The canopy shown on the cover of the 9/17/01 issue of your magazine is not a parachute. It is a paraglider. Paragliders are intended to take off from the ground and to fly upward from the force of the wind or an engine. The cover shows a successful tandem hill launch in progress. Parachutes are intended to come down after opening during freefall. A paraglider could not withstand the forces of opening in freefall.
Perhaps you could do an article on powered paragliding
(PPG). The technical advances that have gone into providing the ability for one
person to foot launch from the ground with a paramotor on your back and fly
upward are truly amazing. A good starting place might be www.USPPA.org .
Nice photo, but it's a paraglider, not a parachute, and the two are not interchangeable. Paragliders are designed to be opened on the ground and foot-launched. They are not designed for high shock loadings and would tear apart if deployed in freefall. The tradeoff is that paragliders have glide ratios and sink rates good enough to allow thermal soaring and cross-country flights.
—Peter Burghardt, Robert Bosch Corp., Farmington Hills, MI
In the early 1980s, the aircraft industry performed bird strike tests on aircraft windshields using live chickens fired from a cannon (DN Editorial 09.03.01). I do not believe PETA existed at the time. The SPCA did exist and asked the industry to stop using live chickens. From that point on, industry practice is to humanely slay each chicken just prior to shooting it from the canon.
To the benefit of chickens, a software package called DYNA-3D became available in the late 1980s. This software could simulate a bird striking a moving blade. The software used quite a lot of computer time so only those with access to a CRAY computer could run this type of simulation. GE used the software to develop the composite fan blade for the GE90 engine. The automakers used it to develop the energy attenuating crumple zones found today in many cars.
You are correct to note that a bird behaves like a fluid stream at high speeds. The density can actually be approximated as about 80% the density of water. This density, the volume of the bird (fit into a cylinder that is twice the diameter in length) and the final velocity of the bird can be entered into Bernoulli's equation to derive a final pressure. This pressure can then be entered in a static FEA model to obtain stresses. The results are very conservative but close enough for when the bird strike lab is in use.
P.S.—My cat also does not approve of bird strike tests.
Thanks for your unbiased and accurate article about Dale Earnhardt's accident (DN Breaktime 08.20.01) As a mechanical engineer for 34 years and a NASCAR fan for 30 years, I have been appalled at the mainstream media's typical ignorance-filled coverage using clichés, metaphors, and the term "almost head-on at 180 mph." The media uses terms like force, energy, pressure, and momentum interchangeably. I have never heard any mention of velocities or vectors. My wife, an RN and also a NASCAR fan, comprehends the applicable high school-level physics concepts after very brief explanations.
I normally do not respond to editorials (08.20.01), but yours struck a sensitive point. As a practicing engineer (30 years) and adjunct university instructor, I have a real problem with the lack of understanding of why young people do not seek engineering degrees. First, as you said, the schools continue to churn out doctors, lawyers, and MBAs. From my experience, the earning potential is much greater for these degrees/professions. Secondly, as an engineer with an MBA, it is a much easier degree to get than even a technical masters.
And as a final thought: Why would a person go to engineering school, take 18 hours a semester for four years, and study hard subjects, only to wind up 20 years later working for a business student or lawyer? The reason I went to engineering school was simple. I came from a poor family and engineering had a good starting salary.
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