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  #1  
Old 08-21-2019, 07:51 PM
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Saber25 Saber25 is offline
 
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Default Can you measure up or down ?

Today I was visiting with an RV-9A builder as he was ready to find the angle of incidence on his project. Does the measurement 4-5/64" ring a bell ? It's the measurement for determining rear spar height from a horizontal plane which sets the angle of incidence for the main wing. Wow, 5/64th is a figure I had never worked with. It gave me a whole new appreciation for builders of the new generation of RV's.

I couldn't get it out of my mind so unfurled my -4 plans 1150, published in 1981, and searched for what was then the generally accepted measurement of the day. It seems Van's at the time favored 1/8 or generally the smallest was some version of the /16th. I did find a 13-11/32 and 13-27/32 on page 13 of my plans concerning the center bulkhead wing carrying structure. Van kept measurements pretty simple and quite effective throughout those plans so what happened?

I'm pretty sure I would have made that 5/64 into a 2/32 or better yet, 4- 1/16 and call it a day. I think I had it pretty easy back in the day.

Cheers, Hans
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  #2  
Old 08-21-2019, 08:32 PM
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So many times in the plans they would give you a dimension to the 64th of an inch and when you would fit the part you could be off by a 1/4". That drove me nuts!

However, when setting the incident on the wings, you can bet I was as close as possible!
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  #3  
Old 08-21-2019, 08:43 PM
TX7A TX7A is online now
 
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Default I remember...

...seeing measurements like that “sprinkled” throughout my build. I figured it was yet another way to meet the 51% rule by annoying the builder.
Or, in actuality, maybe they were measurements derived through CAD drawing software. In this case by virtue of an angle. Who knows!
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Old 08-21-2019, 08:45 PM
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For what its worth....Sonex plans are generally dimensioned to the nearest 64th - but I think that is an artifact of doing them in CAD, and having the program dimension the drawing automatically. In discussing things with their “top dawgs”, the nearest 1/8th will probably work fine.

However, it is a challenge to work to tight tolerances, and when you do - things fit together so nicely.....
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  #5  
Old 08-22-2019, 05:02 AM
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You guys had it easy. There were many instructions in the Lancair manual reading something like, "Approximately 4-5/64". Stuff like that would drive us builders nuts.
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