Sometimes it's easier to get your parkjet in the air if you can use a bungee launcher. Sometimes the plane is too big, sometimes its just hard to hold. There are plenty of stories out there about pilots getting their hand or arm cut in by the propeller and that usually requires a trip to the emergency room.
Here is a great design for a home built bungee launcher that incorporates a foot pedel so the entire thing can be operated by one person.
LINK TO RC GROUPS BUNGEE BUILD THREAD