To take this project further, it's possible to add a trigger to your launcher so you don't have to feed airplanes manually into the wheels.
For the trigger mechanism, we can use a tiny servo motor and a rubber band. Luckily, CRICKIT is capable of controlling multiple different types of motors simultaneously, so all that's needed is to plug the servo in.
If you haven't used servos before, the servo section of the Adafruit Motor Selection Guide will provide a good introduction.
Mark placement of servo on the back edge of the platform.
Be careful to place it so the servo horn is centered perfectly between the guide rails.
Attach servo motor with hot glue.
You may need a servo extension cable to get the servo cable long enough to reach the Crickit based on where you mount things. Adafruit carries the cable as product #972.
Pressing the "B" button on Circuit Playground Express will now activate the trigger and play a notification sound.
Cut through a rubber band.
Lay rubber band on launch platform to measure where to mount it.
Poke holes in cardboard where rubber band will be attached.
Stick ends of rubber band through holes and tie off the ends.
You should now be able to cock back and release your rubber band, which will push your paper airplane forward into the launching wheels.
Note: servo needs to be powered ON to hold rubber band back. Without power it will rotate freely.
It is recommended that you use a small piece of tape to strengthen the back edge of the paper airplane so that it's stiff enough to withstand the impact of the rubber band.
You are now GO for launch!