Induced drag is the part of drag caused by the wing producing lift, and it is most directly affected by how much lift the wing must generate. In steady level flight the lift must equal the aircraft’s weight. As airspeed increases, the wing can generate the same lift with a smaller lift coefficient, because lift is proportional to 1/2 ρ V^2 S CL. Since CL decreases with speed, the strength of the wingtip vortices—and thus the induced drag—decreases. In short, higher airspeed means less induced drag. Raising altitude, increasing weight, or changing Mach can affect overall flight conditions and total drag, but they don’t produce the same consistent inverse relationship with induced drag that increasing airspeed does.

The combined load described is weight. It’s the downward force acting on the airplane due to gravity on the entire mass of the aircraft, including the airframe, crew, fuel, cargo, and baggage. This total weight can change as fuel is burned or payload is added or removed, and it directly determines how much lift is needed to fly. In steady level flight, lift must balance weight. If weight increases, more lift (or a higher angle of attack) is required to maintain level flight; if weight decreases, less lift is sufficient. Lift, thrust, and drag are separate forces: lift acts upward, thrust pushes forward, and drag resists the motion. None of those describe the total downward load—the weight.

Landing gear choices determine how the aircraft sits on the ground and how drag is managed in flight. Some airplanes use fixed landing gear, which stays down at all times, offering simplicity and durability but creating steady aerodynamic drag. Others use retractable landing gear, which folds into the fuselage or wings to reduce drag during flight, at the cost of added mechanical complexity and weight. That makes the statement about landing gear being fixed or retractable true. The idea that a third wheel must always be in front of the main wheels isn’t universal—aircraft come in various configurations, including tailwheel and tricycle gear, so wheel positions aren’t a fixed rule. Propellers belong to the propulsion system, not the landing gear. And a firewall isn’t for thrust; it’s a barrier between the engine compartment and the cockpit to protect occupants from engine heat or fire.

The fuselage is the central body of an airplane that holds the crew, passengers, and cargo. It forms the cabin where people sit, the cockpit where the pilots control the aircraft, and the cargo holds, and it’s built to be strong enough to carry the loads of wings and tail while withstanding pressurization in most airliners. The wings are separate structures that provide lift (and often carry fuel), the empennage is the tail assembly that stabilizes and controls the aircraft, and the landing gear supports the airplane on the ground. So, the main body section is the fuselage.