Started: October 6, 2003
The Bearhawk wing spars are built very similar to the Van's RV series wing spars. The Main Spar is basically a "C" channel of .032 2024-T3 aluminum with 2024-T4 bar stock built up in varying lengths and stacked in varying thicknesses, then riveted top and bottom on the web part of the "C" channel. This provides a very strong spar design. The other spars are similar in design.
To start with, the spar "C" channels were formed. To do this, access to an 8' brake is needed. The wings are longer than 8' so each wing has two 8' channels that are spliced together to form one long spar for each wing. To make all of the wing spars (main, rear, flap and aileron), two sheets of .032 2024-T3 4'x8' are needed. We were very careful to avoid scratching these. I also had Wick's ship these flat instead of rolled. To save on shipping, all of the bar stock and the sheets of aluminum for the spars were ordered and shipped together since truck shipping is required due to the length of the bar stock needed.
To get nice accurate, straight cuts, the sheets were taken to a local sheet metal contractor and sliced on their 10' computerized sheer. This machine leaves very little burr on the edge of the cut and makes really accurate cuts. It only cost me $12.35 to have this done.
Once all of the spar web pieces were cut to the proper width, they were taken over to Mickey Whittenburg's shop to bend up on his 8' metal brake. The brake was set up as per the Beartracks newsletter to make sure we had a nice radius in the corners:
I also brought along one of each rib (nose, center, flap and aileron) so we could bend the spar webs to match the actual ribs. I was glad to have Mickey helping with this part as he is an EAA tech counselor and has over 50 years of experience with building airplanes. My spars came out beautifully straight with a very nice radiused bend. It is imperative that the bend radius be formed rather than just a sharp corner bend like you might get at a HVAC company shop.
Here is a picture of one of the Main Spar "C" channels:
Here is a picture of all of the spar "C" channels together:
The various spar plates are made from .125 aluminum 2024-T3. These plates are used to attach the wing to the fuselage and a couple are used at the splice of the spar halves.
I can't over emphasize how important it is to smooth the edges of all of the aluminum.. There can be no tool marks or scratches, especially on critical pieces like these wing attach plates. Here is a picture comparing the finished plate to the plans:
Two 8' long tables were constructed and placed end to end to make a 16' long table.
The wing attach plate was then located on the center line and the main wing to fuselage mounting hole was located and drilled 1/8" for now.
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