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Bob, Many use the washers method. Built into the mount would be best. Better yet a truly clever counter rotating prop set would be super. Then fin offset could also be zero for max efficiency! Bill Jepson My kit suggest to install washers between my mount and the firewall to get the thrust I need. This doesnt sound like a very good way to do it to me. Is this really the norm for adjusting thrust? Bob Mears Supermarine Spitfire
-----Original Message-----
From: jerryhey@earthlink.net
To: flyrotary@lancaironline.net
Sent: Wed, 11 Apr 2007 3:22 PM
Subject: [FlyRotary] Re: Mount offset
Bobby, I am sure we can get it right. I am interested in Blake's suggestion because I can do the drilling of the S-beam on the mill where I have more control. We can also do something like you have just suggested by measuring from a point on the S beam back to the firewall. And then instead of moving the motor around, I can just move the firewall. Same thing in reverse. Jerry
I have been worrying about accuracy when setting the offset as my fixture does not have an easy point to measure from. I've considered a number of schemes in recent weeks. Most would work but they were not easy to implement. However, the last time the fixture was rebuilt (when the S-beam was moved to the prop flange a year ago) I did put in a way to pivot the engine mount at the prop flange but never used it. All my engine mounts were straight ahead. Off set could be managed with washers at the firewall.
Here is the Dumb part: For at least two years I have used a laser mounted on the fixture to make sure it was on thrust line. It fires right down the engine center line to the "firewall" which has its own center line. I can move the firewall back and forth, side to side, etc. When the laser points exactly to the firewall center line everything is lined up straight ahead. To dial in off set, all I had to do was mark the calculated offset from the center line on the firewall and then pivot the fixture until the laser pointed to the new mark. Honestly, I did not realize I could do it this perfectly easy way which I myself built, until a hour ago. It is now 3:30 am and I can finally get some sleep. Jerry
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