(Here is a short short story I wrote many years ago, for your engineering imagination, vision, and assessment. Is this story possible? Can such a wind tunnel really be operated? If not, why? Does it violate some law of physics or thermodynamics? What are the challenging design issues? What are the environment and safety issues? I look forward to your comments.)
Tunnel Vision – Part I
Here I am, finally, standing in the entrance of a life-long dream, ready to climb aboard a four-seat cylindrical pod and fly through a 600 mile long wind tunnel at speeds approaching Mach 3. It is a beautiful spring morning here in Salt Lake City, Utah. The sun has just risen over the Great Salt Lake, and in 15 minutes, my family and I will be in Anaheim, California, to see it rise again, this time over the Pacific Ocean. We plan to enjoy two full days at our favorite theme park before returning home having missed only two days of work.
As we enter the terminal, to my left are the huge turbo-fans providing the large mass-flow-rate of air to the slowly converging tunnel stretching to the right. My heart accelerates as I witness the party ahead of us enter their pod, secure themselves and their belongings, and look forward down the launch rails in anticipation.
Upon positive detection of all enable circuits, the pod’s onboard computer engages its drive cam with the variable lead, threaded shaft rotating at constant angular velocity and extending a mile into the tunnel. The pod in front of us moves out at a moderate, but aggressive constant acceleration and in a matter of 10 seconds is out of sight.
For a moment, my mind jumps back to a time when I was a child and I went with my mother to the drive-up window at the bank. She put a check or some money in a small plastic canister, placed it in a machine outside the car window, pushed a button, and after 3 seconds and a vacuum like sound, the canister was in the hands of the teller in a nearby building. Oh how fun, I thought, to go on such a ride.
Then it was our turn. We stepped into the airfoil shaped bridge protecting us from the high winds. From here I could see clearly the variable-lead screw drive shaft just below our pod. Its threaded helix was designed with an initial small gradual angle thus importing a small forward velocity to any vehicle engaged to it. This design concept provides for continuous, unchanging operation, fewer moving parts, and less start and stop action. The acceleration of the engaged pod is directly proportional to the rate-of-change of the helix angle with respect to distance along the shaft. The angle increases steadily until at its high helix end, the pods velocity will be approaching Mach point three (0.3).
Just before stepping through the hatch…
(Click Part II below) #engineerclips