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I was reading and article which are sort of like basic directions for building the DA-2 and it talks about needing a bending brake with a .13 bending radius. For other thicker parts the hold down bar on the bending brake needs a different radius.

This is actually a pretty big deal it sounds like. First, a builder is going to need a bending brake. It does not say what size, but I would assume at least a 30" would be needed? Maybe larger?

How does the average guy like me get a bending brake and then get the correct curve or radius to the hold down bar? Some make it sound easy like, "oh, just take it to a local machine shop and have them radius it..."

That's more difficult than it sounds! What local machine shop? I'm having a difficult time finding one around here other than "Joe" working out of his garage advertising as a machine shop!

The other tool I would think is necessary is a shear to cut strips or sheets of aluminum. How large of a shear is needed?

If anyone here actually has a set of plans, do they provide any information on this?

As for other tools, I think we probably all have most of the other tools like a drill press, cordless drill, files, etc...

Needing the proper bending brake and a shear are what's currently scaring me away from buying plans.

Oh, that article is here: https://www.scribd.com/doc/27725481/Building-the-All-Metal-DAVIS-DA-2-AIRCRAFT

Thanks for the input.  I'll have to add this to the FAQ I am working on.

A shear is not really needed to build. It would make it much easier but not necessary at all. You could use hand shears to make the cuts in the lighter material and a jig saw for the larger material. Just need to make sure to clean up the edges after cutting to remove stress risers to prevent cracks down the road. You would need to cleanup the cuts with a shear also.

For a bending brake you don't need to cut a radius. As Leeon wrote in the document you linked to (I include this document retyped and cleaned up in the book and with the plans) you can bend a piece of material over the nose of the brake to provide the radius.

You may be able to get away with not buying brake. There are plans for homebuilt bending brakes available online (I need to find and post links).  These brake designs range from light and simple to heavy shop quality units.

If all else fails, Harold Davis, Leeon's son, has the equipment and is ready and willing to make parts for anyone that needs it.

Hope this helps some,

Bryan

justjohn has reacted to this post.
justjohn

http://www.cannedhamtrailers.com/pdfs/davesbrakeplans.pdf

Bryan,

what do you think of blind rivets vs driven rivets for either the DA 2 or DA 5?

 

cheers,

John

I was thinking about rivets too. There are lots of homebuilts that have faster cruising speeds than the DA-2 that use blind rivets. I don't see any reason why blind rivets can not be used on the DA-2, and that is probably what I will use on mine. One thing that my need changed is the spacing between the rivets compared to solid rivets. I'm not an engineer but I would think that a person could simply measure the rivet spacing on something like the SPA Panther and then use that spacing on the DA-2.

I've also thought going on the other end of the scale and using solid flush rivets like the Vans RV's. I had an RV-7 and built the tail kit, the wings, and then half of the fuselage before I sold it. I sold it because I would get an assembly ready to rivet, and then literally wait for 6 months until I could find someone to help me rivet! In some spots, it requires two people to buck solid rivets.

A DA-2 with all flush rivets would be pretty sweet looking, and maybe a tad bit faster? But, just using solid rivets is a major pain in the....

Quote from justjohn on January 28, 2018, 8:43 pm

http://www.cannedhamtrailers.com/pdfs/davesbrakeplans.pdf

Thanks for posting! seems like a neat and simple way of doing things!

As far as the question of blind vs. bucked rivets, there are blind flush rivets, if you want flush. True, there's the mandrel hole in the center of the rivet, and depending on the type of rivet, the broken off mandrel may be retained inside of the hole. If you're going to paint, you can fill the holes in the center of the rivets (or not). At the speeds these planes fly, and the relative thickness of the boundary layer air, the hole in the center of the flush blind rivet probably doesn't make a whole lot of difference. The Sonex designs use flush blind rivets in the wing leading edge (back to the main spar). There's hundreds of holes in these leading edge flush blind rivets, and the resulting wings fly just fine.

I come from having built 1 Sonex from plans, and having built about 2/3 of the airframe of another Sonex from plans (and a bunch of parts used in a couple more Sonex airframes). It's going way back in my memory, but I spoke with principals at Sonex about the blind vs. bucked rivets. My recollection is they said they sized the design for 3/32 bucked rivets, then they use 1/8 blind rivets nearly everywhere. At least one Sonex has been built by a customer using bucked rivets, so they seem to be fairly simple to interchange, especially if you up-size when going away from the original design.

I don't recall if it was from the Sonex company guys, but I've also heard most of the rivet spacing on the airframe is driven by keeping the skins from oilcanning more so than rivet quantity for actual flight loads. Think of it that way - the airframe structurally might only need 20% of the rivets that it has, but then the skin would bow out and/or oilcan all over the place. So designers have rules of thumb for rivet spacing. It's not a set distance or number, because in many places, the row of rivets is just spanning a gap between structural members which may not have some nice even increment like 10" or 12". It may be 14 3/8", and so the plans will say 6 rivets equally spaced. Thus you use the "rivet fan" to obtain that equal spacing, and don't worry about calculating & measuring a multitude of 1 37/64" increments (or whatever the exact measurement would be).

Measurement trick - do NOT stretch a rivet fan as far as it will go. It will be VERY difficult to shrink it back down. If you need equal spaces on a long increment, measure & mark half the distance, then use the rivet fan stretched to cover half the distance at a time!

As for "needing" a shear - I built all of these Sonex parts, including cutting multiple full-length wing and fuselage skins with ONE particular hand shear that I like that works well - a gazillion little snips, approximately 1/2" at a time. Then smooth the edges out. I even got fancy with putting the hand-cut edges of the wing skins UNDER the overlap of the adjoining wing skin's factory edge, and putting the hand-cut edge of the skin on the bottom of the wing - factory manufactured edge of the wing skin on top (where you're more likely to see it on the ground). Sonex wing skins run span-wise, root to tip, and there's 3 of them on a wing. Upper aft, Lower aft, and a full length leading edge skin.

A bunch of people now are using a certain knife by Olfa. I tried that & didn't like it. Not enough control for my liking, but it's pretty cool to score a line a couple of times with the knife, then snap the sheet apart. Still have to clean up the edge.

As for the bending brake, the reality of high-dollar machine shop brakes is that the bend radius is determined by the set-back of the hold down (clamp) from the bending axis of rotation. They don't have multiple sets of hold downs for different radii.

Cordless drills - never used one for metal airplane work. I use a low-cost air drill for airplane work. It accelerates faster, is lighter weight, and spins at the proper rpm for small-diameter metal drilling. An electric drill just isn't fast enough for small-diameter metal drilling. Sure, it will make holes - .020 Aluminum isn't going to stop a modern cordless drill, but air is the way to go. You're going to need a compressor anyway to run your rivet gun, whether it's for bucked or blind rivets. (You're not going to hand-pull 10000 blind rivets.)

Back to the solid vs. bucked rivet question - if using blind rivets, will they be Stainless Steel or Aluminum? The Zenith family of designs use Aluminum blind rivets. They also use countersunk-head rivets in non-countersunk holes, with a custom rivet puller head that rounds-off the countersunk rivet heads as they're pulled (ridiculous overkill, IMO, but they've got a LOT of airplanes flying with this method). Sonex uses SST blind rivets. Technically, the SST in Aluminum could present a corrosion issue due to the dissimilar metals. Practically, it's not a problem (well, if it is a problem, all Aluminum airplanes in the vicinity have a corrosion problem). I also had a bunch of hours in another blind-riveted Aluminum airplane build, and those plans called for a rivet material that I couldn't even find a source for (might have been Monel?). So I found a SST blind rivet supplier and was using those.

Not sure what's the case now, but Sonex used to be funny about selling rivets to the general public who were not plans holders of their airplanes. So don't count on them as a source if you're going to try SST blind rivets. I sold that other project where I'd sourced the rivets & turned over all the receipts with it, so I don't know that I have any info on that other source I'd located. But they were in the U.S., and reasonably priced. Keep in mind, blind SST rivets may be 10x the cost of bucked aircraft rivets. But the cost is small relative to the entire airplane - if there's $100 worth of aircraft rivets in the design, that might be $1000 to swap over to blind SST rivets.

Then there's the question of weight. The weight difference in 10000 SST blind rivets adds up - not sure the exact number, but in a small/light airplane like these Davis designs, 5 or 6 pounds might matter to you. Or take it as a challenge to reduce the pilot's weight by at least that much before flying!