Date: 07 Oct 97 14:10:17 From: BWMR55B@prodigy.com (Mr. Daniel H. O'neill) Organization: Prodigy Services Company 1-800-PRODIGY References: 1
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It helps if you remember that a turboprop is an ultra high bypass unducted fan. The reason for ducting the fan is that props get wasteful when the tips hit supersonic velocities, and you must paddle faster than Mach 1 to approach Mach 1. Turbofan C-1 disk blade sections are biconvex at their outer spans and the duct keeps the shock waves from propagating all over the place. (all the noise is energy that isn't propelling the airplane). Propellers do a fine job of subsonic propulsion, and the difference between .5 Mach and .8 Mach doesn't mean much on a short flight, most of your travel time is spent in the car and walking around the airport anyway!