Hatz Biplane Association

Hi Gang

Need some advice again. Fuselage is almost complete and am ready to fabricate the 3/4 X 3/4 X .032 angle formers that support the wood side strips and aluminum skin at station 23/25. Anyone care to share how they bent the angle stock to form the curvature needed to get the correct shape?

I have done this in past with aluminum angle by notching the flange to allow a series of short stright legs that approach the curvature I need, but looking at the photos from Jeff I do not see any evidence of this, unless the flange was notched, the piece bent, and then notches welded closed.

Appreciate any advice.

Dave

This was accomplished on NX687HZ by first forming an straight angle piece the desired length or longer. Then the length was marked at 1" intervals on the side that is to be perpendicular to the longitudinal axis of the A/C. Finally, using a crimping tool the marked leg of the angle is crimped a little at a time allowing the formed piece to be compared to the former/plans until the desired curveture is obtained. The finished piece was then attached to the former with machine screws, washers and nuts. Several of these strips are visible in the attached picture.

John Kerr

the file was too large. let me know if you need to see an example of what was described.
John

Thanks John

I think I get the idea. Did you use a fluting tool to crimp the steel or will I need to use something like a dull chisel? Stuff seems kind of stiff to crimp easily.

Dave

I made a plywood pattern representing the contour of the former. Then I bent two narrow pieces of sheet metal into an L-shape slightly longer than what I would end up needing. Then, using a metal shrinker on one of the 'legs' of the L-shaped piece, I gradually shrunk the piece until its shape conformed to the plywood pattern. Using the pattern I was assured the formers on both sides would have the same shape. In addition I welded light weight tabs to the former as attach points for the stringers. Good luck and happy building.

By the way, I used the shrinker on the firewall flange and a small portion of the metal cowling.

I notched, formed, welded notches close, ground smooth

michael
N838mm

Thanks for the input guys.

I have completed the front formers by forming angle pieces of .032 4130 as per plans and crimping one leg to form the curvature as recommended by several of you. This left a lot of small corrigations on the front side but do not think they will be a problem. Am currently thinking about the semicircular piece that welds behind and above the front seat. May have to notch and weld here to wind up with a smooth surface. Am also considering a crimper with smaller jaws to result in a smoother job. I have found that some of my ideas are pure genius, and some are absolute dog crap. Time will tell which catagory my current efforts best fit.

To be honest, am having a ball. When things do not work out first time I figgure I learned something and will try again. Am in no real hurry as I have three airplanes now that I do not have the time or money to fly, but I would like to finish the Classic before I am to old to fly it!

Dave

This method was used on all of the curved metal frames except the headcomb and showed no evidence of less than a smooth curve in the finished form. The fabric, cowling and metal skins around the cockpit overlap nicely. Spacing of the crimps 1" apart allowed for ample mounting surfaces to attach either to the firewall in the front or plywood former to the rear. The crimping tool used had approximate 3/16" depth.

The headcomb was a beast, taking a couple of iterations, ultimately flanged on a break then shaped with a homemade device invoving 2 x 4's set in a steep "V" and using various radiused object to force the blank into the gap.

John