Algodoo

Simple flywheel spring engine prototype.
Top speed = 250 m/s (even 300) right or 500 m/s left (spin flywheel accordingly)
Use up to brake flywheel (the orange wheel)
Use down to brake wheels.
Use left and right to control lever arm.
To start, drag flywheel, wait for it to get to about 500 rad/s, then press only right.
You can then release right when it stabilizes.
Do NOT let the flywheel go over 1000 rad/s, use up (and maybe left) to brake it if it does.

NOTE:
If you go left, decrease the lever arm spring length (below 1, so about 0.75), this way you can reach an incredible 500 m/s going left. I only tested this now. You can also do this for going right, but can only get to 300.