottom skin.

Carl

[tims88]

Thanks for the responses guys.

Originally Posted by Carl Froehlich

With your helper holding the twist in the skin use a hammer with some tape to carefully conform the aft portion of the bend.

A few questions about this step:
How much of a twist were you holding in the skin before you started to use the hammer? Was the aft end twisted to about 90 degrees or farther?

How hard did you have to hit it with the hammer to finish forming the aft bend?

How did you know when you were finished forming the aft portion of the bend? Van's drawing shows the 60 degree angle that the twist should make at the front end of the skin but I'm not sure what the aft end should look like. My attempts have had quite a bit of spring back which leaves a fairly large gap between the skin and the bottom of the fuselage. Clecos are able to pull everything into place but I'm not sure how much force should be needed to pull the skin into placed when it's properly formed.