Mythbusters missed a few!

I just finished watching the new episode of Mythbusters, in which they investigate a famous scene from the movie Point Break: Patrick Swayze leaps from a plane at 4000 feet, and Keanu Reeves hems and haws for fifteen seconds before jumping after him, sans parachute, and manages to catch up, have an argument, and finally pull the parachute some 90 seconds after the first departure, landing together.  As a skydiver myself, I found this somewhat entertaining to watch.

Mythbusters handled 3 myths:  Can you freefall 90 seconds from 4000 feet (no, unless you want to spend 60 of those seconds dead), can you have a conversation in freefall (they say no, though I’ve understood a few shouted phrases in freefall myself), and can you catch a skydiver after giving him a fifteen second head start (yes, you can fall REALLY fast in a ‘head-down’ skydiving position).

They actually missed a few dubious aspects of the Point Break scene, though, that might make good fodder for future episodes…

Opening shock: Parachutes are designed to open at a certain velocity.  If you have two people falling together in freefall, they fall much faster than an individual.  A normal parachute could be ripped apart, or kill its user, if it opens at a higher rate of descent.  (This can happen, for instance, if a single user is head-down at 200 mph when their chute opens.)  In tandem skydiving, where two people are harnessed together for the jump, tandem instructors deploy a drogue parachute soon after leaving the airplane, to slow the pair to a reasonable, and normal, 120 mph freefall.

Holding on:  The opening shock might not be a problem, though: it would be extremely hard to hold onto a skydiver at terminal velocity who opens their parachute.  Skydivers actually do something like this called a “Mr. Bill” jump, in which two jumpers (both with parachutes) leave together, and then one opens their parachute while the other hangs on, only to let go later.  The important distinction, though, is that this is done almost immediately after leaving the plane, when the airspeed is relatively low.

Landing:  The movie shows that Swayze and Reeves look pretty hurt after landing, but it would potentially be even worse than shown.  ‘Wing loading’ (square footage of parachute to lbs of weight) is the most significant factor in the performance and handling of a parachute.  A wing loading over unity is considered to be rather high performance and requires care to avoid serious injury.  If you have two people landing under a single person canopy, the wing loading is essentially double.  It would be really hard to imagine landing that without problems.

The Mythbusters were amazed that they had a movie scene with potentially 3 dubious aspects to it.  I would increase that number to six, myself…

This entry was posted in Physics, Sports and tagged , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.