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[Phys-L] Bernoulli's equation ... or not



On 12/15/2014 06:23 PM, Anthony Lapinski wrote:

While I was searching, I came across this:

francesa.phy.cmich.edu/people/andy/physics110/book/Chapters/Chapter9.htm

On the final page there are ten problems. Here are the last two:

9. The luge is a small sled in which the racer lies on his back and rides
down the course feet first. This is a very dangerous sport and
participants always wear helmets. In 1983 the East German luge team
introduced helmets which were cone shaped. Honestly, it looked like they
had just stepped off the set of “Saturday Night Live.” What
competitive advantage would these helmet give a luge racer?

10. These helmets were quickly outlawed because they were considered as
dangerous as no helmet at all. Why were these helmets considered to be so
dangerous?

Never heard of these helmets before, so I searched and saw some photos
(and found that the year was actually 1976). They really did exist! I was
just a young kid back then. Does anyone remember these controversial
helmets? Were they so aerodynamic that the riders went too fast (how
fast?), which cause accidents?

Aerodynamic helmets are routinely used in bicycle races.

Olympic luge rules permit visors, which can be made somewhat
aerodynamic.
http://www.olympic.org/luge-equipment-and-history

International Luge Federation rules require that all clothing
and equipment must conform to body contours. Aerodynamic
"connections" are specifically prohibited.

Aerodynamics has got nothing to do with safety. If luge
officials were concerned about going too fast, they would
reduce the slope of the course, and then let the fastest
guy win.

An aerodynamic fairing on the helmet does not have to be
"connected" to the upper body. Unless you are pathologically
stupid about it, the fairing would not increase the risk of
injury in a crash, other things being equal (such as speed).


FURTHERMORE none of this has anything to do with Bernoulli.
The purpose of the fairing is to promote pressure recovery.
Any situation where Bernoulli applies already has 100%
pressure recovery; conversely, without the fairing, you
get a lot of "dead air" to which Bernoulli does not apply.

Yes, this is aerodynamics, but no, Bernoulli does not solve
all the world's aerodynamics problems.