Aluminum Fuselage Formers

[alaskabearhawk]

FWIW: http://www.mykitlog.com/users/displa...=217910&row=92

[svyolo]

Donna asked about my unsatisfactory method.

The bottom formers were no problem. When I installed my side formers I did not try starting at the tail like Jim Parker. I was not aware of Mark G's method for bending the formers. Instead I started from the front and worked my way back.

The unmodified formers placed a significant amount of stress on one of the fuselage tubes when I fit into place. By fit, I mean I applied pressure to the stringer to force it into its "clip" and make a nice bend to form the fuselage contour. When I placed pressure on the former, the stringer (Which is really tough material...way stronger than needed...a mark of good quality) would spring into position, but not yield. It did not bend, and this put pressure on the fuselage tubing. I was not comfortable with this at one particular point. Stresses were just too high.

My fix was to remove some material from the former and bend the tubing by using a method I show in photos below. I got the former bent and fit into the clips nicely so I thought. But the shape that resulted from my method did not result in a nice rounded appearance. At every point where I 'shaped' (by drilling a stop hole, cutting into the inside edge of the former, and slightly bending the former at the place where I cut it.) the tubing it resulted in a bend, followed by a straight section of the former. So looking at it from the rear, I got a squarish look rather than a nice rounded shape that it should be. It just looked goofy, and I wasn't going to let it go.

So, I got some replacement stringers from Mark G. (Thanks to scratch Patrol builder Ed Welfred from my neck of the woods for transporting them) and will do them over.

TAKE AWAY for those quick build kit owners just starting: If have some doubt about a task, e-mail Mark G. instead of trying to figure it out on your own. Don't guess, and don't experiment at least until you have found out how Mark does it. I did not do that. I guessed.


You can see the squarish look in the stringer in this photo to the left of the top of the Cleco.
IMG_3256.jpg

jpeg Screen Shot 2018-04-20 at 2.52.47 PM.jpg

I am using spruce for my stringers and they fit the same as the pictures from Brooks. The upper side stringer takes a hard turn inboard at the tail end. No problem for the stringer, but how does the fabric lay? Will it go back naturally to the tailpost, separating from the stringer, or should it be stitched to the stringer and tubing in the tail to keep the fabric against them?

[Archer39J]

Right on, appreciate it Mark!

[Mark Goldberg]

The aluminum for the formers is 5052H32 - also called the "marine" aluminum. So no primer is required. The door sill is 6061T6 (harder) which is also very corrosion resistant. Mark

[Archer39J]

Another question, are people finishing the aluminum formers? I'm not seeing any easy moisture traps, and they mostly get covered in areas they're exposed, so I'm inclined to leave them bare.

[PaulSA]

I used driven rivets in some places but found that there were a lot of places where it was either difficult to get a bucking bar on the back or that things like fuel pipes get in the way. In those places I used pulled C/S rivets.

The tabs are steel and the formers are aluminium so whatever rivets you use, you can't avoid some sort of dissimilar materials. I have primed the aluminium and smeared an anti-corrosive sealant on all the tabs where I have riveted AL to steel.

[Mark Goldberg]

The round heads of SS pops do not protrude so much that they are a problem or are ugly. At least for me. Mark

[svyolo]

Steel or SS fasteners in Aluminum is fine. The other way, not so much

[Archer39J]

I countersunk the formers - problem solved.......

As for the corrosion worries, there are all sorts of places in the aircraft where materials are mixed. Provided there is no moisture, then there won't be corrosion

Countersunk and used csk pop rivets? If I'm doing that I might as well just use solid rivets, which was the plan originally.

For corrosion, yeah that's right, but since I'm at it why not go ahead and use materials that aren't galvanically reactive?

[PaulSA]

I countersunk the formers - problem solved.......

As for the corrosion worries, there are all sorts of places in the aircraft where materials are mixed. Provided there is no moisture, then there won't be corrosion

[Archer39J]

Ok, unfortunately I'm still kind of confused about this so please bear with me. If I attach the aluminum fuselage formers (I'm not talking about the stringers) with protruding head stainless pop rivets, how then am I supposed to lay a scuff shield over the formers that make up the door sills? Won't the protruding heads look odd and possibly interfere with the cargo doors as well? If anyone can shoot a pic of what they've done I would really appreciate it.

I'm also wondering why stainless since it will possibly corrode both the aluminum and steel parts that it's securing? Where did Bob spec these?

[Flygirl1]

That's exactly how we made the top former bend for the removed skylight. I also have a couple of spots where removal of inside former material was necessary for a fuel line to pass through. As I stated before, doesn't seem to be a problem, as of 215 hours anyway.

[Bcone1381]

Donna asked about my unsatisfactory method.

The bottom formers were no problem. When I installed my side formers I did not try starting at the tail like Jim Parker. I was not aware of Mark G's method for bending the formers. Instead I started from the front and worked my way back.

The unmodified formers placed a significant amount of stress on one of the fuselage tubes when I fit into place. By fit, I mean I applied pressure to the stringer to force it into its "clip" and make a nice bend to form the fuselage contour. When I placed pressure on the former, the stringer (Which is really tough material...way stronger than needed...a mark of good quality) would spring into position, but not yield. It did not bend, and this put pressure on the fuselage tubing. I was not comfortable with this at one particular point. Stresses were just too high.

My fix was to remove some material from the former and bend the tubing by using a method I show in photos below. I got the former bent and fit into the clips nicely so I thought. But the shape that resulted from my method did not result in a nice rounded appearance. At every point where I 'shaped' (by drilling a stop hole, cutting into the inside edge of the former, and slightly bending the former at the place where I cut it.) the tubing it resulted in a bend, followed by a straight section of the former. So looking at it from the rear, I got a squarish look rather than a nice rounded shape that it should be. It just looked goofy, and I wasn't going to let it go.

So, I got some replacement stringers from Mark G. (Thanks to scratch Patrol builder Ed Welfred from my neck of the woods for transporting them) and will do them over.

TAKE AWAY for those quick build kit owners just starting: If have some doubt about a task, e-mail Mark G. instead of trying to figure it out on your own. Don't guess, and don't experiment at least until you have found out how Mark does it. I did not do that. I guessed.


You can see the squarish look in the stringer in this photo to the left of the top of the Cleco.
IMG_3256.jpg

jpeg Screen Shot 2018-04-20 at 2.52.47 PM.jpg

[Archer39J]

That is what I did too. Is taking that stress out of the stringers by pre bending important?

I'm planning to. But I've not heard of it being an issue for our stringers, others may have more to say. Just better to not pre-stress components if you can avoid it, especially aluminum.

[SimonNicholson]

Don't know about the other folks, but I found that by starting at the tail, it was pretty easy to just fit the stringers into the U-shaped brackets, and clamp in place with C-clamps. The stringers bent pretty naturally to a nice, smooth curved shape. Then I drilled, de-burred, and riveted with stainless steel pull rivets, as Mark recommended.

That is what I did too. Is taking that stress out of the stringers by pre bending important?