Sunday, April 7, 2013

Bending Of Left Wing Closeout Skin Tabs

Time in the shop today was primarily spent fabricating a wooden bending tool with a slot in it per the plans and then using the tool to bend the tabs on the W-1204D bottom wing tip closeout skin for use on the left wing. Per the drawings, each of the many tabs requires bending to a predetermined angle between 16 and 116 degrees … there was a large grouping of 30 degree bends but many were a unique angle. Bellow is a photo of the drawing showing the angles the builder is striving for. To measure the angles a protractor was purchased many months ago in anticipation of this task … unfortunately, the adjustable protractor proved problematic so a digital level was used and yielded wonderful results.
 Photo of the drawing from the plans showing the angles which each of  the
         W-1204D closeout skin tabs are required to be bent.
To help eliminate confusion going back and forth between the drawing and the part being bent, each tab was marked with the desired bend angle for that tab. The fabricated bending tool was then used to carefully place the tool onto the tab and letting the tab bottom out in the slot cut into the tool and lifting tool to bend the tab followed by an angle check using a digital level.
                   Using the wooden bending “tool” to bend one of the tabs on the W-1204D bottom closeout skin.
During the winter, the DOG Aviation procurement department purchased a digital level after reading about a slick way that particular digital level could be used to ensure the blade angle of the RV-12’s ground adjustable propeller is the same angle for both blades which results in a balanced propeller. This particular digital level has a hole on the bottom with a plug that can be removed revealing a threaded socket for tripod mounting or mounting onto a fixture to quickly and easily check the propeller angle.  Of course, that has nothing to do with bending the W-1204D’s tabs, but thought I would mention it for the sake of other RV-12 builders using DOG Aviation as reference.
One of the slick features of using a digital level is the work bench (or surface being used) does not have to be perfectly level … just place the level on the work surface aligned along the plane the measurement will be made and then press the bevel button. This instantly sets the level to 0 degrees regardless of the surface angle. Moving the level up or down will yield a reading in + or – degrees based on the direction the level is moved. Lay the W-1204D skin flat on the surface with the tab to be measured aligned along the plane the level was zeroed and measure the angle as in the photo below … presto reading. Bending all of the tabs proved to be a little time consuming, it requires patience because you need to tweak and test, tweak and test, etc. . but it is easy and the digital level took all the guess work out of it .
                                                Using a digital level to check the angle of one of the tabs on the W-1204D
                                                bottom closeout skin after bending it with the wooden bending tool.
The W-1204D bottom closeout skin after bending all the tabs except for one.

The tab that gets bent to 116 was not bent at this time … prefer doing a test fitting first as has been suggested by other builders.