From: RWolf99@aol.com
Message-ID: <3f.305385a.261d800f@aol.com>
Date: Thu, 6 Apr 2000 01:52:15 EDT
Subject: Re: EAR Soundproofing
To: lancair.list@olsusa.com
Mime-Version: 1.0

          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
          <<  Lancair Builders' Mail List  >>
          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> 
>>
In a message dated 4/6/00 0:23:18 AM EST, lancair.list@olsusa.com writes:

<< He then went into a quite detailed explanation about
 composites and "surface excitement and resonance" which can cause
 fasteners, nuts etc. to vibrate loose.  He also warned of holes
 penetrated by bolts becoming enlarged by the constant resonating. >>

There are many reasons why NASA's space projects all cost a bazillion 
dollars.  This is one of them.  Armies of intelligent people paid to think of 
anything that could possibly go wrong, no matter how unlikely. (He says, at 
the risk of igniting a firestorm...)

The Space Shuttle and the expendable launch vehicles undergo a horrendous 
amount of vibration unlike anything we see in general aviation.  It can be a 
challenge to get mechanisms and electronics to survive these environments.  
Just becuase they armor their vehicles against this onslaught, it doesn't 
mean we have to.  Ours aren't subjected to anything near what their vehicles 
are subjected to.  (Satellites and space stations, too.  Their worst loads 
are often the launch loads.)

If any screws get loose, there's no opportunity to inspect and correct the 
situation.  That's one reason why every single fastener I used on the Space 
Shuttle payload I flew in 1985 (I was Chief Engineer) had to use a cotter 
pin, safety wire, or other positive locking device.  No self-locking nuts for 
these guys, unless you did a vibration test to prove that it would hold.  
There's another NASA tradition that doesn't exist in general aviation.  

Screws and nuts may loosen due to vibration.  That's why we use self-locking 
nuts, self-locking nutplates, cotter pins and safety wire for safety-critical 
fasteners.  We attach non-critical items like wingtip fairings, access panels 
and such with sheet metal screws and inspect them during preflight and annual 
inspections.

As an engineering manager at Orbital Sciences, I'd have to say that 25-35% of 
all engineering discussions involved vibration and shock qualification of 
electronic components.  We'd never use an FAA-PMA part without an extensive 
vibration qualification program.  Another space flight tradition that isn't 
followed in genral aviation.

(For what it's worth, we did an extensive experimental study of various 
vibration isolation grommets for shock-mounting stuff.  The E*A*R grommets 
were by far the best.)

So in conclusion, keep listening to your NASA engineer patients.  But don't 
blindly apply what they say, since they may be suggesting a solution to a 
problem that doesn't exist in our world.

But then, that's why you sent us this posting, isn't it?

- Rob Wolf
(FWIW, VP/Engineering at Pioneer Rocketplane, www.rocketplane.com)
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
LML website:   http://www.olsusa.com/Users/Mkaye/maillist.html
Builders' Bookstore:   http://www.buildersbooks.com/lancair

Please send your photos and drawings to marvkaye@olsusa.com.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>