Originally posted by Hospital_Rocket
Is there a rule of thumb you can use to compare the size of an x-form parachute to a round one? I want to make my own, however I do not know what size x-form would compare in descent rate to what size quater or half sphere...
A
An X-form has 7/9ths the area of an octagon of the same major dimensionm (I was wrong about the 90% area, it's just under 80%). A round with the diameter = that major dimension would be almost exactly the same area as the octagon. Slightly more area for round if you used diameter = corner-to-corner, but maybe a few percent.
Volume-wise vs. semi-spherical is tougher. There's a speadsheet calc for this someplace, and one of the descent calculators on EMRR ("Tools") takes round, hemisphere, and X-form into account.
The descent rate comparison wouldn't be linear with wind speed. The rounder, the more lift generated with more drift. I don't recall seeing a calc that takes wind speed into account in this way.
