@MylesPlanes Generally speaking, if your plane is unstable, you need to move the centre of lift (CoL) further behind the centre of mass (CoM). On the flipside, this makes your plane turn slower as well - after all, stability is just a resistance to turning. To make up for this, make sure your wing loading is low and your control surfaces are well-placed. Wing loading is the weight of your aircraft divided by the wing area. To get a low wing loading, you want bigger wings and a lighter aircraft. As for your control surfaces, the positioning is important: pitch control surfaces need to be either well in front of the CoM or well behind it; roll surfaces need to be to the left and right; yaw surfaces need to above or below, but honestly those aren't as important and most planes on here have terrible yaw control, most of my own included. If you find that your aircraft turns really slowly, your could maybe make the relevant surfaces a bit bigger. If your aircraft jerks about when turning, the control surfaces are probably too big. So, in summary:
Centre of Lift (the blue sphere) must be behind the Centre of Mass (red sphere)
Bigger wings and a less weight make for a more agile plane
Control surfaces need to be far from the CoM to work well
2 words. Trial and error
@Skua woah Einstein in action super power 'brain' activate
@MylesPlanes Generally speaking, if your plane is unstable, you need to move the centre of lift (CoL) further behind the centre of mass (CoM). On the flipside, this makes your plane turn slower as well - after all, stability is just a resistance to turning. To make up for this, make sure your wing loading is low and your control surfaces are well-placed. Wing loading is the weight of your aircraft divided by the wing area. To get a low wing loading, you want bigger wings and a lighter aircraft. As for your control surfaces, the positioning is important: pitch control surfaces need to be either well in front of the CoM or well behind it; roll surfaces need to be to the left and right; yaw surfaces need to above or below, but honestly those aren't as important and most planes on here have terrible yaw control, most of my own included. If you find that your aircraft turns really slowly, your could maybe make the relevant surfaces a bit bigger. If your aircraft jerks about when turning, the control surfaces are probably too big. So, in summary:
Centre of Lift (the blue sphere) must be behind the Centre of Mass (red sphere)
Bigger wings and a less weight make for a more agile plane
Control surfaces need to be far from the CoM to work well