How do you use templates on curved surfaces?!

[Trailer Trash]

As the title says guys, I've just started on my first curved surface, a motorcycle helmet, and I'm having trouble with stencils. I gave up using a big stencil, I've been getting on OKish with just using small sections at a time, but obviously on a curved surface, a flat stencil can cause problems, when it comes to things lining up. I'm doing Tinkerbell, I did her hair, wings (individually), arm, and body, when I came to doing her body, if I lined it up with where it should meet her wings, the arm was out of line!

If anyone can explain how to do this, I'd be really grateful, or if you can point me in the direction of a video or youtube that explains it well, even better! I've been searching but not come across anything that makes it any easier!

Thanks all ositive:

 

[Sitni]

if you cant do it freehand try using automotive tape and cut your design direct on the surface you are painting.

 

[worldofglasscraft]

Thinking out loud.
Mask the helmet where you need the graphics using a removable mask
Draw and cut out the design then remove it very gently.
Scan the image and cut with plotter
This will allow for the curve on the helmet
And will be able to re-use the stencil.
Of course you will need a big scanner if your stuff over A4 but I think these are available to use in the high stree in some towns.