ULF-1 Discussion Archive
Anonymous static archive of the former Mailman list
Anonymous static archive of the former Mailman list
Re: [ULF-1] Metric versus inch sizes for ULF-1 Member 60
There are far too many generalities here. If someone has every stick listed in a spreadsheet both metric and imperial sizes then all you have to do is look at the larger components and make adjustments. If you cannot select a more optimum imperial component then trim for the really larger components. Come on. Use a little common sense. Your concern is impressive but I think you will have larger variance in weight/density just between samples of the same Member 60 species OR in the amount of glue used etc etc. > Member 25, > > The first set of calculations were just for all the "stick" Member 60 needed for tail feather construction. I can forward the spreadsheet if you would like to see it. Even though the weight gain was small (1.9 oz.), that was 19% greater than the weight of the metric sticks. > Multiply this throughout the airframe, and it will add up. > > By extrapolation, lets say for argument that 100 pounds of metric sticks are used in construction. The inch equivalent sticks would weigh 19 pounds more, or 119 pounds. Now, the overall weight penalty might well be less for a total airframe target weight of 120 pounds, as the ULF-1 specification sheet states. At any rate, even going slightly oversize with the inch equivalent sticks, will add significant weight, especially when you consider all the sticks required for the entire build. > > Member 67 > > > > > ---- Member 27 <[email]> wrote: >> 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 >> _______________________________________________ >> ULF-1 discussion list -- [email] >> >> Subscribe, Unsubscribe, Preferences, List information: >> http://lists.ulf-1.com/listinfo.cgi/ulf-1-ulf-1.com > > _______________________________________________ > ULF-1 discussion list -- [email] > > Subscribe, Unsubscribe, Preferences, List information: > http://lists.ulf-1.com/listinfo.cgi/ulf-1-ulf-1.com _______________________________________________ ULF-1 discussion list -- [email] Subscribe, Unsubscribe, Preferences, List information: http://lists.ulf-1.com/listinfo.cgi/ulf-1-ulf-1.com