It would be intersting to see if the built in stall indicator of a J3 worked on the PA18. It is a bit of a hassel using it in the UK, but works well in Florida.
Oh you want to know what it is.
When the door is left open of the J3 the bottom half start to rise up near the stall, wonderfull device. But bloody parky in the UK.
Show us a picce when you get it fitted
CC
Note the J3 doesn't have flaps