Small Rocket for Rc Copter?

Just wondering if anyone knew of some good ways to make small rockets, i want to make 2 rockets and attach them to my toy helicopter and then activate them in flight for like an uba boost can anyone recomand anyways i could make a small rocket enough to push 500g about 10-20kmph nothing great just a simple rocket that will have effects you can see
References :

A rocket assist on a helicopter will most likely destabilize the vehicle.

You want something with a lower and longer thrust curve, like a jet engine.

There are model jet engines for RC craft, but they tend to be expensive.
References :
http://www.rc-airplane-world.com/model-jet-engine.html

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