Man that looks great... I know how painful it can be to paint a stripe like that.... I did that stripe all around my basement... Took forever and about a million dollars in painters tape...hahah
It was hard to get the exact ratio of the stripe. I was able to find a picture of a real helmet on google images and measured from there to get the ratios right.
Awesome work on your piece.. I am sure he is going to love it.
I used similar ratios for this work
Black 1/4<<<Actual 1/6 of red stripe
White 1/2<<< Actual 3/8 of red stripe
Red 1<<<< 1/12 of wall size so 12' wall would mean 1' stripe