The Dragonfly

Last Update-03/13/2010 01:40 AM           

After many hours of scratching my head as to what to do in regards to bending the almost 8 foot pieces of aluminum for the stab and elevator spars, I decided to put pencil to paper and steel to grindstone. I will build the brake I have been developing in my head.  The idea for this brake came from several different sources.  Most of us who have investigated this problem have seen the wooden brake another zenith builder developed.  I figured if this could be done with a few simple door hinges,  then I should be able to come up with something similar utilizing the 4 x 4 x .250 angle iron I had laying around for another project.  The key to this type of brake is that the hinge centerline doesn't really have to be right at the bend line.  All we need is something stiff enough to "push" the metal around the radius bending bar clamped to the top.

Here is the steel I started with.  It was already 8 foot long so no need to cut to length. It's 4"x4"x .250" .





I had a short chunk of this angle laying around so I cut off four 4" pieces.  I drilled some 1/2" holes in them and welded the first 2 pieces to the ends of the main body piece.









As seen in the middle picture above and the two on each side here, I welded the other two "feet" to the center section evenly spaced from the ends.






Next, I added the hinges to the bending leaf portion.  9 hinges were used.  They are spaced 12 inches apart (roughly).





Here they are all attached.  I counter-sunk the 10-32 machine screws so the leaf would fold down against the body.









I built the folding leaf handle out of 14 gauge, 1 inch square tubing.  I just kinda eyeballed the length and tried to make it look good.

To the right are the countersunk holes for the handle.




I cut some poplar 7/8" square x 3" long and drove them into the 4 open ends of the handle. This helps prevent the tube from crushing under the 5/16" bolts used to secure it to the folding leaf.





Holes drilled through the poplar on the left.

Handle being bolted to the leaf on the right.

(yes, I realize its very obvious what is happening in these pictures, but I have to fill this space with something !)



I used 5/16" counter sunk stove bolts to attach the handle.





Click the picture to the left to download a short video showing the the leaf operating. (or right click and "save target as" to download it to you computer)





I picked up this 4' x 12' piece of .025 6061 today from Airparts Inc.  I love living right down the street from them.  This will be cut into an 8 foot section and the pieces cut out of it for the elevator and stab spar.






Well here we go, the moment of truth.  Lets just see how this bad boy works.  I clamped the end legs to the bench, but bolted the center legs to the table with 1/2" carriage bolts.

I cut the radius bar from a piece of white pine. I routed an 1/8" radius on one edge and then ran it through the table saw to bevel the front 30 degrees back from the leading edge.




Whooo hooo! This thing actually works!  The only thing I had to do to finish up was give the flanges a little tap along their length with a dead blow hammer to get the flanges to the proper angle.  The banana effect was only about an 1/8 in the middle while laying on its back.  Not bad for 100 bucks worth of steel and hinges.!  Give it a shot.  The only thing I would recommend is the best possible clamps to hold down the radius bar. Cheap ones that bend won't cut it.



Now I can get on with building the rest of the tail components.