Rib cuts

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youngd24
Posts: 2
Joined: Tue Oct 02, 2018 3:19 pm

Rib cuts

Post by youngd24 » Sat Jul 13, 2019 7:01 pm

New member here, first time plane build as well.

As I started cutting and assembling the first few wing ribs my decades of woodworking kicked in. What have others done to be able to gang cut multiple parts? I recorded all of the angles for the various parts and was considering making something so I could cut 4-6 pieces are a time.

Prototype master pictured, that’s what I recorded all the angles from. Any ideas would be most appreciated.
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Terry Hand
Posts: 58
Joined: Thu May 18, 2017 2:37 pm

Re: Rib cuts

Post by Terry Hand » Sun Jul 14, 2019 9:10 am

This does not really answer your question, but since no one has yet answered, I thought that I would put my $.02 worth in. I am quoting below from Tony Bingelis, the late author of numerous books on aircraft construction.

"There are two schools of thought about fitting the diagonals. One believes the ends should be beveled, or mitered, to fit tightly against the cap strip and the adjacent upright or diagonal. The other believes the ends can simply be cut square with the corners butted against the cap strip and adjacent upright or diagonal. Take your choice. In my opinion, the method used doesn’t matter. A well glued and gussetted wing rib joint is virtually indestructible. Try to break one apart and see for yourself."

Also, I am enclosing some pictures of steel bridges and their gusset/diagonal construction -
Screen Shot 2019-07-14 at 9.51.44 AM.png
Screen Shot 2019-07-14 at 9.50.05 AM.png
The strength of the joint is not in how perfect your joint is between diagonals. Rather it is the quality of the gusset and gluing. So the reality is this. If you are looking for a fast way to cut ribs, cut them all at 90º angles, as the strength of the joint is in the gusset to diagonal attachment, not the diagonal to diagonal attachment.

Here is a link to the article from which I quoted -

https://www.eaa.org/en/eaa/aircraft-bui ... -wing-ribs
Semper Fi,

Terry Hand
Athens GA

cantdrawatall
Posts: 6
Joined: Thu May 10, 2018 8:43 pm

Re: Rib cuts

Post by cantdrawatall » Sun Jul 14, 2019 10:21 am

The advantage of the bevel cuts in the rib in my opinion would be the solid placement of the bracing stock, ensuring that the ends are consistently positioned for each rib. Simply having the stock squared off would leave a little wiggle rood at the ends. I imagine a well setup Jig would also allow to consistent placement but why not enjoy a belt and suspenders viewpoint for a little extra time in building?

tom kreiner
Posts: 35
Joined: Sat Feb 25, 2017 9:49 am

Re: Rib cuts

Post by tom kreiner » Sun Jul 14, 2019 12:58 pm

This can be reduced to a pretty simple example…

Take the case of two strips at right angles., so that they form a TEE. Send all of the surfaces and prepare them perfectly and then glue them with the finest glue you can you can identify. Now imagine that the stress is on that joint are such that the leg of the tea is being bent away from the crossbar. With 1/2 x 1/4 ribs stock which is what we have in our ribs, you have 1/8 of a square inch of area bonding the two pieces together.

Now imagine the same joint with a gap between the crossbar in the leg of the Tee. This joint, in contrast, has a gusset plate on both sides. The area of a double gusseted joint with dimensions of 1 in. x 3/4 in. ( with 1/4 in. gap) will be six times the area of the original simple T joint described above.

Tightly fitting your truss pieces within the airfoil of the wing will be hidden from view because they’ll be covered by gussets. So why waste the time and effort to produce a joint which only wastes time?

tom kreiner
Posts: 35
Joined: Sat Feb 25, 2017 9:49 am

Re: Rib cuts

Post by tom kreiner » Sun Jul 14, 2019 1:06 pm

This can be reduced to a pretty simple example…

Take the case of two strips at right angles, so that they form a Tee. Sand all of the surfaces and prepare them perfectly and then glue them with the finest glue you can you can identify. Now imagine that the stresses on that joint are such that the leg of the Tee is being bent away from the crossbar. With 1/2 x 1/4 ribs stock which is what we have in our ribs, you have 1/8 sq. In. of area bonding the two pieces together.

Now imagine the same joint with a 1/4 in. gap between the crossbar in the leg of the Tee. This joint, in contrast, has a gusset plate on both sides. The area of this double gusseted joint with gusset dimensions 1 in. x 3/4 in. will be six times the area of the original simple T joint described above.

Think about this; tightly fitting your truss pieces within the capstrips will hide the joints from view because they’ll be covered by gussets. So why waste the time and effort to produce a joint which only wastes time?

Lorenzo
Posts: 6
Joined: Wed Feb 22, 2017 8:59 pm
Location: Tellico Plains, TN

Re: Rib cuts

Post by Lorenzo » Sun Jul 14, 2019 1:20 pm

I did not 'gang cut multiple parts.' I cut hundreds of gussets with a hole saw. I steam bent the cambered cap strip lengths and set them aside. Then, during assembly, I cut each gusset to the shape I needed with shears. I cut each set of parts for each rib as I was putting it together. I cut each straight cap strip piece to length on a benchtop band saw. Then a light touch of each end on a 12" disc sander to get a precise fit in my jig. I made sure that each end was solidly against its crosspiece. Terry Hand is correct that the strength of the joint is carried in the gusset - but there is an element of fine craftsmanship here too. Maybe 5-10 minutes to fit parts for each rib. You need to leave the T-88 setting up overnight anyway. Mixing and spreading the glue takes longer than fitting individual parts. This was actually the most enjoyable part of the process.
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EAB4
Posts: 61
Joined: Mon Mar 06, 2017 2:08 pm

Re: Rib cuts

Post by EAB4 » Sun Jul 14, 2019 9:26 pm

I made all my parts first, then started gluing up in the jig.
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ArthurD
Posts: 19
Joined: Tue Jun 26, 2018 2:00 pm

Re: Rib cuts

Post by ArthurD » Mon Jul 15, 2019 11:28 am

I did mine a little differently. I made use of a CNC router to cut out the gussets, the forms for steaming and the glue-up jig. I rough cut all the cap strip pieces to length and then basically started an assembly line. I steamed the long cap strips and clamped them in the form for 24 hours, then I take them out, clamp them in the glue up jig and just start fitting up the shorter pieces. Fitting up the short pieces is probably the most time consuming part, I got it down to about a 30 minute process. The first set were used to mark the miters on all the other pieces so I could get them all roughly mitered then when I go to fit them up I use a disc sander to fine tune all the miters. The best way I found is to work from one end to the other and get them to fit up to the long pieces before sanding them to fit with each other. I glue these together without putting the gussets on, fortunately t-88 tolerates small gaps although it does tend to drain from the joint if there are any gaps so I did add some milled glass fiber and silica thickener. After 24 hours these are strong enough to come out of the jig and be sanded. They need to be sanded since the glue won't allow the gussets to sit flat. I didn't use any nails on the gussets just put glue on the cap strip sides and slapped them on. Sanded them to 240 grit and they're done.
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