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  #1  
Old 12-29-2019, 02:47 PM
Stockmanreef Stockmanreef is offline
 
Join Date: Nov 2012
Location: Midland, mi
Posts: 805
Default Cowling Question: 45-08 alignment of Top Cowl

Can some explain the use of plumb bobs to align the top cowl? Steps 9-11 are clear as mud. I understand the goal. I just have no idea what the plumb bobs are for and how they do anything useful. I would understand the whole sequence if there were a third plumb bob dropped from the center of the spinner plate to the floor to mark the center of the plane relative to the level. Then measure where the two outer plumb bobs hit the level and then make sure that the two plumb bobs are the same distance away from the center line.

Step 10: Hang plumb bobs from two symmetrical points at the forward edge of the top cowl air inlets so that they touch the level as shown. Mark the cowl and the level with the plumb bob contact points. Remove the plumb bobs.

Step 11: Slide the aft edge of the top cowl left and right until the stance between the pairs of contact points are within 1/16. This will laterally line up the top cowl.

1/16 of an inch of what? At this point there are no plumb bobs in place. So what the heck does this mean?

I am just very confused by what the plans are asking us to do at this point.

Maybe once I do this it will become apparent what this step actually does, but I doubt it.

1. Can some one explain such that a 3rd grader can understand this?
2. Why can't you just make the opening for the prop in the top cowl is aligned versus spinner plate?

Thanks
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RV-14a (serial number 140073)
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  #2  
Old 12-29-2019, 03:49 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
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Default

so it is not installed not leaning to one side or another or possibly twisted. the top half is in one horizontal plane which sets the guide for the bottom half and the hole thing as a unit will be in one horizontal plane. Sorry, I can't explain it any better.
Hope this makes sense.
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  #3  
Old 12-29-2019, 04:43 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by Stockmanreef View Post
2. Why can't you just make the opening for the prop in the top cowl is aligned versus spinner plate?
You can use what ever procedure you want. The instructions were written in a way that helps builders position the cowl accurately in ways that they might not realize could be an issue.

The instructions do have you align the upper cowl to be centered on the spinner, but the cowl can be mis positioned in the roll direction even if it is properly centered on the spinner.
This can be for numerous reasons that I won’t go into because following the instructions negates the issues.
Since the instructions had you level the fuselage laterally (roll direction) the placement of the level on the floor is to assure that the surface below the cowl that you are referencing height measurements to, is also level (many shop floors are far from being level).
The use of the plumb bobs is to mark a point directly below the front corners of the cowl, to assure that you are measuring to the same point below the cowl every time.
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  #4  
Old 12-29-2019, 05:09 PM
Stockmanreef Stockmanreef is offline
 
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OK- that makes more sense.
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  #5  
Old 12-30-2019, 08:36 PM
mrhorspwr mrhorspwr is offline
 
Join Date: Aug 2016
Location: Okc, Oklahoma
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the plumb bobs are just to make a mark on the floor or on a level on the floor to measure from. Without a mark directly below the cowling the measurments could be off. The hanging plumb bobs will give you a refrence point directly down from the points on the cowling to measure from with a tape measure.
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