Bending Stiffeners and Attach Angles

[Chris In Milwaukee]

I performed some experiments this morning in my A&P's shop with the wing angles. I found that I *really* like the press brake. Very repeatable, and the bend works from the center, not the edge. When finished, the width of the angle from the flat edge to the outside of the bend is pretty much right on (1/2" in this case).

I tried various pressing points to see where the bend ended up, and was quite predictable. A few examples below:



After I shear them all, I'll bring them back to the shop here at home to bend them. You can see here that the press brake needs a depth adjustment

The spars on the other hand... Practice many, bend once...


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[Bcone1381]

Chris,

Two possible Common Errors that I found bending my spars are to either bend that angle too much or not far enough. I tried to measure the angle that I was moving the bending leaf with a level app on my iPhone...it did not produce reliable results. If you have a Wixey (Digital Protractor) that might help.

I did not have one, but here is what worked well for me. Regarding the flange angle, I recommend erring on the side of "not quite there yet" I did not bend my flap spars past 90 degrees on the bending break.

You have a little contraption at home that you made and used to fine tunes the 90 angle that you are looking for on your ribs (a photo is in this thread, post #3, 5th photo down from the top. http://bearhawkforums.com/forum/bear...-fluting-party )

Well, if you need to fine tune those Spar angles after your done using the big bending brake, trust me, that little guy works real good. I just re-made the base of mine to fit the angle I desired and stomped away 1.5 inches at at time. I now have an exact fit.

But, If you bend the angle too far using the big break, it takes a lot of force to reduce that angle. Ask me how I know. I learned a lot about the force it takes to bend these angles while raising that bending leaf. If you think of this while forming yours, you will understand.

Brooks Cone
Chelsea, MI
Scratch Building Patrol #303

[Chris In Milwaukee]

Thanks for that tip! I'll keep that in mind as we do this. I'm absolutely terrified of screwing these up, so I'll be sure to do a lot of tests first.

[Chris In Milwaukee]

And the .025" stuff is traced out. All packed up and ready for a day of cutting and bending tomorrow! May also sneak in some time at the EAA Museum to see the nose art exhibit from CAF.




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[Glenn Patterson]

We sheared the metal then stacked and gang drilled the pieces for the rib stiffeners and the rib side of the attach angles. We then rounded the corners and bent the angles. We tacked wood strips on a board to keep the stacks together for drilling & did about 8 - 10 at a time. We primed the angles ready for mounting. That way as soon as the stiffener is put against the rib there is a drill template. The hole pattern does not need to be laid out for individual stiffeners as they are placed so it can speed up installing the stiffeners. After the rib attach angles are located on the spars then the ribs mate up & the holes are predrilled on the rib leg are the template to attach the ribs. No measuring and it is easy to drill with the bit guided by predrilled parts.
Glenn
BH727

[Chris In Milwaukee]

Great idea. The one thing I considered before bending is if I should drill them or not. I ended up bending them, and I'm drilling them now, one rib at a time.

I wondered if drilling first, then bending, would result in stretched/elongated holes. Did you experience that, or was it not noticeable enough to worry about ti?

[Glenn Patterson]

We had no issues with the holes. Everything went together tight. The stiffeners go on the ribs really quick as they are install ready. If a person was concerned with the holes they could use a smaller drill bit and use the predrilled as a pilot hole. It makes it easy to attach the ribs as it is hard to get the drill in so the long aircraft drill bit is distorted to drill in square parallel to the spar. The hole keeps the drill bit from skidding around so it goes through the second layer quick & clean. Drilling holes in stiffeners are a mundane & repetitious task that I was not looking forward to. That is when I thought just gang drill them before folding. Each set is cut to length so we just kept adjusting the drill jig to accommodate the length. The ribs were primed and the stiffeners primed so it was drill, clecoe, debur, rivet & done. The plane pieces come on an off so many times during processes that eliminating process save time.

We did a lot of unique things to try to speed things up like gang drilling the cap strips on the table the table then mount them & do the final drilling. I did not have access to a lathe so I developed the process to make all the tool & die with a router. Once I had the concept all the tool & die was done in a couple days. I do my best to simplify things and get the best result that I can. We tried every different method to do the stiffeners for the fuel tank bay skins and failed miserably. I put two wood wing templates together to form the stiffeners accurately & then use the wood templates in the fuel bays to be the missing ribs during skinning. I try to keep the tooling simple & effective.

We modified our skinning drilling process from the normal along the way. The wings were in the stands when they were inspected and the inspector was bent over looking through the end of the wings for a long time & I was getting nervous. I said we built the wings straight & he said that was the thing that he was looking at. All the jig pin holes look like one hole through the wing ribs & all the rivets are dead center of the ribs in perfect rows. He finally said that there were no issues with our work & if he took out a magnifying glass that he might find a rivet to comment on but nothing that would have to change. The inspector was extremely impressed and asked if he could direct other builders our way if they needed guidance. I was invited to Winnipeg to do a presentation on building the wings from scratch for the RAA home builder association at Lyncrest.

Back to my point is that a builder should take every step to conserve time where possible without sacrificing quality. Some builders go to some length to do things that the side processes consume too much time to make the pieces being brought into the build. Think of the work as what you would pay for. For example drilling ribs one by one or gang drilling. The gang drilling would be the least cost per pc.. The mass production approach is a better time economy. Building an airplane from scratch is a massive undertaking and a persons perspective on life and things change a lot during the process so shorten as best as possible so it has the highest possibility of being completed.


Back to my point that a builder should look at his time like it is gold and a perspective of what would you pay someone to do. Gang drill all the parts or drill them one by one. It is a matter of economics be it time or money. A scratch built takes too long & a builder should take every opportunity to remove time from the process & maintain quality.
Good luck with your build.
Glenn
BH727

[Bcone1381]

I nominate Glenn to be the author of "The Bearhawk Scratch Builder's Best Practices Manual". I suspect we spend too much time accidentally discovering, or reinventing or not ever discovering the best way of doing things.

[marcusofcotton]

We modified our skinning drilling process from the normal along the way.

Lots of great input Glenn! Would be interested in learning more of this modified process when you have a chance.
Thanks!!!