The amount of thrust needed depends on how you want to fly.
A slow flying trainer, the thrust will need to be 60-80% of the weight of the plane.
A typical plane, 80-100%. A war bird or one with a little zip will be 100-150%. A 3D plane will need 150-200% thrust to plane weight.
Here is a FT thread with more information.
I'm scratch building the FT Cruiser and would appreciate all the help that anyone can provide in designing the power system from the ground up. I know that I can use the parts specified by Flite Test but I really want to learn the fundamentals for future builds. I'm not into 3D flying yet so I...
Watts per pound is another useful guideline. You'll need to weigh the plane and estimate the weight of the motor and battery.
• 50 to 70 watts per pound is the minimum level of power, good for park flyers and lightly loaded slow flyers.
•70 to 90 watts per pound is perfect for trainers and slow-flying aircraft.
•90 to 110 watts per pound is good for fast-flying scale models and some sport aerobatic aircraft.
•110 to 130 watts per pound is what you want for advanced aerobatics and high-speed aircraft.
•130 to 150 watts per pound is needed for lightly loaded 3D models and ducted fans.
•150 to 210+ watts per pound gives unlimited performance for any 3D model.
When it comes to Kv, think transmission. High Kv generally use smaller diameter higher pitch props. Resulting in higher top end speed and lower thrust at low air speed. Just like a high gear in a transmission. Lower Kv generally use larger diameter lower pitch props. Resulting in lower top end speed but greater thrust at low air speed. Just like a low gear in a transmission.
Two motors can output the same power (watts) but at different air speeds. A race car and a tractor may both have the same horsepower but at different speeds.