[TenTec] [Orion] harmonics. O2 versus Orion

[CATFISHTWO@aol.com]

Years ago My Dad used to be a flight engineer on a C-124 Globemaster.   These 
aircraft had 4 large piston radial engines.  I can still tell if a  C-124 is 
flying over head by the resonance and throb to those  engines. 
 
 Another good example was the C-130 with 4 turbo fans and had a  different 
pitch but you can still hear the beat frequency  in the engines,  , the c-130 A 
was the worst..  
 
I had a 33 hour flight time trip to Okinawa as a kid (1960) on a C-121 also  
know a a super constellation or super connie with the 3 tails. this was 33 
hours  of a very loud and cyclic harmonic noise that you could barley talk  over. 
It took a couple of days to get normal hearing back.
 
  Its funny but I and a lot of others can tell you what is flying  overhead 
just by the sound , C-5, B-52, Huey, F-4C, Pedro choppers.. they all  have 
distinctive pitch, throb and loudness.. I guess we are better at this zero  beat 
than we think.
 
In class at Keesler AFB we would tak 2 audio frequency generators and set  on 
at 25k and on at 26 k and you would never hear the note but the 1000 cycle  
tone would drive the instructors nuts, but it only works once..
 
tom N6AJR  
 
In a message dated 1/10/2006 8:23:21 P.M. Pacific Standard Time,  
ghoffman at spacetech.com writes:

One  listens not to the two tones, in an effort to discriminate them, but
rather  to the slow "thrummmm  thrummmmm...." that repeats at very low  speeds
when you get the tones close.  That is, the amplitude of the  thrummmm builds
and fades at the beat frequency.

You can hear this  when you tune a piano, and the beating goes away when the
two strings are  matched.  Some of us like to tune our pianos for a little
"roll" to  add a certain sound, and so you then tune the strings so the
thrummming is  slightly there.

One used to hear this occasionally on older airplanes  also, where two piston
engines would be slightly apart in speed.  You  could hear a very slow
build-up and drop off of the amplitude of the sound,  until the pilot matched
speeds.  Of course you don't hear that any  more with modern equipment.