Core components you need
Every flyable aircraft needs at least a 
hull, an 
engine, and a 
propeller, plus a 
gyroscope for stability. Start by placing the hull block to form the body, then attach the engine to it and mount the propeller on the engine. Add a Gyroscope, 
Electronic Gyroscope, or 
Advanced Gyroscope depending on how much stability and control you want — better gyroscopes make the aircraft easier to fly. If you want cargo capacity, use a 
Cargo Airship hull; for combat, add weapon hardpoints.
Optional upgrades
Improved Landing Gear lets you touch down harder without damage. 
Hull Reinforcement makes the frame tougher against crashes and enemy fire. Sails are for airships and give extra lift or propulsion without an engine. Boilers and Steel Boilers power certain engine types and need their own fuel and water. Once assembled, right-click to board and test-fly at low altitude. If the aircraft will not lift, check that the propeller is actually connected to a fueled engine and that a gyroscope is present — those three things solve most "it won't fly" problems.