Finally starting

[brady.blake55]

I accidentally posted in the QB group. Here is the post anyways.

Hey everyone. I’ve been researching, some might say obsessing, over all things Bearhawk for 10 years. I finally have the money, and the wife’s approval, to build. I called Bob this week and talked for a little bit. My wife said I was like a fan girl. I can neither confirm, nor deny that accusation.

Anyways, I’ve had an idea rattling around for a couple years. I’ve watched nearly every Bearhawk build video on YouTube. One that stuck out was N3UW’s hydro forming video using rubber. I wanted to ask y’all about another option for forming. Do y’all think it would work to press a cavity forming block over a normal block to sandwich the rib between? In my mind I could form ribs quickly and even put the crimps in the block. I’d cut the blocks with my CNC machine, so they would be accurate(ish). Im new to CNC stuff and CAD designing.

[U2fletch]

Pictures of your CNC machine please! I’ve used Fusion360 for many years and designing parts and jigs for 3d printing is very rewarding. Add the CNC machine to the mix and possibilities become endless. I recently had to cut to size a 10’ long 3” square steel down tube for industrial BigAssFan and it needed a certain hole pattern in the end. Started laying out the holes and marking with layout fluid on the tube to drill, and realized I don’t have a 14mm drill. 12mm was big as I had. So clamped the tube in the jaws of my mill table vice, did some edge finding to set the DRO, then wrote a quick code snippet to make a 14mm hole with 3/8” endmill. Problem solved.

[brady.blake55]

My CNC isn’t anything to write home about. It’s about $1,000 new. I’m going to get the expansion to do 4ft sheets. It should help with repetitive parts and also keep them uniformed.

https://www.amazon.com/gp/aw/d/B08L6314MW?psc=1&ref=ppx_pop_mob_b_asin_title

[TrueAirSpeed]

That aircraft in your picture looks familiar to me. Flew one out of Kandahar 2004 to 2005.

[SpruceForest]

General Comment: Love to see another builder commit to doing it all... good luck and enjoy the process!


Issues re: your proposed striking dies:

- Negative clearance angles on the die set with flutes and the flange over-bend to handle spring-back of around 12 degrees with grain of the sheet ideally situated

- You'd need closer to 50 to 100 tons to get enough pressure to form the flutes without some sort of secondary operation... one of the reasons why rubber press operations work in this use case (making the process doable without $25K worth of press)

- Multiple die sets needed with main and tip ribs... unless you have a press that can handle something as long as those components. 20 ton will press out a 10" x 10" area (12" x 12" x 3/4" steel platens and 12" x 12" urethane rubber/stall mat stack) to around 70 degree flange angle... to do the center ribs in one shot is at least a 50 ton press with a pretty beefy containment box to get the most out of that tonnage (we get a lot of efficiency/wasted force losses in an unconstrained press operation)... tip ribs would run closer to 100 ton.

- Flutes need to be micro-tuned to get a straight/true rib... there is a LOT of post-press tuning, as even factory replacement ribs for Piper/Cessna, etc. need tweaking and lots of clean-up before use


Discussion:

- The 20 ton rubber press method is doable because the tech is small-shop doable and can produce a much better component than the Piper and Cessna factories are shipping (ask Bob - he's got one of my nose ribs in his shop... not an easy guy to impress). Even long ribs may be formed with multiple/ consecutive presses working from one end to the other

- I would use your CNC to produce the forming blocks in MDF... harden with BSI Thin CA (mask up) and you have a budget version of phenolic tooling that will do a half dozen or more rib sets (mine is currently doing airplane #3 over in Michigan), and MDF is way cheaper than 1" phenolic stock

- Worth searching for my summary doc on press forming as well as the doc on doing the aileron, flap, etc. nose ribs referenced in my stuff... adds some additional info on press operations, etc.

Again - good luck!

Re: the photo: we used to call those 'realistic sling load training blocks' when I was driving the 'essential bus'.

[brady.blake55]

TrueAirSpeed I did enjoy my time on 64’s. I was an armament guy in the 211th, which I assume you were in based on some of your post history.

SpruceForest I’m not going to pretend to understand all the science behind that response. What I do understand is, my idea would not be viable. Thank you for the very detailed response! I can put that idea to rest and stop coming up with “short cuts.”

[Frank]

Great to have another scratch builder! Too bad with the new factory owner that hybrid builds are out the window. Regarding rib forming, notice in the Bearhawk LSA Book that Bob suggests the crude but effective methods. That's pretty much the route I took. Whatever method you use, make sure to debur and smooth the edges before forming. Especially before pressing the lightening hole flanges. You're gonna have a blast!

[geraldmorrissey]

Buy the ribs and the spar channels. Build everything else.

[sjt]

I also used the method N3UW. But the absolute limit of its utility is the forming of the chamfered lightening holes.

The flange is best made with a rubber mallet.

hammer2.jpg

I did find a press to be useful for holding things down so I could smack them better.
hammer3.jpg

If I had to do the lightening holes again I would do the method in Eric Newton's manual.



In almost all cases the simplest fastest and cheapest method are all the same.

My 20 ton press is the exception to simple tools. And I can only justify it so that I can also repair honda wheel bearings.


The first part of the project is MDF forms lots of them. To that end you need a jig saw.
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and a nice router table.

ab.jpg ac.jpg af.jpg ag.jpg


The other tool that is useful is a drill press.
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Forget about fancy ways of cutting aluminum sheets, just get a hand shear from an estate sale.


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The following is a luxury item:
ah.jpg Blow all of the aluminum chips and mdf dust out into the neighbors yard.

[davzLSA]

Hi Gerald as far as I know and talking to Bob the new owner of bearhawk Virgil is not selling parts. Bob did say that the manufacturer of the rib kits that Mark used to sell are made by the same company that makes RV ribs. I bought my rib and spar set before Mark sold the company. It knocked a huge chunk of time off the wing build. Also with my one piece cap strip Im thinking that will also eliminate a bunch of build time. I am considering to start making parts for the LSA. I havent decided yet, I need to look into the feasibility of it. If I could make the venture pay for its self I would do it.

[SpruceForest]

Lightening holes were super-easy with the press... set the angle and the chamfer width per the attached and press the trigger on the air-over hydraulic bottle jack. Easy-peasy.

Forming Wing Ribs V2.pdf

On .025, the ribs can be pressed out with lightening hole flange to design angles and the rib flanges at about 70 degrees. On .032 stuff, the flanges needed some additional help to get them to the point where a shop-made Vans flange tool can be used to finish them to 90 degrees... the rivet gun flow-forming technique and some dead blow hammer mojo as described by SJT worked well. Fluting removed the potato chipping, with my Delrin Bob sticks used just for final tuning. There are 160 ribs in the Patrol, so the temptation to go to more manual methods (tin snips and Bob stick) was something I managed to resist.

I did the wing ribs first as it was a series of smaller tasks early in the project when the spars looked a bit more intimidating (they were far easier than ribs!). If joggling, mill that stuff into your rib forms... and test fit ribs against your spars to fine-tune the molds before production.

I loved the actual rib forming part of the project after hating the MDF dust-production portion... life is filled with love-hates, eh? Easy to love a process that generates a final product that is so much better than what you see out of Cessna, Piper, or Beech.

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