Waalsdorp Museum

August 8, 2006 11:46 AM

"From the first world war until the 30's air acoustics played an important role in the air defence. Air vehicles carrying a weapon could not be located from the ground e.g. at night time or under cloudy conditions. As radar was still to be discovered, vision had to be supplemented by hearing using the sound of the engines."
posted by mr_crash_davis (8 comments total)

Along with those stylish portable models, there were also giant permanent concrete sound mirrors. Here's a previous MeFi FPP about them.
posted by zsazsa at 11:58 AM on August 8, 2006

yes. time for me to post my link to soundmirrors.org again.
posted by silence at 1:23 PM on August 8, 2006

Wow, the soundmirrors.org project looks really cool. But I find it hard to believe that even a 30 foot sound mirror could catch a human voice from 25 miles away. Is this just a flight of fancy from a non-scientific artist, or can it really be done?
posted by Triplanetary at 1:56 PM on August 8, 2006

the 30 foot mirror at dungeness is meant for detecting sounds in the sky... it wouldn't work. The 200ft one there is more like the kind they would have to use, as it is aimed at the horizon.

These things are extremely directional, and they would need careful engineering.
posted by LoopSouth at 4:20 PM on August 8, 2006

More about sound mirrors is here. Just ignore the first sentence on the page. It has some links at the bottom for even more acoustic goodness. Thanks for a great post!
posted by TedW at 5:07 PM on August 8, 2006

More.
posted by Heywood Mogroot at 6:51 PM on August 8, 2006

D'oh.
posted by Heywood Mogroot at 6:53 PM on August 8, 2006

Cuties and Yo-Yos^{^} were ultra-quiet night reconnaissance aircraft designed by Lockheed for DARPA during the Vietnam War (photos):

A prop shaft ran awkwardly above the cockpit, driven by rubber belts that both eliminated gear- and chain-drive noise and substantially reduced crankshaft-to-propeller rpms. It is, Horn points out, the “only full-size aircraft in the world driven by rubber bands.” The shaft stretched to a four-blade wooden prop atop a big pylon on the nose of the airplane—a pylon that was, in effect, an extra vertical fin, which did little to enhance the handling qualities of the already awkward QTs.

The props (several were tried, including a six-blader) were handmade by a man named Ole Fahlin, whose reputation had been established not in the military-industrial complex but as a supplier of custom wood props to homebuilders and formula air racers. Fahlin would come out to the ramp between test flights of the original QT-2 and tune the prop by eye with a common wood rasp—take a little off here, reshape the blade there. “I don’t know how he did it,” Horn admits.

The Quiet Aircraft Association has more operational details and images about the QT-2 and YO-3A. Schweizer Aircraft still offers two low-acoustic reconnaissance planes (see also GlobalSecurity.Org.)
posted by cenoxo at 7:42 PM on August 8, 2006