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NC12350 Monocoupe 110 |
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Firewall forward |
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NC12350 was delivered in 1932 with the 125 hp Warner Scarab. The previous owner of the project, Don Sitta, had planned on turning NC12350 into a clipwing and he had Ed Saurenman (holder of the Monocoupe 110 Type Certificate) remove the original motor mount and install the Edmondson Owl motor mount as described by Monocoupe drawing SK-02 for the anticipated installation of a 185 hp Warner Super Scarab.
After receiving the project and a fair amount of deliberation, I decided to keep NC12350 in the original “long wing” configuration, and decided on installing a 145 hp Warner Super Scarab 50A.
I needed to fabricate the motor bracket assemblies as described by Monocoupe drawing SK-01. I initially had a set made up per the print, but when it came time to assemble things, they just didn’t fit right. The fact is, as I now know, the only correct was to fabricate the SK-01 bracket assemblies is “in assembly” with the motor mount and a template of the motor mounting circle made from your rear case.
Here are the SK-01 and SK-02 drawings:
SK-01 motor bracket assemblies (7.2 MB .jpg file)
SK-02 motor mount assembly (11.4 MB .jpg file)
Legend has it that, particularly on clipwings, the SK-01 brackets are fabricated to give between 1—2 degrees downward thrust. I spoke to several people about this and the answer was always—yeah I think mine was done that way…… When asked why do this?, the answer was usually to help the clipwing “get up on the step” due to the very small fixed position horizontal stabilizer.
Now if you think about it after studying the drawings, in order to get 1-2 degrees down thrust or tilt of the motor, you would need to make each SK-01 bracket slightly different, or, make the fingers on the motor mount that capture the bracket assemblies different. Regardless on how you approach this, the task involves spatially orienting the rear case of the motor where you want it (no tilt, or some tilt, and centered properly) and fabricating bracket assemblies between that orientation of the rear case and the motor mount.
In the end, I decided on zero degrees of tilt. The reason being that my plane has an adjustable horizontal stabilizer, via the jackscrew assembly, and actually has quite a bit of in flight adjustment.
One of the really nice things about the Edmondson Owl motor mount is the use of Lord bushings for vibration isolation. The correct part is Lord H3006-1 or Continental 23411 shock mounts. Pictures below. |
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Here are two pics received from Len Hebert of a 90A at Creve Coeur that has the Edmondson Owl mount for a 185 hp Warner. |
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My motor is still up at Alan Holloway’s shop, but I was able to use an old fuselage from N501W, from when it had a Warner 145 on it, which just happens to be hanging in the top of my hangar, to make a template of the motor mount holes. This is a nice flat piece of 3/4” thick MDF. |
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There is one of those Lord Bushings and a finished bracket. I purchased a foot long piece of 1” round steel rod and cut it into five pieces the same length as the Lord bushing, then center drilled them on a lathe.
This gave me five steel bushings to use to hold things in position for tack welding. |
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I fabricated all five of the round steel tube pieces that “capture” the Lord busing, put them on the sacrificial steel bushings and mounted them on the “fingers” on the motor mount.
Jigged the MDF motor mount hole template “in space” so that it was centered on the motor mount ring and vertical (zero degrees of tilt) with the fuselage jigged straight and level.
Cut and bent the steel pieces that bridge the gap between the bushing and the motor rear case.
Then tacked things up. Remove for final welding with a lot of back and forth fitting check along the way. |
