Aircraft landing gear as primary design constraint

Boeing 747 replacement example. Used to teach that the heaviest load case (landing) determines the keel-beam design, which determines everything else.

Another example — we've got some Boeing people here. What's the first part of a major aircraft you design if you're starting your design? You design the landing gear first, because the landing gear has to take the weight of the structure when it lands, and the whole rest of the structure has to be built around that to transfer those loads. So if you talk to a designer at Boeing, they project: okay, we're going to build a replacement for the 747, it's going to weigh half a million pounds, so we've got to have a landing gear that supports half a million pounds. And we're going to have to design structures like the keel beam. Everybody knows there's a keel beam in an aircraft — just a great big I-beam goes front to back. It's called a keel beam because it's like a ship; ships in the water have a keel beam. The aircraft has a keel beam and you build everything off that, and that keel beam has to support the loads from the landing gear when it lands.