Ribs forming blocks

[TiagoNR]

Hello there, I'm planning to scratch build a -6, I'm currently drawing all the plans in CAD to make sure that I understood them before start cutting any metal

The builder manual says about forming the wing ribs but I can't find some details and measurements like flanges length, radius and depth, if someone can give-me some help I'll be very thankfull

I'm also searching for olds threads of someone who plans built a RV6 (or a -3, -4 for reference) any informations is welcome, thanks

 

[Marc Bourget]

The ribs, themselves, should be made from form blocks. The holes, flanges and beading are best by secondary operations.

You'll need two form blocks, R & L for the overall form.
Suggest a 7 deg. (R&L) relief angle to allow for spring back.

Radius depends on material and temper of the alloy used for ribs.

Use a solder bar to "slap down" the flanges (actually will shrink the flange material to conform to form block).

Is the "T" shaped bead shown in the nose area of your dwg included in the plans? Highly curved, fasteners close, do you need the additional stiffness there? Might induce warping - adding difficulty to assembly/riveting.

 

[fixnflyguy]

A few more things to understand

Hello, welcome to a looong road! I scratch built some of my RV-4, and I also work my career day job in heavy aircraft and GA/EXP aircraft repair and modification. I have 43 years of aircraft metal fabrication in my pocket. Because your post is fairly vague, I don't know how deep your knowledge is, and I don't need to preach what you may already know. Formed 2024 aluminum fabrication is relatively simple to those of us who have done it, but a lot is left unknown if your simply reading the VANs plans. Cliff notes version: The ribs of an RVXX are formed from 2024-0 ALCLAD (annealed) sheet stock in a hydro press (mass production) or hand formed over a male form with plastic hammers/ rivet gun nylon sets, ect. if doing it at home. The final formed rib must then be heat treated in a controlled oven sequence to achieve the final 2024-T42 condition. The heat treat process is not a DIY at home process unless you have an controlled oven capable of over 900 degrees, and a suitable quench tank and the means to prevent excessive warp at quench. Even after that, a Rockwell hardness test or conductive density check to assure hardness uniformity needs done..do not attempt to form 2024-T3 (pre-heat treated) over the form blocks, as you will have problems and possibly induce cracking. Feel free to PM me if you'd like further information or tech data for heat treating.

 

[Marc Bourget]

Dittoes, I've formed ribs from 2024-O, as described by Fixnflyguy, for my current wing ribs. (I have an Accutherm HT Oven in my shop! )

You can fixture the 2024-O for the HT oven to reduce warp, and deal with the remainder with post-work or plan to spend more time in post work.

I've also used 6061, returning the material to "W" Temper, as needed.

I substituted slip-ring and die in place of Hydroforming. Something to consider if a suitable facility isn't convenient.

I went the 2024 route back in the 70's using an analog controlled HT oven. It was easy for the oven to "drift" out of the temp range, scrapping your parts. Easy-peasy with digital temp controllers.

Consider investigating whether 6061 can be used for the ribs as they are basically loaded in compression and the properties of 6061 are close to 2024 in that respect.

 

[TiagoNR]

I saw some videos on youtube of people forming ribs with T3, T4 sheets, it can be done, right? I think its more difficult

 

[rvbuilder2002]

I saw some videos on youtube of people forming ribs with T3, T4 sheets, it can be done, right? I think its more difficult

Yes
A good majority, may be all, of forming on RV kit. Parts is now done in the T3 condition.
It just has to be designed into the process.

 

[TiagoNR]

Yes
A good majority, may be all, of forming on RV kit. Parts is now done in the T3 condition.
It just has to be designed into the process.

Sorry english isn't my first language, I didn't catch what you meant with "It just has to be designed into the process.", you mean like the radius of the bend? I think if it's too tight it can crank on t3 or t4 condition right? What would be a ideal radius on this case?

 

[idubrov]

For what it worth, I formed one part from 2024-T3 for my RV-7 (a bulkhead).

I had some concerns about 2024-T3 cracking due to forming (and still do to be honest), but the process itself wasn't anything special. I used mallet and tried to form with as few hits as possible, kind of smearing the hits over the edge of the forming block. Then finished with light tapping with the mushroom set on a rivet gun.

Never formed anything else before, so I cannot compare to the 2024-O experience. Also, the part was a simple one -- like a rib, but without any internal "beads" or lightening holes. Just a flat part with some flanges.

I looked on the internet if I need to do anything special in regard of forming -T3 vs -O, but didn't find anything in particular. I used hardwood (red oak) for the forming block with the edges rounded a bit.

I did some destructive testing of scrapped parts. Basically, I bent the small / short tabs (flanges) back and forth to see how easy they are to break off, and compared that with the factory part. I did not find any significant difference.

Not sure what the scientific value of this "testing" was, but at least my tabs didn't break off when I sneezed at them. If anything, my tabs were a bit harder to break off compared to the factory part, probably, because of a slightly larger radius of the bend.

 

[rvbuilder2002]

Sorry english isn't my first language, I didn't catch what you meant with "It just has to be designed into the process.", you mean like the radius of the bend? I think if it's too tight it can crank on t3 or t4 condition right? What would be a ideal radius on this case?

Yes

There are minimum bend radii for different materials and different thicknesses.
As long as the correct bend radii is used, bending in T3 condition works just fine (just like bending T3 sheet material on a bending brake), though there is a lot more spring back that needs to be compensated for.

 

[Ralph Inkster]

& you get bend radius information & a lot more in reference books like these, I think they are available from EAA.ORG & other aviation book outlets.

 

[TiagoNR]

& you get bend radius information & a lot more in reference books like these, I think they are available from EAA.ORG & other aviation book outlets.

I'll take a look on those, thanks