Besiege --- Mirage 2000 Notes #1

Notes of Delta Wing Tuning

I built this plane twice. The first one has stability problem and didn't look quite right so I built another.

Here is the stability problem. It flies alright at medium speed but pitches down badly at high speed. I thought positions of the center of lift (CoL) and the center of aerodynamics (CoA) was the problem.

While I usually build the whole plane with flat propeller blocks then add 20° lift propeller blocks after, CoL and CoA are clearly separated. In this case CoA is decided by flat propeller blocks and CoL is decided by the lift propellers.

Note that lift will increase as the speed builds up. So when the CoL is ahead of the CoA, it should pitch up at high speed, while is CoL is behind CoA it should do the opposite. My plane might be the latter.

pitches up

pitches down

might be balanced

So I came up with this solution, angling up some of the flat propeller block in the front. The new plane flies okay now.

In theory it was the toque generated by CoL and CoA that cause the pitching problem. I still don't understand how the CoL and CoA shifts in different speed  when I apply this solution. I'll find out.