Tonight's Dumb Idea...

[Del K. Rykert]

Earl...
    Not to disagree with your findings but could you shed some light on why we often gained rpm when solid mounting our engines to good maple mounts compared to some of the fiber man made mounts of that same era? 
    As I remember there was much discussion that went around why soft mounting wouldn't work and it was felt the trade off in lost rpm was worth it for the savings on airframe and equipment. Course about that time gobs more power was becoming available to those that were sponsored or could afford dumping their engines for the new crop.
 
                         del 
               NSRCA - 473
  ----- Original Message ----- 
  From: EHaury at aol.com 
  To: discussion at nsrca.org 
  Sent: Thursday, February 19, 2004 7:50 AM
  Subject: Re: Tonight's Dumb Idea...


  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. 

  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!

  Earl
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