Re: [ULF-1] Metric versus inch sizes for ULF-1 Member 60

From: Member 27
Date: 2012-02-02 11:15 UTC-08:00
Message: #0356

I would not want to argue with your calculations but 20 percent extra weight seems
wildly exaggerated.   What components are you seeing the largest weight gain in ?
Spars ?  Longerons ?  

--- On Thu, 2/2/12, [email] <[email]> wrote:

From: [email] <[email]>
Subject: [ULF-1] Metric versus inch sizes for ULF-1 Member 60
To: [email]
Date: Thursday, February 2, 2012, 2:06 PM

We are getting ready to order all the sitka spruce necessary to complete the tail feathers.  We can only find Member 60 in inches in the US.  We did a weight differential analysis comparing the two.  In most cases, going with the nearest sizes in inches, we will have to use slightly larger pieces dimensionally than the equivalent sizes in whole mm's as specified on the plans.  According to our calculation, we will suffer a +20% increase in weight penalty by going slightly oversize with the US Member 60.  This could add up for the whole airframe.  Since we will be powering with electric motors and batteries, weight is of great concern. 

Are builders in the US concerned about this weight increase, or are they planing down each stick to its exact dimensions in mm?  This would add a lot of work to the build. 

Thanks,
Member 67 
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