Designing in the right CG
09-28-2002, 12:10 PM
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Designing in the right CG
I'm working on the latest and greatest design - my own take on an Edge 540. The burning question - how do others anticipate the balance point of their finished plane at design time? I've attempted various approaches in the past - from TLAR (which surprisingly worked out more than once! Only had to add an extra ounce or two to a .60 size plane), to Andy Lennon's idea of piling everything on a board to see where it balances, to massive spreadsheets calculating moment arms (failed miserably - in the end had to add 1 1/2 pounds to the nose!) This plane is going to have an 80" span, and a dry weight of 11-12 lbs, with a 2.4 gas engine (ambitious, aren't I?). Would really hate to have to do the massive amounts of lead thing...Stretching or shrinking the nose/moving the wing is soo much easier in CAD than on the plane after it's done! Any methods that worked for you???
09-28-2002, 02:50 PM
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Designing in the right CG
Build the plane but leave the plug-in wing joiner holes in the fuselage out until the plane is almost finished. Also leave off the landing gear and make the gear mount in the fuselage big enough that the gear can be mounted anywhere over a reasonable fore and aft position. Position the wing and gear so that the plane balances where you want it and then cut the holes for the wing joiners and mount the gear accordingly.
Alternatively, build the fuselage with fore and aft slots for the wing joiner. After the fore and aft position of the wing is set for the desired CG, use doublers inside the fuselage sides to fix the fore and aft location of the joiner and cover the slots. Filler pieces can be glued in the slots to make the fuselage sides flush. A similar technique can be used for positioning the gear. The gear can be sandwiched between two ply mounts across the fuselage with the slot wide enough fore and aft for adjustment. After the gear is properly positioned relative to the CG, pieces of ply filler can be added in the front and back of the slot to lock the gear in position.
Alternatively, build the fuselage with fore and aft slots for the wing joiner. After the fore and aft position of the wing is set for the desired CG, use doublers inside the fuselage sides to fix the fore and aft location of the joiner and cover the slots. Filler pieces can be glued in the slots to make the fuselage sides flush. A similar technique can be used for positioning the gear. The gear can be sandwiched between two ply mounts across the fuselage with the slot wide enough fore and aft for adjustment. After the gear is properly positioned relative to the CG, pieces of ply filler can be added in the front and back of the slot to lock the gear in position.
