Bad Piggies Flight in the Night Bonus Level 4-IX (4-9) can be 3-starred with a single contraption. Use a helicopter as your vehicle. The helicopter can reach the star box in the extreme top-right of the level under its own power, then ride the ramp back to the finish line. Having a firework on the undercarriage, pointing left, may be worthwhile in case things go wrong during the ramp descent.
If you have a different strategy for completing this level feel free to leave a comment below.
I found that I had to place the pig, egg and motor to bias the contraption leftwards to the finish–but you need to move rightwards to approach it! That makes the initial rightwards momentum down the first, lower hill very important. I used the momentum on the second (star box) hill to move my pig to the finish, too.