Source: 1/2004 Patrol Newsletter, Bob Barrows

I hope this issue will be helpful in getting you started on the Bearhawk Patrol. We will, through this newsletter, try to pass on to you helpful tips and methods that others and myself have found useful in building an aircraft of this type. We recommend that the builder first start with the wings. The wings are the most time consuming and complex part of the project- if you can finish the wings, you should have no problem with the rest of the aircraft. After completing the wings, you will next build the tail surfaces and finally the fuselage. All of the tips in this issue will deal with wing construction. Building an aircraft should be a fun learning experience.

Shopping List:
You will need to obtain the following clecos for wing assembly and construction. If someone in your EAA Chapter has finished a metal aircraft you may be able to buy or borrow their supplies, save yourself some money.
3/32″ – 300 pieces
1/8″ – 200 pieces
5/32″ – 50 pieces
3/16″ – 10 pieces
And don’t forget the cleco pliers too!

Tips for Rib Making
Prime paint one side of sheet aluminum for easy marking.

Marking Tool
One of the more useful tools is the marking tool guide. The guide is nothing more than a plastic circle of 1/4″ thick material with a 3/8 hole in the center to fit the marking tool into. The tool rolls along the edge of the form block as you mark out the proper size flange. You will need to make two of these guides- one for a 9/16″ flange and one for a 1/2″ flange.

After marking the rib, remove it from the form block. Cut out the rib blank with large duck bill snips. Polish all edges and radius all corners.

Rib Forming
Hold the assembly in a large vice. C-clamp as needed to keep the blocks together. Lightly tap down the flange over the rib form block, being sure the radius is set. The flange will be wavy. Take your time and work your way around the rib.

After you are finished forming the flange, remove the rib from the form block and set it on a 2×4. Using your mallet, lightly tap the flange over to a 90-degree angle. Again, take your time and work around the rib.

After forming the ribs, it is time to cut the lightening holes and flange them. Using a fly cutter and drill press, cut the proper sized holes in the rib. Now you will use the flanging tool to put a 30-degree angle on the lightening holes. Pull up on the tool and slide around the hole 2-3 turns until approximately a 30-degree angle is formed. Wax the aluminum as needed for smooth operation of the flanging tool. After forming the flange the rib will be slightly warped. To correct this, set the rib on two wood blocks with the flange portion pointing down. Using the butt end of the flanging tool apply pressure to the flange and slide it around to straighten out the rib.

Fluting Pliers
You can buy a set of fluting pliers or you can make your own. To make your own you will need a large set of pliers. Clamp the pliers in a vice and drill a 1/4″ hole between the jaws. It may help to soften the pliers first with a torch. Then braze a section of 3/16″ rod on one side of the pliers. File as needed to produce a nice smooth radius around the rod and along the rim of the jaws. Using your fluting pliers flute each rib at approximately 1-1/2″ spacing to straighten out the rib. Flute all of your ribs the same so the rivets will space. As not to interfere with the skin rivets.

Build the Spar and Wing Parts
Having completed all of your ribs, it is now time to move on to bending and building up your spar webs. To build airworthy spar webs will take some practice. Keep some scrap metal around to work on until you are confident that you can do it. The information here should help get you started on the right foot, but if you think you need extra help, here is where your EAA friends can help. You are going to want to maintain close tolerances if you want a smooth skin layout.
Bend your spars to match your ribs.
Cut blanks from aluminum sheet with large duck billed snips. Ends are to be square with length and edges are to be polished smooth. Mark approximate bend lines on blanks using a felt tip pen. Keep blanks free of scratches.

Width=spar web finished height plus 2x flange width plus 1/16″ (see plans).
Using a Bending Brake
You will need to gain access to an 8′ bending brake. Most medium-sized towns will have one somewhere, check with sheet metal shops or at the local High School (make your tax dollars work for you this time). Most bending brakes you will have access to with not have enough radius on the foot- thus the hard aircraft aluminum will crack. You can eliminate the problem by making a foot cover for the bending brake.

Install foot cover on brake foot. Hold the foot in place with wire or bungee cords in 3 holes. Adjust the brake set back to 1/16″ from the edge of the brake frame with the foot cover in place.

Before bending the actual spar webs, make 3-4 test pieces 6″ long and the same width as the spar webs. Bend one flange on each of the test pieces to the proper width and angle. Reinstall the test pieces to bend the other flange and determine the proper setting to get a spar web that fits the ribs. Bend spars using the information learned from working on the small test pieces.
Construction Table
The construction table shown will be used as a platform to assemble the wing spars and ribs before mounting in the wing jig. Also the table will be used as a welding jig for the fuselage and tail assembly. The table should be built of a sturdy construction.