Charles is right. Sometimes that's the only way, especially with a multiple framed canopy as on the P40. Another way is to coat the whole canopy in masking fluid, such as Humbrol 'Maskol'. Let it dry, and then, using a SHARP craft knife/scalpel, carefully cut the lines of the frames, peel away the dried fluid, which should now be a flexible, rubbery substance, and paint. When the paint is TOTALLY dry, peel-off the remaining 'Maskol'.
A word of warning though; as it dries, masking fluid tends to shrink-basck from the edges. Ensure the dried fluid is covering those areas, totally, that DON'T need painting. If not, re-coat the area(s) again.
Generally, I prefer the tape method, but a combination of both the above can sometimes be useful. The fluid is handy when the curve of the canopy, or any other part, is complex, and difficult to mask with tape.