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<DIV>Earl,</DIV>
<DIV>I really enjoy the scientific approach you take to things, and the level of
effort to get objective results. Thanks.</DIV>
<DIV> </DIV>
<DIV>I wanted to respond to the people that are looking for that elusive
resonant frequency that, if found, could be designed out of the mount. It
ain't possible. The resonance of a plane is not the result of its
composition, or its mount, or the isolation, or its stiffness or weight.
It is all of these and more. In fact it is possible to change these
frequencies by installing a servo rail at the right location, or by going to a
harder or softer mount.</DIV>
<DIV> </DIV>
<DIV>I had the opportunity to test a high resolution laser system that I
designed in the Kodak imaging labs on a vibration table. This thing was
cool. After putting accelerometers at key locations the very expensive
table began to vibrate. The frequence and amplitude was computer
controlled to cover the range of operating requirements and after running
for an hour or so would print out graphs and charts of all the data.
</DIV>
<DIV> </DIV>
<DIV>I learned that the difference by changing the type and thickness of rubber
isolators was amazing. An unquantified "Soft mount" is so imprecise it's
laughable. Each mount has its own range of effectiveness and range of
ineffectiveness. Besides changing shock absorption we also moved parts
closer to the vibration source or farther away, depending on their mass, to find
the right balance. I was not the expert in this area but learned that our
practice of slapping rubber on our mount (be it Hyde style, or lord mouns, or
Gator grommets) is crude, but effective enough. Just don't expect it
to be equally effective at all RPMs or comparable from plane to plane.</DIV>
<DIV> </DIV>
<DIV>--Lance</DIV>
<DIV> </DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=JOddino@socal.rr.com href="mailto:JOddino@socal.rr.com">JOddino</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=discussion@nsrca.org
href="mailto:discussion@nsrca.org">discussion@nsrca.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, February 19, 2004 10:34
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Tonight's Dumb Idea...</DIV>
<DIV><BR></DIV>
<DIV>Hi Earl,</DIV>
<DIV>Can you give us some idea of the frequencies where you measured the peak
amplitudes? I assume you saw some narrow band peaks where various things
went into resonance. I was talking to Jerry Budd and he figures the
resonant frequency of the modern light weight airframe is down around 1.5
Hz. There is probably a way to "ring" the airframe and measure the
resonances if you've still got the measuring equipment available.</DIV>
<DIV>Interesting stuff but it will probably all go away when we switch to
electrics.</DIV>
<DIV>Regards, Jim</DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=EHaury@aol.com href="mailto:EHaury@aol.com">EHaury@aol.com</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=discussion@nsrca.org
href="mailto:discussion@nsrca.org">discussion@nsrca.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, February 19, 2004 4:50
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Tonight's Dumb
Idea...</DIV>
<DIV><BR></DIV>
<DIV>When the suggestion that soft mounting provided more advantages than
not was proposed, most of us subscribed to the theory that power loss from
anything less than solid was unacceptable. I set up a test using a fuselage
that could be equipped with either a hard (cast aluminum) mount or soft
(same mount with radial Lord mounts and a Lord mounted nose ring). A
miniature accelerometer was mounted to the inside of the firewall by the
lower mount bolt and another to the mount at the same location. (Stud for
solid, Lord studs for soft.) The accelerometers were connected to a dual
channel spectrum analyzer to display amplitude g's as millivolts on a
vertical scale vs. frequency on the horizontal. Engine was a piped OS 61
with the MK prop of the time. </DIV>
<DIV> </DIV>
<DIV>After gathering full throttle data several times, and reversing the
accelerometers to ensure similar output, the results dramatically told
the story. The solid mount produced a 600mv amplitude signal and the soft a
6mv signal. A 100 / 1 difference. BTW, no measurable difference in engine
rpm. Switched to soft mounts and never looked back!</DIV>
<DIV> </DIV>
<DIV>Earl</DIV></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>