We decided to try the die-press method for flanging our lightening holes. Basically, this means we created a die to press the hole flanges, instead of using a “Bob-stick” to bend the hole flanges by hand. It took a while to make the dies, but now that they’re made, it’s going real fast.
A quick review of basic wing rib theory as I understand it: we cut lightening holes to save weight, then flange those holes to add strength to the rib. This way the final product is both lighter and stronger, both good qualities in airplane design.
The final hole in the center ribs is an oval hole, so for that one we will be using the “Bob-stick” method. We’ll be sure to report how that goes.