I remember something from years ago about the speed of propellers being limited because the tips broke the sound barrier. Then they came along with fanjets. It would seem that the fanject blade tips would have the same problem as the propeller blade tips. Did your experiments help solve that problem? Gerry (Cousin was at Purdue Engineering, went to WW-2, came back and got his degree, worked 30 years for S.I.G.&E., and died several years ago.) ---------------------------------------- ----- Original Message ----- From: "Rich Thomas" <[EMAIL PROTECTED]> > One of my professors in college (Purdue, Aero/Astro), who went to MIT, > and later became head of the Dept at Purdue, told a story in our > Aerodynamic Noise class of having made a large speaker while an > undergrad at MIT, which was installed in a dorm room (or, rather, the > modified dorm room was the speaker enclosure) and pointed through the > window across the Charles River at Boston and Beacon Hill. The testing > was curtailed when the Cambridge and Boston police visited to explain > that some good citizens were complaining of loud noises and that windows > had been broken and could they please do something about that. No > charges were filed but the students were put on notice that anymore such > behavior would result in severe penalties. Of course they complied... > > My project in that class was to build and test a supersonic propeller. > This was a 24" radius propeller turning at approx 12000 RPM, driven by a > very large electric motor with a 20:1 pulley ratio (drive to driven). > Everything was working well until a piece of plastic sheet about 10'x20' > got sucked into it from across the hangar, and bent the 1" steel drive > shaft about 30deg and ripped off the jack bearings from the stand. We > fixed that and started more runs when we were advised that experiments > were complete. Other students in the lab (a converted large hangar at > the airport) complained of loud noise, too much wind, and other asserted > and considerable dangers, the Nuke E guys wanted their safety equipment > (a chain link fence deal with a 2" thick piece of plexiglas for viewing > the activities) returned, and the lab techs determined that too much > power was being drawn off a 220V circuit to be safe for any length of > time. It generated a lot of noise from the supersonic shock waves > generated off the tips (running at about 1200fps) and a good portion of > the blades, and the waveforms looked really cool on an oscilloscope. > That experiment and some guys who built a seriously nasty rocket engine > got high accolades. > > That was the most fun I had in college, well in class anyway. We didn't > know sh*t about much we were doing, but threw a bunch of castoff stuff > together we found laying around the lab and let her rip. Oh, and I got > an A in the class. > > --R
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