Quick top quilt question - differential?

[doogie]

The following photo of the head end corner of a TQ produced by one of our "cottage" vendors, has the inner shell stretched tight while the outer differential cut shell wraps around the edge allowing full loft.

IMG_3371 (Medium).JPG

Here's a sketch to further illustrate the principle.

TQ Cross Section.jpg

That's not what we are referring to...at least I'm not. That is a given that you need extra fabric for the sides. I actually made true boxed sides to my TQ and posted how i did it. A differential is when the top is wider than the bottom due to it being a larger radius. So if we assume a person has a radius of 12" the minimum bottom layer of fabric would be 24*pi/2 (divide by 2 since we are only covering the top half of the person....about 38" The top layer of fabric for 2" of loft would need to be 28*pi/2...about 44" You would still need to add another 4 inches (2 for each side), but this could be added onto the top or bottom piece of fabric. The tricky part is figuring out how to make the baffles conform. I think these numbers a a little extreme, but hopefully you get the idea.