Weighing risk

January 2019

Q. A man wants to take his wife for a ride on a hot air balloon for their anniversary. He learns from a safety advocacy group that balloon companies in the U.S. average a fatal accident once every 50 years. One company in his area has never had a fatal accident in its 98-year history. Should the man immediately cross that company from his list because it’s obviously due for a fatal accident or should he get out his credit card and make a reservation? What do probability and statistics say about this dilemma, if anything?

ABOUT THE AEROPUZZLER

Draft a response of 250 words and email it to: aeropuzzler@aiaa.org for a chance to have it published in the February issue.

From the December issue:

Q. We asked you why a professor tossed a paper airplane at a student who was attempting to explain lift. We invited Mark Guynn of NASA Langley in Virginia, Anya Jones of the University of Maryland, and David Mayhew, retired from Boeing, to review the responses independently. They were unanimous about the winner: 

A. The professor likely reached for the paper as soon as he heard that “it’s all about the curved upper surface” because it is, in fact, not all about the curved upper surface! While the slacker had a point that the faster moving particles would cause a corresponding decrease in static pressure over the upper surface of the airfoil (as per Bernoulli’s equation), he incorrectly attributed the speeding up of particles solely to the camber of the airfoil. Many shapes, objects, and airfoils can generate lift as long as they can impart a change in the wind velocity flowing around them. Symmetric airfoils at a positive angle of attack can induce flows similar to those around cambered ones, and even spinning cylinders will cause a differential in the relative wind across their surfaces which would then lead to a lift force. It is likely for this reason that the professor began creating an aircraft with ‘flat plate’ wings: to share a little bit of knowledge on flat plates, angle of attack, and origami!

Winner: Daniel Yu

Land O’ Lakes, Florida

Danielyu14@gmail.com

Yu is a software engineer at TRU Simulation + Training and a 2018 graduate of the University of Illinois at Urbana-Champaign.