Rob, etal,

 

FYI:  25fps ~= 17 mph.  About like running (full sprint) into solid wall.  Perhaps survivable, by OUCH.

 

More math…

Gravitational acceleration is approx 32ft/sec^2 (drag-less freefall at the Earth’s surface)

Doing some algebra to solve for the time to reach 25 fps results in:  (25/32)^.5 = 0.88 seconds

Doing some integral calculus (not shown) results in a distance traveled of approx 7.5 feet

Thus, 25 f/s is about the impact speed from falling off the top step of an 8’ step ladder

Be careful when cleaning your gutters out there J

 

Or another analogy (in case you haven;t fallen off the top of a 8’ step ladder lately), terminal velocity from the top of a 34” bar stool would be approximately 12.5 fps (note: 1/2 speed = 1/4 of the impact energy).

 

Rick

 

 

 

Guys --

Richard Titsworth pointed out to me that the 25 foot-per-second descent rate with a BRS *is* 1500 feet per minute.  Gee, I get the "turkey of the day" award...

Anyway, they claim that 25 fps (1500 fpm) is survivable.  They told us that they want the airplane to land slightly nose down.  If we were going to land tail first, they would have insisted on head-rest-type protection features.

You know, 25 fps didn't sound all that fast to me, but 1500 fpm seems pretty darn fast to be crunching into the ground.

- Rob Wolf