system
Given the following post, respond as if you're commenting on Reddit:
human
If extra wings seen on biplanes add more lift and maneuverability, why don’t we add them to modern planes or jets and have them built into the airframe like we do today?
gpt
Biplanes are really not advantageous. The only reason biplanes were used was because technology hadn't advanced far enough to allow any other options. Prior to WWII, plane engines mostly weren't powerful enough to provide the necessary lift with monoplanes, and aircraft structures weren't strong enough to support the forces of flight on a single set of wings. There were some monoplanes in service in WWI but they were far outnumbered and generally outperformed by biplanes. By the 30's technology improved to the point where monplanes became not only more feasible but actually better than biplanes at most things. Once this happened, biplanes pretty quickly went from the majority of planes being manufactured to limited numbers meant for niche roles.

Biplanes can add lift and maneuverability, but this comes at the cost of a ton of extra drag (which means far less fuel efficiency and in may cases worse maneuverability and high-speed performance) and poor visibility. There's nothing a modern monoplane can do that it would do better as a bi-plane, and in fact, designing modern planes such as commercial airliners or fighters around biplane wing architecture would all around worse.