RE: How do I make a plug from this heli canopy?
You have the plug already, the canopy. Using the canopy as a plug a mold can be made. There are two choices here. Either way some sort of internal structure to stiffen and support the canopy will be needed. This structure can be balsa formers.
One method would be to fit a parting board around the canopy along the centre line. This can be a chore.
I would split the canopy along the centre line. fit the two halves along the centre line to a flat board .
In both cases the back end can be left open, hence the need for stiffeners. The pictures do not show the underside of the canopy. Are there any reverse angles that would lock the canopy in the mold.
If you agree to the foregoing I will describe the next step.
Ed S